Use of multiple I/sub DDQ/ test metrics for outlier identification

With increasing circuit complexity and reliability requirements, screening outlier chips is an increasingly important test challenge. This is especially true for I/sub DDQ/ test due to increased spread in the distribution. In this paper, the concept of current ratio is extended to exploit wafer-level spatial correlation. Two metrics - current ratio and neighbor current ratio - are combined to screen outliers at the wafer level. We demonstrate that a single metric alone cannot screen all outliers, however, their combination can be used for effectively screening outlier chips. Analyses based on industrial test data are presented.