Phase-Shift Photomask Designed by Scalar Diffraction Theory

Abstract

This work describes the design of a phase shift lithographic photomask for operation in proximity printing mode. The design explores the freedom of the diffraction of light by travelling along the distance between the mask plane and the wafer plane. To this end, a phase and amplitude modulation distributions was generated, which have to be used in the fabrication of the proposed photomask. Then a photomask with test structures containing several geometric features was fabricated. It is able to modulate both phase and amplitude of the incoming wavefront during exposure of a wafer. The lithographic image to be patterning must be projected onto the wafer plane, located at a distance of 50 µm behind the mask. The 50 µm gap is a necessary condition to explore the diffraction of light in order to improve the resolution when compared with traditional binary masks in proximity printing mode.