Non-destructive depth measurement using SEM signal intensity

In this paper, we introduce a novel approach measuring the pattern depth, using non-destructive CD-SEM platform. We derived a dimensionless metrics called as “depth index,” that is designed to be proportional to the pattern depth. The depth index is calculated by using the SEM signal intensity and the pattern geometry accessible by normal CD-SEM. As a proof-of-concept, the depth index is obtained on the etched hole patterns fabricated in 300 mm wafer with different depth, and the depth correlation with reasonable measurement repeatability of 1% is confirmed. The depth index has been applied to the process variation monitor in NAND Flash memory, and the local depth variation of the holes of 4% is confirmed. The intra-wafer variation of 7-10%, and the wafer-to-wafer variation have been also detected.