In situ real-time ellipsometry for film thickness measurement and control

A rotating compensator type polarizer-compensator-sample-analyzer ellipsometer is used in situ to provide real-time thickness measurements and control of process end point during the etching of polysilicon. The ellipsometer can measure the thickness of the polysilicon layer every 0.15 s. The measured thickness was used to determine end point to obtain a desired film thickness. The polysilicon films etched using in-process ellipsometer control had a thickness accuracy and reproducibility of 4 Å. In comparison, timed etching of polysilicon films in the same reactor had a thickness reproducibility of only 150 Å.