Simultaneous In situ Measurement of Silicon Substrate Temperature and Silicon Dioxide Film Thickness during Plasma Etching of Silicon Dioxide Using Low-Coherence Interferometry

Abstract

We have successfully performed real-time noncontact monitoring of substrate temperature and thin film thickness during plasma etching using optical-fiber-based low-coherence interferometry. The simultaneous measurement of the silicon (Si) substrate temperature and the etching depth of the silicon dioxide (SiO2) thin film on this substrate was performed in a dual-frequency capacitively coupled Ar/C4F8/O2 plasma. The SiO2 film thickness was deduced from the ratio of the interference intensity at the SiO2/Si interface to that at the Si/air interface. The measurement error in the SiO2 film thickness was less than 11 nm. The temperature variation of the Si wafer was derived from the temperature change of its optical path length. The temperature measurement error, caused by the shift in optical path length due to the change in SiO2 film thickness, was reduced from 7.5 to 0.6 °C by compensating for the shift using the SiO2 thickness data. This method enables precise control of etching performance and improves process reproducibility.