FLUORINE-CONTAINING PHOTOREACTIVE POLYIMIDES .6. SYNTHESIS AND PROPERTIES OF A NOVEL PHOTOREACTIVE POLYIMIDE BASED ON PHOTOINDUCED ACIDOLYSIS AND THE KINETICS FOR ITS ACIDOLYSIS

Polyimide (6FDA-AHHFP) prepared from the polycondensation of fluorinated acid dianhydride (6FDA) and diamine (AHHFP) is soluble in an aqueous base due to the presence of a hydroxyl group in the phenyl group of the diamine segment. Easy acidolysis of the protecting groups of the hydroxyl group was demonstrated with several model compounds of the polyimide that were protected by a number of acyland (alkyloxy)carbonyl groups. The tert-butoxycarbonyl group showed the highest acidolysis rate in these tests. A polyimide (6F-t-BOC) with a tert-butoxycarbonyl (t-BOC) group was thus prepared. On the basis of the results obtained from the model compound, it was expected that 6F-t-BOC would have a high sensitivity because the t-BOC group, as the protecting group, showed the highest acidolysis rate. Although 6F-t-BOC is insoluble in an aqueous base, it is easily converted to an alkaline-soluble polyimide by the acidolysis of this t-BOC group. This implies that polyimide 6F-f-BOC acts as a positive-working photoreactive material in the presence of a photoacid generator. Actually, 6F-f-BOC in the presence of (p-nitrobenzyl)-9,10- diethoxyanthracene-2-sulfonate (NBAS) as a photo acid generator showed excellent positive-working characteristics in an aqueous base developer because of the polarity change induced by removing the t-BOC group. The sensitivity and contrast after a postexposure bake at 120 °C for 10 min were 180 mJ/cm2 (365 nm) and 3.4. Resolution higher than 1.0 μm was obtained in the 5-μm-thick film. The kinetics of thermolytically deprotecting the 6F-1-BOC film, when catalyzed by p-toluenesulfonic acid (p-Tos), was studied further in its solid state. The results clearly indicated that the reaction was first order, suggesting it was a typical AAL-1 type reaction requiring no water. The activation energy for the acidolysis was 19.5 kcal/mol. It further became apparent that the diffusion radius of an acid in a 6F-f-BOC film containing p-Tos was ca. 14.2 Å when heated for 10 min at 80 °C. 6F-t-BOC has 2 mol of t-BOC groups per repeating unit. Examination of their thermolytic acidolysis showed that acidolysis of the first t-BOC group proceeded more slowly than that of the second one in each repeating unit. This was attributed to the fact that an acid could attack the second t-BOC group easier than the first one and was responsible for the steric inhibition of tert-butyl groups around the t-BOC that protected an acid. © 1990, American Chemical Society. All rights reserved.