Method of fabricating phase shift mask

摘要

A method of fabricating a phase shift mask (PSM) is described. A patterned photoresist layer is formed on an opaque layer over a transparent plate. A thin mask layer is formed on the sidewalls of the patterned photoresist layer. The exposed opaque layer and transparent plate thereunder are then removed while using the patterned photoresist layer and mask layer as a mask. A phase shift opening is formed in the transparent plate, and thereby a phase shift layer is formed at the place where the phase shift opening is located. The patterned photoresist layer and the opaque layer thereunder are then removed to expose the transparent plate. The opaque layer under the mask layer can precisely self-align the phase shift layer to prevent alignment deviation caused by multiple lithography processes. The precision of the phase shift mask can be increased, and mask manufacture cost can be lowered.