Patent ID: 7820343

Claim:
A method for producing a photomask, which comprises: providing a mask substrate comprising first and second structure layers, the second structure layer disposed above the first structure layer and having a surface defining a substrate surface; applying a first resist material on the substrate surface, the first resist material having a first sensitivity with respect to an exposure dose; applying a second resist material above the first resist material to produce a resist stack, the second resist material having a second sensitivity with respect to the exposure dose, the second sensitivity being lower than the first sensitivity; carrying out an exposure step in which the resist stack is subjected to a locally different exposure dose in defined regions of the substrate surface, the exposure dose varying locally between a first exposure and a second exposure dose and the first exposure dose being less than the second exposure dose; developing the resist stack to uncover the substrate surface only at locations at which the resist stack was subjected to the second exposure dose; etching the first and second structure layers of the mask substrate at the locations where the substrate surface is uncovered using the resist stack as an etching mask; completely removing the second resist material after etching the first and the second structure layers; developing the first resist material after removing the second resist material, the substrate surface being uncovered at locations at which the resist stack was subjected to the first exposure dose; etching the second structure layer of the mask substrate at locations where the substrate surface is uncovered using the first resist material as an etching mask; and completely removing the first resist material after etching the second structure layer.