Electron Cyclotron Resonance Chemical Vapor Deposition Research Articles

Effects of deposition temperature on the structure and thermal stability of a-C:F films with low dielectric constant

Fluorinated amorphous carbon films (a-C:F) with low dielectric constant were prepared at different temperatures by electron cyclotron resonance chemical vapor deposition (ECR-CVD) using CHF 3 and C 2H 2 as precursors. The changes of structures, chemical compositions, and dielectric properties with deposition temperature were investigated by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy and capacitance–voltage characteristics. We found that a-C:F films prepared at high deposition temperature of 300 °C remained amorphous, but the dielectric constant increased from 2.2 for the films deposited at room temperature to 2.75 while F/C composition ratio in the films decreased from 2.3 to 1.5. In order to study the thermal stability the samples were annealed up to 500 °C in vacuum ambience. The films deposited at high substrate temperature have lower F/C, less CF 3, CF 2 bonding and more cross-linking structures, and thereby lead to better thermal stability.

Low-temperature Si epitaxy on large-grained polycrystalline seed layers by electron–cyclotron resonance chemical vapor deposition

The epitaxial thickening of polycrystalline Si films on glass substrates is of great interest for the realization of crystalline Si thin film solar cells and other large-area thin film devices. In this paper we report on the epitaxial growth of Si at temperatures below 600∘C on polycrystalline seed layers using electron–cyclotron resonance chemical vapor deposition. The Si seed layers were prepared by aluminum-induced crystallization. The quality of the ECRCVD-grown films strongly depends on the orientation of the underlying seed layer grains. Due to a mainly favorable orientation of the seed layers more than 73% of the substrate area were epitaxially thickened. It turned out that a (100) preferential orientation is favorable for epitaxial thickening. This, however, is not the only requirement for successful low-temperature epitaxial growth of Si.

Comparisons on properties and growth mechanisms of carbon nanotubes fabricated by high-pressure and low-pressure plasma-enhanced chemical vapor deposition

Effects of plasma pressure and the presence of nitrogen on growth of carbon nanotubes (CNTs) and their properties were studied by using microwave plasma chemical vapor deposition (MPCVD) (pressure=600–3300 Pa) and electron cyclotron resonance chemical vapor deposition (ECR-CVD) (pressure=0.3–0.6 Pa) systems. CH 4/H 2 and CH 4/N 2 were used as source gases, and Co as the catalyst. The structures and properties of CNTs were characterized by using field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Raman spectra, and field emission I– V measurements. The results show that CNTs made by higher plasma pressure system have a higher growth rate (typically 1–3 μm/min), smaller tube diameter, better field emission properties, and better tube quality. The growth rate is related to the availability of carbon source. The morphology change from spaghetti-like to well-aligned CNTs is discussed in terms of directed ions. The change in field emission properties is reasoned in terms of geometric enhancement factor and screening effect for different tube morphologies. The presence of nitrogen plasma can have the following effects: increasing tube diameter, increasing straightness of CNTs, forming of bamboo-like CNTs, deterioration of field emission properties, and shifting of Raman peak toward lower-frequency side (or increasing residual tensile stress).

Anodic aluminum oxide template assisted growth of vertically aligned carbon nanotube arrays by ECR-CVD

Highly aligned carbon nanotubes (CNTs) have been successfully grown in vertical channels of the anodic aluminum oxide (AAO) template by microwave plasma electron cyclotron resonance chemical vapor deposition (ECR-CVD). Nanoporous AAO templates with hexagonal pore pattern were prepared by the two-step anodization of Al films. Following the electroplating of Co catalyst into the pore bottom, multiwalled CNTs were synthesized in the ECR-CVD system using a gas mixture of CH 4 and H 2. The microstructure of the CNTs was studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The CNTs with a very high packing density and a uniform size distribution are well graphitized, and Co particles embedded at their tips implies the tip growth mechanism. The segments of CNTs stretching out of the AAO nanopores still maintain relatively good alignment, and have a very slow growth rate, which allows us to obtain reproducible tube length by tuning the growth time. Field emission measurements of the CNTs showed derivable electron emission properties, attributed to their uniformity in size, good alignment, and good graphitization properties.

Density distribution of gap states in extremely thin a-Si:H layers on crystalline silicon wafers

Stimulated by the application of a-Si:H as ultra thin emitter layer in a-Si:H/c-Si heterostructure solar cells the electronic properties of 2–30 nm thin undoped and doped a-Si:H films have been explored using photoelectron yield spectroscopy excited with UV-light (4–7 eV). The films were deposited by plasma enhanced chemical vapor deposition (PECVD) or electron cyclotron resonance chemical vapor deposition (ECR-CVD) onto c-Si wafers. It was found that the Fermi level shift toward the conduction band saturates at 1.47 eV above the valence band edge at a phosphine gas phase concentration of 10 4 ppm. The Urbach energy increases with doping from 65 to 136 meV. For doped samples the main features of the density of states distribution change only little when the thickness decreases to values as low as 2.8 nm. In nominally undoped material the high Urbach energy and high defect density indicate enhanced disorder.

Density distribution of gap states in extremely thin a-Si:H layers on crystalline silicon wafers

Stimulated by the application of a-Si:H as ultra thin emitter layer in a-Si:H/c-Si heterostructure solar cells the electronic properties of 2–30 nm thin undoped and doped a-Si:H films have been explored using photoelectron yield spectroscopy excited with UV-light (4–7 eV). The films were deposited by plasma enhanced chemical vapor deposition (PECVD) or electron cyclotron resonance chemical vapor deposition (ECR-CVD) onto c-Si wafers. It was found that the Fermi level shift toward the conduction band saturates at 1.47 eV above the valence band edge at a phosphine gas phase concentration of 104 ppm. The Urbach energy increases with doping from 65 to 136 meV. For doped samples the main features of the density of states distribution change only little when the thickness decreases to values as low as 2.8 nm. In nominally undoped material the high Urbach energy and high defect density indicate enhanced disorder.

Creation of metastable defects in microcrystalline silicon films by keV electron irradiation

The effect of electron irradiation with 40 keV electrons on the sub-gap optical absorption, dark conductivity and photoconductivity of μc-Si:H films has been investigated. The experiments are carried out on undoped μc-Si:H film, prepared on quartz substrate by electron cyclotron resonance chemical vapor deposition (ECRCVD). The absorption coefficient in the sub-gap region ( hν<1.2 eV) as well as the photoconductivity of μc-Si:H films change considerably after electron irradiation. Annealing of the irradiated films for 1 h at 180 °C temperature restored the initial state. The observed parameter changes are attributed to the creation of metastable defects (silicon dangling bonds) in the disordered phase of the material near the surfaces of the microcrystalline columns in μc-Si:H films induced by electron irradiation. The inversely proportional dependence of photoconductivity on the concentration of these defects suggests that the dangling bonds created by electron irradiation are the dominant recombination centers in electron irradiated μc-Si:H films.

Homo-epitaxial Si absorber layers grown by low-temperature ECRCVD

We studied the homo-epitaxial growth of Si absorber layers at temperatures of 420–560 °C by electron-cyclotron resonance chemical vapour deposition. We deposited the Si films at rates of 15 nm min−1 on (1 0 0)-, (3 1 1)-, (1 1 1)- and multicrystalline Si wafers. Both substrate temperature and orientation have a pronounced influence on the structural quality. On Si(1 0 0) substrates films grew epitaxially above 480 °C and are of excellent crystallographic quality up to thicknesses of 2.5 μm. On Si(3 1 1) the epitaxy breaks down rapidly by the formation of polycrystalline regions. On Si(1 1 1) the films are always fine polycrystalline. Using multicrystalline substrates the quality of the films is related to the orientation of the grains ranging from excellent epitaxy to pure fine polycrystalline growth. The electrical properties of the intentionally undoped films grown on Si(1 0 0) are discussed in relation to the crystal quality.

Homo-epitaxial Si absorber layers grown by low-temperature ECRCVD

We studied the homo-epitaxial growth of Si absorber layers at temperatures of 420–560 °C by electron-cyclotron resonance chemical vapour deposition. We deposited the Si films at rates of 15 nm min −1 on (1 0 0)-, (3 1 1)-, (1 1 1)- and multicrystalline Si wafers. Both substrate temperature and orientation have a pronounced influence on the structural quality. On Si(1 0 0) substrates films grew epitaxially above 480 °C and are of excellent crystallographic quality up to thicknesses of 2.5 μm. On Si(3 1 1) the epitaxy breaks down rapidly by the formation of polycrystalline regions. On Si(1 1 1) the films are always fine polycrystalline. Using multicrystalline substrates the quality of the films is related to the orientation of the grains ranging from excellent epitaxy to pure fine polycrystalline growth. The electrical properties of the intentionally undoped films grown on Si(1 0 0) are discussed in relation to the crystal quality.

Purification of multi-walled carbon nanotubes by microwave digestion method

Here developed is an efficient method for purification of multi-walled carbon nanotubes synthesized by electron cyclotron resonance chemical vapor deposition (ECRCVD). Carbon nanotubes may find their limited use for some applications as they contain a small fraction of metal catalysts in the tubes and tend to have defects along the graphene tube wall. Defects within the multi-walled carbon nanotubes would reduce electrical and structure properties. A two-step acidic treatment in microwave digestion system is used to dissolve metal catalysts. HNO 3 or HCl can rapidly absorb microwave heat and energy and completely dissolve metal, which reside in carbon nanotubes without damage. The processing time of the two-step microwave-assisted and acid-treated time to dissolve metal in the MWCNTs is below 1 h. After purification, the amount of residual catalyst metals in samples is estimated by using the thermogravimetric analysis (TGA). The results show that a high-yield of multi-walled carbon nanotubes with approximately 5% of metal is obtained.

Influence of the power on the processes controlling the formation of ECR-CVD carbon nitride films from CH4/Ar/N2 plasmas

Carbon nitride films have been synthesized by means of electron cyclotron resonance chemical vapour deposition (ECR-CVD) using different power values (50–212 W) at constant pressure conditions (0.03 mbar). Optical emission spectroscopy and mass spectrometry were used for the characterization of the plasma. The films were analysed using energy dispersive x-ray spectroscopies. It was found that all signal peaks in the optical emission spectra increased monotonically following the increase in microwave power. Moreover, we have observed that the radiative emission from the 4p(2p9) resonant state of Ar is the most affected by CH4 addition to a pure argon plasma. The latter suggests that a Penning mechanism controls the activation of CH4 molecules with increasing power levels at relatively low pressures. Besides, the increase of excited N atoms indicates a higher activity of the etching mechanisms of carbon nitride films with increasing power.

Compositional analysis of thin SiO xN y:H films by heavy-ion ERDA, standard RBS, EDX and AES: a comparison

The composition of silicon oxynitride (SiO x N y :H) films deposited by electron cyclotron resonance chemical vapour deposition (ECR-CVD) was analysed by ion beam techniques, heavy-ion elastic recoil detection analysis (HI-ERDA) with 150 MeV 86Kr ions and Rutherford backscattering spectroscopy (RBS) with 1.4 MeV 4He ions. The results were compared with energy dispersive X-ray analysis (EDX) and Auger electron spectroscopy (AES). Since HI-ERDA provides absolute atomic concentrations of all film components including hydrogen with a sensitivity of at least 0.005 at% the data from this method were used as a quantitative reference to assess the applicability of RBS, EDX and AES to the analysis of silicon oxynitrides. For each of these techniques the comparison with HI-ERDA allowed a discussion of the different sources of error, especially of those causing systematic deviations of the measured concentration values. A novel approach to determine from RBS spectra also the hydrogen concentrations appeared to be applicable for hydrogen levels exceeding 2 at%. Furthermore, it is shown that the film density can be determined from the HI-ERDA results alone or in combination with single-wavelength ellipsometry.

Effects of Deposition Temperature on the Properties of Fluorinated Amorphous Carbon Films

Fluorinated amorphous carbon films (a-C:F) were prepared at different temperatures using a microwave electron cyclotron resonance chemical vapor deposition (ECR-CVD) reactor with CHF3 and C2H2 as source gases. Films were annealed at 500°C in vacuum ambience in order to investigate the relationship of their thermal stability, optical and electrical properties with deposition temperature. Results indicate that the films deposited at high temperature have a less CFx bonding and a more cross-linking structure thus a better thermal stability. They also have a lower bandgap, higher dielectric constant and higher leakage current.

The role of nitrogen in carbon nanotube formation

To examine the role of nitrogen, Co- and Ni-coated substrates were pretreated with three different gas compositions to compare the pretreated catalyst surfaces; the Fe, Co and Ni foils were subjected to carbon nanotube (CNT) growth experiments with CH 4/H 2 and CH 4/N 2 as source gases; the catalyst pretreatment plus the CNT growth experiments on Co- and Ni-coated Si substrates were carried out using both microwave plasma chemical vapor deposition and electron cyclotron resonance chemical vapor deposition (ECR-CVD) under different nitrogen-containing gases. The results show that the role of nitrogen may be summarized as follows: by comparing with hydrogen plasma, the bombardment energy of nitrogen plasma is greater. Therefore, the presence of nitrogen during CNT growth can keep the front catalyst surface clean and active to prolong surface passivation to enhance carbon bulk diffusion. The higher temperature due to higher bombardment energy of nitrogen plasma can promote agglomeration effects during catalyst pretreatment and the initial stage of CNT growth to produce larger size nano-particles. The presence of nitrogen is a favorable condition for formation of the bamboo-like CNTs, but not a necessary condition. Another favorable condition for formation of the bamboo-like CNTs is to deposit CNTs by ECR-CVD.

Surface and structural properties of ultrathin diamond-like carbon coatings

Nanoscale wear resistance, friction, and electrical conduction tests using atomic force microscope (AFM) have been conducted on ultrathin diamond-like carbon (DLC) coatings, including tetrahedral amorphous carbon (ta-C) deposited using pulsed cathodic arc (PCA) and filtered-PCA, and hydrogenated amorphous carbon (a-C:H) deposited using electron cyclotron resonance—chemical vapor deposition (ECR-CVD). The low-resistant layers at the surfaces of these thin DLC coatings were revealed by AFM-based nanowear tests. Their thickness is mainly determined by the deposition methods and does not show an obvious variation with the coating thickness decreasing from tens of nm to a few nm. The ∼3 nm ta-C coatings from PCA and filtered-PCA deposition were found to have the stable bulk structure beneath the thin (0.3–0.95 nm) surface layers. The ∼3 nm a-C:H coating from ECR-CVD had the extremely low load-carrying capacity and exhibited the evidence of coating delamination, which can be related to the thicker (1.5±0.1 nm) soft surface layers of a-C:H coatings. The results from conducting-AFM measurements indicate that a-C:H coatings have H and sp 3 C enrichment surface layers while the soft surface layers of ta-C coatings have graphite-like structure. The nanoscale friction coefficients of these thin ta-C and a-C:H coatings were compared by AFM-based lateral force microscope. The lower friction coefficient of ta-C coatings can be attributed to the existence of graphite-like surface structure.

Structure and Electrical Studies of Fluorinated Amorphous Carbon Films Prepared by Electron Cyclotron Resonance/Chemical-Vapor Deposition

Fluorinated amorphous carbon (a-C:F) films of high fluorine content were prepared by radio-frequency (RF) bias assisted electron cyclotron resonance/chemical-vapor deposition (ECR-CVD) with a variable fluorine-to-carbon (F/C) ratio of the feed gases. The films were characterized by X-ray photoelectron spectroscopy (XPS), electron energy loss spectroscopy (EELS) and transmission electron microscopy (TEM). A low dielectric constant of around 1.5 and high dielectric strength beyond 35 MV/cm were obtained under the as-deposited and annealed conditions, respectively. The measured huge current surge and electrical conductivity of the films were discussed on the basis of the nanovoids and sp2/sp3 bonding fractions as derived from the above characterizations.

Characterization of protective-layer-coated LiMn 2O 4 cathode thin films

We introduced a post-annealing process for the preparation of spinel-phase LiMn 2O 4. The annealed films had proper crystallinity and surface roughness. In order to reduce the interface reaction during operation, we introduced a diamond-like carbon (DLC) film. The DLC films were deposited on LiMn 2O 4 films by using electron cyclotron resonance chemical vapor deposition (ECRCVD). A DLC-coated LiMn 2O 4 film was more stable during the charging–discharging reaction and showed higher discharge capacity over a wide voltage window than the uncoated LiMn 2O 4 film.

An a-C:F:H Film with High-Thermal Stability by ElectronCyclotron Resonance Chemical Vapour Deposition at Room Temperature

Using CHF3/C6H6 gases, amorphous fluorinated hydrocarbonfilms (a-C:F:H) were deposited by electron cyclotron resonance (ECR)chemical vapour deposition at room temperature. Dependence of the filmproperties on variable flow ratiosR[CHF3]/{ [CHF3]+[C6H6]} was investigated byinfrared absorption, x-ray photoelectron spectroscopy, measurements ofthe film thickness and dielectric constant. Evidence shows that the filmdeposition rate decreases linearly with the increasing flow ratios R andthe adding of C6H6 source gas to ECR plasma enhancesstructural cross-linking in the a-C:F:H films. In order to obtain goodstructural stability of these films, it is necessary to reconcileconfigurations between C-C bond and H or F terminal atoms carefully. Theexperimental results indicate that an a-C:F:H film with low dielectricconstant (k<3) and high thermal stability (>400°C) has beendeposited successfully at R = 56.3%.

Blue photoluminescence of aSiOxNy films prepared by ECR-CVD

Amorphous silicon oxygen nitride (aSiOxNy) films are prepared by microwave electron cyclotron resonance chemical vapor deposition (ECR-CVD) method using 10% SiH4 in N2/O2 mixtures. The Fourier transform infrared absorption spectroscopy shows that the main bonding configuration of the films is SiO and SiN. If O2 is input, the dominant composition of the films is SiOx, while it is SiNx at zero O2 flow rate. A blue photoluminescence (PL) band at 460nm produced by 565eV laser excitation is observed at room temperature from these films, and the emission intensity increases with decreasing O2 flow rate. The blue PL for aSiOxNy films, mainly composed of aSiOx, comes from oxygen deficient defects in the SiOx matrix. For aSiOxNy films, mainly composed of aSiNx, its blue PL is due to the electronhole radiative recombination from the defect states in the SiNx matrix.

Improved productivity on diamond-like carbon coating optical disk stamper

We report on a proposed process for depositing a diamond-like carbon (DLC) film on the back surface of a submaster stamper after a nickel electroforming process. This process could keep friction low and improve the productivity of an optical disk. Hydrogenated amorphous carbon films were deposited from a mixture of argon and acetylene by electron cyclotron resonance-chemical vapor deposition at pressures of about 5–9×10−3 mbar. In order to improve the adhesion strength of DLC films, functionally gradient Ti/TiN/TiCN supporting mutilayers were deposited on the stampers. The structural characteristics of DLC films were investigated by Raman spectroscopy. The properties of a DLC film coating on a stamper are summarized as follows: microhardness (five times improved), roughness less than 4 nm, excellent adhesion of 65 N, and coefficients of friction less than 0.1. The characteristics of the back surface coated by DLC film were improved, and the productivity of an optical disk per stamper is estimated at about 1.7 times more than obtained. Finally, the DLC submaster stamper could be used to overcome the barrier and dramatically improve the economics and yield of increased productivity of polymer compact disks.