Exposure characteristics of ternary copolymerization positive tone electron beam resist containing p-chloro-α-methylstyrene

p-Chloro-α-methylstyrene (PCMS) has the chemical structure as the chlorine atom is introduced in phenyl group of α- methylstyrene (MS). In the present study, we synthesized a ternary copolymer consisted with methyl-α-chloroacrylate (ACM), PCMS and MS having the composition ratio of 53:16:31 with the averaged molecular weight (Mw) of 370k, in order to improve sensitivity while maintaining the same resolution as conventional ACM-MS resist. ACM-MS resist having the composition ratio of 46:54 with Mw of 290k is also synthesized to compare exposure characteristics. Firstly, solubility of ACM-PCMS-MS resist without the electron beam exposure for ester solvents is investigated. The dissolving rate of ACM-PCMS-MS resist for amyl solvent is markedly lower compared with ACM-PCMS resist having the composition ratio of 49:51 with Mw=30k reported before, which also includes the effect of the larger molecular weight. Sensitivity curves are made and line and space (L/S) patterns down to 20/20 nm (design value) are formed by using an electron beam writing system with an acceleration voltage of 50 kV. The 20/20 nm L/S pattern is successfully formed in ACM-PCMS-MS resist as well as ACM-MS resist. No significant difference between ACM-PCMS-MS resist and ACMMS resist is observed in L/S pattern shapes. The exposure doses required for pattern fabrication are larger in all L/S patterns compared to ACM-MS resist, reflecting sensitivity curves of them. The dry etching resistance of ACM-PCMSMS resist is also presented.