Application of model-based library approach to Si 3 N 4 hardmask measurements

Abstract

ABSTRACT The model-based library (MBL) matching technique was applied in hardmask linewidth metrology with a critical-dimension scanning electron microscope (CD-SEM). The MBL matching measures the edge positions and shapes of samples by comparing simulated images to measured images . To achieve reliable, stable measurements, two important simulation parameters were determined empirically. One was the beam width, and the other was a material parameter, the residual energy loss rate. This parameter is especially important for measurement of hardmask patterns, which have relatively high SEM image contrast. These simulation parameters were estimated so as to fit to actual SEM images, and then pinned to the estimated values during MBL matching. Hardmask patterns made of Si 3 N 4 were measured by MBL matching with the estimated parameters. The accuracy of the measurements was evaluated by one-to-one comparison with atomic force microscope (AFM) re sults. The pattern profile deduced from only the top-down CD-SEM image with MBL matching agreed well with the AFM profile and a scanning transmission electron microscope (STEM) cross-sectional image. The average measurement bias between the MBL matching and AFM results was 1.58 nm for the bottom CD and -0.64 nm for the top CD, with a standard deviation of about 1.3 nm. Keywords: CD-SEM, measurement bias, model-based library, hardmask metrology, Monte Carlo simulation