Proton beam written hydrogen silsesquioxane (HSQ) nanostructures for Nickel electroplating

Hydrogen silsesquioxane (HSQ) behaves as a negative resist under MeV proton beam exposure. HSQ is a high-resolution resist suitable for production of tall (< 1.5 μ m) high-aspect-ratio nanostructures with dimensions down to 22 nm. High-aspect-ratio HSQ structures are required in many applications, e.g. nanofluidics, biomedical research, etc. Since P-beam writing is a direct and hence slow process, it is beneficiary to fabricate a reverse image of the patterns in a metallic stamp, e.g. by Ni electroplating. The Ni stamp can then be used to produce multiple copies of the same pattern. In this study we investigate the possibility to produce Ni stamps from p-beam written HSQ samples. HSQ high aspect ratio nanostructures, however, tend to detach from Au/Si substrates (typically used in electroplating) during the development process due to the weak adhesive forces between the resist and the substrate material. To determine an optimal substrate material and the proton irradiation doses for HSQ structures, a series of 2 μm long and 60-600 nm wide free-standing lines were written with varying doses of 2 MeV protons in 1.2 μm thick HSQ resist spun on Ti/Si, Cr/Si and Au/Cr/Si substrates. The results indicate that both Ti/Si and Cr/Si substrates are superior in terms of adhesion. The adhesion of high aspect ratio HSQ nanostructures to Au/Cr/Si is poor with a maximum aspect ratio of the adhering structures not exceeding two. Cr/Si is not suitable as a substrate for HSQ resist as debris is formed around the structures, presumably due to a chemical reaction between the resist and Cr.