Determining the Technological Window for High-Aspect X-ray Lithography

Deep X-ray lithography is often used to produce high-aspect 3D structures. At the same time, the quality of the structures formed by this method depends not only on the conditions of transfer of the topology of the pattern formed on the X-ray template by X-ray radiation, but also on the conditions of the development of the resist (the solvent used, development modes, etc.). To optimize the matching of conditions, it is also necessary to define a technological window, within which the exposure dose range and template contrast are matched to the specific conditions of development of the resist used. In this article, the results of determining the technological window for high-aspect X-ray lithography are presented. The algorithm used is based on the analysis of the behavior of the function of a given ratio of the rates of resist dissolution under transparent and opaque areas of the lithographic mask (X-ray template).Two different types of polymethylmethacrylate (PMMA) are used as resist. The conditions of PMMA polymerization significantly affect its final properties including lithographic characteristics. The proposed algorithm assumes assignment of the ratio of the maximum and minimum rates of development of irradiated PMMA and knowledge of the mathematical formula of the characteristic curve describing the development process in a certain solvent and under given conditions. It is shown that this algorithm ensures experimental repeatability of results, as well as high quality of the relief being formed. The results can be used in the production of high-aspect structures from X-ray resist or X-ray sensitive material (a material, whose dissolution rate varies depending on the received exposure dose). In addition, the developed algorithm can be applied to other types of lithographic processes if the formula describing the characteristic curve is known.