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

Abstract

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.