New SWEAT method for fast, accurate and stable electromigration testing on wafer level

The Standard Wafer Level Electromigration Accelerated Test (SWEAT) is one of a few highly accelerated stress tests of metal-line test structures that are used to monitor electromigration resistance. Earlier works and our own examinations have shown that when the JEDEC standard SWEAT method is used, unexpectedly large sigmas are observed that could sometimes be traced to the existence of bimodal failure-time distributions. We show that the cause for these anomalous behaviors is the algorithm in the JEDEC standard method that is used in the control loop to adjust the stress current so that a constant target failure time is maintained. A new algorithm is described and experimental results are given to demonstrate its effectiveness