Characterization of high-pressure capacitively coupled hydrogen plasmas

Abstract

Capacitively coupled very-high-frequency hydrogen plasmas have been systematically diagnosed in a wide range of a gas pressure from 5 mTorr to 10 Torr. The plasma parameters, ion species, and ion energy distributions (IEDs) are measured using a Langmuir probe, optical emission spectroscopy, and energy filtered mass spectrometer. The measurement results show that the ion species in a hydrogen plasma is determined from ionization channels and subsequent ion-molecule reactions. The ions are dominated by H2+ at a less-collisional condition of ≲20 mTorr, whereas those are dominated by H3+ at a collisional condition of ≳20 mTorr. The IED is determined by both the sheath potential drop and ion-neutral collisions in the plasma sheath. The IED is broadened for a collisional sheath at ≳0.3 Torr and the ion bombardment energy is lowered. For high-pressure discharge operated at ≈10 Torr, plasmas are characterized by a low electron temperature of ≈0.8 eV and a low ion bombardment energy of ≲15 eV.