The technological window determining for high-aspect x-ray lithography

Deep X-ray lithography is often used to produce high-aspect 3D structures. The quality of the structures formed by this method depends not only on the conditions of X-ray transfer of the topology of the pattern formed on the X-ray mask, but also on the conditions of resist development (the solvent used, development modes, etc.). To optimize the matching of conditions, it is also necessary to determine the process window, within which the range of exposure doses and the contrast of the mask are matched with the specific conditions of development of the resist used. The paper presents the results of determining the process window for high-aspect X-ray lithography. The algorithm used is based on the analysis of the behavior of the function of a given ratio of the dissolution rates of the resist under transparent and opaque areas of the lithographic mask (X-ray mask). Two different types of polymethyl methacrylate (PMMA) were used as a resist. The polymerization conditions of PMMA significantly affect its final properties, including its lithographic characteristics. The proposed algorithm assumed the 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 specified conditions. It is shown that this algorithm provides experimental repeatability of results and high quality of the formed relief. The obtained results can be used in the manufacture 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.