Patent ID: 7998355

Claim:
A method of forming a mask for printing a pattern comprising a plurality of features, said method comprising the steps of: depositing a layer of transmissive material having a predefined percentage transmission on an upper surface of a mask substrate; depositing a layer of opaque material on said transmissive material; etching a portion of said mask substrate to achieve a partial etching depth less than a target depth, said partial etching depth being based on an etching selectivity between said transmissive layer and said mask substrate; exposing a portion of said patterned transmissive layer by etching said opaque material; and etching said exposed portion of said transmissive layer so as to expose a portion of said upper surface of said mask substrate from underneath the patterned transmissive layer, said etched portion of said mask substrate being further etched along with said transmissive layer, thereby achieving the target depth; wherein said exposed portion of said upper surface of said mask substrate and said etched portion of said mask substrate further etched along with said transmissive layer exhibit a predefined phase shift relative to one another with respect to an illumination signal impinging on the mask.