Properties of inductively coupled rf Ar/H_2 plasmas: Experiment and global model

摘要

Experiments with a Langmuir probe and optical emission spectroscopy combined with actinometry are carried out in inductively coupled rf (13.56 MHz) Ar/H_2 discharges at total pressures of 20 m, 40 m, and 60 mTorr in hydrogen fractions ranging from 0% to 50%. The measured electron energy probability functions (EEPFs), which deviate from the Maxwellian distributions owing to the depletion of high-energy electrons, can be approximated using two temperatures. The electron temperatures, which can be deduced from the slopes of low-energy and high-energy parts of the EEPFs, relatively abruptly increase with increasing the hydrogen fraction in the hydrogen fractions below 10%, whereas the measured electron density markedly decreases with increasing the hydrogen fraction in the hydrogen fractions below 20%. The effective ion mass, which can be estimated from the ion current collected into the probe, markedly decreases with increasing the hydrogen fraction. The density of hydrogen atoms estimated by actinometry markedly increases as molecular hydrogen is added to Ar discharges, and then gradually increases with increasing the hydrogen fraction at the hydrogen fractions higher than 10%-20%. A global model is used to study the effect of Ar dilution to hydrogen discharges on the plasma parameters assuming the Maxwellian electron energy distribution. The model results are compared with the experimental results, obtaining reasonably good agreement.