In situ examination of the plasma processes during the deposition of hard carbon coatings from a low-pressure arc plasma

Abstract

A low-pressure arc plasma discharge from a hollow LaB 6 cathode with up to 100 A discharge current is used to create plasmas of high density. The configuration of the magnetic field allows a homogeneous distribution of the plasma density in front of the substrate surface. Typical values for the electron density and temperature in the PETRA facility (Plasma Engineering and Technology Research Assembly) are n e= 10 12–10 13 cm −3 in the region of high plasma density and up to 10 11 cm −3 in front of the substrate surface. The electron temperature is T e = 5–20eV. The ionization ratio is typically 1–10%. In this facility, amorphous carbon films were deposited on Si(100) substrates by admixing CH 4 and C 2H 2 to He plasmas. The deposition rate reached to date is 1μm per 10 min. During the deposition, local measurements with electric double probes were performed to determine the spatial distribution of the electron density and electron temperature. In addition, mass spectroscopy of the neutral gas was performed to investigate the dissociation of the hydrocarbon precursors and to measure the amount of liberated hydrogen. After the experiments the carbon deposits were examined with regard to film homogeneity and film morphology as determined by SEM and Raman spectroscopy,