Plasma-enhanced Chemical Vapor Deposition Technique Research Articles

Nano indentation measurements on nitrogen incorporated diamond-like carbon coatings

Nanoindentation testing was performed on nitrogen (N2) incorporated diamond-like carbon (N-DLC) films and deposited using radio-frequency plasma-enhanced chemical vapor deposition technique, with varied percentage of nitrogen partial pressures of 0, 44.4, 66.6, and 76.1%. The values of nanohardness (H) and elastic modulus (E) of these films were obtained from 38 to 22 GPa and 462 to 330 GPa, respectively, as the partial pressure of N2 increases from 0 to 76.1%. Further, these films were studied for % elastic recovery, ratio between residual displacement after load removal and displacement at maximum load (dres/dmax ), plastic deformation energy and plasticity index parameter (H/E). Both hardness per unit stress and plasticity index per unit stress were found to be maximum at N2 partial pressure of 76.1%. X-ray photoelectron spectroscopy measurements confirmed the presence of N2 in these films.

Microwave plasma- enhanced chemical vapour deposition growth of carbon nanostructures

The effect of various input parameters on the production of carbon nanostructures using a simple microwave plasma-enhanced chemical vapour deposition technique has been investigated. The technique utilises a conventional microwave oven as the microwave energy source. The developed apparatus is inexpensive and easy to install and is suitable for use as a carbon nanostructure source for potential laboratory-based research of the bulk properties of carbon nanostructures. A result of this investigation is the reproducibility of specific nanostructures with the variation of input parameters, such as carbon-containing precursor and support gas flow rate. It was shown that the yield and quality of the carbon products is directly controlled by input parameters. Transmission electron microscopy and scanning electron microscopy were used to analyse the carbon products; these were found to be amorphous, nanotubes and onion-like nanostructures.

ZnO interface layer and CO 2 plasma treatment for improving efficiency of micromorph silicon solar cells

We have developed zinc oxide (ZnO) film and CO 2 plasma treatment for the use as an intermediate layer between top and bottom cell in order to improve performance of micromorph silicon solar cells. The CO 2 plasma treatment was performed by very high frequency plasma-enhanced chemical vapor deposition (VHF PECVD) technique, and the ZnO interface layer was deposited by DC-magnetron sputtering method. Effects of both techniques on the cell performance were comparatively investigated. We found that the ZnO interface layer and CO 2 plasma treatment were effective in enhancing V oc, J sc as well as FF of the cells as the same. The micromorph solar cells using an optimized ZnO interface layer and the CO 2 plasma treatment indicated initial conversion efficiency of 11.4% and 11.2%, respectively. Experimental results indicated that the CO 2 plasma treatment technique is more suitable for using in cell fabrication process than the ZnO interface layer since it is simpler and has no negative impact of possible shunts.

Dual-dome micromechanical resonator fabricated with reactive ion etching and plasma-enhanced chemical vapor deposition techniques

A novel dual-dome micromechanical resonator and a method for fabricating it into a single or amorphous crystal silicon film layer is demonstrated. An electrostatic effect on the input resonator induces high-frequency resonant mechanical motion in the first dome plate, which is mechanically conducted into the second equivalent dome plate. Transduction from the input resonator to the output resonator is me- chanically performed not by using coupling rods but by overlapping the plates. Oscillations are obtained at 8.5 MHz and 17 MHz when the reso- nator is buffered with a high-impedance junction gate field-effect transis- tor amplifier. © 2010 Society of Photo-Optical Instrumentation Engineers.

Residual stress in diamond-like carbon films: Role of growth conditions and ion irradiation

The dependence of the internal residual stress in thin diamond-like carbon films grown by the plasma-enhanced chemical vapor deposition technique on the most important growth parameters, namely, the radio-frequency (RF) power and direct-current (DC) bias voltage, was studied. It was shown that the compressive stress reaches its highest value of 2.7 GPa at the low RF power and DC bias values. Both increase and decrease of these parameters result in stress decrease. The stress increases with increase in the growth temperature from 250 to 350°C. Thermal annealing of up to 350°C does not affect the stress value. Subsequent irradiation of the films by In+ and P+ ions with the energy of 350 and 120 keV, respectively, results in the decrease in the compressive stress followed by its inversion to the tensile one. The stress linearly depends on the effective dose of up to 0.5 DPA with the slope of (8.7 ± 1.3) Gpa/DPA.

Structure of PbTe(SiO2)/SiO2multilayers deposited on Si(111)

The structure of thin films composed of a multilayer of PbTe nanocrystals embedded in SiO2, named as PbTe(SiO2), between homogeneous layers of amorphous SiO2deposited on a single-crystal Si(111) substrate was studied by grazing-incidence small-angle X-ray scattering (GISAXS) as a function of PbTe content. PbTe(SiO2)/SiO2multilayers were produced by alternately applying plasma-enhanced chemical vapour deposition and pulsed laser deposition techniques. From the analysis of the experimental GISAXS patterns, the average radius and radius dispersion of PbTe nanocrystals were determined. With increasing deposition dose the size of the PbTe nanocrystals progressively increases while their number density decreases. Analysis of the GISAXS intensity profiles along the normal to the sample surface allowed the determination of the period parameter of the layers and a structure parameter that characterizes the disorder in the distances between PbTe layers.

Characterization and tribological application of diamond-like carbon (DLC) films prepared by radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD) technique

Diamond-like carbon (DLC) films were successfully prepared on glass substrates and surfaces of selenium drums via radio frequency plasma enhanced chemical vapor deposition method. The microstructure, surface morphology, hardness, film adhesion, and tribological properties of the films were characterized and evaluated by X-ray photoelectron spectroscopy, atomic force microscopy, and micro-sclerometer and friction-wear spectrometer. The results showed that DLC films have smooth surfaces, homogeneous particle sizes, and excellent tribological properties, which can be used to improve the surface quality of the selenium drums and prolong their service life.

Nanostructured silicon and its application to solar cells, position sensors and thin film transistors

This paper reports the performance of small area solar cells, 128 linear integrated position sensitive detector arrays and thin film transistors based on nanostructured silicon thin films produced by plasma-enhanced chemical vapour deposition technique, close to the onset of dusty plasma conditions, within the transition region from amorphous to microcrystalline. The small area solar cells, produced in a modified single chamber reactor, exhibited very good electrical characteristics with a conversion efficiency exceeding 9%. The 128 integrated position sensitive detector arrays, based on a similar pin structure, allow real-time 3D object imaging with a resolution higher than 90 l p/mm. The thin film transistors produced exhibited field effect mobility of 2.47 cm2/V/s, threshold voltage of 2 V, on/off ratio larger than 107 and sub-threshold slopes of 0.32 V/decade, which are amongst the best results reported for this type of device.

Phase evolution in nanocrystalline silicon films: Hydrogen dilution and the cone kinetics model

Our cone kinetics model of heterogeneous thin film growth explains the evolution of the crystalline inclusions that form during chemical vapor deposition (CVD) growth of silicon films. Various morphologies, including isolated crystallites and conical nanocrystalline formations, form during plasma-enhanced (PE) and other CVD techniques when isotropic growth is coupled with the point nucleation of a second phase with a higher growth rate. Cone angles are determined by the relative growth rates alone. By generalizing the physics of cone formation, we create a qualitative phase diagram that predicts film morphology from two factors during deposition: the relative amorphous and crystalline growth rates and the rate of crystallite nucleation. It is well known that both of these factors are influenced by the H-dilution of the film precursor gases. Analysis of the statistics of cone geometries and densities in published experimental data on PECVD-grown nanocrystalline silicon shows that the cone angle increases monotonically with H-dilution. In the context of the cone kinetics model, this implies that increased H-dilution results in an increase of the ratio of the nanocrystalline silicon growth rate (νnc) to the amorphous silicon growth rate (νa). At a specific H-dilution, νnc/νa exceeds unity and nanocrystalline cone formation results.

Effects of gas pressure and plasma power on the growth of carbon nanostructures

Effects of gas pressure and plasma power on the growth of carbon-based nanostructures (CNSs) have been studied in detail. Multi-walled carbon nanotube (MWCNTs) and carbon nanowalls (CNWs) were synthesized on glass substrates via radio frequency plasma-enhanced chemical vapor deposition (RFPECVD) technique. Surface morphologies of the films have been studied by SEM and TEM. When the gas pressure increases from 120 to 300 Pa, the deposited carbon material changes from MWCNTs to carbon nanowalls (CNWs). Additionally, the density of carbon nanostructures increases with the gas pressure. The radio frequency (RF) plasma power ranging from 600 to 2400 W was applied during the activation and deposition process. The plasma enhances the decomposition of carbon atoms to deposit onto the surfaces of catalyst particles. Whereas an exorbitant RF plasma power can destroy the already deposited carbon nanostructures.

Control of growth mode of multiwalled carbon nanotubes

We have conducted an experimental study to investigate the synthesis of multi-walled carbon nanotubes (CNTs) by a dc plasma-enhanced chemical vapour deposition (PECVD) technique. The synthesis of base and tip-type of CNTs was selectively controlled by changing the catalyst size, catalyst film thickness correlated with altering the NH3 pretreatment plasma current. These types of CNT showed distinctive properties in nanotube structure, growth rate and vertical alignment, which were confirmed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and in situ optical interference measurement. The vertically aligned behaviour of CNT was systematically studied by using a fine-patterned catalyst layer with diverse critical dimensions. Freestanding single CNT was successfully realized by optimum tip-type CNT growth, conventional photolithography and wet-etch process.

Structural, mechanical and tribological characterizations of a-C : H : Si films prepared by a hybrid PECVD and sputtering technique

a-C : H : Si films were prepared under different CH4/Ar ratios by a hybrid radio frequency plasma-enhanced chemical vapour deposition (RFPECVD) and unbalanced magnetron sputtering technique. Characterizations showed that the CH4/Ar ratio affected not only the content but also the chemical state of the doped Si, thus further affecting the microstructures, mechanical and tribological performances of the a-C : H : Si films. Generally, when the CH4/Ar ratio was low (⩽4/2), the Si-doping content dropped with increased CH4 percentage, accompanied by a decreased sp3(C–Si+C–C)/sp2(C=C), increased ID/IG ratio and up-shift of the G peak position, as can be seen from the Raman spectra, while at a higher CH4 percentage (e.g. CH4/Ar = 5/2), the prepared a-C : H : Si films exhibited a series of aberrant properties due to the incorporation of abundant H and the high oxidization of the doped Si. Another unique characteristic of our films was the presence of numerous Si–Si bonds at high Si content, which was not observed in the a-C : H : Si films produced by the decomposition of Si-containing gaseous precursors. Moreover, although Si incorporation improved such properties of the DLC films as adhesion strength, internal stress and tribological moisture sensitivity, its effectiveness in enhancing the mechanical and tribological performances were governed not by the Si-doping content or sp3-C fraction but by the film continuity or adhesion (minimized interlinking destruction by the Si–H, C–H, Si–O–Si bonds) and sp2(C=C) fraction (based on the film continuity).

Nanocomposite Metal Amorphous-Carbon Thin Films Deposited by Hybrid PVD and PECVD Technique

Carbon based films can combine the properties of solid lubricating graphite structure and hard diamond crystal structure, i.e., high hardness, chemical inertness, high thermal conductivity and optical transparency without the crystalline structure of diamond. Issues of fundamental importance associated with nanocarbon coatings are reducing stress, improving adhesion and compatibility with substrates. In this work new nanocomposite coatings with improved toughness based in nanocrystalline phases of metals and ceramics embedded in amorphous carbon matrix are being developed within the frame of a research project: nc-MeNxCy/a-C(Me) with Me = Mo, Si, Al, Ti, etc. Carbide forming metal/carbon (Me/C) composite films with Me = Mo, W or Ti possess appropriate properties to overcome the limitation of pure DLC films. These novel coating architectures will be adopted with the objective to decrease residual stress, improve adherence and fracture toughness, obtain low friction coefficient and high wear-resistance. Nanocomposite DLC's films were deposited by hybrid technique using a PVD-Physically Vapor Deposition (magnetron sputtering) and Plasma Enhanced Chemical Vapor Deposition (PECVD), by the use of CH4 gas. The parameters varied were: deposition time, substrate temperature (180 degrees C) and dopant (Si + Mo) of the amorphous carbon matrix. All the depositions were made on silicon wafers and steel substrates precoated with a silicon inter-layer. The characterisation of the film's physico-mechanical properties will be presented in order to understand the influence of the deposition parameters and metal content used within the a-C matrix in the thin film properties. Film microstructure and film hybridization state was characterized by Raman Spectroscopy. In order to characterize morphology SEM and AFM will be used. Film composition was measured by Energy-Dispersive X-ray analysis (EDS) and by X-ray photoelectron spectroscopy (XPS). The contact angle for the produced DLC's on silicon substrates were also measured. Thin film adherence was studied by micro-scratch test. Residual stresses in the produced coatings will be analysed by bending technique.

Second-order optical nonlinearity in thermally poled phosphorus-doped silicon dioxide thin-film waveguides

A phosphorus-doped silicon dioxide nonlinear planar waveguide on a GE124 fused silica substrate using plasma-enhanced chemical vapour deposition and thermal poling technique is implemented. The stable second-order nonlinear susceptibility induced in the waveguide is estimated to be around 0.58 pm/V by means of hydrofluoric acid etching, Maker's fringe measurement and grid search curve fitting using a double-step nonlinear profile. This nonlinear planar waveguide may be applied to fabricate an electrooptic device on the silicon photonic chip.

Evaluation of microstructures and carrier transport behaviors during the transition process from amorphous to nanocrystalline silicon thin films

Hydrogenated amorphous Si thin films were prepared by plasma-enhanced chemical vapor deposition technique. As-deposited samples were thermally annealed at various temperatures to obtain nanocrystalline Si. The microstructures and carrier transport behaviors were evaluated during the transition process from amorphous to nanocrystalline structures. Raman scattering spectroscopy and Fourier-transform infrared spectroscopy were used to characterize the changes in microstructures and bonding configurations. It is found that hydrogen is completely effused from the film at the annealing temperature of 600 °C, while crystallization occurs at around 700 °C. The carrier transport characteristics in nanocrystallized films are different from those in the amorphous Si films. The carrier transport in the amorphous silicon films is strongly influenced by the defect states resulting from the effusion of hydrogen. The dual activation energies are found in temperature-dependent conductivity results which can be attributed to the two different conduction paths in the samples. In the case of the nanocrystallized Si films obtained by high temperature annealing, the transport process is accounted for in the framework of a three-phase model comprised of amorphous and nanocrystalline phases and the grain boundary in the films.

Antibacterial activity of DLC and Ag–DLC films produced by PECVD technique

Diamond-like carbon (DLC) films have been the focus of extensive research in recent years due to its potential application as surface coatings on biomedical devices. Doped carbon films are also useful as biomaterials. As silver (Ag) is known to be a potent antibacterial agent, Ag–DLC films have been suggested to be potentially useful in biomedical applications. In this paper, DLC films were growth on 316L stainless steel substrates by using Plasma Enhanced Chemical Vapour Deposition (PECVD) technique with a thin amorphous silicon interlayer. Silver colloidal solution was produced by eletrodeposition of silver electrodes in distilled water and during the deposition process it was sprayed among each 25 nm thickness layer DLC film. The antibacterial activity of DLC, Ag–DLC and silver colloidal solution were evaluated by bacterial eradication tests with Escherichia coli ( E. coli) at different incubation times. With the increase of silver nanoparticle layers in Ag–DLC, the total compressive stress decreased significantly. Raman spectra showed the film structure did not suffer any substantial change due to the incorporation of silver. The only alteration suffered was a slightly reduction in hardness. DLC and Ag–DLC films demonstrated good results against E. coli, meaning that DLC and Ag–DLC can be useful to produce coatings with antibacterial properties for biomedical industry.

Fabrication of amorphous silicon carbide films using VHF-PECVD for triple-junction thin-film solar cell applications

Preparation of intrinsic hydrogenated amorphous silicon carbide (i-a-SiC:H) thin films for use as a top cell of triple junction solar cells is presented. These films were deposited using very-high-frequency plasma-enhanced chemical vapor deposition (VHF-PECVD) technique with monomethyl silane (MMS) gas as the carbon source. Deposition conditions were explored to obtain films with a wide gap and low defect density. It was confirmed that the hydrogen dilution ratio plays an important role in enhancing the film properties. Employing a-SiC:H film as an intrinsic layer of single junction cell, open-circuit voltage as high as 0.99 V has been achieved.

Effect of N-doping on the microstructure and properties of amorphous SiC:H diffusion barrier films

Hydrogenated amorphous a-SiC:H and a-SiCN:H with different nitrogen-concentration dielectric barrier films are prepared using the plasma-enhanced chemical vapor deposition technique （RF-PECVD）. The chemical and structural nature, mechanical property, dielectric constant and copper diffusion property of these films are characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy measurement, nano-indentation, Agilent 4294A precision impedance analyzer, Auger electron spectroscopy and field emission transmission electron microscopy. The results indicated that the dielectric constand of the film can be adjusted btween the values of 38 and 52 by controling the NH3/3MS ratio. With the increasing of NH3/3MS ratio, the concentration of Si-N and C-N bond structure is gradually increase and micro-structure of the film becomes more dense, which is the mechanism of the improvement in the mechanical property, thermal stability and copper diffusion property of the a-SiC:H based film produced by N-doping.

Thin film silicon n–i–p solar cells deposited by VHF PECVD at 100 °C substrate temperature

The applicability of the very high frequency (VHF) plasma-enhanced chemical vapor deposition (PECVD) technique to the fabrication of solar cells in an n–i–p configuration at 100 °C substrate temperature is being investigated. Amorphous and microcrystalline silicon cells are made with the absorber layers grown in conditions close to the amorphous-to-microcrystalline transition, which proved to give the best quality layers. It was observed that post-deposition annealing at 100 °C resulted in a relative increase of the efficiency of up to 50% for both amorphous and microcrystalline cells. For an amorphous solar cell deposited on stainless steel foil with a non-textured back reflector, an efficiency of 5.3% was achieved. A too rough substrate (textured back reflector), with an rms roughness higher than 80 nm, was found to give rise to shunting paths.

Superlow friction behavior of Si-doped hydrogenated amorphous carbon film in water environment

Si-doped hydrogenated amorphous carbon (a-C:H:Si) film was prepared using hybrid radio frequency plasma-enhanced chemical vapor deposition (R.F. PECVD) and non-balanced magnetron sputtering deposition technique. The microstructure of the film was characterized by means of Raman spectrometry, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD), while its friction behavior in water environment was investigated using a ball-on-disc tribometer. Results show that the a-C:H:Si film has typical diamond-like characteristics, and Si doped with a relative atomic concentration of about 3.9% in the film mainly exists in the form of Si, SiC, and SiO 2, while it shows a superlow friction coefficient of about 0.005 in water environment when sliding against Si 3N 4 ball. The superlow friction behavior of the hybrid diamond-like-carbon (DLC) film could be attributed to the formation of a tribochemical reaction film and boundary lubrication layer mainly consisting of colloidal silica generated from tribochemical reactions between silicides and water molecules.