Improvement of film uniformity stability of PECVD silicon nitride deposition process by addition of fluorine removal to the plasma clean sequence

A multi-station PECVD silicon nitride deposition process was implemented in a high volume manufacturing environment. However the occurrence of film thickness uniformity out-of-control became a chronic issue when chamber utilization was increased. Physical characterizations indicated formation of a fluoro-compound on the showerhead surface on the 1st deposition station was responsible for the failure. A hypothesized failure model suggests fluorine introduced during the plasma clean as well as the substrate materials on the incoming wafers play a role in the formation of the fluoro-compound. Marathon runs incorporating a fluorine removal treatment at the post plasma clean were carried out with results demonstrating significant improvement in the thickness uniformity stability. In addition to the detailed results of the investigation and marathon runs, the mechanism behind showerhead degradation is also discussed from the aspects of chemistry and fundamentals of plasma CVD in this paper