Methods for forming thick self-supporting masks

Abstract

A method of constructing a relatively thick, self-supporting mask suitable for electron beam projection processes. Thickness is achieved by multiple steps of coating with resist, exposure and development. Either positive or negative resist may be used for second and subsequent coatings. Second and subsequent exposures are directed through the first relatively thin mask formed and through the substrate to eliminate critical alignment of subsequent masks. When desired thickness is achieved an even thicker frame may be fabricated for support purposes and the mask may then be lifted off the substrate on which it had rested during the fabrication steps. When positive resist is employed, the resist remaining after development is baked on to give added structural strength to the mask. This baked resist can be coated with an additional layer of metal by evaporation or sputtering to give greater mechanical strength. When negative resist is employed, the portions of the resist protected by the relatively thin previously formed mask are removed and additional material is plated to increase the thickness and strength of the mask. The unprotected resist material is then also removed. The completed mask can be further strengthened by evaporating or sputtering an additional layer of metal or oxide.