Using radio-frequency electrical measurements as a plasma diagnostic

Abstract

Summary form only given. Radio frequency (RF) current and voltage measurements are an important and convenient tool for monitoring RF discharges. These measurements are compatible with commercial reactors and with the manufacturing environment. Recently, methods have been proposed for using RF electrical measurements to monitor process-relevant plasma properties. These methods rely on models that relate measured electrical parameters to physical properties such as the densities, fluxes, and energies of electrons and ions. Unfortunately, the models that are used often rely on untested assumptions. In particular, the sheath regions of the plasma are difficult to model without the aid of simplifying assumptions. To test these assumptions and to provide a firmer foundation for RF-based diagnostics, electrical studies were performed in high-density discharges in an inductively coupled GEC Reference Cell, at pressures of 0.67-4.0 Pa, inductive source powers up to 370 W, RF bias powers up to 150 W, and RF bias frequencies of 0.1-13.56 MHz. External measurements of current and voltage waveforms were combined with capacitive probe measurements of the RF plasma potential and independent measurements of ion current and ion energy. Together, these measurements provide enough information to test electrical diagnostic techniques and the models that these techniques are based on. Here, a comprehensive test and comparison of methods for determining the ion flux in argon and CF/sub 4/ discharges will be presented. Methods which use high-frequency or low-frequency approximations to ion motion were found to be less accurate than methods based on a new, complete model of the time-dependent ion dynamics in the plasma sheath. Methods for obtaining ion energies from RF measurements will also be presented.