Fabrication of polyimide masks for x-ray lithography

Abstract

The dimensional stability of a polyimide membrane is a key to the successful fabrication of x-ray masks. It depends upon fractionation, purification, and the degradation prevention of polyamic acid. The polyimide membranes thus obtained have a great tensile stress so that the membrane flatness and distortion in a 30×40 mm rectangular window area are less than 1 μm and 0.2 μm, respectively. The advantages of using a polished glass plate as a substrate are good flatness, low cost, ease of fabrication, and also that the masks’ dimensions can be made large enough at will.