Patent ID: 7033947

Claim:
A method for fabricating a dual-trench alternating phase shift mask (PSM) comprising: patterning an opaque layer over a mask layer over a transparent layer of the PSM according to a semiconductor design; first dry etching the mask layer according to deep trenches of an alternating PSM design to remove the mask layer from the deep trenches of the alternating PSM design; first dry etching a first plurality of times the transparent layer through a first photoresist layer applied over the opaque layer and patterned according to the deep trenches of the alternating PSM design by using backside exposure, to initially form deep trenches of the PSM; second dry etching the mask layer according to shallow trenches of the alternating PSM design to remove the mask layer from the shallow trenches of the alternating PSM design; second dry etching a second plurality of times the transparent layer through a second photoresist layer applied over the opaque layer and patterned according to the shallow trenches and the deep trenches of the alternating PSM design by using backside exposure, to completely form shallow trenches and the deep trenches of the PSM; and wherein first dry etching the first plurality of times the transparent layer comprises first dry etching the transparent layer sixty degrees for each of the first plurality of times.