overview of optical metrology of advanced semiconductor materials

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Vimal K. Kamineni

College of Nanoscale Science and Engineering,

University at Albany – SUNY, Albany, NY 12203

Overview of Optical Metrology of Advanced Semiconductor Materials

May 25, 2011

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Linear Optical Response of Materials

Spectroscopic Ellipsometry

Advanced Materials in the Semiconductor Industry

Photoreflectance

Photoluminescence

Conclusions

Acknowledgements

Outline

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Metals

Semiconductors

Dielectrics


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Reflection of Polarized Light

φ’ φ’

P

S φ N1 air

N2 Film index d β

β

22312

22312

1 iPP

iPPP

errerr

R−

−

++

= β

β

22312

22312

1 iSS

iSSS

errerrR −

−

++

=

( ) '2 cos2 φλπβ Nd=

'12

'12

12 coscoscoscos

φφφφ

NNNNr P

+−

= '12

'21

12 coscoscoscos

φφφφ

NNNNr S

+−

=

S

Pi

RRe =Ψ ∆tan

Fresnel Reflection Coefficients different for S and P polarizations

=Ψ −

S

P

R

R1tan ri δδ −=∆,


N3 substrate index

Spectroscopic Ellipsometry: Light polarized in plane of reflection reflects differently than light polarized perpendicular to plane of reflection.

P designation used for light polarized in plane of reflection (parallel) S designation for light perpendicular to plane of reflection (senkrecht)

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α

1 2 3 4 5 6 7

-20

0

20

40

60

01020304050

1 2 3 4 5 6 70

2

4

6

8

0123456

1 2 3 4 5 6 70.0

5.0x105

1.0x106

1.5x106

2.0x106

2.5x106

Photon Energy (eV) Photon Energy (eV) Photon Energy (eV)

n k

ε1 ε2

cm-1

Refractive Index Dielectric Function Absorption Coefficient

Optical Model

Regression

inkkniknNi 2)()()~(~ 222221 +−=+==+= εεε

(Ψ, Δ)

λπα k4

=

Ψ - amplitude ratio, Δ – phase difference, R– Fresnel reflection coefficient , n - real part of the refractive index, k – extinction coefficient, ε1 – real part of the dielectric function, ε 2 – imaginary part of the dielectric function, α – absorption coefficient, λ – wavelength of light.

Bulk Si Bulk Si Bulk Si


Thickness and optical properties

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SOI

3D interconnects

Low-κ

High-κ

EUV Resists

III-nitrides

Graphene

Metals (NiSi, W)

SE

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Metals

Semiconductors

Dielectrics

Drude Lorentzian


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Optical Metrology of thin metal films (Ni, NiSi, TiN and W)

V.K. Kamineni, M. Raymond, E.J. Bersch, B.B. Doris, and A.C. Diebold, Journal of Applied Physics, 107 (2010) 093525.

Nitride Spacer

Poly-Si Gate Electrode

Thermal SiO2

Nickel Silicide

N+ Doped Silicon Source Drain P well

Thin Metal Films

Presenter

Presentation Notes

Nickel Monosilicide (NiSi) is used in advanced CMOS devices to reduce the contact resistance between the tungsten studs and silicon. Low resistive NiSi with self-aligned silicidation process of Ni is grown on the source, drain and gate stack. Determining the thickness of the thin Nickel metal film and NiSi is a significant metrology step.

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SE Methods & Limitations

VUV VASE Ψ & Δ ∆= i

s

p err

ψ)(tan n, k & t

Interference enhancements measurements (angle) Transmission intensity In situ measurements Optical constant parameterization

ñ = n - ik Kramers-Kronig Consistency

221 )( ikni −=+ εε

Introduction

Transparent

Semi-absorbing film

x Absorbing

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E

ω=E ω=E

Fermi Level

Drude Oscillator - Free Electron Lorentz Oscillator - Bound Electron

k

b1

f11 εεε +=

b2

f22 εεε +=

Background

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λν

ττF

bulkf+=

11 ( )gR

ℜℜ−

=312λ

Optical model for metals

S. Marsillac, N. Barreau, H. Khatri, J. Li, D. Sainju, A. Parikh, N.J. Podraza, and R.W. Collins, physica status solidi (c) 5, 1244-1248 (2008).

1)()(

22

22

22222

2222

1+

−+−

−+= ∞

ωτ

τω

ωωωτωωτ

ωεεf

fpf

ob

obpb

)1()( 222

222222

2+

++−

+= ∞ωτω

τω

ωωωτ

ωτωεε

f

fpf

ob

bpb

From Ellipsometry you can extract τf

Mayadas and Shatzkes -

Thickness Dependent Optical Properties

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-20

-15

-10

-5

0

5

10

0 1 2 3 4 5 6Photon Energy (eV)

Real part of the dielectric function of Ni 50 Å

105 Å

210 Å

800 Å

ε 1

6.007.008.009.00

10.0011.0012.00

0 100 200 300

Thickness (Å)

τ (1

0-16

sec

)

Results and Discussion (Ni)

Mayadas and Shatzkes

λν

ττF

bulkf+=

11 ( )gR

ℜℜ−

=312λ

(1)

(2)

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Results and Discussion (Ni)

0

50

100

150

200

0 100 200 300Thickness (Å)

Gra

in S

ize -

R g (Å)

0.7

0.75

0.8

0.85

0.9

0 100 200 300Thickness (Å)

R

Conclusions 1. An Optical model was developed to determine the thickness of thin metal films. 2. Model was built to show that the thickness-dependent optical properties of thin metal

films are correlated to the change in Drude free electron relaxation time. 3. The change in free electron relaxation time was traced to the change in grain boundary

reflection coefficient and grain size.

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Metals

Semiconductors

Dielectrics


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Investigation of Optical Properties of BCB Wafer Bonding Layer used for 3D Interconnects via Infrared Spectroscopic Ellipsometry

V.K. Kamineni, P. Singh, L.-W. Kong, J. Hudnall, J. Qureshi, C. Taylor, A. Rudack, S. Arkalgud, and A.C. Diebold, Thin Solid Films, 519 (2011) 2924.

P. Singh, J. Hudnall, J. Qureshi, V.K. Kamineni, C. Taylor, A. Rudack, A. Diebold and S. Arkalgud, Mater. Res. Soc. Symp. Proc., 1249 (2010) 309.

2D Interconnects – 45 nm node 3D Interconnects – TSV

1 Fujitsu Sci. Tech. J., Vol. 46, No.1 4ASM International

TEM

3D Interconnects (Benzocyclobutene)

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Why 3D Interconnects?

4ASM International

Replacing long horizontal lines with short vertical interconnects

•Addresses RC delay, crosstalk and power consumption

Enables integration of heterogeneous devices & technologies (memory, logic, RF, analog, sensors)

• Enables new functionalities

• Cost reduction compared to SoC

3rd Level (thinned substrate)

2nd Level (thinned substrate)

1st Level after backgrinding

Substrate

DRAM

DRAM

DRAM

SRAM

Micro Processor

Device layer / IMD Bonding Layer

BCB (Benzocyclobutene)

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Thinned TSV wafer

BCB

Handle wafer

Top wafer peeling due to air pockets in the BCB film

Integration Issues

37% cross-linked BCB bond

SEM cross-section image

SAM image

Dendritic structures

Void

Presenter

Presentation Notes

100 MHz

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IR Semi-absorbing Film on a Transparent Substrate

Transparent Region

( )

( )

, ( , )

( , )

n t k

t n k

Ψ ∆ → = ⇒

⇒ Ψ ∆ →

when 0 in a transparent region and determining thickness

, in the entire spectrum

Wave Number (cm -1)0 2000 4000 6000 8000

Ψ in

deg

rees

0

20

40

60

80Model Fit Exp E 70°

Absorptions

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IRSE Absorption Spectra of BCB

BCB o-quinodimethane

+

Residual alkene

1st 2nd Diels-alder

Trisubstituted THN

The thermal curing of BCB polymers is a two step process: 1. Thermally activated opening of the BCB ring to form an o-quinodimethane

intermediate.

2. The o-quinodimethane reacts with residual alkene groups in the via a Diels-Alder reaction, forming a tri-substituted tetrahydronaphthalene (THN).

Dow Chemicals: Cyclotene

Presenter

Presentation Notes

The Diels–Alder reaction is an organic chemical reaction (specifically, a cycloaddition) between a conjugated diene and a substituted alkene, commonly termed the dienophile, to form a substituted cyclohexene system

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0

500

1000

1500

2000

2500

3000

3500

5001000150020002500300035004000Wavenumber (1/cm)

Ab

sorp

tio

n C

oef

fici

ent

(1/c

m)

Tetrahydronaphthalene (THN - 1498 cm-1)

BCB Stretch (1472 cm-1)

Si-CH3 (1255 cm-1)

Vinyl Rocking (1194 cm-1)

Si-O Stretch (1050 cm-1)

Vin

yl m

oiet

y(9

85 c

m-1

)

0

500

1000

1500

2000

2500

3000

3500

5001000150020002500300035004000Wavenumber (1/cm)

Ab

sorp

tio

n C

oef

fici

ent

(1/c

m)

Tetrahydronaphthalene (THN - 1498 cm-1)


Si-CH3 (1255 cm-1)

Vinyl Rocking (1194 cm-1)

Si-O Stretch (1050 cm-1)

Vin

yl m

oiet

y(9

85 c

m-1

)

IRSE Absorption Spectra of BCB

BCB o-quinodimethane

+

Residual alkene

1st 2nd Diels-alder

Trisubstituted THN

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Hardcured12551498

12551498

95curing %

=

AA

AA

0

200

400

600

800

1000

1200

14501470149015101530Wavenumber (1/cm)

Abs

orpt

ion

Coe

ffici

ent (

1/cm

)

1800 1 minHard Cured


Tetrahydronaphthalene (THN – 1498 cm-1)

IRSE Percentage Cure

Si-CH3 (1255 cm-1)

THN (1498 cm-1)

Wavenumber (1/cm)

Film of interest

π2)2ln(2

F.W.H.MPeakArea2

××=

250 oC

1.8 μm 1min

Presenter

Presentation Notes

The Si-CH3 absorbance peak at 1255 cm−1, which is not affected by polymerization, was used to normalize the absorbance at 1498 cm−1 The Diels-Alder reaction is dependent upon the oquinodimethane and residual alkene groups seeking each other in the polymer film and reacting. As the reaction proceeds, the glass transition temperature of the film increases and the film eventually vitrifies around a conversion of 90 to 93%. At this point it is difficult for these groups to be mobile in the film, to seek each other, and to react. From the vitrification point (90–93%) to 95% (the maximum level of curing as measured by infrared spectroscopy) there is some small number of groups that react with each other even in the solid phase [10]. At 95% cure level the groups are essentially frozen and can no longer react. Thus, the data has been normalized to 95% curing level.

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SAM image

Ideal Bonded Wafer: 60% Cross-linked BCB Bond

Future Directions: Bonding using adhesive materials is relatively new in

the semiconductor industry. • IRSE can aid in screening newly investigated materials. • IRSE will aid in process tuning and development.

Presenter

Presentation Notes

A 300 mm wafer that was permanently bonded using BCB without any dendritic structures or voids; it passed the razor blade test. Conclusions: The thickness non-uniformity data assisted in tuning the spin-on deposition. The curing % in BCB films and change in chemistry was measured. This aided in reducing the voids, dendritic structures, and the bonding passed the razor blade test.

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Spectroscopic Ellipsometry of Porous Low-κ Dielectric Thin Films

Cu Cu Lo

w-κ

Cu Cu

Porous low-κ

V.K. Kamineni, C.M. Settens, A. Grill, G.A. Antonelli, R.J. Matyi, and A.C. Diebold, Frontiers of Characterization and Metrology for Nanoelectronics, AIP Conference Proceedings, 1173 (2009) 168. C.M. Settens, V.K. Kamineni, G.A. Antonelli, A. Grill, A.C. Diebold, and R.J. Matyi, Frontiers of Characterization and Metrology for Nanoelectronics, AIP Conference Proceedings, 1173 (2009) 163.

Porous Low-κ

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Silicon

PECVD of dual-phase materials (matrix and organic precursors)

Silicon

UV cured to desorb porogens

(organic precursor)

Silicon Silicon

PECVD of porous low-κ with different dielectric constant

Sample κ Thickness (nm)

ULK1 2.75 150 ULK2 2.65 150 ULK3 2.55 150

Sample κ Thickness (nm)

SiCOH1 3.0 1000 SiCOH2 2.2-2.4 333 SiCOH3 2.2-2.4 363

IBM (Porous SiCOH) Novellus (ULK)

Pores reduce the effective dielectric constant of the material

Decrease signal propagation delays (faster switching speed)

Reduction in crosstalk and power consumption

Lower heat dissipation

Pore volume fraction and pore size will effect the thermo-mechanical properties

Introduction to Low-κ dielectrics

Presenter

Presentation Notes

As components have scaled and transistors have got closer together, the insulating dielectrics have thinned to the point where charge build up and crosstalk adversely affect the performance of the device. Replacing the silicon dioxide with a low-κ dielectric of the same thickness reduces parasitic capacitance, enabling faster switching speeds and lower heat dissipation.

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VUV-VASE Results (IBM)

Graded BEMA Layer (590 nm)

0

5

10

15

20

25

30

0 100 200 300 400Distance From Substrate in nm

Por

e V

olum

e Fr

actio

n

MSE 6.559 Thickness 356.184

0.773 nm Pore Volume 24.862

0.31 %

Graded BEMA Layer (590 nm)

0

5

10

15

20

25

30

0 100 200 300 400 500Distance from Substrate in nm

Por

e V

olum

e Fr

actio

n

MSE 5.768 Thickness 386.982

0.361 nm Pore Volume 23.83

0.136 %

Pore Volume Fraction

Thickness (nm)

Control 0% 1055.0

0.2

333 nm 24.8

0.3 % 352.6

1.0

363 nm 23.8

0.1 % 379.5

0.4 Silicon Silicon

02

f2

fb

bb

a

aa =

+−

++−

εεεε

εεεε

Bruggeman expression for effective medium approximation on porous SiCOH samples

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Molecular Bond Vibrations (Novellus)

500 600 700 800 900 1000Wavelength (nm)

Ref

ract

ive

Inde

x (n

)

500 600 700 800 900 1000Wavelength (nm)

Ref

ract

ive

Inde

x (n

)

500 600 700 800 900 1000Wavelength (nm)

Ref

ract

ive

Inde

x (n

)

(a)

500 600 700 800 900 1000Wavelength (nm)

Ref

ract

ive

Inde

x (n

)

500 600 700 800 900 1000Wavelength (nm)

Ref

ract

ive

Inde

x (n

)

500 600 700 800 900 1000Wavelength (nm)

Ref

ract

ive

Inde

x (n

)

(a)

0

2000

4000

6000

8000

10000

12000

900 1000 1100 1200 1300 1400

Si-CH3

Si-O

0

2000

4000

6000

8000

10000

12000

900 1000 1100 1200 1300 1400

Si-CH3

Si-O

Si-CH3

Si-O

Si-CH3

Si-O

Si-CH3

Si-Oκ = 2.75κ = 2.65κ = 2.55Si-CH3

Si-O

Si-CH3

Si-O

Si-CH3

Si-Oκ = 2.75κ = 2.65κ = 2.55

κ = 2.75κ = 2.65κ = 2.55

Abso

rptio

n Co

effic

ient

(1/c

m)

Wavenumber (1/cm)

Abso

rptio

n Co

effic

ient

(1/c

m)

Wavenumber (1/cm)

ACRelative Carbon Concentration (%) = A +AO C

F.W.H.MArea = Peak × × 2π2ln(2)

AC - area under the Si-CH3 peak AO - area under the Si-O peak

κ n Carbon (%)

2.55 1.48 4

2.65 1.461 2.4

2.75 1.453 1.5

Presenter

Presentation Notes

IR-VASE offers increased sensitivity over FTIR spectroscopy in thin film measurements Sensitive to the chemical bonding and the % of Relative carbon concentration It is expected that the refractive index of films with lower dielectric constant will be lower. VK3981537/12/2010 Si-O-Si Stretching,Si-O Cage like stucture

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Ellipsometry Porosimetry (ULK)

∑=+

−⋅= ii

eff

effeff N

nn

B απ )2(

)1(43

2

2Lorentz-Lorenz

21

21

21

2

2

20

20

2

2

+−

+−

−+−

=

tol

tol

sat

sat

nn

nn

nn

P

Sample Refractive Index (n) Porosity (%)

κ = 2.55 1.48 13.19

κ = 2.65 1.461 11.76

κ = 2.75 1.453 7.92

Silicon Silicon

Toluene (low contact angle < 5o)

Beff – effective polarizability

neff – effective refractive index (RI)

Ni - number of molecules

αi – molecular polarizability

nsat – RI of film filled with toluene

ntol – RI of toluene

no – RI of film without toluene

P - porosity

tol

sat

BBBP 0−

=

02468

101214

0.0 0.2 0.4 0.6 0.8 1.0

Pore

Vol

ume

(%)

Relative Pressure (P/Po)

Adsorption

Desorption

Presenter

Presentation Notes

N is the number of molecules per unit volume, and α is the mean polarizability, Beff is the effective polarizability From this consideration we see that during adsorption higher pressure is needed for condensation to occur as compared to desorption. As a result of this difference, a typical adsorption-desorption isotherm usually exhibits a hysteresis loop

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Micropore Size (ULK)

=

PP

RTA 0ln

2lnln BAVV O −=

−=

2

02

00 ln

)(1exp

PPRT

EVV

β

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.0 0.2 0.4 0.6 0.8 1.0P/Po

Adsorption

Desorption

Volu

me

frac

tion

of so

lven

t ads

orbe

d

Sample Refractive Index (n) Pore radius (nm)

κ = 2.55 1.48 0.82

κ = 2.65 1.461 0.79

κ = 2.75 1.453 0.84

Dubinin and Radushkevitch (DR)

A – adsorption potential

R – universal gas constant

V – adsorbate volume

V0 – total micro pore volume

β – function of toluene only

E0 - solid characteristic energy

towards a reference adsorbate

K – empirical constant ≈ 12

02EKr =

20 )(

1=

EB

β

Presenter

Presentation Notes

nm). For such sizes comparable with size of adsorptive molecule (0.6 nm fro toluene) the Kelvin equation is no longer valid. Not only would the values of the surface tension and the molar volume deviate from those of the bulk liquid absorptive, but also the concept of a meniscus would eventually become meaningless. A method based on a semi-empirical theory developed by Dubinin and Radushkevichiv (DR) is used to analyse films containing micropores. The DR method uses change in adsorption potential when the pore diameter is comparable with the size of the adsorptive molecules. The process involved is the micropore volume filling rather then layer-by-layer adsorption on the pore walls.

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Young's modulus is a measure of the stiffness of the porous low-κ dielectric material A low CTE will prevent a connection failure between via/M1 and/or via/M2

Mechanical Properties (ULK)

Copper CTE ~ 20 x 10-6/

C

SE can measure critical mechanical parameters (Young’s modulus, CTE)

SEMATECH (Alain Diebold) CTE – Coefficient of thermal expansion

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Young’s Modulus (ULK)

00 ln

PPkdd −=

LkVRTd

E 0=

Sample Porosity (%) Pore radius (nm) EP Young’s Modulus (GPa)

κ = 2.55 13.19 0.82 2.74

κ = 2.65 11.76 0.79 3.96

κ = 2.75 7.92 0.84 7.08

153

153.5

154

154.5

155

155.5

156

0.0 0.2 0.4 0.6 0.8 1.0P/Po

Thic

knes

s (n

m)

Adsorption

Desorption

K. P. Mogilnikov and M. R. Baklanovz

VL – molecular volume

E – Young’s modulus

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High Temperature Thickness Measurements (ULK)

Sample Refractive Index (n) 632.8 nm TER (10-6/oC) CTE (10-6/oC)

κ = 2.55 1.48 70.2 44.72

κ = 2.65 1.461 54.9 35.54

κ = 2.75 1.453 29.5 20.30

y = 2.95E-05x - 6.82E-04R2 = 0.934

-0.0005

0

0.0005

0.001

0.0015

0.002

0.0025

0.003

0.0035

20 40 60 80 100

Cooling

Heating

Linear (Cooling)

Temperature (oC)

Δd/d

o

κ = 2.75

subfilm

filmfilm

film

film

o dTdL

Lα

νν

ανν

−−

−

+=

12

111

0.25

62.6 10 /

Poisson's Ratio filmoCsubstrate

ν

α

= =

−= ×

Film on substrate (CTE)

Note: Fitting for the substrate expansion using the silicon temperature library (J.A.Woollam)

Free standing film (thermal expansion rate)

α=dTdL

Lo

1

CdTdL

Lo

o/105.291 6−×==α

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Summary on Low-κ

The following parameters were determined using SE. SICOH (IBM)

o Porosity (BEMA) o Grading in porosity

ULK (Novellus) o Carbon content o Porosity (EP) o Pore size o Young’s modulus o Coefficient of thermal expansion

Complementary techniques such as specular XRR, off-specular XRR and SAXS were also performed on these films. Both, the optical and x-ray metrology agreed reasonably well.

Sample Thickness (nm)

n (632.8 nm)

Carbon %

Porosity (%)

Pore radius (nm)

EP Young’s Modulus

(GPa)

TER (10-6/oC)

CTE (10-6/oC)

κ = 2.55 155.6 1.48 4 13.19 0.82 2.74 70.2 44.72

κ = 2.65 154.7 1.461 2.4 11.76 0.79 3.96 54.9 35.54

κ = 2.75 147.1 1.453 1.5 7.92 0.84 7.08 29.5 20.30

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Metals

Semiconductors

Dielectrics


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Extension of Far UV spectroscopic ellipsometry studies of High-κ dielectric films to 130 nm

V. K. Kamineni, J. Hilfiker, J. Freeouf, S. Consiglio, R. Clark, G.J. Leusink, and A. C. Diebold, Thin Solid Films, 519 (2011) 2894.

Bulk Si

10 Å SiO2

30 Å HfO2

High-κ

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Absorption Cross-section

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0 2 4 6 8 10

Rela

tive

Inte

nsity

(offs

et)

2 theta (Degrees)

Si_Chemox_30A HfSiO (0 %)Si_Chemox_30A HfSiO (10 %)Si_Chemox_30A HfSiO (30 %)SI_Chemox_30A HfSiO (60 %)Si_Chemox

00.20.40.60.8

11.21.41.6

3 4 5 6 7 8 9 10

Extin

ctio

n Co

effic

ient

(k)

Photon Energy (eV)

HfSiO (0%, 30A)HfSiO (10%, 30A)HfSiO (30%, 30A)HfSiO (60%, 30A)

0

0.01

0.02

0.03

0.04

3 4 5 6 7 8 9 10

Chemox

Photon Energy (eV)

Extin

ctio

n Co

effic

ient

(k)

150 nm

XRR SE

Thickness metrology

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Metals

Semiconductors

Dielectrics


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Metrology of Strain Engineered GaN/AlN/Si(111) Thin Films Grown by MOCVD

M. Tungare, V. K. Kamineni, F. Shahedipour-Sandvik and A. C. Diebold, Thin Solid Films, 519 (2011) 2929.

http://images.iop.org/objects/compsemi/features/thumb/7/11/5/csnit1_11-01.jpg

III-Nitrides

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Substrate Engineering Technique

Implanted (Amorphized layer) AlN

Si (111) AlN

Si (111)

Si (111) Polycrstalline Si

AlN GaN

Si (111) Polycrystalline Si

AlN

Implantation

1 2

3

4

Substrate engineering consists of 4 major steps: 1) Growth of an epitaxial AlN buffer layer on Si 2) Implantation of AlN/Si with N+ ions to create a defective layer in Si below AlN buffer 3) Annealing of AlN/Si to recover any loss of crystallinity due to implantation 4) Growth of thick (2 µm) GaN on AlN/Si

Wide Band Gap Optronix Lab Prof. Shadi Shahedipour-Sandvik and Mihir Tungare

Si (111)

Presenter

Presentation Notes

Lack of availability of inexpensive native substrate RAMAN, TEM, HXRD High dislocation density (109-1010)/cm2 Issues dislocation defects cracks in the epilayer Significant reduction in edge dislocations in a 2 mm thick GaN film grown on an engineered substrate by an order of magnitude to 108 cm-2 and reduction of screw dislocations by a factor greater than four Crack separation >1 mm in a 2 mm thick GaN layer Significant decrease in in-plane strain in the GaN films grown on nitrogen implanted substrates Raman spectroscopy shows 84% stress reduction Improved optical properties, crystal quality, and smoother surface morphology as a result of this substrate engineering technique Need for non-invasive characterization of thickness and changes to properties of each layer at every stage of substrate engineering

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p

Wave Number (cm -1)300 600 900 1200 1500 1800 2100

Ψ in

deg

rees

0

5

10

15

20

25

Exp E 70° Si_AlN_Implanted_AnnealedExp E 70° Si_AlN_ImplantedExp E 70° Si_AlN

Implantation

Bulk Si

AlN

(1) AlN/Si (2) Implanted (60 keV N14+) (3) Annealed (1100 oC)

Bulk Si Implanted

Bulk Si EMA Layer

AlN AlN

IRSE of Substrate Engineered AlN Layers

E1

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Sample List E1(TO) cm-1 γ (cm-1) Δω (cm-1) dωo/dP Stress (GPa)

Si_AlN 662.2

0.08 19.5

0.2 3.8 4.5 0.84

Si_AlN_Implanted 664.5

0.24 56.0

0.4 1.5 4.5 0.33

Si_AlN_Annealed 663.8

0.16 21.2

0.2 2.1 4.5 0.48

Resolution = 2 cm-1

E1 (TO) Bulk AlN = 666 cm-1

Isotropic model due to very thin AlN films (IR Probe)

Tensile Biaxial Strain

Broadening of the E1 (TO) phonon mode in implanted AlN is clear sign of presence of defects

Not sensitive to the A1 (TO) due to c-plane orientation

Stress Measurements

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Graphene

Semiconductors

Dielectrics


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Spectroscopic Ellipsometry of CVD Graphene

F. J. Nelson, V. K. Kamineni, T. Zhang, E. S. Comfort, J. U. Lee, and A. C. Diebold, Appl. Phys. Lett., 97 (2010) 253110.

Glass

Surface Roughness Graphene 3.35 Å

0 300 600 900 1200 1500 18001.0

1.5

2.0

2.5

3.0

3.5

4.0

Wavelength (nm)

n1.0

1.5

2.0

2.5

3.0

3.5

4.0

k

Van Hove Singularity

*Graphene’s infrared-to-visible absorbance: ~2.3%

Presenter

Presentation Notes

Growth consisted of a combined flow of hydrogen and methane onto copper foils at 1000° C, 130 mTorr CVD graphene was then transferred to a substrate using the process below

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Wafer Mapping- CVD Graphene on 300nm SiO2/Si

Presenter

Presentation Notes

A linear Effective Medium Approximation (EMA) was used to model the CVD graphene film transferred to a 300 nm SiO2/Si substrate Film medium is made of 2 components: graphene + void space Dielectric function is a weighted combination of each component by its volume fraction fA,B:

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Metals

Semiconductors

Dielectrics


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V. K. Kamineni and A. C. Diebold, “Evidence of the phonon confinement on the linear optical response of nanoscale silicon films”, arXiv:1103.4102v2.

Temperature and thickness dependence of the dielectric function and interband critical points in ETSOI

Bulk Si

1400 Å SiO2

ETSOI (10 – 2 nm)

Bulk Si

Extremely thin silicon-on-insulators (ETSOI)

Dielectric response of bulk Si and nanoscale silicon films in different

Silicon-on-insulator (SOI)

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Introduction to Silicon-on-insulator (SOI)

A. Diebold, TEM compliment of Mark Clark, ATDF

2 nm BOX

SOI ~ 10 nm

Epoxy

BOX – buried oxide layer

Drain

Silicon substrate

Buried Oxide (BOX)

n+ n+ n p+ p+ p

n+ n+

Source

Gate

Drain Source Gate

NMOSFET PMOSFET

Advantages of SOI technology:

• Excellent isolation of active devices

• Lowers the parasitic capacitance

• Lower leakage current

• Faster device operation

• Lower power consumption

STI STI

Presenter

Presentation Notes

The last HF etch was processed at RT and the ratio is 100:1 to 300:1 (DI:HF). Tools: Wet oxidation: TELINDY PLUS (TEL) Dry oxidation: Vantage RadiancePlus RTP (Applied Materials) Etching: DNS DU 3000 (DNS) In-line metrology: Aleris 8500 (KLA-Tencor)

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2M. Cardona and F. H. Pollak, Phys. Rev. B 142, 530 (1966).

Band structure of Si calculated from the k·p method2 1C. Kittel, Introduction to Solid State Physics (Wiley, New York, 1996)

First Brillouin zone (truncated octahedron) of FCC Lattice1

[100] Direction: Γ Δ X [111] Direction: Γ Λ L [110] Direction: Γ Σ K

Critical Point • Constant energy difference between the valence and conduction band. • In optical physics terms – a high joint density of states

ε2: Imaginary part of the dielectric function

E1

Electronic transitions

Presenter

Presentation Notes

First Brillouin zone is a uniquely defined primitive in reciprocal space. Several points of high symmetry are of special interest – these are called critical points Showing symmetry labels for high symmetry lines and points.

http://upload.wikimedia.org/wikipedia/commons/c/c1/Brillouin_Zone_(1st,_FCC).svg

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Direct space analysis:

C – amplitude β – phase factor Eg – threshold energy (ECP) Γ – lifetimebroadening μ – order of singularity

μ = ½ (3D one-electron approximation) μ = 0 (2D one-electron approximation) μ = -½ (1D one-electron approximation) μ = 1 (excitonic critical points)

( ) µβε −Γ+−= iEECe gi

( )( )

=Γ+−≠Γ+−+

= −

−−

0,0,)1(

2

2

2

2

µµµµε

β

µβ

iEECeiEECe

dEd

gi

gi

E1

Eo’

Excitonic critical point

2D one-electron approximation

Photon energy

ε 2

Direct space analysis

Lorentzian line shape

Double derivative of the Lorentzian line shape

-4000

-3000

-2000

-1000

0

1000

2000

1 2 3 4 5 6

d2 ε2/

dE2

Photon energy

Dielectric function of Si (experimental):

1P. Y. Yu and M. Cardona, Fundamentals of Semiconductors (Springer, Berlin, 2001).

Presenter

Presentation Notes

For strong electron–hole attraction, as in ionic crystals, the electron and the hole are tightly bound to each other within the same or nearest-neighbor unit cells. These excitons are known as Frenkel excitons. In most semiconductors, the Coulomb interaction is strongly screened by the valence electrons via the large dielectric constant. As a result, electrons and holes are only weakly bound. Such excitons are known as Wannier–Mott excitons [6.37, 38] or simply as Wannier excitons. In this book we shall be concerned with Wannier excitons only In order to enhance the structure present in the spectra and to obtain the CP parameters, we calculate numerically the second-derivative spectra, d 2e/dco2, of the complex dielectric function from our ellipsometric data. These parameters are generally determined by least squares regression in direct space energy or wavelength space in the case of optical spectra, where a segment of the spectrum containing the structures of interest is chosen, a model line shape is assumed, and the parameters are determined by minimizing the mean-square deviation between the model line shape and the spectral segment. Since in direct-space analysis the choice of baseline is usually critical, one common method of nominally improving accuracy, enhancing CP structures, and suppressing baseline artifacts is to numerically differentiate the spectrum one or more times with respect to energy before performing the least-squares analysis. However, differentiation enhances noise, and direct-space convolution algorithms, even rather sophisticated versions such as the convolution algorithms tabulated by Savitsky and Golay, distort the information content of the data.

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• Change in the dielectric function of c-Si nanoscale films at different thickness

• Blue shift in the critical point energy is observed

A. Diebold et al., phys. stat. sol. (a) 205, 896 (2008)

0

10

20

30

40

50

60

2 3 4 5

9.2 nm6.5 nm5.1 nm2.5 nm2 nm

Photon Energy (eV)

ε 2

d2 ε2/

dE2

Imaginary part of the dielectric function and its second derivative

-3000

-2000

-1000

0

1000

2000

3000

3.1 3.3 3.5 3.7 3.9

9.2 nm6.5 nm5.1 nm2.5 nm2 nm

Photon Energy (eV)

Blue Shift Broadening

Direct space analysis

Presenter

Presentation Notes

strain is expressed as the ratio of total deformation to the initial dimension of the material body in which the forces are being applied

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0

10

20

30

40

50

60

2 3 4 5

Hafnium oxide (10 nm)Silicon dioxide (20 nm)Native oxide

ε 2

Photon Energy (eV)

Altering the optical response by changing the top dielectric layer: changes in quantum confinement and electron-phonon interaction

Surface dielectric layer

Imaginary part of the dielectric function of c-Si QWs (~ 5 nm)

0

0.5

1

1.5

2

2.5

3

0 2 4 6 8 10Photon Energy (eV)

SiO2 (9 eV)

HfO2 (6 eV)

ε 2

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In-line optical metrology

Silicon

SiO2

Silicon

Silicon SiO2

Silicon

HfO2

Silicon SiO2

Silicon

Silicon SiO2

Silicon

Thickness dependent dielectric function

Surface dielectric dependent dielectric function

What does it mean to in-line metrology ? • A recipe which has thickness dependent optical properties • A recipe which has top dielectric layer dependent optical properties

SiO2 SiO2 SiO2

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Photoreflectance

Photoluminescence

Conclusions

Acknowledgements

Outline

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Photoreflectance

EC

EV

Ef

Vacuum

+ +

+ + +

• Space charge layer at the surface due to Fermi level pinning

Surface acceptor states

- - - - -

Laser on

Electron

Hole

-

• Carriers neutralize charge at the interface

n-type semiconductor

• Laser light produces carriers

• Modulation of light alters band bending

• Complex dielectric functions changes with band bending

Modulation spectroscopy (non-linear optical spectroscopy)

Complementary technique to measure the shift in the energy and lifetime broadening of the E1 critical point

Presenter

Presentation Notes

Space charge layer exists at interface due to the pinning of Fermi level EF - Layer of opposite charges presents at oxide surface - Pump light produces carriers, which neutralize charge at interface - Internal electric field consists of DC (gate voltage) & AC (modulated pump light) parts - Modulation of electric field alters band bending - Complex dielectric function changes with band bending - Difference of reflectance is resulted

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CCD Monochromator

Xenon source (probe)

X,Y sample Stage

Chopped 1.38 k Hz

532 nm (pump)

( ) ( )( )

( )off on

off

R RRR R

ω ωω

ω−∆

=

Filter

Photoreflectance

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221121 ),(),( εεεεεε ∆+∆=∆ baRR

a & b are the Seraphin coefficients

1

1ε∂∂

=R

Ra

2

1ε∂∂

=R

Rb

Changes in the dielectric function due to the perturbation

Low field regime: Third Derivative Functional form:

( )

Γ+−∝

∆n

CP

i

iEEAe

RR θ

Re

A: Amplitude

Θ: Phase

ECP: Critical point

Γ: Lineshape Broadening

n: Determined by type of CP

21 & εε ∆∆

Theory

Photon Energy (eV)

( )510RR

−∆

E1 – 3.39 eV

Experimental

Photoreflectance ε 2

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Photoreflectance of Strained SOI

Nuclear Instruments and Methods in Physics Research B 253 (2006) 18–21

• Three transitions energies are (i) 3.19 eV, (ii) 3.30 eV and (iii) 3.45 eV.

• Calculations show tensile strain of 1% in the strained Si overlayer

• This value is again in good agreement with the nominal tensile strain and with the values obtained from RS and Low Temp PhotoLuninescence.

Presenter

Presentation Notes

Three transitions energies are deduced (i) 3.19 eV, (ii) 3.30 eV and (iii) 3.45 eV. From theoretical band diagram calculation in strained Si, these transitions are attributed to (i) the lower Conduction band to lh band transition Eg0(lh) = 3.19 eV, (ii) the lower conduction band to hh band transition EC g0(hh) =3.30 eV and (iii) a higher conduction band to lh band Eg1(lh) = 3.45 eV. Using the deformation potential values reported by Pollak and Cardona [16] and the band gap shrinkage measured in our experiment (Eg(e-lh) =0.19 eV and Eg(e-hh) = 0.08 eV) we extracted a tensile strain of 1% in the strained Si overlayer. This value is again in good agreement with the nominal tensile strain and with the values obtained from RS and LTPL.

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Franz Keldysh Oscillations

Franz Keldysh Oscillations Due to internal electric field in polar GaN

OPTO-ELECTRONICS REVIEW 12(4), 435.439

cnse.albany.edu Chouaib, APL 93, (2008) 041913

GaAsSb

Internal E Field

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Photoreflectance

Photoluminescence

Conclusions

Acknowledgements

Outline

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Band structure of Si calculated from the k·p method1

1M. Cardona and F. H. Pollak, Phys. Rev. B 142, 530 (1966).

PLωgE

Photoluminescence

( )2 2 2

2 212

x yygap QC

k kRE E E

Mn

+= + − +

−

Photoluminescence peak energy (2D)

2* 2

2 4Rydbergy

m eRπε

= →

Photoluminescence is used to study the changes in the indirect transitions due to quantum confinement and change in dielectric medium

2 2

22QCEMLπ

=

Presenter

Presentation Notes

In photoluminescence experiments on high purity and high quality semiconductors at low temperatures, we expect the photoexcited electrons and holes to be attracted to each other by Coulomb interaction and to form excitons. As a result, the emission spectra should be dominated by radiative annihilation of excitons producing the so-called free exciton peak. When the sample contains a small number of donors or acceptors in their neutral state (a common occurrence at low temperature) the excitons will be attracted to these impurities via van der Waals interaction. Since this attraction lowers the exciton energy, neutral impurities are very efficient at trapping excitons to form bound excitons at low temperature

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a) Free Excitons (Wannier-Mott Excitons)

(Delocalized states)

b) Bound Excitons (Frenkel Excitons)

(Localized states)

As the power is increased, at high densities, and at low temperatures the free excitons condense to form a liquid phase.

This liquid phase manifests itself in the formation of EHD (Electron-hole droplets) – a broad feature in luminescence.

32

2 22

mk T EgBn Expk TBπ

− <<

BE ~ 0.01 eV BE ~ 0.1 to 1 eV

Photoluminescence

BE – Binding Energy

Presenter

Presentation Notes

Electrons and holes are bound in free exciton (FE) at low temperatures by Coulomb attraction. Low density of FE is regarded as the gas phase. As the exciton density increases, the excitons begin to dissociate into plasma, which is explained well by the Mott transition. 14 The Mott criterion is shown in Fig. 1: the left-hand side of the criterion is the excitonic (gas) phase and the right-hand side is the electron hole plasma (EHP) phase. Excessive excitons are also known to form electron-hole liquid (EHL) if the sample temperature is lower than the critical temperature.

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Photoluminescence of SOI Quality

N. Pauc et al., Phys. Rev. B 72, 205325 (2005) Tajima

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Photoreflectance

Photoluminescence

Conclusions

Acknowledgements

Outline

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Conclusions

• A wide range of wavelengths makes Spectroscopic Ellipsometry a very powerful method capable of measuring more than just thickness and refractive index

• Non Linear Optical methods such as Photoreflectance and Photoluminescence provide information not available from spectroscopic ellipsometry

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Any questions?

Presenter

Presentation Notes

1927 Fifth Solvay International Conference on Electrons and Photons

overview of optical metrology of advanced semiconductor materials

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