Mean residence time and removal rate studies in ILD CMP

Mean residence time (MRT) in the wafer-pad region was shown to be highly dependent on slurry flow rate, wafer pressure, and relative pad-wafer velocity. MRT was also shown to be a linear function of coefficient of friction. The latter was envisioned to be an indication of the tortuosity of the path bounded in the wafer-pad interface. The extent of process transients during chemical mechanical polishing (CMP) was quantified, and it was shown that the average time it took for fresh incoming fluid (i.e., slurry, water, or other active agents) to displace the existing fluid in the pad-wafer region yielded important information regarding fluid concentration near the wafer as well as the kinetics of the process. A new parameter, the turnover ratio, which is defined as the ratio of the MRT to the polish time, was developed to quantify the extent of abrasive concentration transients during a typical polish. This parameter was found to significantly impact the interlayer dielectric (ELD) removal rate and was deemed critical for process optimization considerations.