Effects of chamber wall conditions on Cl concentration and Si etch rate uniformity in plasma etching reactors

Experimental measurements of the etch rate and ion flux distributions on the wafer are combined with modeling to elucidate the effects of reactor wall conditions on Cl concentration and polysilicon etch rate uniformity in an inductively coupled plasma etching reactor. The spatially averaged etch rate across the wafer increases with time as etch products react with residual oxygen in the chamber and coat the reactor walls with a thin layer of silicon oxychloride film. Chlorine concentration in the plasma and the Si etch rate increase due to lower recombination probability of Cl on this film as compared to the "clean" anodized aluminum wall surface. Etch rate is highest at the wafer center when the walls are maintained in the clean state. In contrast, the etch rate peaks at the wafer edges when the walls are coated with the silicon oxychloride film. The drift in etch rate and uniformity is primarily due to a drift in Cl concentration and its spatial distribution. As the reactor walls are coated, the etch rate distribution changes from a center-fast profile to an edge-fast profile due to a change in the dominant Cl depletion mechanism from wall recombination to recombination on the wafer surface.