Patent ID: 7442472

Claim:
A method of forming a reticle, comprising: providing a reticle substrate having a relatively transparent base, a phase-shifting material over the base, and a relatively opaque material over the phase-shifting material, the relatively opaque material being at a first relatively opaque material thickness; the substrate comprising a defined main-field area having a lateral periphery, and a defined boundary area surrounding an entirety of the lateral periphery of the main-field area; the relatively opaque material within the main-field and boundary areas being first and second portions of the relatively opaque material, respectively; providing a first photoresist mask which covers a region of the second portion of the relatively opaque material and leaves a region of the first portion exposed, the first photoresist mask having a first photoresist thickness; thinning the exposed relatively opaque material while protecting the remainder of the relatively opaque material with the first photoresist mask, the thinning causing at least some of the relatively opaque material within the main-field area to have a second relatively opaque material thickness which is less than the first relatively opaque material thickness, while leaving at least some of the relatively opaque material within the boundary area at the first relatively opaque material thickness; removing the first photoresist mask, and thereafter forming a second photoresist mask which is patterned over thinned relatively opaque material across the main-field area, the second photoresist mask having a second photoresist thickness which is less than the first photoresist thickness; and transferring the pattern from the second photoresist mask into the main-field area to pattern the phase-shifting material.