Effects of abrasive particle size and molecular weight of poly(acrylic acid) in ceria slurry on removal selectivity of SiO2/Si3N4 films in shallow trench isolation chemical mechanical planarization

Abstract

The effects of the molecular weight and concentration of poly(acrylic acid) (PAA) with different primary abrasive sizes in ceria slurry on the nitride film loss, removal rate, film surface roughness, and removal selectivity of SiO2-to-Si3N4 films were investigated by performing chemical mechanical polishing (CMP) experiments using blanket and patterned wafers. In the case of the blanket wafers, we found that for a lower PAA molecular weight, the removal selectivity of SiO2-to-Si3N4 films increased more significantly with increasing PAA concentration in slurry containing a larger primary abrasive size. For the patterned wafers, with a higher PAA molecular weight in the ceria slurry suspension, the erosion of the Si3N4 film was less, but the removed amount was also smaller, and the surface roughness became worse after CMP. These results can be qualitatively explained by the layer of PAA adsorbed on the film surface, in terms of electrostatic interaction and rheological behavior.