Abstract

A major objective of the microelectronics industry is to perfect methods for controlling dimensional accuracy during plasma etching of submicrometer features in wafer substrates. Optical sensors as monitors of gas phase etch chemistry are attractive because they offer the potential of nonintrusive in situ measurements for use as real time inputs to process control. In this study, lead salt infrared diode lasers were used to measure CF₄ feed gas dissociation, neutral CF₂ reactive intermediates, and CF₂O etch products in fluorocarbon-based plasmas used for etching of silicon and silicon dioxide. These measurements were conducted in situ in a GEC reference cell reactor by using high frequency diode laser wavelength modulation techniques and a single-pass optical configuration. Correlations between measured species concentrations and process characteristics, such as etch rates, end point, and selectivity, were identified. For example, diode laser measurement of CF₂ concentration was found to be useful as an indicator of etch selectivity. End point detection by diode laser monitoring of CF₂O during etching of SiO₂ was also demonstrated. Further research and development based on these results are expected to lead to new process control strategies for improved reliability and product yield in plasma etching.

© 1992 Optical Society of America