Method of forming small contact holes using alternative phase shift masks and negative photoresist

摘要

A phase shifting mask set and method of using the phase shifting mask set to pattern a layer of negative photoresist. The mask set comprises a first phase shifting mask and a second phase shifting mask. The first and second phase shifting masks have regions of 90° phase shift and -90° phase shift in the contact hole regions of the masks. In the second phase shift mask the phase shift regions are rotated 90° spatially with respect to the phase shift regions of the first phase shift mask. A layer of negative photoresist is exposed with the first and second phase shift masks and developed to form the photoresist pattern used to form contact holes.