Pattern density and pitch effects on chemical-mechanical polishing

Test masks for characterizing pattern dependent variations in the thickness remaining after chemical-mechanical polishing (CMP) were designed taking the experimentally obtained interaction distance into consideration. Polishing behaviors were characterized with layout pattern density and pitch variations using these masks. The deposition profile effects were also compared between PETEOS (Plasma Enhanced Tetra Ethyl Ortho Silicate) and HDP (High Density Plasma) oxide. Both measured post-CMP thickness and the expected oxide pattern density from a consideration of the deposition profile effects showed good correlation with respect to pitch variation for a constant layout pattern density. Also, the relationship between the remaining thickness and true layout pattern density were deduced. Secondly, chip-level CMP modeling was investigated to obtain the post-CMP thickness distributions across a die from its design layout and a few oxide film and CMP parameters. The experimental CMP results agreed well with the modeling results. The effective dummy filling results were shown to achieve a smaller pattern density variation, which resulted in uniformly better post-CMP thickness. Finally, whether the resulting oxide thickness can be predicted for any location on a die for an arbitrary layout if the effective pattern density distributions are calculated is discussed.