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09/13/2006 FLCC - Plasma

1

FLCC

Plasma Technology

Professors Jane P. Chang (UCLA), Michael A. Lieberman,David B. Graves (UCB)

andAllan J. Lichtenberg, John P. Verboncoeur, Alan Wu, Emi

Kawamura, Chengche Hsu, Joe Vegh, Insook Lee (UCB),and John Hoang (UCLA)

FLCC Workshop & ReviewSeptember 13, 2006


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FLCC

Coordinated research involving three PI’s

• Michael A. Lieberman (UCB)- Theory and kinetic (PIC-MCC) simulations

• David Graves (UCB)- Chemistry, plasma and neutral transport, and transient effects - Fluid simulations (FEMLAB) and molecular dynamics simulations of plasma-surface interactions

• Jane P. Chang (UCLA)- Profile evolution in Si, SiO2, porous dielectrics, high-k dielectrics- Feature scale simulations (DSMC) and experiments (SEM)

Dual/Triple Frequency Capacitive and Inductively Coupled Discharges for Etch


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FLCC

Relationships Among the Plasma Projects

Lieberman(Theory, PIC-MCC)

Graves(Fluid and MD)

Reactor-scale modelsSurface-scale simulations

Chang(DSMC)

Feature-scale experiments

Electron energy deposition

Ion energy distribution

Ion and neutral fluxes

Plasma-surface interactions: molecular dynamics

Feature level profile evolution

and control


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FLCC

Plasma Sources for Feature Level Compensation and Control


David B. Graves, Chengche Hsu, Insook Lee, and Joe Vegh

UC Berkeley


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FLCC

Summary of Research (Graves)

• Develop 2-D reactor-scale fluid models of multiple frequency capacitive and inductively coupled discharge tools for etch and deposition

• Focus on development of comprehensive, computationally efficient models that can be coupled to profile simulations (Chang),using kinetic simulation information (Lieberman) and that predict tool/feature uniformity


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FLCC

One Dimensional Dual Frequency Fluid Model Results*

Argon, p = 50 mtorr, 800 V rf @ 27 MHz, , 800 V rf @ 2 MHz applied at left electrode

2 MHz

27 MHz

0.02 m

*Mark Nierode; (FLCC student; graduated 5-05)


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FLCC

Currents at Powered Electrode


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FLCC

Neutral Flow Configuration

– Commercial tools typically feature dual flow configurations to allow for greater process control(e.g. balance fluorocarbon deposition and etching)

– Investigate the transport of the tuning gas and its effect on reactor chemistry

Pressure ~ 30 mtorr

400/20/9 sccm Ar/c-C4F8/O2 | 0-100 sccm O2


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FLCC

2-D Capacitive Fluid Models

- Electrostatics model (Poisson equation only)- Ignores EM effects- Resolves sheath motion; computationally expensive- Investigated role of radial plasma grounding – important

effects on plasma uniformity

RF

RF

Case 2Case 1


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FLCC

2-D Inductive Plasma Fluid Models*

*Chengche (Jerry) Hsu; (FLCC student; graduated 5-06)

Nonlinear solveru,v,p,T

Nonlinear solverwj

Time dependent solverni,j, Te

Linear solverEθ

Converged?No Yes


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FLCC

2-D Inductive Plasma Fluid Models*

150W ICP power, 10mT pressure, Ar 15 sccm, O2 19.5sccm, and Cl2 19.5sccm.

*Hsu, Coburn, and Graves, J. Physics D, 2006


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FLCC

2-D Multi-frequency Plasma Fluid Models: EM Effects*

• Use electromagnetic model in FEMLAB, couple to plasma fluid models for parallel plate electrode geometries– Solve Maxwell equations in 2-D axial symmetry – Assuming a transverse magnetic (TM) mode having only the magnetic

field component Hφ ~ e jwt, the Maxwell equations are

en

pep

pen

pep

zr

zp

rp

j

jj

Hjr

Ez

E

Ejr

rHr

Ejz

H

νωωε

σ

σωενωω

ωκ

ωµ

κωε

κωε

φ

φ

φ

+=

−=−

−=

−=∂∂

−∂∂

=∂

∂

−=∂∂

20

0

2

0

0

0

,1)(

1 where

,

,)(1

,

*Insook Lee


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FLCC


*Insook Lee

TM wave launched

EM Model(E)

Plasma Model(ne, Te)

Enew(r,z) = Eold(r,z) + ∆E

ne,new(r,z) = ne,old(r,z) + ∆ne,Te,new(r,z) = Te,old(r,z) + ∆Te


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FLCC


60 MHz, 200 mtorr, 20W, Ar*Insook Lee


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FLCC

Future Milestones

• Extend tool-scale reactor simulation to industrially-relevant tool chemistries and geometries, focusing on plasma tool uniformity and electromagnetic power coupling


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FLCC

Plasma Sources for Feature Level Compensation and Control


Michael A. Lieberman, Allan J. Lichtenberg,John P. Verboncoeur, Alan Wu, Emi Kawamura

UC Berkeley


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FLCC

Summary of Research (Lieberman)

• Develop kinetic simulation models of multiple frequency capacitive discharge tools for dielectric etch and deposition

• Focus on electron energy depositions and ion energy distributions


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FLCC

Theory of Dual Frequency Stochastic Heating • Theory completed and compared to PIC simulations1.

• Future goal: Incorporate into 2D reactor-scale (Graves) and into 3D feature-scale (Chang) practical simulators.

1Kawamura et al., Physics of Plasmas 13, 053506 (2006).

nsm = plasma density at ionsheath boundary.

ubh = amplitude of high f bulkoscillation velocity.

Hl = a normalized low fbulk oscillation amplitude.

For Hl >> 1, Hl ∝ (Vsh/Te)1/2.

44444 344444 2144 344 21tEnhancemenFrequencyLow)(limitFrequencyHigh

)]2.2/()[4/1(5.0 2

=

++=

lHF

lllbhsmeestoc HHHunvmS π Kawamura


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FLCC

Multi-Frequency Theory of Ion Energy Distributions

• Theory developed and compared toparticle-in-cell simulations

• Future goal: Incorporate into 2D reactor-scale (Graves) and into 3D feature-scale (Chang) practical simulators.

• Improve filter function• Address issues of ion-neutral collisions in the sheath and fast

neutral generation

Vs(f)

Sheath Voltage Vs(t) Ion response Vi(t)

Vi(f)

Fourier Transform Inverse Fourier Transform

Apply filter α(f)

Σ|dVi/dt|-1 IED (shown on next slide)

Wu


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FLCC

IED – 400 V @ 64 MHz / 800 V @ 2 MHz

10000 Energy

(eV)

IED – 400 V @ 64 MHz / 800 V @ 8 MHz, 2 MHz

10000 Energy (eV)


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FLCC

Future Milestones

• Perform particle-in-cell simulations with dual and/or triple frequency source power to determine ion energy distributions at substrate


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FLCC

Feature Profile Evolution during Shallow Trench Isolation (STI) Etch in Chlorine-based Plasmas


Jane P. Chang and John HoangUCLA

•Special Acknowledgements: Helena Stadniychuk at Cypress


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FLCC

Summary of Research (Chang)

• Feature Scale Modeling– Develop a pseudo 3-dimensional simulator based on direct simulation

Monte Carlo (DSMC) method– Enable process development by shortening experimental time and cost – Feature scale model can be coupled to tool scale (Prof. Graves, UCB)– Feature scale model can be coupled with PIC/MC model (Prof.

Lieberman, UCB)

• Shallow Trench Isolation (STI)– Analyze the outcome of design of experiments in STI etch to correlate

experimentally measured parameters with simulation input variables – Predict profile evolution during STI etch and confirm simulation with

experimental SEM images


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FLCC

STI Process • ITRS dictates stringent conditions for optimal trench isolation as minimum feature size decreases

• Positive trench tapering angles desired to avoid sharp recesses leading to “poly wrap-around”

• Smooth sidewalls needed for less physical and electrical damage

• Round bottom corners to minimize stress and avoid voids in gapfill

SWA: sidewall angle; † Adapted from ITRS 2003 Thermal Films Supplemental

Desired Properties:

D4 > D2/2Recess < 0.1×D2Curvature: rSi top = rSi bottom = 0.1×D2

Definitions:

θnitride = 90º – arctan[(D1-D2)/2/tx1]

θtop Si = 90º – arctan[(D2-D3)/2/tx2]

θbot Si = 90º – arctan[(D3-D4)/2/tx3]

Isolation stack Pattern nitride and strip PR

Trench etch

PRnitrideoxide

Silicon

Sidewall oxidation and deposit trench

oxide

Strip nitride and remove pad oxide

CMP planarizationSEM Measured Parameters

D1

D2

D3

Total Si Depth

tx1(nitride)

tx2(top Si)

tx3(bot Si)

Nitride SWA

top Si SWA

bot Si SWA

D4


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FLCC

Correlation between Process and Simulation Parameters

Cl2N2O2

Ws

Ws

Wb

Coil Power

Substrate Bias

Iouter Iinner

Pressure

• Other simulation parameters defined by elemental assignment of the initial profile

• Additional simulation parameters defined by different plasma compositions

Chamber Pressure (mTorr)

Source Power (Ws)

Wafer bias (Wb)

DC ratio = Iouter/Iinner

Cl2 flowrate (sccm)

N2 flowrate (sccm)

O2 flowrate (sccm)

Ion Angle Distribution (IAD)

Ion Energy Distribution (IED)

Mean Ion Energy

Cl Neutral to Ion Ratio

N to Ion Ratio (in development)

O to Ion Ratio (in development)

Process Parameters Simulation Parameters

E-Field lines (future plans)


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FLCC

Surface Representation and NormalOriginal

representationCell-centered representation

Surface

Modified Cell-centered rep. (to be implemented)

Actual representation

Cells with high Flux

0 40 80 120 160 200 240 280 3200.0

10.020.030.040.050.060.070.080.090.0

100.0

Leas

t Squ

ares

Nor

mal

Position Along Interface

Four point check Least Squares Modified Least Squares

0 40 80 120 160 200 240 280 3200.0

10.020.030.040.050.060.070.080.090.0

100.0

Leas

t Squ

ares

Nor

mal

Position Along Interface

“bumps”in sloped side walls removed

0-82

218-348

82-218

218-348

Mask

Silicon


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FLCC

Integrating Results from Plasma, Reactor, and MD Simulations

Source Plane in Feature EvolutionSpecies Conc. from Reactor/Plasma models

Mask (SiNx)

Cl+:Cl:Cl2:O:O2:SiCl2

Silicon

Vacuum

n +

75º Grazing85º Grazing

Ions at Source Plane in Feature EvolutionIEDF and IADF from PIC Model

φ

Scattering Function in Feature EvolutionMolecular Scale Scattering by MD

C.F. Abrams and D. B. Graves, JVST A 16(5), 3006 (1998) A. Wu and M. Lieberman, FLCCC. Hsu and D. Graves. FLCC


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FLCC*( )( )* ion thA E EY c φ −=

Reaction Kinetics for Etching/Deposition

• Kinetics affected by ion energy and angle:

Selectivity Angular Dependency

⎟⎠⎞

⎜⎝⎛

+ArCl

Flux Ratio

Yield

Poly

Oxide

0

1

2

3

4

0 50 100 150 2000.0

0.1

0.2

0.3

0.4

Ion incident angle φ (degree from normal)

Poly

Oxide

0

1

2

3

4

0 30 60 900

0.1

0.2

0

1

2

3

4

0 100 200 300 400

S iC l +

⎛⎝⎜

⎞⎠⎟

Etching Yield

75eV Cl+/Cl

55eV Cl+/Cl

35eV Cl+/Cl

ClCl +

⎛⎝⎜

⎞⎠⎟Flux Ratio

ClCl +

⎛⎝⎜

⎞⎠⎟Flux Ratio

80 eV(Lam TCP)

0

0.4

0.8

1.2

0 10 20 30

Cl/Cl+ = 120 with SiCl2

Cl+ alone with SiCl2

S iC l +

⎛⎝⎜

⎞⎠⎟

S iC lC l

2+

⎛⎝⎜

⎞⎠⎟Flux Ratio

SiCl SiCl Cle4 2 2

−

⎯ →⎯ +

Etching Yield

0

0.4

0.8

1.2

0 10 20 30



S iC l +

⎛⎝⎜

⎞⎠⎟

S iC lC l

2+

⎛⎝⎜

⎞⎠⎟Flux Ratio

SiCl SiCl Cle4 2 2

−

⎯ →⎯ +

Etching Yield

Effect of Eion and n/+ ratio Effect of deposition on etching

Selectivity Angular Dependency

⎟⎠⎞

⎜⎝⎛

+ArCl

Flux Ratio

Yield

Poly

Oxide

0

1

2

3

4

0 50 100 150 2000.0

0.1

0.2

0.3

0.4

Ion incident angle φ (degree from normal)

Poly

Oxide

0

1

2

3

4

0 30 60 900

0.1

0.2

0

1

2

3

4

0 100 200 300 400

S iC l +

⎛⎝⎜

⎞⎠⎟

Etching Yield

75eV Cl+/Cl

55eV Cl+/Cl

35eV Cl+/Cl

ClCl +

⎛⎝⎜

⎞⎠⎟Flux Ratio

ClCl +

⎛⎝⎜

⎞⎠⎟Flux Ratio

80 eV(Lam TCP)

0

0.4

0.8

1.2

0 10 20 30



S iC l +

⎛⎝⎜

⎞⎠⎟

S iC lC l

2+

⎛⎝⎜

⎞⎠⎟Flux Ratio

SiCl SiCl Cle4 2 2

−

⎯ →⎯ +

Etching Yield

0

0.4

0.8

1.2

0 10 20 30



S iC l +

⎛⎝⎜

⎞⎠⎟

S iC lC l

2+

⎛⎝⎜

⎞⎠⎟Flux Ratio

SiCl SiCl Cle4 2 2

−

⎯ →⎯ +

Etching Yield

Effect of Eion and n/+ ratio Effect of deposition on etching


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FLCC

Fractional Factorial DOE for Si Etch

• 7 factors, 2 levels, and 16 experiments• Pressure (plasma density) and DC ratio had

statistically significant effects• Need to quantify the effect of oxygen addition

DOE to assess the effect of oxygen

ID1 - - - - - - -2 - + - + - + -3 - + - - + - +4 + - + - + - +5 + + - - + + -6 + + - + - - +7 - - + + - - +8 + - - + + - -9 + - + + - + -10 + - - - - + +11 - - + - + + -12 - + + + + - -13 - - - + + + +14 - + + - - + +15 + + + - - - -16 + + + + + + +

Pres

sure

(mT)

W s(W

) W b

(W)

DC ratio

Cl 2

(sccm

) N 2

(sccm

) O 2

(sccm

)

0 (1 )( ) ( )

Cl Cl Osg sCl Clζ ζ− −+∗⎯⎯⎯⎯⎯→

( )( ) ( )

cg sCl Clφ++∗⎯⎯⎯→

( )( ) ( ) 4( )4 4c Cls s gSi Cl SiClφ β +

+ ⎯⎯⎯⎯→ + ∗

Chlorination:Sorption of Chlorine ion:Ion-enhanced etching:SiCl2 Deposition:Oxygenation:Sputtering:Sorption of sputtered Si:Recombination of chlorine:

0

2

2( ) ( ) ( )3 2SiCls

g s sSiCl Si Cl⎯⎯⎯→+ +∗0 (1 )

( ) ( )O OCls

g sO Oζ ζ− −+ ⎯⎯⎯⎯⎯⎯⎯→∗

( ) ( )SPSiY

s gSi Si⎯⎯⎯→ +∗0

( ) ( )Sis

g sSi Si⎯⎯⎯→+∗

2( ) ( ) ( )Clr

g s gCl Cl Cl⎯⎯⎯→+ +∗

Mechanisms considered in simulation

Cho, H.S. et al. Mat. Sci. in Semi. Process. 8 (2005) 239Ulal, S.J et al. J. Vac. Sci. Technol. A 20(2) 2002


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FLCC

Simulations vs. Experiments

• Simulated more microtrenching and lesstapering in a lower density plasma

• Identified the effect of neutral-to-ion ratio and IAD

Cl2/N2/O2 Plasma Cl2/N2 Plasma

• Simulated no microtrenching and muchtapered sidewalls due to oxygen addition

• Assumption for deposition: the etching kinetics for SiOxCly similar to SiCl2

Low density plasma

Eff

ect o

f Pla

sma

Effect of Chemistry

High density plasma

265

236125

214

20071.1º

86.9º154

137

236

145

256

157

84.2º

176

183

86.1º 218

264

247136

293

130

82.5º

86.9º

74.1º

189

161

274

139

220

174

195

172

86.2º

86.6º

67.6º

251


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FLCC

High density plasma, with O2 in Cl2Low DC ratio

High density plasma, with O2 in Cl2, low DC ratioLow substrate bias

• More hard mask erosion, resulting in slight bowing • Higher etch rate, more hard mask erosion, resulting in slight bowing

Simulations vs. Experiments

264

247136

293

130

82.5º

86.9º

74.1º

189

161

264

247136

293

130

82.5º

86.9º

74.1º

189

161

High DC ratio

High substrate bias

275

208137

270

164

85.6º

70.5º

226

164

72.9º

363

195

181

320

137

87.7º

69.8º

250

89

71.4º

30033.7º


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FLCC

Year 3 MilestonesYear 3: January 27, 2006 ~ January 26, 2007

• Quantified the effect of O2 addition to the etch profile evolution during STI etch

• Predicted feature profile evolution during STI etch and confirm simulation with experimental measurements

• Validate the simulation results beyond specially planned DOE results

• Correlate plasma operating parameters to simulation input profiles to allow a more direct comparison of the simulation results to experimental outcomes

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