Defect characterization and light scattering by PSL spheres on tungsten CMP wafers

Abstract

Chemical mechanical polishing (CMP) generates unique difficulties for defect metrology using wafer scanners. Polishing residue, scratches, pits, normal contaminant particles and the pattern covered by the planarized material provide scattering signatures that differ from normal patterned or unpatterned wafers. This relatively young application area for wafer inspection instruments needs a rapid infusion of experience and knowledge infrastructure in order to bring it along to the level of more conventional applications. To that end, a series of relevant experiments have been completed on three types of tungsten (W) CMP test wafers including (1) partially-polished blanket W, (2) fully-polished blanket wafers (polished to oxide), and (3) fully-polished patterned W wafers. Various contamination particles and defects on these wafers were characterized and identified by means of optical microscopy, surface scanning inspection, scanning electron microscopy, energy-dispersive x-ray spectrometry, and atomic force microscopy. A number of defect types including: particles of polished material, substrate, abrasive, oxidizer, and chemical products of polished material and oxidizer; scratches; and pits were expected based on an analysis of the CMP process, and were thereafter confirmed by experiment. Surface roughness was measured on the two types of blanket wafers. W line roughness and dishing depth were measured as a function of line width and pattern density on the patterned W wafers. For light scattering experiments, 0.482 micrometers polystyrene latex spheres were deposited on a patterned W CMP test wafer. Differential light scattering cross sections of particles located in the 0.5 micrometers line/1.0 micrometers pitch region at various locations relative to the W lines were then measured at 488 nm wavelength using the Arizona State University scatterometer.