ArF-resist line width slimming variation with threshold level in high precision CD-SEM measurement

Line width slimming (LWS) occurring in ArF photo-resist is measured with various threshold levels. The LWS decreases as the threshold level decrease, with electron’s landing voltage (Ve) = 800 V. Contrary to this, with Ve = 300 V the LWS slightly increases as the threshold level decrease. The line edge detected by threshold = 20% locates in the sidewall where the elevation angle is nearly zero, whilst the line edge by threshold = 80% locates in the top corner where the elevation angle is more than 30 degrees. To estimate the electron dose that is sensitive to the elevation angle of the incident electron, we used an in-house made Monte Carlo simulator. The LWS variation with the threshold level can be explained by calculated electron dose ratio that is sensitive to the elevation angle.