Optimization of pre and post recipe sensitivity for unpattemed wafer defectivity inspection

Abstract

As dimensions shrink with each successive semiconductor technology node, the critical size of defects that can impact yield also shrinks. Monitoring the health of process equipment rigorously and regularly for key sources of contamination must be performed. Comparison of the critical feature size per technology node with the typical defectivity size used for process control shows a widening disparity over time. The need to close this gap is more important than ever in order to improve chip yields as the industry drives toward the 10nm and 7nm nodes. The latest generation defectivity inspection equipment can measure defect sizes close to technology critical feature size. Getting accurate data of real added defects is complicated for processes that involve film deposition due to decoration effects caused by the film conforming over the pre-existing defects. In this study, we bring out a clear methodology in optimizing the pre/post monitoring sizes of defects in order to minimize the effect of false adders. The relationship between pre and post sizing is well understood for mechanical checks. However, the impact on the sizing of defects because of film interaction is of critical interest. In this work, a series of different films and deposition methods are studied. Decoration effects of defects (as shown in Figure 1) are analyzed in depth and an extensive methodology of optimization of post-scan thresholds is elaborated. This methodology has proven to be extremely effective and has successfully been implemented at Global Foundries Fab 8 and 10.