Phase-shift mask for printing high-resolution images and a method of fabrication

摘要

An improved phase-shift photomask and method of fabrication are described. The method for making this phase-shift mask involves depositing an opaque film, such as chromium (Cr), on a transparent plate, such as SiO2 (quartz plate). An electron beam photoresist layer is deposited on the Cr film and is partially exposed in regions A and completely exposed in closely spaced alternate regions B by an electron beam. The exposed photoresist is then developed. The Cr film is etched in regions B while the remaining resist in regions A protect the Cr from etching. The e-bean resist is plasma etched back to remove the resist over regions A and then the quartz plate in regions B is recessed to a depth d by plasma etching while the Cr protects the quartz in regions A from etching. The recess is etched to a depth to provide an optical path difference between A and B of ½ wavelength (180°) when UV light is transmitted through the mask to expose resist on a product substrate. This 180° phase-shift minimizes the diffracted light under the Cr film between regions A and B and improves the DOF and therefore the photoresist resolution. Since a single e-beam resist is used to make the mask it is more manufacturing cost effective with improved alignment accuracy between regions A and B.