Stress Aware Quiescent Current Test Optimization

Abstract

The test escapes due to latent gate oxide (GOx) shorts have been challenging the relentless pursuit of zero defects, despite of voltage stress testing executed to screen such defects. This scenario underscores a prevailing uncertainty in semiconductor testing, "Are we stressing enough?". Moreover, the increasing complexity of digital circuits, coupled with stringent test time requirements, makes 100% fault coverage an unrealistic targetThis paper presents a solution to optimize voltage stress methodology, and quantify and maximize stress coverage for Integrated Circuits (ICs). The proposed solution involves three key methods. The first method, Critical Thickness Model (CTM), addresses the question "Are we stressing enough?" by determining the minimum stress period of n and p type MOSFET with gate oxide (GOx) thickness in the sub-3nm range. The second method, Stress Coverage Quantification Algorithm (SCQA), assesses actual defect coverage by calculating the percentage of transistors stressed. The third method, Coverage Maximization Algorithm (CMA), aims to reduce customer returns due to GOx shorts by minimizing test escapes. Finally, the paper explores the possibility of Stress Aware ATPG and discusses the trade-offs between under-stressing and over-stressing. The application of CTM resulted in stress time reduction by a factor of 103, thereby reducing test cost and improving yield. Furthermore, SCQA reveals that the ATPG reported coverage is overestimated and differs with SCQA by 6.2%. CMA selected patterns resulted into 2.88% higher coverage, reducing voltage stress test escapes by 10%, improving the quality of voltage stress test.