Inline wafer edge inspection system for yield enhancement of thin wafers

Abstract

Wafer edge defects can occur anywhere throughout production, and only continuous monitoring allows wafer-damaging equipment or processes to be identified quickly in order to apply corrective measures, to avoid in-process wafer breakage by removing affected wafers from further processing, and to maximise yield. A thorough wafer edge inspection that covers the entire circumference in as densely spaced intervals as reasonably possible, becomes crucial. This particularly holds true for microscopic defects, which eventually grow and ultimately lead to breakage. For such a monitoring to be most effective, it should cover many processing steps, work for any wafer material, and do so reliably and fully automated, without the need of an operator processing images and changing recipe settings in production tools for being able to handle various wafers with different optical surface properties. This research presents a novel optical non-reflective measurement technology, that could satisfy exactly these requirements by combining wafer edge inspection with widely used pre-alignment in one single step. The so-called Ranging Edge Detection (RED) technology is independent of optical wafer surface properties such as transparency, reflectivity or absorption, and able to operate inline without the need of frequent recalibration or adaptation of settings for different materials. Based on this technology the proprietary Wafer Edge Screener has been developed to profile and quantify the wafer edge thickness alongside the wafer cirumference. Combined with absolute edge positioning data to gain additional information about defect size, shape and location, a Wafer Edge Screener can also derive parameters such as e.g. wafer alignment or bow. Measurements of wafers made of different materials and with various defects were performed and are presented. Each defect was quantified in shape and extension, showing that Wafer Edge Screeners are promising and reliable automatic inline wafer edge inspection tools which are gathering only useful information in order to determine the integrity of wafer edges.