Study on Polishing Profile at Wafer Edge by CMP Using Floating Head.

The purpose of this investigation is to clarify the origin of the removal rate variation at the wafer edge in Chemical Mechanical Polishing (CMP) by using the floating head with the retaining ring. Within-wafer non-uniformity of removal rate is often determined by the removal rate variation at the wafer edge. Polished edge profile varies with the pressure distribution at the wafer edge. It is strongly affected by the pressure load applied on the retaining ring. Therefore, the non-uniformity of the pressure distribution at the retaining ring could result in the removal rate variation at the wafer edge. It is realized that the flatness of the retaining ring is very important factor for the polished edge profile variation. The same head with the same conditioned retaining ring gives almost the same removal rate variation at the wafer edge, even if the polishing condition is different.