Effects of Nitrogen Dilution on the Photoresist Removal Rate by Hydrogen Radicals

Abstract

We have previously demonstrated that photoresist removal rate comparable to oxygen plasma is accomplished by optimizing the removal conditions with H radicals produced on hot metal filament surfaces from H 2 /N 2 mixtures (H 2 :N 2 = 10:90 vol%). N 2 gas was used to dilute the concentration of the H 2 gas and to reduce the risk of explosion. However, it is not clear how the dilution of H 2 by N 2 affects the removal rate. In this paper, we examined the relationship between the removal rate and the H 2 content; the flow rate ratio of H 2 to H 2 +N 2. The removal rate increased with increasing the H 2 content. In addition, the removal rate increased with increasing the substrate temperature according to an Arrhenius equation, when the H 2 content was over 90%. However, below 60%, the removal rate decreased with increasing the temperature over 230 ± 5 °C. Denaturation of photoresist, e.g. hardening and/or crosslinking, may be induced by substrate heating when the H-radical density is low. The removal rate decreases not only by the deficiency of H radicals but also by the denaturation of films in H 2 /N 2 mixed systems.