Chromeless phase-shifting photomask with undercut rim-shifting element

A method of manufacturing a phase-shifting photomask having a self-aligned rim-shifting element, the method comprising:

• applying a first patterning film and a second patterning film to a first portion of a transparent substrate;
• etching the transparent substrate to a depth to remove a second portion of the transparent substrate not beneath the first and second patterning films to thereby define a third portion of the transparent substrate above the depth to which the transparent substrate is selectively etched, and a fourth portion of the transparent substrate above the depth to which the transparent substrate is selectively etched;
• applying a conformal film to the transparent substrate;
• using anisotropic etching to form a first sidewall spacer on the third portion of the transparent substrate, and a second sidewall spacer on the fourth portion of the transparent substrate;
• applying an additional photoresist layer atop the second patterning film, the second sidewall spacer, and an area of the transparent substrate adjacent the second sidewall spacer;
• etching the third portion of the transparent substrate and the first portion of the transparent substrate, beneath the first sidewall spacer to undercut an area beneath the first patterning film;
• etching the first portion of the transparent substrate beneath the additional photoresist layer, to undercut the area of the transparent substrate adjacent the second sidewall spacer;
• removing the additional photoresist layer to thereby yield a positive sidewall portion of the transparent substrate, above the first portion of the transparent substrate;
• and
• removing the first and second patterning films;
• wherein the etched transparent substrate forms a self-aligned undercut rim-shifting element.