Design and study of resist materials for 157-nm lithography

We investigated the structure-property relationships of several polymer platforms containing hexafluoroisopropanol (HFIP) and tertiary alkyl ester functionalities in order to identify and develop fluorine-containing polymers suitable for 157nm lithography. We observed that the aqueous base solubility of homopolymers containing HFIP was highly dependent on the monomer structure, number of HFIP group per monomer unit, substituent on the alcohol and the polymer architecture. Copolymers of tert-butyl acrylate (TBA), tert-butyl 2-fluoroacrylate (TBFA) and tert-butyl 2-trifluoromethylacrylate (TBTFMA) with styrene hexafluoroisopropanol (STYHFIP) or norborene hexafluoro-isopropanol (NBHFIP) were also investigated to determine the effect of substitution at the acrylate α-position. Under the same ration of STYHFIP, the transparency of the co-polymers improved in the or der of CF3>F>H while the dry etch stability decreased in the order of CF3>F>H. When exposed to 157 nm radiation, photoresists of P(STYHFIP-TBA), P(STYHFIP-TBFA) and P(STYHFIP-TBTFMA) showed an increase in E0 ni the order of H<F<CF3, but the difference was marginal. The PEB sensitivity was nearly identical for all three co-polymers suggesting that the nature of the substituent at the α-position of the acrylate monomer did not have a significant impact on the deprotection chemistry. The photospeed of P(NBHFIP-TBTFMA) was much slower than that of P(STYHFIP-TBTFMA) due to a slower dissolution rate of NBHFIP than that of STYHFIP and to the influence of the polymer matrix on the deprotection reaction.