Mechanism of high selectivity in ceria based shallow trench isolation chemical mechanical polishing slurries

dl-aspartic acid as a removal rate selectivity enhancer for shallow trench isolation chemical mechanical polishing slurries was investigated over a pH range. The effects of downward pressure, rotational speed of the turntable as well as the ceria abrasive loading were also examined. The selectivity is very sensitive to changes in the pressure but not to changes in the rotational speed. Select experiments were also conducted with other types of abrasives with and without the additive. A comparison of the pKa values of the amino acid with the variation of the selectivity with pH indicates that the form of amino acid plays a vital role in determining the polishing behavior and the selectivity. Further, the results corroborate the hypothesis that chemically active sites on the abrasive may be blocked by certain forms of the amino acids, leading to changes in the selectivity.