Impact of Wafer Geometry and Thermal History on Pressure and von Mises Stress Non-Uniformity During Chemical Mechanical Planarization

This study employs pressure measurements and von Mises stress simulations across surfaces of wafers in order to examine the effect of wafer-ring gap size, extent and direction of wafer bow, and the effect of thermal history on within wafer pressure non-uniformity (WWPNU). WWPNU analysis for nominally flat, thermally untreated, wafers indicates that the wafer's 'central zone' has average pressure profiles, which remain constant, while the 'edge region' exhibits a sharp pressure peak. Dependence of wafer-ring gap size for the 'central zone' of bowed and thermally untreated wafers on WWPNU indicates that pressure profiles at larger gap sizes remain constant regardless of wafer shape. The 'edge zone' shows that the extent and direction of wafer bow has no effect on average pressure and variability. The effect of wafer-ring gap size on WWPNU for thermally treated wafers indicates that heat treatment reduces, or masks, the effect of gap size on average pressure in the 'central zone' of the wafer. A major effect of thermal treatment is the increase in overall pressure variability at the 'edge zone' of wafers.