Electron Cyclotron Resonance Chemical Vapor Deposition Research Articles

Efficacy of ECR-CVD silicon nitride passivation in InGaP∕GaAs HBTs

High quality passivation silicon nitride films have been obtained requiring no surface pretreatment and being fully compatible with monolithic microwave integrated circuits. The nitride film is deposited by electron cyclotron resonance—chemical vapor deposition directly over GaAs-n substrate and over InGaP∕GaAs heterojunction structures, which are used for heterojunction bipolar transistors (HBTs). Metal∕nitride∕GaAs-n capacitors were fabricated for all the samples. Effective charge densities of 3×1011cm−2 and leakage current densities of 1μA∕cm2 were determined. Plasma analysis showed a reduced formation of molecules such as NH in the gas phase at low pressures, allowing the deposition of higher quality films. The process was used for InGaP∕GaAs HBT fabrication with excellent results, such as higher current gain of passivated device comparing to unpassivated HBTs.

Line defects in epitaxial silicon films grown at [formula omitted

We present an investigation of line defects in epitaxially grown silicon layers using Secco defect etching and transmission electron microscopy (TEM). 1 μ m thick layers were deposited onto Si (1 0 0) wafers at a substrate temperature of 560 ∘ C using electron cyclotron resonance chemical vapour deposition (ECRCVD). Defect etching reveals a variety of etch pits related to extended defects. A detailed analysis of the orientations and shapes of etch pits related to line defects is carried out. Using this information it is then possible to assign different types of etch pits to line defects observed by TEM. The investigations show, that one type of defect are extended dislocations parallel to 〈 1 1 2 〉 , while the direction of two other types are 〈 1 1 0 〉 as well as 〈 3 1 4 〉 , a direction uncommon for line defects in silicon.

Large-grained polycrystalline silicon on glass for thin-film solar cells

We have investigated the formation of large-grained polycrystalline silicon (poly-Si) films on glass for thin-film solar cells using the ‘seed layer concept’ which is based on the epitaxial thickening of a thin large-grained poly-Si template (seed layer). Due to the glass substrate all process steps are limited to a temperature of about 600 °C. The aluminium-induced layer exchange (ALILE) process based on the aluminium-induced crystallisation (AIC) of amorphous Si has been used to prepare p +-type seed layers featuring large grains and a high preferential (100) orientation of the surface. The seed layers have been thickened by electron cyclotron resonance chemical vapour deposition (ECRCVD) to form the p-type absorber of the solar cell. First poly-Si thin-film solar cell structures have been prepared by deposition of an n +-type a-Si : H emitter. So far an open circuit voltage of 284 mV has been reached without any additional treatments like defect annealing and defect passivation.

Effects of post treatment on the field emission properties of CNTs grown by ECR-CVD

Field emission display (FED) has been considered as one of the most promising application of carbon nanotubes. In FED application, the CVD assisted grown CNT cathodes have major problems, i.e., the screen effect of the well aligned CNT array reduces the field emission characteristics. The post treatments for cathode become necessary to improve the field emission characteristics and uniformity of the CNT emitters. In this study, well-aligned carbon nanotube array on Si substrate were synthesized by using a catalyst-assisted microwave plasma electron cyclotron resonance chemical vapor deposition (ECR-CVD) system with methane as source gas. Then a series of post treatment, including hydrogen plasma, oxygen plasma and electroless nickel plating, were conducted on the as grown CNT arrays. The results show that the H-plasma may damage the stems of CNTs at longer etching time. Consequently, the field emission characteristic of CNTs is reduced. In contrast, oxygen plasma increases the field emission characteristic of CNTs by reducing CNTs diameter and increasing inter-tube distance. Comparing to plasma post-treatment, electroless nickel-plating post-treatment is apparently improve the field emission characteristic of CNTs. This process results in the gathering of nickel catalysts at the top of CNTs and concentration CNTs field emission ability.

Influence of Defect Post-deposition Treatments on poly-Si Thin-film Solar Cells on Glass grown by ECRCVD

AbstractThe epitaxial thickening of a thin polycrystalline Si (poly-Si) film (seed layer) is a promising approach to realize an absorber layer of a poly-Si thin-film solar cell on glass. Such cell concept combines the benefits of crystalline Si and the high potential for cost reduction of a thin-film technology. Here, we discuss the influence of post-deposition treatments on the properties of absorber layers grown by electron-cyclotron resonance chemical vapor deposition (ECRCVD) and the solar cell performance, respectively. After the absorber growth and prior to the emitter deposition, defect annealing was used to improve the structural quality of the absorber layers and to increase the doping efficiency. For this, we used rapid thermal annealing (RTA) processes as well as thermal annealing in a conventional quartz furnace. In order to avoid damaging of the glass, only short annealing times (up to 400 s) were applied at temperatures of up to 950 °C. Defect passivation treatments were carried out at temperatures of about 350 °C to passivate the remaining defects in the films by hydrogen. The impact of both treatments on the solar cell parameter will be discussed. Excellent VOC's of up to 361 mV were achieved without hydrogenation showing the high potential of ECRCVD-grown absorbers. Applying both treatments resulted so far in an increase of VOC of about 400 mV. Because of the fact, that both post-treatments (particularly hydrogenation) are still not yet optimized, further improvements can be expected.

Preparation and characterization of hydrogenated microcrystalline silicon films by HW-MWECR-CVD

Hydrogenated microcrystalline silicon (μc-Si∶H) films with high crystalline volume fraction were deposited using a novel hot wire assisted microwave electron cyclotron resonance-chemical vapor deposition (HW-MWECR-CVD) system. The Raman scattering spectrum and X-ray diffraction measurements were carried out to characterize the microstructure of the films. It was shown that, in a wide range of silane dilution ratio, all the deposited films had high crystalline volume fractions. The transition phase from amorphous to microcrystalline silicon was more easily grown with higher silane dilution ratio, which was attributed to the higher ionization and decomposition of the source gases in HW-MWECR-CVD system than in other systems.

Study of fluorinated amorphous carbon films prepared by electron cyclotron resonance chemical vapor deposition

Fluorinated amorphous carbon(a-C:F) films were deposited using C4F8 and CH4 as precursor gases by electron cyclotron resonance chemical vapor deposition (ECR-CVD). Analysis of chemical compositions and bond structures by Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) shows that the loss of CF3 and C—C termination bonds are liable for inducing reduction of film thickness after heat treatment through out-gassing process. The dielectric constant of a-C:F films increases due to increased electronic polarization and enhanced film density and the interface trap density decreases from (5—9)×1011eV-1cm-2 to (4—6)×1011eV-1cm-2 after 300℃ annealing in a nitrogen environment. The current-voltage characteristics of α-C:F films was explained by ohmic conduction at low fields and Poole-Frankel conduction at high electric fields. The trap energy of the traps at band tails formed by the delocalized π electrons decreases after annealing, leading to the increase of leakage current due to field-enhanced thermal excitation of trapped electrons into the conduction band.

Extended defects in Si films epitaxially grown by low-temperature ECRCVD

Si films grown epitaxially by low-temperature electron–cyclotron resonance chemical-vapor deposition (ECRCVD) were investigated by analyzing extended defects in these films. Extended defects were made visible by Secco etching and scanning (SEM) and transmission (TEM) electron microscopy were used to analyze them in detail. Films grown on Si(1 0 0) wafers show different kinds of etch pits with characteristic shapes, sizes and crystallographic alignments. Their correlation to crystallographic defects is discussed. The typical total etch pit density for boron-doped samples grown at 580 °C on Si wafers is in the range of 10 8 cm −2. Films grown on poly-Si seed layers on glass are strongly affected by Secco etch due to growth regions of different structural qualities and a high density of extended defects. Solar cell test structures were prepared from both types of samples and their results discussed in view to the density of extended defects.

X-ray photoelectron spectroscopy and structural analysis of amorphous SiOxNy films deposited at low temperatures

We establish, using a tetrahedral model, the bonding properties of amorphous silicon oxynitride (a-SiOxNy) films deposited at low temperatures (LTs) by electron-cyclotron resonance chemical-vapor deposition (ECRCVD) on several substrates and under various conditions of gas flows and total gas pressure in a dilute mixture of SiH4+N2 in Ar. The atomic percentage of each tetrahedral unit incorporated in the film network is calculated from the deconvolution of the high-resolution x-ray photoelectron spectroscopy (XPS) spectra in the Si 2p3∕2 region and corroborated by the results obtained from both survey scans and the high-resolution XPS spectra in the N 1s region. The Si3N4 phase is the most important one and the only bonding unit which is incorporated in all our LT ECRCVD SiOxNy films. The incorporation of all the other component tetrahedrons depends strongly on growth conditions. The threshold values of the N∕Si atomic ratio for which intrinsic defects, such as Si–Si bonds, are not incorporated in the network depend on the O∕Si ratio incorporated in the films, mainly due to the competition between oxygen and nitrogen atoms in their reaction with silicon dangling bonds. The effect of the total gas pressure on the atomic percentages of the oxidation states present in the LT ECRCVD SiOxNy films is qualitatively similar to the effect of the ion bombarding energy or the plasma density. O–N bonds are present only in samples having high amount of oxygen and nitrogen in their networks. For these films, our results show unambiguously the presence of the N–Si2O tetrahedron and suggest that N–Si3−νOν tetrahedrons with ν⩾2 are not incorporated in their networks. A correlation is observed between the N–Si2O and the Si–O3(ON) tetrahedrons whose component peak is localized at (104.0±0.2)eV in the Si 2p3∕2 region of the XPS data, which suggests that both bonding units coexist in these films as some sort of complex bonding configuration.

Nanofabrication and the structure-property analyses of phase-change alloy-ended CNTs

In order to cap the tip cavities of the open-ended carbon nanotubes (CNTs) with the phase-change alloy for potential applications as the nano-resolution storage media, the Co-assisted CNTs were first synthesized by electron cyclotron resonance chemical vapor deposition (ECR-CVD) with H 2 and CH 4 as the gas sources. Then, the as-grown CNTs were post-treated in H-plasma atmosphere to remove the carbon layers covered on catalysts, and subsequently immersed in HNO 3 solution to remove the catalysts from the tips. The open-ended CNTs with a bowl-like-shape tips were followed by coating with a phase-change alloy layer of GeSbTeSn via sputtering process, and then heat treated in vacuum for 30 min to trim the alloy off from the sidewalls of CNTs to obtain the alloy-ended CNTs. The structures and properties in each processing step were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy and Auger electron spectroscopy (AES). The experimental results show that the well-oriented phase-change alloy-ended CNTs over a large area are fabricated successfully. Furthermore, the Auger analyses show the compositions of the phase-change alloys may be changed from Te-rich to Ge-rich after being capped on the tips of CNTs.

Influence of hot wire on the formation of microcrystalline silicon in MWECR–CVD system

The high-crystallinity and low-defect-density microcrystalline silicon films ( μc-Si:H) was prepared by using a new hot-wire-assisted microwave electron cyclotron resonance–chemical vapor deposition (HWAMWECR–CVD) system. In this system the hot wire plays an important role in suppressing the growth of a-Si:H in favor of μc-Si:H, thus improving the physical properties. The experimental results show that the μc-Si:H film prepared by using this new system, the crystalline volume fraction is increased from 16.4% to 63.2%, the photoconductivity is increased by two orders of magnitude, the optical band gap is decreased to 1.59 eV, and the light-induced degradation keeps almost constant compared to that prepared by conventional system.

Structural evolution of SiN x films deposited by ECR and its light emission

Structural and optical properties of a-SiN x films deposited by electron cyclotron resonance chemical vapor deposition (ECRCVD) have been investigated. The Fourier transform infrared (FTIR) spectroscopy shows the structural evolution of the SiN x films, which are defined as Si-rich SiN x and N-rich SiN x films, also confirmed by Raman spectroscopy. The origin of the light emission for SiN x films may be attributed to two mechanisms, i.e., quantum confinement effect (QCE) and transition of defect energy levels. The correlation between light emission and structures of SiN x films is discussed.

Preparation of high-quality hydrogenated amorphous silicon film with a new microwave electron cyclotron resonance chemical vapour deposition system assisted with hot wire

The preparation of high-quality hydrogenated amorphous silicon (a-Si:H) film with a new microwave electron cyclotron resonance-chemical vapour deposition (MWECR-CVD) system assisted with hot wire is presented. In this system the hot wire plays an important role in perfecting the microstructure as well as improving the stability and the optoelectronic properties of the a-Si:H film. The experimental results indicate that in the microstructure of the a-Si:H film, the concentration of dihydride is decreased and a trace of microcrystalline occurs, which is useful to improve its stability and that in the optoelectronic properties of the a-Si:H film, the deposition rate reaches above 2.0nm/s and the photosensitivity increases up to 4.71×105.

Process and characteristics of the large area well-aligned CNTs with open ends by electron cyclotron resonance chemical vapor deposition

This work presents a simple and highly reproducible method for fabricating well-aligned carbon nanotubes (CNTs) with open ends and large areas. The process involves the following steps. Co-assisted well-aligned CNTs were firstly synthesized by electron cyclotron resonance chemical vapor deposition (ECR-CVD) using H 2 and CH 4 as source gases. Then, the as-grown CNTs were post-treated in an atmosphere of H-plasma to remove the carbon layers that covered the surface of the catalyst. They were then immersed in 0.25 M HNO 3 solution to remove the catalysts from the tips. Their structures and characteristics in each processing step were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and field emission (FE) J-E measurements. The results indicate that the open-ended CNTs may behave better properties than the as-grown tubular CNTs because they have a higher local aspect ratio around the open-ended tips, if their structural integrity is maintained after post-treatment.

Structural defects and photoluminescence of epitaxial Si films grown at low temperatures

Silicon layers grown by low-temperature Electron Cyclotron Resonance Chemical Vapour Deposition (ECR-CVD) were investigated using photoluminescence (PL) and defect etching. Different forms of etch pits could be observed using Scanning Electron Microscopy. The densities of the etch pits and the intensities of defect-related PL bands are compared. A correlation between two kinds of elliptical etch pits, two PL peaks and the impurity content was found. One of these PL peaks has an energy of 903 meV, usually attributed to the so-called rod-like defects. The orientation of the related etch pits is, however, not consistent with the orientation of rod-like defects. Possible explanations for this behaviour are discussed.

Structure and property features of the catalyst-assisted carbon nanostructures on Si wafer by catalyst ion implantation and ECR-CVD

Experiments to examine effects of ion-implanted catalyst on the structure and property features of carbon nanotubes (CNTs) and nanostructures on Si wafer were conducted by electron cyclotron resonance chemical vapor deposition (ECR-CVD) with CH 4 and H 2 as source gases, under both ion-implanted and PVD-coated catalysts with different H-plasma pretreatment conditions. The deposited CNTs and substrates at every processing step were characterized by FESEM, TEM, SIMS, XRD and Raman spectroscopy. The results show that the growth mechanism of the CNTs under condition with the ion-implanted catalyst is different from that with the PVD-coated catalyst. It results in a greater hollow size of the tubes for the former condition. Furthermore, under conditions of a higher catalyst dosage and higher H-plasma concentration pretreatment, it indicates better field emission properties, more Co-silicide formation and more percentage of base-growth CNTs due to an increase in the amount of Co source and process temperature. The main effect of the implanted catalyst is essentially to enhance the adhesion strength of CNTs with the substrate through the Co-silicide formation and embedding the catalyst into the substrate, as shown by XRD and SIMS analyses. Additionally, it is also favor to form CNTs with a lower I D/ I G ratio and so a lower defect density. Under the present conditions, the best field emission properties are: turn-on voltage ∼6 V/μm and current density>0.72 mA/cm 2. In summary, the structure, growth mode, adhesion strength with the substrate, defect density and field emission properties of CNTs can be manipulated by changing the ion-implantation dosages and H-plasma pretreatment conditions, which may not be able to be produced by other methods.

Tube number density control of carbon nanotubes on anodic aluminum oxide template

We demonstrate that the tube number density of well-aligned carbon nanotubes (CNTs) grown over the nanoporous anodic aluminum oxide (AAO) template can be directly controlled by adjusting the CH 4/H 2 feed ratio during the CNT growth in a microwave plasma electron cyclotron resonance chemical vapor deposition (ECR-CVD) system. During the CNT growth, the nanotube growth and the amorphous carbon deposition on the AAO pore wall take place simultaneously. The amorphous carbon sediment will gradually cover up the AAO nanopores and prevent the nanotubes to grow out of the nanopores. By adjusting the CH 4/H 2 feed ratio, one can control the amount of the deposited amorphous carbon and thus the number of CNTs grown over the AAO nanopores. It was found that the CNT density decreases linearly with increasing the CH 4 concentration. The CNT density decreased by a factor of about 4.5 when the CH 4 concentration increased from 9% to 91%.

Improvement on the conventional MWECR-CVD system and preparation of hydrogenated amorphous silicon films

In order to obtain a compact-structure, saving-energy and good-property system based on the conventional microwave electron–cyclotron resonance chemical vapor deposition (MWECR-CVD) system, we proposed a new technique using a magnetic field combination of an electromagnetic coil and a permanent magnet unit, as well as adopting a dedicated microwave coupling structure. The experiment results showed that by using this new optimized system the deposition rate can reach more than 2.5 nm/s, and the photosensitivity of a-Si:H films can be up to 1.1×10 5.

Effect of CH4-doping on configuration and dielectric properties of SiCOH low-k films

Carbon-doped oxide materials (SiCOH films) with k of 2.45 and good thermal stability at temperature 485℃ are prepared by electron cyclotron resonance chemical vapor deposition (ECR-CVD) from the mixture of decamethylcyclopentasioxane (D5, ［Si(CH3)2O］5) and methane (CH4). T he chemical structures of D5 as a liquid source and films deposited with differe nt methane flux are studied by Fourier transform infrared spectroscopy. The resu lts indicate that the increase of methane is of great advantage to the reservati on of ring structure of D5 as well as the formation of high density CHn fragments in films. The decrease of dielectric constant is induced by the com bined action of several factors: lower density of films caused by high density o f CHn fragments and formation of intrinsic pores, lower polarization caused by the formation of Si-C bond and decrease of-OH bonds.

Synthesis and characterization of large area well-aligned carbon nanotubes by ECR-CVD without substrate bias

Large area, well-aligned carbon nanotubes (CNTs) were synthesized on porous silicon by electron cyclotron resonance chemical vapor deposition (ECR-CVD). No bias was applied on the substrate in this experiment. CH 4 and H 2 were used as source gases and Fe 3O 4 nanoparticles as the catalyst. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction spectroscopy (XRD), and Raman spectrum were used to evaluate the structure and composition. The results show that these CNTs have varying outer diameters from 10 to 90 nm and uniform length over 10 μm. They display hollow tubular and chain structures. The possible formation mechanism of aligned CNTs is discussed.