Roughness of EUV resists exposed to EUV, ArF and KrF radiation as evaluated using three tools: spectroscopic ellipsometry, AFM and SEM

Abstract

Surface roughness(SR) of the EUV resists exposed to EUV, ArF and KrF radiation has been investigated using three tools: spectroscopic ellipsometry (SE), AFM and SEM. The purpose of this paper is to do determine whether SE can effectively monitor the change in resist SR, and also whether we can see the effect of photon shot noise in resist patterning. EUV resists were coated on three blank wafers, and on the shot basis, exposed to different dose of each radiation. After completion of resist process, the SR was measured first with SE. Then the wafer was sliced into patches of different dose before AFM and SEM measurements were made. SE used effective medium approximation to calculate the roughness-layer thickness as a parameter for fitting to experimental data. Thus obtained thicknesses showed a monotonic correlation with AFM-measured roughness, indicating SE can be a fast, precise and nondestructive tool to evaluate resist SR, once being calibrated with AFM. In order to examine the photon shot noise effect on the resist pattern, all the steps of the resist process was kept the same except the exposure wavelength and its dose. SE results for the three exposures were compared over the full range of doses in common. The three roughness values near the dose to clear, Eclear, apparently provide an evidence that the photon shot noise played a significant role in our experiment.