ILD CMP with Silica Abrasive Particles: Interfacial Removal Kinetics and Effect of Pad Surface Textures

Abstract

The removal mechanism for interlevel dielectric (ILD) chemical mechanical polishing (CMP) with fumed silica abrasive slurry was studied by measuring silicon dioxide wafer removal rates as a function of abrasive concentration and pH and also by examining the surface charges of the abrasive particles at different pH’s. The interfacial removal kinetics indicates that the wafer removal rate is consistent with a first-order reaction and is proportional to the concentration of surface silanolates on the abrasive particles. The actual removal is proposed to be achieved by a direct nucleophillic attack of the silica particle silanolates on the wafer Si–O bond. Pad surface texture provides the means to transport the slurry to the contact zone and the effective concentration of abrasive particles doing actual removal is greatly influenced by the pad surface macrotexture by grooving design and the microtexture by conditioning. The observed correlation between the pad surface parameters that are used to characterize the pad microtexture and the removal rate highlights the importance of the pad surface texture to ILD CMP.