Characteristics and mechanism of etch process sensitivity to chamber surface condition

Process variation with chamber surface condition in high density plasma reactors can seriously affect the process performance and productivity of device manufacturing. In this work, the impact of chamber surface coating on polycrystalline-silicon (polysilicon) gate etching with Cl2- and HBr-based plasma has been studied. The dependence of process sensitivity to surface coating on various processing conditions has been characterized and the mechanism of process shift has been analyzed. Based on the experimental results, the root cause of process sensitivity has been attributed to the change of surface recombination rate of free radicals on different chamber surfaces which leads to a variation in reactive neutral density. Under a certain discharge condition, the Cl and Br densities in a clean chamber with anodized aluminum and alumina surfaces are >60% lower than those in a seasoned chamber with silicon oxide deposition, resulting in lower polysilicon and oxide etch rate in the former case. In general, the process sensitivity to chamber surface condition depends on process regime and is higher for those processes where etching is more chemical in nature, such as processes at higher pressure and with Cl2-based chemistry. Processes with higher oxygen concentration and higher source power are also more sensitive due to the accelerating surface oxidation of polysilicon surface in a clean chamber. Approaches to reduce the effect of process sensitivity have been discussed.