The Impact of Wafer Edge Roll-Off on CMP Performance

Abstract

The impact of wafer edge roll-off on CMP performance was investigated. Distributions of removal rates at the periphery of wafers were estimated by pressure distributions of front-side surfaces of wafers calculated by FEM analysis. Results showed that the edge roll-off influenced distributions of the removal rates at periphery of the wafers when both a stacked pad and a solo pad were used. The influence was reached 4 mm from the edge of a wafer with a stacked pad, and 10 mm from the edge with a solo pad. When ROA was 1.27 μm, ratios of surface pressure near the edge compared to the center part of a wafer, were about 30% with a stacked pad and about 23% with a solo pad. Moreover, in the case of a stacked pad, we found that the influence of the wafer edge roll-off to CMP process could be compensated by adjusting a pressure of a retainer ring. Also, ranges of allowable ROA with the stacked pad were not uniform when the pressure of a retainer ring was changed from 23 kPa to 30 kPa. On the other hand, in the case of the solo pad, the ranges of allowable ROA did not change very much, which was from 0 to about 0.4 μm, even if the pressure of a retainer ring was changed.