Comparison of wafer-level spatial IDDQ estimation methods: NNR versus NCR

Extending the useful life of I_DDQ test to deep submicron technologies has been a topic of interest in recent years. I_DDQ test loses its effectiveness as the signal to noise ratio degrades due to rising background current and fault-free I_DDQ variance. Defect detection using I_DDQ test requires separation of deterministic sources of variation from defective current. Several methods that use deterministic variation in I_DDQ at the wafer level for estimating fault-free I_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.