Chemical Mechanical Planarization for Cu Through-Wafer Interconnects

The effects of slurry pH, hydrogen peroxide (H2 O2) concentration, and their interactions on a thick Cu chemical mechanical planarization (CMP) process for through-water interconnect (TWI) applications were investigated using a two-level full factorial design of experiment. Four permutations of high and low levels of slurry pH and H2 O2 were investigated to determine the level of impact or significance on the CMP process. At constant machine parameters and pad types, significant changes in removal rate and within-wafer-nonuniformity (WIWNU) were observed based on the different slurry combinations used during the CMP process. Although slurry pH and H2 O2 concentration were observed to be the dominant main effects on the CMP process, the interaction between the two variables was also found to have a significant impact on the average removal rate of Cu and WIWNU during CMP. Based upon a direct correlation between the type of Cu species formed and the level of H2 O2 concentration in the slurry, the pH and H2 O2 concentration of the slurry should be carefully formulated to obtain optimal results for TWI fabrication. The interaction plots between slurry pH and H2 O2 concentration also provide a possible optimization level to achieve the maximum copper removal rate while minimizing WIWNU.