Evaluation of defect detection schemes for CMP process monitoring using rigorous 3-D EM simulations

Abstract

In this paper, various defect detection schemes are investigated for the post chemical mechanical polishing (CMP) inspection application using the simulation tool, METRO. Both bright field and dark field detection schemes have been studied to determine the methods of reducing the impact of layer thickness variation. Two critical CMP process defects, microscratches and particles, are evaluated. Using METRO, high resolution bright field is shown to have superior sensitivity to lower resolution bright field. Several illumination bandwidths and optical resolutions are studied in the presence of CMP color noise or oxide thickness variation. Ultra broad band (UBB) bright field detection is shown to have reduced color noise compared to traditional bright field detection. For dark field detection at a grazing angle of illumination, circular polarization is shown to have a scattering cross-sectional intensity that will provide better detection of the defects. Tungsten adhesion deposition, used after oxide CMP and contact patterning, is presented as an excellent zone monitor inspection point while significantly reducing the impact of layer thickness variation and underlying pattern noise. At this step, dark field simulations at multiple illumination angles illustrates that using a grazing angle of illumination, slurry particles will be detected exponentially better than at a higher angle.