SEM based overlay measurement between Via patterns and buried M1 patterns using high voltage SEM

The miniaturization of semiconductors continues, importance of overlay measurement is increasing. We measured overlay with analysis SEM called Miracle Eye which can output ultrahigh acceleration voltage in 1998. Meanwhile, since 2006, we have been working on SEM based overlay measurement and developed overlay measurement function of the same layer using CD-SEM. Then, we evaluated overlay of the same layer pattern after etching. This time, in order to measure overlay after lithography, we evaluated the see-through overlay using high voltage SEM CV5000 released in October 2016. In collaboration between imec and Hitachi High-Technologies, we evaluated repeatability, TIS of SEM-OVL as well as correlation between SEM-OVL and Opt-OVL in the M1@ADI and V0@ADI process. Repeatability and TIS results are reasonable and SEM-OVL has good correlation with Opt-OVL. By overlay measurement using CV 5000, we got the following conclusions. (1) SEM_OVL results of both M1 and V0 at ADI show good correlation to OPT_OVL. (2) High voltage SEM can prove the measurement capability of a small pattern( Less than 1 similar to 2um) like device that can be placed in-die area. (3)"In-die SEM based overlay" shows possibility for high order control of scanner.