Electron Cyclotron Resonance Hydrogen Plasma Research Articles

Radiation hardness of bipolar transistor based integrated circuits improved by ECR hydrogen plasma treatment and Si-wafers gettering

We demonstrate significant improvement of the radiation immunity of the integrated circuits based on silicon bipolar transistors. Strong decrease of the current gain degradation and significant yield improvement after high-energy gamma irradiation are both shown. This was achieved by development of efficient hydrogenation process for the silicon bulk and the surface dielectric layer using electron cyclotron resonance (ECR) plasma, as well as implementation of effective Si-wafer gettering option. Keywords: integrated circuits, bipolar transistors, ECR-plasma, hydrogenation of semiconductor structures, trap state passivation, gettering of semiconductor wafers, γ-irradiation, radiation hardness, yield of workable transistors.

Qualification of uniform large area multidipolar ECR hydrogen plasma

The design and characterization of a multi-dipolar microwave electron cyclotron resonance (ECR) hydrogen plasma reactor are presented. In this configuration, 16 ECR sources are disposed uniformly along the azimuthal direction at a constant distance from the center of a cylindrical reactor. Several plasma diagnostics have been used to determine key parameters such as neutral species temperature; electron density and temperature; and H+, H2+, and H3+ ion energy distributions. The experimental characterization is supported by electromagnetic and magnetostatic field simulations as well as Particle In-Cell Monte Carlo Collisions simulations to analyze the observed ion energy distribution functions. Especially, we show that both electron density and temperature are spatially uniform, i.e., 1011 cm−3 and 3 eV, respectively. This plasma enables generating ion flux and energy in the ranges 1019–1022 ions m−2 s−1 and few keVs, respectively. The H2+ ion distribution function shows two populations which were attributed to surface effects. These features make this reactor particularly suitable for studying hydrogen plasma surface interaction under controlled conditions.

Measurements of electron energy distribution on electron cyclotron resonance plasma operated with hydrogen gas

This article deals with the production of electron cyclotron resonance hydrogen plasma in a closed gas chamber called Menja device. For this purpose, 2.45 GHz frequency and various power i.e. 0 - 500 W are employed. The flow of hydrogen gas is controlled manually with the range 1.5 – 10 sccm maintaining pressure range 10-5 – 10-4 mbar. The Langmuir probe technique is used to drag the electrons and ions by biasing the probe positively and negatively to study the key parameters such as ion saturation current, floating potential, plasma potential, electron temperature and plasma density. Besides these, to obtain information on electron energies and their interaction with plasma, the electron energy distribution function (EEDF) has been studied with the help of 2nd derivative of current obtained from the differentiator. For this purpose, an analogue differentiation circuit was built and tested.

Atomic and Electronic Structure of SiOx Films Obtained with Hydrogen Electron Cyclotron Resonance Plasma

The silicon oxide thin films obtained by thermal SiO2 treatment in hydrogen electron cyclotron resonance plasma at various exposure times are investigated. Using X-ray photoelectron spectroscopy, we have established that such treatment leads to a significant oxygen depletion of thermal SiO2, the more so the longer the treatment time. The atomic structure of the SiOx < 2 films obtained in this way is described by the random bonding model. The presence of oxygen vacancies in the plasma-treated films is confirmed by comparing the experimental valence band photoelectron spectra and those calculated from first principles, which allows the parameter x to be estimated. We show that thermal silicon oxide films treated in hydrogen plasma can be successfully used as a storage medium for a nonvolatile resistive memory cell.

Optical Properties of the SiOx (x &lt; 2) Thin Films Obtained by Hydrogen Plasma Processing of Thermal Silicon Dioxide

The optical properties and composition of thermal silicon oxide thin films processed in a hydrogen electron cyclotron resonance plasma have been studied by ellipsometry, quantum-chemical modeling, and photoluminescence spectroscopy. It has been found that the plasma processing of the films leads to their oxygen depletion and the formation of nonstoichiometric oxide SiOx < 2. The parameter x of the obtained SiOx films has been determined by comparing the experimental spectral dependence of the refractive index with the dependence obtained theoretically using the ab initio calculation. It is shown that an increase in the time of processing of thermal dioxide SiO2 in a hydrogen plasma leads to an increase in the refractive index of the film, as well as in the degree of its oxygen depletion. The dependence of the parameter x of the investigated films on the hydrogen plasma processing time is plotted.

Phonon-assisted electron tunneling between traps in silicon oxide films treated in hydrogen plasma

The charge transport in thin thermal silicon oxide films treated in electron cyclotron resonance hydrogen plasma at different exposure times was investigated. X-ray photoelectron studies show that such treatment leads to the oxygen deficiency of the films. It was established that the treatment of the films in plasma leads to an increase of their conductivity by a factor of about 102. The film charge transport properties were studied at different temperatures and analyzed within four theoretical dielectric conductivity models. It was found that the charge transport mechanism is described by Fowler-Nordheim model in the initial silicon oxide and by the model of phonon-assisted electron tunneling between neutral traps after the treatment in hydrogen plasma. The thermal trap ionization energy value (Wt = 1.6 eV) measured from transport experiments is in agreement with that obtained from ab initio calculations for the oxygen vacancy (Si-Si bond) in SiO2.

Surface modification influenced properties of silicon nanowires grown by Ag assisted chemical etching with ECR hydrogen plasma treatment

Silicon nanowires (SiNWs) are fabricated by Ag assisted chemical etching and are treated with hydrogen plasma created by electron cyclotron resonance (ECR) plasma system at 600 watts microwave power for various time durations (0–30 min). The hydrogen plasma exposure on the surface of the SiNWs reduced the surface roughness and increased the crystalline nature. SEM analysis revealed that the diameter of the SiNWs decreased on plasma exposure. The electrical conduction measurements suggested that the hydrogen plasma exposure for 5 min on the SiNW surface enhanced the electrical conductivity when compared to as fabricated SiNW surface. The hydrophobic nature of fabricated SiNWs was transformed to hydrophilic at plasma exposure for lower time duration. On plasma exposure of NWs for 30 min the sample turned hydrophobic. Study of different properties of the SiNWs before and after plasma treatment revealed that there is pronounced effect of plasma on the nature of SiNWs.

Оптические свойства тонких пленок SiO-=SUB=-x-=/SUB=- (x&amp;lt;2), полученных обработкой термического диоксида кремния в водородной плазме

Using the methods of ellipsometry, quantum chemical modeling, and photoluminescent spectroscopy, the optical properties and composition of thin films of thermal silicon oxide processed in a hydrogen electron-cyclotron resonance plasma are studied. It has been established that treatment of films in plasma leads to their depletion in oxygen and the formation of non-stoichiometric oxide SiOx &lt;2. By comparing the experimental spectral dependence of the refractive index with the theoretically calculated from the first principles, the values ​​of the parameter x in the obtained SiOx films are determined. It was shown that an increase in the processing time of thermal SiO2 in hydrogen plasma leads to an increase in the refractive index of the film, as well as the degree of depletion of the film with oxygen. For the studied films, the dependence of the value of the parameter x on the treatment time in a hydrogen plasma is constructed.

Study of hydrogen ECR plasma in a simple mirror magnetic trap heated by 75 GHz pulsed gyrotron radiation.

Plasma of electron cyclotron resonance (ECR) discharge sustained by millimeter wave radiation is widely used for production of ion beams of different kind. The main trend in ECR ion sources development nowadays is an increase of frequency and power of microwave heating. The most advanced systems use gyrotrons in 24-60 GHz frequency range. In previous studies at IAP RAS it was demonstrated that ECR source SMIS 37 (Simple Mirror Ion Source) with 37.5 GHz heating operating in quasigasdynamic regime of plasma confinement is able to produce proton and deuteron beams with ion current density about 700 mA/cm2. As the next step of these investigations plasma properties of the discharge sustained by 75 GHz radiation have been studied. Plasma density and electron temperature were determined using spectroscopic and Langmuir probe techniques. It was demonstrated that plasma density could reach values close to 1014 cm-3 and that is of great interest for further development of high current ion sources for various applications.

Influence of microwave driver coupling design on plasma density at Testbench for Ion sources Plasma Studies, a 2.45 GHz Electron Cyclotron Resonance Plasma Reactor

A comparative study of two microwave driver systems (preliminary and optimized) for a 2.45 GHz hydrogen Electron Cyclotron Resonance plasma generator has been conducted. The influence on plasma behavior and parameters of stationary electric field distribution in vacuum, i.e., just before breakdown, along all the microwave excitation system is analyzed. 3D simulations of resonant stationary electric field distributions, 2D simulations of external magnetic field mapping, experimental measurements of incoming and reflected power, and electron temperature and density along the plasma chamber axis have been carried out. By using these tools, an optimized set of plasma chamber and microwave coupler has been designed paying special attention to the optimization of stationary electric field value in the center of the plasma chamber. This system shows a strong stability on plasma behavior allowing a wider range of operational parameters and even sustaining low density plasma formation without external magnetic field. In addition, the optimized system shows the capability to produce values of plasma density four times higher than the preliminary as a consequence of a deeper penetration of the magnetic resonance surface in relative high electric field zone by keeping plasma stability. The increment of the amount of resonance surface embedded in the plasma under high electric field is suggested as a key factor.

Ultra-fast intensified frame images from an electron cyclotron resonance hydrogen plasma at 2.45 GHz: Some space distributions of visible and monochromatic emissions

First results from an ultra-fast frame image acquisition diagnostic coupled to a 2.45 GHz microwave hydrogen discharge are presented. The plasma reactor has been modified to include a transparent doubled shielded quartz window allowing to viewing the full plasma volume. Pictures describing the breakdown process at 1 μs exposure time have been obtained for integrated visible light signal, Balmer-alpha, Balmer-beta lines, and Fulcher-band. Several different plasma emission distributions are reported. The distribution depends on the magnetic field configuration, incident microwave power, and neutral gas pressure.

Temperature and density evolution during decay in a 2.45 GHz hydrogen electron cyclotron resonance plasma: Off-resonant and resonant cases

Time resolved electron temperature and density measurements during the decay stage in a hydrogen electron cyclotron resonance (ECR) plasma are presented for a resonance and off-resonance magnetic field configurations. The measurements are conducted on a ECR plasma generator excited at 2.45 GHz denominated test-bench for ion-sources plasma studies at ESS Bilbao. The plasma parameters evolution is studied by Langmuir probe diagnostic with synchronized sample technique developed for repetitive pulsed plasmas with a temporal resolution of 200 ns in typical decay processes of about 40 μs. An afterglow transient is clearly observed in the reflected microwave power signal from the plasma. Simultaneously, the electron temperature evolution shows rebounding peaks that may be related to the interplay between density drop and microwave coupling with deep impact on the Electron Energy Distribution Function. The correlation of such structures with the plasma absorbed power and the coupling quality is also reported.

Evaluation of Absolute Flux of Vacuum Ultraviolet Photons in an Electron Cyclotron Resonance Hydrogen Plasma: Comparison with Ion Flux

We compared the absolute flux of positive ions with the flux of photons in a vacuum ultraviolet (VUV) wavelength range in an electron cyclotron resonance hydrogen plasma. The absolute flux of positive ions was measured using a Langmuir probe. The absolute flux of VUV photons was evaluated on the basis of the branching ratio between the Lyman and Balmer lines emitted from electronic states with the same principal quantum numbers. The absolute intensities of the Balmer lines were obtained by calibrating the sensitivity of the spectroscopic system using a tungsten standard lamp. It has been found that the flux of VUV photons is, at least, on the comparable order of magnitude with the positive ion flux, suggesting the importance of VUV photons in plasma-induced damage in fabrication processes of ultralarge-scale integrated circuits.

Evaluation of Absolute Flux of Vacuum Ultraviolet Photons in an Electron Cyclotron Resonance Hydrogen Plasma: Comparison with Ion Flux

Evaluation of Absolute Flux of Vacuum Ultraviolet Photons in an Electron Cyclotron Resonance Hydrogen Plasma: Comparison with Ion Flux

A comparison of nitrous oxide and hydrogen ECR plasma discharges for silicon solar cell passivation

The passivation of crystalline Si solar cells using nitrous oxide (N 2O) electron cyclotron resonance (ECR) plasma discharges has been studied and compared with ECR hydrogen passivation. The cells consisted of ECRCVD grown microcrystalline Si emitter layers on single crystal Si (sc-Si) and multicrystalline Si (mc-Si) substrates, without anti-reflective coatings or surface texturing. For cells on sc-Si substrates, hydrogen passivation is more effective at a substrate temperature of 300 °C and low microwave power (300 W). With increased power (500 W) H 2 is less effective than N 2O due to hydrogen plasma damage leading to a significant fall in the cell fill factor. In comparison with H 2, N 2O discharges lead to a significantly better (by > a factor of 2) improvement in the performance of cells on mc-Si substrates for treatment times of ≤15 min at a passivation temperature of 300 °C and 300 W microwave power. XPS measurements suggest that a surface oxide layer containing N and C atoms is formed by the N 2O plasma which, most likely, reduces the surface state density and, hence, carrier recombination.

Coupling effect of electron cyclotron resonance hydrogen plasma and dc biasing in fabricating diamond nanotips

The electron cyclotron resonance (ECR) hydrogen plasma with substrate dc biasing was investigated by using a Langmuir probe and optical emission spectroscopy during the formation of nanotips from as-grown diamond films. It is found that the coupling effect between the substrate biasing and the bulk plasma plays an important role in the fluxes of active species incident on the substrate. The energy of incident hydrogen ions is determined by the substrate biasing, while the densities of incident hydrogen ions and atoms are adjusted jointly by the substrate biasing and the bulk plasma. Diamond nanotips were fabricated from as-grown films under ECR-dc conditions. The shapes and sizes of the nanotips vary with the processing parameters, which are correlated with the change of active species on the film surface due to the coupling effect.

Morphological transformations of vanadium oxide films during low-temperature reduction in hydrogen electron cyclotron resonance plasma

Morphological transformations of amorphous vanadium oxide films obtained by the sol-gel method and polycrystalline V2O5 films are studied during their low-temperature (295–623 K) reduction in a hydrogen electron cyclotron resonance plasma. The morphology of films is analyzed using atomic force microscopy and high-resolution electron microscopy. It is found that a homogeneous amorphous film during the reduction process transforms to an island film and then bulk amorphous islands of a regular shape appear. These islands resemble microcrystals, and their concentration depends on the temperature and the reduction time. The low-temperature reduction of polycrystalline V2O5 films leads to their amorphization; however, the microcrystals in the polycrystalline film do not change their shape in this process. A mechanism of the reduction process is proposed. This mechanism explains the regularities of morphological transformations in amorphous sol-gel films of vanadium oxides based on the suggestion of a competition between the ion-stimulated nucleation and growth of nuclei of the crystalline phase and the amorphization of the growing nuclei.

Preparation of aligned Cu nanowires by room-temperature reduction of CuO nanowires inelectron cyclotron resonance hydrogen plasma

Aligned Cu nanowires were prepared by the reduction of aligned CuO nanowiresin electron cyclotron resonance (ECR) hydrogen plasma at room temperature.They are single-crystalline and maintain the original alignment of the CuOnanowires. In contrast, the reduction of CuO nanowires by thermal processing inH2 has failed to produce the expected Cu nanowires because of morphological changes and thecoalescence of newly formed Cu nanowires, leading to the formation of films consisting ofmicron-sized particles. The morphological changes and coalescence of Cu nanowires resultfrom their low melting temperature. The reduction mechanism under ECR conditions hasbeen discussed. The application of ECR plasma can effectively avoid the hightemperature demand for CuO reduction when using the thermal processing method.This template-directed method assisted by ECR plasma can be extended for thetransformation of other one-dimensional (1D) nanomaterials at low temperature and lowpressure.

Scanning tunneling microscopy investigations of hydrogen plasma-induced electron scattering centers on single-walled carbon nanotubes

The authors report on the generation of localized defects on single-walled carbon nanotubes by means of a hydrogen electron cyclotron resonance plasma. The defects have been investigated using scanning tunneling microscopy (STM) and show an apparent topographic height in the STM of 1–3Å. In the vicinity of defects, characteristic superstructures could be observed and the patterns could be simulated using a simple model based on large momentum scattering of the valence electrons. The combination of low structural damage and high electronic activity opens the possibility to tune the electronic transport properties using such defects.

Surface Cleaning Effects of Silicon Substrates by ECR Hydrogen Plasma on Subsequent Homoepitaxial Growth

We have demonstrated the preparation of the almost defect-free homoepitaxial layer and the defective layer, respectively, with and without applying the in-situ cleaning of the silicon substrate surface using electron cyclotron resonance hydrogen plasma. Secondary ion mass spectroscopy indicated that the interfacial oxygen and carbon concentrations, respectively, decreased and increased with the in-situ cleaning. We have investigated the effect of process parameters such as microwave power, d.c bias, and cleaning time, on the epitaxial growth, by evaluating the cross-sectional transmission electron microscopy images of the subsequently deposited Si homoepitaxial film.