Real-Time Measurement of W, TiN, and TaSiN Thicknesses Comprising Full-Metal Gates during Plasma Etching by Optical Interference of Etching Plasma

摘要

Film thicknesses of W, TiN, and TaSiN in a full-metal gate stack with photoresist masks were measured in real time during plasma etching with an in situ thickness monitor. The accuracy of such measurement was approximately ±1 nm. The monitor functions on the basis of the interference of plasma optical emission, reflected from the surface and base of the film. Although W and TiN have large absorption indexes, their thicknesses were more accurately measured when they became thinner. In particular, W thickness was estimated more accurately when it was smaller than approximately 10 nm.