Manufacturers of integrated circuits (IC) frequently utilize c-charts to monitor wafer defects. The clustering of wafer defects increases with the surface area of the wafers. The clustering of defects causes the Poisson-based c-chart to show many false alarms. Although Neyman-based c-chart has been developed to reduce the number of false alarms, it has some shortcomings in practical use. This study presents a process control chart that applies Fuzzy theory and the engineering experience to monitor the clustered defects on a wafer. The proposed method is simpler and more efficient than that of the Neyman-based c-chart. A case study of an IC company in Taiwan demonstrates the effectiveness of the proposed method.
Tong, Leeing; Yang, Chienhui; Chen, Min-Hsiang; Yu, Hsiang-Pai; and Wang, Min-Chia, "Process Chart for Controlling Wafer Defects using Fuzzy Theory" (2003). ICEB 2003 Proceedings. 146.