Effect Of Resist Side-Wall Slope Variations On Confocal Optical Metrology

This paper presents results from an experimental study of the effects of resist side-wall slope variations on the linewidth measurement accuracy of a Confocal Scanning Laser Microscope (CSLM), as compared with a Scanning Electron Microscope (SEM). Both the top and bottom dimensions of patterned resist features from 0.51 μm to 2.0 μm wide were measured using CSLM, cross-sectional SEM and on-axis SEM. Substrates tested included bare silicon and three thicknesses of oxide on silicon. The resist was patterned with a range of deliberate stepper defocus which provided a 15° variation in side-wall angle. Data for the three methods is compared and shows that in this case the CSLM demonstrated good measurement accuracy for independent top and bottom width measurements. Errors due to resist sidewall slope variation were small, random and consistent with the experimental noise level.