Patent ID: 7754399

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 substrate comprising a defined main-field region having a lateral periphery, and a defined boundary region surrounding an entirety of the lateral periphery of the main-field region; the relatively opaque material within the main-field and boundary regions being first and second portions of the relatively opaque material, respectively; providing a first mask which covers a majority of the second portion of the relatively opaque material and leaves the first portion exposed, the first mask having a first thickness; reducing the thickness of the first portion of the relatively opaque material while protecting at least the majority of the second portion of the relatively opaque material with the first mask; removing the first mask, and thereafter forming a second mask which is patterned over the main-field region, the second mask having a second thickness which is less than the first thickness; and transferring the pattern from the second mask into the main-field region to pattern the phase-shifting material.