Effect of Transition Metal Compounds on Amorphous SiC Removal Rates

Abstract

We show here that transition metal compounds when used as additives to silica dispersions enhance a-SiC removal rates (RRs). Silica slurries containing KMnO4 gave RRs as high as 2000 nm h−1 at pH 4. Addition of CuSO4 to this slurry further enhanced the RRs to ∼3500 nm h−1 at pH 6. Furthermore, addition of a low concentration of 250 ppm Brij-35 to this slurry suppressed the RRs of SiO2 to zero, while retaining the RRs of a-SiC at ∼2700 nm h−1, a combination of RRs that is appropriate for hard mask polishing. The underlying mechanisms causing the enhancement in the RRs of a-SiC in the presence of transition metal compounds is discussed based on the RR data and XPS analysis of post-polished wafer surfaces. It is shown that a mixed redox system consisting of the oxidation of a-SiC by KMnO4 enhanced by the catalytic activity of the Cu(II) salt is responsible for the rapid oxidation of a-SiC and the observed enhancement in polish rate with silica based slurries. The adsorption characteristics of Brij-35 on the oxide and carbide surfaces are described based on thermogravimetry data and in achieving the desired polish rate selectivity.