<i>In situ</i> diode laser absorption measurements of plasma species in a gaseous electronics conference reference cell reactor

Abstract

A major objective of the microelectronics industry is to perfect methods for controlling dimensional accuracy during plasma etching of submicron 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, infrared lead-salt diode lasers are used to probe fluorocarbon-based plasmas used for etching of silicon and silicon dioxide in a gaseous electronics conference reference cell reactor. The diode laser sensor is used for in situ measurements of neutral CF2 reactive intermediates and CF2O etch product. Possible correlations between etch process outcomes and parameters measured by diode laser absorption are identified. The diode laser measurement of CF2 concentration is found to be possibly useful as an indicator of etch rates or selectivity. In addition, diode laser monitoring of CF2O during etching of SiO2 is potentially useful as an end point monitor. 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.