In situ cleaning of LPCVD furnaces using a thermal NF3 etch process

Summary form only given. This paper describes an in situ clean process for the ASM A400 (200 mm) and A412 (300 mm) vertical LPCVD batch furnaces. The clean is based upon a thermal NF₃ etch process. The furnace is maintained near the deposition temperature (500 to 600 °C) whilst introducing a NF₃/N₂ gas mixture. NF₃ thermally decomposes at these temperatures, generating fluorine atoms that react with the CVD residue. For development purposes, the clean process was monitored using a quadrupole mass spectrometer QMS and Fourier transform infrared (FTIR) spectroscopy. The time evolution of the NF₃ and SiF₄ concentration was used to determine when the clean was complete and to optimize the etch process with respect to etch rates and selectivity. QMS and FTIR were also used to measure volumetric PFC emissions. Methods for monitoring the process in production are also described.