Kenji Seko

Study on thermal crosslinking reaction of o-naphthoquinone diazides and application to electrodeposition positive photoresist

The thermal reactions of o-naphthoquinone diazide (NQD) compounds as a material for photoresists were studied in comparison with their photochemical reactions. An NQD compound decomposed at around 140°C and further reacted in the presence of an alcohol in the solution to yield an indenecarboxylic ester. The photochemical reaction of the NQD compound with alcohol also provided the same ester in a solution, as expected. In a polymer matrix, the thermal reaction of a multifunctional NQD compound with a copolymer having hydroxyl groups yielded sufficiently crosslinked structures at 140°C in 10 min. On the other hand, when the copolymer matrix containing the NQD compound was exposed to UV, and subsequently to heating (140°C for 10 min), no crosslinked structure was obtained. Consequently, it was confirmed that the heating provides a large difference in solubility between unexposed and exposed areas, quite a useful feature from the viewpoint of efficient development of photoimage. We have applied this finding to an electrodeposition positive photoresist incorporating a post exposure bake (PEB) in resist processing. The PEB afforded a very wide process window in an alkaline developer.