Maintaining reproducible plasma reactor wall conditions: SF6 plasma cleaning of films deposited on chamber walls during Cl2/O2 plasma etching of Si

Abstract

Silicon oxychloride films deposited on plasma etching reactor walls during the Cl2/O2 plasma etching of Si must be removed to return the reactor to a reproducible state prior to etching the next wafer. Using multiple surface and plasma diagnostics, we have investigated the removal of this silicon oxychloride film using an SF6 plasma. In particular, a diagnostic technique based on the principles of multiple total internal reflection Fourier transform infrared spectroscopy was used to monitor the films that formed on the reactor walls. The silicon oxychloride film etching proceeds by incorporation of F, which also abstracts and replaces the Cl atoms in the film. If the SF6 plasma is not maintained for a sufficiently long period to remove all the deposits, the F incorporated into the film leaches out into the gas phase during the subsequent etch processes. This residual F can have undesirable effects on the etching performance and the wafer-to-wafer reproducibility. The removal of the silicon oxychloride film from the reactor walls is inherently nonuniform and the end of the cleaning can be detected most easily by monitoring reactor averaged F and SiF emissions.