Investigation of step structure in CMP retainer ring to improve within-wafer non-uniformity

Abstract

A retainer ring structure was investigated to improve non-uniformity in a chemical mechanical planarization (CMP) process. During the CMP process, the stress distribution on the wafer affects the CMP performance in terms of material removal rate (MRR) and within-wafer non-uniformity (WIWNU). The non-uniformity is related to edge exclusion and affects the process yield. For this purpose, the stress distribution between pad and wafer was calculated via the finite-element method (FEM) and compared with the experimental results of a 300 mm wafer polishing test. The retainer ring with a step structure exhibited an improved stress distribution along the wafer surface. Consequently, the non-uniformity was improved by 16.6 %. These results can be used to optimize CMP processes (in particular, CMP retainer ring structures) and determine adequate process conditions.