The application of control chart for defects and defect clustering in IC manufacturing based on fuzzy theory

c-Chart was frequently used to monitor wafer defects during IC manufacturing. The clustering degree of defect on a wafer will increase along with the area of wafer gradually enlarging. The defect clustering causes the Poisson-based c-chart to exhibit many false alarms. Although several revised control charts have been developed to reduce the number of false alarms, those control charts still have some disadvantages in practical use. This study proposes a control chart that applies fuzzy theory and engineering experience to monitor wafer defects with the consideration of defect clustering. The proposed control chart is simpler and more rational than those revised c-charts. Finally, a case study of an IC company, owing to the HsinChu Scientific part at Taiwan, is used to demonstrate and verify the rationality and effectiveness.