Optical monitoring in a two-step chemical mechanical polishing process

摘要

An optical monitoring system for a two-step polishing process which generates a reflectance trace for each of plurality of radial zones. The CMP apparatus may switch from a high-selectivity slurry to a low-selectivity slurry when any of the reflectance traces indicate initial clearance of the metal layer, and polishing may halt when all of the reflectance traces indicate that oxide layer has been completely exposed.