Molecular resists based on cholate derivatives for electron-beam lithography

We have designed and synthesized cholate derivatives (1,4-Bis(methyloxymethylcholate)cyclohexane: C2ChDM and 1,2-Bis(oxymethylcholate)ethane: C2E) to investigate the properties as a chemically amplified (CA) positive-tone Electron-beam (EB) resist material. C2ChDM and C2E which were easily obtained by one-step esterification from cholic acid and dichloride showed glass transition temperatures (Tgs), 85 and 84 degrees C, respectively. These compounds were dissolved in propylene glycol monomethyl ether acetate (PGMEA) and formed amorphous thin films onto silicon wafers by using a spin-coat method. The etch rates of C2ChDM and C2E, which were measured under CF4/CHF3/Ar mixed gas process, were almost the same as poly (p-hydroxystyrene) (PHS). The model resist samples were formulated with C2ChDM and C2E as base matrix and photo-acid generator (PAG) originated from sulfonium-salt (resist-A and B, respectively). These resists showed good sensitivities with 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 of resist-A and B films, we confirmed that a cleavage reaction of ester bond occurred by EB irradiation and bake treatment, and these resists worked as common CA positive-tone resist. The evaluation results with the resist-A and B by using EB exposure tool indicated the resolution of 120 nm lines and spaces pattern.