Diamond-like Carbon Growth Research Articles

Processing of diamondlike carbon using plasma immersion ion deposition

Plasma immersion ion deposition (PIID) has been used to synthesize hard amorphous hydrogenated carbon or diamondlike carbon (DLC) thin films on Si substrates with rf inductive plasmas of various Ar and C2H2 gas mixtures. The surface hardness and stress of the films were highly dependent on the magnitude of the total rf power and the pulse-bias duty factor. The ratios of the ion flux and the film deposition flux, Ji/Jd, were estimated and correlated with DLC film stress, hardness, and the amount of argon and hydrogen content retained. The DLC properties (hardness and film stress) were maximal when the Ji/Jd value ranged between 0.6 and 0.8. The balance between ion-energy transfer and relaxation in the surface and subsurface carbon atoms may explain the DLC growth in this work. The role of ion-current flux in the PIID process was found to be as important as it is in conventional ion beam assisted deposition processing.

Bond-order potentials: Can they bridge the electronic-atomistic length-scale gap?

Materials modelling involves research over a broad range of hierarchies from the electronic at the Angstrom length scale, through the atomistic and microstructural, to the continuum at the meter length scale. In this paper the theory of giant magnetoresistance and the simulation of the growth of diamond-like carbon are given as illustrative examples of modelling at the electronic and atomistic length scales, respectively. The question is then addressed as to whether the gap between the electronic and atomistic hierarchies can be bridged by the novel many-atom bond-order potentials that may be derived as an exact description of the covalent bond within the tight-binding approximation to the electronic structure.

Hydrogen-free amorphous carbon films: correlation between growth conditions and properties

Hydrogen-free amorphous carbon films with properties ranging between those of graphite and diamond were deposited using a variety of experimental methods. All the different deposition systems apply energetic (E> 10 eV) species to modify the properties of the films (usually called diamond-like carbon (DLC), a name that describes films very different from one another), but they vary in the way in which the energy is transferred to the evolving film and in the amount of control over the deposition parameters.This study reviews our present understanding of DLC growth mechanisms and discusses the correlation between the deposition parameters (e.g. species energy, substrate temperature, substrate material, angle of incidence, deposition rate and environment) and the film properties (density, surface morphology, sp3/sp2 ratio) studied using a host of experimental methods. The data are described in terms of the “subplantation model” which regards the deposition process as a shallow implantation. The properties of the films are determined by the amount of carbon species trapped in subsurface positions (internal growth governed by stress) or on the surface (surface growth).

Optical emission spectroscopy during growth of diamond-like carbon from a methane plasma

The influence of the CH 4 flow rate on the emission intensity of the CH radical has been investigated by optical emission spectroscopy in the 190–315 nm and 378–503 nm wave bands. Emission intensities of two neutral carbon lines at 193.0 nm and 247.9 nm were observed to have a similar dependence on process parameters as the intensity of the CH 430.9 nm emission line. For a given r.f. power a critical value of the CH 4 flow rate is observed. For flow rates lower than this critical value the dynamic equilibrium between C x H y and hydrogen is shifted towards higher hydrogen partial pressures. Thin films of diamond-like carbon deposited at such low flow rates were measured to have a lower density than those grown at higher flow rates. The intensities of the CH 430.8 nm and the H y lines were studied at pressures from 1 to 30 Pa, and only at the lowest values was a significant pressure dependence found. The deposition rate and the intensity of the CH 430.9 nm emission line is found to scale with the effective current defined as the ratio between the applied r.f. power and the negative self-bias.

Influence of the electron cyclotron resonance microwave plasma on growth and properties of diamond-like carbon films deposited onto r.f. biased substrates

Growth of diamond-like carbon (DLC) thin films on r.f. (13.56 MHz) biased substrates was modified by application of microwave (2.4 GHz) electron cyclotron resonance (ECR) plasma. Microhardness measurements, ellipsometry, optical absorption measurements, electrical conductivity measurements and Raman spectroscopy were used for complex characterization of the prepared DLC films. Application of the microwave ECR plasma resulted in an increase in the microhardness and index of refraction of the prepared films, probably via densification enhanced by more intensive ion bombardment. The film deposition rate remained practically unchanged, provided the absorbed microwave power was lower than a certain threshold value. The deposition rate, however, decreased, if the threshold value was exceeded. The optical band gap and the electrical conductivity of the films were influenced by the substrate bias during film deposition, but they were insensitive to the absorbed microwave power. IR absorption spectra demonstrated the prevalent content of sp 3 carbon and only a small fraction of sp 2 carbon bonds in the prepared films. Raman spectra exhibited features characteristic of DLC films.

Formation of diamond-like carbon films by 50 Hz sputtering from dual graphite targets

Experiments on the growth of diamond-like carbon (DLC) films were carried out in a stainless steel chamber by means of 50 Hz sputtering from dual graphite targets following an original method, and using 200 mTorr, 3000 V, 50 mA and 4 h deposition time. Glass, copper and stainless steel plates were used in turn as the substrate, in orientations both parallel to and normal to the target plane. The temperature of the substrate was equilibrated with the argon plasma kinetic energy which controlled the deposition and etching rate. The films were characterized by means of transmission electron diffraction, optical microscopy and electrical resistance measurements. The films on stainless steel appeared transparent, yellow, brown and blue on different areas of the substrate where different deposition or etching parameters had been employed. Transmission electron diffraction analysis of the films confirmed the presence of a DLC cubic phase with a lattice constant of about 3.44 Å. The films on glass were transparent and yellow. The deposition rate was determined with an optical microscope and was found to be about 2–3 μm h -1. The electrical resistance in the direction normal to the film was measured through the polycrystalline copper substrate with a tungsten tip probe. This gave high values in the range 10–100 kΩ. This method is a promising alternative for DLC film growth because it is low cost and quite simple.