M. Weiler

DEPOSITION OF TETRAHEDRAL HYDROGENATED AMORPHOUS CARBON USING A NOVEL ELECTRON CYCLOTRON WAVE RESONANCE REACTOR

Highly tetrahedral hydrogenated amorphous carbon (ta-C:H) is deposited with a novel, 13.6 MHz excited electron cyclotron wave resonance (ECWR) plasma source. The ion flux of an acetylene and a nitrogen plasma was investigated by mass spectrometry and retarding field measurements. The ECWR gives a dissociation degree between 15% and 80% depending on gas flow rate. Ion current densities up to 2 mA/cm2 can be achieved, corresponding to ta-C:H deposition rates of 2 nm/s. The fraction of sp3 bonded carbon atoms and mass density are strongly related to the amount of hydrogen in the ion flux. For low hydrogen ion fluxes (10%), a sp3 fraction of 70% and a mass density of 2.85 g/cm3 can be achieved. At higher hydrogen ion fluxes (40%), the sp3 fraction and the mass density fall to 55% and 2.55 gm/cm3, respectively.

Doping of highly tetrahedral amorphous carbon

The doping of amorphous carbon films with over 80% sp3 bonding is examined. It is shown that n-type doping with P and N is possible. p-type doped with B has been unsuccessful. The electronic properties of this form of amorphous carbon which has an optical band-gap of 2eV is taken as being governed largely by the π and π∗ states which arise due to the much smaller fraction of sp2 bonded C. With low levels of N doping there is evidence for compensation of p-type defects in the undoped material. It is thought that dopants which have deep levels in diamond appear as shallow dopants in tetrahedral amorphous carbon due to the presence of the π states.

Plasma beam deposition of highly tetrahedrally bonded amorphous carbon

Abstract A new type of amorphous hydrogenated carbon was produced by an r.f. plasma beam. Using C2H2 as the precursor gas, the film-forming particle flux consists mainly of C2H+2 ions with well-defined energies. Corresponding to the subplantation (Lifshitz et al., Phys. Rev. B, 41 (1990) 10486) model of Robertson (Diamond Relat. Mater., 2 (1993) 984) and Davis (Thin Solid Films, 30 (1993) 276), the sp3 content and density are correlated with the ion energy and current density. The films are analysed by optical spectroscopy and photodeflection spectroscopy. The hardness and elastic properties are studied by indenter measurements. The film properties are strongly determined by the energy per C atom. The current density only governs the mass deposition rate. For an energy of about 90 eV an sp3 content of about 70% ± 10% can be achieved, which corresponds to a density of about 2.9 g cm−3, whereas the hydrogen content is still as high as about 25 at.%. The optical band gap of these 50–200 nm films is in the range 2.3–2.4 eV. The room temperature conductivity of 10−9 Ω−1 cm−1 is shown to be thermally activated with an activation energy of about 0.45 eV.

Structure of amorphous hydrogenated carbon: experiment and computer simulation

Abstract The microstructure of amorphous hydrogenated carbon films has been studied by electron diffraction measurements and comparison of the results with simulated diffraction data which have been modelled by molecular dynamics (MD) calculations. The films have been produced partly by a plasma-enhanced chemical vapour deposition process and partly by a plasma beam deposition method. The MD simulation is based on an annealing process cooling down a liquid phase ensemble of 64 carbon and a corresponding number of hydrogen atoms using a density functional approach to account for the interatomic forces.

Ion energy and plasma characterization in a silicon filtered cathodic vacuum arc

The plasma generated by a silicon filtered cathodic vacuum arc has been investigated using a Faraday cup and Langmuir probes. Ion energy distributions for arc currents ranging from 30 to 80 A were measured. Mean ion energies were found to range from 8 to 18 eV. The ion saturation current density varied from 0.1 to 1 mA/cm2 depending on both the arc and filter coil currents. The energy distributions were fitted by a sum of Gaussians spaced according to the gas dynamic model for ion acceleration at the cathode spot.

LOW-TEMPERATURE ANODIC OXIDATION OF SILICON USING A WAVE RESONANCE PLASMA SOURCE

A rf wave resonance plasma (WARP) source has been used to plasma oxidize Si at temperatures below 100 °C. Oxidation under positive substrate bias in constant current mode gives an oxidation rate of 1–8 nm/min for current densities of 0.4–5.5 mA/cm2. This corresponds to an ionic (O−) current of about 10% of the total current, which is 2–5 times higher than previously reported, due to the high plasma density of 1012–1013 cm−3 achieved by the WARP source. The breakdown field of ∼10 MV/cm and the etch rate of 60 nm/min of the oxide are independent of the oxidation rate and similar to those of the thermal oxide. Results from capacitance–voltage measurements, Fourier transform infrared absorbance spectroscopy, null ellipsometry, and Rutherford backscattering spectroscopy suggest that the oxide grown at low rates ( 3 nm/min) is Si rich (35%–40% atomic Si).

High Rate Deposition of Ta-C:H Using an Electron Cyclotron Wave Resonance Plasma Source

A compact electron cyclotron wave resonance (ECWR) source has been developed for the high rate deposition of hydrogenated tetrahedral amorphous carbon (ta-C:H). The ECWR provides growth rates of up to 1.5 nm/s over a 4-inch diameter and an independent control of the deposition rate and ion energy. The ta-C:H was deposited using acetylene as the source gas and was characterized as having an sp content of up to 77%, plasmon energy of 27 eV, refractive index of 2.45, hydrogen content of about 30%, optical gap of up to 2.1 eV and RMS surface roughness of 0.04 nm. q 1999 Elsevier Science S.A. All rights reserved.