We examined an environmentally friendly photoresist removal method using radicals produced by decomposing mixtures of hydrogen and oxygen on a hot iridium catalyst. We earlier reported that the decomposition of photoresists was hastened by adding oxygen gas to a hydrogen flow using a tungsten hot-wire catalyst. The rate increased with the oxygen additive amount up to about 1.0% and then decreased gradually. The decrease is caused by the catalytic poisoning of O atoms on the catalyst surface because of its poor oxidation resistance. In present study, we show that oxygen addition without catalytic poisoning is effective to increase the decomposition rate. The poisoning can be avoided by using an Ir catalyst. The decomposition rate increased with the substrate temperature. The rate also increased rapidly with increasing amounts of added oxygen to 1.0% and then the increase became more gradual. OH radicals must play an important role to hasten the decomposition reactions.
Photoresists play a key role in lithography processes for the fabrication of electronic devices, but must be removed after processing. The removal method using hydrogen radicals, which are produced on a tungsten hot-wire catalyst, is effective to resolve some environmental and industrial problems in usual methods. However, the removal rate is not as good as that of the usual methods. We have previously described that the removal rate is enhanced just by decreasing Hydrogen pressure but the rate limitations not clarified. In present study, we examined the removal rate dependence on the pressure and revealed that the upper limitation of the enhancement is achieved at 0.50 Pa. The removal rate at 0.50 Pa was 8.3 times higher than that at 20 Pa when the surface temperature was 250 °C.
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