Comparative study of two KLA-Tencor advanced patterned wafer inspection systems

As device minimum feature sizes shrink, IC manufacturers face a challenge to increase wafer yields with minimum learning cycles. The use of in-line patterned wafer inspection systems for rapid product ramp and high yield is critical. Two KLA-Tencor patterned wafer inspection tools were evaluated in Texas Instruments´ KFAB: the Optical Ultra Broadband 2138, and the Laser Double Dark Field AIT2. The strength of the AIT2 is its low illumination angle, which highlights surface particles, scratches, and pattern issues, while minimizing effects due to previous level defects. On the other hand, the 2138 is a very powerful tool in detecting very small defects in dense patterned areas such as the SRAM. TI and KLA-Tencor undertook a study to characterize the operating characteristics and benefits of these two inspection tools. The AIT2´s inspection performance on several process levels were evaluated against the 2138´s results with the goal of maximizing capture rate of total defects and critical defect types in order to justify transitioning inspections to the AIT2. Performance of each tool was monitored by two metrics: defect capture rate and defect pareto. In this paper, we report the comparative results that led to the transition of several process level inspections from the 2138 to the AIT2 without jeopardizing the integrity of the inspection, effectively providing more capacity on the 2138´s