Effect of lens aberration on oblique-illumination stepper system

Abstract

In this paper, detailed simulation and some experimental studies on stepper lens aberration effect in the case of oblique illumination source are presented. The results are compared to that of conventional illumination source. Due to the unique feature of oblique illumination source imaging, i.e., imaging by using only zero and first diffraction order light, both stepper resolution limit and depth of focus (DOF) are extended. As a result, the effect of lens aberration in resist printing are also different from that of conventional illumination source. Unlike the conventional illumination source, the net effect of stepper lens aberration in resist printing depends not only on both the amount and type of the lens aberration, but also on the mask feature pattern. In the case of lens distortion, unlike the other types of lens aberration, the oblique illumination source does not show any improvement as compared to that of conventional illumination source. It does not show pattern dependent distortion either. In the experiment, an effect of a stepper lens aberration in resist printing for both conventional illumination and quadrapole illumination sources (mostly astigmatism) were measured. The results were in agreement with our simulation results.