Mask-structure and process to repair missing or unwanted phase-shifting

Abstract

A phase-shifting mask is composed of material including a substrate carrying a first phase-shifting layer having a phase-shift of .THETA., a second phase-shifting layer stacked upon the first layer having a phase-shift of (2.pi.-.THETA.), and a third phase-shifting layer stacked upon the second layer next with a phase-shift of .THETA.. Missing phase-shifters, unwanted phase-shifters, or defects in the transparent films are repaired by removing one or two layers depending upon whether the phase-shifting status has to be retained or altered. In one alternative a large etch selectivity exists between the first, second and third layers, or else a lack of etch selectivity is complemented with etch stop layers embedded between the phase-shifting layers as follows: a) if an defect is found in a phase-shifted area and the defect must be removed without turning the phase-shifted area into a non-phase-shifted area, then two successive layers in the phase-shifted area are removed; b) if an error is found in a non-phase-shift area, then the mask can be repaired in the area surrounding the error by removing the layer in the area to make the area a phase-shifted area; c) if a defect is found in a non-phase-shifted area and the defect must be removed without turning the phase-shifted area into a phase-shifted area, then two successive layers in the non-phase-shifted area are removed.