A Quantitative Analysis of Multi-Scale Response of CMP Pad and Implication to Process Assessments

Abstract

The multiscale characteristics of the pad deformation and its surface morphology control the quality and efficacy of the chemical mechanical planarization (CMP) process. The pad microstructure comprised of cell size, wall thickness and surface roughness exhibit temporal variations in the effective pad stiffness at the pad abrasive interface. An experimental and analytical approach is developed to examine a dry IC-1000 pad response at different length scales, utilizing a nano-indentation with a conical tip of 1μm radius and a flat-punch of 60μm diameter. The quasi-static load-indentation depth plots showed different characteristic trends with varying stiffness at different loading ranges. The measurements showed the role of the porous microstructure to drive a competition between the local cell-membrane indent, bending of cell membrane and the bulk response of the porous pad. These different deformation mechanisms are employed in constructing an equivalent mechanical model for the effective pad elastic stiffness. The model prediction matches well with the force-indentation depth measurements. The developed model is used to investigate the influence of pad property evolution on the propensity of scratch generation during the CMP process. Such physically based models can be utilized to optimize the pad microstructure and morphology to control the spatial and temporal modulation of the material removal rate and the propensity for scratch generation.