Development and empirical verification of an accuracy model for the power down leakage tests

Power down leakage (PDL) test is one of the most sensitive tests to verify device integrity during production test. Generally, the PDL current is measured once at the beginning and once at the end of the production test cycle in order to verify that the test process has not degraded device integrity. This current measurement is typically repeated 100 times or more to achieve accurate results. A wide variation in the measurement results usually necessitates additional measurements and averaging. However, without the proper modeling and analysis, repeating the measurement and averaging results alone will not guarantee the accuracy. In this paper, we analyze root causes of the error for the PDL current measurements. Our analysis indicates that while quantization error and thermal noise have negligible impact on the error of the measurements, the instrument accuracy, timing, and temperature based variation are the major contributors to accuracy. We develop a new accuracy model for the PDL current measurement to account for these major contributors. Using this model, we propose a new systematic optimization method for the test process to achieve the desired accuracy without increasing the test time unreasonably. This method and the model are empirically verified with hardware experiments. With hardware experiments we also show that we can reduce the test time nearly 3-fold using the optimized test sequencing strategy.