Characterizing contamination inspection capabilities using programmed defect test reticles

Abstract

The ORIONTM series of test reticles have been used for many years as the photomask industry standard for evaluating contamination inspection algorithms. The deposition of Polystyrene Latex (PSL) spheres on various reticle pattern designs allow STARlightTM tool owners to measure the relative contamination inspection performance in a consistent and quantifiable manner. However, with recent inspection technology advances such as shorter laser (light source) wavelengths and smaller inspection pixels, PSL spheres were observed to physically degrade over relatively short time periods: especially for the smallest sized spheres used to characterize contamination inspection performance at the most advanced technology nodes. Investigations into using alternative materials or methods that address the issue of PSL shrinkage have not yet proven completely successful. Problems such as failure to properly adhere to reticle surfaces or identification of materials that can produce consistent and predictable sphere sizes for the reliable manufacture of these critical test masks are only some of the challenges that must be solved. Even if these and other criteria are met, the final substance must appear to inspection optics as pseudo soft defects which resemble actual contamination that inevitably appears on production reticle surfaces. In the interim, programmed pindot defects present in the quartz region of the SPICATM test reticle are being used to characterize contamination performance while a suitable long-term solution to address the issue of shrinking PSL spheres on ORION masks can be found. This paper examines the results of a programmed pindot test reticle specifically designed to evaluate contamination algorithms without the deposition of PSL spheres or similar structures. This alternative programmed pindot test reticle uses various background patterns similar to the ORION, however, it also includes multiple defects sizes and locations making it more desirable than the limited range of defects found on the SPICA.