An efficient scan diagnosis methodology according to scan failuremode for yield enhancement

摘要

Yield has always been a driving consideration during fabrication of modern semiconductor industry. Statistically, thelargest portion of wafer yield loss is defective scan failure. This paper presents efficient failure analysis methods forinitial yield ramp up and ongoing product with scan diagnosis. Result of our analysis shows that more than 60% of thescan failure dies fall into the category of shift mode in the very deep submicron (VDSM) devices. However, localizationof scan shift mode failure is very difficult in comparison to capture mode failure because it is caused by the malfunctionof scan chain. Addressing the biggest challenge, we propose the most suitable analysis method according to scan failuremode (capture / shift) for yield enhancement. In the event of capture failure mode, this paper describes the method thatintegrates scan diagnosis flow and backside probing technology to obtain more accurate candidates. We also describeseveral unique techniques, such as bulk back-grinding solution, efficient backside probing and signal analysis method.Lastly, we introduce blocked chain analysis algorithm for efficient analysis of shift failure mode. In this paper, wecontribute to enhancement of the yield as a result of the combination of two methods. We confirm the failure candidateswith physical failure analysis (PFA) method. The direct feedback of the defective visualization is useful to mass-producedevices in a shorter time. The experimental data on mass products show that our method produces average reduction by13.7% in defective SCAN & SRAM-BIST failure rates and by 18.2% in wafer yield rates.