EDGE EFFECTS IN REACTIVE ION ETCHING: THE WAFER- FOCUS RING GAP* Natalia Yu. Babaeva and Mark J. Kushner Iowa State University Department of Electrical and Computer Engineering Ames, IA 50011, USA [email protected][email protected]http://uigelz.ece.iastate.edu AVS 53 rd International Symposium November 2006 * Work supported by Semiconductor Research Corp. and NSF AVS2006_Natalie_01
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EDGE EFFECTS IN REACTIVE ION ETCHING:THE WAFER- FOCUS RING GAP*
Natalia Yu. Babaeva and Mark J. Kushner
Iowa State UniversityDepartment of Electrical and Computer Engineering
November 2006* Work supported by Semiconductor Research Corp. and NSF
AVS2006_Natalie_01
Iowa State UniversityOptical and Discharge Physics
AGENDA
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• Wafer edge effects
• Description of the model
• Penetration of plasma into wafer-focus ring gaps in Ar/CF4 CCPs
• Gap width• Focus ring conductivity• Focus ring height
• Concluding remarks
Iowa State UniversityOptical and Discharge Physics
WAFER EDGE EFFECTS
• Gap (< 1 mm) between wafer and focus ring in plasma tools is for mechanical clearance.
• The wafer is often beveled at edge allowing for “under wafer” plasma-surface processes.
AVS2006_Natalie_03
• Penetration of plasma into gap can lead to deposition of contaminating films and particles.
PENETRATION OF PLASMA INTO WAFER-FOCUS RING GAP
Iowa State UniversityOptical and Discharge Physics
AVS2006_Natalie_04
• Penetration of plasma into wafer-focus ring gap was computationally investigated for a capacitively coupled discharge for polymerizing (Ar/CF4) conditions.
• 2-dimensional model using an unstructured mesh use used to resolve multiple scale lengths.
• Improvements to algorithms to revolve on momentum into gaps were made.
nonPDPSIM CHARGED PARTICLE TRANSPORT• Poisson equation: electric potential
• Transport of charged species j
• Surface charge balance
• Full momentum for ion fluxes
• Transport of secondary electrons from biased substrate is addressed with a Monte Carlo simulation.
• Neutral transport addressed with Navier-Stokes equations.
( ) )( ρε +−=Φ∇∇ ∑j
jj Nq
StN j =Γ∇+∂
∂ r
( ) ( )( )materialj
j Sqt ⎥
⎦
⎤⎢⎣
⎡Φ∇−∇−+Γ∇−=
∂∂ ∑ σρ r
( ) ( )iji
ijjj
jjj
jjj
j vvNMENq
PM
vt
rrr
rvr
−−+∇−=Γ∇+∂
Γ∂∑ ν1
AVS2006_Natalie_05
Iowa State UniversityOptical and Discharge Physics
Iowa State UniversityOptical and Discharge Physics
SURFACE-KINETICS-MODULE (SKM)
• SKM uses fluxes to surface to produce coverage of surface species, sticking coefficients and returning fluxes to the plasma.=
• For demonstration purposes, a simple polymer depositing reaction mechanism.
• Neutral deposition CFn on surfaces W producing multiple layers of polymer Polyn
• Ion sputtering of polymer to generate CFn
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nmm
n
mmn
n
CFPolyPolyM
CFWPolyM
PolyPolyCFWPolyWCF
+→+
+→+
→++→+
−+
+
+
1
1
1
1
MESHING TO RESOLVE FOCUS RING GAP
Iowa State UniversityOptical and Discharge Physics
AVS2006_Natalie_07
• Unstructured meshes resolve wafer-focus ring gaps of < 1 mm.
POTENTIAL, E-FIELD,
ELECTRONS
Iowa State UniversityOptical and Discharge Physics
• High electric field heats electrons in the sheath regions.
• Off-axis maximum in [e] consequence of focus ring-uncorrelated to gap.