DEVELOPING A NEW DEFECT CLUSTER INDEX

Abstract

ABSTRACT The wafer yield is a critical index for evaluation of productivity of integrated circuit manufacturers. There are many factors affecting wafer yield. However, defect number and defect clustering are two determinants of wafer yield. Defect clustering tends to grow with increasing wafer size, making yield prediction erroneous when using yield model to predict wafer yield. Additionally, the false alarm will be produced in monitoring manufacturing process using C control chart. Even the number of defects is identical on respective wafer; the wafer yield will not be the same, because the defect pattern and defect clustering degree are different on each wafer. Normally, a serious defect clustering have higher yield than low defect clustering in the case of the same defects number, because defects are concentrated on a small number of chips. Therefore, evaluating defects clustering on wafer is an important issue in determination of wafer yield. Although many studies regarding development of defect clustering indexes had been released, some drawbacks still exists. Therefore, this study primarily developed a new clustering index to retrieve these drawbacks. The developed new clustering index not only can identify the clustering pattern but also can accurately evaluate the defect clustering given different type of typical clustering patterns. Several simulated experiments based on 12 inches wafer demonstrate the effectiveness of the developed clustering index. Finally, a wafer yield model based on a real case of 6 inches from semiconductor manufacturer in Taiwan was employed using the developed index to verify the improvement in predicted accuracy.