Molecular Resists Based on Cholate Derivatives for Electron-Beam Lithography

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We have designed and synthesized cholate derivatives [1,4-bis(methyloxymethylcholate)cyclohexane: C2ChDM and 1,2-bis(oxymethylcholate)ethane: C2E] to investigate their properties as chemically amplified (CA) positive-tone electron-beam (EB) resist materials (Fig. \ref{f1}). C2ChDM and C2E which were easily obtained by one-step esterification from cholic acid and chloride compound, showed glass transition temperatures ($T_{\text{g}}$s) of 85 and 84 °C, respectively. These compounds were dissolved in propylene glycol monomethylether acetate (PGMEA) and formed amorphous thin films onto silicon wafers by a spin-coat method. The etch rates of C2ChDM and C2E, which were measured under CF4/CHF3/Ar mixed gas, were almost the same as poly($ p$-hydroxystyrene) (PHS). Model resist samples were formulated with C2ChDM and C2E as a base matrix and photo-acid generator (PAG) originating from a sulfonium salt (resist-A and -B, respectively). These resists showed good sensitivities to EB exposure. Furthermore, the FT-IR spectra of resist-A and -B films unexposed and exposed by the EB lithography tool were measured. From the spectral changes in resist-A and -B films, we confirmed that a cleavage of the ester bond occurred with EB irradiation and bake treatment, and that these resists worked as common CA positive-tone resists. The results with the resist-A and -B using EB exposure indicated a resolution of a 120 nm lines and spaces pattern.
2006-06-30