Removal of Novolac Photoresist with Various Concentrations of Photo-active Compound Using H-2/O-2 Mixtures Activated on a Tungsten Hot-wire Catalyst

We earlier reported that addition of a small amount of O-2 gas in the atmosphere where H radicals are generated on a high-temperature tungsten filament improves the photoresist removal rate of positive-tone novolac photoresists for i/g lines. This study investigated effects of photo-active compound (PAC) on the photoresist removal. Addition of more than 1.5 sccm of oxygen to 100 sccm of hydrogen gas flow decreased the removal rate. In pure novolac resin, cross-linking of the resin can be one of the causes of this decrease at temperatures higher than 240 degrees C. The rate of removal with PAC decreased much more than with pure novolac resin over 240 degrees C. This removal rate decrease might be ascribed to cross-linking not only between the resin and the PAC but also between the resins. OH radicals can be used effectively for photoresist removal by generating sufficient H radicals to prevent such cross-linking.