2-D Modeling Capability Certification of Optical Critical Dimension (OCD) Metrology Tool by Sigma Shape PMOS Silicon Recess Structure

Abstract

Optical Critical Dimension (OCD) metrology is a much popular and efficient way to monitor structure sizes such as heights, side wall angles (SWAs), and critical dimensions (CDs). Due to the continuous shrinkage of feature sizes, the IC process is becoming more and more complicated. The growing demand on the OCD applications always outpaces the development of OCD-technology capabilities. Thus, we have to find a more reliable method and a special structure to certify the capability of OCD modeling and library stability, so as to improve the measurement performance as much as possible. In this paper, we selected a 2-D Sigma Shape PMOS Silicon Recess (Σ-PSR) structure for the OCD modeling evaluation and established a certification procedure as well as a relevant evaluation method, which includes the design of DOE (Design of Experiment) wafers, the handbook for data collections, the scoreboard for OCD result analysis for verifying both OCD 2-D modeling performance and library stability. The DOE wafers were processed to form different PSR structures such as total silicon recess depth, sigma height, pull back, tip-off-gate, undercut, and spacer width splits, etc. There are 17-output required parameters for the OCD modeling. At least, 9 floating parameters are necessary to build the Σ-PSR model. The accuracy of the DOE trend and the precision, stability, and GRR (Gauge Repeatability and Reproducibility) of all output parameters were analyzed to evaluate the capability of the OCD modeling. TEM data were also collected to demonstrate the OCD performance of Σ-PSR profile monitor. Finally, we summarized the evaluation method and discussed the future OCD certification work by advanced reference metrology tools.