ROLE OF CONTAMINANTS IN ELECTRON-CYCLOTRON-RESONANCE PLASMAS

In this article, we examine the influence of contaminants on an electron cyclotron resonance discharge. For our discharge, the measured level of contaminant was highest just after startup, decreasing to a stable level after approximately 20 min.This is consistent with a limited source of gas trapped in the chamber walls. It is shown that the presence of these contaminants cause both the plasma and floating potentials vary by several volts. These potential variations are largest when the contamination is largest. Such variations were found in N2, CF4, and CHF3 discharges. The observed variation in the plasma potential should be of great concern in plasma-aided manufacturing environments. The larger variations represent approximately 10% of the potential that one would typically apply between a device and the plasma. Such large changes in the potential might result in substantial changes in both etch rate and anisotropy. This can have particularly adverse effects on those devices having fine structures. Thus, one should monitor these contaminants and not process devices while the contaminant level varies.