Comparison of wafer-level spatial I/sub DDQ/ estimation methods: NNR versus NCR

Extending the useful life of I/sub DDQ/ test to deep submicron technologies has been a topic of interest in recent years. I/sub DDQ/ test loses its effectiveness as the signal to noise ratio degrades due to rising background current and fault-free I/sub DDQ/ variance. Defect detection using I/sub DDQ/ test requires separation of deterministic sources of variation from defective current. Several methods that use deterministic variation in I/sub DDQ/ at the wafer level for estimating fault-free I/sub DDQ/ of a chip are proposed. This paper compares two such methods: nearest neighbor residual (NNR) and neighbor current ratio (NCR). These methods are evaluated using industrial test data for a recent technology.