ION ENERGY AND ANGULAR DISTRIBUTIONS INTO SMALL FEATURES IN PLASMA ETCHING REACTORS:
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Transcript of ION ENERGY AND ANGULAR DISTRIBUTIONS INTO SMALL FEATURES IN PLASMA ETCHING REACTORS:
ION ENERGY AND ANGULAR DISTRIBUTIONS INTO SMALL FEATURES IN PLASMA ETCHING
REACTORS:THE WAFER- FOCUS RING GAP*
Natalia Yu. Babaeva and Mark J. Kushner
Iowa State UniversityDepartment of Electrical and Computer Engineering
Ames, IA 50011, USA [email protected] [email protected]
http://uigelz.ece.iastate.edu
AVS 54th International Symposium
October 2007
* Work supported by Semiconductor Research Corp., Applied Materials and NSF
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AGENDA
Wafer edge effects Description of the model Ion energy and angular distribution on different surfaces
in wafer-focus ring gap for focus ring: Capacitance Height Conductivity
Concluding remarks
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Orientation of electric field and ion trajectories, energy and angular distributions depend on details of the geometry and materials.
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Gap (< 1 mm) between wafer and focus ring in plasma tools for mechanical clearance.
Beveled wafers allow for “under wafer” plasma-surface processes.
Penetration of plasma into gap can deposit of contaminating films.
PENETRATION OF PLASMA INTO WAFER-FOCUS RING GAP
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The ion energy and angular distributions (IEADs) into the wafer-focus ring gap are important;
Angular distribution determines erosion (e.g., maximum sputtering at 60o.
Time between replacement of consumable parts depends on erosion.
Spacing, materials (e.g., dielectric constant, conductivity) determine electric field in gap and so IEADS.
In this presentation, results from a computational investigation of IEADs onto surfaces in wafer-focus ring gap will be discussed.
Model: nonPDPSIM using unstructured meshes. Goal: How does one control the IEADs?
INVESTIGATION OF IEADs INTO WAFER-FOCUS RING GAP
nonPDPSIM: BASIC EQUATIONS Poisson equation: Electric potential
Transport of charged species j
Surface charge balance
Full momentum for ion fluxes
Neutral transport: Navier-Stokes equations.
Improvements to include Monte Carlo simulation of Ion Energy and Angular distributions (IEADs).
)( j
jj Nq
StN j
materialj
j Sqt
iji
ijjj
jjj
jjj
j vvNMENq
PM
vt
1
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MESHING TO RESOLVE FOCUS RING GAP
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2-dimensional model using an unstructured mesh to resolve wafer-focus ring gaps of < 1 mm.
Numbering indicates materials and locations on which IEADs are obtained.
Ar, 10 MHz, 100 mTorr, 300 V, 300 sccm
POTENTIAL, ELECTRIC FIELD, IONS
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E/N
Potential
[Ar+]
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Off-axis maximum in [Ar+] is due to electric field enhancement near focus ring and is uncorrelated to gap.
Ar, 10 MHz, 100 mTorr, 300 V
Gap: 1 mm
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POTENTIAL AND CHARGES (RF CYCLE) 1.0 mm Gap
Animation Slide
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-1.1 x 1011 cm-3
Highly conductive wafer with small capacitance charges and discharges rapidly.
Focus ring acquires larger negative surface charges. Large potential drop in focus ring.
MIN MAX Log scale
Surface Charges Cycle averaged potential
Powered Electrode Powered Electrode
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Directions of electric fields near surfaces evolve slowly during rf
cycle due to slowly changing surface charge. Direction of ion fluxes changes during rf cycle from nearly vertical to
perpendicular to surface with transients in electric field.
ION FLUX VECTORS (RF CYCLE)
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1.0 mm Gap
Animation Slide
Powered Electrode
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ION ENERGY AND ANGULAR DISTRIBUTIONS
Broad IEAD on top bevel due to ions arriving during positive and negative parts of rf cycle.
Grazing angles for ions striking vertical surfaces.
MIN MAX Log scale
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Cathodic cycle: High energy ions at
grazing incident on side wall.
Near vertical to bevel.
Anodic rf cycle: Low energy ions
near vertical on side wall.
High energy angles a large angle to bevel.
ION FLUXES AT DIFFERENT PHASE OF RF CYCLE
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1.0 mm Gap
9
9
MIN MAX Log scale
Cathodic rf cycle
5
5
Anodic rf cycle
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Log scale
Wafer charges quickly (almost anti-phase with focus ring).
More surface charges collected on focus ring with larger capacitance.
Ions penetrate into gap throughout rf cycle with larger capacitance.
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1.0 mm Gap
Ar+
0.5 mm GapAnimation Slide
-7.8 x 1010 cm-3
Ar+
/o= 4 /o= 20
CAPACITANCE OF FOCUS RING: ION DENSITY AND CHARGES
Powered electrode Powered electrode
Powered electrode Powered electrode
-1.2 x 1011 cm-3
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MIN MAX Log scale
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/o= 4
/o= 20
CAPACITANCE OF FOCUS RING: IEAD
Penetration of potential into focus ring with low capacitance produces lateral E-field.
IEAD on substrate is asymmetric.
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Log scale
Ions do not fully penetrate into the gap with high focus ring.
Ion focusing on edges.
Substantial penetration of ion flux under bevel with low focus ring.
FOCUS RING HEIGHT: ION DENSITY AND FLUX
1.0 mm Gap
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Animation Slide
Powered Electrode Powered Electrode
Powered Electrode Powered Electrode
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1.0 mm Gap 0.25 mm Gap
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“Open” edge produces skewed IEADsMIN MAX
Log scale
FOCUS RING HEIGHT: IEAD
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Configuration of wafer-focus ring gap can be used to control IEADS.
Example: Extension of biased substrate under dielectric focus ring of differing conductivity.
DESIGN TO CONTROL IEADs
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Same conductivity wafer and FR.
More uniform and symmetric sheath and plasma parameters.
0.1 Ohm-1 cm-1
MIN MAX Log scale
EXTENDED ELECTRODE : CHARGE, E-FIELD AND ION FLUX
Animation Slide
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Powered Electrode
Powered ElectrodePowered Electrode
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On all surfaces more narrow and symmetric IEAD with uniform electrical boundary condition.
Wafer: 0.1 Ohm-1 cm-1
Ring: 10-8 Ohm-1 cm-1
Wafer and Ring: 0.1 Ohm-1 cm-1
EXTENDED ELECTRODE: IEAD
MIN MAX Log scale
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MIN MAX Log scale
Always broad and asymmetric IEAD on tilted surface.
FR Conductivity
BROADENING OF IEAD ON TOP BEVEL: EFFECT OF FR
/o= 4 /o= 20 High FR Low FR
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CONCLUDING REMARKS
Ion energy and angular distributions were investigated on surfaces inside wafer-focus ring gap.
Different regions of the IEADs are generated during different parts of the rf cycle. Even vertical surfaces receive some normal angle ion flux.
Narrow IEAD are obtained with High focus ring High focus ring capacitance High focus ring conductivity.
Uniform electrical boundary conditions leads to more symmetric sheath over the gap and narrows IEADs.
On tilted surfaces broad and asymmetric IEADs are obtained for most conditions.
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