SHEWMA: An end-of-line SPC scheme using wafer acceptance test data

In this paper, an end-of-line quality control scheme based on wafer accepta nce test (WAT) data is presented, Due to the multiple-stream and sequence-d isorder effects typically present in the WAT data, an abnormal process shif t caused by one machine at an in-line step may become vague for detection u sing end-of-line WAT data. A methodology for generating robust design param eters for the simultaneous application of Shewhart and EWMA control charts to WAT data is proposed. This SHEWMA scheme is implemented in a foundry env ironment and its detection and diagnosis-enhancing capabilities are validat ed using both numerical derivations and fab data. Results show that the SHE WMA scheme is superior to the current practices in detection speed. Its use is complementary to the existing in-line SPC for process integration.