The present study describes a novel class of ketal-protected chemically amplified positive deep UV photoresist. Poly(1,4-dioxaspiro[4.4]nonane-2-methyl methacrylate) (DNMMA) was synthesized and evaluated as a matrix polymer. The glass transition temperature and decomposition temperature of the polymer were 135℃ and 200℃, respectively. The absorbances were $0.015 \mum^{-1}$ at 248 nm and $0.163 \mum^{-1}$ at 193 nm. The ketal group of the polymer hydrolyzes under acid catalysis to give two alcohols and a ketone. The ketal polymer is insoluble in an aqueous developer, while the hydrolyzed products are soluble. The resist composed of the polymer and photoacid generator gave 0.34㎛ line/space patterns.
In this polymer system to clarify the diffusion path, the effect of the remaining ketone after deprotection in the resist film was evaluated on the acid diffusion property for various post-baking temperature and protection levels. It was considered that the concentration of the remaining ketone after deprotection in the resist film corresponds to the acid diffusion paths. Based on the experimental analysis, it was found that the existence of the remaining ketone improves sensitivity by guiding diffusion channel. For enhancing dry etching resistance, we synthesized the copolymer composed of DNMMA and cholate based material, t-butylcholyl methacrylate (TBCMA). The etching rate of poly($TBCMA_{0.2}-co-DNMMA_{0.8}$) was 1.18 times that of novolac-based, so TBCMA was confirmed to have good dry etching resistance.
