ISPM characterization of gas phase nucleation in a Novellus C1 WCVD process chamber

An High Yield Technology model 70 in-situ particle monitor (ISPM) has been installed on the pumpline of a Novellus C1 WCVD process chamber in an effort to better characterize and control the particle performance of the chamber, especially as it pertains to gas phase nucleation (GPN) in the tool. GPN results when the SiH₄:WF₆ ratio exceeds 1:1 at the system operating pressure and temperature. During experimentation the GPN boundary conditions were identified and the factors which controlled the phenomena were explored. The ISPM was used to detect the occurrence of a GPN event. A good correlation between high ISPM counts and in-film particles was established. The ISPM was a crucial element in identifying process boundary conditions as they related to GPN; this in turn helped assure control of the process wafers. An additional effect was noted as relates to formation and deposition of the nucleation sites on the wafer. In a two wafer test GPN was purposely generated, with the ISPM detecting comparable levels of particles during the processing of both wafers; however, very few particles were detected on the first wafer whereas several hundred particles were detected on the second wafer. This effect has been attributed to thermophoretic effects protecting the first wafer, with the second wafer being contaminated before it was heated.