The impact of nanotopography was studied in oxide chemical mechanical polishing (CMP). In order to investigate the film removal depth and polishing pad dependencies, oxide films on wafers were repeatedly polished using two types of polishing pads having different compressibility (soft pad and hard pad). The power spectral density (PSD) of the film thickness variations got closer to that of nanotopography during CMP. We proposed a transfer function defined as the ratio of PSD of the film thickness variation to that of nanotopography. The calculated transfer functions clearly showed that nanotopography has an impact on film thickness variation for longer wavelengths as the removal depth gets larger and when using the hard pad. In addition, single-side-polished (SSP) wafers prepared using six different methods were examined following unpatterned oxide CMP. We found a clear and positive correlation between the standard deviation of the nanotopography profile and that of the film thickness variation after CMP. Through this correlation, the slurry type dependency (commercial silica and ceria slurry) of nanotopography was also investigated. With each optimized condition, ceria slurry caused greater film thickness variation due to nanotopography than silica slurry after unpatterned oxide CMP.
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