J.L. Andújar

Preparation of BCN thin films by r.f. plasma assisted CVD

Abstract Boron-carbon-nitrogen (BC x N y ) films were grown on silicon substrates heated at 300 C by r.f. plasma assisted chemical vapour deposition from CH 4 -N 2 -B 2 H 6 gas mixtures. Dense and smooth films with different x:y composition ratios were obtained by varying the flow rate of the precursor gases. The analysis by X-ray photoelectron and infrared spectroscopies of the films revealed the formation of an hybrid B-C-N phase. Microhardness measurements performed with a nanoindenter showed that the mechanical properties of the BC x N y films depended on their composition and some of them presented a hardness higher (13 GPa) than that of hexagonal boron nitride films (12 GPa).

Study of the mechanical properties of tetrahedral amorphous carbon films by nanoindentation and nanowear measurements

Abstract Nanoindentation and nanowear measurements, along with the associated analysis suitable for the mechanical characterization of tetrahedral amorphous carbon (ta-C) films are discussed in this paper. Films of approximately 100-nm thick were deposited on silicon substrates at room temperature in a filtered cathodic vacuum arc evaporation system with an improved S-bend filter that yields films with high values of mass density (3.2 g/cm3) and sp3 content (84–88%) when operating in a broad bias voltage range (−20 V to −350 V). Nanoindentation measurements were carried out on the films with a Berkovich diamond indenter applying loads in the 100 μN–2 mN range, leading to maximum penetration depths between 10 and 60 nm. In this measurement range, the ta-C thin-films present a basically elastic behavior with high hardness (45 GPa) and high Youngs modulus (340 GPa) values. Due to the low thickness of the films and the shallow penetration depths involved in the measurement, the substrate influence must be taken into account and the area function of the indenter should be accurately calibrated for determination of both hardness and Youngs modulus. Moreover, nanowear measurements were performed on the films with a sharp diamond tip using multiple scans over an area of 3 μm2, producing a progressive wear crater with well-defined depth which shows an increasing linear dependence with the number of scans. The wear resistance at nanometric scale is found to be a function of the film hardness.

Growth of hydrogenated amorphous carbon films in pulsed d.c. methane discharges

Abstract We report the preparation of hydrogenated amorphous carbon (a-C:H) films from asymmetrical bipolar pulsed d.c. methane discharges. The films were deposited at 10 Pa of pressure on c-Si substrates placed onto an electrode powered by a pulsed d.c. generator. The asymmetrical bipolar pulsed d.c. voltage waveform consisted of a fixed positive pulse amplitude of 40 V followed by a variable negative pulse whose peak amplitude was varied from −400 up to −1400 V. Pulse frequencies of 100, 125, 150 and 200 kHz were used at a constant positive pulse time of 2 μs. In addition, a series of a-C:H samples were grown from r.f. capacitive discharges at bias voltages from −200 to −800 V. Pulsed d.c. a-C:H films 1-μm-thick were deposited at growth rates up to 60 nm/min and with internal compressive stress values between 1 and 1.5 GPa. Fourier transform-infrared and Raman analyses revealed the diamond-like character of the films. The effects of pulse parameters on the growth and structural properties of the films are discussed and compared to those of films obtained by conventional r.f. plasma-enhanced chemical vapour deposition.

MICROMECHANICAL PROPERTIES OF BN AND B-C-N COATINGS OBTAINED BY R.F. PLASMA-ASSISTED CVD

Abstract We have obtained highly transparent and hard BN films in a capacitively coupled r.f. plasma-assisted CVD reactor from three different gas mixtures: B2H6–H2–NH3, B2H6–N2 and B2H6–N2–Ar. It was found that the films were smooth, dense, and had a textured hexagonal structure with the basal planes perpendicular to the film surface. The microhardness, friction coefficient and adhesion of these coatings were measured by nanoindentation and microscratching. BCxNy films were also prepared in the same plasma-assisted CVD reactor from B2H6–N2–CH4 gas mixtures. The carbon content in the films was varied by using different CH4 flow rates. These films had a less ordered structure. The mechanical properties of these films had been compared to those of hexagonal BN films. Microhardness measurements showed that there is a correlation between film composition and hardness of the BCN films.

Effects of gas pressure and r.f. power on the growth and properties of magnetron sputter deposited amorphous carbon thin films

Abstract We discuss the effects of both the electrical power supplied to an r.f. magnetron discharge and the Ar gas pressure on the growth of amorphous carbon (a-C) films on silicon substrates by sputtering of a graphite target. The power applied to the magnetron cathode was provided in a continuous wave mode as well as in a pulsed mode where the amplitude of the r.f. signal was square-wave modulated. In the continuous wave deposition mode the power was varied from 100 to 300 W at a fixed pressure of 0.2 Pa, and the pressure from 0.2 to 2 Pa at a constant power of 300 W. The pulsed mode processes were performed by varying the r.f. peak power from 200 to 400 W at 100 Hz of modulating frequency and 20% of duty cycle. At 0.2 Pa pressure the deposition rate increased from 1 to 6 nm/min with increasing power, and decreased to 2 nm/min as pressure was increased up to 2 Pa. The compressive stress was approximately 3 GPa for films grown at low pressure and low power, and decreased below 1 GPa at higher pressure or power. Raman analysis revealed that increasing pressure favours the growth of a-C films with more disordered sp 2 domains, whereas the increase in r.f. power first leads to a reduction and then to an increase in the number and clustering of sp 2 sites into ordered rings. The friction coefficient measured using a ball-on-disk tribometer ranged between 0.1 and 0.2, being the films deposited at higher power levels that possessed the lowest values. These results were discussed in terms of the effects induced by pressure and power on the energy and flux of the species impinging the film-growing surface.

Nucleation and initial growth of bias-assisted HFCVD diamond on boron nitride films

Abstract Diamond was grown on boron nitride thin films deposited on silicon substrates. The effects of substrate biasing on the nucleation and growth of diamond were studied. Boron nitride (BN) films were obtained by rf plasma CVD. FT-IR analysis of the BN films revealed a hexagonal structure and a high transparency. The diamond deposition process was carried out in a bias-assisted hot filament reactor. Both positive and negative biases relative to the filament were applied to BN-coated Si substrates. The density and morphology of the diamond crystallites in the early stages of the nucleation were studied by scanning electron microscopy. We found that negative substrate biases higher than 200 V greatly increased the nucleation density of diamond, reaching a maximum of 1010 cm−2 for −250 V. After the nucleation stage, continuous diamond films were grown under standard deposition conditions and Raman analysis revealed the high quality of the diamond films.

Plasma parameters of pulsed-dc discharges in methane used to deposit diamondlike carbon films

Here we approximate the plasma kinetics responsible for diamondlike carbon (DLC) depositions that result from pulsed-dc discharges. The DLC films were deposited at room temperature by plasma-enhanced chemical vapor deposition (PECVD) in a methane (CH4) atmosphere at 10 Pa. We compared the plasma characteristics of asymmetric bipolar pulsed-dc discharges at 100 kHz to those produced by a radio frequency (rf) source. The electrical discharges were monitored by a computer-controlled Langmuir probe operating in time-resolved mode. The acquisition system provided the intensity-voltage (I-V) characteristics with a time resolution of 1u2002μs. This facilitated the discussion of the variation in plasma parameters within a pulse cycle as a function of the pulse waveform and the peak voltage. The electron distribution was clearly divided into high- and low-energy Maxwellian populations of electrons (a bi-Maxwellian population) at the beginning of the negative voltage region of the pulse. We ascribe this to intense stoc...

Cubic boron nitride thin films by tuned r.f. magnetron sputtering

Abstract Cubic boron nitride (c-BN) thin films were deposited on silicon by tuned substrate r.f. magnetron sputtering. A total gas flow of 3 seem (90% Ar and 10% N 2 ) was introduced in a vacuum chamber at a pressure of 1 × 10 −3 Torr. Films were deposited at two r.f. target powers (360 and 500 W) developing d.c. potentials of −220 and −350 V respectively. The substrate holder, heated to 350 °C, was biased from −40 to −95 V and its influence on the cubic content in the films was studied. The c-BN percentage in the films was between 20 and 90%, as calculated by FTIR measurements. The stress effects were also analyzed by SEM. The grain sizes of the c-BN and h-BN crystals, measured by TEM, were about 30 and 20 nm, respectively.

Comparative study of metal/amorphous-carbon multilayer structures produced by magnetron sputtering

Abstract The present study discusses the structural and mechanical properties of metal/amorphous carbon (a-C) multilayer structures of a-C/Mo/a-C/…/Mo/substrate and a-C/W/a-C/…/W/substrate deposited by magnetron sputtering. To this end, the effects of deposition parameters on multilayered nanometric structures were examined. Samples consisted of structures with alternate metallic and a-C layers with thicknesses in the nanometric range (1–3 nm). The films were deposited on crystalline silicon and glass substrates at room temperature using two opposing magnetron sputtering heads, which allowed the alternate deposition of the metallic and a-C films on the substrates placed on a directional holder. The substrate negative bias voltage was varied between 40 and 300 V and the process was performed at Ar pressures in the range 0.2–2 Pa. The structural and morphological properties and local order of the layers and interfaces were analysed by transmission electron microscopy and X-ray diffraction. Mechanical stress, and critical load for coating failure were measured by profilometry and the microscratch technique, respectively, and the results are discussed in terms of the deposition conditions and the multilayer nanostructure. Potential applications of films based on metal/a-C multilayers include the production of hard, protective, wear-resistant coatings for corrosion-resistant and high temperature-resistant applications.

Hard coatings for mechanical applications

Abstract Thin film hard coatings are produced by either intensive ion bombardment of surfaces during the deposition of hard materials or ion bombardment (primarily nitrogen) of metallic surfaces, under vacuum conditions. These techniques can be applied to mechanical tools, pieces subjected to wear and surfaces needing protective coatings such as optical recording devices and fibres. We describe an experiment combining physical and chemical vapour deposition to produce hard coatings for mechanical applications. The system comprises a hybrid plasma process combining reactive magnetron sputtering and ion beam bombardment from a capacitively coupled rf ion source in a vacuum chamber. To illustrate the results, a carbon target was used to deposit amorphous carbon (a-C) and amorphous carbon nitride (a-CN) thin films using a variable Ar and N 2 gas mixture. These were then compared with films produced by rf-plasma CVD. Single and multilayer structures of these materials were produced and characterized. The deposition techniques are compared in terms of film properties and their own parameters.