High signal-to-noise ratio inspection of sub-quarter micrometer oxide CMP defects by using laser scattering inspection tool

Abstract

This paper discusses high S/N (signal-to-noise) ratio inspection of sub-quarter micrometer oxide CMP defects, e.g. surface particles, micro-scratches, and pits, using a laser scattering inspection tool. For high S/N inspection, (1) reduction of noise signals from embedded particles, and (2) improvement in sensitivity are the objectives. Optimal selection of the incident-light angle of the laser tool, polarization of the scattered light, and optimized sample structures enable us to achieve the objectives. By applying the new high S/N inspection method, a new insight has been found, i.e. total defect count is in proportion to defect size (threshold value) with the rule of power of -6, which is much larger than the conventional value of -2. Among the killer defects, pits mainly increase very rapidly with the decrease in size. The slope is approximately -7 in the log(count)-log(size) plot.