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

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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.

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