Synthesis of silsesquioxanes with steroid derivatives and their application as photoresist

Abstract

In this paper, new silsesquioxane based polymers with cholic acid derivatives were synthesized. They were synthesized by hydrolysis of ethoxy group with base catalyst. The polymers have etch-resistance moiety (cholic acid derivatives), adhesion promotion moiety (polar ester groups in spacer), and solubility change moiety (t-butoxy group in cholates) in every repeating unit. Two monomers with similar structure were prepared. The difference between two monomers is that it has one more $CH_2$ bond. Bilayer resist consists of two layers, which are imaging layer and planarizing layer. Bilayer resist system has several advantages. First of all, imaging layer of the system could have relatively high absorbance. Second, anti-reflective planarizing layer diminishes defects caused by reflection like standing wave effect. Third, depth of focus problem doesn’t exist because imaging layer is thin. Finally, high aspect ratio features can be obtained by $O_2-RIE$. Polymers are thermally stable up to 160℃. While poly(allyl-TBC-SSQ) did not show no L/S pattern, poly(AC-TBC-SSQ) revealed L/S patterns with 15mJ/㎠ . The 3μm pattern line and space pattern was obtained from positive type resist, poly(AC-TBC-SSQ), applying hard baked novolac resin to planarizing layer. They showed latent image caused by evaporation of isobutylene. Poly(AC-TBC-SSQ) has some resistance for the $O_2$ RIE, but the resistance was not enough for fine pattern formation. Because low content of silicon in the polymer may be the cause of this, effort to increase the content will be proceeded.