Reduction of AlF3 and ALFO defects by replacing aluminum purge ring heaters with ceramic purge ring heaters in AMAT tungsten CVD systems

One style of heater used within an Applied Materials (AMAT) Tungsten Chemical Vapor Deposition (WCVD) chamber comprises both the heater and integral (outer) purge-ring made of Aluminum (Al); such heater units are designated Rev-G, and the chamber, WxZ. In this work, the degradation and collapse (thermal fatigue) of the Al purge-ring has been studied at different stages in the lifetime of a Rev-G heater in a Centura (5200) WCVD system, together with its influence on W film defectivity. It is shown that the manufacture of such heaters (using a high temperature forging method) has a significant impact upon both the defectivity levels and thickness uniformity of the subsequently deposited tungsten films; i.e., it has been reported by AMAT that heaters containing an excess of β-phase Al grains, compared with α-phase, can induce significant levels of AlF₃ (Aluminum Fluoride) and AlFO (Aluminum, Fluorine, and Oxygen) defects into the deposited films. The defect generation is basically due to the attack of the β-phase Al grains by fluorine ions during the "periodic (plasma) clean " part of the cycle, where NF₃ gas is used to clean the chamber/components after a specific number of wafers have been deposited. It was observed that the degradation in the defect performance and thickness uniformity started to occur after the deposition of a few thousand wafers. A temporary solution to the uniformity issue was to adjust the deposition edge-purge (H₂+Ar) gas flows; however, the entire problem was solved by replacing the Rev-G heaters with alternative "Ceramic Purge-Ring" (CPR) heaters. The latter comprised a (removable) ceramic purge-ring in place of the integral Al purge-ring of the Rev-G heater; such chambers are designated WxZ+.