Real-time monitoring of test fallout data to quickly identify tester and yield issues in a multi-site environment

摘要

Variations in test fallout during the testing of high-volume devices may arise from a variety of sources. Some of these, such as process variations and design marginalities, correspond to actual problems with the devices being tested and should lead to those devices being scrapped and/or changes being made to the fabrication process. However, in other cases, the test equipment itself could be unreliable or require an alteration in the test procedure, leading to either bad chips tested as good or good chips failing the test. Thus, a real-time monitor of the yield data and the quality of the test result data is essential for assuring high test quality and for ruling out possible issues arising from the test hardware. The real-time monitoring of the yield can save the chip manufacturer time and cost by finding issues with the testing system in the early stages of production (or as soon as those issues arise), avoiding the scrapping of good devices, and preventing the penalty of sending bad units to the customer. In this paper, a low-cost algorithm to monitor the yield of multiple test sites is presented. The method is capable of being implemented in the test program of a standard tester, and the ability of the approach to provide early warning of test site problems during wafer test is demonstrated through an industrial case study.