Open air photoresist ashing by a cold plasma torch: Catalytic effect of cathode material

Abstract

A beam plasma was generated and exhausted into air by applying rf voltage to the atmospheric pressure argon flowing through a cylindrical gap between a needle cathode and a grounded cylindrical anode whose surface was covered with an insulator. This torch-type plasma with gas and electron temperatures of 240 °C (44.2 meV) and 1.0 eV, respectively, has been verified to be useful for ashing a photoresist without using a pumping system. High rate (≥1.2 μm/min) photoresist ashing was achieved by using Ar plasma containing a small amount of oxygen. Also reported are optical emission analysis of plasma and analyses of ashed Si surface by scanning electron microscopy. Fourier transform infrared spectroscopy, electron microprobe analysis, and x-ray photoelectron spectroscopy. The use of the Pt cathode was found to provide not only a better ashed surface but also a higher ashing rate than the use of the stainless-steel cathode.