| AVS 61st International Symposium & Exhibition | |
| Plasma Science and Technology | Friday Sessions |
| Session PS1-FrM |
| Session: | Plasma Sources |
| Presenter: | Julian Schulze, West Virginia University |
| Authors: | J. Schulze, West Virginia University E. Schuengel, West Virginia University A. Derzsi, Hungarian Academy of Science, Hungary I. Korolov, Hungarian Academy of Science, Hungary Z. Donko, Hungarian Academy of Science, Hungary |
| Correspondent: | Click to Email |
An overview of a novel method to control process relevant plasma parameters and particle flux-energy distribution functions in multi-frequency capacitive radio frequency (CCRF) plasmas is presented. Based on experimental, simulation, and modeling studies in different gases (Ar, H2, SiH4, CF4) we demonstrate that the ion flux-energy distribution function at the substrate can be controlled separately from the ion flux by adjusting the harmonics’ phases and amplitudes in a CCRF discharge driven by multiple consecutive harmonics based on the Electrical Asymmetry Effect. The quality of this separate control is significantly better compared to classical dual-frequency plasmas driven by two largely different frequencies. Adding more harmonics enlarges the control range. Tuning the ion energy by phase control in H2-SiH4 plasmas allows to control the morphology of deposited Si:H thin films. In large area CCRF plasmas radial inhomogeneities of the ion flux due to standing wave effects can be prevented by customizing the driving voltage waveform.
These optimizations of process control are based on a detailed scientific understanding of the non-local particle heating mechanisms in technological plasmas. Such mechanisms are complex and strongly depend on global control parameters such as the gas mixture, pressure, and voltage amplitudes. Differences of the electron heating mechanisms in electropositive and electronegative plasmas and their effects on process control will be discussed. In electronegative and/or dusty plasmas, e.g. operated in CF4 or SiH4, a novel heating mode, the Ω-mode, and novel coupling mechanisms between the driving frequencies are present and strongly affect process relevant plasma parameters. Moreover, resonance phenomena such as the Plasma Series Resonance play a major role in multi-frequency CCRF plasmas driven by customized voltage waveforms at low pressures of a few Pa.
Existing processing reactors can be easily upgraded to use the method of phase control in multi-frequency plasmas by modifying the external RF supply only. No modifications of the reactor itself is required, but a detailed understanding of the plasma physics is needed to optimize plasma-surface interactions.