Photoresist Ashing by Atmospheric Pressure Glow Plasma.

Abstract

We investigated the mechanism and application of photoresist ashing by means of atmospheric pressure glow (APG) plasma. APG plasma using a mixture gas of He and O2 could ash the photoresist with a rate of about 1μm•min-1, which was roughly the same value as that of O2 plasma ashing at a low pressure. The dependences of etch-rate on O2 gas flow rate, discharge power and substrate temperature suggested that the APG plasma ashing process was mainly the oxidation of the photoresist by oxygen radicals. The XPS and optical emission spectroscopy suggested that excited helium promoted the desorption of oxides on the surface of the photoresist. To reduce cost, we tried to use Ar, acetone (Ac) and O2 mixture gas instead of He and O2 mixture gas. Ar/Ac/O2 plasma could etch the photoresist as fast as He /O2 plasma, although the O2 content was one sixth of that of He/O2 plasma. Minute area ashing using a pray type discharge tube was also investigated. Its ashing rate was the fastest, about 4.0μm•min-1, when Ar/O2 mixture gas was used.