Local variables measured using large field of view SEM images

In this work, the measurement of local variables such as Line Edge Roughness (LER) and Line Width Roughness (LWR) in large field of view (FoV) Scanning Electron Microscopic (SEM) images is demonstrated. We show that larger FoV images include more of the lower frequency components in the roughness profile and hence these variables are measured more accurately. We also show that larger FoV images provide a better statistics which improves the precision of the measurement significantly. We also address the impact of image distortion on LER as the main challenge of large FoVs. The study is performed on large FoV 8µm×8µm images with line/space features, acquired by massive metrology capability of a high throughput eP5 SEM. We crop the images to smaller ones and compare the results measured for different FoVs, with and without distortion correction. We see that by the distortion correction, especially in low frequency, we can calculate the local variables accurately.