Chemical/mechanical balance management through pad microstructure in CMP

Abstract

CMP is a complex process that combines the synergistic effect of a chemical action performed by the slurry and a mechanical one done by the pad and the abrasive particles of the slurry. The pad plays a key role in the CMP process as it contributes to both chemical and mechanical actions. In this paper, we focused on the pad pores, which act on the two sides of the chemical/mechanical balance. Pads with different porosities were investigated. The effect of pad microstructure on CMP performance were studied. A 3D confocal microscope was used to analyze pad roughness parameters, height distributions and asperities properties. Silicon blanket wafers were polished using different pads and were then characterized in order to extract surface roughness, removal rate and defect level. The surface quality of the wafer post process presents a direct correlation with pad topography. A smaller pad pore size (i.e. smooth surface) shows a beneficial effect on the wafer roughness.We further discuss the effect of pore size on pad topography by studying asperities properties and volume available for slurry transportation. The consequences of pore characteristics are then correlated to CMP performance. This study allows us to understand how we can manage the chemical/mechanical actions through the pad microstructure.