ECR Plasma Research Articles

Growth and properties of amorphous Ge:H solar cells

We report on the growth and properties of a-Ge:H materials and solar cells. The materials and cells were grown using remote ECR plasma deposition with high (∼50:1) hydrogen dilution. Both p–i–n and n–i–n structures were made with this material on stainless steel substrates. The solar cells showed reasonable fill factors (59%). The measurement of subgap quantum efficiency revealed that the Urbach energy of valence band tails in devices was also very low, being ∼43 meV. Measurement of space charge limited current in n–i–n structures showed that the midgap defect density was in the mid-10 16/cm 3 eV range. Defect densities in the range of mid 10 16/cm 3 were also measured using drive level capacitance, and they were in agreement with SCLC results. Graded bandgap cells were made with this material. They showed an increase in voltage to 0.47 V when appropriate buffer layers were used. These results indicate that good quality a-Ge:H can be made for potential applications in solar cells and image sensors.

Parallel particle-mesh code for ECR plasma simulation

The three-dimensional particle-mesh parallel code for ECR plasma simulation is presented.

Imaging of ECR plasmas with a pinhole x-ray camera

X-ray plasma images were made at the 14.5 GHz electron cyclotron resonance ion source of ATOMKI using a pinhole and a high resolution CCD camera. This method has good spatial resolution as well as the capability of postprocessed energy filtering of the images. During the measurements low and high charge state Ar, Xe, and Fe plasmas were produced with simultaneous beam extraction. Full-size and selected region images were recorded and analyzed. Full-size x-ray images show the spatial positions of different sources of x rays (bremsstrahlung, characteristic lines of plasma and wall ions) within low-charged ECRIS plasmas. Images of selected plasma regions (extraction slit, magnet pole, magnet gap) offer a better understanding of the effect of important tuning parameters (bias disk voltage, gas mixing, microwave power, magnetic field strength, etc.) commonly used to produce highly charged plasmas and beams.

ECR Plasma Pretreatment on Sapphire and Silicon Substrates for ZnO ALE

ECR Plasma Pretreatment on Sapphire and Silicon Substrates for ZnO ALE

Properties of a-Si:H and a-(Si,Ge):h films grown using combined hot wire–ECR plasma processes

It has been suggested previously that ion bombardment with low energy ions is necessary in order to obtain the growth of high quality a-Si:H materials. Ion bombardment is presumed to play a major role both in the removal of excess hydrogen and in assisting in the surface movement of heavy radicals such as germyl during the growth of amorphous films. We report on an unambiguous experiment which shows that one needs low energy ion bombardment to promote the growth of high quality amorphous materials. The experiment consists of growing a-Si:H and a-(Si,Ge):H using hot wire deposition, while simultaneously subjecting the growing film to low energy (∼10 eV) H and He ions generated in a low-pressure (electron cyclotron resonance) ECR reactor. Experiments show that the primary mode of film growth is from the catalytic decomposition of silane and germane from the hot wire, with less than 10% growth resulting from plasma decomposition. A systematic set of measurements of film properties made at different substrate temperatures and ion bombardment conditions reveals that ion bombardment results in a decrease of H concentration and in the ratio of dihydride to monohydride bonded silicon and germanium. The presence of ions resulted in a significant decrease of the Urbach energy of valence band tails to below 50 meV. Photoconductivity improves by orders of magnitude, as does the photosensitivity ratio.

Effects of Pretreatments of PET Substrate on the Adhesion of Copper Films Prepared by a Room Temperature ECR-MOCVD Method

Effects of various pretreatments on the adhesion of copper-coated polymer films were investigated. Copper-coated polymer films were prepared by an electron cyclotron resonance-metal organic chemical vapor deposition (ECR-MOCVD) coupled with a DC bias system at room temperature. PET(polyethylene terephthalate) film was employed as a substrate material and it was pretreated by industrially feasible methods such as chromic acid, sand-blasting, oxygen plasma and ion-implantation treatment. Surface characterization of the copper-coated polymer film was carried out by AFM(Atomic Force Microscopy) and FESEM(Field Emission Scanning Electron Microscopy). Surface energy was calculated by based on the value of the contact angle measured. The adhesion of copper/PET films was determined by a pull-off test according to ASTM D-5179. It was found that suitable pretreatment of the PET substrate was required for obtaining good adhesion property between copper films and the substrate. In this study the highest adhesion was observed in sand-blasting, and then followed by those of acid and oxygen plasma treatment. However, the effect of surface energy was insignificant in our experimental range. This is probably due to compensating the difference in surface energy from various pretreatments by exposing substrate to ECR plasma for 5 min or longer at the early stage of the copper deposition. Therefore, it can be concluded that surface roughness of the polymer substrate plays an important role to determine the adhesion of copper-coated polymer for the deposition of copper by ECR-MOCVD.

Investigation of the electron energy distributions in Ar/N 2 ECR plasmas with magnetic mirror

The electron energy distribution function (EEDF) or the electron temperature in the case that the EEDF is Maxwellian, in Ar/N 2 ECR plasmas is investigated experimentally. The mirror-type magnetic field was applied to generate low-electron-temperature plasmas. As a result of the experiments, it was found that the EEDF of Ar/N 2 plasmas over about 0.7 Pa and 500 W is almost Maxwellian and the electron temperature has a local and remarkable increase in the downstream region under certain experimental conditions of the magnetic field and the mixture ratio. The local heating of the electrons which was high enough to influence the production of radicals and ions near the substrate was positioned regularly by changing the magnetic field configuration.

Control of the electron temperature by varying the resonance zone width in ECR plasma

The electron temperature ( T e) in an electron cyclotron resonance plasma is clarified to depend on the spatial profiles of the microwave-power absorption by both the electromagnetic-waves measurement and the simulation of microwave power absorption. It is found that T e is controlled by varying the magnetic field configuration and/or the microwave frequency since the power absorption profile is influenced by the effective resonance width. In fact, T e is observed to decrease with decreasing the magnetic field gradient at the resonance point for N 2, Ar and O 2/Ar plasma.

Electrical properties of diamond-like carbon films grown using ECR plasma decomposition of methane

Diamond-like carbon films were deposited on p-type silicon substrates by ECR-plasma decomposition of methane. The films have been characterized by scanning electron microscopy and Fourier transformed infrared spectroscopy. The current–voltage ( I– V) and capacitance–voltage ( C– V) characteristics were measured allowing interface trapped charges to be estimated. The density of states near to the Fermi level was calculated from the measurements to be of the order of 10 19 cm −3 eV −1.

Surface interaction of polyimide with oxygen ECR plasma

Polyimide (Kapton-H), was subjected to atomic oxygen from an electron cyclotron resonance plasma. An optical emission spectrometer was used to characterize the atomic oxygen produced in the reactor chamber. The energy of the ions was measured using a retarding field analyzer, placed near the substrate. The density of atomic oxygen in the plasma was estimated using a nickel catalytic probe. The surface wettability of the polyimide samples monitored by contact angle measurements showed considerable improvement when treated with plasma. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopic studies showed that the atomic oxygen in the plasma is the main specie affecting the surface chemistry and adhesion properties of polyimide. The improvement in the surface wettability is attributed to the high degree of cross-linking and large concentration of polar groups generated in the surface region of polyimide, after plasma treatment. The changes in the surface region of polyimide were observed by atomic force microscopic analysis.

1.3-.MU.m InGaAlAs-BH laser with Cl2/N2 ECR plasma etched mesas

We developed a dry etching process suitable for fabricating InGaAlAs laser mesa stripes. We used optimized Cl2/N2 ECR plasma for etching an InGaAlAs laser multilayer structure. This Cl2/N2 ECR plasma led to a uniform etching rate and an anisotropic profile using a nitrified side-protection mechanism. This smooth and anisotropic dry etching produced a well-matched interface for semi-insulated Fe-InP regrowth. It also enabled successfully fabricating an InGaAlAs buried heterostructure laser. The laser showed stable operation at 85°C and long-term reliability over 5000 hrs.

Defect Densities, Diffusion Lengths and Device Physics in Nanocrystalline Si:H Solar Cells

ABSTRACTWe report on the properties of nanocrystalline Si:H solar cells. The solar cells were of the p+nn+ type, with the n+ layer deposited first on a stainless steel substrates. The solar cells were prepared under high hydrogen dilution conditions using either ECR plasma deposition, or VHF diode plasma deposition processes. The deposition pressures were kept low, 5 mTorr in the ECR reactor and 50 mTorr in the VHF reactor. All the solar cells reported showed a high Raman ratio of crystalline to amorphous peaks. Properties such as dark current, deep level defects and shallow doping densities, and hole diffusion lengths were measured in these cells. It was found that the base layer was always n type, but that its doping could be changed by adding ppm levels of B during growth. A sufficient B doping even type converted the base layer to p type. It was found that there was a good one-to-one correlation between the shallow doping and deep level defects, suggesting that the same element, probably oxygen, is responsible for generating both shallow dopants and deep levels. The diffusion length of holes was measured in these cells using quantum efficiency vs. voltage techniques, and it was found that the diffusion length data could be explained very well by invoking trap-controlled recombination statistics. The dark I(V) curves could be represented by a standard diode model for highly crystalline materials, but as the degree of crystallinity was reduced, the diode factor increased. Voltage could be improved by reducing the crystallinity of the layer, but doing so resulted in a decrease in quantum efficiency in the infrared regions of the solar spectrum.

Effect of substrate bias voltage under growth on characteristics of InN films grown by molecular‐beam epitaxy assisted by electron cyclotron resonance plasma

We grew InN films on Si(111) substrates, to which a biased electric filed was applied positively or negatively, by electron cyclotron resonance plasma-assisted molecular-beam epitaxy (ECR plasma-assisted MBE) in order to suppress ion damage due to N2+ ions or/and impurity incorporation due to some ions of residual impurities generated by ECR plasma and have investigated the effects of bias voltage on film characteristics. The surface morphology was improved, the carrier concentration decreased, and the Hall mobility increased with increase of the bias voltage probably because of the two reduction effects of impurity incorporation and ion damage due to N2+ ions generated by ECR plasma. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Quasilinear modification of the spectra of cyclotron emission from a toroidal plasma near the ECRH frequency

A study is made of the modification of the spectra of electron cyclotron emission from an ECR heated plasma in a toroidal magnetic confinement system into which the heating radiation is launched from the low-field side. It is shown that, at frequencies close to the heating frequency, cyclotron emission can become more intense because of the deformation of the distribution function of the resonant electrons. This effect can be used to diagnose the slightly pronounced quasilinear perturbations of the electron distribution in the thermal energy range, which are typical of experiments on ECR plasma heating. Results of a qualitative analysis carried out for model electron distribution functions are presented, and examples of three-dimensional numerical simulations of a circular tokamak are described.

Growth Kinetics and Electrical Properties of Ultrathin Si Oxide Film Fabricated Using Krypton-Diluted Oxygen Plasma Excited by Electron Cyclotron Resonance

The growth characteristics and electrical properties of a thin Si oxide film formed by Kr and O2 mixed ECR plasma irradiation at a low temperature of 130°C have been investigated. The Kr gas is better than Ar for diluting the O2 plasma for Si oxidation according to the current–voltage characteristics of the Si oxide film. It is found that the surface-reaction-limited growth dominates the initial stage of oxidation while the diffusion-limited growth dominates the thicker region. A large positive bias and a small O2 gas flow rate lead to the decrease in the leakage current and the increase in the breakdown electric field of the Si oxide film, implying that the oxidation in the initial stage is essential for obtaining good electrical properties. Under the optimum condition, the as-grown Si oxide film shows a breakdown electric field of 10–12 MV/cm, and for more than 80% of the samples a leakage current density at an electric field of 5 MV/cm distributes in the range of 10-9 or 10-8 A/cm2.

The characterization of nanocrystal graphite films deposited by ECR plasma sputtering

We investigated the deposition of carbon films at the condition of high plasma density using ECR plasma sputtering. High density of plasma with low electron temperature was obtained in the neighborhood of the substrate by the control of the magnetic flux density. The nanocrystal graphite in size less than 60 nm was deposited on the Si(1 0 0) substrates by the sputtering of graphite target in argon atmosphere at room temperature. The nanocrystal graphite films deposited at high plasma density (5.0×10 11 cm −3) and low pressure (1.2×10 −1 Pa) showed good tribological properties. New Raman peaks of G band were obtained. From the analysis of XPS, the nanocrystal graphite gives C1s binding energy of 284.8 eV. The electrical resistivity of the films was 10 −2 Ω cm.

Thin film transistors on nanocrystalline silicon directly deposited by a microwave plasma CVD

In an effort to develop a low-cost process to fabricate high mobility thin film transistors (TFTs), we present TFTs on nanocrystalline Si formed by a microwave plasma ECR-CVD. Compared with conventional rf plasma, microwave ECR plasma has the advantages of a higher ionization ratio and a lower gas pressure, which lead to higher deposition rate and lower cost for large area electronics. The purpose of this work is to fabricate TFTs on directly deposited nanocrystalline Si films and correlate the TFT performance with the deposition conditions of the nanocrystalline Si. This process produced nanocrystalline Si TFTs on glass with a high field effect mobility of 15.3 cm 2/V s and a small subthreshold swing of 0.45 V/dec for the Si film deposited at 400 °C with 15% H 2 dilution without post-fabrication annealing.

Preparation of hydrogenated amorphous silicon by ECR plasma sputtering and the effect on retinoic acid and membrane protein polypeptides

Thin films of amorphous silicon and hydrogenated amorphous silicon were prepared by ECR plasma sputtering and their characteristics are studied. These films exhibited several amorphous states and smoothness of less than 0.8 nm. Langmuir–Blodgett (LB) films of retinoic acid or polypeptide including the alpha helix region of membrane protein were jointed with these amorphous silicon films. The hybrid films exhibited an oriented arrangement of molecules. The UV absorption spectrum of the LB films of retinoic acid based on hydrogenated amorphous silicon films exhibited a novel absorption at the wavelength 500 nm not reported before.

Tribological properties of diamond-like carbon films produced by different deposition techniques

DLC films were deposited on Si wafers using RF plasma CVD, hot filament (HF) plasma CVD and ECR plasma CVD with plasma-based ion implantation (PBII). Tribological properties of the films were tested using a ball-on-plate friction tester sliding against a steel ball under wide range of conditions. DLC films produced by the three techniques were classified into two groups. DLC films prepared by ECR had good tribological properties over the wide range of conditions tested. DLC films prepared by RF and hot filament techniques showed low friction coefficient and high wear resistance, except for the lower load condition. The wear debris and the worn surfaces were analyzed by a Micro-laser Raman instrument. Micro-structural analyses of the wear debris reveals that ECR-DLC film is different from that of the other two, while the debris of HF-DLC and RF-DLC shows almost the same structure. The change in the structure appears to be correlated with the differences in the tribological behavior of each film.

Optical emission study of CH 4+CHF 3 ECR plasma and properties of a-C:F:H films

a-C:F:H films were prepared with a mixture of CH 4 and CHF 3 gases by microwave electron cyclotron resonance chemical vapor deposition method. An actinometer optical emission spectroscopy was used to reveal the trend in the concentration of some species (H, F, C 2, CH etc.) as a function of flow ratio R {[CHF 3]/([CHF 3]+[CH 4])}. The results from Fourier transform infrared transmission spectroscopy showed the structural evolution of a-C:F:H films with variable gas flow ratios R. This structural evolution had an influence on the film optical band gap. The optical band gap decreased with the increasing flow ratios R in the polymer-like region, while it increased in the PTFE-like region. The correlation between the C 2 species density and the properties of a-C:F:H films is also discussed.