Evolution of the electron energy probability function in Ar/SiH4 inductively coupled plasma

We investigate the electron energy probability function (EEPF), electron density, and electron temperature in an Ar/SiH4 inductively coupled plasma (ICP) as a function of the SiH4 mixing ratio (RSiH4) using a Langmuir probe. A noticeable change in plasma behavior occurs around RSiH4=0.40: below this value, the EEPF remains approximately Maxwellian, while the effective electron temperature decreases gradually, whereas above it, the EEPF develops a non-Maxwellian distribution characterized by pronounced intermediate-energy depletion in the 3–6 eV range, accompanied by a sharp reduction in electron density. Measurement of the neutral species densities using a quadrupole mass spectrometer reveals that the discharge is dominated not by SiH4 but by its dissociation product H2, with Ar, H2, and H identified as the three principal neutral species. Weighting the inelastic cross sections by measured neutral densities reveals an enhanced H2-driven inelastic collision probability per unit path length in the 1–6 eV range, which closely overlaps with the energy region of the observed EEPF depletion, suggesting H2 as a plausible driver of the intermediate-energy electron loss. These results show that electron kinetics in an Ar/SiH4 ICP are governed by the discharge-phase neutral composition rather than the input gas mixture.