Thermochemical laser writing of chromium grayscale masks and their application for fabrication of multilevel diffractive optical elements

Abstract

The paper presents the results of developing a technology for direct laser writing of grayscale photomasks on thin (30-50 nm) chromium films. The contrast of grayscale microimages reaches 10, which is comparable to the characteristics of LDW-glass. The technique is based on dependence of chromium oxide layer thickness formed at laser heating on exposure dose. The oxide layer is then used as a analog mask for underlaying Cr film. The written grayscale masks are used to fabricate multilevel diffractive optical elements by the method of grayscale lithography. The photoresist layer was exposed by contact printing through the grayscale mask. Diffractive optical elements with a sawtooth profile depth in the range of 1-4 μm are made. The angle of the backward slope of the diffractive zones was 60 degrees. The article discusses examples of the use of chromium grayscale masks for fabrication of various 3D structures.