In situ monitoring of the effects of gas mixtures on ion beam depositions of diamond-like carbon films

摘要

A quadrupole mass spectrometer and a total ion-current measuring device have been utilized to monitor the ion compositions of gas mixtures of CH_4/H_2 and CH_4/H_2/O_2 during the deposition for quality control and process optimization. An ultra high vacuum system using a 20 cm diameter RF excited (13.56 MHz) ion gum and a four-axis substrate scanner has been developed for deposition of diamond-like carbon films for electrical, optical, and tribological applications. At a constant RF power of 179W, the mass spectra of gas mixture CH_4/H_2 (1:2.5) showed the most abundant ion is CH_3~+. Addition of O_2 to the ion source has been found to affect the adhesion, deposition rate, and physical and chemical properties of the DLC films. By use of a mass spectrometer with and without the electron beam, the degree of ionization of CH_4 was calculated to be about 10 percent. As the concentration of O_2 was increased, all hydrocarbon ions decreased and H_3O~+ increased, resulting in a decrease in the film growth rate and an increase in etching of Si and glass substrates. In general, the optical bandgap, adsorption coefficients and refractive index decreased as oxygen concentration increased. Raman spectra showed the G-peak position shifted toward the graphitic peak with narrow peak width as oxygen concentration increased. At ultra high vacuum, the coefficient of friction increased with increased adhesion on substrates as oxygen was increased.