Electron Cyclotron Resonance Chemical Vapor Research Articles

Angle-dependent photoluminescence spectra of hydrogenated amorphous silicon thin films

Multiple sharp peaks were observed in the visible photoluminescence spectra of amorphous silicon thin films, prepared by ultrahigh vacuum electron cyclotron resonance chemical vapor deposition on oxidized silicon substrates. The angular dependence of the photoluminescence, measured by a home-built fiber-optics device, revealed that the origin of these sharp features was due to Fabry–Pérot cavity interference effects. The interference is enhanced by deposition on thermally grown oxide layers with relatively smooth surfaces. We also consider how thin-film interference effects can add to the already existing confusion regarding the photoluminescence (PL) mechanism of porous and other luminescent forms of silicon and propose angle-dependent PL spectroscopy as a remedy for identifying spectral features due to interference effects.

Effect of microwave power on diamond-like carbon films deposited using electron cyclotron resonance chemical vapor deposition

Diamond-like carbon (DLC) films have been deposited using electron cyclotron resonance chemical vapor deposition (ECR-CVD) under various microwave power conditions. Langmuir probe measurement and optical emission spectroscopy (OES) were used to characterize the ECR plasma, while the films were characterized using Raman and infrared (IR) spectroscopies, hardness and optical gap measurements. It was found that the ion density and all signal peaks in the optical emission (OE) spectra increased monotonously following the increase in microwave power. Raman spectra and optical gap measurements indicate that the films become more graphitic with lower content of sp 3 -hybridized carbon atoms as the microwave power was increased. IR and hardness measurements indicate a reduction in hydrogen content and decrease in hardness for the film produced at relatively high microwave powers. A deposition mechanism is described which involved the ion bombardment of film surfaces and hydrogen–surface interactions. The deposition rate of DLC film is correlated to the ion density and CH 3 density.

Application of fluorinated SiO2 interlayer dielectrics for ferroelectric memory

Fluorine-doped silicon oxide (SiOF) as interlayer dielectric (ILD) was deposited over PZT capacitors by electron cyclotron resonance (ECR) chemical vapor deposition using SiF4 and N2O gases. In the conventional deposition of SiO2 ILD layer using hydrogen-contained source gases, the properties of ferroelectric capacitors are known to be degraded during the formation of SiO2 layer. In this study, we examined the degradation of electrical properties of SiOF-deposited PZT capacitors. The remnant polarization and leakage currents were not degraded after the deposition of SiOF. We observed that the fluorine atoms were not diffused into the metal electrode in both cases of the SiOF deposited PZT capacitors and post-deposition annealed capacitors. The SiOF films deposited in the high CF4 flow rate exhibited rough columnar structure on the metal electrodes. We can successfully deposit SiOF in a smooth morphology by introducing TiO2buffer layer or using the novel deposition method of changing the SiF4 flow rate, namely two-layer-deposition method.

Conduction mechanism in molybdenum-containing diamond-like carbon deposited using electron cyclotron resonance chemical vapor deposition

The conduction mechanism of molybdenum-containing (Mo) diamond-like carbon films deposited using electron cyclotron resonance chemical vapor deposition was investigated. It is found that there is a conductivity turning point at around 115 K, above which the conductivity is strongly temperature dependent. This indicates that two types of conduction mechanisms, thermal activation and tunneling coexist in the films, and they dominate the conduction behavior in the high and low temperature regimes, respectively. Within the temperature range investigated, the Poole–Frenkel effect is to be expected for thermal activation. However, due to the low concentration of Mo in the films, this effect was not observable. Tunneling is thought to occur between the Mo clusters or the sp2 clusters. A conductivity model, based on the thermal activation and tunneling, is proposed, and showed good agreement with the results obtained at low field. The conduction behavior at high field is also discussed and some possible mechanisms are proposed.

Evolution of structure in thin microcrystalline silicon films grown by electron-cyclotron resonance chemical vapor deposition

The growth of microcrystalline silicon, μc-Si, films has been studied by infrared spectroscopy and x-ray diffraction. Thin films of various thickness have been prepared from SiH4–H2 mixtures by electron-cyclotron resonance chemical vapor deposition. Two structural transitions were observed during film growth. The first transition at a critical thickness of dac=9 nm manifested itself by a change from an initially amorphous growth to polycrystalline growth. The second structural transition was related to an increasing amount of silicon grains of preferred orientation with (110) lattice planes parallel to the substrate. The population of such (110)-oriented grains N110 was found to become dominant at about d110=310 nm, which may be considered as a second critical thickness above which the film exhibits a (110) fiber texture. The increase of N110 with increasing thickness follows a d1/6 dependence. The effect is understood in terms of an interplay between etching and deposition during growth.

Investigation of molybdenum-carbon films (Mo–C:H) deposited using an electron cyclotron resonance chemical vapor deposition system

We have recently proposed a technique for depositing metal incorporated carbon films (Me–C:H) based on an electron cyclotron resonance chemical vapor deposition (ECR) process. This technique employs an ECR plasma derived from the excitation of source gases CH4 and Ar, together with two grids embedded within the chamber that serve as the source of the metal. It has been successfully applied for the deposition of tungsten–carbon films (W–C:H) which have been shown to exhibit a wide range of electrical, optical, and microstructural properties. These properties can be controlled through varying the deposition conditions such as the bias voltages at the grids and the substrate holder, and the flow ratio of CH4/Ar. In this work, we report on the growth and characterization of molybdenum–carbon (Mo–C:H) films deposited using the above technique incorporating two pure Mo grids. The effect of radio-frequency induced direct-current (dc) bias at the substrates was investigated. It was found that the resistivity of the films decreased by 9 orders of magnitude, and the optical gap decreased by more than 2 eV with increasing bias voltage from −38 to −130 V. The results suggest that the substrate dc bias has a crucial effect on the incorporation of Mo into the a-C:H films and the resulting microstructures, with larger bias voltages leading to an increase in the Mo fractions in the films. Concurrently, the hardness of the films was found to deteriorate from 22 to 10 GPa. The structures of these Mo–C:H films were characterized using x-ray diffraction and Raman scattering. Mo was found to exist in the forms of Mo and MoC and Mo2C. The experimental results are interpreted in terms of the effects of ion energy on the structure of the films having Mo clusters embedded within an amorphous carbon matrix.

Analysis of silicon–oxide–silicon nitride stacks by medium-energy ion scattering

This article describes medium-energy ion scattering (MEIS) measurements of [N] and [O] profiles using protons incident on nitride–oxide (NO) films produced by oxidizing Si(100) substrates in N2O plasmas and nitride–oxide–nitride stacks formed by depositing silicon nitride on the NO films. Concentrations were obtained from the MEIS spectra using a multiparameter Marquardt–Levenberg fitting procedure. Integral [N] and [O] were separately measured by nuclear reaction analyses and compared to the concentrations obtained from the MEIS profile. The analysis shows that nitrogen diffuses through oxide films during the deposition of silicon nitride by electron–cyclotron resonance chemical-vapor deposition and accumulates at the Si/SiO2 interface.

Electron field emission from amorphous carbon nitride nanotips

Amorphous carbon nitride nanotips were synthesized on silicon for the first time as electron emitters by means of electron cyclotron resonance chemical vapor deposition (ECR-CVD) system in which a negative dc bias was applied to the graphite substrate holder and a mixture of C 2H 2, N 2 and Ar was used as precursors. An onset emission field of as low as 1.5 V μm −1 can be achieved, a rate that is significantly lower than that achieved by other carbon-based electron field emitters. The morphology of amorphous carbon nitride nanotips was clearly verified by field-emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). Auger electron microscopy (AES) indicated that these nanotips are composed of nitrogen and carbon. Raman spectra show the same feature to possess a G-band at 1599 cm −1 and a D-band at 1382 cm −1 with the amorphous carbon film.

Surface Treatment by Ar Plasma Irradiation in Electron Cyclotron Resonance Chemical Vapor Deposition

To reduce the surface states of GaAs and related semiconductors which originate from native oxides on a surface, we developed a simple surface treatment method in which the surface oxides could be physically sputtered by Ar plasma irradiation in an electron cyclotron resonance chemical vapor deposition (ECR-CVD) apparatus. In the experiment of Ar irradiation of a GaAs surface, we were able to determine the optimum irradiation time at which the native-oxide-related surface states were almost removed without damaging the irradiated surface. Then, we applied this method to an actual 0.98-µm semiconductor laser in which catastrophic optical damage (COD) failure occurred due to the surface states of the output facet. By irradiating Ar plasma to the output facet of the laser and removing the oxide-related surface states there, tolerance to COD was remarkably improved compared with that of a conventional non-Ar-irradiated one.

Synthesis and characterization of the aligned hydrogenated amorphous carbon nanotubes by electron cyclotron resonance excitation

Aligned hydrogenated amorphous carbon nanotubes on porous anodic alumina have been synthesized by electron cyclotron resonance chemical vapor deposition (ECR-CVD) using the precursor gases, acetylene and argon. The composite film, with the aligned hydrogenated amorphous carbon nanotubes embedded in the porous anodic alumina, was found to be robust and is expected to have potential application in optic, electronic and optoelectronic devices. It is possible to prepare a large area of such a film by taking advantages of the ECR-CVD process, e.g. high plasma density at low temperature, less ionic damage, contamination-free and high deposition rate. By adjusting the pore size of anodic alumina, hydrogenated amorphous carbon nanotubes of various diameters can be produced in a range from 230 down to 30 nm. Characterization of the nanotubes in anodic alumina was carried out by field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), transmission electronic microscopy (TEM) and electron energy loss spectroscopy (EELS). The results indicate that the nanotubes consist of amorphous hydrogenated carbon, which are grown at a temperature of ∼100°C for 4 min.

Molybdenum-containing carbon films deposited using the screen grid technique in an electron cyclotron resonance chemical vapor deposition system

Abstract A novel technique involving the incorporation of two molybdenum (Mo) screen grids embedded in an electron cyclotron resonance chemical vapor deposition (ECR–CVD) system is presented in this paper. A comprehensive set of film deposition experiments based on this screen grid sputtering technique has been carried out. The Mo-containing carbon films were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS). The film resistivity, optical bandgap and hardness were evaluated as a function of the gas flow ratio (CH4/Ar). XPS analysis showed that the fraction of Mo incorporated in the carbon film decreased drastically from 15.11 to 0.32% following an increase in the CH4/Ar flow ratio. The optical absorption also decreases strongly and the film with the lowest Mo fraction has a bandgap of 2.0 eV. The film resistivity was found to increase by 11 orders of magnitude following the decrease in the metal fraction. It is found that Mo can exist in the forms of MoC, Mo2C, Mo, and even MoO3 in the films, the last being mainly due to air exposure. The results showed that our ECR-based screen grid technique for Me-C:H deposition is highly effective and flexible with good control over the amount of metal incorporated.

Hydrogenated amorphous carbon films deposited in an electron cyclotron resonance–chemical vapor deposition discharge reactor using acetylene

Hydrogenated amorphous carbon (a-C:H) films have been deposited from acetylene gas in a microwave electron cyclotron resonance (ECR) plasma reactor. The films were deposited at a pressure of 0.2 mTorr and at radio frequency (r.f.) induced substrate biases from 80–300 V. Selected film properties, including optical bandgap and bonded hydrogen content, were measured. At r.f. induced biases from 150 to 300 V, corresponding to ion energies for C 2 H 2 + of approximately 150–300 eV, the hydrogen content remains constant and the optical bandgap peaks at a bias of 200 V, or approximately 100 eV per carbon in the C 2 H 2 + ions. This ECR system result is in agreement with those observed by other researchers using different deposition methods where an optical bandgap maximum and an sp 3 maximum occurs at ion energies of 90–100 eV per carbon atom. The discharge properties measured include a partial pressure analysis of the residual exit gas and the substrate current density.

CHARACTERISTIC OF MOLYBDENUM-CONTAINING a-C:H FILMS DEPOSITED USING ELECTRON CYCLOTRON RESONANCE CVD

Metal-containing carbon (Me-C:H) films are presently attracting wide interests due to their unique properties such as good adhesion, low resistivity and friction value. As a result, numerous techniques for depositing such films have been proposed. In this paper, a novel technique which involves the incorporation of two molybdenum (Mo) screen grids embedded in an electron cyclotron resonance chemical vapor deposition (ECR-CVD) system is presented. A set of film deposition experiments based on this screen grid sputtering technique has been carried out. The Mo-containing carbon films were charcterized using x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS). The changes in film resistivity were evaluated as a function of changes in the gas flow ratio ( CH 4/ Ar ). XPS analysis showed that the fraction of Mo incorpated in the carbon film decreases drastically from 15.11% to 0.32% following an increase in the CH4/AR flow ratio. The film resistivity was found to increase by 11 orders of magnitude following the decrease in the metal fraction. It is found that Mo can exist in the forms of MoC, Mo 2 C , Mo, and even MoO 3 in the films, the last being mainly due to air exposure. The results showed that our ECR-based screen grid deposition technique for Me-C:H is highly effective and flexible with good control over the amount of metal incorporated.

Silicon-Carbon Alloys Synthesized by Electron Cyclotron Resonance Chemical Vapor Deposition

ABSTRACTSilicon-carbon alloys were deposited by electron cyclotron resonance chemical vapor deposition (ECR-CVD) using either halogenated or non-halogenated precursors for the Si and C sources. Halogenated precursors were chosen for initial experiments to try to reduce the H content and to improve the microstructure of the silicon carbide (SiCx) films. While a wide range of compositions has been deposited using the halogenated precursors, only a limited range has been deposited so far with the non-halogenated precursors. Electron spectroscopy for chemical analysis (ESCA) and Fourier transform infrared (FTIR) spectroscopy show that compositions ranging from near-stoichiometric SiCx to extremely C-rich can be deposited by controlling the deposition temperature, plasma power and C/Si ratio of the halogenated precursors. At the highest C/Si-precursor ratio, the deposited film is electrically conductive with a measured resistivity of 0.067ω-cm, contains only 3-atomic-percent Si and should be considered a Si-doped carbon (C:Si) film. The excellent transparency, especially that of the C:Si films, allowed the assignment of FTIR absorption bands that are usually masked by graphitic inclusions and other impurities. A weak absorption band at 1180cm−1 was found to correlate with the electrical conductivity of the films and was attributed to the asymmetric “bond-and-a-half” Si=C stretch in a Si=C=C functional group where the pi electrons are distributed equally between the three atoms. Additional results show etching of the substrate by reactive Cl from the halogenated precursors can have a dramatic effect on the microstructure, porosity and moisture stability of the films. For experiments involving halogenated precursors, the C:Si films are much more stable than the near-stoichiometric SiCx because C:Si is deposited at lower plasma powers that do not etch the Si substrate. Finally, preliminary results show that near-stoichiometric SiCx films deposited using non-halogenated precursors are much more stable with respect to moisture incorporation than those deposited with halogenated precursors.

Barrier-Controlled Transport in Doped Microcrystalline Si

ABSTRACTThin μc-Si films doped with P and B are grown on glass at temperatures between 300 °C and 400 °C by electron cyclotron resonance chemical vapor deposition (ECR-CVD). Hall mobilities in the films are found to be temperature-activated with activation energies being correlated to the doping concentrations. The in-grain mobility as determined by an electron spin resonance investigation is much higher than the Hall mobility the values of which are typically near 1 cm2/Vs at 300 K. The experimental results suggest that transport is dominated by potential barriers at the grain boundaries. An extended Seto model is used to probe the interface trap distribution. We obtained the best fitting results by assuming band-tail states decaying exponentially from the respective band edges.

Intense Photoluminescence and Photoluminescence Enhancement upon Ultraviolet Irradiation in HYydrogenated Nanocrystalline Silicon Carbide

ABSTRACTHydrogenated nanocrystalline silicon carbide (nc-SiC:H) films were deposited in an electron cyclotron resonance chemical vapor deposition (ECR-CVD) system using silane (SiH4) and methane (CH4) as source gases. It was discovered that under the deposition conditions of strong hydrogen dilution and high microwave power, nanocrystalline grains embedded in an amorphous matrix can be obtained, as confirmed by TEM study. Steady state and time-resolved photoluminescence (PL) from these films were investigated. The films exhibit intense visible PL at room temperature under laser excitation. The PL emission peaks at 2.64 eV, which is higher in energy compared to the bandgap of cubic SiC. Temporal evolution of the emission peak exhibits a double-exponential decay. Two distinct decay times of 179 ps and 2.88 ns were identified, which are at least 2 orders of magnitude faster than that of bound excition transitions in bulk 3C- SiC at low temperature. It was found that upon ultraviolet irradiation using an Ar+ laser (351nm) the PL intensity of the films was enhanced. After 20 minutes irradiation, the PL intensity increased by about three times. This result suggests that the UV light may lead to modification of nonradiative recombination centers in the films. These nc-SiC:H films are promising for application in large area flat panel displays and in optoelectronic storage technology.

Well-aligned carbon nanofibers synthesized by electron cyclotron resonance chemical vapor deposition

AbstractAligned carbon nanofibers and hollow carbon nanofibers were grown by MW ECR-CVD method using methane and argon mixture gas at the temperature of 550••. Carbon nanofibers and hollow carbon nanofibers were deposited perpendicularly on Si substrate and on Si substrate coated with Ni catalyst, respectively. Raman spectra of aligned carbon nanofibers and hollow carbon nanofibers showed new bands of 1340 and 1612 cm-1 of the first-order Raman scattering and 2660, 2940 and 3220 cm-1 of the second-order Raman scattering. The second-order Raman scattering bands were assigned to two overtone and one combination bands on the basis of a similar assignment of micro crystal graphite. Combination bands are intense unusually. Field emitter characteristics of the well-aligned carbon nanofibers and hollow carbon nanofiberswere investigated and the current densities were 7.25 mA/cm2 and 0.69 mA/cm2at 12.5 V/μm, respectively.

Amorphous hydrogenated carbon film formation from benzene by electron cyclotron resonance chemical vapor deposition

Amorphous hydrogenated carbon thin films have been deposited from benzene vapor in an electron cyclotron resonance plasma-enhanced chemical vapor deposition reactor. The effects of gas flow rate, pressure, and microwave power on deposition rates, chemical structure and composition, and on film density were investigated. Plasma enhanced dissociation and ionization reactions were monitored by mass spectrometry and by optical emission spectroscopy. Dissociation products included a variety of unsaturated hydrocarbon species (primarily ethylene) and hydrogen. Deposited films were characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, and fluorescence spectroscopy. Films displayed a condensed, aromatic, hydrocarbon-like structure, albeit without extensive conjugation. Possible reaction sequences leading to the observed film structures have been proposed.

Effect of head slider DLC overcoats produced by various deposition techniques on the interface failure

Diamond-like carbon (DLC) coatings were deposited on Al/sub 2/O/sub 3/-TiC substrate of head sliders by filtered cathodic arc (FCA), ion beam (IB), electron cyclotron resonance chemical vapor deposition (ECR-CVD) and sputtering (SP) with thicknesses of 5, 10 and 20 nm. Drag and CSS tests were performed using a commercial laser-textured disk. The interface failures, correlated to tribological properties of coatings on the head slider and disk surfaces, are discussed. The TB coatings show the longest interface durability whereas sputtered DLC coatings show the lowest interface durability. However, if DLC coatings on the head slider and disk surfaces are deposited with the compatible elastic modulus, based on mechanical characterization it is believed that FCA and ECR-CVD may also hold a promise for superior tribological performance.

Structural Properties of 3C-SiC Layers Grown on Si Substrates by Electron Cyclotron Resonance CVD Technique

ABSTRACTIn this work we mainly report on the analyses of polycrystalline silicon carbide films grown by Electron Cyclotron Resonance Chemical Vapor Deposition (ECR-CVD) on Si (100) and Si (111) substrates. Structural properties of the films have been analyzed by X-ray diffractometry, transmission electron microscopy and micro-Raman spectroscopy. Samples deposited with optimized deposition conditions, show a polycrystalline columnar structure with lateral crystal dimensions ranging from 300 up to 1400 Å and an orientation close to that of the Si substrates.