1. Modeling and experiments on surface charge accumulation during plasma processing
SFR Workshop
November 8, 1999
A.B. Wengrow, and N.W. Cheung
Berkeley, CA
Multiple-species model developed to investigate effect of
high density plasmas (HDP) on wafer charging
11/8/99

2. Plasma Assisted Materials Processing Lab
Large Area Plasma Source
Plasma Immersion Ion Implanter
General purpose HPD tools for plasma research (charging studies, etching, implantation, materials modification)
Large selection of species available (BF3, O2, H2, Ar, N2, F, He, CO2, H2O, plus others).
Substrate bias 0-80kV DC, and 0-20 kV pulsed-AC.
Transformer Coupled Plasma Source
11/8/99

3. Multiple-Species Effects on Charging
Plasma composition will effect charging flux
(e.g. molecular gas sources CFx+, carrier gas ionization, and plasma instability)
11/8/99

4. Single Ion Species Model
Ion Current
Sheath Diff. Eq.
Electron Current
Secondary Electrons
Displacement n i
ion density u b
ion Bohm
velocity s
sheath width M
ion mass V
sheath voltage v e
electron velocity p
plasma potential k
secondary electron constant o
applied voltage C
sheath capacitance
11/8/99

5. Multiple Ion Species Model and Results
Effective mass concept:
Effective ion Bohm velocity concept:
BF3 Plasma Results
11/8/99

6. Plasma Mass Attenuator Set-up
Processing Chamber
Wafer Bias
Plasma
Sheath
ECR Plasma
Source
Microwave &
Gas Input
Magnetic Coils
Biased Ion Shutter
Mass/Energy
Spectrometer
3/2 " diameter
3/4 " diameter
3/8 " diameter
11/8/99

7. Small Diameter Shutter (3/8”)
300W m-wave power
5 sccm of both Ar and H
Multi-cusp magnet mode (240Amps, plasma confined)
No wafer bias
300W m-wave power
10 sccm of Oxygen
Multi-cusp magnet mode (220Amps, plasma not confined)
No wafer bias
11/8/99

8. Progress vs. Milestones
Year 1
Develop an ion flux model for multiple-species plasma
Preliminary results demonstrating mass attenuation effect with different source apertures
Year 2
Work in progress to verify effective mass separation using mass attenuation concept
Verification of multiple-species charging model with various antenna ratios and thin dielectrics
11/8/99

9. Future Work for
Development and verification of a unified model to predict particle flux and charge flux related to HDP processing.
11/8/99