A. Raveh

Critical ion energy and ion flux in the growth of films by plasma‐enhanced chemical‐vapor deposition

Dual‐mode microwave/radio frequency plasma‐enhanced chemical‐vapor deposition allows one to decouple ion bombardment effects from processes in the discharge volume. This approach has been used to deposit three types of hydrogenated amorphous films at low substrate temperature and high deposition rate (∼10–20 A/s): SiNx, SiO2, and a‐C:H. For each of these materials, we have determined critical values of the negative bias potential, VB,C, of the average ion energy, Ei,c, and of the ion/condensing‐atom flux ratio (φi/φn)c, which characterize the transition from a porous to a densely packed microstructure. The evaluations are based on measurements of the films’ resistivity, dielectric loss tangent, microhardness, density, and stress. The Ei,c, (φi/φn)c values found are: 170 eV, 0.60 for SiNx; 70 eV; 0.26 for SiO2; and 80 eV, 0.28 for a‐C:H. Ion bombardment at energies above Ei,c has been found to account for a large portion of hydrogen in the films which is not chemically bonded. The results are interprete...

Deposition and properties of diamondlike carbon films produced in microwave and radio‐frequency plasma

Hard a‐C:H films were grown in a dual frequency plasma sustained simultaneously by microwave and radio‐frequency power. ‘‘Optimum’’ growth conditions, namely those leading to the most pronounced sp3 structural features in the films, depend very strongly on the methane feed gas flow rate and on the argon concentration, in the case of CH4/Ar mixtures. These optimum conditions have been found to correspond to maximum values of ion flux at the growing film surface, and high concentrations of precursor species such as CH, C2, C3, and atomic hydrogen in the plasma, as revealed by optical emission spectroscopy. Films grown under optimum conditions have very high microhardness (∼50 GPa), high density (1.8 g/cm−3), and low internal stress (0.5 GPa). Addition of argon to the methane is shown to enhance the gas phase fragmentation and to raise the microhardness, but argon atoms trapped in the films’ structure increase the internal stress.

Surface characterization of thin layers of aluminium oxide

Abstract Thin oxide layers of commercial pure aluminium (1100-Al) and AlZnMgCu alloy (7075-Al) were characterized after oxidation in a 2.45 GHz microwave discharge in oxygen plasma at low temperature (400 ± 50 °C). The composition and structure of the oxide layers were studied by Auger electron spectroscopy (AES) and Fourier transform IR (FTIR) spectroscopy. In addition, atomic force microscopy (AFM) and micro-indentation techniques were used for surface topography observations and for the evaluation of the coating-surface deformation response. It was found that the 1100-Al layer was composed of duplex sublayers, namely an external γ-Al 2 O 3 layer followed by an interdiffused Al-O sublayer. Under similar oxidation conditions the oxide structure of 7075-Al alloy was mainly composed of Mg-O. The surface features largely depended on the plasma processing parameters. The oxide-substrate composite layer was characterized by higher microhardness values up to about twice that of an untreated substrate. The microhardness value was mainly determined by the oxide composition, microstructure and thickness. An indentation dimensional effect (IDE) was evident in the treated sample, and was confirmed by microscale measurements. The chemical and structural characterization of the oxide layers is presented and discussed with emphasis on the role of processing and micro-alloying effects on the fine layer characteristics.

Etching of a‐C:H films by an atomic oxygen beam

Hydrogenated amorphous carbon (a‐C:H) films are considered for real time monitoring of atomic oxygen in Low Earth Orbit, and during plasma etching processes. a‐C:H layers were deposited onto quartz crystal microbalances (QCM) in a dual microwave/radio frequency (mw/rf) plasma in methane and methane/argon mixtures. The QCMs were exposed to a neutral atomic oxygen beam in a system simulating the space environment, using a flux of ∼1016 atoms/cm2 s at 2.5 eV average incident energy. The etch rate Er was determined from the mass loss by in situ measurement of frequency shift of the QCM oscillator. The Er values, ranging from 1 to 20 ng/cm2 s, were found to increase with the hydrogen concentration in the films, and to decrease with increasing film density. Systematically higher Er values were found for a‐C:H with a polymerlike character and for very hard ‘‘diamondlike films’’ with bonded hydrogen, in contrast to films with predominantly unbonded hydrogen. For comparison, Er values for crystalline chemical vapo...

Characterization of carburized tantalum layers prepared in inductive RF plasma

Abstract Tantalum surfaces were carburized in order to improve their mechanical properties and corrosion resistance. The carburized layers were produced in an inductively coupled radio-frequency (r.f.) plasma using argon/methane or argon/methane/hydrogen mixtures, and substrate temperatures of between 773 and 1123 K, while the main process variables were: total gas pressure, p (6–100 torr); power, P (0.3–2.0 kW); CH4 concentration (0.1–0.8 vol.%); hydrogen concentration, CH2 (1–50 vol.%); and process duration, t (0.5–20 h). The carbide phases and film composition were determined by X-ray diffraction, Auger electron spectroscopy, and temperature-programmed desorption using a mass spectrometer. The mechanical properties were measured by microindentation and microscratch techniques, and the corrosion resistance was examined by impedance analysis. For the same treatment time, it was observed that the thickness of the carburized layer and the phase content (TaC or Ta2C) were different for three distinct ranges of fabrication conditions: (a) p

Carburizing of tantalum by radio-frequency plasma assisted chemical vapor deposition

Tantalum carbide (TaC) has great potential as an alternative to tantalum and tantalum oxide for applications requiring thermal stability and corrosion resistance. In this study TaC layers were produced by inductive rf plasma-assisted chemical vapor deposition that combines diffusion with chemical vapor deposition. The maximum temperature of the tantalum substrates measured during a 6 h processing time was 900 °C using Ar–CH4 or Ar–CH4–H2 gas mixtures. The microstructure of the layers was characterized by X-ray diffraction and Auger electron spectroscopy, and the mechanical properties were studied by micro- and nanoindentation and by microscratch techniques. A close correlation among the carburizing parameters, the microstructure, the mechanical behavior of the layers, and the corrosion resistance was found. The best performing films, several μm thick, consisting of TaC phase with the highest hardness (∼25 GPa), were obtained under the following conditions: input power of 1400 W, pressure of 40–60 mbar, an...

Effect of Radio-Frequency and Low-Frequency Bias Voltage on the Formation of Amorphous Carbon Films Deposited by Plasma Enhanced Chemical Vapor Deposition

The effect of radio-frequency (RF) or low-frequency (LF) bias voltage on the formation of amorphous hydrogenated carbon (a-C:H) films was studied on silicon substrates with a low methane (CH4) concentration (2–10 vol.%) in CH4+Ar mixtures. The bias substrate was applied either by RF (13.56 MHz) or by LF (150 kHz) power supply. The highest hardness values (~18–22 GPa) with lower hydrogen content in the films (~20 at.%) deposited at 10 vol.% CH4, was achieved by using the RF bias. However, the films deposited using the LF bias, under similar RF plasma generation power and CH4 concentration (50 W and 10 vol.%, respectively), displayed lower hardness (~6–12 GPa) with high hydrogen content (~40 at.%). The structures analyzed by Fourier Transform Infrared (FTIR) and Raman scattering measurements provide an indication of trans-polyacetylene structure formation. However, its excessive formation in the films deposited by the LF bias method is consistent with its higher bonded hydrogen concentration and low level of hardness, as compared to the film prepared by the RF bias method. It was found that the effect of RF bias on the film structure and properties is stronger than the effect of the low-frequency (LF) bias under identical radio-frequency (RF) powered electrode and identical PECVD (plasma enhanced chemical vapor deposition) system configuration.

Graded TiAlN layers deposited by electron cyclotron resonance-assisted reactive sputtering

Graded TiAlN layers were deposited by plasma reactive sputtering assisted by electron cyclotron resonance (ECR). For reactive sputtering, dual cathode radio-frequency magnetron targets, Ti and Al, were used. The layers were deposited using various combinations of variables such as power input, bias substrate voltage, and gas feed composition. The deposition process was monitored by optical emission spectroscopy (OES). The OES results indicate that microwave excitation added to radio-frequency plasma has contrasting effects on the Ti and Al concentration in the gas phase, enhancing titanium and quenching aluminum species reaching the deposited substrate. Thus, by the regulation of the ECR power and the ratio of nitrogen to argon flow, formation of graded layers is possible. The layers formed in this way were characterized with regard to structure, composition, and mechanical properties using an x-ray diffractometer, an Auger electron spectroscopy microscope, and a Vickers microhardness and scratch tester (...

Fourier Transform Infrared Photoacoustic Spectroscopy of Amorphous Carbon Films

Phase Fourier Transform Infrared Photoacoustic Spectroscopy (PHAS-FTIR/PAS) can distinguish between surface and bulk chemical structure. In the present work, PHASFTIR/PAS is applied to the study of hydrogenated amorphous carbon (a-C:H) films deposited in a dual microwave/radio-frequency plasma. It is shown that spectra correlate well with physico-chemical properties of a-C:H films.