Photoresists with reduced environmental impact: Water-soluble resists based on photo-cross-linking of a sugar-containing polymethacrylate

A family of water-soluble, negative-tone, high-resolution, chemically ampli fied photoresists based on partially or fully deprotected poly( 1,2:5,6-di- O-isopropylidene-3-O-methacryloly-alpha-D glucofuranose) is described. Both the molecular weight of the parent ketal-protected polymer and the extent of its deprotection to a water-soluble polymer containing 3-O-methacryloyl- D-glucopyranose repeat units must be carefully controlled to provide good c oating and imaging properties. The two ketal protecting groups of the poly( 1,2:5,6-di-O-isopropylidene-alpha-D-glucofurancose have different reactivit y, and their complete removal requires long reaction times under hydrolytic conditions. The detailed deprotection chemistry of the polymer is readily understood through model studies with the fully and partially protected ana logues of the polymer pendant groups: 1,2:5,6-di-O-isopropylidene-alpha-D-g lucofuranose and 1,2-isopropylidene-alpha-D-glucopyranose. When combined wi th a water-soluble photochemical precursor of acid such as (4-methoxyphenyl )dimethylsulfonium trifluoromethanesulfonate, films of the deprotected or p artially deprotected poly(1,2:5,6-di-O-isopropylidene-3-O-methacryloyl-alph a-D-glucofuranose) undergo acid-catalyzed cross-linking. The enhanced perfo rmance of the partially deprotected polymers over that of poly(3-O-methacry loyl-D-glucopyranose) suggests that the presence of remaining hydrophobic g roups that afford water dispersibility rather than full solubility may be k ey to their performance. Imaged negative-tone features as small as 0.2 mu m are obtained with these materials that have sensitivities of ca. 30 mJ/cm( 2) with wholly aqueous casting and processing.