Regioisomeric effects regulating the physicochemical properties of complex copolymers in thin films

초록

We demonstrate that minimal alterations to the chemical structure of a hydroxystyrene (HOST)-containing terpolymer lead to significant changes in its physicochemical properties, which in turn govern photolithographic pattern formation in chemical amplification mechanism. While the structures of the three repeating units, their compositions, and the molecular weight characteristics of the terpolymers were controlled to be similar, the location of the phenolic OH groups was adjusted by copolymerizing o-, m-, and p-acetoxystyrene, subsequently transformed into o-, m-, and p-HOST through deacetylation. In the studies to examine the physicochemical properties of the copolymers, the copolymer with p-HOST showed dissolution rate in n-butyl acetate (nBA) of approximate to 15 nm/s, which was lower than that of copolymer with m-HOST (approximate to 18 nm/s) and o-HOST (approximate to 27 nm/s), further showing high linear correlation with the Hansen space distance between the copolymers and nBA. Moreover, the acid diffusions in the thin film, which plays a significant role in acid-catalyzed deprotection of the copolymers to solubility modulation, was affected by the location of the phenolic OH: the fastest and slowest acid diffusions were observed in the copolymers of p-HOST and o-HOST, respectively. The regioisomerism further affects the photolithographic performance collectively: (i) in contrast curve, light energy required to change the solubility was in order of p-HOST m-HOST >o-HOST, highlighting the significance of chemical structure design and the fundamental understanding of structure-property relationships.

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