FLCC March 28, 2005 FLCC - Plasma 1 Fluid Modeling of Capacitive Plasma Tools FLCC Presentation...
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Transcript of FLCC March 28, 2005 FLCC - Plasma 1 Fluid Modeling of Capacitive Plasma Tools FLCC Presentation...
March 28, 2005 FLCC - Plasma
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FLCC
Fluid Modeling of Capacitive Plasma Tools
FLCC PresentationMarch 28, 2005Berkeley, CA
David B. Graves, Mark Nierode, and Yassine KabouziUC Berkeley
March 28, 2005 FLCC - Plasma
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Motivation• Capacitively-coupled plasma etch tools commonly
used, especially in dielectric etch• Popular strategy: dual frequency operation to separate
control of ion flux and plasma density (high frequency) from ion energy control (low frequency)
• Overall goal is to develop a 2-D, time-dependent fluid plasma model that can be used for tool design and process control studies
• Tool-scale model can be coupled to feature scale (e.g. Prof. Chang, UCLA)
• Fluid model can complement PIC/MC model (Prof. Lieberman, UCB)
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1. Fluid model of 1-D dual frequency (27 MHz, 2 MHz) Ar discharge.
2. Fluid model of 2-D single frequency (13.5 MHz) Ar discharge.
3. Fluid model of non-isothermal, reacting neutral flow in typical industrial capacitive etch tool with split inlet flows.
Today’s Talk
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Plasma Model Equations
( )ee ioniz ioniz e e N
nR k T n n
t
Γ
iiiiiii
ii enZpt
mn MEuuu
eabseeee EPekTnt
ΓEQ
2
3
iiie nZne 2
0
biasVtV )sin(
AJJJdt
dVc die
biasb
EΓ
ene
eee
enee m
enkTn
m
1
eene
eeeee kT
vm
kTnkT
2
5
2
5ΓQ
ii i ioniz
nn R
t
u
Equations solved via FEMLAB
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One Dimensional Dual Frequency 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
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Potential on Powered (Left) Electrode
Argon, p = 50 mtorr, 800 V rf @ 27 MHz, , 800 V rf @ 2 MHz applied at left electrode
0.5
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Dual Frequency Results: Plasma Density
Argon, p = 50 mtorr, 800 V rf @ 27 MHz, , 800 V rf @ 2 MHz applied at left electrode
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Right Sheath Structure
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Left Sheath Structure
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Electron Density in Sheaths: 27 MHz Variation
Electron loss at both sheaths
Electron loss at right sheath only
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Electric Field and Plasma Potential: 2 MHz
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Potentials on Powered Electrode and in Plasma
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Currents at Powered Electrode
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Electron Temperature
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Two-Dimensional, Axisymmetric (r,z) Single Frequency
Argon, p = 50 mtorr, 80 V rf @ 13.56 MHz, applied at top electrode
0.25 m radius
0.025 m height
Powered electrode
Grounded
Preliminary 2-D results obtained
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Period-Averaged Electron DensityArgon, p = 50 mtorr, 80 V rf @ 13.56 MHz, applied at top electrode
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Period-Averaged Electron Temperature
Argon, p = 50 mtorr, 80 V rf @ 13.56 MHz, applied at top electrode
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Period-Averaged Ion DensityArgon, p = 50 mtorr, 80 V rf @ 13.56 MHz, applied at top electrode
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Period-Averaged Plasma Potential
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Neutral Reacting Flow Model
nvv EpTCt
TC
v:vqv
nRt
v
npt
Mτvvv
iiii rt
imDv
pM
kT
Equations solved via FEMLAB
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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
400/20/9 sccm Ar/c-C4F8/O2 | 0-100 sccm O2
Pressure ~ 30 mtorr
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Mesh and Numerics
• 3363 elements, 115106 d.o.f.• All variables use quadratic Lagrangian elements
except pressure which is linear• Steady state solution obtained 1-2 hours using
iteration script (FEMALB feature; eqns solved iteratively and sequentially)
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Chemistry ModelREACTIONS
1 Ar + e --> Ar+ + 2e2 c-C4F8 + e --> 2 C2F4 + e3 C2F4 + e --> 2 CF2 + e4 CF2 + e --> CF + F + e5 O2 + e --> 2 O + e6 CF2 + O --> COF + F7 COF + O --> CO2 + F
Assum ed plasm a density , tem peratureNo surface react ions
1. Simplistic model will assume CF as the ‘depositing’ species and F as the ‘etching’ species
2. Increased O2 flow in the outer annulus leads to increased O2 and O in the outer region
3. Increased O increases rxns 6 & 7 producing F on the same order as rxn 4
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Assumed Plasma Density
Assume constant Te = 3
Assume radial plasma profile flat except when r > 0.2
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Neutral Temperature
• Neutral gas heating is proportional to the (assumed) plasma density
• ‘Jump’ temperature and ‘slip’ velocity boundary conditions
• Temperature profile not affected by outer tuning flow up to 100 sccm O2
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Pressure and Temperature Effects
• Radial pressure drop is significant ~30% leading to a similar neutral number density profile (n); recall n ~ p/T
• Axial pressure gradients are minimal
Total neutral density
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Neutral Species Radial ProfilesQtune = 0 sccm
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Neutral Species Radial Profiles
– Note: scale different from previous slide
Qtune = 100 sccm
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Effects of Altering O2 ‘Tuning’ Gas Flow
•Propose CF/F as model deposition/etch ratio index•Varying the outer O2 flow (Qtune) the ratio of CF to F can be modified radially although the overall ratio of CF to F changes too
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Concluding Remarks
• FEMLAB-based fluid modeling powerful tool to simulate complex, multi-dimensional, reacting plasma tools– Tool-scale design/analysis possible
– Fully transient, coupled neutral-plasma versions can simulate process control
• Two major limitations to tool-scale fluid models:– No feature profile evolution
– No plasma kinetic information (e.g. EEDF, IEDF, IADF)
• FLCC plasma project couples fluid modeling (DBG, UCB), feature evolution modeling (JC, UCLA) and PIC/MC modeling (MAL, UCB)