The chemistry of g‐line photoresist processes

Abstract

AbstractThe chemistry that underlies positive imaging, Image Reversal (ImRe) and Built In Mask (BIM), has been investigated. For this purpose the photoactive compound 2, 1 ‐diazonaphthoquinone‐5‐(4‐cumylphenyl)‐sulfonate (PAC‐5), the corresponding indenecarboxylic acid (ICA‐5) and the decarboxylated derivative of ICA‐5 (indene), were isolated and characterized. The study revealed that dissolution of ICA‐5 in aqueous base developers gives rise to the formation of an indenyl carboxylate dianion, which decarboxylates in several hours. In the case that ICA‐5 is dissolved in weakly alkaline media or in organic solvents such as methanol, the formation of this ion does not occur, but the rate of decarboxylation is almost the same. It is suggested that the decarboxylation reaction proceeds via the indene carboxylate monoanion, which reacts to indenyl anion. The latter is a strong base and is readily protonated to give indene (two isomers). In the case of aqueous base this leads to precipitation of the indene. In agreement with the finding that the indene derived from ICA‐5 does not dissolve in aqueous base developers, it was found that mixing indenes into novolak has a considerable inhibitive effect on the dissolution rate of a layer of this material in aqueous base. After a bake (in ImRe this would be the reversal bake), the dissolution rate is almost the same as for unexposed photoresist. Similar experiments with mixtures of novolak and indenecarboxylic acid revealed that there is no difference in the dissolution rate of such layers as compared with exposed photoresist. This excludes the putative effect of porosity, caused by nitrogen extrusion. In the case that 1‐phenyl‐3‐morpholinotriazene is added to the photoresist (in order to produce a dye in the BIM concept), azo‐dyes are formed by coupling of diazonium ions on the 1‐ and 3‐position of 3‐indenecarboxylic acid. The paper starts with a brief review of the mechanisms of photolysis of 2, 1 ‐diazonaphthoqui nones, as have been proposed in the literature. Although the formation of ketene as an intermediate is generally accepted, there appears to be no consensus about the existence of carbene.