Nanometer-scale fabrication of hydrogen silsesquioxane (HSQ) films with post exposure baking

A nanometer-scale grating structure with a 60-nm-wide gap and 200-nm-wide ridge has been successfully demonstrated on a silicon-on-insulator substrate by using a 220-nm-thick hydrogen silsesquioxane (HSQ) negative tone electron beam resist. A post exposure baking (PEB) process and hot development process with low concentration (3.5 wt%) of tetramethylammonium hydroxide (TMAH) solution were introduced to realize the grating pattern. To study the effects of post exposure baking on the HSQ resist, Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) analyses were carried out. From the FT-IR and XPS analyses, it was verified that a thin SiO2 with high cross-linked network structure was formed on the HSQ surface during the PEB step. This SiO2 layer prevents the formation of unwanted bonds on the HSQ surface, which results in clearly defined grating structures with a 60-nm-gap and 200-nm-wide-ridge on the 220-nm-thick HSQ resist. The nanometer-scale grating pattern was successfully transfered to the 280-nm-thick silicon layer of a silicon-on-insulator (SOI) substrate by using inductively-coupled-plasma-reactive-ion-etching (ICP-RIE).