Investigation of diamond effect on pad topography, friction force and removal rate during ILD CMP Process

In this study, two 4.25-inch Mitsubishi Materials Corporation 100-grit discs were used to investigate the effect of diamonds on pad topography, friction force and removal rate for ILD CMP process. Diamonds of Disc A are harder and have longer cutting lengths than Disc B. Before the polishing tests, a proprietary method was used to analyze the number of active diamonds and the mean furrow shape on a pad substitute material for each disc under 3.6 and 6.1 lb loads. The two discs have similar number of active diamonds. On the other hand, the furrow shape analysis indicates Disc A cuts deeper into the pad substitute material than Disc B. In addition, Disc A has higher pad substitute material cut rates than Disc B. Both discs were used to condition an IC1020 M-groove pad, on which 200-mm blanket TEOS wafers were polished. For both discs, the coefficients of friction (COF) increase with the sliding velocity. This trend is consistent with the previously developed COF model. The Wilcoxon signed-rank test indicates that the COF and removal rates for Disc A are higher than Disc B, and the removal rate within wafer non-uniformities for Disc A are better than Disc B. For each disc, a pad sample was taken after the polishing tests and interferometry analysis was performed to establish pad surface height probability density functions and extract pad surface abruptness. Results show that Disc A generates a rougher pad surface than Disc B, resulting in higher COF and removal rates.