Patent ID: 7718535

Claim:
A method of partially removing a polysilicon layer formed over silicon nitride structures from a major surface of a substrate comprising: applying a first abrasive slurry to a polishing surface of a polishing pad, the first abrasive slurry having a first target slurry pH; causing relative motion between the substrate and the polishing pad in a plane generally parallel to the major surface of the substrate while applying a force tending to bring the major surface and the polishing surface into contact; polishing the major surface of the substrate with the first abrasive slurry to remove a first portion of the polysilicon layer from the major surface of the substrate to form an intermediate polished polysilicon surface; applying a second abrasive slurry to the polishing surface of the polishing pad, the second abrasive slurry having a second slurry pH of at least 7; causing relative motion between the substrate and the polishing pad in a plane generally parallel to the major surface of the substrate while applying a force tending to bring the major surface and the polishing surface into contact; polishing the major surface of the substrate with the second abrasive slurry to remove a second portion of the polysilicon layer from the major surface of the substrate to form a final polished polysilicon surface and expose a surface of the silicon nitride structure, the final polished polysilicon surface and the exposed surface of the silicon nitride being substantially coplanar, wherein the first abrasive slurry is substantially free of all surfactants that will selectively form a passivation layer on the polysilicon layer and the second abrasive slurry includes a non-ionic surfactant that will selectively form a passivation layer on the polysilicon layer.