Enhancing the electron beam sensitivity of hydrogen silsesquioxane (HSQ)

The electron beam sensitivity of hydrogen silsesquioxane (HSQ) has been enhanced by including sensitizers that decompose to generate nucleophiles which catalyze the conversion of the silicon hydride (Si-H) moieties in HSQ into the insoluble siloxane (Si-O-Si) network. In this study, the consequences of including triphenylsulfonium hydroxide (TPS-OH) and 2-nitrobenzyl N-cyclohexylcarbamate (NBC) as a photodecomposable base (PDB) and photobase generator (PBG) were investigated, respectively. It was found that using 5 wt% loadings of TPS-OH or NBC in HSQ in conjunction with a post-exposure bake process enhanced the sensitivity of large features exposed at 25 keV accelerating voltage by approximately 50 and 40 %, respectively. Similarly, the electron beam doses required to print single pixel wide lines exposed at an accelerating voltage of 25 keV were enhanced by 70 and 50%, for 5 wt% loaded TPS-OH or NBC films, respectively. It was also found that the basicity and nucleophilic strength of the sensitizer affects the rate of the undesired hydrolysis reaction of HSQ which occurs in solution. For the sensitizers used in this study, the sterically hindered TPS-OH is a poor nucleophile which stabilized the solution against condensation and formation of a siloxane network, while the moderately nucleophillic NBC slightly decreased the stability of the solution. Also, it was found that thermal baking alone could be utilized to enhance the sensitivity of HSQ, but a drastic loss in contrast was observed. The combination of either TPS-OH or NBC and a post-exposure bake produced superior results, as compared to thermal baking alone, in terms of increasing the sensitivity of HSQ while maintaining good contrast.