An in-situ ellipsometer was used to provide real-time thickness measurements and control of process end point during plasma etching of silicon dioxide. In-situ ellipsometer thickness values were obtained at intervals of 0.15 seconds. The measured thickness was used to determine end point to obtain a desired film thickness. The oxide films etched using in-process ellipsometer control had a thickness accuracy and reproducibility of 3 A. In comparison, timed etching of silicon dioxide films in the same reactor, a thickness reproducibility of only 69 A was obtained.
Steven A. Henck,
"In-process thin film thickness measurement and control", Proc. SPIE 1594, Process Module Metrology, Control and Clustering, (1 January 1992); doi: 10.1117/12.56635; https://doi.org/10.1117/12.56635