Hydrogen influence on the structure and properties of amorphous hydrogenated carbon films deposited by direct ion beam

The present work provides results for amorphous hydrogenated carbon (a-C:H) films grown by direct ion beam deposition method. Acetylene and its mixtures with hydrogen were used. The films were characterized by Rutherford backscattering spectrometry, elastic recoil detection, Raman spectroscopy, ellipsometry, infrared spectroscopy, and microhardness measurements. These techniques indicated that an admixture of hydrogen yields a lower deposition rate, a higher content of total and bounded hydrogen in the a-C:H films, and a lower film density. The optical and mechanical properties depend on both, hydrogen concentrations in the gas phase and in the films, and show a strong diamond-like component, which reaches maximum at 34 at.% of hydrogen. Further hydrogen dilution enhanced only sp² clustering and possible reduced a number of both sp³ and C-C sp³ bonds. We suppose that these effects (in the high hydrogen concentration range) are not only related to the ion irradiation difference between the light hydrogen and the much heavier carbon but also to the diffusion in the a-C:H films.     

Effects of methane flow rate on the optical properties and chemical bonding of germanium carbon films deposited by reactive sputtering

Amorphous hydrogenated germanium carbon (a-Ge_1−xC_x:H) films were prepared by radio frequency (RF) reactive magnetron sputtering of a pure Ge (111) target in a CH₄ + H₂+Ar mixture and their composition, optical properties, chemical bonding were investigated as a function of gas flow rate ratio of CH₄/(Ar + H₂). The results showed that the deposition rate first increased and then decreased as gas flow rate ratio of CH₄/(Ar + H₂) was increased from 0.125 to 0.625. And the optical gap of the a-Ge_1−xC_x:H films increased from 1.1 to 1.58 eV accompanied with the increase in the carbon content and the decrease in the relative content of Ge–C bonds of the films as the CH₄ flow rate ratio was increased, while refractive index of the films decreased and the absorption edge shifted to high energy. Through the analysis of X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy, it was found that the formation of Ge–C bonds in the films was promoted by low CH₄ flow rate which is connected with relatively high H₂ concentration and Ge content. Especially in low CH₄ concentration, the formation of sp²-hybridised C–C bonds was suppressed considerably both due to the etching effect on weak bonds of H and the fact that chemical bonding for germanium can be only sp³ hybridization.     

UV Raman spectroscopic probing into nitrogen-doped hydrogenated amorphous carbon

From the viewpoint of hardness, chemical bonding states of nitrogen-doped hydrogenated amorphous carbon film were characterized by Ultra violet (UV) Raman spectroscopy and Fourier transform infrared (FT-IR) spectroscopy. UV Raman spectra revealed that disorder of the structure in nitrogen-doped hydrogenated amorphous carbon was promoted by applying higher bias voltages in the preparation. FT-IR spectra showed that NH bonds decreased and sp³Csp³N bonds increased with the increase of the bias voltages. The content of sp³Csp³N bonds was maximized at the bias voltage of −800 V. We found out a guarantee that the content of sp³Csp³N bonds against bias voltages correlated with the hardness obtained by nanoindentation test. The structural disorder and the increase of sp³Csp³N bonds are possible source of the hardness in the case of nitrogen-doped hydrogenated amorphous carbon.     

Deposition of hydrogenated amorphous carbon films from CH4/Ar plasmas: Ar dilution effects

Hydrogenated amorphous carbon (a-C:H) films were deposited, at room temperature, from a CH₄/Ar plasma produced by a radio frequency (r.f.) glow discharge system at 13.56 MHz, and different power values. Two different characterisation techniques, Raman and FTIR spectroscopies, have been used to investigate correlations between deposition conditions and properties of hydrogenated amorphous carbon films. The composition of the initial gaseous mixture and the r.f. power input are shown to affect significantly both mechanical and microstructural properties of deposited films. As the fraction of argon in the feed gas is increased, the deposition rate increases and the deposited film shows a higher friction coefficient, thus suggesting the production of a softer material. On the other hand, Raman measurements suggest the occurrence of a lower degree of structural order in the sp² lattice. Experimental findings are discussed in terms of the different chemical composition of the plasma.     

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 sp³ 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.     

The role of hydrogen in a-C:H films deposited from hexane or acetylene using direct ion beam deposition method

The present work provides results of amorphous hydrogenated carbon (a-C:H) films deposited by direct ion beam deposition method. Hexane (C₆H₁₄+H_delivery) or acetylene (C₂H₂) precursors and their mixture with hydrogen (H₂) were used. The films were characterized by Raman spectroscopy (RS), ellipsometry, and electrical resistance measurements. RS indicates increase in sp³/sp² bonding ratio and disorder in graphite clusters, upon increasing of hydrogen content (from 0% to 50% for acetylene precursor) in the deposition gas mixture. The opposite trend is observed when the hydrogen concentration exceeded 50% (for acetylene) or additional hydrogen was added (for hexane). The data of electrical resistance measurements support the correlations defined by RS.     

High aspect ratio contact hole etching using relatively transparent amorphous carbon hard mask deposited from propylene

In this study, a high aspect ratio contact pattern, beyond 70 nm technology, in a very-large-scale integrated circuit, was achieved using hydrogenated amorphous carbon (a-C:H) film as the dry etching hard mask. The effect of temperature on the a-C:H deposits prepared by plasma enhanced chemical vapor deposition was studied. The a-C:H films resulting from propylene (C₃H₆) decomposition exhibited high transparency incorporated rich hydrogen concentration with a decreasing deposition temperature. A matrix of dispersed cross-linked sp³ clusters in a-C:H films, which has an increasing optical band gap and higher hydrogen content, is attributed to reduce the defect density of status and obtain high transmittance rate. Moreover, the higher transparency of a-C:H films could afford lithographic aligned capability as well as compressive stress and dry etching resistance. These explorations provided insights into the role of hydrogen in a-C film and also into the practicality of its future nano-scale device applications.     

Laser-induced transformation of a-C:H thin films

In this work, we report the laser irradiation effects on the properties of various types of amorphous hydrogenated carbon (a-C:H) films. The influence of the initial carbon film (hydrogen concentration, sp³/sp² ratio, and sp² clustering) is studied. The results show that a loss of hydrogen and an increase of the sp² phase are the main processes in the laser power range between 1.8 and 5 MW/cm². Only these processes are stronger for “more polymer-like” and “graphite-like” films than for “more diamond-like” films.     

Kinetic modeling of laser annealing processes in a-C:H films

In this research work, a nanosecond-pulsed YAG:Nd laser was used to modify the properties of an amorphous hydrogenated carbon film, which was deposited on c–Si substrate. Experimental examination has revealed that the primary effect of irradiation is diamond-to-graphite transformation or, more specifically, carbon sp³-to-sp² hybridization transition. These findings were qualitatively verified by numerical simulation of kinetic processes that proceed in the film under laser irradiation.     

Multilayer antireflective and protective coatings comprising amorphous diamond and amorphous hydrogenated germanium carbide for ZnS optical elements

To effectively protect and improve the transmittance of ZnS optical elements in the far infrared band, combined amorphous diamond (a-D) and amorphous hydrogenated germanium carbide (a-Ge_1−xC_x:H) films have been developed. The optical interference coatings were designed according to the layer optics theory. The a-D films, of which refractive index and film thickness were controlled by changing substrate bias and deposition time respectively, were deposited by filtered cathodic vacuum arc technology. The a-Ge_1−xC_x:H films were prepared by radio frequency sputtering technology. During this process their refractive index was modulated by changing the gas flow rate ratio and their film thickness was controlled by the flow rate ratio and deposition time. It has been shown that the combined films are superexcellent antireflective and protective coatings for ZnS optical elements.     

Optical and electrical properties of hydrogenated amorphous Si1-xGex alloy thin films prepared by planar magnetron sputtering

Thin films of hydrogenated amorphous Si_1-xGe_x were prepared by the r.f. diode planar magnetron sputtering method using composite targets of silicon and germanium in an atmosphere of H₂ diluted with argon. The optical absorption coefficient, d.c. conductivity, photoconductivity and IR transmission spectra were measured, and the dependence of these characteristics on the germanium content x was investigated. For films with x ≈ 0.1, it is found that the dark conductivity decreases and the ratio of the photoconductivity to the dark conductivity increases by about one order of magnitude compared with those for hydrogenated amorphous silicon. This phenomenon seems to be caused by a reorganization of the tetrahedrally bonded structure. Films of this composition are considered to be of interest as an opto-electronic material requiring a high resistance. Photoconductive effects are not observed for films with x > 0.3. This is considered to be due to an alloying effect. The decrease in the amount of bonded hydrogen in the films becomes appreciable for the films with x > 0.6.     

Properties of rapidly deposited amorphous hydrogenated carbon films

The properties of hydrogenated amorphous carbon films prepared by the rapid and low-temperature decomposition of toluene in an r.f. glow discharge have been investigated. The films are composed of a mixture of sp² and sp³ bonded carbons. Measurements of the optical gap show that the optical gap decreases with an increase of the r.f. power and increases with increasing pressure. The room-temperature dielectric constant decreases with increasing pressure with a dielectric loss tangent of 1%.     

Kinetic modeling of laser annealing processes in a-C:H films

In this research work, a nanosecond-pulsed YAG:Nd laser was used to modify the properties of an amorphous hydrogenated carbon film, which was deposited on c-Si substrate. Experimental examination has revealed that the primary effect of irradiation is diamond-to-graphite transformation or, more specifically, carbon sp³-to-sp² hybridization transition. These findings were qualitatively verified by numerical simulation of kinetic processes that proceed in the film under laser irradiation.     

Periodically Laser Patterned Fe?B?Si Amorphous Ribbons: Phase Evolution and Mechanical Behavior

The properties of amorphous alloys are significantly influenced by structural relaxation and partial/full crystallization induced by thermal annealing of the alloy. In this paper, the phase evolution and mechanical behavior of laser‐patterned Fe? B? Si amorphous alloys are reported. The laser patterning was employed to cause localized thermal effects on the surface of amorphous ribbons. The laser irradiation with a lower fluence (12 J · cm^?2) caused significant embrittlement of the alloy due to the structural relaxation. The partial crystallization of an amorphous alloy into α‐Fe(Si) was also observed with laser irradiation using higher laser fluences (15 and 17 J · cm^?2). The embrittlement effect due to laser‐irradiation‐induced crystallization was more severe than that due to structural relaxation.     

Effects of applied power on hydrogenated amorphous carbon (a-C:H) film deposition by low frequency (60 Hz) plasma-enhanced chemical vapor deposition (PECVD)

Hydrogenated amorphous carbon (a-C:H) films were deposited onto glass substrates using low frequency (60 Hz) plasma-enhanced chemical vapor deposition and the effects of the applied power on a-C:H films deposition were investigated. During deposition, the electron temperature and the density of CH₄-H₂ plasma were 2.4-3.1 eV and about 10⁸ cm⁻³, respectively. The main optical emission peak of the carbon species observed in the CH₄-H₂ plasma is shown to be excited carbon CH* at 431 nm. The sp³/sp² ratio, band gap, hydrogen content, and refractive index of a-C:H films gradually increased up to a power of 25 W and then saturated at higher power. This tendency is similar to the variation of plasma parameters with varying applied power, thereby indicating that a strong relationship exists between the properties of the films and the plasma discharge.     

Structure and optical properties of hydrogenated amorphous carbon-tin alloys prepared using the sputter-assisted plasma chemical deposition technique

In this work the results of studies on hydrogenated amorphous C-Sn semiconducting alloys whose optoelectrical properties were found to be attractive for optical applications in solar energy conversion technology are reported and discussed.

The films were obtained by sputtering β-Sn targets in a plasma atmosphere of methane and argon in variable proportions at room temperature. The optical and electrical parameters were measured and correlated to the elemental composition, the chemical bondings and the amorphicity of the material.

Moreover, the effects of the deposition parameters on the composition and the structure of the films were identified so that control of the photoelectrical and structural parameters could be affected by choosing suitable values for the deposition parameters.     

Superconducting properties of amorphous Zr-Ge binary alloys

A new type of refractory metal-metalloid amorphous alloys exhibiting superconductivity has been found in a binary Zr-Ge system by a modified melt-spinning technique. Specimens are in the form of continuous ribbons 1 to 2 mm wide and 0.02 to 0.03 mm thick. The germanium content in the amorphous alloys is limited to the range of 13 to 21 at%. These amorphous alloys are so ductile that no cracks are observed even after closely contacted bending test. The Vickers hardness and crystallization temperature increase from 435 to 530 DPN and from 628 to 707 K, respectively, with germanium content, and the tensile fracture strength is about 1460 MPa. Furthermore, the amorphous alloys exhibit a superconducting transition which occurs very sharply. The superconducting transition temperature (T _c) increases with decreasing germanium content and reaches a maximum value of 2.88 K for Zr₈₇Ge₁₃. The upper critical magnetic field for Zr₈₇Ge₁₃ alloy was of the order of 21.8 kOe at 2.0 K and the critical current density for Zr₈₅Ge₁₅ alloy was about 175 A cm^–2 at 1.70 K in the absence of an applied field. The upper critical field gradient atT _c and the electrical resistivity at 4.2 K increase significantly from 24.6 to 31.5 kOe K^–1 and from 235 to 310cm, respectively, with the amount of germanium. The Ginzburg-Landau (GL) parameter and the GL coherence length §_GL (0) were estimated to be 72 to 111 and about 7.9 nm, respectively, from these experimental values by using the Ginzburg-Landau-Abrikosov-Gorkov (GLAG) theory and hence it is concluded that the Zr-Ge amorphous alloys are extremely soft type-II superconductor with high degree of dirtiness which possesses theT _c values higher than zirconium metal, in addition to high strength combined with good ductility.     

Difference of deposition process of an amorphous carbon film due to source gases

We compared the deposition process of an amorphous carbon film using acetylene as a source gas with the deposition process using methane. The process was investigated by using infrared absorption spectroscopy in multiple internal reflection geometry (MIR-IRAS). The infrared spectra showed that sp³-hydrocarbon species was observed in both cases: on the other hand, the sp- and sp²-carbon and/or hydrocarbon species was clearly observed in the film deposited using acetylene. Moreover, we observed the changes in predominant adsorbed species with film thickness in both cases; these facts suggest that an amorphous carbon film grows with the structural changes of adsorbed species in both deposition processes.     

Field emission characteristics of fast grown nanocrystalline diamond/amorphous carbon composite films by microwave plasma-enhanced chemical deposition method

This study synthesized the nanocrystalline diamond/amorphous carbon (NCD/a-C) composite films by the microwave plasma-enhanced chemical vapor deposition (MPCVD) system with Ar/CH₄/N₂ mixtures. A localized rectangular-type jet-electrode with high density plasma was used to enhance the formation of NCD/a-C films, and a maximum growth rate of 105.6 µm/h was achieved. The content variations of sp² and sp³ phases via varying nitrogen gas flow rates were investigated by using Raman spectroscopy. The NCD/a-C film which synthesized with 6% nitrogen concentration and no hydrogen plasma etching treatment possessed a low turn-on electric field of 3.1 V/µm at the emission current of 0.01 µA.     

The influence of nanosecond pulse laser irradiation on the properties of a-C:H films

Plasma-deposited amorphous hydrogenated carbon (a-C:H) films are determined both by the carbon sp³/sp² bonding ratio and the hydrogen content. As the energy of the bonds C-H (C-C) is considerably smaller than that of CC or CC bonds, so the hydrogen concentration and the physical properties of a-C:H films can be varied by laser irradiation. The properties of produced films were investigated by Rutherford backscattering (RBS) and elastic recoil detection (ERD) spectroscopy, null-ellipsometry, and Raman spectroscopy (RS). It was found that films with higher hydrogen concentration are more sensitive to nanosecond pulse laser irradiation.