Diagnostics of Gas-Phase and Surface Reactions of Atomic Radicals in Processing Plasmas by Vacuum Ultraviolet Laser Spectroscopy

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Atomic species such as H, C, N, F and Cl play important roles in gas-phase and surface reactions for various kinds of plasma material processing. In this project, we have developed a tunable VUV (vacuum ultra-violet) laser absorption spectroscopy system in the range from 800 to 1700 nm by using the two-photon resonant four-wave mixing method (ν_<VUV> = 2ν_1 + ν_2), and applied it to the diagnostics of those species in order to make clear the reaction mechanisms and obtain the guiding principles for the process control.Following the quantitative measurement on F atoms, we applied the VUV absorption method Successfully to the measurement of C atoms in various kinds of fluorocarbon gas plasmas. The obtained results were analyzed for the role of C atoms in the etching of SiO_2 (see the paper published in J. Appl. Phys for more details). Then, we proceeded to the measurement of O atoms for better understandings of photo-resist ashing and Si oxidation processes.For the measurements of H and N atoms, the wavelengths corresponding to ν_1 and ν_2 become 210 and 800 - 900 nm, respectively, for the VUV generation around 120 nm. Therefore, We have modified the laser system by substituting the pumping excimer laser with a YAG-laser for the better VUV conversion efficiency. As the result, we have succeeded in the measurement of H atoms in H_2 and CH_4 gases, and are continuing the quantitative measurement in the processing plasmas for the surface cleaning and diamond-like carbon deposition.