Effects of process parameter variations on the removal rate in chemical mechanical polishing of 4H-SiC

The effects of temperature, slurry pH, applied pressure, and polishing rotation rate on the material removal rate during chemical mechanical polishing (CMP) of 4H-silicon carbide wafers using colloidal silica slurry and polyurethane/ polyester fiber polishing pads have been studied. Measured removal rates varied from around 100 Å/hr to nearly 2500 Å/hr depending on the values of the various parameters. The amount of material removed was determined by measuring the wafer mass before and after polishing. Variations in temperature and slurry pH did net produce significant changes in the measured removal rates. Higher polishing pressures resulted in increased material removal rates from 200 to 500 Å/hr but also produced excessive polishing pad damage. Variations in pad rotational speeds produced the largest changes in material removal rates, from around 200 to around 2000 Å/hr for rotational speeds between 60 and 180 rpm, but the variations were non-linear and somewhat inconsistent. This CMP formula is shown to consistently produce damage free surfaces but the optimum removal rate is slow.