A Technique for the Non-Destructive EUV Mask Sidewall Angle Measurement Using Scanning Electron Microscope

Abstract

EUV mask absorber sidewall angle should be measured for mask Optical Proximity Correction and shadow effect estimation. Hence, verifying the three-dimensional profile of mask topography has become a challenge in EUV mask inspection. This paper evaluates EUV mask sidewall angle measurement by Field-Emission Critical Dimension (CD)-Scanning Electron Microscope (SEM) using JEOL JSM-7401F. SEM only produces two-dimensional gray images. Forming three-dimensional profiles from these images is a critical requirement for the sidewall angle measurement. To obtain three-dimensional information, absorber edge width has to be measured first to measure sidewall angle. We can calculate absorber sidewall angle with the exactly measured edge width and absorber height. Edge width narrows with steeper sidewall angle. We used the image processing function of Matlab to obtain absorber edge width accurately. In the end, every measured sidewall angle was compared to Transmission Electron Microscope (TEM) images to evaluate the validity of SEM results. Measured sidewall angles by SEM and TEM cross-section images have average tolerances of 0.62 degrees.