Progress Report #2Sept 1, 1996 - August 31, 1997

Nanoscale Devices and Novel Engineered MaterialsDOD/AFOSR MURI

Grant Number F49620-96-1-0026

Prepared by:

S.J. PeartonJ.R. Childress

Dept of Materials Science and EngineeringUniversity of Florida

Gainesville, FL 32611-2066Tel: (352) 846-1086Fax: (352) 846-1182

e-mail: spear@mse.ufl.edujchil@mse.ufl.edu

Participants:

University of FloridaP.H. HollowayR.E. HummelE.P. Goldberg

Dept. of Materials Science and Engineering

S. HershfieldF. Sharifi

Dept. of Physics

Florida State UniversityS. Von MolnarDept. of Physics

University of California San DiegoR.C. Dynes, F. Hellman, and I.K. Schuller

Department of Physics

Microelectronics Center of North CarolinaG.E. McGuire

Naval Research LaboratoryR.J. Colton and L.J. Whitman

Table of Contents

Status of Effort ------------------------------------------------------------- 3

Research Report

Etching of Magnetic Thin Films ----------------------4

Ultrathin Magnetic Films-----------------------------17

E-beam Fabricated Nanostructures ----------------------25

Theoretical Modeling of Electron Transportin Magnetic Structures -------------------------------------27

Deposition and Patterning of Magnetic Materials ------30

Nanostructured Display Materials ---------------------37

Etching of Flat Panel Display Materials --------------40

Nano-crystalline Silicon -------------------------------------44

Nanostructures and Magnetic Particles --------------46

Magnetic Nano-Particles -----------------------------49

Activity Report

Publications ---------------------------------------------52

Technical Presentations -------------------------------------56

Personnel Supported ------------------------------------- 59

Technology Highlights -------------------------------------60

Patents -----------------------------------------------------61

Honors / Awards ---------------------------------------------61

Status of Effort

The second reporting period was a highly productive one for the program. Features in the

100-1000Å scale were fabricated in a number of different materials systems, and the spectrum of

activity ranged from the basic physics of superconducting nanostructures and interactions of

small magnetic particles, to novel fabrication techniques for creation of ultra-small features,

theory of GMR and potentially advanced spin-valve materials, to deposition and processing of

display materials. The work supported by the MURI has both a long-term and a shorter-term

focus, with the latter guided by input from several companies that have an interest in

development of next and future generations of magnetic devices. Coordination between the

different groups has been outstanding and has been one of the highlights of the program.

Etching of Magnetic Thin Films

S.J. Pearton, University of FloridaJ.R. Childress, University of Florida

F. Sharifi, University of FloridaS. von Molnar, Florida State University

We were able to demonstrate efficient dry etch processes for three different systems

applicable to GMR- and CMR-based devices, namely NiFe, NiMnSb/Al2O3 and

LaCaMNO3/SmCo. Each is summarized below:

1) NiFe-based Materials

A Cl2/Ar plasma chemistry operated under Electron Cyclotron Resonance (ECR)

conditions is found to produce etch rates for NiFe and NiFeCo of >3,000Å⋅min-1 at ≤80oC. The

etch rates are proportional to ion density and average ion energy over a fairly wide range of

conditions. Under the same conditions, fluorine or methane/hydrogen plasma chemistries

produce rates lower than the Ar sputter rate. The high ion current under ECR conditions appears

to balance NiClx, FeClx and CoClx etch product formation with efficient ion-assisted desorption,

and prevents formation of the usual chlorinated selvedge layer that requires elevated ion etching

conditions. Post Cl2-etch removal of surface residues is performed with an in-situ H2 plasma

exposure.

Thin films of NiFe and NiFeCo are commonly used in magnetic devices such as

read/write heads, sensors, non-volatile memories and microactuators. A general problem with

these materials is that they are relatively inert in conventional plasma processes, and thus

alternative methods such as ion milling, lift-off or electroplating have been employed for pattern

transfer. As the areal recording density of magnetic read/write heads increases towards 10

Gbit⋅in-2, the heads will need to have sub-micron track widths. At these dimensions it is

imperative to have smooth anisotropic feature sidewalls, and a drawback with simple ion milling

processes is that redeposition on the sidewalls may occur. Furthermore, mask erosion due to the

low etch selectivity may produce sloped sidewalls and trenches or notches at the base of etched

features. The etch rates of Fe-containing alloys may be increased by elevating the sample

temperature during plasma exposure, but this is undesirable in manufacturing applications due to

difficulties in process repeatability and may not be possible with some magnetic materials due to

thermal stability concerns.

We show that NiFe and NiFeCo can be etched at rates a factor of approximately two

faster than Ar milling under the same conditions, using a high ion density Cl2/Ar discharge. The

chemical enhancement derives from balancing formation and ion-assisted sputter desorption of

the chloride etch products and avoiding formation of a thick, chlorinated selvedge layer.

Chlorine residues have been removed by an in-situ H2 plasma clean. Under our high ion flux

conditions, photoresists masks display unacceptable dimensional degradation, and dielectric

masks must be used. For SiO2, typical etch selectivities of 3.5-5 are found for NiFe and NiFeCo

over the dielectric mask.

Layers of Ni0.8Fe0.2 and NiFeCo in the thickness range 3000-5000Å were deposited on Si

by dc magnetron sputtering, and patterned lithographically with photoresist. In some cases the

photoresist was used to transfer the pattern into an underlying SiO2 or SiNx (1500-3000Å thick)

layer that had been deposited by plasma-enhanced chemical vapor deposition at <300oC. In this

fashion we were able to compare the relative merits of photoresist and dielectric as mask

materials. Dry etching was performed in a Plasma Therm SLR 770 system in which the plasma

is generated in an ASTEX 4400 low profile Electron Cyclotron Resonance (ECR) source

operating at 2.45 GHz. As the source power is increased in this tool from 0-1000W the ion

density increases from ~109-5x1011 cm-3. The He backside-cooled sample chuck is separately

biased with rf power (13.56 MHz) between 50-250W to control ion energy between -40 and -

275eV (this depends on both rf chuck power and ECR source power). The process pressure was

generally held at 1.5 mTorr. Electronic grade gases were fed into the ECR source through mass

flow controllers at a total flow rate of 15 standard cubic centimeters per minute (SCCM).

Several different gas chemistries were examined, and the sample temperature was ≤80oC at all

times. Etch rates were determined by stylus profilometry after removal of the mask material (in

acetone for resist, HF/H2O for SiO2 or CF4/O2 barrel etching for SiNx). The near-surface

composition was examined by Auger Electron Spectroscopy (AES) and feature anisotropy by

scanning electron microscopy (SEM).

Figure 1 shows the etch rates of NiFe as a function of microwave ECR source power at

fixed rf chuck power (top) and as a function of rf chuck power at fixed source power (bottom).

There are several features to note in each plot. Firstly, only Cl2/Ar provides a clear etch-rate

enhancement over simple Ar sputtering and this rate is proportional to source power over the

range 400-1000W. We found from separate experiments that the etching is not limited by the

supply of Cl2 to the surface under these conditions, since increasing the ratio of Cl2-to-Ar

actually decreased the etch rate. Rather, the key feature is maintaining an argon ion-to-chlorine

neutral ratio that allows a continuous balance between formation of NClx and FeClx products,

and their efficient ion-assisted desorption. If the Ar-to-Cl2 ratio is allowed to become too large,

we revert to basically physical sputtering. Conversely, if the Cl2 coverage density becomes too

high (via discharge composition, pressure or having too low an ion flux or energy), then the

etching is quenched, and one may even have net deposition through formation of a chlorinated

selvedge layer. The second feature of the data in Figure 1 is that SF6/Ar or CH4/H2/Ar plasma

chemistries produce etch rates lower than simple sputtering, indicating that the fluoride and

methyl-adduct reaction products are not volatile, and actually shield the NiFe surface, reducing

the sputter rate. Similarly, in a Cl2/Ar discharge the NiFe etch rate is again lower than that of Ar

sputtering. These are two possible contributions to this result - the light H2+ ions are inefficient

in sputtering the nickel and iron chlorides and optical emission spectroscopy shows that the

atomic Cl density is reduced in a Cl2/H2 discharge relative to Cl2/Ar at the same conditions

through recombination with atomic hydrogen. The similar dependencies of NiFe removal rate in

Cl2/Ar and pure Ar with microwave power indicates that the rate-limiting step with the former is

still the desorption of the chloride etch products since the main effect of increasing source power

is the associated increase in ion flux to the sample.

Figure 1. NiFe etch rates in different plasma chemistries at fixed rf chuck power (150W) and pressure (1.5mTorr) as a function of microwave source power (top) or rf chuck power (bottom).

The data in the lower part of Figure 1 shows that there is a threshold ion energy (at

constant ion flux) to efficiently remove the etch products. The NiFe rate increases rapidly with

chuck power (or equivalently ion energy) and is above sputter rate at a power of ~70W,

corresponding to a dc self-bias of -65V. Above a chuck power of ~150W (dc self-bias of -135V)

the etch rate decreases. This type of behavior is commonly observed in ECR etch processes, and

is usually ascribed to the active etch species (Cl materials in this case) being removed by ion-

assisted desorption before they have a chance to complete formation of the etch products. We

observed the same qualitative trends in etch rate of NiFeCo with both source and chuck power,

with all rates being roughly 50-80% lower than for NiFe.

Figure 2 shows AES surface scans of NiFeCo after a brief etch in 1.5 mTorr, 150W rf

chuck power discharges of 10Cl2/5Ar, with either 0W ECR source power (top), which

corresponds to conventional reactive ion etching (RIE), or with 1000W source power (bottom).

In the former case there is a large peak due to chlorine resides, consistent with formation of a

thick (≥100Å) chlorinated selvedge or reaction layer that prevents further etching. However with

a high ion flux simultaneously incident with chlorine adsorption, the chlorinated etch products

are removed as quickly as they form, and a balance is maintained between product formation and

product removal by ion-assisted desorption. This mechanism exposes a fresh surface for the

process to occur all over again. Similar results have been reported previously for ECR Cl2/Ar

etching of InP, where again the InCl3 etch product is normally involatile at normal temperatures

under RIE conditions. Note in Figure 2 that the Cl-to-Ni ratio (in raw, uncorrected counts)

decreases from ~2:1 for the RIE sample to ~0⋅4:1 for the ECR sample.

The presence of chlorine-related surface (and sidewall) residues is clearly of concern with

respect to subsequent corrosion of the metal. This is a similar situation to that of Cl2/BCl3

plasma etching of Al in Si microelectronics technology, and in the current case we have

investigated a number of in-situ post Cl2-etch cleaning steps to remove these surface residues.

AES depth profiling of the ECR etched samples showed the Cl was restricted to ≤20Å from the

immediate surface. The Cl concentration could be reduced to the sensitivity limit of AES (≤1

at⋅%) by a 3 min, 15 mTorr H2 plasma treatment at 1000W ECR source power with zero Watts rf

chuck power. We expect that the chlorine residues are volatilized as HCl during exposure to the

H2 plasma. Note that we have only examined surface residues on the field between features and

at this point not on the feature sidewalls where the initial residue thickness might be expected to

be greater because of the absence of ion bombardment during the initial etch step.

Figure 2. AES surface scans of NiFeCo after a brief etch in 10Cl2/5Ar, 1.5 mTorr, 150W rf chuck powerdischarges with either 0W microwave source power (top) or 1000W microwave source power(bottom).

SEM micrographs of features etched into 5000Å thick NiFe layers masked by 1500Å

thick oxide are shown in Figure 3. The sidewalls are smooth and straight, and we have not seen

any obvious visual effects of corrosion over a period of several months indicating there is not

gross contamination of the sidewall with chlorine residues. Note that photoresist masks did not

hold up well for microwave source powers above ~600W because the high ion flux leads to

significant preferential sputtering of H from the near-surface and degrades the resist morphology

and dimensional integrity. Under these conditions, the oxide and nitride masks were stable and

are better choices as masking materials.

The selectivity for etching NiFe and NiFeCo over the dielectrics in 150W chuck power,

10Cl2/5Ar discharges is shown in Figure 4 as a function of microwave source power. For both

magnetic materials, oxide provides higher selectivity than nitride, and the selectivities are higher

relative for NiFe due to its higher etch rates compared to NiFeCo.

Figure 3. SEM micrographs of features etched into NiFe layers using an ECR 10Cl2/5Ar plasma (800Wmicrowave source power, 150W rf power, 1.5 mTorr). The oxide masks are still in place.

In summary high rate etching of NiFe and NiFeCo is possible at ≤80oC under high ion

density ECR plasma conditions by balancing the ion-neutral ratio and preventing the formation

of a selvedge layer. The high ion flux essentially provides the impetus for etching, replacing the

need for the elevated sample temperatures (≥200oC) necessary under conventional RIE

conditions. These new etch regimes accessible with high density plasma reactors may have

useful application to fabrication processes for advanced magnetic devices.

Figure 4. Etch selectivity of NiFe and NiFeCo over SiO2 and SiNx mask materials in 10Cl2/5Ar, 1.5 mTorr,150W rf chuck power discharges, as a function of microwave source power.

2) NiMnSb Heusler Alloy Thin Films

A variety of plasma etching chemistries were examined for patterning NiMnSb Heusler

alloy thin films and associated Al2O3 barrier layers. Chemistries based on SF6, Cl2 and BCl3 were

all found to provide faster etch rates than pure Ar sputtering. In all cases the etch rates were

strongly dependent on both the ion flux and ion energy. Selectivities of ≥ 20 for NiMnSb over

Al2O3 were obtained in SF6 - based discharges, while selectivities £ 5 were typical in Cl2, BCl3,

and CH4/H2 plasma chemistries. Wet etch solutions of HF/H2O and HNO3/H2SO4/H2O were

found to provide reaction-limited etching of NiMnSb that was either non-selective or selective,

respectively, to Al2O3.

Ferromagnetic thin films and multilayers are currently being used in various magnetic

recording and non-volatile memory applications. Interest in these materials for microelectronic

applications has increased dramatically since th4e discovery of giant magnetoresistance (GMR)

in multilayers comprised of alternating ultrathin (10-50Å) ferromagnetic/noble metal layers.

Briefly, the GMR effect can be understood in terms of spin-dependent scattering of conduction

electrons within the ferromagnetic layers and/or at ferromagnetic/non-magnetic interfaces. Given

a difference in resistivity between spin-up and spin-down electrons ("=D↑/D↓≠1), the resistance

of the multilayer can be varied by changing the relative magnetic orientation of the ferromagnetic

layers within an electron mean free path. Ideally, this spin-selectivity would be infinite, so that

complete control over spin-currents in magnetic devices could be achieved. This can be realized

in principle in so-called half-metallic materials which are metallic for one spin type and

insulating (or semiconducting) for the other. While a number of ferromagnetic half-metals have

been predicted based on band structure calculations, there has not been straightforward

experiments that demonstrate this behavior. The Heusler alloy NiMnSb is a strong candidate for

useful half-metallic behavior, due to its high Curie temperature (720K). Recently, significant

experimental effort has been expanded to deposit high-quality thin-films of NiMnSb for

magnetoresistive applications. The spin filtering effect of NiMnSb thin layers will be maximized

when the current flows normal to the layer plane, either resistively or by tunneling through an

oxide barrier such as Al2O3. Therefore, the fabrication of small, high-quality etched patterns is

particularly important to the potential application of these films. In this paper, we report on the

plasma etching of sputter-deposited NiMnSb thin films, and on selective wet and dry etch

processes for NiMnSb and Al2O3 structures.

Etch rates were faster than with Ar alone obtained for both materials in Cl2/Ar discharges,

as shown in Figure 5 (top). The enhancement in NiMnSb etch rates relative to pure Ar under the

same conditions ranged from ~10% at low microwave source powers to ~30% at 1000W, even at

lower ion energies. The etch rates for NiMnSb were up to a factor of two higher than for Al2O3 at

high source powers. While etch products such as SbCl5 and AlCl3 are quite volatile, nickel and

manganese chlorides have relatively low vapor pressures and require ion assistance to promote

their desorption. The advantage of the high ion fluxes under ECR conditions is two-fold. First, in

strongly bonded materials such as Al2O3, one of the rate-limiting steps will be the ability to

initially break bonds in order to allow the etch products to form. Therefore, at constant etch yield

(i.e. atoms of the substrate removed per unit incident ion ), a higher ion flux will produce a

higher etch rate. The second advantage of the ECR discharges is that the high ion flux more

effectively assists etch product desorption. Under more conventional reactive ion etching

conditions this ion-assisted desorption is inefficient, allowing a thick selvedge or reaction layer

of the involatile etch products to form on the sample surface. This layer shields the surface from

further interaction with the plasma and etching stops. The selectivity for etching NiMnSb over

Al2O3 is ≤ 2 in Cl2/Ar over the microwave source power range 300-800W. Qualitatively similar

results were obtained with BCl3/Ar discharges, with selectivities of 1 at 600W microwave power

and ~5 at 1000W source power.

The most efficient etching of NiMnSb was found with the SF6/Ar plasma chemistry. In

fact the etch rates were ≥1.6Êm min-1 even for the lowest microwave source power at which ECR

discharges were stable, namely 400W. The etch rates were impossible to accurately quantify at

high powers because the entire NiMnSb film disappeared in ≤ 15secs under these conditions. By

contrast, as shown in Figure 5 (bottom), the etch rates of Al2O3 are ≤1200Å min-1 over the entire

range of source powers, leading to selectivities of NiMnSb over Al2O3 of ≥20. This is not too

surprising given that AlF3 is significantly less volatile than AlCl3, reducing the etch rate of Al2O3

in fluorine-based plasma chemistries relative to that in chlorine-based chemistries.

To summarize the dry etch results, we find that Cl2-, BCl3-,and SF6-based plasmas all

provide some chemical enhancement of etch rates relative to pure Ar sputtering under the same

conditions. The etch rates increase with both ion flux and ion energy as sputter-assisted

desorption of the etch products is enhanced. The etched surfaces of NiMnSb retain their

stoichiometry beyond the top ~75Å. Near equi-rate etching of NiMnSb and Al2O3 is achieved in

Cl2/Ar or BCl3/Ar at microwave source powers ≤ 600W at low rf chuck power (150W), while

selectivities up to 5 are obtained in CH4/H2/Ar over a wide range of conditions, or with Cl2/Ar

and BCl3/Ar at high microwave powers. The highest selectivities (≥20) were achieved with the

SF6/Ar plasma chemistry.

Figure 5. Etch rates of NiMnSb and Al2O3 as a function of microwave source power in 1.5mTorr, dischargesof Cl2/Ar at 150W rf chuck power (top) or SF6/Ar at 250W rf chuck power (bottom).

3) LaCaMnO3/SmCo Thin Films

A number of different plasma chemistries have been employed for patterning of

LaCaMnO3 and SmCo thin films for application in magnetic field-biased structures based on the

colossal magneto-resistive effect. For LaCaMnO3 there was no chemical enhancement in etch

rate over simple Ar sputtering for Cl2, SF6 and CH4/H2 plasmas under high ion density

conditions. This is expected based on the vapor pressures of the prospective etch products. For

SmCo however, etch rates up to 7,000 Å·min-1 were obtained in Cl2/Ar plasmas, which is an

order of magnitude faster than Ar sputtering under the same experimental conditions. Smooth

etched surface morphologies and anisotropic sidewall were obtained for both materials over a

wide range of plasma source and chuck powers.

New interest in the design of magnetic sensors, magnetic memories and other devices

based on magnetic and magneto-resistive materials has been initiated by the discovery of

multilayered “giant magnetoresistive” (GMR) materials and more recently by the study of la-

manganite perovskite “colossal magnetoresistive” (CMR) materials. In both cases the

implementation of practical microelectronic devices requires the development and control of

etching and patterning procedures which do not degrade the magnetic properties of the materials.

Generally, the magnetic field response of magnetic thin-film materials is highly sensitive to their

microstructural and interfacial properties. In the case of La-manganite materials, another

limitation at present is that the observed field-induced resistivity transition is most sensitive

above magnetic fields of about 1 Tesla. Thus the necessary bias field is too large to be produced

by an electrical current within the device, as is done for typical low-field magnetoresistive

sensors. Consequently it may be necessary to provide a fixed, built-in bias field within the

device, from a hard magnet material such as SmCo. In that case etch and patterning recipes must

also be developed for such materials. In this paper we report on the Ar-based plasma etching of

LaCaMnO3 and Sm-Co-based materials which may be used as the basis for CMR-device

structures, and on the effect of different plasma chemistries, namely SF6, CH4/H2 and Cl2

additions, on the etch characteristics.

Table I lists boiling points of some potential etch products in the plasma chemistries

investigated here. To achieve smooth etched surfaces, it is obviously necessary to remove the

etch products at equal rates for all of the elemental constituents and ion assistance is critical in

desorbing the less volatile products.

Figure 6 shows the dependence of LaCaMnO3 etch rate on dc self-bias on the sample

chuck for the four different plasma chemistries. Note that the results for Cl2/Ar basically follow

those for pure sputtering (Ar), indicating that the La, Ca and Mn chlorines are not particularly

volatile even at the high ion fluxes (~1015 ions·cm-2·sec-1) available in the ECR tool. In other

words, the etching is limited by the sputter yield at each ion energy; to increase the volatility of

the chloride etch products it would be necessary to increase the substrate temperature. This is

generally not an attractive option from a practical viewpoint because of the limitation it places on

mask materials and the requirement for reproducible thermal contact for each sample. The

results for the SF6/Ar and CH4/H2/Ar plasma chemistries show that the etch products for these

are even less volatile and the etching is most likely retarded by formation of a selvedge or

reaction layer with these chemistries.

Table I: Boiling Points of Potential Etch Products of LaxCa1-xMnO3 and SmCo.

Etch Products Boiling Point

(oC)

Etch Products Boiling Point

(oC)

LaCl3 >1000 SmCl2 >740LaF3 …… SmCl3 ……La2S3 2100 vac. SmF2 >2400(CH3)3La …… SmF3 2323CaCl2 1935.5 SmH2 ……CaF2 2533.4 (CH3)2Sm ……CaH2D 816 …… CoCl2 1049(CH3)2Ca …… CoCL3 ……CaS d CoF2 ≈1400MnCl2 1190 CoF3 ……MnCl3 d CoH2 ……MnF2 > 856 (CH3)2Co ……MnF3 dMnH2 ……(CH3)2Mn ……Cl2O 2.2ClO2 11Cl2O3 ……Cl2O6 ≈200O2 -183Cl2O7 82F2O -144.75F2O2 -57H2O 100(CH3)2O -23.6

Figure 6. Etch rate of LaCaMnO3 in various plasma chemistries as a function of chuck self-bias. The ECRsource power was held constant at 1000W.

There was a substantial degree of chemical enhancement observed for the etching of

SmCo in Cl2/Ar chemistries, as shown in Figure 7. The etch rate is approximately a factor of 10

to 12 higher than for pure Ar up to dc self-biases of ~-217V; at higher biases the etch rate with

Cl2/Ar saturates and then decreases. The self-bias corresponds fairly closely to the acceleration

voltage experienced by ions impinging on the sample. As this voltage increases so does the

average ion energy. Up to a particular energy, the etch rate is increased by the higher sputtering

efficiency that more effectively desorbs the etch products. However above this energy (in these

experiments ~250eV) the ions are able to desorb the chlorine radicals before they are able to

react with the SmCo and hence the etch rate decreases. The SF6/Ar plasma chemistry provides

etch rates faster than pure sputtering at biases up to ~-200V, but show a dependence on bias that

is less than that for Ar at higher values.

Figure 7. Etch rate of SmCo-based films in various plasma chemistries as a function of chuck self-bias. TheECR source power was held constant at 1000W.

As predicted by the volatilities of the potential etch products, we were unable to obtain

any degree of chemical enhancement in plasma etching of LaCaMnO3 in any of the common

chemistries (Cl2, F2 or CH4/H2). For this material, therefore, simple Ar ion milling at modest

acceleration voltages to avoid preferential sputtering effects is probably the best choice for

pattern transfer processes. This is a disadvantage if deep features are required, because the

associated mask thickness would need to be similar to the etch depth in the LaCaMnO3. Smooth,

anisotropic pattern transfer is achieved at modest ion energies under ECR plasma conditions. By

contract, chemical etch enhancements relative to pure Ar sputtering were obtained for SmCo

with Cl2/Ar over the whole range of dc self-biases examined and with SF6/Ar at low biases (up to

approximately -200V). The sidewalls on etched features were again vertical, and the etched field

quite smooth. Selectivities as high as ~12 were obtained for SmCo with respect to SiO2 and SiNx

in Cl2/Ar discharges.

Ultrathin Magnetic FilmsJ.R. Childress, University of Florida

F. Sharifi, University of Florida

1) Magnetic and Magnetoresistive Properties of Low-Dimensional Multilayers

We have succeeded in establishing a reproducible fabrication process for forming one-dimensional magnetic structures. Our present nanowire fabrication process requires three steps:1) deposition of wire material, 2) e-beam patterning, and 3) ion-milling. Before deposition,approximately 1 micrometer of SiO2 is grown on a Si wafer by wet thermal oxidation.

(a)

(b)Fig.1

After the oxide growth, the appropriate magnetic films are sputter deposited underoptimal growth conditions. For the Ni nanowires, the growth is done at 2 mT Ar pressure, at arate of 1nm/minute for a total film thickness of 50 nm. After the film deposition, an electronbeam resist bi-layer consisting of 50 nm (PMMA-MAA) and 100 nm of PMMA is spun andbaked. At this stage, the samples are e-beam patterned and developed. The pattern is thenmetallized by DC sputter deposition of Nb using a collimating body in front of the samplefollowed by lift-off. Once the Nb mask pattern is transferred, the Nb structure is used as a plasmaetch mask resulting in Ni nanowire pattern with integrated leads (Fig.1(a))

A major concern in this effort was to ensure that the processing techniques did not resultin degradation of the transport or magnetic properties of these epitaxial films. To this end,

resistivity measurements were performed on Ni wires produced through this fabrication processwith preliminary linewidths down to 75 nanometers (Fig.1(b)). These wires showed noappreciable change in room temperature resistivity after processing (Fig.2). Size scale effectswere manifested by an enhanced residual resistivity due to geometrically induced boundaryscattering (Fig.2) and a decreased AMR sensitivity (Fig.3 & 4).

Fig.2 Resistivity vs. temperature for processed and patterned Ni nanowires

Fig.3 Magnetoresistance vs. field-current angle for processed and patterned Ni nanowires

Fig.4 Magnetoresistance vs. temperature for processed and patterned Ni nanowires

Having established the feasibility of our processing procedure, we are now extendingthese measurements to smaller structures. Furthermore, these 1-d magneto-transport studies willalso be performed on the giant magnetoresistance multilayer structures.

2) Development of spin-polarized magnetic layers

This project is concerned with the fabrication and characterization of thin-film structures

based on sputter-deposited NiMnSb, which has been predicted to be half-metallic, i.e., be

conducting for only on spin polarization. This property is useful for giant-magnetoresistive

materials, as well as for the development of devices based on electronic spin currents. During

the past year, we have expanded our work from single-layer to multilayer films, and have begun

testing transport properties to evaluate the potential of NiMnSb-based structures. First, single-

layer films have been characterized by magneto-optical Kerr spectrometry (in collaboration with

IBM), to determine the band-structure similarity between our films and high-quality bulk samplesof NiMnSb. As shown in Fig.1, Kerr spectra of optimized films (Tsubstrate= 250• C, PAr= 2

mTorr, Rate = 0.25 Å/sec) match very closely with the published bulk spectra. While this does

not establish the band structure of the films, it demonstrates that the film properties match those

of high-quality bulk structures.

-0.35

-0.30

-0.25

-0.20

-0.15

-0.10

-0.05

0.00

0.05

1 1.5 2 2.5 3 3.5 4 4.5 5

Ker

r R

otat

ion

(deg

rees

)

Energy (eV)

Fig.1: (a) Kerr rotation spectra for 1000Å-thick NiMnSb thin films grown at 15W rf power,2mTorr Ar sputtering pressure and substrate temperatures of 300• C and 250• C. For comparison,the data from ref.(7) obtained on bulk NiMnSb samples is also shown.

To test the possibility of ultra-thin film deposition and multilayering, we have studied the

properties of NiMnSn/Cu and NiMnSb/Ag multilayers. As shown in Fig.2, the expected

magnetization of NiMnSb is conserved for ultrathin (30Å) NiMnSb layers in NiMnSb/Cu

multilayers, while that for NiMnSb/Ag multilayers is reduced by about 10-15%. This suggest

that greater interdiffusion occurs for Ag-based multilayers compared to Cu. Consequently, we

will focus on Cu as an interlayer material in the future. Also note (Fig.2) that as the Cu thickness

is increased above 50Å, a rapid degradation of the properties is observed, and that a gradualincrease in coercivity occurs at tcu is increase. This suggest that the overall structural quality of

the multilayers (with 10 repeated bilayers) decreases as tCu is increased. We believe that this

effect is due to a degradation of the multilayer interface upon layering, and that a reduction in the

total number of layers will be necessary in future structures, such as in the spin-valve multilayers

described below.

300

400

500

600

700

800

900

0

50

100

150

200

250

300

350

0 10 20 30 40 50 60 70

MS (

emu/

cm3 ) C

oercivity (Oe)

tCu

(Å)

Ref[7]

T=10K

Fig.2: Saturation magnetization (MS) as a function of tCu for [NiMnSb(30Å)/Cu(tCu)]10

deposited at 250oC (closed circles) and 200oC (open circles). The discontinuous line correspondsto the MS value for 1000Å-thick NiMnSb films from ref[1]. Coercivity versus tCu is also shown

for multilayers deposited at 250oC (open diamonds).

Finally, we have begun to fabricate trilayer spin-valve structures, to test the GMR

response of NiMnSb films combined with Co, NiFe and NiMnSb. Cu was chosen as the

interlayer based on our study of NiMnSb multilayers. Structures were made to measure both

current-in-plane (CIP) magnetoresistance and current-perpendicular-to-plane (CPP)

magnetoresistance (in collaboration with Michigan State University). In the event of a large

spin-polarization in NiMnSb, it is expected that the CPP geometry will yield large GMR effects

due to the strong spin-dependent scattering within the volume of the NiMnSb layers. Fig.3

shows the results of magnetic and CIP-MR measurements of NiMnSb/Cu/NiMnSb spin-valves

where the top NiMnSb layer has been "pinned" by a 100Å-thick film of the antiferromagnet

FeMn. Ideal spin-valve behavior is obtained, with a near-perfect antiparallel alignment of the

magnetization in a field of 100-200Oe, where an increase in the resistivity is observed as

expected, with a small effect size due to the dominance of the thick Cu layers in this geometry.

Measurement in the perpendicular (CPP) direction are currently underway to better investigate

the scattering within the volume of the NiMnSb layers.

Fig.3: Magnetoresistance (top) and magnetization loop (bottom) for aNiMnSb(200Å)/Cu(150Å)/NiMnSb(100Å)/FeMn(100Å) spin-valve structure deposited on Si.

3) Molecular Beam Epitaxy Capability

As projected in the previous report, we have completed this year the development of our

molecular beam epitaxy capability. The system has very recently been outfitted with its final

components, including a substrate manipulator and heater, load-lock system, and reflection high-

energy electron diffraction system. This new evaporation capability (Fig.4) will be used to

fabricate low-dimensional magnetic structures using in-situ nanomasks (see project 1 above), as

well as patterned Pt/Co multilayers structures.

K-Cell 4-pocket e-beam

e

Quartz

SubstrateRHEED

Ion Pump

Rotation 0-20 rpm

300-1300K

1400ÞC

Ion Pump Ti Sublimation LN2 shroud P-5x10-10 Torr

ion clean & etch

Computer Control

Turbo Pump

Fig.4: Schematic of new e-beam evaporation system

4) Granular Multilayers

Granular Co-Cu alloys, which contain nanometer-size Co grains precipitated in a Cu

matrix, have been of interest for both their enhanced magnetic properties and magneto-transport

characteristics. Their enhanced magnetic properties are consistent with those of single-domain

magnetic grains. These properties include shape dominated magnetic anisotropy, high coercivity,

and enhanced remanence.[1-3] Giant magnetoresistance (GMR) can be observed in these

materials upon alignment of the magnetization of individual grains in an applied field. We haveinvestigated the blocking temperature and coercivity of granular [Co25Cu75 / Cu] multilayer

films deposited at 100• C, 150• C, and 250• C, as a function of Cu thickness tCu (0-50Å) and

Co25Cu75 composite thickness tG (5-250Å), as shown schematically in Fig.5. In particular, the

role of 2-D confinement and interlayer coupling was investigated to evaluate the possibility of

enhancing both the coercivity and superparamagnetic blocking temperature to values more useful

for further applications.

tGCo/Cu

Cu

Cu

Glass Substrate

x n

Co/Cu

tCu

Fig.5: Schematic of granular (CoCu)/Cu multilayer structure

Both the coercive field at 10K and the maximum superparamagnetic blockingtemperature TB are found to be sensitive to finite-size effects in single-layer films, and to

interactions between layers in multilayer films. Our results indicate that the magnetic properties

of granular alloy layers can be engineered to a large extent by selectively modifying the local

environment of the Co particles, in particular, altering the nature and degree of magnetic

coupling between particles. One striking example of the effect of multilayering at the nanometer

scale in these materials is shown in Fig.6, which displays the measured GMR ratio as a function

of Cu spacer layer thickness. The GMR is increased by a factor 2 both at low temperatures and

room temperature upon spacing the granular layers by 2 nm of pure Cu. The origin of this

increase is either the decrease of direct (pinhole) coupling between neighboring magnetic

particles, or the increase in dipolar or indirect exchange coupling at these length scale, favoring

an anti-parallel orientation of the particle moments in zero magnetic field.

0

5

10

15

20

25

30

35

0 10 20 30 40 50 60

MR

(%

)

Cu spacer thickness (Å)

T=10 K

T=300 K

TSUBSTRATE

=150ÞC

Bulk

Fig.6: Saturation magnetoresistance ratio at 10K and 300K, as a function of Cu spacer layerthickness, for granular (CoCu)50Å /Cu multilayer films deposited at 150• C.

E-beam Fabricated NanostructuresF. Sharifi

University of Florida

1) High-Density GMR Multilayer Structures

We have developed processing techniques to fabricate ultra-high density MRAM devicesbased on GMR multilayer structures. The process involves creating an etch mask out of the toplayer of back sputtered quartz (BSQ) by e-beam lithography. First, we remove any excess BSQby etching the top surface in dilute HF until there are 400-500 angstroms of BSQ left. Next, wespin 3% PMMA at 5000 RPM for 60 seconds on the BSQ, and bake the PMMA for 6 hours at155° C. This produces a resist layer about 1300 angstroms thick. We then use a modified SEM towrite a bit pattern at 35 kV and a total dosage of 15-20 µC/cm2. Next, we develop the patternedresist in MEK/ETOH, rinse first in MIBK/IPA, and rinse a second time in IPA. We then RIE etchthe patterned BSQ in CCl2F2 for 20-30 minutes until all of the BSQ is removed from within thepatterned area. Finally, we RIE etch for 10 minutes in O2 to remove any polymerized resist fromthe surface. The patterned BSQ is now ready to be used as a mask for etching the underlyinglayers.

Figure 1 shows two SEM micrographs of BSQ patterned by e-beam lithography. Themicrographs were taken after the CCl2F2 etch and before removal of polymerized resist. The goalof this project is to manufacture non-volatile MRAM structures at a 64 Gbit/in2 pattern density.We have exceeded this density and are now developing patterning techniques to extend suchdensities over large-area substrates.

2) Electron Tunneling in Magnetic Semiconductors

We have undertaken an exhaustive series of electron tunneling studies of the rare-earthhexaboride magnetic semiconductors. These measurements have determined the band structureof these materials and the role magnetic interactions play in their electron transport properties.Our measurements have shown that the accepted model of d and f band hybridization isinadequate in explaining the observed transport properties. Rather, we have shown that a latticedistortion, possibly due to a Jahn-Teller effect, causes an indirect band gap at the k-space X pointof these structures. It is this indirect bad gap that is responsible for the transport properties ofthese materials.

(a)

(b)Fig. 1 SEM micrographs of BSQ patterned by e-beam lithography. Image a) was taken at 45° to samplesurface. Image b) was taken at 30° to sample surface with the sample rotated by 90° with respect to imagea). The areal density is 3.3 Gbits/cm2. The graininess is due to polymerized resist.

Theoretical Modeling of Electron Transportin Magnetic StructuresS. Hershfield, University of Florida

1) GMR in laterally confined multilayers

One of our initial goals in this project was to determine the effect of reducing the size of

GMR devices. With Kingshuk Majumdar (student) and Jian Chen (post-doc) we have solved the

Boltzmann equation for the giant magnetoresistance as a function of the width in laterally

confined multilayers. As expected the surfaces induce more scattering. Unless special

precautions are taken, this scattering is not strongly spin dependent, and the GMR is reduced as

the width of the laterally confined multilayers is decreased. However, if the surfaces can be

made to have strong spin-dependent scattering, with for example a special coating, then the GMR

can actually be enhanced as one reduces width. In any case, the length scales at which these

changes from ordinary multilayer behavior become important is quite small, of order the mean

free path and the thickness of the layers, which can be 100 Å or less (see Fig.1)

2) Effect of spin-flip scattering on the CIP GMR

Traditional calculations of the GMR in the CIP geometry have not included the effect of

spin-flip scattering because the spin-diffusion lengths are usually assumed to be quite large.

From recent experiments done at Michigan State and in France, it has become apparent that the

spin diffusion length in permalloy, which is one of the most widely used magnetic materials, is

actually quite small, possibly only a few times the elastic mean free path. Thus, we have solved

the Boltzmann equation in the CIP geometry in the presence of strong spin-flip scattering. For

the GMR due to bulk spin scattering anisotropies we find that the GMR is greatly reduced by a

small spin diffusion length; however, quite surprisingly, the GMR due to surface scattering

anisotropies is not reduced. Thus, having a small spin diffusion length selectively enhances the

role of surface spin scattering anisotropies.

Fig.1: Giant magnetoresistance of a three wire structure as a function of width for (a) bulk scattering, (b) surfacescattering and (c) both bulk and surface scattering. The symbols refer to different film thicknesses, tPM = tFM = 8Å(circle), 20Å (box), and 30Å,(triangle). In all cases the GMR decreases as we laterally confine the multilayers. Theorigin of this decrease in the GMR can be understood in terms of changing the effective mean free paths in the wires.As the wire width is reduced the effective mean free path within each wire decreases. To make this more quantitative

we obtain an effective mean free path for each wire and use these mean free paths in a multilayer calculation (infinitewidth wire). The results, which are shown as the solid lines, are in good agreement with the exact calculation(symbols). The parameters are chosen for a Co/Cu/Co structure.

3) Full quantum microscopic calculations

While the Boltzmann equation calculations are excellent for obtaining trends, to obtain a

full quantitative understanding of the giant magnetoresistance, one needs to include materials

details, such as realistic electronic structure and surface scattering. We have developed an

algorithm and a computer code based on the impurity averaged Green function technique and

Kubo's formula. Tat-Sung Choy, a graduate student, has tested this algorithm against the

Landauer formula averaging over different configurations of the disorder and found excellent

agreement.

We have chosen two classes of experiments to compare our calculations to: (i) the effect of

coating the interfaces of magnetic multilayers with different materials and (ii) recent experiments

of Schuller's group on very clean magnetic multilayers which show large oscillations in the

resistivity as a function of sample thickness at zero magnetic field.

In the case of interface coating, we have computed the GMR for Fe/Cr multilayers with

interfaces coated with V, Mn, Al, Ag, or Au. A large change in the GMR is obtained when the

coating layer is only one or two atomic layers thick, in qualitative agreement with the

experiments. We are waiting for a recently ordered computer to perform more extensive

calculations and compare quantitatively to the experiments.

In case (ii) Tat-Sung Choy has found a superlattice effect observable in samples where most of

the scattering comes from sharp interfaces. As the layer thicknesses change, oscillations in the

resistivity of up to 100% are found at zero magnetic field. Again we will compared directly to

the experiments once we have the computing power to include full band structure.

4) Magnetic Tunnel Junctions

For samples with very small grains and insulating barriers, such as nanoparticles and

quantum dots, one sees the effect of the Coulomb blockade, which comes from the charging

energy of a grain being larger than the temperature. Kingshuk Majumdar has recently computed

the conductance vs. voltage curves for double tunnel junction Coulomb blockade devices with

magnetic materials. The scale of the magnetoresistance in these systems is set by the junction

magnetoresistance of the two junctions in series. There are oscillations in the magnetoresistance

as a function of voltage which are closely correlated to the effects of the Coulomb staircase seen

in these and ordinary Coulomb blockade devices. The oscillations can either enhance or reduce

the magnetoresistance, depending on the materials used.

Deposition and Patterning of Magnetic Materials

Gary E. McGuire, Dorota Temple, MCNC

I. Summary

MCNC’s Role in the Program

The primary objective of the effort at MCNC, subcontractor in the present program, is to supportdevelopment of magnetic multilayer materials through:

• development of liftoff processes for patterning of magnetic materials on the micron and sub-

micron scale

• providing liftoff patterns for deposition of magnetic multilayers at the University of Florida

(UF)

• design of lithographic masks/reticles for use in patterning

• characterization of multilayers deposited at UF and MCNC using transmission electron

microscopy (TEM) with enhanced phase contrast

The secondary objective of the MCNC’s program is to develop an ion beam sputtering technique

for deposition of selected multilayer structures.

Accomplishments During the Last Reporting Period

• High resolution liftoff process capable of providing patterned layers with critical dimensions

as small as 0.5 µm has been developed and tested with several different materials and film

deposition techniques (rf sputtering and e-beam evaporation).

• Wafers with high resolution liftoff patterns were delivered to UF.

• A new reticle set with the layout optimized for investigation of magnetic and

magnetotransport properties of patterned layers has been designed and fabricated. A

fabrication run utilizing the new reticle set is in progress. Wafers with the new liftoff pattern

will be delivered to UF by the end of August.

• MCNC has developed expertise in TEM analyses of magnetic multilayers utilizing the phase

contrast originating at interfaces between the constituent layers. It was also demonstrated

that the focused ion beam (FIB) method of the TEM sample preparation leads to good quality

images of the multilayers. Eleven samples deposited at UF were analyzed via TEM at

MCNC.

• Construction of the ion beam sputter deposition system is nearing completion at MCNC. The

system will be used for depositing magnetic multilayers, properties of which will be

compared with properties of the same materials deposited by rf magnetron sputtering.

II. Detailed Description of the Progress

1) Development of Liftoff Patterning Techniques for Magnetic Multilayers

Motivation

Patterning techniques being developed at MCNC target pattern dimensions on the

submicron and micron scale. Although the focus of the overall program is on nanoscale-size

patterns, in order to understand magnetic and electrical properties of such nanostructures one

needs to examine a continuum of materials: from blanket films through micron and submicron

patterns to the nanoscale features.

In addition, the ability to pattern GMR materials on the submicron scale is critical for

applications of the films in the area of sensors and nonvolatile magnetic memory. The design

rules used currently in the device development are at a mark of a several micrometers. This limit

is imposed by the use of wet etching techniques for patterning. In order to fabricate devices with

submicrometer design rules one needs to employ either dry etching or liftoff techniques. The

advantage of the latter is that the process is generic with respect to the material being patterned,

so the same lithographic process can be used for all components of the multilayers.

High Resolution Liftoff

In lift-off, an inverse pattern is first formed in a sacrificial layer deposited on a substrate,

using lithographic techniques. Next, the metal film is deposited over the layer and in the

openings of the pattern. Those portions of the metal film which are deposited on the sacrificial

layer are removed (lifted-off) when the substrate is immersed in a suitable solvent, leaving

behind the desired metal pattern.

Figures 1a and b show a Cu film which was patterned via liftoff using the high resolution

process developed by MCNC. The same liftoff technique was used successfully to pattern

Ta(50Å)/Ag(28Å)/NiFe(20Å)/[Ag(55Å)/NiFe(20Å)]x4/Ag(28Å)/Ta(20Å) films and

Ta(50Å)/NiFe(500Å)/Ta(20Å) films deposited by rf magnetron sputtering at the University of

Florida.

(a) (b)Figure 1. SEM micrographs of a copper film patterned by high resolution liftoff process developed at MCNC: a)

plane view of the overall pattern, b) plane view of 0.6 µm lines.

Figure 2. SEM micrograph of a cross section of the photoresist liftoff pattern

The process utilizes a low viscosity (8 cp) negative resist manufactured by JSR, Inc.

under the trade name of NFR016D2. Following a 130°C hot plate bake and an HMDS vapor

prime of silicon substrates, the resist is spun on the substrates to a thickness of about 1 µm.

Coated wafers receive a 90°C 60 sec. hot plate soft bake. Wafers are exposed using the I-line

stepper (wavelength of 365 nm; expected resolution of 0.6 µm). Following a 90°C post-exposure

bake to facilitate reactions in the exposed photoresist, wafers are developed for 60 sec. in the

PD523D developer.

The process described above results in a pattern in the photoresist, a cross section of

which is shown in the SEM micrograph in Figure 2. As seen in the micrograph, the sidewalls of

the photoresist pattern have a negative slope which is critical for successful lifting off of metal

layers which are deposited on top of the pattern.

Reticle Design

SQUID Sample

SQUID Sample

SQ

UID

Sam

ple

Memory Cells

Sensors

SQ

UID

Sam

ple

Fig. 3. Diagram of the first level of the reticle set for patterning by liftoff.

The reticle which was used to obtain patterns shown in Figures 1 and 2 was chosen from

reticles already in MCNC’s possession, and, although it served well the purpose of testing the

high resolution liftoff process, it was not optimal for examination of magnetic and

magnetotransport properties patterned multilayers. We have therefore, together with the

University of Florida, designed a new reticle set specifically for investigating properties of

patterned GMR materials and devices. A schematic diagram of the first level of this reticle set is

shown in Figure 3.

The 4x4 array in the middle of the die depicted in Figure 3 contains lines with widths

varying from 0.5 µm to 20 µm, as shown in the appropriate insert in Fig. 3. The line length in

each element of the array is 500 µm, and the spacing between the lines is 3 times of the line

width. These structures will be used for magnetotransport measurements, and will allow for

examination of magnetoresistance of GMR materials as a function of the pattern dimension. For

these measurements, the lines will be shorted by metal pads patterned using the next reticle level,

not shown in Fig. 3.

The four rectangular samples, marked “SQUID Sample” in Fig. 3, will be used for

measurements of magnetization as a function of external magnetic field and temperature. As

shown in the magnified insert, these regions also contain lines; the line length is again 500 µm

and the spacing between the lines is 3 times of the line width. The line width is different for each

of the SQUID samples, and is equal to 0.5 µm, 0.8 µm, 1.2 µm or 2.2 µm.

In addition to the level shown in Figure 3, the reticle set contains three other levels which

will be used for patterning of contact metal layers using single and dual level contact

metallization schemes.

The reticle set was fabricated by DuPont Photomasks, Inc. and was delivered to MCNC

in August 1997. A fabrication run utilizing the new reticle set is in progress. Wafers with the

new liftoff pattern will be delivered to UF by the end of August.

2) Development of Techniques for Characterization of Magnetic Multilayers.

MCNC has developed capability in transmission electron microscopy of magnetic

multilayers. The multilayer structures generally have layer thicknesses ranging from 0.5-5 nm

with the critical constituent layers being 0.5-1.5 nm thick. These dimensions make TEM a

valuable tool for studying the atomic-scale structure of the layers and delineating interface

characteristics.

Figure 4. TEM micrograph of a multilayer stack Fe(50Å)/[Co(15Å)/Cu(20Å)]x20/Cu(30Å) deposited by sputtering.The image was recorded with -1.72 µm defocus to enhance the phase contrast. One unit in the scale visible in theFigure represents 2 nm.

Two methods of sample preparation were used for TEM analyses at MCNC. One was

dimpling of the examined film followed by argon ion milling. The other was based on focused

ion beam (FIB) milling. The FIB method allows for analyzing specific locations on a sample.

This is particularly useful when analyzing patterned layers. It was found that the FIB method

was at least as good in terms of the quality of the sample preparation as the dimpling-based

method; in some cases the quality of images obtained using FIB samples was even better than

when using the dimpled films.

As an example, Figure 4 shows a TEM image obtained from a sample of a

Fe(50Å)/[Co(15Å)/Cu(20Å)]x20/Cu(30Å) film deposited on a silicon substrate. The sample was

prepared for TEM by the FIB method. Since Co and Cu, with atomic numbers of 27 and 29,

respectively, are close neighbors in the Periodic Table of Elements, there is little compositional

contrast. However, when the TEM image is recorded at underfocus, as shown in Fig. 4, the layers

are clearly delineated due to the phase contrast between Co and Cu layers. The ability to bring

out the phase contrast allows for examination of the roughness and waviness of the individual

layers, which is an important microstructural characteristic impacting magnetotransport

properties of GMR materials.

3) Development of Ion Beam Sputtering Technique for Deposition of Magnetic MultilayerStructures

Motivation

Ion beam sputtering deposition (IBSD) is a promising technique for formation of GMR materials

as it offers a greater control over the microstructure of the films than rf or dc sputtering

techniques. Microstructural control might be critical to understanding magnetic and electrical

properties of the GMR multilayers due to the atomic scale of the thin films involved. We are

planning to investigate properties of selected GMR materials deposited by the IBSD technique,

and compare them with properties of the same materials formed by rf magnetron sputtering at the

University of Florida.

IBSD System

The IBSD system is currently under construction at MCNC. Figure 5 shows a schematic diagram

of the equipment. The main vacuum chamber is connected to a turbomolecular vacuum pump

capable of bringing the pressure in the chamber down to the lx10-8 Torr range. The pressure

during deposition is expected to be ~1x10-4 Torr. Specimen multilayers will be deposited on Si

(100) wafer substrates from Xe+ ion bombardment of metal targets using an rf ion source. The

rotating target holder has the capacity for four 5” targets. The holder is motorized and its

movement is controlled via computer. The substrates can also be rotated to enhance uniformity

of the deposition. The IBSD system is equipped with a load lock which will be used to exchange

substrates without breaking vacuum, thus avoiding long pump down times between film growth

experiments. The load lock is equipped with a turbo pump and capable of base pressure in the

2x10-7 Torr range.

The IBSD system has been assembled, and the vacuum chamber pressure of below 1x10-7

Torr has been achieved. We are currently installing the rf matching network and gas lines for the

ion gun. We are planning to begin sputter deposition qualification in September 1997.

Load Lock

Rotating Target Holder

RF Ion Gun

Substrate Heater

Turbo Pump

Turbo Pump

Fig. 5. Schematic diagram of the IBSD system

III. Plans for the Next Reporting Period

• Continue to support University of Florida by providing high resolution liftoff patterns for

patterning of magnetic multilayers

• Provide TEM analyses of multilayer magnetic films

• Complete construction of the IBSD system and begin development of sputter deposition

processes for selected magnetic multilayers

• Together with University of Florida, conduct a comparative study of properties of magnetic

multilayers deposited by ion beam sputtering and rf sputtering. Examine effects of the

process-specific microstructure on magnetic and magnetotransport behavior of the materials

• Optimize processes for formation of contacts to patterned magnetic multilayers using single

and dual level metallization schemes

Nanostructured Display MaterialsP.H. Holloway, University of Florida

During the past year, we have continued our research on optical emission from large

bandgap compound semiconductors whose size and geometry has been engineered to vary from

the nanometer to micrometer range, and from powder particles to thin films. This effort is aimed

at understanding the factors controlling the perceived optical brightness from powder versus thin

film solids, and the effects of grain and/or particle size for powders versus thin films. Ultimately,

we will study the emission from nanometer size grains/particles in which quantum size effects

will be expected and controlled. We have also developed a significant activity in self-consistent-

field molecular orbital-configuration interaction modeling of the optical transitions from the

semiconductors doped with rare earth activators. The objectives of this effort is to understand

the effects of ligand fields, crystal fields and point defects upon optical emission energies and

intensities, and to "defect or alloy engineer" the emission from the solids. The results of these

studies are presented below.

The efforts to engineer thin films of Y2O3:Eu for greater brightness has continued by

studies of pulsed-laser deposition (PLD) of films onto either bare Si or diamond coated Si

wafers. The microstructure and surface morphology of the deposited films were examined after

deposition using both scanning electron microscopy (SEM) and atomic force microscopy (AFM).For films on bare polished Si wafers, the Y2O3:Eu films consisted of crystallites about 100 nm

and 150 nm in diameter after deposition at 500 or 700• C, respectively. On hot filament CVDdiamond coated (»2.5 µm thick) Si wafers, the Y2O3:Eu crystallite size was larger (150 nm and

300 nm at 500 and 700• C deposition temperature, respectively) and in addition the nodular

growth of the diamond on the Si led to a secondary nodular morphology with dimensions of

about 3 mm. The brightness from as deposited films increased as the deposition temperature was

increased from 200 to 700• C, as shown in Fig. 1. Also shown in Fig. 1, at 700• C the films

exhibited photoluminescent intensities twice that from smooth Si substrates and intensities equal

to 80% that of a monolayer powder particle film of equal thickness.

PLD films on sapphire which were post annealed at 1200• C were tested for brightness

under cathodoluminescence conditions, and were five times brighter than any previous sampleexamined, including films and screened Y2O3:Eu powders. At an excitation energy of 7 KV and

current of 5 µA, a brightness of 7000 cd/m2 was measured. At the same voltage and a current of

50 µA, the brightness was 15,000 cd/m2 suggesting that some thermal quenching of

luminescence was occurring. However even after irradiation for 30 minutes with a beam size of

3 mm, no degradation of emitted intensity was detectable. All of these data indicate that optical

scattering in a thin film is extremely critical to the perceived brightness from optical emission,

and the film geometry must be controlled in order to increase the brightness.

Fig.1. Photoluminescent intensity from Y2O3:Eu films on bare or diamond-coated Si wafersversus deposition temperature.

With respect to theoretical modeling of optical transitions in wide bandgap compound

semiconductors, the effect that different alkaline earth sulfide (AES) host materials have on the

Ce+3 5d→4f optical transitions was investigated using both crystal field and self-consistent-field

molecular orbital-configuration interaction (SCF/CI) techniques. The details of each model were

discussed and their results compared for MgS:Ce, CaS:Ce, SrS:Ce and BaS:Ce. The results from

crystal field theory did not match well with experimental data for BaS:Ce without introducing

factors to account for non-ideal lattice and phase behavior. The predictions from SCF/CI were in

excellent agreement with the experimental data from these samples, as shown in Table 1. Even

the red shift of the spectroscopy from BaS:Ce relative to that of SrS:Ce was correctly predicted.

In addition, calculated oscillator strengths of the electronic transitions in SrS:Ce and BaS:Ce

were fit with Gaussian shapes to model the vibronic structure. Both the absorption and emission

spectra were generated and were found to be in good agreement with experimental spectra. A

population analysis of the configuration interaction states indicates that the trend in emission

energies is caused by differing extents of covalency experienced by the Ce 5d orbitals in the

various host matrices.

Table I: Calculated and Experimental electron energy levels for Ce in sulfide hosts of MgS, CaS,SrS or BaS.

Etching of Flat Panel Display Materials

S.J. Pearton, University of FloridaP. Holloway, University of Florida

Thin film electroluminescent (EL) displays occupy a small sector of the total flat panel

display market relative to non-emissive devices such as those based on liquid crystals, but

potentially offer advantages with respect to broader operational temperatures. A typical thin film

electroluminescent device has a metal-insulator-semiconductor-insulator-metal (MISIM)

structure in which the phosphor layer is sandwiched between two dielectric layers, which in turn

are sandwiched by two conductive layers. The phosphor layer emits light when a sufficiently

high electric field strength (typically ≥2MV⋅cm-1) is maintained across it. Typical materials are

ZnS (doped with Mn for red emission or Tb for green) and SrS (doped with Ce for blue

emission). The insulating layers on either side of the phosphor act as current limiters - typical

materials are Al2O3 and alumina/titania. Finally, the transparent conducting electrode material is

generally indium tin oxide (or ITO), In2O3 for the viewing side, with metal electrodes such as

TiW or Al on the other side of the EL device or panel.

A number of recent reports have appeared on reactive ion etching of materials for flat

panel displays. SnO2 and ITO have been etched with CH4/H2, HBr, Cl2/Ar and HI, while

aluminum oxide was etched in CF4/O2. Kuo has given a review of plasma processing of a-Si:H,

ITO, TaOx and glass substrates for active matrix LCD-type displays. It is apparent that improved

dry etch processes are necessary for volume production of the various types of displays. High ion

density plasma sources such as inductively coupled plasma (ICP), helicon and electron cyclotron

resonance (ECR) offer near-independent control of ion density and energy and hence a wider

range of processing conditions than conventional capacitively coupled reactive ion etch (RIE)

systems. Some promising results on application of high density plasmas have already appeared,

mainly directed at amorphous Si thin film transistor fabrication.

Figure 1 (top) shows etch rates as a function of Cl2 percentage (by flow) in Cl2/Ar

discharges (800W microwave power, 150W rf power, 1.5 mTorr). There is a degree of chemical

enhancement for all the materials, as evidenced by the increases in the rate as the discharge

composition changes from pure Ar to pure Cl2. The general drawbacks of pure Ar sputtering for

pattern transfer include poor selectivity with respect to mask materials and redeposition onto

feature sidewalls. Similar etch rate data is shown for BCl3/Ar discharges at the bottom of Figure

1 - the same basic trend of a small chemical enhancement with increasing BCl3 percentage is

found as for Cl2/Ar, with the overall etch rates for TiW and ZnS lower than with the latter

chemistry.

Figure 1. Etch rates of display materials as a function of discharge composition in (top) Cl2/Ar or (bottom)BCl3/Ar plasmas (800W microwave power, 150W rf power 1.5 mTorr pressure).

As microwave power and hence ion density increases in the Cl2/Ar discharges, there is

again a general trend of increased etch rates although the increased plasma conductivity does

reduce chuck dc self-bias and at the highest microwave powers this reduction in average ion

energy reduces the removal rate of ATO, ZnS and ITO. This suggests the etch rates of these

materials are still desorption-limited at 1000W ECR power under our conditions.

The CH4/H2 chemistry is attractive because it is not corrosive and does not require gas

cabinets for storage of the cylinders, but it provides significant etch rates only for SrS and ZnS

(Figure 2, top). The etch products in these cases are probably metalorganic strontium and zinc

species, plus H2S, i.e. the reverse of their metalorganic growth chemistries. From extensive work

on III-V and II-VI semiconductor etching with CH4/H2 it is well established that a significant

degree of ion bombardment is necessary for efficient removal rates, as shown by a comparison of

N2 addition (Figure 2, bottom) to that of the heavier Ar. Note that for this chemistry relatively

high rf chuck powers (250W) were necessary relative to the chlorine-based discharges (150W).

Figure 2. Etch rates as a function of microwave source power in (top) CH4/H2/Ar or (bottom) CH4/H2/N2

plasmas (250W rf chuck power, 1.5 mTorr).

The other non-corrosive plasma chemistry is SF6/Ar. Once again a relatively high rf

chuck power is required to enhance sputter desorption of the etch products, and the rates for all

materials increase with both source power (ion flux) and rf power (ion energy). Both parameters

are important in determining the ultimate etch rate in this chemistry. Not surprisingly since AlF3

and InF3 have low vapor pressures (melting points of 1291oC and 1170oC respectively), the etch

rates of ATO, ITO and Al2O3 are the lowest among the materials at high process pressures, most

likely due to increased collisional frequencies and an associated decrease in average ion energy.

The removal rates initially increase with pressure for ZnS, TiW, Al2O3 and ATO as more active

fluorine radicals are supplied to the surface. These trends are typically of ECR etch processes.

A number of different plasma chemistries have been investigated for dry etching of the

typical materials used in electroluminescent display devices. Since a typical MISIM structure has

a thickness of 1.5-2.0µm, and typical average etch rates at 800W microwave and 150-250W rf

power are 500-1000Å⋅min-1 for all the materials in the chemistry we investigated, process times

to etch a complete stack should be in the range 15-40 mins. It is likely that a sequence of etch

chemistries, tailored to the particular component layers comprising the stack, is the best approach

for minimizing etch time. In-situ monitoring techniques such as laser reflectometry, optical

emission spectroscopy or mass spectrometry could be used to measure progress through the

multi-layered structure. In general the chemical enhancements observed relative to pure Ar

sputtering are modest in the materials investigated here because of the high average bond

energies and low volatilities of such of the etch products. It is necessary to have both a high ion

flux and a reasonable ion energy (≥125eV) in order to achieve practical etch rates with materials

such as ATO, Al2O3 and SrS, and thus high density plasmas appear well-suited to patterning of

electroluminescent display devices incorporating these materials

Nano-crystalline Silicon

R.E. Hummel, University of Florida

Spark-processing of silicon has been shown to generate a strongly luminescing, stable,

and fast-responding substance. The occurrence and properties of photoluminescence (PL) and

cathodoluminescence (CL) bands have been documented in our first progress report. A

comprehensive compilation about preparation, luminescing properties, and applicational aspects

of spark-processed silicon (sp-Si) can be found in the publications list.

During the past 12 months detailed investigations were performed with the goal to

distinguish between several possible mechanisms which may be the cause for the intense

radiative transitions at room temperature in sp-Si. Specifically, the microstructure, which

consists of an amorphous silicon oxide and oxynitride matrix with imbedded silicon

nanoparticles, was under investigation to probe a possible relationship between the presence and

size of nanoparticles and PL emission wavelengths. Spatially resolved Raman spectra were

measured across spark-processed regions by scanning several areas which varied in PL intensity

but not in wavelength. The shifts and broadenings of the Raman signals indicate the presence of

Si particles having diameters of about 15 nm in the central, photoluminescing section, while

slightly smaller Si particles (d<8 nm) exist in the surrounding, optically inactive halo region.

Furthermore, the Raman signals are essentially identical for UV/blue and green luminescing sp-

Si. These results suggest that the PL of sp-Si is not caused by a quantum-size effect which is

coupled to the presence and size-distribution of nanoparticles.

Based on these results, a different series of experiments was conducted with the goal to evaluate

a possible chemical / structural nature of the radiative centers in sp-Si. The preparation of sp-Si

was performed in air, pure oxygen, and pure nitrogen atmospheres as well as in various mixtures

of both gases. Depending on the exact conditions during the preparation, five different PL bands

can be distinguished. Three of them can be related to defect structures in damaged silicon oxide

matrixes. The two most intense PL bands (UV/blue and green emissions), which are only present

when the preparation is performed in the presence of both oxygen and nitrogen, see Figure 1

below, could not be traced to known radiative centers. However, preliminary theoretical

calculations indicate that a molecular structure consisting of an over-coordinated Si atom bonded

to four O atoms and an additional N2 molecule may account for the unusual optical properties of

sp-Si. Further calculations and comparisons with experimental data are in progress.

In summarizing these data, it can be stated that the luminescing properties of sp-Si cannot be

related immediately to the presence of Si nanoparticles or to a quantum-dot derived PL

mechanism as previously assumed. It is instead proposed that the two most intense PL bands

stem from radiative transitions within a specific chemical configuration, consisting of silicon,

nitrogen, and oxygen. The generation of this particular structure needs an extremely high energy

input which explains why the method of spark-processing is of advantage where others (such as

CVD or sputtering) cannot compete.

Further, ongoing experiments are directed toward a detailed characterization of the configuration

and properties of the above-mentioned molecular structures. Concurrently, we have initiated a

series of experiments to sputter-deposit thin films utilizing spark-processed sputter targets. Our

intention is to fabricate a thin layer which inherits the specific molecular structure and is suitable

for thin-film electroluminescing device applications.

Fig.1: Photoluminescence intensities of sp-Si prepared in various ratios of oxygenand nitrogen atmospheres.

Nanostructures and Magnetic ParticlesR.C. Dynes, F. Hellman, I.K. Schuller

University of California - San Diego

In the past year the efforts towards growth and fabrication of magnetic an

superconducting nanostructures have resulted in two publications (submitted) and enhanced

abilities. This is a continuation of our efforts to investigate the basic physics and applications of

nonmagnetic and superconducting particles and the effect of coupling between metals,

superconductors and magnetic materials.

1) Superconducting Nanostructures

In a study of small granular superconductors, we have performed a transport study of

granular superconducting films with lateral dimensions as small as 1000Å and typical grain sizes

of 100Å. On average then, the film is only about 10 grains in width and the effects of transport

in this finite granular array are substantial. The IV characteristics of these sample are hysteretic

and exhibit sharp discontinuous jumps. These features are due to the local superconducting

phase coherence between grains. Furthermore, we observe a rich profile of conductance

fluctuations with amplitudes that scale with the conductivity. These features stem from

interference of the superconductive wave function modulated by external magnetic field or the

self flux from the current passing through the random granular network. With increasing size of

structure, these effects disappear and are clearly caused by the small and finite number of current

paths through such a device. A preprint (submitted) is attached.

Novel Electron beam lithography techniques allow preparation of structures with

characteristic sizes which are comparable to characteristic sizes important for physical

phenomena, such as the penetration depth, coherence length, or magnetic domain size. We have

developed in our laboratory these types of techniques, to prepare a variety of submicron magnetic

dot arrays, in different geometric configurations. To study the physical properties of these arrays

we have covered them by a superconductor (Nb). In this fashion, we were able to observe a

matching effect between magnetic dot array and the vortex lattice. The effects observed are

considerably enhanced when compared to earlier observations with much larger (above 1 micron)

magnetic dots or holes. We are presently comparing the behavior of identical structures of holes

and magnetic dots to understand the effect of magnetism on this matching.

2) Magnetic Materials and Structures

a) Structures

We wish to study interactions between pairs of small magnetic particles. The question of

how adjacent particles influence each others’ magnetic state through interactions is an interesting

one. We anticipate substantial shape dependence in the interactions. Circular particles should

respond substantially differently from ellipsoidal ones. To study these effects, we have

constructed microscopic magnetic field sensors. Using e-beam lithography we have fabricated a

Pb SQUID with a pair of weak links in parallel. (See Figure 1.) The weak links act as Josephson

junctions in a SQUID loop. The SQUIDS fabricated have a loop area of ≈25µm2. The next step

is to deposit particles inside these loops and study their magnetic moments and dynamics.

Fig.1: Fabricated Pb superconducting Quantum Interference Device (SQUID)

b) Magnetic Materials

We have been working on understanding the nature of the proximity effect in magnetic

materials. This is an effect that is well understood in superconducting materials and has led there

to practical devices as well as interesting physics. In magnetism, the effect is less well

understood and is generally believed to be extremely local. However, it is clear that in metals

which are nearly magnetic, such as Pd or Pt, this length scale will be much longer. As little as

1% Co in Pt leads to a ferromagnetic Curie temperature of over 5K, indicative of the ability of

Co to induce magnetism in Pt on a relatively long length. It is also well known that spin

diffusion lengths in clean materials (e.g. Cu) can be tremendously long (microns). Finally, in

giant magnetoresistive devices, the coupling between the magnetic layers depends strongly on the

nature of the intervening non-magnetic material. The nature of the induced polarization in the

non-magnetic material, and its length scale is thus relevant in several areas. We have prepared

epitaxial single crystal bilayers of Co-Pt alloys in various combinations of concentrations (hence

of various combinations of Tc). Except for the most Co-rich specimens, these all can easily be

grown in our UHV evaporation system in the fcc structure as a solid solution (chemically

disordered) epitaxial alloy. In-situ RHEED and (in the future) Auger analysis plus ex-situ X-ray

analysis have and will be done to characterize the structure and chemistry of these films.

Polarized neutron reflectometry has been done on one set of bilayers, showing the

magnetization profile as a function of depth in the sample. Analysis is still incomplete, but it is

already clear that in the lower Tc material, above its Tc there is significant induced polarization

form the higher Tc material. That is, there is a significant ferromagnetic proximity effect. More

analysis of data is needed before additional conclusions can be reached, such as the length scale.

Careful magnetization and specific heat measurements are planned for the future. We also will

then investigate materials such as Copper, where understanding the role of the proximity effect

may lead to better magnetoresistive devices, or at least better understanding of the physics of the

existing devices. The basic question ot be answered is: how does this length scale and the

magnitude of the ferromagnetic proximity effect depend on the properties of the two materials.

Magnetic Nano-ParticlesS. Von Molnar, Florida State University

Magnetic Nano-ParticlesS. von Molnár, Florida State University

1) STM fabrication of nanometer-scale iron particles

Arrays of ferromagnetic iron particles have been fabricated by a combination of chemicalvapor deposition and scanning tunneling microscopy (STM). The quality of the grown particleand its size is controlled through the growth parameters. These parameters, which include theprecursor pressure of Fe(CO)5 inside the UHV chamber of the STM and the lithography biasvoltage, have been refined continuously. The morphology of the grown particle arrays has beeninvestigated by SEM and AFM and their magnetic properties by MFM, both in house and at U.C.Santa Barbara (in collaboration with D. Awschalom). An example of an array consisting of 500dots is shown in Fig. 1. This array has been grown onto a Hall gradiometer made from aGaAs/GaAlAs two-dimensional electron system. Magnetic characterization using the Hall signalproduced by the magnetic structure is currently in progress.

Fig. 1. SEM migrograph of an array of 20 x 25 iron dots (approx. 30-50 nm diam., 150 nmheight). The underlying Hall bar was prepared by wet etching of a GaAs/GaAlAs two-dimensionalelectron system enabling magnetization measurements.

2) Focused Ion Beam micromachining and imaging

The installation of a Focused Ion Beam (FIB) column in an ultra-high vacuum chamberhas been completed and preliminary experiments to image and micromachine samples havecommenced. This equipment will be used primarily for patterning of thin films. The sample,mounted on a high-precision home-made stage, is exposed to a high energy Ga ion beam. In Fig.2 an AFM image is presented showing the effect of the ion beam (25 kV beam voltage, I ≈ 100pA, exposure 5 min) on a GaAs sample. A rectangular hollow (depth approx. 50 nm) has beenproduced. Micromachining can be performed by scanning the FIB inside a smaller area as seenin the upper right corner of Fig. 2 where an additional hollow (0.8 µm x 0.8 µm, exposure 20 s)has been sputtered. Redeposition effects can be seen around this additional hollow. Experimentsaiming toward a more precise determination of the system parameters and of sputter yield ofLaMnO thin films are presently in progress.

Fig. 2. AFM image of a GaAs sample showing the sputter effect of the FIB. Note the darker areanear the upper right corner of the sample image where micromachining has been performed.

3) Novel measurement devices and techniques

Over sufficiently small (<10 micron) distances, and at sufficiently low temperatures (<10K), transport in high mobility two-dimensional electron systems occurs ballistically; i.e., theelectrons do not undergo scattering over these distances. Hence, their path can be predictablyinfluenced by applying a magnetic field perpendicular to their plane of motion. In the presentapplication, the deflection in the electron's path is used in two ways: 1) a homogeneous externallyapplied magnetic field steers the electron beam toward a contact where its presence can beprobed, and 2) the influence of a local and inhomogeneous field due to a small magnetic structurecan be discerned by the perturbation it causes in the electron path.

In the lower structure (see micrograph, Fig. 3B) electrons are injected through one narrowopening, and the applied homogeneous magnetic field deflects them by 180 degrees so theyimpinge on an adjacent opening. This opening then develops a voltage that is a substantialfraction of the injection voltage and which can thus be easily measured (see measured data, Fig.4; the periodicity in the signal is due to specular reflection of the electrons off the barrierseparating the two openings).This voltage changes if the semicircular electron trajectory isdeformed by the presence of the fringing field of a small magnetic structure located close to theelectron path.

The upper structure (Fig. 3A) operates on a similar principle, the difference lying in the360 degree deflection between injection and detection. This allows one to position the magneticparticle in a location where the electron current density is high (see trajectory simulations).Electron beam lithography is necessary to produce these structures as the dimensions are small(Fig. 3) and tolerances tight. The base material was an MBE-grown GaAs/AlGaAsheterostructure (obtained from QUEST, U.C. Santa Barbara) with a mean free path of 13 micronat temperatures below 5 K. After electron beam lithography (carried out at the U. of Florida withF. Sharifi), the material was gently wet-etched to produce the insulating barriers.

Fig. 3. Self-focusing 2DES structures. A) (top) Electrons eminating from one orifice (uppercenter of micrograph) are deflected by the application of a magnetic field perpendicular to thesurface, 360° to enter the orifice just below the first; B) (bottom) electrons leave the left orifice(lower center), are deflected by 180° and impinge on one of the two openings to the right.

Fig. 4. Trace of voltage as a function of applied magnetic field in the device.

Publications

“Dry Etching of SrS Thin Films,” J.W. Lee, M.R. Davidson, B. Pathangey, P.H. Holloway andS.J. Pearton, J. Electrochem. Soc. (submitted).

“Dry and Wet Etch Processes for NiMnSb Heusler Alloy Thin Films,” J. Hong, J.A. Caballero,J.R. Childress and S.J. Pearton, J. Electrochem. Soc. (Oct. issue 1997).

“ECR Plasma Etching of Materials for Magneto-resistive, RAM Applications,” K.B. Jung, J.W.Lee, Y.D. Park, J.R. Childress, S.J. Pearton, M. Jensen and A.J. Hurst, J. Electron. Mater. (inpress).

“Dry Etch Patterning of LaCaMnO3 and SmCo Thin Films,” J.J. Wang, J.R. Childress, S.J.Pearton, F. Sharifi, K.H. Dahmen, E.S. Gillman, F.J. Cadieu, R. Rani, S.R. Qian and Li Chen, J.Electrochem. Soc. (submitted).

“Cl 2/Ar Plasma Etching of Binary, Ternary and Quaternary In-based CompoundSemiconductors,” J.W. Lee, J. Hong, C.R. Abernathy, E.S. Lambers, S.J. Pearton, W.S. Hobsonand F. Ren, J. Vac. Sci. Technol. B14 2567 (1996).

“Dry Etching of InGaAlP Alloys in Cl2/Ar High Ion Density Plasmas,” J. Hong, J.W. Lee, E.S.Lambers, C.R. Abernathy, C.J. Santana, S.J. Pearton, W.S. Hobson and F. Ren, J. Electron.Mater. 25 1428 (1996).

“High Ion Density Dry Etching of Compound Semiconductors,” S.J. Pearton, Mat. Sci. Eng. B40101 (1996) - invited review.

“Comparison if ICl and IBr Plasma Chemistries for Etching of InGaAlP Alloys,” J. Hong, J.W.Lee, E.S. Lambers, C.R. Abernathy, S.J. Pearton, C. Constantine and W.S. Hobson, J.Electrochem. Soc. 143 3656 (1996).

“Comparison of Plasma Chemistries for Dry Etching Thin Films EL Display Materials,” J.W.Lee, B. Pathangey, M. Davidson, P.H. Holloway, E.S. Lambers, B. Davydov, T.J. Anderson andS.J. Pearton, J. Vac. Sci. Technol. (submitted).

“Etching Products for Fabrication of GaN/InGaN/AlN Microdisk Laser Structures,” J.W. Lee,C.B. Vartuli, C.R. Abernathy, J.D. MacKenzie, J.R. Mileham, R.J. Shul, J.C. Zolper, M.H.Crawford, J.M. Zavada, R.G. Wilson and R.N. Schwartz, J. Vac. Sci. Technol. B14 3637 (1996).

“Reactive Ion Etching of III-V Nitrides,” S.J. Pearton, R.J. Shul, G. McLane and C. Constantine,Solid State Electron. 41 159 (1997).

“Dry Etching of GaSb and InSb in CH4/H2/Ar,” J.R. Mileham, J.W. Lee, E.S. Lambers and S.J.Pearton, Semicond. Sci. Technol. 12 338(1997).

“ICP Plasma Etch Damage in GaAs and InP Schottky Diodes,” J.W. Lee, C.R. Abernathy, S.J.Pearton, F. Ren, W.S. Hobson, R.J. Shul, C. Constantine and C. Barratt, J. Electrochem. Soc. 1441417 (1997).

“Dry Etch Damage in ICP Plasma Exposed GaAs/AlGaAs HBTs,” F. Ren, J.W. Lee, C.R>Abernathy, S.J. Pearton, C. Constantine, C. Barratt and R.J. Shul, Appl. Phys. Lett. 70 2410(1997).

“Plasma Etching of III-V Semiconductors in BCl3 Chemistries - Part I, GaAs and RelatedCompounds,” J.W. Lee, J. Hong, E. Lambers, C.R. Abernathy, S.J. Pearton, W.S. Hobson and F.Ren, Plasma Chem. & Plasma Proc. 17, 155 (1997); Part II 17, 169 (1997).

“Electrical and Optical Changes in AlGaAs and InGaP During Dielectric Etching in ECR SF6

Plasmas,” K.N. Lee, J.W. Lee, C.R. Abernathy, S.J. Pearton, W.S. Hobson and F. Ren, SolidState Electron. 41 401 (1997).

“Dry Etching of III-V Semiconductors in IBr/Ar ECR Plasmas,” J.W. Lee, J. Hong, E.S.Lambers, C.R. Abernathy, S.J. Pearton, W.S. Hobson and F. Ren, J. Electron. Mater. 26 429(1997).

“Effects of H2 Plasma Exposure on GaAs/AlGaAs HBTs,” J.W. Lee, C.R. Abernathy, S.J.Pearton, F. Ren, R.J. Shul, C. Constantine and C. Barratt, Solid State Electron. 41 849 (1997).

“Damage Investigation in AlGaAs and InGaP Exposed to High Ion Density Ar and SF6 Plasmas,”J.W. Lee, K.N. Lee, R.R. Stradman, C.R. Abernathy, S.J. Pearton, W.S. Hobson and F. Ren, J.Vac. Sci. Technol. A15 890 (1997).

“Comparison of Etch Chemistries for SiC,” G. McDaniel, J. Lee, E. Lambers, S.J. Pearton, P.H.Holloway, F. Ren, J.M. Crow, N. Bhaskaran and A.C. Wilson, J. Vac. Sci. Technol. A15 885(1997).

“Patterning of Cu, Co, Fe and Ag for Magnetic Nanostructures,” K.B. Jung, .W. Lee, Y.D. ark,J.A. Caballero, J.R. Childress, S.J. Pearton and F. Ren, J. Vac. Sci. Technol. A15 1780 (1997).

“Critical Issues of Semiconductor Processing,” S.J. Pearton, Mat. Sci. Eng. B44 1 (1997) -invited review.

“Characterization of Damage in ECR Etched Semiconductors,” S.J. Pearton, Appl. Surf. Sci.117/118 597 (1997) - invited review.

“High Rate Dry Etching of NiFe and NiFeCo,” K.B. Jung, E. Lambers, J.R. Childress, S.J.Pearton, M. Jenson and A.T. Hurst, Appl. Phys. Lett. (September 1997 issue ).

J.A. Caballero, F. Petroff, Y.D. Park, A. Cabbibo, R. Morel and J.R. Childress, Deposition ofHigh-Quality NiMnSb Thin Films at Moderate Temperatures, J. Appl. Phys. 81, 2740 (1997).

Y.D. Park, J.A. Caballero, A. Cabbibo, J.R. Childress, H.D. Hudspeth, T.J. Schultz and F.Sharifi, Fabrication of Nanometer-Size Magnetic Structures Using e-beam Patterned DepositionMasks, J. Appl. Phys 81, 4717-4719 (1997).

A. Cabbibo, Y.D. Park, J.A. Caballero and J.R. Childress, Magnetic Properties of Granular Co-Cu Ultrathin Films and Multilayers, in Chemistry and Physics of Nanostructures, Edited by E.

Ma, B. Fultz, R. Shull, J. Morral and P. Nash (The Minerals, Metals & Materials Society, 1997)p.227.

J.A. Caballero, Y.D. Park, A. Cabbibo, and J.R. Childress, Sputter-Deposition of NiMnSbMagnetic Thin Films from a Composite Target onto Si substrates, J. El. Mat., to be publishedNovember 1997.

A. Cabbibo, Y.D. Park, J.A. Caballero and J.R. Childress, Magnetic Properties of MultilayeredCo-Cu Granular Composites, Materials Research Society Symposium Proceedings, spring 1997,to be published.

J.R. Childress, J.A. Caballero, W.J. Geerts, F. Petroff, P. Galtier, Y. Suzuki, J.-U. Thiele and D.Weller, Low-temperature Growth of NiMnSb Heusler Alloy Thin Films, Materials ResearchSociety Symposium Proceedings, spring 1997, to be published.

J.A. Caballero, F. Petroff, A. Cabbibo, Y.D. Park and J.R. Childress, Structural andMagnetotransport Properties of NiMnSb/Cu and NiMnSb/Ag Multilayers, Materials ResearchSociety Symposium Proceedings, spring 1997, to be published.

Y.D. Park, H.D. Hudspeth, T.J. Schultz, A. Cabbibo, J.A. Caballero, F. Sharifi and J.R.Childress, Transport Measurements of Magnetic Multilayers at Reduced Lateral Dimensions,Materials Research Society Symposium Proceedings, spring 1997, to be published.

J.A. Caballero, W.J. Geerts, F. Petroff, J.-U. Thiele, D.Weller and J.R. Childress, Magnetic andMagneto-Optical Properties of NiMnSb Thin Films, J. Magn. Magn. Mat., to be published.

J.A. Caballero, W.J. Geerts, J.R. Childress, F. Petroff, P.Galtier, J.-U. Thiele and D. Weller,Structure and Magneto-Optical Properties of Sputter-Deposited NiMnSb Thin Films, Appl. Phys.Lett., to be published.

“Electron-beam fabricated nanostructures” F. Sharifi, to appear in Rev. Sci. Intrum. (invitedreview)

“Electron tunneling studies of the hexaboride materials SmB6, EuB6, CeB6, and SrB6”, B.Amsler, Z. Fisk, J. L. Sarrao, S. von Molnar, M. W. Meisel, and F. Sharifi, submitted to Phys.Rev. Lett.

S. Hershfield, "Charge and spin current flows in spin transistors and similar devices", Journal ofApplied Physics 81, 4353 (1997).

"Charge and spin transport through a metallic ferromagnetic-paramagnetic-ferromagneticjunction", Selman Hershfield and Hui Lin Zhao, Physical Review B 56, 3296 (1997).

"Calculation of Giant Magnetoresistance in Laterally Confined Multilayers", KingshukMajumdar, Jian Chen, and Selman Hershfield, submitted to Physical Review B.

"Effect of spin-flip scattering on the current-in-plane giant-magnetoresistance", Jian Chen andSelman Hershfield, submitted to Physical Review B.

"Junction Magnetoresistance of a magnetic double-tunnel-junction in the Coulomb Blockaderegime", Kingshuk Majumdar and Selman Hershfield, submitted to Physical Review B.

S.L. Jones, D. Kuman, R.K. Singh and P.H. Holloway, "Luminescence of pulsed laser depositedEu doped yttrium oxide films", Appl. Phys. Lett. 71, 404 (1997).

K.G. Cho, D. Kumar, S.L. Jones, P.H. Holloway and R.K. Singh, "Improved luninescenceproperties of pulsed laser deposited Y2O3:Eu thin films on diamond coated silicon substrates",Appl. Phys. Lett, in press.

T.A. O‚Brien, P.D. Rack, P.H. Holloway and M.C. Zerner, "Crystal field and molecular orbitalcalculation of the optical transitions in Ce doped alkaline earth sulfide (MgS, CaS, SrS, and BaS)phosphors", J. Luminescence, in press.

"X-ray Emission Spectra and the Effect of Oxidation on the Local Structure of Porous and Spark-Processed Silicon", E.Z. Kurmaev, S.N. Shamin, V.R. Galakhov, V.I. Sokolov, M.H. Ludwig,and R.E. Hummel, J. Phys.: Condens. Matter, 9, (1997) 2671.

"On the Formation Process of Luminescing Centers in Spark-Processed Silicon", M.H. Ludwig,A. Augustin, R.E. Hummel, and Th. Gross, J. Appl. Phys., 80 (1996) 5318.

"Raman Study of the Relationship Between Nanoparticles and Photoluminescence in Spark-Processed Silicon", S. Rupp, J. Quilty, H.J. Trodahl, M.H. Ludwig, and R.E. Hummel, Appl.Phys. Lett., 70 (1997) 723.

"Multicolor-Effects of Luminescing, Nanostructured Silicon After Spark-Processing in Pure andComposite Gases", M.H. Ludwig, A. Augustin, and R.E. Hummel, MRS Proceedings,AAdvances in Micro-Crystalline and Nano-Crystalline Semiconductors,@ 452 (1997) 153.

"Ferromagnetic Properties of Spark-Processed Photoluminescing Silicon,@ J. Hack, M.H.Ludwig, W. Geerts, and R.E. Hummel", MRS Proceedings, Advances in Micro-Crystalline andNano-Crystalline Semiconductors,@ 452 (1997) 147.

"Color-Switching Effect of Photoluminescing Silicon After Spark-Processing in Oxygen", M.H.Ludwig, A. Augustin, and R.E. Hummel, Semiconductor-Science and Technology, 12, (1997).

"Optical Properties of Silicon-Based Materials: A Comparison of Porous and Spark-ProcessedSilicon", M.H. Ludwig in ACritical Reviewed in Solid State and Materials Science,@ 21, 4(1996), CRC Press, Boca Raton.

“Flux Pinning in a Superconductor by an Array of Submicrometer Magnetic Dots,” J. Martin, M.Velez, J. Nogues and Ivan K. Schuller (submitted).

“Conductance Fluctuations in Mesoscopic Granular Superconductors,” A. Frydman, E. Price andR.C. Dynes (submitted Phys. Rev. Lett.)

Technical Presentations

"Dry Etch Processes for NiMnSb, LaCaMnO3 and Related Materials", J. Hong, J.J. Wang, E.S.Lambers, J.A. Caballero, J.R. Childress, S.J. Pearton, K.-H Dahmen, S. Von Molnar, F.J. Cadieuand F. Sharifi, 1997 Fall MRS Meeting, Boston.

"High Rate Etching of Metals for Magnetoelectronic Applications", S.J. Pearton, K.B. Jung, J.Hong, J.W. Lee, J.A. Caballero, J.R. Childress, M. Jensen and A.T. Hurst, Jr., ElectrochemicalSociety Meeting, Paris, France, September 1997 (invited).

"Development of ECR and ICP High Density Plasma Etching for Patterning", K.B. Jung, J.R.Childress, S.J. Pearton, M. Jensen and A. Hurst, 1997 Am. Vac. Soc. National Symp., San Jose,CA.

"ECR Plasma Etching of Oxides and SrS and ZnS-based EL Materials for Flat Panel Displays",J.W. Lee, M.R. Davidson, B. Pathangey, P.H. Holloway, A. Davydov, T.J. Anderson, S.J.Pearton and F. Ren, 1997 Am. Vac. Soc. National Symp., San Jose, CA.

"High Rate ECR Plasma Etching of Cu at 25oC in Cl2/Ar", K.B. Jung, J.W. Lee, Y.D. Park, J.R.Childress, S.J. Pearton and F. Ren, 1996 Fall MRS Meeting, Boston.

"Fabrication of Nanometer-Size Magnetic Structures Using e-beam Patterned DepositionMasks", Y.D. Park, J.A. Caballero, A. Cabbibo, J.R. Childress, H.D. Hudspeth, T.J. Schultz andF. Sharifi, 41st annual conference on Magnetism and Magnetic Materials, Atlanta, GA,November 12-15, 1996.

"Magnetic Properties of Multilayered Co-Cu Granular Composites", A. Cabbibo, Y.D. Park, J.A.Caballero and J.R. Childress, 1997 Spring Meeting of the MRS, San Francisco, CA, March 31-April 4, 1997.

"Low-temperature Growth of NiMnSb Heusler Alloy Thin Films", J.R. Childress, J.A. Caballero,W.J. Geerts, F. Petroff, P. Galtier, Y. Suzuki, J.-U. Thiele and D. Weller, 1997 Spring Meetingof the MRS, San Francisco, CA, March 31-April 4, 1997.

"Structural and Magnetotransport Properties of NiMnSb/Cu and NiMnSb/Ag Multilayers", J.A.Caballero, F. Petroff, A. Cabbibo, Y.D. Park and J.R. Childress, 1997 Spring Meeting of theMRS, San Francisco, CA, March 31-April 4, 1997.

"Transport Measurements of Magnetic Multilayers at Reduced Lateral Dimensions", Y.D. Park,H.D. Hudspeth, T.J. Schultz, A. Cabbibo, J.A. Caballero, F. Sharifi and J.R. Childress, 1997Spring Meeting of the MRS, San Francisco, CA, March 31-April 4, 1997.

"UHV Sputter-Deposition of Ultrathin Magnetic Films and Multilayers", J.R. Childress (invited),126th TMS annual meeting, February 9-13 1997, Orlando, FL.

"Magnetic Properties of Granular CoCu Ultrathin Films", A. Cabbibo, Y.D. Park, J.A. Caballeroand J.R. Childress, 126th TMS annual meeting, February 9-13 1997, Orlando, FL.

"Magnetism and Magnetoresistance in NiMnSb Multilayers" (in French), J.R. Childress, J.A.Caballero, F. Petroff, L.F. Schelp, P. Galtier, 5th Colloque Louis Néel, June 5-7 1997, Banyuls-sur-Mer, France.

"Magnetic and Magnetotransport Properties of Granular Multilayer Composites", (invited) J.R.Childress, A. Cabbibo and W. Geerts, 4th International Conference on Composites Engineering,July 6-12 1997, Big Island, Hawaii.

"Magnetic and Magneto-optical Properties of NiMnSb Thin Films", J.A. Caballero, W.J. Geerts,F. Petroff, J.-U. Thiele, D.Weller and J.R. Childress, International Conference on Magnetism,July 27-August 1 1997, Cairns, Australia.

"Magnetic and Magnetotransport Properties of (CoCu)/Cu Multilayer Films, A. Cabbibo, Y.D.Park and J.R. Childress, International Conference on Magnetism, July 27-August 1 1997, Cairns,Australia.

"Characterization of Optical Materials Using Auger Electron Spectroscopy", Mark R. Davidsonand Paul H. Holloway, invited talk, SPIE Meeting on Critical Review of Analytical Techniquesfor Optical Materials, San Diego, CA, July 27-29, 1997.

"Semiempirical calculations of spectroscopy of Ce+3 in metal sulfide host crystals", T.A.O‚Brien, P.D. Rack, P.H. Holloway and M.C. Zerner, Florida Chapter of the American ChemicalSociety, Orlando, FL, May 2-3, 1997.

"Pulsed laser deposition of thin film phosphors for field emission flat panel displays", S. Jones,D. Kumar R.K. Singh and P.H. Holloway, 43nd Annual National Symp. of the AVS,Philadelphia, PA, October 14-18, 1996.

"Pulsed laser deposition of Y2O3:Eu CL phosphors", S.L. Jones, D. Kumar, R.K. Singh and P.H.Holloway, Second Intl. Conf. on Display Phosphors, San Diego, CA, November 18-20, 1996.

"Pulsed Laser Depostion of Thin Film Phosphors for Field Emission Flat Panel Displays", S.L.Jones, D. Kumar, R.K. Singh and P.H. Holloway, 190th Meeting of the Electrochemical Society,San Antonio, TX, October 6-11, 1996.

"Deposition and Characterization of Eu:Y2O3 Red Phosphor Thin Films", D. Kumar, R.K.Singh, S. Jones and P.H. Holloway, 1997 Spring Meeting of the MRS, San Francisco, CA,March 31-April 4, 1997.

"Semiempirical Calculations of 4f-5d Spectroscopy of Ce3+ in Metal Sulfide Host Crystals" TedO‚Brien, Philip Rack, Paul Holloway and Mike Zerner, 1997 Sanibel Conference, Palm City, FL,May, 1997.

"Ferromagnetic Properties of Spark-Processed Photoluminescing Silicon" J. Hack, M.H. Ludwig,and R.E. Hummel, Materials Research Society 1996 Fall Meeting, December 2-6 1996, Boston.

"Multicolor-Effects of Luminescing, Nanostructured Silicon After Spark-Processing in Pure andComposite Gases", M.H. Ludwig, A. Augustin, and R.E. Hummel, Materials Research Society1996 Fall Meeting, December 2-6 1996, Boston.

"Calculation of Giant Magnetoresistance in Laterally Confined Multilayers", KingshukMajumdar, Jian Chen, and Selman Hershfield, March 1997 Meeting of the American PhysicalSociety.

"Effect of spin-flip scattering on giant magnetoresistance with current-in-plane", Jian Chen andSelman Hershfield, March 1997 Meeting of the American Physical Society.

"Role of interface scattering on the resistivity in metallic multilayer wires", Tat-Sang Choy, JianChen, and Selman Hershfield, March 1997 Meeting of the American Physical Society.

"Flux Pinning in Nb by an Array of Magnetic Dots", Maria Velez, Jose I. Martin, Josep Noguesand Ivan K. Schuller, March Meeting, The American Physical Society, Bull. Am. Phys. Soc. 4263 (1997).

"Fabrication of Submicrometer Magnetic Structures by e-Beam Lithography", Yvan Jaccard, JoseI. Martin, Josep Nogues, J.-M. George and Ivan K. Schuller, March Meeting, The AmericanPhysical Society, Bull. Am. Phys. Soc. 42, 506 (1997).

"Pinning Effects by Arrays of Magnetic Dots on Niobium Film", J.I. Martin, M. Velez, J.Nogues, A. Hoffmann, Y. Jaccard and Ivan K. Schuller, International Conference on Magnetism(ICM) 1997, Cairns, Australia, July 27-August 1, 1997.

"Domain Structure and Magnetoresistance in Chains of Submicron Co Dots", M.J. Van Bael, K.Temst, C. Van Haesendonck, V.V. Moshchalkov, Y. Bruynseraede, J.I. Martin, J. Nogues andIvan K. Schuller, 16th General Conference, EPS, Condensed Matter Division, Leuven, Belgium,August 25-28, 1997.

"MFM Study of the Magnetic Domain Structure in Chains of Submicrometer Sized Co Dots",M.J. Van Bail, K. Temst, C. Van Haesendonck, V.V> Moshchalkov, Y. Bruynseraede, J.I.Martin, J. Nogues and Ivan K. Schuller, Annual Meeting, Belgian Physical Society, 1997.

"Pinning of the Vortex Lattice in Nb Film by a Regular Magnetic Dot Array", Y. Jaccard, A.Hoffmann, M.-C. Cyrille, J. Nogues, I.K. Schuller, J.I. Martin, M. Velez, J.L. Vicent, 16th

General Conference, EPS, Condensed Matter Division, Leuven, Belgium, August 25-28, 1997.

"Mesoscopic and Strongly Correlated Electron System", Aviad Frydman, Landau Institute fortheoretical Physics, Moscow (Kosygina), Russia, June 14-26, 1997.

"Polarized Neutron Reflectometry Study of Ferromagnetic Proximity Effect in MagneticBilayers", A.L. Shapiro, B.M. Maranville, M. Fitzsimmons and F. Hellman, Poster presentationat the Los Alamos Neutron Science Center User Group Meeting.

Personnel Supported

Post-doctoral Associates and Visiting Researchers

Jung-Sik Bang, Visiting Scientist with Dr. Holloway

Xiao-ming Zhan, Visiting Scientist with Dr. Holloway

Jian Chen, Post-doctoral Associate, with Dr. Hershfield

Michael Coey, Visiting Professor at UCSD

Aviad Frydman, Post Doctoral Fellow at UCSD

M.-C. Cyrille, Post Doctoral Fellow at UCSD

S. Kim, Post Doctoral Fellow at UCSD

Jean Heremans, Post-doctoral fellow with Dr. von Molnar

S. Wirth, Post-doctoral fellow with Dr. von Molnar

Graduate Students:

Kee Bum Jung with Dr. Pearton

Jin Hong with Dr. Pearton

Xianan Cao with Dr. Pearton

Juan Cabbalero with Dr. Childress

Dan Park with Dr. Childress

Anthony Cabbibo with Dr. Childress

Heather Hudspeth with Dr. Sharifi

Timothy Schultz with Dr. Sharifi

Kingshuk Majumdar with Dr. Hershfield

Tat Sang Choy with Dr. Hershfield

Sean Jones with Dr. Holloway

Jonathan Hack with Dr. Hummel - Graduated with M.S., May 1997.

Shi-Dong Yu with Dr. Hummel

Ed Price at UCSD

A. Hoffman at UCSD

J. Choi at UCSD

B. Maranville at UCSD

Undergraduate Students

David Hays with Dr. Pearton

Technology Highlights

1. Discovered a dry etching process for NiFe and related alloys based on a balance between

chemical surface reaction with Cl, and ion-assisted desorption of the reaction products,

followed by in-situ removal of chlorine resides to prevent corrosion. This is being

transitioned to Honeywell for use in fabricating high density, rad-hard, non-volatile Magnetic

Random Access Memories (MRAMs).

2. Growth of the first high quality, potentially 100% spin-polarized NiMnSb thin films at low

(250oC) temperatures. These are attractive candidates for advanced magnetic storage devices

with improved Giant Magneto-Resistance response.

3. Development of techniques for reducing the ultimate limits of e-beam lithography, and

resultant achievement of individual features with dimension <300Å, and dense arrays (>10

Gbits·in-2) of 500 Å features for next generation information storage devices.

4. Growth of improved SrS:Ce, F thin films which emit in the blue, using addition of GaS

during rf-magnetron deposition. These have application for full color electroluminescent

displays. A plasma etching process for patterning of these films has also been discovered

(work done in collaboration with Planar Systems, the only domestic supplier of EL displays).

5. Use of novel, non-corrosive etching chemistries (eg. Co/NH3) for magnetic materials

(NiFeCo, FeAlN, CoCu), with application to read/write heads (in conjunction with Plasma-

Therm, a manufacturer of etching systems, and Seagate, a manufacturer of computer hard

drives).

Patents

"Method of Manufacturing Photoluminescing Semiconductor Materials Using Lasers", PatentNo. 5,597,621; Date Granted: January 28, 1997

"Method for Altering the Magnetic Properties of Materials by Spark Processing", FiledNovember 27, 1996

Honors/Awards

Dr. Sharifi obtained the Teaching Incentive Program award from the University of Florida.

Dr. Holloway obtained the Professional Excellence Program award from the University ofFlorida

Dr. Holloway obtained the Research Foundation Professorship award from the University ofFlorida