Characterization of Argon/Hydrogen Inductively Coupled Plasma for Carbon Removal over Multilayer Thin Films
Yi Wang, Tim Gehring, Qihao Jin, Jan Dycke, Rainer Kling
Abstract
Inductively coupled plasma with an argon/hydrogen (Ar/H2) mixture is a potential solution to many surface treatment problems, especially when encountering carbon contamination in optical X-ray and extreme ultraviolet instruments. Removing carbon contamination on multilayer thin films with Ar/H2 plasma extends the lifetime of the above devices. To further investigate the reaction between plasma and carbon, both optical emission spectroscopy and finite element method with multiphysics fields were employed. The results demonstrated that the intensities of the Balmer lines were in good agreement with the densities of the radical hydrogen atoms from the simulation model, showing a dependence on the mixing ratio. At an electrical input power of 165 W and a total pressure of 5 Pa, an optimum mixing ratio of about 35 ± 5 % hydrogen produced the highest density of hydrogen radicals, coinciding with the highest carbon removal rate. This shows that the carbon removal with Ar/H2 plasma was mainly controlled by the density of hydrogen radicals, and the mixing ratio showed a significant impact on the removal rates.