High-aspect-ratio microstructures fabricated by X-ray lithography of polymethylsilsesquioxane-based spin-on glass thick films

Abstract

 In this paper, a process for 200 μm high-aspect-ratio micro-optical (HARM) structures fabricated by deep X-ray lithography (DXRL) of polymethylislesuioane-based spin-on glass (SOG) thick films is presented. The SOG material used in the whole procedures is polymethylsilsesquioxane (GR650), which is a kind of sol-gel derived material and can be cured at a reasonable low temperature (75 °C). A technique to cast thick GR650 films was established in the overall process. After consolidation, the GR650 thick films were machined to reach 200 μm uniformly. Then, as negative resists, the GR650 thick films were patterned directly by DXRL. X-ray irradiated regions can be selectively retained with high structural resolution by development in an organic solvent, such as methanol. Parameter screening was done to find minimum and maximum doses needed for patterning/cross-linking, to vary development time, and to explore different film thickness. The whole process is a novel of technique to create HARM structures based on SOG materials without using molds. This technique can be extended to considerably larger structural heights. Surface and bulk compositions of the irradiated films were measured by XPS and Fourier transform infrared spectroscopy. Surface quality by roughness testing system (WYKO RST) was investigated to fabricate the microstructure with a high-accuracy surface.