Use of Rotating Compensator Spectroscopic Ellipsometry for Monitoring the Photoresist Etching on Si Wafer

Abstract

Etching is one of the important process of semiconductor production. In this study, we monitored surface etching process, which is used for dielectric barrier discharge (DBD) at atmospheric pressure and room temperature, of photoresist (PR) on Si wafer by using rotating compensator spectroscopic ellipsometry (RCSE). Ellipsometry has mono-layer sensitivity and we can use it in a severe atmosphere such as a reactive gas, plasma and high temperature etc. Also, it is possible to perform non-destructive, real-time, and in-situ measurement. DBD reactor used 20 kV pulse power. We used alumina as dielectric material. The atmosphere of DBD plasma was operated without dark period (nondischarge period) in optimal frequency. We 248 nm PR as sample. The PR is coated by spin coater on Si wafer with 248 nm anti-reflection coating (ARC), and wafer is baked after that. Samples are not exposed and are not developed, but are etched after bake. The PR is removed linearly with respect and temperature. We obtained several results at various experimental conditions - temperatures, gas flow, process time and frequency. On the assumption that PR is removed homogeneously, we can calculate the etching rate by measurement of thickness of PR by ellipsometry.