Prediction of Pad Profile with Pressure Distribution on Diamond Disk at Pad Edge

Abstract

The conditioning process in chemical mechanical polishing (CMP) has an important role to maintain the uniform CMP performance using the diamond attached on a rotating disk. This process maintains the uniform surface roughness and profile of the pad, which results in the steady material removal rate (MRR) and within wafer non-uniformity (WIWNU). The pad uniformity varies greatly by mechanical action in the conditioning process, which is controlled by three mechanical actions: pad/conditioner rotation and sweeping motion of the conditioner arm.When diamonds scratch on a pad, it is possible to assume that the pressure distribution of a diamond disk is uniform when the disk fully contacts the pad, however, the pressure distribution on a diamond disk is not uniform anymore in a condition with the disk getting off the pad edge. For this reason, when a disk is set to sweep over the pad edge, there were problems with a hump area at the near edge of the pad. This hump area can affect the WIWNU and disturb the elimination of waste matter from the results of CMP.In this study, the process of conditioning in CMP was analyzed topologically and the program was developed through it. First, the movement of diamond grits calculated and the wear amount was obtained by accumulating the number of points in the mesh containing the coordinates of the diamonds moving at a specific time or distance. Second, indentation depth was analyzed according to the structural properties of a disk and the wear depth of the pad was analyzed in uniform-pressure condition. Third, the pressure distribution on a disk at the pad edge was analyzed as shown in Fig. 1 and adapted to an algorithm predicting pad profile. Finally, we got a simulated pad profile by the algorithm and the results were compared with experimental results in the same condition as shown in Fig. 2.