Electron Cyclotron Resonance Microwave Research Articles

Growth of ultrathin SiO2 on Si by surface irradiation with an O2+Ar electron cyclotron resonance microwave plasma at low temperatures

Ultrathin SiO2 films were grown by Si surface irradiation with an O2+Ar electron cyclotron resonance (ECR) microwave plasma at low temperatures. These films without hydrogen and silicon deposition were easily grown in a few minutes at low temperatures and at relatively low working pressures (1.0–3.9×10−1 Pa). The promoting growth process of an ultrathin oxidized layer (1–9 nm) was analyzed by in situ Fourier transform infrared reflective absorption spectroscopy. By using the sputter erosion technique, the dependence of x-ray photoelectron spectroscopy on the depth profiling of the films was obtained. The compositional deviations of the films from the stoichiometric SiO2 were also discussed in the interface region of Si/SiO2. This study indicated that an O2 ECR microwave plasma was efficient to form controlled ultrathin SiO2 dielectric films. The dependence of the film quality on the working pressure and gas flow rate ratios of the O2 to Ar was discussed.

Improved hydrogenated amorphous silicon thin films by photon assisted microwave electron cyclotron resonance chemical vapor deposition

The conventional microwave electron cyclotron resonance chemical vapor deposition process has been modified by illuminating the substrate with a tungsten halogen lamp beam of intensity 0.1–1 W/cm2 during the deposition of hydrogenated amorphous silicon films. Compared to the conventional process without photon assist, this technique provides improved photoconductivity, carrier lifetime, and solar cell efficiency, as well as reduced light-induced degradation. The efficiency of undoped hydrogenated amorphous silicon/p-type crystalline silicon solar cells fabricated by this process is 10%, without an antireflective coating, and has degraded to only 9.8% after 3 weeks continuous exposure to light.

Structure and Magnetic Properties of Fe-N Thin Films Grown by ECR Deposition

ABSTRACTThe growth of FexNy thin films on GaAs, In0.2Ga0.8As, and SiO2/Si substrates using an ultra high-vacuum (UHV) deposition chamber equipped with electron cyclotron resonance (ECR) microwave plasma source is presented. The structural properties of the deposited films have been measured using various techniques as x-ray diffraction (XRD), Auger electron spectroscopy (AES), and transmission electron microscopy (TEM). The results of XRD measurements show that the films consist of a combination of α-Fe, α'-Fe, y-Fe4N, and α”- Fe16N2 phases. The depth profiles, calculated from the Auger peak intensities, show a uniform nitrogen concentration through the films. The TEM reveals a columnar structure of these films. The properties of the different Fe-N layers have been exploited in the fabrication of Fe(N) / FexNy / Fe trilayer structures, where Fe(N) means a slightly nitrogen doped Fe film. The magneto-transport properties of this trilayer structure grown on In0.2Ga0.8As substrates are presented.

Structure And Magnetic Properties Of Fe-N Thin Films Grown By Ecr Deposition

ABSTRACTThe growth of FexNy thin films on GaAs, In0.2Ga0.8As, and Si02/Si substrates using an ultra high-vacuum (UHV) deposition chamber equipped with electron cyclotron resonance (ECR) microwave plasma source is presented. The structural properties of the deposited films have been measured using various techniques as x-ray diffraction (XRD), Auger electron spectroscopy (AES), and transmission electron microscopy (TEM). The results of XRD measurements show that the films consist of a combination of α-Fe, α'-Fe, γ-Fe4N, and α”- Fe16N2 phases. The depth profiles, calculated from the Auger peak intensities, show a uniform nitrogen concentration through the films. The TEM reveals a columnar structure of these films. The properties of the different Fe-N layers have been exploited in the fabrication of Fe(N) / FexNy / Fe trilayer structures, where Fe(N) means a slightly nitrogen doped Fe film. The magneto-transport properties of this trilayer structure grown on In0.2Ga0.8As substrates are presented.

Compositional and structural studies of amorphous silicon-nitrogen alloys deposited at room temperature using a sputtering-type electron cyclotron resonance microwave plasma

Abstract High-quality amorphous silicon-nitrogen alloys (a-SiN x ) have been deposited at room temperature by a sputtering-type electron cyclotron resonance (ECR) plasma. A detailed analysis of the properties of a-SiNx films in terms of their composition, microstructure and dielectric characteristics was performed using X-ray photoelectron spectroscopy, infrared (IR) spectroscopy and ramp current-voltage measurement techniques. Their characteristics were correlated with the N2 gas flow rate (NGFR) in the ECR plasma formation. The dependence of solid-state [N]/[Si] ratios in the films on the NGFR indicated that the film composition changed from non-stoichiometry to stoichiometry as the NGFR increased from 0.5 to 1 seem. The dependence of the IR spectra on the NGFR indicated that silicon nitride network was well ordered for an NGFR of 1 seem, in which the dielectric breakdown-field was over 4 MVcm−1. However, when the NGFR was over 1 seem, significant N≡N triple bonds (gaseous N2 molecule) were formed ...

Compositional and structural studies of amorphous silicon-nitrogen alloys deposited at room temperature using a sputtering-type electron cyclotron resonance microwave plasma

Compositional and structural studies of amorphous silicon-nitrogen alloys deposited at room temperature using a sputtering-type electron cyclotron resonance microwave plasma

Ultrafast carrier dynamics in wide gap hydrogenated amorphous silicon

We report on picosecond and femtosecond pump and probe measurements of the dynamics of photoexcited carriers in wide gap a-Si : H prepared by microwave electron–cyclotron resonance plasma-enhanced chemical-vapour-deposition. We interpret the picosecond dynamics of transient absorption under strong picosecond excitation in terms of a bimolecular recombination process with the rate constant B≈5×10 −10 cm 3 s −1, followed by a slower nanosecond decay. In the femtosecond measurements, we observed an initial decay with effective time constant ≈20 ps. We have not found any change in the picosecond dynamics when tuning the excitation wavelength through photoluminescence (PL) excitation spectrum profile. The ultrafast dynamics do not differ in the samples with PL efficiency differing in more than one order of magnitude, and they agree well with those in standard a-Si : H.

Influence of microwave plasma parameters on the nitriding of T-304 stainless steel

A microwave ( f = ω⧹2π = 2.45 GHz) electron cyclotron resonance (ECR) plasma source was employed to carry out the nitriding of T-304 stainless steel at low pressures (∼10 −4 torr.) with samples at the plasma floating potential. Even for nitriding times as short as 40 min the surface hardness was found to increase up to 6× the initial value; the nitrogen concentration and penetration depth were typically up to 27 at.% and 15 μm, respectively. These quantities were determined by measurements of the nitrogen concentration profiles obtained by Nuclear Reaction Analysis (NRA) and by means of energy dispersion X-ray spectroscopy (EDX) analysis of surface perpendicular to that which received the nitrogen flux. Three different mixtures of N 2⧹H 2 were used as working gases with an electron plasma density which was greater than the critical value. This density was achieved by lowering the external magnetic field to almost half of its resonant value (B r = 875 G—resonant magnetic field); in this way the samples received enhanced surface ion bombardment during the treatment. The plasma specifications were determined using electric probes.

Structural and electrical properties of thin microcrystalline silicon films deposited by an electron cyclotron resonance plasma discharge of 2% SiH4/Ar further diluted in H2

Microcrystalline silicon (μc-Si) was deposited in a simple, low cost microwave electron cyclotron resonance plasma system by H2 dilution of 2% SiH4/Ar. The film growth and properties have been examined with substrate temperatures between 300 and 450 °C for pressures of 1–40 mTorr. Raman spectroscopy has been used extensively to study the microstructure of the film, and to determine the crystallized fraction and grain sizes in the film, for growth variations caused by H2 dilution, growth pressure, and temperature. H2 dilution of the plasma is found to increase the grain size and the crystallized fraction of the deposited films. Crystallization could also be initiated in the films deposited using only the Ar diluted SiH4 by increasing the power coupled to the discharge. Increasing the H2 dilution results in compact films with a low hydrogen content, while a decrease is seen to create more voids in the film. The μc-Si films (∼70% crystallized fraction), prepared at 400 °C, with grain sizes between 200 and 300 Å, exhibit a low dark conductivity of 3×10−6 S/cm with conduction activation energies between 0.3 and 0.43 eV. The structural properties of the film, evaluated by Raman spectroscopy and evolved gas analysis, are correlated with the dark/photoconductivity observed in the film. The experimental data suggest etching by atomic hydrogen to be the primary mechanism responsible for the crystallization of the films.

Microwave plasma nitrided austenitic AISI-304 stainless steel

A microwave ( f= ω/2π=2.45 GHz) electron cyclotron resonance (ECR) plasma source was employed for low-temperature (350 °C) and low-pressure (3–4×10 −4 Torr) nitriding of AISI-304 stainless steel. Even for nitriding times as short as 40 min, the surface hardness was found to increase by up to six times the initial value, and the nitrogen concentration and penetration depth were typically up to 27 at.% and 15 μm, respectively. These quantities were determined by measurements of the nitrogen concentration profiles obtained by nuclear reaction analysis (NRA) and by means of energy-dispersive X-ray spectroscopy (EDX) analysis of a surface perpendicular to that which received the nitrogen flux. Three different mixtures of N 2/H 2 were used as working gases with an electron plasma density that was greater than the critical value. This density was achieved by lowering the external magnetic field to almost half of its resonant value ( B r=875 G—resonant magnetic field). In this way, the samples underwent enhanced surface ion bombardment during the treatment. The plasma specifications were determined using electric probes.

Distribution of species within an ethylene electron cyclotron resonance-microwave plasma

Electron cyclotron resonance microwave plasmas consisting of 2% ethylene in hydrogen and 2% ethylene in deuterium have been probed using the pulsed supersonic, plasma sampling technique. Comparison of the compositions of these two chemically equivalent plasmas provides the basis for examining the details of species interconversion and overall hydrocarbon chemistry within these plasmas. The ethylene/hydrogen plasma is shown to be composed of 9% ethane radical (C2H5), 38% ethylene (C2H4), 8% ethylene radical (C2H3), and 41% acetylene (C2H2), with the remaining counts attributed to impurities in the plasma. Due to interferences between the daughter ions of the radical species and the parent ions of ethylene and acetylene, the concentrations of radical species, reported above, represent only a lower limit estimate, based only on the parent ion intensity. Analysis of the mass spectrum obtained for the analogous deuterium plasma, based on the results from the hydrogen plasma experiments, reveal the acetylene components of the deuterium plasma to be 14% undeuterated (C2H2), 43% singly deuterated (C2HD), and 43% doubly deuterated (C2D2). The extensive deuteration of the acetylene indicates that the majority of the chemistry in these plasmas is repeated cycles of hydrogen (deuterium) atom addition to acetylene followed by abstractions from the radical species (C2HxD3−x). The absence of any significant intensity due to doubly, triply, or fully deuterated ethylenes indicates that the addition of hydrogen (deuterium) to the radical species C2HxD3−x is a much more rare event than abstraction.

Formation of silicon carbide and amorphous carbon films by pulse biasing silicon to a high voltage in a methane electron cyclotron resonance microwave plasma

Silicon was pulse biased to −45 kV in a methane plasma generated by microwave excitation in the electron cyclotron resonance (ECR) mode. Hydrocarbon ions were accelerated in the electrical field and implanted into the silicon. Rutherford backscattering (RBS) measurements showed that it is possible to incorporate a concentration of up to 95 at.% C into the Si. Cross-section transmission microscopy (XTEM) showed that the resulting surface layer was amorphous. Annealing at 1250 °C resulted in the formation of 10 to 60 nm thick, crystalline SiC layers.

Plasma nitriding in low pressure in an ECR microwave plasma

Pure iron and 38CrMoAl samples have been plasma-nitrided by using electron cyclotron resonance (ECR)-microwave (2.45 GHz) N 2–H 2 discharge plasmas at low pressures (4–8×10 −2 Pa) and at a temperature of 500 °C. The experiment results show that both phases of γ′- and ϵ-iron nitrides are formed on the surface of the nitrided samples. The thickness of the compound layer depends on the plasma nitriding time. After 4 h of nitriding, a 5–6-μm iron nitride layer and 200 μm diffusion layer are formed. The surface microhardness of the nitrided sample is increased.

Monte Carlo simulations of argon ion transport in the downstream region of electron cyclotron resonance plasmas

A Monte Carlo method to simulate the plasma characteristics of an electron cyclotron resonance (ECR) microwave discharge system is presented. We use the method to predict the ion behavior in the downstream region of an ECR argon plasma. The pressure and space dependences of the plasma potential, the effects of gas pressure on the ion velocity and angle distribution and the evolution of distributions are examined and discussed in detail. Our results of the simulation show that the ion parallel velocity distribution appears to be bimodal and is strongly dependent on the gas pressure, whereas the ion perpendicular velocity distribution is mainly determined by the applied magnetic field, and the ion beam tends to be parallel to the magnetic field.

Hydrogenated amorphous silicon deposited by glow discharge of SiH4 diluted with He: photoluminescence and electroluminescence in the visible region

Samples of a-Si:H having a wide gap (≥2.1 eV) were prepared using routine rf glow discharge decomposition of silane (SiH4) strongly diluted with He. Also, microwave electron–cyclotron–resonance plasma-enhanced chemical-vapour-deposition was used to prepare wide-gap a-Si:H via decomposition of He diluted SiH4. The wide-gap a-Si:H samples, containing above 30 at.% of hydrogen, exhibit visible photoluminescence at room temperature. From the temperature dependence of photoluminescence intensity and from the observed shift of the maximum with temperature we deduce that the customary model of radiative recombination of carriers localised in tail states is not directly applicable to the case of wide-gap a-Si:H. Instead, we propose that the photoluminescence arises in parallel from tail states and from isolated (extrinsic) centres. Electroluminescence results obtained on a p–i–n structure with wide-gap a-Si:H are reported.

Effects of plasma immersion ion implantation of oxygen on mechanical properties and microstructure of Ti6Al4V

Plasma immersion ion implantation (PIII) is a surface treatment with increasing interest, as it offers the possibility of performing three-dimensional ion beam treatments, reducing the need for manipulation under vacuum to obtain a uniform treatment in geometrically complex parts. In this work the PIII process has been used to perform surface treatment on Ti6Al4V alloy. This Ti alloy is commonly used in aerospace and biomedical applications, due to its good combination of mechanical and chemical properties, such as strength to weight ratio, corrosion resistance or bioinertness. However, due to its poor tribological properties, the use of surface treatments to improve wear resistance or decrease friction coefficient is often recommended. PIII has been used to implant the surface of Ti6Al4V alloy with oxygen ions. The oxygen plasma was generated by electron cyclotron resonance microwave excitation, working at two different pressures. At the lower pressure plasma density was increased by means of an external ring magnet. High voltage pulses of −40 kV, at of 400 and 600 Hz pulse repetition rates, were applied. Elastic recoil detection (ERD) analysis showed retained doses in the range of 3×10 17 to 1×10 18 O atoms cm −2, with oxygen concentration values ca 65% in the near surface region. Surface mechanical properties such as hardness, wear and friction have been evaluated. Microindentation tests showed an increase of up to 100% in the surface hardness of the ion implanted samples compared to the non implanted material. Dry pin-on-disk tests with spherical ended UHMWPE pins showed a very significant increase in wear resistance in oxygen implanted Ti6Al4V samples. Scanning electron microscopy and optical profilometry showed an important roughening of the Ti alloy surface after PIII treatment under selected conditions.

Formation of silicon carbide and nitride by ECR microwave plasma immersion ion implantation

Silicon was pulse biased to −45 kV in a methane or nitrogen plasma, generated by electron cyclotron resonance microwave excitation. Hydrocarbon or nitrogen ions were accelerated in the electrical field and implanted into the silicon. The depth distribution of the implanted ions was measured by Rutherford backscattering spectrometry (RBS) before and after annealing. For the case of nitrogen implantation, one observes a saturation concentration of incorporated nitrogen, which is below the value of stoichiometric Si 3N 4. In contrast to that, carbon implantation can result in far overstoichiometric C:Si ratios and therefore in the formation of an amorphous carbon rich (95 at.%) phase. Annealing of the wafers results in partial oxidation of the surface layers and in the formation of crystalline phases. The structure of the implanted silicon wafers has been determined by cross-section transmission electron microscopy (XTEM) for the as implanted and annealed samples. For both implanted ion species, carbon and nitrogen, the implantation resulted in an amorphization of the wafer surface. No crystalline phases except silicon could be detected by electron diffraction. Annealing of the carbon implanted silicon results in the formation of a continuous, 50 nm thick polycrystalline β-SiC layer. For the case of nitrogen implantation, the formation of a 25 nm thick, continuous α-Si 3N 4 film below a 50 nm thick amorphous surface zone has been observed.

Formation of silicon nitride layers by nitrogen ion irradiation of silicon biased to a high voltage in an electron cyclotron resonance microwave plasma

Silicon was pulse biased to −50 kV in a nitrogen plasma generated by microwave excitation in electron cyclotron resonance mode. Nitrogen ions from the plasma were accelerated in the electrical field and implanted into the silicon. Cross-section transmission electron microscopy showed that the resulting surface layer was amorphous. Tempering at 1500 K led to the formation of a 25 nm thick continuous crystalline film of α-Si3N4 buried under a 50 nm thick amorphous surface zone.

Composition and microstructure of titanium nitride formed on Ti6Al4V by nitrogen plasma immersion ion implantation

Ti6Al4V has been treated with nitrogen Plasma Immersion Ion Implantation (PIII). Implantations with high-voltage pulses have been carried out at 50- and 400-Hz pulse repetition rates for varying process times in a nitrogen plasma generated by electron cyclotron resonance (ECR) microwave excitation. Due to the different power input at these repetition rates, the corresponding sample temperature reached 200 and 450 °C, respectively. Nitride formation was studied in relation to the retained dose. The composition of the modified surface layer was determined by elastic recoil detection analysis (ERD), and the structure and morphology were studied by means of X-ray diffraction (XRD) and cross-section transmission electron microscopy (XTEM). The nitrogen content increases with total pulse number irrespective of the pulse repetition rate. Nitride formation could be proved by the presence of the (200) TiN reflection. A homogeneous fine crystalline TiN layer was built up, exhibiting a strong crystallographic orientation relationship to the substrate grains.

Plasma source ion carburizing of steel for improved wear resistance

Plasma source ion carburizing is a low-temperature, low-pressure carburizing approach for improved wear resistance of steel with specific advantages over plasma carburizing and plasma source carbon ion implantation. A carburizing apparatus based on an electron cyclotron resonance (ECR) microwave plasma source has been developed. Carbon (as methane and hydrogen) ions are accelerated from the ECR plasma by a low-pulsed negative bias (typically −2 kV), which is applied directly to the sample, implanted, and are finally diffused into the steel at elevated temperatures that are regulated up to 550 °C by an auxiliary heater. Plasma source ion carburizing into pure iron and 35CrMo low alloy steel at a process temperature of 350 °C has been investigated. The carburized samples were characterized using Auger electron spectroscopy, electron probe microanalysis, microhardness measurement, and glancing incidence x-ray diffraction. Significant increases in microhardness have been observed on the carburized pure iron and 35CrMo steel, because of 10 μm thick carburized layers composing a Fe3C phase on the outer surface and a hardened diffusion zone in the matrix that were formed after the carburizing at 350 °C for 8 h. The wear tests were performed on a crank/connecting rod reciprocating tribometer in a flat-on-flat configuration. The test results indicate that the carburized 35CrMo steel improved the abrasive wear resistance and decreased the coefficient of friction in comparison with the uncarburized steel.