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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
09/13/2006 FLCC - Plasma
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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
09/13/2006 FLCC - Plasma
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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
09/13/2006 FLCC - Plasma
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FLCC
Plasma Sources for Feature Level Compensation and Control
FLCC Workshop & ReviewSeptember 13, 2006
David B. Graves, Chengche Hsu, Insook Lee, and Joe Vegh
UC Berkeley
09/13/2006 FLCC - Plasma
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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
09/13/2006 FLCC - Plasma
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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)
09/13/2006 FLCC - Plasma
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FLCC
Currents at Powered Electrode
09/13/2006 FLCC - Plasma
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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
09/13/2006 FLCC - Plasma
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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
09/13/2006 FLCC - Plasma
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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
09/13/2006 FLCC - Plasma
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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
09/13/2006 FLCC - Plasma
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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
09/13/2006 FLCC - Plasma
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FLCC
2-D Multi-frequency Plasma Fluid Models: EM Effects*
*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
09/13/2006 FLCC - Plasma
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FLCC
2-D Multi-frequency Plasma Fluid Models: EM Effects*
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
09/13/2006 FLCC - Plasma
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FLCC
Plasma Sources for Feature Level Compensation and Control
FLCC Workshop & ReviewSeptember 13, 2006
Michael A. Lieberman, Allan J. Lichtenberg,John P. Verboncoeur, Alan Wu, Emi Kawamura
UC Berkeley
09/13/2006 FLCC - Plasma
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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
09/13/2006 FLCC - Plasma
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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
09/13/2006 FLCC - Plasma
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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
09/13/2006 FLCC - Plasma
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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)
09/13/2006 FLCC - Plasma
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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
09/13/2006 FLCC - Plasma
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FLCC
Feature Profile Evolution during Shallow Trench Isolation (STI) Etch in Chlorine-based Plasmas
FLCC Workshop & ReviewSeptember 13, 2006
Jane P. Chang and John HoangUCLA
•Special Acknowledgements: Helena Stadniychuk at Cypress
09/13/2006 FLCC - Plasma
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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
09/13/2006 FLCC - Plasma
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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
09/13/2006 FLCC - Plasma
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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)
09/13/2006 FLCC - Plasma
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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
09/13/2006 FLCC - Plasma
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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
09/13/2006 FLCC - Plasma
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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
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
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
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
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
Effect of Eion and n/+ ratio Effect of deposition on etching
09/13/2006 FLCC - Plasma
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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
09/13/2006 FLCC - Plasma
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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
09/13/2006 FLCC - Plasma
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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
09/13/2006 FLCC - Plasma
32
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