S. Sattel

HIGHLY TETRAHEDRAL, DIAMOND-LIKE AMORPHOUS HYDROGENATED CARBON PREPARED FROM A PLASMA BEAM SOURCE

A highly tetrahedral, diamond‐like form of hydrogenated amorphous carbon (a‐C:H) with density of 2.9 g cm−3, sp3 fraction of 0.75, and hardness of 61 GPa, the highest values so far attained from a hydrocarbon source gas, has been deposited from acetylene in a novel plasma beam source. The ion energy for highest sp3 fraction is measured to be about 100 eV per C atom, similar to that for a‐C, indicating that the subplantation deposition model of a‐C also describes a‐C:H.

MECHANISM OF BIAS-ENHANCED NUCLEATION OF DIAMOND ON SI

The nucleation of diamond on Si is enhanced for negative substrate bias of 200–250 V. We show that the ion flux is the critical factor causing the enhanced nucleation. The ion energy distribution has a maximum at about 80 eV, the optimum to subplant C ions into a‐C. We propose that subplantation causes deposition of nanocrystalline graphitic C, and that diamond nucleates where the graphitic planes are locally oriented perpendicular to the surface. An atomic model is proposed that allows a matching of the diamond, graphite, and Si lattice.

Effects of deposition temperature on the properties of hydrogenated tetrahedral amorphous carbon

The properties of hydrogenated carbon films deposited from a highly ionized hydrocarbon plasma beam are studied as a function of deposition temperature. At low temperatures, the films have high sp3 bonding, density, and compressive stress and are very smooth. Two transition temperatures are observed, a lower transition T1 around 250 °C, dependent on ion energy, due to graphitization of C–C bonds, and a higher one T2 at about 450 °C due to the loss of hydrogen. The roughness rises at T1 and falls above T2. These transitions are used to understand the subplantation deposition mechanism. The optical gap varies differently, decreasing gradually across T1 due to ordering of sp2 sites. We also report the temperature dependence of the x-ray diffraction, Raman spectrum, elastic modulus, hardness, substrate adhesion, friction coefficient, refractive index, and paramagnetic defect density. The friction coefficient of ta-C:H is low (0.05–0.1), and is maintained at ambient humidities, unlike for a-C:H. The friction m...

Experimental characterisation of bias-enhanced nucleation of diamond on Si

Abstract This paper reports an extensive characterisation of the bias process used to increase the nucleation density of diamond on Si. The nucleation density has been measured as a function of bias voltage, methane gas flow ratio and temperature. The nucleation density is found to be increased above 650 °C and reach a maximum at around −250 V. The nucleation density increases rapidly with time, up to a saturation value of about 10 10 cm −2 . The ion energy distribution is measured by a retarding field probe and has a maximum at ≈ 70–90 eV. This is close to the optimum energy for ion subplantation, responsible for sp 3 bonding in diamond-like carbon, which suggests that bias aids nucleation by some form of subplantation process.

Influence of ion energy and flux composition on the properties of plasma-deposited amorphous carbon and amorphous hydrogenated carbon films

Abstract The impact energies of C + ions strongly influence the density of sp 2 and sp 3 CC bonds in amorphous carbon and hydrogenated amorphous carbon films via collisions causing vacancies and subplantations. The importance of these momentum-transferring collisions has been shown experimentally for three different particle fluxes, namely those from magnetron sputtering, plasma beam and r.f. plasma deposition. The concentrations of neutrals, radicals and ions in the different fluxes and the energies of these particles are discussed and compared with the film properties density, hardness and internal stress (typical properties which strongly depend on sp 3 CC bonds), and band gap and spin density (properties which depend mostly on sp 2 CC bonds). It is found that collisions producing vacancies and interstitials (subplantations) play the predominant role with regard to the macroscopic properties of the films, even for the complex particle fluxes emerging from r.f. discharges.

Investigation of bias enhanced nucleation of diamond on silicon

The process of bias enhanced nucleation of microwave chemical vapor deposited diamond on silicon has been extensively characterized using plasma diagnostics, scanning and transmission electron microscopy (TEM), Raman spectroscopy, and x‐ray diffraction. The nucleation kinetics were measured as a function of bias voltage, methane partial pressure, and substrate temperature. The nucleation is found to be transient in character, with a delay time followed by an exponential increase in nucleation density with time, and finally a saturation. The ion flux and ion energy distribution was measured by a retarding field probe. The nucleation density was found to reach a maximum at a bias at which the ion energy distribution has a maximum of 80 eV, independent of the substrate temperature. This is taken as strong evidence that nucleation enhancement involves ion subplantation. The Raman spectra and x‐ray diffraction suggests that the films during nucleation consist primarily of sp2 bonded noncrystalline carbon. The ...

Temperature dependence of the formation of highly tetrahedral a-C:H

Abstract Deposition from a low pressure plasma beam source creates a highly tetrahedral form of hydrogenated amorphous carbon (ta-C:H)) which is analogous to the ta-C formed by deposition from a filtered cathodic arc or mass-selected ion beam. The properties of ta-C:H have been studied as a function of the substrate deposition temperatureTs and ion energy using electron energy loss spectroscopy, X-ray diffraction and atomic force microscopy. The density decreases suddenly for deposition temperatures above a threshold value, which is found to decrease with increasing ion energy. The films above the threshold are mainly sp2 bonded, with graphitic layering and high roughness. The variation of the film density with the ion energy andTs is consistent with deposition occurring by subplantation.

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.

FORMATION OF HIGHLY TETRAHEDRAL AMORPHOUS HYDROGENATED CARBON, TA-C-H

Abstract A highly tetrahedral form of hydrogenated amorphous carbon (ta-C:H) with maximum density of 2.9 g cm−3, sp3 fraction of 0.75 and hardness of 61 GPa has been deposited from acetylene using a low pressure plasma beam source. The ion energy dependence of its properties suggests that the subplantation deposition model of a-C also describes the deposition of a-C:H.

Ion assisted growth of diamond

Diamond crystallites up to 40 nm in size have been grown from a highly ionized plasma beam of acetylene for ion energies close to 100 eV per C atom and substrate temperatures above 450 °C. This shows that diamond can be grown by physical vapor deposition from an ion‐rich plasma as well as by chemical vapor deposition from a radical‐rich plasma. The formation mechanism is argued to be one of nucleation and growth rather than a stress induced transformation from graphite.