Insitu spectral ellipsometry for real-time measurement and control

Abstract

Described in this work is a spectral ellipsometer designed and built specifically for adaptive control in single wafer processing. This instrument is capable of precisely measuring thicknesses and compositions of multilayer structures in situ and in real time. Utilizing phase modulation, multichannel detection and digital signal processing techniques, this ellipsometer is capable of acquiring spectra in less than 75 ms. Efficient algorithms have also been developed for extracting layer parameters (thicknesses and composition) from measured spectra of multilayer stacks in one second or less. This spectral ellipsometer has been applied to on-line monitoring of wafer properties during etch in a single-wafer, remote microwave plasma chamber. Of interest has been etching of Si 3N 4, SiO 2, Si 3N 4 and SiO 2 mixtures, polycrystalline Si, and multilayer combinations of these materials. Film thicknesses and etch rates are updated during etch such that interfaces can be anticipated and endpoints determined. Spectral ellipsometry allows overdetermination of variables in multilayer stacks, hence, structure models and layer parameters can be verified using statistical methods. Spectral information also allows self-calibration of incidence angles.