Effect of polish by-products on copper chemical mechanical polishing behavior

Abstract

The stains on the pad caused by polishing by-products can be observed in a copper chemical and mechanical polishing (CMP) process. In this study, the effects of stains on CMP performance such as erosion, dishing, and nonuniformity were evaluated as a function of the degree of stains accumulated on the pad. The stains on the pad deteriorate the nonuniformity of removal rate and result in the increase in erosion and dishing. CMP by-products adhere on both pores and grooves of the pad and block the flow of slurry through the grooves, resulting in the deterioration of nonuniformity. The selectivity (ratio of removal rate, Cu to TaN or dielectric film) is important in order to minimize erosion. When wafers were polished on a stained pad, the removal rate of Cu decreased similar to 30% due to the poor slurry distribution and the selectivity decreased more than 40% because the mechanical abrasion was enhanced by the presence of by-products on pad surfaces. The lower the selectivity, the higher the level of erosion on the polished patterned wafers. The higher frictional force on a stained pad results in higher temperature and etch rate of Cu which might be the reason for recess and dishing of Cu lines. (c) 2007 The Electrochemical Study.