A Study of the Optical Emission from an rf Plasma during Semiconductor Etching

Abstract

Spectroscopic analysis of optical emission during rf plasma etching of semiconductor materials has been used to gain a better understanding of the plasma chemistry involved in these systems. The emission was studied principally in CF₄-O₂ gas mixtures, but other gases were observed as well. It is known that the addition of a relatively small percentage of O₂ to CF₄ yields a much faster etching rate for silicon and silicon nitride. With the addition of 0₂ to CF₄ discharges we have studied emission from atomic O and molecular CO with a large increase in the emission of atomic F. When the plasma is actively etching silicon or silicon nitride, the emission intensities of both F and O atoms are significantly lower. The etching process can be monitored by observing the intensities of these lines. Analysis of the emission features has also been used to determine abnormal conditions which can adversely affect the etching process.