Hydrogen silsesquioxane double patterning process for 12 nm resolution x-ray zone plates

Soft x-ray zone plate microscopy is a powerful nanoanalytic technique used for a wide variety of scientific and technological studies. Pushing its spatial resolution to 10 nm and below is highly desired and feasible due to the short wavelength of soft x rays. Instruments using Fresnel zone plate lenses achieve a spatial resolution approximately equal to the smallest, outermost zone width. In this work, a double patterning zone plate fabrication process is developed. based on a high resolution resist, hydrogen silsesquioxane (HSQ), to bypass the limitations of conventional single exposure fabrication to pattern density, such as finite beam size, scattering in resist, and modest intrinsic resist contrast. To fabricate HSQ structures with zone widths on the order of 10 nm on gold plating base, a surface conditioning process with (3-mercaptopropyl) trimethoxysilane, 3-MPT, is used, which forms a homogeneous hydroxylation surface on gold surface and provides good anchoring for the desired HSQ structures. Using the new HSQ double patterning process, coupled with an internally developed, subpixel alignment algorithm, the authors have successfully fabricated in-house gold zone plates of 12 nm outer zones. Promising results for 10 nm zone plates have also been obtained. With the 12 nm zone plates, they have achieved a resolution of 12 nm using the full-field soft x-ray microscope, XM-1.