Investigation of diamond-like carbon films synthesized by multi-jet hollow cathode rf plasma source

Abstract

Diamond-like carbon films were prepared by use of a hollow cathode discharge plasma source (HCD), operating at 13.56 MHz. At a distance of 6 cm from the plasma source, a water-cooled substrate holder was positioned, which was biased at 13.56 MHz as well. A plasma-enhanced chemical vapor deposition (PECVD) process was used. Helium as a carrier gas and methane as a source of carbon were used for diamond-like carbon (DLC) film deposition. DLC films were characterized with a micro Raman spectroscopy and spectroscopic ellipsometry. In the wavelength range of 300–900 nm the measured spectra were analyzed by a regression-fitting algorithm, according to the nominal sample structure in which the optical properties of DLC were described by a Cauchy dispersion model. Optimum film quality was obtained in a bias voltage range, between −(350–420) V, which produces the films with the highest index of refraction, close to 2.15; a wavelength of 550 nm; lowest optical band gap close to 1.3 eV; and a Vickers hardness of 30 GPa. It was found that, even in the stationary deposition, mode film thickness variations across a 5-inch wafer did not exceed ±3.5%. A maximum deposition rate of 70–80 nm/min at room temperature was achieved.