Measurement of electron temperatures of Argon Plasmas in a High-Density Inductively-Coupled Remote Plasma System by Langmuir Probe and Optical-Emission Spectroscopy

We measured electron density and electron energy distribution function (EEDF) in our reactor by a Langmuir probe. The EEDF of Ar plasma in the reactor could largely be described by the Maxwell-Boltzmann distribution function, but it also contained a fraction (~10) of electrons which were much faster (20-40 eV). The peak of the fast-electron tail shifted from E ~ 35 eV at 11 μbar to E ~ 25 eV when we increased pressure to 120 μbar or applied an external magnetic field of 9.5 μT. We also measured relative mean electron temperatures (kTe) by optical emission spectroscopy (OES). This method is especially sensitive to the fraction of fast electron in the plasma. The relative kTe measured by OES decreased from 1.6 eV at 11 μbar to 1.4 eV at 120 μbar. OES can be used, in addition to Langmuir-probe measurements, when depositing plasmas are used. Combining the Langmuir-probe and OES measurements in non-depositing plasmas, we can further verify the EEDF in depositing plasmas by means of OES measurements only. Knowing EEDF in e.g. silane-containing plasmas is very important for chemical modeling.