AVS 49th International Symposium
    Plasma Science Tuesday Sessions
       Session PS2-TuA

Paper PS2-TuA2
Effect of Plasma Chamber Wall Conditions on Atomic Chlorine Concentration and Polysilicon Etch Rate Uniformity

Tuesday, November 5, 2002, 2:20 pm, Room C-105

Session: Plasma Surface Interactions I
Presenter: T.W. Kim, University of California, Santa Barbara
Authors: T.W. Kim, University of California, Santa Barbara
E.S. Aydil, University of California, Santa Barbara
Correspondent: Click to Email
The effect of reactor wall conditions on atomic chlorine concentration and polysilicon etch rate uniformity was studied in a high-density inductively coupled plasma reactor. Experimental measurements of etch rate and two dimensional ion flux distributions on the wafer are combined with a simple transport and reaction model for Cl atoms in the plasma to elucidate the effect of reactor wall conditions on the etch rate uniformity. Specifically, we focus on the effects of wafer-to-wafer drifts from the wall conditions and effects of such drifts on the uniformity of etching. The spatially averaged etch rate across the wafer surface 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. Etch rate is highest at the center of the wafer when the anodized aluminum reactor walls are maintained in a "clean" state, free of silicon oxychloride deposits. In contrast, the etch rate peaks at the edges of the wafer with a local maximum near the pumping port when the reactor walls are coated with the silicon oxychloride film. The spatially averaged ion flux increases slightly while ion flux uniformity does not change as the reactor walls are covered with the silicon oxychloride film indicating that the drift in etch rate and etch uniformity is primarily due to the drift in atomic chlorine concentration and its spatial distribution. The increase in atomic chlorine concentration is due to its lower recombination probability on the silicon oxychloride film surface as compared to the "clean" anodized aluminum wall. As the reactor walls are coated with the silicon oxychloride film the etch rate distribution changes from a center-fast profile to a edge-fast profile due to a change in the dominant atomic chlorine depletion mechanism from wall recombination to recombination on the wafer surface.