Silicon-containing Diamond-like Carbon Films Research Articles

Effect of Soft X-ray Irradiation on Film Properties of a Hydrogenated Si-Containing DLC Film.

The effect of soft X-ray irradiation on hydrogenated silicon-containing diamond-like carbon (Si-DLC) films intended for outer space applications was investigated by using synchrotron radiation (SR). We found that the reduction in film thickness was about 60 nm after 1600 mA·h SR exposure, whereas there was little change in their elemental composition. The reduction in volume was attributable to photoetching caused by SR, unlike the desorption of hydrogen in the case of exposure of hydrogenated DLC (H-DLC) film to soft X-rays. The ratio of the sp2 hybridization carbon and sp3 hybridization carbon in the hydrogenated Si-DLC films, sp2/(sp2 + sp3) ratio, increased rapidly from ~0.2 to ~0.5 for SR doses of less than 20 mA·h. SR exposure significantly changed the local structure of carbon atoms near the surface of the hydrogenated Si-DLC film. The rate of volume reduction in the irradiated hydrogenated Si-DLC film was 80 times less than that of the H-DLC film. Doping DLC film with Si thus suppresses the volume reduction caused by exposure to soft X-rays.

Local Structure Analysis on Si-Containing DLC Films Based on the Measurement of C K-Edge and Si K-Edge X-ray Absorption Spectra

In this paper, the local structure of silicon-containing diamond-like carbon (Si-DLC) films is discussed based on the measurement of C K-edge and Si K-edge near-edge x-ray absorption fine structure (NEXAFS) spectra using the synchrotron radiation of 11 types of Si-DLC film fabricated with various synthesis methods and having different elemental compositions. In the C K-edge NEXAFS spectra of the Si-DLC films, the σ* band shrunk and shifted to the lower-energy side, and the π* peak broadened with an increase in the Si content in the Si-DLC films. However, there were no significant changes observed in the Si K-edge NEXAFS spectra with an increase in the Si content. These results indicate that Si–Si bonding is not formed with precedence in Si-DLC film.

Enhancing the adhesion and tribological performance of Si-DLC film on NBR by Ar plasma pretreatment under a high bias

Silicon-containing diamond-like carbon (Si-DLC) films were successfully deposited on nitrile-butadiene rubber (NBR) via magnetron sputtering Si target in Ar and CH4 mixture atmosphere. The influence of Ar plasma pretreatment bias on the adhesion and tribological properties of the Si-DLC coated NBR were investigated systematically. The results indicated that the surface roughness of NBR substrate decreased monotonously with the increase of bias. Compared with the virgin NBR, the surface topography did not change significantly under a low bias, but a shallow layer and considerable chain scission could be observed by SEM and FTIR analysis under a high bias. As a consequence, the excellent adhesion could be obtained by Ar plasma pretreatment under a high bias (>-500 V), while the adhesion of the samples pretreated by a low bias (≤-500 V) were even worse than that of untreated samples. Furthermore, the samples pretreated at a relatively high bias of -1000 V exhibited the lowest and stable friction coefficient of 0.25 and outstanding wear resistance, while the tribological performance of the samples pretreated with a low bias (≤-500V) were even worse than that of untreated ones. The research results of this work are of great surface engineering significance for the design and fabrication of hard films with a high adhesion and excellent tribological performance on rubber substrates.

Long-term thermal stability of Si-containing diamond-like carbon films prepared by plasma source ion implantation

The long-term stability of silicon-containing diamond-like carbon films was investigated. The samples were prepared by plasma source ion implantation with a mixture of tetramethylsilane (TMS) and acetylene (C2H2) using negative high voltage pulses. The film composition was changed by varying the flow rates of the TMS and C2H2 gases, resulting in a Si content from 0 to 44 at.%. After deposition the films were annealed at temperatures from 523 K to 773 K for 168 h in ambient air. The effect of the Si content on the structure, the mechanical and tribological properties of the DLC films was investigated. A silicon oxide layer is produced on the surface of the film which improves the thermal stability. Mechanical and friction characteristics of the Si-DLC were not much affected by the long-term thermal annealing if the temperature was kept below 573 K.

Plasma parameter investigation during plasma-enhanced chemical vapor deposition of silicon-containing diamond-like carbon films

In this work, tetramethylsilane-based plasma-enhanced chemical vapor deposition (PECVD) processes were studied, and the deposited silicon-containing diamond-like carbon (DLC) films were analyzed. The main goal was to identify correlations between plasma parameters and the film structure and properties. The electron temperature, gas temperature, and hydrogen and silicon particle densities in these plasmas were calculated using optical emission spectroscopy measurements; the electron density and elastic electron collision rate were determined using self-excited electron resonance spectroscopy. The elemental composition of the films was determined by glow discharge optical emission spectroscopy, and the hardness and Young's modulus were characterized using nanoindentation. The plasma parameters of the gas temperature and electron temperature revealed stringent correlations with the film composition and properties and thus can already monitor the resulting properties during the deposition process. Increasing the gas temperature using power variation leads to reduced incorporation of silicon and hydrogen in the diamond-like carbon films with a simultaneous increase of the film hardness. However, a gas temperature increase using a higher gas flow rate results in a decrease in the film hardness and an increase in the silicon and hydrogen contents. These results are promising concerning the use of plasma parameters for process control of CVD processes.

Comprehensive Classification of Near-Edge X-ray Absorption Fine Structure Spectra of Si-Containing Diamond-Like Carbon Thin Films

Structural analysis by the measurement of carbon K-edge near-edge X-ray absorption fine structure (NEXAFS) using synchrotron radiation was performed on 23 types of silicon-containing diamond-like carbon (Si-DLC) film fabricated by various synthesis methods. In addition, elementary composition in the Si-DLC films was determined by the combination of Rutherford backscattering spectrometry (RBS) and elastic recoil detection analysis (ERDA) using an electrostatic accelerator. In the C K-edge NEXAFS spectra of Si-DLC films, the σ* band shrunk and shifted to the lower-energy side, and the π* peak broadened with increasing silicon content in the Si-DLC film. The observed NEXAFS spectra of Si-DLC films were classified into four types.

Temperature dependent properties of silicon containing diamondlike carbon films prepared by plasma source ion implantation

Silicon containing diamondlike carbon (Si-DLC) films were prepared on silicon wafer substrates by a plasma source ion implantation method with negative pulses superposed on a negative dc voltage. A mixture of acetylene and tetramethylsilane gas was introduced into the discharge chamber as working gases for plasma formation. Ions produced in the plasma are accelerated toward a substrate holder because of the negative voltage applied directly to it. After deposition, the films were annealed for 0.5 h in ambient air at temperatures up to 923 K in order to evaluate the thermal stability of the Si-DLC films. The films were analyzed by x-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy, and Raman spectroscopy. The surface morphology of the films and the film thickness were observed by atomic force microscopy and scanning electron microscopy. The mechanical and tribological properties were investigated by an indentation method and a ball-on-disk test. The results show the silicon containing DLC films were amorphous and the surface roughness of the Si containing DLC films was very smooth and no special structure was observed. Integrated intensity ratios ID/IG of Raman spectroscopy of the Si containing DLC films decreased with Si content. The Raman spectra showed that the structure of the Si-free DLC film changed to a graphitelike structure with increasing annealing temperature, whereas that of the 24 at. % Si containing DLC films did not change at the maximum temperature used in this study. A very low friction coefficient was obtained for the 13 at. % Si containing DLC film. The surface roughness and the hardness of the films changed with increasing annealing temperature. The formation of Si oxide in a near surface layer was confirmed by XPS and it prevents further oxidation of the inside of the film. Heat resistivity of DLC films can be improved by Si addition into the DLC films.

Deposition of silicon-containing diamond-like carbon films by plasma-enhanced chemical vapour deposition

Silicon-containing diamond-like carbon (Si-DLC) films were prepared on silicon wafer substrates by DC glow discharge. Acetylene and mixture with tetramethylsilane gases were used as working gases for the plasma. A negative DC voltage was applied to the substrate holder. The DC voltage was changed in the range from − 1 kV to − 4 kV. The surface morphology of the films and the film thickness were observed by scanning electron microscopy. The compositions of the Si-containing DLC films were examined by X-ray photoelectron spectroscopy. The film structure was characterized by Raman spectroscopy. A ball-on-disc test with 2 N load was employed to obtain information about the friction properties and sliding wear resistance of the films. The films were annealed at 723 K, 773 K and 873 K in ambient air for 30 min in order to estimate the thermal stability of the DLC films. The surface roughness of the Si-containing DLC films was very low and no special structure was observed. The deposition rate increased linearly with Si content. The positions of D- and G-bands in Raman spectra decreased with Si content. The integrated intensity ratios I D/ I G of the Si-containing DLC films decreased with Si content. A very low friction coefficient of 0.03 was obtained for a 24 at.% Si-containing DLC film. The heat resistivity of DLC films can be improved by Si addition into the DLC films.

Small amplitude reciprocating wear performance of diamond-like carbon films: dependence of film composition and counterface material

Small amplitude (50 μm) reciprocating wear of hydrogen-containing diamond-like carbon (DLC) films of different compositions has been examined against silicon nitride and polymethyl-methacrylate (PMMA) counter-surfaces, and compared with the performance of an uncoated steel substrate. Three films were studied: a DLC film of conventional composition, a fluorine-containing DLC film (F-DLC), and silicon-containing DLC film. The films were deposited on steel substrates from plasmas of organic precursor gases using the Plasma Immersion Ion Implantation and Deposition (PIIID) process, which allows for the non-line-of-sight deposition of films with tailored compositions. The amplitude of the resistive frictional force during the reciprocating wear experiments was monitored in situ, and the magnitude of film damage due to wear was evaluated using optical microscopy, optical profilometry, and atomic force microscopy. Wear debris was analyzed using scanning electron microscopy and energy dispersive spectroscopy. In terms of friction, the DLC and silicon-containing DLC films performed exceptionally well, showing friction coefficients less than 0.1 for both PMMA and silicon nitride counter-surfaces. DLC and silicon-containing DLC films also showed significant reductions in transfer of PMMA compared with the uncoated steel. The softer F-DLC film performed similarly well against PMMA, but against silicon nitride, friction displayed nearly periodic variations indicative of cyclic adhesion and release of worn film material during the wear process. The results demonstrate that the PIIID films achieve the well-known advantageous performance of other DLC films, and furthermore that the film performance can be significantly affected by the addition of dopants. In addition to the well-established reduction of friction and wear that DLC films generally provide, we show here that another property, low adhesiveness with PMMA, is another significant benefit in the use of DLC films.

X-ray absorption spectroscopy, simulation and modeling of Si-DLC films

Amorphous silicon-containing diamond-like carbon (Si-DLC) films were deposited on silicon wafers by Ar+ Ion Beam Assisted Deposition (IBAD) at various energy conditions. The films were examined with X-ray Absorption Near Edge Structure (XANES) spectroscopy and Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. The Si K-edge X-ray Absorption Spectroscopy (XAS) results indicate that Si-DLC films have an amorphous structure, where each Si atom is coordinated to four carbon atoms or CHn groups. This short-range order, where a Si atom is surrounded by four C atoms, was found in all Si-DLC films. The XANES spectra do not indicate Si coordination to oxygen atoms or phenyl rings, which are present in the precursor material. A structural model of Si-DLC is proposed based on XAS findings. Simulated X-ray absorption spectra of the model produced by FEFF8 show a good resemblance to the experimental data.

フッ化炭素プラズマ処理シリコン含有ダイヤモンドライクカーボン膜の機械特性

Diamond like carbon (DLC) and silicon containing DLC (Si-DLC) films were deposited by EBEP (electron beam excited plasma)-CVD. The effects of CF4 plasma treatment and Si-inclusion on DLC film on surface energy, nanoindentation hardness and nanoscratching properties were investigated. DLC and Si-DLC films were surface modified by CF4 plasma treatment. CF4 plasma treatment decreases surface energy evaluated by the liquid drop method. Si-inclusion decreases the nanoindentation hardness. CF4 plasma treatment decreases nanoindentaion hardness of DLC film, however increases the hardness of 20% Si containing DLC film. Micro wear depth increases by Si-inclusion evaluated by nanoscratch test. CF4 plasma treatment increases the micro wear of DLC film, however decreases the micro wear of 20% silicon containing DLC film. Friction coefficients of both DLC and Si-DLC films were decreased by CF4 plasma treatment.

The effect of residual stress on adhesion of silicon-containing diamond-like carbon coatings

The silicon-containing diamond-like carbon film was deposited by r.f. plasma CVD with reactant gases of CH4, SiH4 and Ar on the substrates of silicon wafer, Corning 7059 glass and Ti–6Al–4V alloy respectively. In this study, the effects of residual stress in the film on adherence and the failure mode of silicon-containing diamond-like carbon film deposited on different substrate materials are investigated. The results show that all the coated films suffer a compressive stress the magnitude of which depends on coating process parameters. By raising r.f. power for deposition the internal stress is increased and the scratch critical load is improved. On the other hand, by raising the substrate temperature the thermal stress is increased and the scratch critical load is decreased slightly. The scratch tests for the films coated on both silicon wafer and Corning 7059 glass reveal tensile failure mode whereas for the one coated on Ti–6Al–4V alloy reveals chipping failure mode. From the observation of the results of indentation test for the films coated on Ti–6Al–4V, the sample deposited at higher r.f. power and lower substrate temperature exhibits less damage which demonstrates that the film obtained has a better adherence behavior.

Wear behavior of silicon-containing diamond-like carbon coatings

Abstract The silicon-containing diamond-like carbon (DLC) films have been deposited on SKD61 steel by r.f. PECVD (plasma-enhanced chemical vapor deposition). A pin-on-disk wear test with a higher normal load, 30 and 40 N, was conducted to investigate the wear behavior of the DLC films. Various structures of the films obtained by different deposition conditions lead to different wear lives of the DLC-coated steels. A DLC film with small amount of silicon addition has a lower friction coefficient (0.01) than an undoped film (0.1). Raman analysis showed that in the wear test, graphitization of the pure DLC film occurs at the initial stage, whereas for the silicon-containing DLC film, graphitization of the wear debris or transferred film was not observed after the wear test, which indicates that the silicon-containing DLC film exhibits a better thermal stability than the pure DLC film. The lower friction coefficient value of silicon-doped DLC may be due to the formation of SiO 2 that might arise from the contamination in the deposition system or oxidation in processing.

Diamondlike Carbon Materials as Low-k Dielectrics for Multilevel Interconnects in Ulsi

AbstractA variety of diamondlike carbon (DLC) materials were investigated for their potential applications as low-k dielectrics for the back end of the line (BEOL) interconnect structures in ULSI circuits. Hydrogenated DLC and fluorine containing DLC (FDLC) were studied as a low-k interlevel and intralevel dielectrics (ILD), while silicon containing DLC (SiDLC) was studied as a potential low-k etch stop material between adjacent DLC based ILD layers, which can be patterned by oxygen-based plasma etchingIt was found that the dielectric constant (k) of the DLC films can be varied between >3.3 and 2.7 by changing the deposition conditions. The thermal stability of these DLC films was found to be correlated to the values of the dielectric constant, decreasing with decreasing k. While DLC films having dielectric constants k>3.3 appeared to be stable to anneals of 4 hours at 400 °C in He, a film having a dielectric constant of 2.7 was not, losing more than half of its thickness upon exposure to the same anneal. The stresses in the DLC films were found to decrease with decreasing dielectric constant, from 700 MPa to about 250 MPa. FDLC films characterized by a dielectric constant of about 2.8 were found to have similar thermal stability as DLC films with k >3.3. The thermally stable FDLC films have internal stresses <300 MPa and are thus promising candidates as a low-k ILD.For the range of Si contents examined (0-9% C replacement by Si), SiDLC films with a Si content of around 5% appear to provide an effective etch-stop for oxygen RIE of DLC or FDLC films, while retaining desirable electrical characteristics. These films showed a steady state DLC/SiDLC etch rate ratio of about 17, and a dielectric constant only about 30% higher than the 3.3 of DLC.