New diagnostic method for monitoring plasma reactor walls: Multiple total internal reflection Fourier transform infrared surface probe

Films and adsorbates that deposit on reactor walls during plasma etching and deposition affect the discharge properties such as the charged particle and reactive radical concentrations. A systematic study of this plasma - wall interaction is made difficult by a lack of diagnostic methods that enable one to monitor the chemical nature of the reactor wall surface. A new diagnostic technique based on multiple total internal reflection Fourier transform infrared (MTIR-FTIR) spectroscopy was developed to monitor films and adsorbates on plasma etching and deposition reactor walls with monolayer sensitivity. Applications of this MTIR-FTIR probe are demonstrated. Specifically, we use this probe to (i) detect etch products and films that deposit on the reactor walls during Cl₂ plasma etching of Si, (ii) determine the efficacy of a SF6 plasma to clean films deposited on reactor walls during Cl₂/O₂ etching of Si, and (iii) monitor wafer-to-wafer etching reproducibility.