Langmuir-probe characterization of an inductively-coupled remote plasma system intended for CVD and ALD

We measured electron density and electron energy distribution function (EEDS) vertically through our reactor for a range of process conditions and for various gases. The EEDF of Ar plasma in the reactor could largely be described by the Maxwell-Boltzmann distribution function, but it also contained a fraction (~10-3) of electrons which were much faster (20-40 eV). At low pressures (6.8-11 µbar), the tail of fast electrons shifted to higher energies (Emax ~50 eV) as we measured more towards the chuck. This tail of fast electrons could be shifted to lower energies (Emax ~30 eV) when we increased pressure to 120 µbar or applied an external magnetic field of 9.5 µT. Addition of small amounts of N2 (1-10%) or N2O (5%) to Ar plasma lowered the total density of slow electrons (approx. by a factor two) but did not change the shape of the fast-electron tail of the EEDF. The ionization degree of Ar-plasma increased from 2.5 104 to 5 104 when an external magnetic field of 9.5 µT was applied.