Chemical Mechanical Planarization for Cu Through-Wafer Interconnects: An Investigation of Slurry Chemistry Interaction Effects Using a Design of Experiments Approach

Abstract

The effects of slurry pH, hydrogen peroxide 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 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 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 concentration in the slurry, the pH and concentration of the slurry should be carefully formulated to obtain optimal results for TWI fabrication. The interaction plots between slurry pH and concentration also provide a possible optimization level to achieve the maximum copper removal rate while minimizing WIWNU.