Langmuir probe study of the charged particle characteristics in an analytical radio frequency-glow discharge. Roles of discharge conditions and sample conductivity

摘要

The application of a tuned Langmuir probe to the measurement -of the charged particle characteristics of electron number density, ion number density, electron energy distribution function, average electron energy and election temperature, in an analytical radio frequency (r.f.)-glow discharge is described. Studies focus on the roles of discharge operating conditions and plasma sampling position for conductive (copper) and nonconductive (Macor) samples. Based on the data obtained here, apparent differences in plasma characteristics between conductive and nonconductive samples can be reasonably explained. For example, the sputtering of conductive samples results in plasmas with obviously higher electron and ion number densities than the sputtering ofnonconductive samples (e. g.- n_i = 1.8 x 10~10 cm~(-3) and n_e = 1.5 x I0~9 cm~(-3) for copper, and n_i = 8 x 10~9 cm~(-3) and n_e = 5 x 10~8 cm~(-1) for Macor under the conditions of argon pressure = 4 Torr, r.f. power = 30 W and sampling distance = 4.5 nini). Conversely, nonconductive samples yield electrons with higher energies (average electron energies of 15 and 7.5 eV and temperatures of 6.5 and 3.5 eV respectively for the Macor and copper samples). Lower d.c. bias potentials for the case of sputtering nonconductive samples yield reduced sputtering rates and charged particle densities, though the electrons in the latter case have higher energies and thus improved excitation capabilities. The differences between r. f. - and d. c, -glow dischargeoptical emission spectra are also discussed relative to reported electron energy characteristics Studies such as these will lay the groundwork for extensive evaluation of inter-matrix type standardization for r.F.-glow discharge atomic emission spectrometpy.