Electron Cyclotron Resonance Chemical Vapor Research Articles

Effect of unintentionally introduced oxygen on the electron–cyclotron resonance chemical-vapor deposition of SiNX films

We establish the role of oxygen atoms on the structural, chemical, and mechanical properties of SiOXNY films grown on Si and InP substrates by electron–cyclotron resonance chemical-vapor deposition (ECR CVD) using a diluted SiH4 and N2 mixture in Ar, under controlled conditions. The mechanical and chemical properties of ECR-CVD SiNX films depend on the oxygen contamination even when this element is present in low concentrations. The compressive stress of SiNX films deposited with a low (and constant) content of oxygen (less than 12%) is shown to be in qualitative agreement with a model of repulsive Coulomb forces related mainly to polar N–H+− units in the SiNX network. We observe a decrease of the film compressive stress when the N2/SiH4 flow ratio increases, which is due to the increase of Si–N bonds in detriment of N–H bonds. Films deposited with high oxygen content in the plasma show a decrease of nitrogen incorporation. Oxygen radicals species compete with those of nitrogen in their reaction with silicon dangling bonds, which has as a consequence a decrease in the incorporation of nitrogen. Additional creation of oxygen radicals, with no hydrogen dilution, is more effective in decreasing the number of N–H bonds, or the compressive stress in the SiNX films, than the corresponding creation of nitrogen radicals. The mechanical properties of SiNX films contaminated with oxygen are controlled, in general, by the total number of both nitrogen plus oxygen atoms relative to silicon. The buffered HF (BHF) film etch rate is enhanced and thus is mainly controlled by the oxygen content. Low values of the compressive stress do not necessarily imply low values of BHF etch rate or a high N/Si ratio. We also present a discussion of the origin of the unintentional incorporation of oxygen in a ECR-CVD system designed for industrial production.

Composition and optical properties of silicon oxynitride films deposited by electron cyclotron resonance

Silicon oxynitride films covering the whole composition range from silicon nitride to silicon oxide have been deposited by electron cyclotron resonance chemical vapor deposition from SiH 4, O 2 and N 2 gas mixtures. The composition of the films has been determined by heavy-ion elastic recoil detection analysis (HI-ERDA), providing absolute concentrations of all elements, including H, and by Auger electron spectroscopy. Additionally, Fourier transform infrared (FTIR) spectroscopy and ellipsometry measurements have been performed on the same samples for optical characterization. The concentration of the different species (Si, O, N and H) and the density of the films have been calculated and compared to the theoretical values for stoichiometric films. The presence of N–H bonds and non-bonded H results in a significant decrease of the Si concentration with respect to the theoretical value, especially for samples close to silicon nitride composition. The decrease of the Si concentration results in a decrease of both the N and O concentrations. The overall result is a decrease of the density and therefore a decrease of the refractive index with respect to stoichiometric films. The total H content determined by ERDA has been compared with the area of the FTIR N–H stretching band, which is frequently used to obtain the H content. It has been found that the calibration factor for this band depends on composition, increasing with increasing the O content.

Gap state distribution in amorphous hydrogenated silicon carbide films deduced from photothermal deflection spectroscopy

The density of gap states distribution in silicon (Si) rich hydrogenated amorphous silicon carbide (a-Si1−xCx:H) films with varying carbon (C) fraction (x) is investigated by the photothermal deflection spectroscopy (PDS). The films are grown using the Electron Cyclotron Resonance Chemical Vapor Deposition (ECR-CVD) technique. By using different methane-to-silane gas flow ratios, a-Si1−xCx:H with x ranging from 0 to 0.36 are obtained. A deconvolution procedure is performed based on a proposed DOS model for these Si rich a-Si1−xCx:H. Good fits between the simulated and experimental spectra are achieved, thus rendering support to the model proposed. Deduction of the DOS enables us to obtain various parameters, including the optical gap and the valence band tail width. The fitted mobility gap Eg is found to be well correlated to the Tauc gap Etauc and E04 gap deduced from the optical absorption spectra. A correlation is also seen between the fitted valence band tail width Evu, the Urbach energy Eu and the defect density. All these parameters are seen to increase with C alloying. A shift in the defect energy level in the midgap with increasing C incorporation is observed, together with a broadening of the defect distribution and a stronger correlation between the defect bands, which can be accounted for in terms of the influence of C dangling bonds on the deep defect density distribution.

DEPOSITION OF HYDROGENATED NANOCRYSTALLINE SILICON CARBIDE BY ECR-CVD

In this work we report on the deposition of hydrogenated nanocrystalline silicon carbide (nc-SiC:H) films using an electron cyclotron resonance chemical vapor deposition (ECR-CVD) system with silane (SiH4) and methane (CH4) as source gases. It was found that the conditions of strong hydrogen dilution and high microwave power are necessary for the fabrication of nanocrystalline SiC grains, which are found to be embedded in an amorphous matrix. The films have been studied using high resolution transmission electron microscopy, infrared absorption, Raman scattering and x-ray photoelectron spectroscopy. All the results have confirmed the prescence of SiC nanocrystallites. Very strong photoluminescence (PL) could be observed from these films at room temperature, with a peak energy of 2.64 eV. This energy, being higher than the optical bandgap of 3C-SiC, can be possibly due to quantum size effect in these crystals, which are embedded in an amorphous matrix of larger bandgap. Time-resolved PL at the peak emission energy exhibits a bi-exponential decay process with lifetimes that are in the order of picoseconds and nanoseconds, which are at least 2 orders of magnitude faster than that of bound excition transitions in bulk 3C-SiC at low temperature. The strong light emission and short PL lifetimes observed strongly suggest that the radiative recombination is a result of direct optical transitions in the SiC nanocrystallites. It was found that upon ultraviolet irradiation using an Ar + laser (351 nm), the PL intensity of the films was enhanced. After 20 minutes of 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.

Electrical properties of SiN/GaN MIS diodes formed by ECR-CVD

Silicon nitride (SiN) film was deposited at 300 °C as the insulating layer of a GaN-based metal–insulator–semiconductor (MIS) diode by using electron cyclotron resonance chemical vapor deposition (ECR-CVD) with silane-to-nitrogen (SiH 4/N 2) flow ratio of 5/45. The deposited film had the refractive index of 1.9–2.0 and the relative dielectric constant of 6. Capacitance–voltage ( C– V) characteristics were measured at 1 MHz and interface state densities were obtained by Terman's method. The negative fixed charge density of the SiN film was 1.1×10 11 cm −2 and its breakdown field was greater than 5.7 MV/cm even at 350 °C. The value of the interface state density was less than 4×10 11 cm −2 around the mid-gap and its minimum was 5×10 10 cm −2 eV −1 at 0.6 eV below the conduction band edge. From these results, the SiN film deposited by ECR-CVD is a promising gate dielectric for high temperature GaN-MISFET application.

Dielectric properties of molybdenum-containing diamond-like carbon films deposited using electron cyclotron resonance chemical vapor deposition

The dielectric properties from a set of molybdenum-containing (Mo) diamond-like carbon (DLC) films deposited using electron cyclotron resonance chemical vapor deposition (ECR-CVD) were investigated. It is shown that the film permittivity can be greatly increased by the introduction of Mo, and a sharp decrease in permittivity occurs at low frequencies. The AC conductivity exhibits three characteristic regions in the frequency range investigated. The high ε″ and tanδ at low frequencies resulted from the high DC conductivity of the films. The peaks at approximately 0.8 kHz in ε″ and at approximately 4 kHz in tanδ for the film with Mo content of 3% are attributed to the relaxation polarization which has a lagging effect in response to an AC field. It is found that the film permittivity decreases following the decrease in temperature, followed by saturation, and for the film with high Mo content, it is frequency dependent at low temperature. However, for the high frequency of 1 MHz, the film permittivity is weakly Mo dependent at temperatures below 145 K. The relaxation time decreases with increasing Mo content in the films at room temperature. Several possible polarization mechanisms were proposed for our films based on the measurements. The effect of voltage on the film permittivity was also investigated and was found to be insignificant at frequencies above 10 kHz.

Growth mechanism and properties of the large area well-aligned carbon nano-structures deposited by microwave plasma electron cyclotron resonance chemical vapor deposition

Large area (4-inch diameter) well-aligned carbon nano-structures on Si substrate were successfully synthesized by using a catalyst-assisted microwave plasma electron cyclotron resonance chemical vapor deposition (ECR-CVD) system with CH4 as source gas. The catalysts include Fe, Co and Ni. The catalysts and the deposited nano-structures were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman and field emission I–V measurements. Effects of process parameters on morphologies, structures and properties of the nano-structures were examined. The results show that the deposited nano-structures can include normal nano-tubes, split catalyst nano-tubes, seaweed-like nano-sheets and carbon film, depending mainly on substrate temperature and bias, catalyst materials and their application methods. Deposition mechanisms for different nano-structures, especially, the unique split catalyst nano-tubes and seaweed-like nano-sheets, were proposed. The differences in oxidation resistance and field emission properties between different nano-structures will be compared and discussed.

On the bonding structure of hydrogenated carbon nitrides grown by electron cyclotron resonance chemical vapour deposition: towards the synthesis of non-graphitic carbon nitrides

This work compares the composition and bonding structure of hydrogenated carbon nitride films (CNx:H) obtained by electron cyclotron resonance chemical vapour deposition (ECR-CVD) with those of hydrogen-free carbon nitrides (CNx) obtained by nitrogen ion beam assisted deposition (IBAD) of graphite. The composition and structure of the films was analysed by ion scattering techniques well suited to the detection of hydrogen, in addition to the more conventional infrared spectroscopy. The bonding structure was examined by X-ray absorption spectroscopy (XANES). The typical IBAD CNx films are graphitic with a N/C content below 0.3. However, the ECR-CVD films show a less graphitic bonding structure. The ECR-CVD films were synthesised in a conventional microwave ECR reactor (2.25 GHz, 875 Gauss, 250 W) using as precursor gases N2 and Ar in the reactor chamber, and CH4 directly in the deposition chamber.

Morphology and characterization of highly nitrogenated, aligned, amorphous carbon nano-rods formed on an alumina template by ECR-CVD

Highly nitrogenated amorphous carbon (a-C:N) nano-rods on a porous alumina template were synthesized using an electron cyclotron resonance chemical vapor deposition (ECR-CVD) system, in which a negative DC bias was applied to the graphite substrate holder to promote the flow of ionic fluxes through the nano-channels of the alumina template in a microwave-excited plasma of C2H2 and N2 as precursors. The aligned structure of a-C:N nano-rods was verified by field-emission scanning electron microscopy (FE-SEM). Transmission electron microscopy (TEM) micrographs of a-C:N nano-rods showed that the nano-rods are well aligned with a diameter of approximately 100–250 nm and a length of approximately 50–80 μm. The amorphous nature of the nano-rods was confirmed by the absence of crystalline phases arising from selected-area diffraction (SAD) patterns. X-Ray photoelectron spectroscopy (XPS) spectra indicated that these nano-rods were composed of nitrogen and carbon, and the N/C ratios could reach as high as 56%. The absorption bands between 1250 and 1750 cm−1 in Fourier-transform infrared (FTIR) spectra provided direct evidence for the effective incorporation of nitrogen atoms into the amorphous carbon network. Raman spectra showed the same feature, with a G-band at ∼1580 and a D-band at ∼1370 cm−1 in the amorphous carbon film. The well-aligned a-C:N nano-rods are expected to have potential applications in optic, electronic and optoelectronic devices.

Characteristics of nickel-containing carbon films deposited using electron cyclotron resonance CVD

Two sets of nickel-containing carbon (Ni-C/H) films were deposited using an electron–cyclotron resonance chemical vapor deposition system in conjunction with two biased screen grids. The films were characterized using Raman scattering. Their resistivity and hardness were evaluated as a function of the gas flow ratio (CH4/Ar). Rutherford back scattering analysis showed that the atomic fraction of Ni incorporated in the films decreases drastically from 35 to 1.4%, following increase in the CH4/Ar ratio. Correspondingly, the film resistivity increases by 11 orders of magnitude. In contrast, the hardness decreases and the film with a Ni atomic fraction of 12% has a hardness of approximately 16 GPa. Vacuum annealing at 200 °C for 1 h immediately after the film deposition resulted in an increase in resistivity. The threshold field for field emission decreases with decreasing Ni incorporation in the film and a value of approximately 4 V/μm can be obtained for the film with the lowest Ni atomic fraction of 1.4%.

ECR-plasma parameters and properties of thin DLC films

We studied the correlation between CH 4-plasma parameters and the properties of thin diamond-like carbon films deposited using electron–cyclotron–resonance chemical vapor deposition. The deposition was done with the contribution of the ions incident to the sample. We attribute the high quality of the films to the ions penetrating the sample and transferring their energy at 16 eV/Å with a flux density same as that of radicals.

Modeling and analysis of the electron cyclotron resonance diamond-like carbon deposition process

Diamond-like carbon (DLC) films were deposited using the electron cyclotron resonance (ECR) chemical vapor deposition process. The behavior of the ECR plasma was formulated using deposition conditions such as microwave power, pressure, and hydrogen/methane (H2/CH4) ratio as input parameters. Thereafter, the outputs were used to formulate a DLC film deposition model, which takes into account the ion bombardment at the film surface, attachment of carbon-carrying ions, and chemisorption of hydrocarbon radicals on the film and hydrogen–surface reactions. The DLC film deposition model suggests that under conditions of high hydrogen atom flux, the main precursors are carbon-carrying ions. Hydrocarbon radicals, such as CH3, only contribute to ∼20% of the total film deposition rate.

Modeling and analysis of hydrogen–methane plasma in electron cyclotron resonance chemical vapor deposition of diamond-like carbon

Diamond-like carbon films were deposited using the electron cyclotron resonance chemical vapor deposition (ECR-CVD) system. A model for the ECR plasma was formulated using deposition parameters, such as microwave power, pressure, and hydrogen/methane ratio as inputs. Using the model, electron energy, rate constant of electron impact reactions, and density of species in the plasma are calculated. The outputs of the model are analyzed as a function of deposition conditions, such as microwave power, pressure, and hydrogen/methane ratio and compared to experimental data measured using a Langmuir probe. The results show that ion density increases following the increase in microwave power and hydrogen/methane ratio, and decreases following the increase pressure. Results from the model are in agreement with experimental data, and show that the main neutral species are H2, CH4, H, CH3, CH, C2H5, CH2, and C2H6. The main ionic species are H2+, CH4+, CH3+, CH2+, H+, CH5+, C2H4+, C2H5+, and CH+.

Effects of CH 4/SiH 4 flow ratio and microwave power on the growth of β-SiC on Si by ECR-CVD using CH 4/SiH 4/Ar at 200 °C

The effects of CH 4/SiH 4 flow ratio and microwave power on the formation of SiC at 200 °C by electron cyclotron resonance chemical vapor deposition is investigated. When the CH 4/SiH 4 flow ratio is varied from 0.5 to 10, crystalline phase of films vary from polycrystalline silicon to polycrystalline β-SiC, and finally to amorphous silicon carbide. However, as the microwave power increases from 300 to 1500 W, the film microstructure changes from polycrystalline Si to amorphous SiC, and finally to polycrystalline β-SiC. The deposition mechanism which controls the film characteristics is also presented.

CBN Films grown by hot filament assisted microwave electron cyclotron resonance CVD

BN films were deposited by hot filament-assisted microwave electron cyclotron resonance (ECR) chemical vapor deposition (CVD) technique. It was found that hot filament in the general ECR CVD system is helpful to the formation of cubic BN phase (cBN). Although a negative bias to the substrate is probably a key to cBN formation, hot filament may be a way to enhance the activation of the precursors and be beneficial to the deposition of cBN at a proper bias and substrate temperature of 400°C, while at the same condition no cBN was observed in the films when deposited without hot filament.

The Silicon Nitride Film Formed by ECR-CVD for GaN-Based LED Passivation

Most GaN-LED epilayers are grown on sapphire, which is a kind of insulating substrate. From the top view, a GaN-based LED has two bonding pads, one for p-type conduction and the other for n-type conduction. These pads would affect the packaging yield because it is probable to touch the p-type material when a conducting wire is bonded to the n-pad. Besides, the reactive ion-etched sidewall is easily contaminated or adsorbed by moisture when exposed to the air. Consequently, a passivation layer is necessary to isolate these conduction paths. In this paper, we used electron cyclotron resonance chemical vapor deposition (ECR-CVD) to form the silicon nitride (SiN x ) passivation film at room temperature. The film was patterned by lift-off process and the surface of the whole wafer was covered except the bonding pads. After passivation, no distinguishable variation was found in the statistical data of forward voltage and leakage current, but the illumination intensity was raised by at least 6%. The bonding yield and reliability would be increased much. The change of electrostatic discharge (ESD) characteristics was also investigated.

Characterization of metal-containing carbon films using Raman scattering

Metal-containing carbon (Me-C:H) films were deposited using the electron cyclotron resonance chemical vapor deposition technique in conjunction with a metal screen-grid system. Four sets of Me-C:H films were analyzed using Raman scattering. Two sets were molybdenum-containing carbon (Mo-C:H) films deposited at fixed dc bias (at different CH4/Ar ratios), and at fixed CH4/Ar ratio (at different dc bias). Another two sets of nickel-containing carbon (Ni-C:H) films were deposited at fixed rf power, but at a different CH4/Ar ratio, with and without postgrowth thermal annealing at 200 °C. All films showed the characteristic G and D peaks except for those with high metal content. The D peak is very pronounced in the Ni-C:H films, and both the G and D peaks follow an opposite trend; downshifting and upshifting in wave number, respectively, as the CH4/Ar ratio was increased. In the case of Mo-C:H films deposited at fixed dc bias, both peaks downshifted in wave number, following an increase in the CH4/Ar ratio. The G peak full width at half maximum for both the Ni- and Mo-C:H films increased slightly with an increase in CH4/Ar ratio, consistent with the variation in the relative integrated intensity of the D to G peak (ID/IG). Thermal annealing experiments conducted on the film samples revealed relatively stable characteristics with a minor effect on the film structure. The results showed that the impinging ion energy plays an important role in the structural properties of the Me-C:H films.

The Silicon Nitride Film Formed by ECR-CVD for GaN-Based LED Passivation

Most GaN-LED epilayers are grown on sapphire, which is a kind of insulating substrate. From the top view, a GaN-based LED has two bonding pads, one for p-type conduction and the other for n-type conduction. These pads would affect the packaging yield because it is probable to touch the p-type material when a conducting wire is bonded to the n-pad. Besides, the reactive ion-etched sidewall is easily contaminated or adsorbed by moisture when exposed to the air. Consequently, a passivation layer is necessary to isolate these conduction paths. In this paper, we used electron cyclotron resonance chemical vapor deposition (ECR-CVD) to form the silicon nitride (SiNx) passivation film at room temperature. The film was patterned by lift-off process and the surface of the whole wafer was covered except the bonding pads. After passivation, no distinguishable variation was found in the statistical data of forward voltage and leakage current, but the illumination intensity was raised by at least 6%. The bonding yield and reliability would be increased much. The change of electrostatic discharge (ESD) characteristics was also investigated.

A comparative study of Ar and H 2 as carrier gases for the growth of SiC films on Si(100) by electron cyclotron resonance chemical vapor deposition at low temperature

Electron cyclotron resonance chemical vapor deposition (ECR-CVD) of SiC films from silane and methane gas mixtures at low temperature has been investigated using two different carrier gases, namely, argon and hydrogen. The results obtained are compared. The chemical composition and crystalline microstructure were investigated by Fourier transform infrared spectroscopy (FTIR) and cross-sectional transmission electron microscopy (XTEM), respectively. The results indicate that the carrier gases have a greater influence on the film composition and microstructure as compared to the growth parameters like pressure, power and flow ratio. The deposition mechanism which controls the film characteristics is also presented.

Surface Modification of Low Dielectric Fluorinated Amorphous Carbon Films by Nitrogen Plasma Treatment

The effects of nitrogen post-plasma treatment on the properties of fluorinated amorphous carbon (a-C:F) films were investigated. In this study, the a-C:F films were prepared by an electron cyclotron resonance chemical vapor deposition (ECRCVD) system (ASTeX AX4505) using a gas mixture of fluorocarbon (C2F6) and hydrocarbon (CH4). The post-plasma treatment was carried out for various strengths and durations after deposition without breaking the vacuum seal. As the power and time of the treatments increased, the fluorine concentration of the film surface decreased, yet the surface energy increased sharply. The dielectric constant and the refractive index of a-C:F films remain nearly constant regardless of the plasma treatment power. From this study, it was found that the plasma treatment of a-C:F films produces a more reactive surface and affected the fluorine concentration of the surface, the structure of chemical bonding and the electric properties.