Advanced CD-SEM metrology to improve total process control performance for hyper-NA lithography

In this research, we improved litho process monitor performance with CD-SEM for hyper-NA lithography. First, by comparing litho and etch process windows, it was confirmed that litho process monitor performance is insufficient just by CD measurement because of litho-etch CD bias variation. Then we investigated the impact of the changing resist profile on litho-etch CD bias variation by cross-sectional observation. As a result, it was determined that resist loss and footing variation cause litho-etch CD bias variation. Then, we proposed a measurement method to detect the resist loss variation from top-down SEM image. Proposed resist loss measurement method had good linearity to detect resist loss variation. At the end, threshold of resist loss index for litho process monitor was determined as to detect litho-etch CD bias variation. Then we confirmed that with the proposed resist loss measurement method, the litho process monitor performance was improved by detection of litho-etch CD bias variation in the same throughput as CD measurement.