continuity in plasma processing: yesterday’s ... · (app) have had tremendous technological...

AVS03_01

CONTINUITY IN PLASMA PROCESSING: YESTERDAY’S ACCOMPLISHMENTS, TODAY’S INNOVATIONS, TOMORROW’S CHALLENGES*

Mark J. KushnerUniversity of Illinois

Dept. of Electrical and Computer EngineeringUrbana, IL 61801

[email protected] http://uigelz.ece.uiuc.edu

November 2003

* Work supported by SRC, NSF, Sematech, GE and EPRI

University of IllinoisOptical and Discharge PhysicsAVS03_02

ACKNOWLEDGEMENTS

• Andre Anders• Eray Aydil• Kurt Becker• Ned Birdsall• Matt Blain• Nick Braithwaitte• Jane Chang• Frank Chen• Joel Cook• J. Gary Eden• Brett Cruden• Ashok Das• Rajesh Dorai

• Pietro Favia• Bish Ganguly• Valery Godyak• Matt Goeckner• Martin Gundersen• Bill Holber• Alan Howling• Fred Huang• Ulrich Kogelschatz• Uwe Kortshagen• Toshiaki Makabe• Joelle Margot• Dennis Manos

• Tom Mantei• Jim Olthoff• Larry Overzet• Ajit Pranjpe• Zoran Petrovic• Louis Rosocha• Karen Seward• Phillipe Schoeborn• Tim Sommerer• L. Tsendin• Peter Ventzek• David Wharmby• Gerald Yin


AGENDA

• What is our legacy in plasma processing?

• How have we leveraged that legacy to innovate plasma based technology?

• What challenges and opportunities lie ahead for plasma technologies? (50th Anniversary PSTD Talks)

•Materials Processing and Sources (R. Gottscho, F. Chen, T. Dalton, J. Schmitt, H. Sawin)

•Diagnostics (V. Donnelly)• Lighting•Nanoscience•Bioscience

• Concluding remarks

University of IllinoisOptical and Discharge PhysicsAVS03_

WORKING DEFINITION OF PLASMA PROCESSING


University of IllinoisOptical and Discharge Physics

• Technological plasmas are a power transfer media.

• Electrons transfer power from the "wall plug" to internal modes of atoms / molecules to make “benign” species into “reactive” species.

• Once activated, their physical or chemical potential may be used to make products (add or remove materials, photons…)

• Plasma processing is the use of partially ionized gases in technology to create "products."

WALL PLUG

POWER CONDITIONING

ELECTRIC FIELDS

ENERGETIC ELECTRONS

COLLISIONS WITHATOMS/MOLECULES

EXCITATION, IONIZATION, DISSOCIAITON (CHEMISTRY)

LAMPS LASERS ETCHING DEPOSITIONE

eA

PHOTONS RADICALS

IONS

• Displays

• Materials Processing

COLLISIONAL LOW TEMPERATURE PLASMAS

• Lighting

• Thrusters

• Spray Coatings

UTA_1102_05


CONTINUITY IN PLASMA TECHNOLOGY

• Our striking record of innovation in developing plasma based

technologies has relied on leveraging a continuity of progress

through generations of these technologies.

AVS03_06

(a very incomplete) TIME LINE: OUR ROOTS IN SCIENCE

→→→→→Breakdown

Crooke W.s1880'

DBDsSiemens W.

s1850'

SputteringGrove R. W.

s1850'

DischargesGlow Faraday M.

s1830'

DischargesGlow First Hawsbee F.

s1790'

• R. Powell, S. Rossnagel, “PVD for Microelectronics”• J. Hopwood and T. Mantei, JVSTA, 2003• Y. P. Raiser, “Gas Discharge Physics”• J. R. Roth, “Industrial Plasmas Part I”• Joel Cook, private communication.

• D. Manos, D. Flamm, “Plasma Etching: An Introduction”• J. Waymouth “Electric Discharge Lamps”• J. Hecht, “Laser Pioneer Interviews”• J. Schmitt, AVS 50th Symposium• www.siemens.com

→→→Plasmas Microwave

Brown C. S.s1940'

Functions onDistributi AllisW.

s1930'

ICPsBabat I. G. Thomson, J. J.

s1920'

sElectronic Gaseous ModernPhelps A.

s1960'

Transport ModernHolstein & Bernsteins1950'

ECRBrown Allis,Lax,s1950'

→→

→→→→→Shielding

Debye P.s1920'

Plasma Sheaths,Langmuir I. Tonks, L.

s1920'

Transport Townsend S. J.

s1900'

Discharges RFTesla N.

s1890'

ICPsHittroff W.

s1880'


PLASMA MATERIALS PROCESSING:WHAT DO WE DO WELL?

• The fabrication of conventional microelectronics has met and bested extreme challenges as the nm scale is approached and exceeded.

• Plasma science has played a critical role in virtually all aspects of meeting these challenges

• Physical Vapor Deposition• Plasma Enhanced Chemical Vapor Deposition• Etching• Cleaning• Passivation• Plasma sources of UV radiation for lithography (Hg lamps

to EUV)

AVS03_08

→→→→→ySelectivit

Heinecke A.R.s1970'

Etcher DiodeReinberg R. A.

s1970'

Stripping t Photoresis

Irving S.s1970'

PECVDSwann & Sterlings1960'

↓ECR-Brown Allis,Lax,

s1950'

ICP PlanarKeller Ogle,

s1990'

ECRs1990'

TegalWaferSingle

s1980'

Labs BellProcessing Batch

s1970'

n ActivatioIonWinters&Coburn

s1970'→→→→

(very incomplete) TIME LINE: MATERIAL PROCESSING

PVD Metal IonizedRossnagel S.

s1990'

RIE encyMultifrequs1990'

THelicon/PMs1990'

→→→

HeliconBoswellChen, −↑

↓

↑ICPs-Hittrof-s1880'

SputteringGroves1850' −−↑

Ref: J. P. Chang


ADVANCES IN EQUIPMENT DESIGN ENABLES ADVANCED DEVICE FABRICATION

• Perhaps our most challenging accomplishments have been the design of reliable plasma sources for these processes.

• The continuity of progress through generations of advances in plasma fundamentals, diagnostics, modeling and empiricism have been leveraged to produce reliable manufacturing tools.


SOPHISTICATED PLASMA TOOLS

• Ref: Ashok Das• AMAT Ionized Metal PVD

• AMAT-Komatsu PECVD

Ref: W. Holber

Ref: R. Dorai


PLASMA DIAGNOSTICS HAVE PLAYED A CRITICAL ROLE AND ARE MOVING CLOSER TO THE PRODUCT

• Plasma process and equipment design have and will continue to critically rely on advanced plasma diagnostics.

• Real time control strategies, a requirement for sub-100 nm processing, will also rely on robust, cost-effective diagnostics.

• The most mature plasma diagnostics are typically too far removed from critical measurements of activation of surface processes.

• Non-intrusive diagnostics which provide the state of activating species impinging on surfaces are required for a complete picture.


LANGMUIR PROBES IN HARSH ENVIRONMENTS

• Development of basic diagnostics, such as Langmuir probes, for use in harsh rf environments improved our knowledgebase and provided stringent test of models.

• Ref: V. Godyak

• RF CCP in Argon

Ref: E. Aydil

80 mTorr SF6, 200 W

• New materials (metal gates, low-k dielectrics, high-k dielectrics, SiGe/SOI substrates, porous materials).

• Increasing demands on etch selectivity.• Shorter development cycle.• Lower thermal budgets.• More controllable knobs.• Use of plasmas as processing tools (e.g., self assembly) as

opposed to pattern replication.• Reduced cost of ownership through plasma tools which are

used for multiple processes.• Improved and more relevant contributions from modeling.

MATERIALS PROCESSING: CHALLENGES


• Ref: J. Cook, T. Mantei, P. Schenborn, P. Ventzek, D. Manos

AVS03_13


CHALLENGES IN TAILORING PLASMAS FOR SELECTIVE ACTIVATION


• As in most relationships, it’s all about control.

• Advanced applications will depend on selectively promoting desired plasma chemical reactions and preventing undesirable reactions.

• The ability to tailor the energy distributions of plasma particles is key to this selectivity.

• Tailored electron energy distributions: Control formation of radicals and ions; best if also spatially segregated.

• Tailored Ion energy distributions: Determine activation of surface processes; must be narrow to differentiate thresholds.

• Tailored synergy between ions and neutrals: Necessary for monolayer control of selectivity, deposition, end-point.

Model results from HPEMRef: K. Seaward, S. Samakawa


TAILORING f(ε) BY FREQUENCY


• Plasma tools for multiple processes or recipes (different chemistries) require control of electron energy distribution for optimum generation of precursors.

• [e], ICP, 10 mTorr, Ar/Cl2 = 70/30.

• f(ε) 50 MHz

• f(ε) 5 MHz

• Model results from GLOBAL_KINRef: K. Seaward


TAILORING FLUXES THROUGH PULSING


• Processing of thin films depends on the synergy between energetic ions and radical fluxes. Pulsed plasmas which control these contributions produce unique films not otherwise attainable.

• Pulsed ICP Ar/C4F8=70/30, 15 mTorr • Deposition of low-k fluorocarbon film from perfluoroallyl benzene [L. Han, JVSTB 18, 799 (2000)]

• Self assembling nanostructures

• Non-invasive MEMs based plasma sensors with L < λD.

AVS03_17

ROLE OF PLASMA SCIENCE TO MEET CHALLENGES

• Multi-process plasma tools with frequency and pulse power agility to selectively activate species

• On wafer and plasma diagnostics which enable real-time-control to sub-monolayer accuracy.



PLASMA LIGHTING TECHNOLOGIES

• Annual US energy use for lighting is 750 TWH (8.2 quads)

• 8.3 % of total energy consumption• 22% of total electrical energy consumption.

• Plasmas are 59% of lighting energy use (13% of total). There are 2.6 billion plasma lighting sources in the US.

• Replacing incandescent lamps with plasma sources will decrease US electrical energy use 5% [20 nuclear power plants or 1.2 Million barrels of oil/day (10% of imports)].

• Improving efficiencies and utilization of plasma lighting will enormously impact our economy, environment, foreign policy.

• Ref: U.S. Lighting Market Characterization, Navigant Consulting, 2002

• DOE Annual Energy Outlook 2003

AVS03_19

(very incomplete) TIME LINE: LIGHTING TECHNOLOGIES

→→→→Excimers

Goldstein F. Curtis, W.s1910'

Hg PressureLow P.C.Hewitt

s1900'

Ozonizers DBDs,Siemens W.

s1850'

radiation Line PlasmaGiessler H.

s1850'

Lamps Excimer DBDKogelshatz & Elliason

s1980'

Displays PlasmaSlottow & Blitzer

s1960'

Trapping RadiationHolstein T.

s1940'

Lampst Fluorescens1930'

→→→

Lighting PanelFlat ExcimerHitzschke and Vollkommer

s2000'

PDPs Commercials1990'

→→


LIGHTING: ACCOMPLISHMENTS AND CHALLENGES

• Efficient white sources based on Hg plasmas in fluorescent and arc lamps; and non-white metal vapor lamps. Environmental impacts are debatable but not ignorable.

• Challenges:

• Highly efficient non-Hg plasma white-light sources (rare gases, excimers, metal halides, molecular radiators)

• Improving understanding of plasma-surface interactions to extend lifetimes (cathodes)

• Quantum splitting phosphors to improve utilization of UV (2 visible photons from 1 UV reduces US energy use 5-10%).

• Leverage advances plasma lighting to other applications (and vice-versa)

• Solid State Lighting? (next talk…M.G. Craford, Lumileds Lighting)


ATMOSPHERIC PRESSURE PLASMAS

• Atmospheric Pressure Plasmas (APP) have had tremendous technological impact

• High power lasers (e.g., Excimer lasers)

• Lighting Sources (e.g., HID lamps)

• Ozone generators

• Modification of surfaces

• Toxic gas abatement

• The potential for APPs to perform “high value” manufacturing is literally untapped.

• Atmospheric pressure DBD ozone generator

Ref: U. Kogelshatz


PLASMA SURFACE MODIFICATION OF POLYMERS• To improve wetting and adhesion of

polymers atmospheric plasmas are used to generate gas-phase radicals to functionalize their surfaces.

Untreated PP

Plasma Treated PP

• M. Strobel, 3M

AVS03_22

Hydrophobic

Hydrophilic

• Polyethylene, Humid-air• Akishev, Plasmas Polym. 7, 261 (2002).


POLYMER TREATMENTPLASMA TOOL

AVS03_23

• Web based corona plasmas treated sheet polymers for improved surface functionality.

Tantec Inc.


FUNCTIONALIZATION OF POLYPROPYLENE

• Air, 300 K, 1 atmAVS03_24

• Control of surface energy by plasma treatment results from functionalization with hydrophilic groups.

• Carbonyl (-C=O) • Alcohols (C-OH)• Peroxy (-C-O-O) • Acids ((OH)C=O)

• Functionalization depends on process parameters such as gas mix, energy deposition and relative humidity (RH).


OPPORTUNITIES: ATMOSPHERIC PRESSURE PLASMASTHE CHALLENGE

• APP’s provide the potential to selectively generate activated species (radicals, ions and photons) for modification and cleaning of surfaces.

• Most (many) industrial processes performed with liquid solvents could in principle be performed with APP generated radicals.

• The environmental impact of eliminating liquid solvents for cleaning of parts, removal of paint, functionalizing or sterilizing surfaces would be immense.

• Advanced concepts include improvement of combustion processes, homeland defense (chemical and biological remediation), and microplasma devices.

Ref: B. Ganguly

Ref: L. Rosocha

Ref: M. Gundersen

In-situ H2 Generation for Small Scale (i.e. Low Power) Fuel Cells Using a Microhollow Cathode Discharge

0 20 40 60 80 100 120 1400

10

20

30

40

50

60

Plasma offPlasma on

N2

H2

NH3

Part

ial P

ress

ure

(Tor

r)Time (min)

• High throughput is facilitated by microplasma arrays

• Ref: Kurt Becker


THE ROLE OF PLASMAS IN BIOSCIENCE

• Plasmas, to date, have played important but limited roles in bioscience.

• Plasma sterilization

• Plasma source ion implantation for hardening hip and knee replacements.

• Modification of surfaces for biocompatibility (in vitro and in vivo)

• Artificial skin

• The potential for commodity use of plasmas for biocompatibility is untapped.

• Low pressure rf H2O2 plasma (www.sterrad.com)

PE-CVD -COOH functional coatingsPLASMA TREATMENT N-grafted polymer surfaces

cell growth covalent binding of molecules

-COOH

-COOH

-COOH

-COOH

>C=O

-OH

>C=O

-OH

C CO

CH2=CCOOHH

-NH

2

-CN

>C=O

--OH

--NH

2

=NH

-NH

2

-CN

NH3

KEY ISSUESretention of monomer structurelow power, modulated discharges

process controldensity of groups

stability

cell adhesive surfaces

-CN

Ref: P. Favia


ATMOSPHERIC PRESSURE PLASMAS:THE CHALLENGE

• Controlling functional groups on polymers through fundamental understanding of plasma-solid interactions will enable engineering large area biocompatible surfaces.

• 10,000 square miles of polymer sheets are treated annually with atmospheric pressure plasmas to achieve specific functionality.

• Cost: < $0.05 /m2

• Low pressure plasma processing technologies produce biocompatible polymers having similar functionalities.

• Cost: up to $100’s /cm2 ($1000’s/cm2 for artificial skin)

• Can commodity, atmospheric pressure processing technology be leveraged to produce high value biocompatible films at low cost? The impact on health care would be immeasurable.


THE ROLE OF PLASMAS IN NANOSCIENCE

• Plasma science has been absolutely critical to the development of conventional microelectronics structures.

• What will the role of plasma science be in facilitating these advances in truly nanoscale science and technology?

• Atomic layer processing (etch and deposition)• Plasma aided lithography (trimming)• Selective activation or functionalization of materials on

molecular scales (inanimate and living)• Self- and directed-assembly• Commodity production of nanostructures

Cruden et al., J Appl Phys, 12, 363 (2001).

SELECTIVE, ALIGNED PLASMA GROWTH OF CARBON NANOTUBES

DC Plasma CVD

DC Plasma (C2H2/NH3)

RF Plasma (C2H4/NH3)

Ref: B. Cruden

• Aligned CNT growth can be obtained in a low pressure rf and dc plasmas using different feedstocks.

• Catalyst choice and configuration may dominate.

AVS03_29

PLASMA BASED SELF- AND DIRECTED ASSEMBLY

J. Appenzeller et al, Trans. Nanotech. 1, 184 (2002)W. Choi, Appl. Phys. Lett. 79, 3697 (2001)J. Zou et al, Trans. Microw Theory Tech. 51, 1067 (2003)M. Meyyappan et al, PSST 12, 205 (2003)


• As plasma tools become more sophisticated and reproducibility more critical, mastery of the fundamentals becomes essential.


MODELING IMPROVES FUNDAMENTAL UNDERSTANDING:ANAMOLOUS SKIN DEPTH EFFECTS IN ICPS

AVS03_29

• Ref: V. Godyak, “Electron Kinetics of Glow Discharges” • Ar, 10 mTorr, 7 MHz, 100 W

ANIMATION SLIDE

Ref: V. Kolobov

Ref: F. Huang, P. Ventzek, P. Stout


CHALLENGE FOR MODELING AND SIMULATIONChallenge…..Become a tool for design and optimization of

equipment and processes as reliable as Computational Fluid Dynamics.

Requirements

• Knowledge bases (cross sections, sticking coefficients):

The time required to generate knowledge bases for new materials must be weeks-to-months, not months-to-years.

• Manufacturing friendliness:

Autocad → Prediction/Recommendation → Autocad

• Acceptance:

Realistic expectations and critical assessment of ROI (one scrapped 300 mm wafer funds a modeling activity for a year).


THE CONTINUUM OF PLASMA TECHNOLOGIES

Werner von Siemens, 1872

Ozone Tube of W. Siemens

Annalen der Physik und Chemie (1857)

Ref: U. Kogelschatz,www.siemens.com, www.samsung.com

• The road to PDPs began in a lab in Germany in 1857


STATUS OF OUR DISCIPLINE• The diversity of technological plasmas is its strength.

• Interdisciplinary• Wide range of applications• Entry point from many educational backgrounds• Extraordinary economic and social impact

• The weakness of this diversity is there is no recognized “discipline” of plasma processing (as for fusion plasmas).

• No home in funding agencies• Lack of formal programs in universities resulting in lack

of hiring priorities.• Excessive reliance on supporting disciplines• Often indirect path from academic innovation to

commercialization

• Ref: Frank Chen


NURTURING OUR DISCIPLINEOur greatest challenge: Create a self-sustaining, self identified discipline of plasma processing. The result will

• Attract the best-and-the-brightest• Provide educational and professional opportunities for

young scientist and engineers (and replace rapidly graying university faculty)

• Insure critical funding to improve core competencies and motivate relevant work in supporting sciences

• Recognize and advertise social and economic benefits• Provide a lobbying base for proactiveness by academics

and industry• Establish paths for innovation to be commercialized• Create and benefit from unrealized synergies


OUR GREATEST CHALLENGE: NURTURING OUR DISCIPLINE

Recommend Executive Summary from:

"The Impact of Academic Research on Industrial Performance"(National Academies Press, Washington DC, 2003, www.nap.edu)

continuity in plasma processing: yesterday’s ... · (app) have had tremendous technological...

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