Fabrication tolerance analysis of mask grating for pattern-specific off-axis illumination

초록

In general, an off-axis illumination provides the effect of the oblique illumination over the whole area of a mask. Sometimes, this global nature causes a problem that the illumination cannot be adaptive to local specific patterns. So, a new off-axis illumination method using a phase grating formed on the mask plate has been proposed by several authors [1-8]. In order to realize pattern-specific off-axis illumination under a normal illumination, we use a transparent phase grating formed on the top side of a photo mask. Unlike the conventional off-axis illumination, the mask grating allows locally different illumination depending on the Cr pattern defined on the bottom side of the mask. In this paper, the structure of the mask grating was determined from the feature characteristics of the Cr pattern and its performance was evaluated with the simulated aerial images and the intensity profiles. Lastly, the fabrication tolerance of the mask grating was also evaluated by putting additional error in width and phase of the optimized mask grating.