Effect of bias in patterning diamond by a dual electron cyclotron resonance-radio-frequency oxygen plasma

Arrays of microhole patterns are fabricated on the surfaces of diamond films through a physical mask in a dual microwave electron cyclotron resonance/radio-frequency oxygen plasma. It is found that nanotips with high aspect ratio form in the microholes, and then through-holes are fabricated with a further increase of etching time. Optical emission spectroscopy was employed to calculate oxygen atom density and evaluate the variation of the plasma excitation temperature. The plasma excitation temperature and the O atom density present significant dependences on the voltage of rf bias V_b at a high frequency of 13.56 MHz, suggesting that the application of the rf bias not only strengthens ion bombardment on the material surface, but also induces the variations of the bulk plasmas including the increase of O atom density. Whereas, both the plasma excitation temperature and the O atom density remain nearly unchanged with V_b under the bias frequency of 400 kHz. The etching process depends on the rf-bias frequency and voltages, which are correlated with the measured plasma characteristics.     

Mass spectrometric studies of the mechanism of film inhibition in hydrogen/methane plasmas in the presence of nitrogen

Complete suppression of amorphous C:H film deposition has been reported for N₂/CH₄ ratios ∼1, in low-pressure technical plasmas. This finding has been recently used by the authors for the proposal of a possible technique for the inhibition of re-deposited T-containing carbon films at the divertor region of fusion devices. Although several works aiming to the understanding of the underlying physicochemical processes have been published, the complexity of the system is far from being properly described by the proposed models. In the present work, experiments in DC glow discharges at low pressure of H₂/CH₄/N₂ admixtures (90:0-5:0-5) are described. Mass spectrometry of neutral species as well as plasma mass spectrometry for ion detection have been used as the main diagnostics. Several plasma conditions (plasma current, gas composition, etc.) as well as isotopic exchange (H/D) have been investigated. Also, the effect of progressive film growing on the metal walls of the reactor in the composition of gas-phase species has been investigated. It is concluded that wall carbonisation is required to trigger the inhibition process. Ethylene and acetylene are found as the main reaction products.     

Structure evolution on annealing of copper-doped carbon film

Thin copper-doped (8 at.% Cu) carbon film was deposited by direct current magnetron sputtering of composite graphite/copper target in argon plasma. The evolution of film structure on annealing at 600 °C in a vacuum has been studied by transmission electron microscopy and electron diffraction. The as-deposited film was amorphous with copper atoms uniformly distributed over the film volume. Annealing resulted in precipitation of copper particles within carbon film followed by the decrease in the density of copper particles and increase in particle average size with annealing time due to diffusion coalescence within the ensemble of copper particles. The coalescence occurred by the mixed mechanism of bulk and surface diffusion of copper atoms within carbon film that contained a large number of structural defects. As a result, the mean radius of copper particles in ensemble changed as R¯⁵ ∼ t.