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Investigation of Optimum Biasing and Undercut for Single Trench Alternating Phase Shift Mask in 193 nm Lithography

The use of an alternating phase shift mask is an effective method of improving resolution compared with binary and embedded attenuated phase shift mask technologies, but the intensity imbalance between the light propagating through the zero- and π-shifted spaces is the main obstacle to be overcome. Several technical methods are proposed to compensate for such an imbalance in the mask manufacturing process. The known general solutions for the intensity imbalance are applying a space bias and/or an undercut of the space region of the alternating phase shift mask. We evaluated the uniformity of the resist profile after the application of a space bias or an undercut of the mask space region in order to minimize the pattern position displacement and the critical dimension difference between the phase-shifted and unshifted regions for the 90 and 65 nm nodes. Additionally, we found that the imperfect side wall angle of an undercut or a space bias obviously affected the quality of pattern fidelity and hence investigated how the side wall angle affects pattern printability.