Reduction of NF3 consumption during the cleaning of a PECVD cham-ber

Abstract:
A PECVD system in the IHP's equipment pool is equipped with an endpoint system for the process chamber clean. The chamber is cleaned with nitrogen trifluoride (NF3), which is split into nitrogen and fluorine radicals using a plasma source. The free fluorine radicals react with the chamber coatings to create volatile compounds such as silicon tetrafluoride (SiF4), which can be easily pumped out. The endpoint system detects the current occurrence of the SiF4 waste product. The falling edge of the measurement signal for SiF4 indicates when the deposits have been completely removed by the cleaning process. By examining the effects of variations in NF3 flow, process pressure and substrate holder position on the endpoint curve, additionally determining the removal rate and subsequently monitoring the particle level, we were able to approx-imate the minimum NF3 consumption for efficient cleaning. We were therefore able to optimize the process for chamber cleaning to such an extent that the consumption of NF3 was reduced by at least 70%.