Electron Cyclotron Resonance Nitrogen Plasma Research Articles

Spectroscopic characterization of the plasma generated during the deposition of AlxGa1−xN films by pulsed laser co-ablation of Al and GaAs targets in electron cyclotron resonance nitrogen plasma

A nitrogen–aluminum–gallium–arsenic plasma is formed by pulsed laser co-ablation of an Al target and a GaAs target in electron cyclotron resonance discharge-generated nitrogen plasma for AlxGa1−xN film deposition. The formed plasma was characterized by time-integrated and time-resolved optical emission spectroscopy measurements and the process of AlxGa1−xN deposition was discussed. The plasma contains excited species originally present in the working N2 gas and energetic species ablated from the targets, and its emission is abundant in the emission bands of diatomic nitrogen molecules and molecular ions and the emission lines of monoatomic aluminum, gallium, and arsenic atoms and atomic ions. The temporal and spatial features of the plasma emission reveal that the nitrogen species in the electron cyclotron resonance nitrogen plasma experience additional excitations due to the expanding ablation plumes, and the ablated species are excited frequently when traveling with the expanding plumes in the nitrogen plasma, making the formed plasma very reactive, which is very important in the process of AlxGa1−xN film deposition. The deposited film was evaluated for composition analysis by energy-dispersive x-ray spectroscopy and structure characterization by x-ray diffraction. The AlxGa1−xN film is slightly nitrogen rich with an aluminum content x of about 0.6 and featured with hexagonal wurtzite crystal structure with preferred c-axis orientation.

High excitation of the species in nitrogen–aluminum plasma generated by electron cyclotron resonance microwave discharge of N2 gas and pulsed laser ablation of Al target

A reactive nitrogen–aluminum plasma generated by electron cyclotron resonance (ECR) microwave discharge of N2 gas and pulsed laser ablation of an Al target is characterized spectroscopically by time-integrated and time-resolved optical emission spectroscopy (OES). The vibrational and rotational temperatures of N2 species are determined by spectral simulation. The generated plasma strongly emits radiation from a variety of excited species including ambient nitrogen and ablated aluminum and exhibits unique features in optical emission and temperature evolution compared with the plasmas generated by a pure ECR discharge or by the expansion of the ablation plume. The working N2 gas is first excited by ECR discharge and the excitation of nitrogen is further enhanced due to the fast expansion of the aluminum plume induced by target ablation, while the excitation of the ablated aluminum is prolonged during the plume expansion in the ECR nitrogen plasma, resulting in the formation of strongly reactive nitrogen–aluminum plasma which contains highly excited species with high vibrational and rotational temperatures. The enhanced intensities and the prolonged duration of the optical emissions of the combined plasma would provide an improved analytical capability for spectrochemical analysis.

Reactive expansion of laser-induced boron/carbon plasma in ECR nitrogen plasma during the deposition of BCN films

The expansion of the boron/carbon plasma induced by pulsed laser ablation of B 4C in the nitrogen plasma generated by electron cyclotron resonance (ECR) microwave discharge of N 2 gas was studied by optical emission spectroscopy (OES). OES measurements show that at the initial stages the mono-atomic species ablated from B 4C are the dominant emitting species and after 0.5 μs the plasma emission evolves to be dominated by the emission bands from nitrogen molecules and nitrogen molecular ions, revealing that the N 2 gas is highly excited by the hybrid processes of ECR microwave discharge and pulsed laser ablation. In addition to the emissions emitted from the species ablated from the target and present in the reactive background, C 2 and CN emissions are also observed. The characteristics of the emissions from various species provide an access to the reactive expansion of the boron/carbon plasma in the nitrogen plasma and the gas-phase reactions occurring in the plasmas during the deposition of BCN films by nitrogen plasma assisted pulsed laser deposition. The mechanisms for efficient incorporation of nitrogen in the films were also discussed.

Spectroscopic Characterization of Plasmas Generated by ECR Microwave Discharge of N2 Gas and Pulsed Laser Ablation of a B4C Target

AbstractThe plasmas generated by co‐action of electron cyclotron resonance (ECR) microwave discharge of N2 gas and pulsed laser ablation (PLA) of a B4C target were spectroscopically characterized using time‐ and space‐resolved optical emission spectroscopy (OES). The plasmas exhibit rapid variations in time and space and the optical emissions of the plasmas show unique characteristics in comparison with the plasmas generated solely by ECR discharge or PLA. At the early stages of the expansion of the PLA boron/carbon plasma in the ECR nitrogen plasma, the plasma emission is dominated by emission lines from atomic and ionic boron and carbon which decrease rapidly during the expansion of the PLA plasma, and then evolves to be dominant in emission bands from nitrogen molecules and nitrogen molecular ions. The emission bands of the C2 Swan system and the CN violet system were also distinguished. The processes including gas‐phase reactions occurring in the plasmas were discussed based on the characteristics of the plasma emissions.magnified image

Significant Improvement of SiO2/4H-SiC Interface Properties by Electron Cyclotron Resonance Nitrogen Plasma Irradiation

The effect of the insertion of a SiN film on the SiO2/4H-SiC interface properties was studied. The SiN interlayer was grown using electron cyclotron resonance (ECR) nitrogen plasma irradiation prior to the SiO2 deposition. It was found that the insertion of a SiN interlayer led to a significant decrease in interface-state and fixed-charge densities in a SiO2/4H-SiC gate stack. This insertion also induced elimination of the near-interface traps in the oxide. It was clarified from X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry analyses that Si dangling bonds were terminated by nitrogen, and the SiN interlayer effectively suppressed the formation of carbon generated by the thermal reaction between SiC and O atoms.

Dual Role of Purification and Functionalisation of Single Walled CNT by Electron Cyclotron Resonance (ECR) Nitrogen Plasma

The Electron Cyclotron Resonance (ECR) plasma is a relatively new and scalable technique which opens up possibilities for a more environmentally friendly and rapid method of nanotube purification. We report a single step, dual purification and functionalisation technique using nitrogen-ECR plasma and compare results to those from standard RF plasma via Raman, Thermal Gravimetric Analysis (TGA), X-ray Photon spectroscopy (XPS) and static contact angle measurement. The purity of the nanotubes was evaluated by TGA which showed ∼96% for the N-ECR treated and ∼91% for the N-CCRF. Defects introduced by plasma exposure acted to functionalise the nanotubes by nitrogen attachment as evidenced by Raman, XPS and static contact angle measurements. The impact of nitrogen ion bombardment with two different plasma ion energies is fingerprinted by the defects induced in the nanotube matrix. [DOI: 10.1380/ejssnt.2009.337]

Spectroscopic Study on the Enhanced Excitation of an Electron Cyclotron Resonance Nitrogen Plasma by Pulsed Laser Ablation of an Aluminum Target

The influence of pulsed laser ablation of an aluminum target on the nitrogen plasma produced by electron cyclotron resonance (ECR) microwave discharge has been studied by optical emission spectroscopy (OES) with time and space resolution. The continuous wave (CW) feature of the optical emissions from the ECR nitrogen plasma turns to vary with time and space due to pulsed laser ablation and the expansion of the ablation-induced aluminum plume in the nitrogen plasma. The optical emissions from the nitrogen plasma increase significantly and the emission intensity of nitrogen molecular ions is observed to be more than 20 times higher with the target being ablated in comparison to the case without target ablation. The comparison of the optical emissions from the nitrogen plasma with those from the aluminum plume indicates that the excitation enhancement of the nitrogen plasma occurs in the region where the aluminum plume is expanding, revealing that the expansion of the aluminum plume leads to the excitation enhancement of the nitrogen plasma. Relevant mechanisms responsible for the excitation enhancement of the nitrogen plasma through hybrid processes of ECR microwave discharge and pulsed laser ablation are also discussed.

Thermal stability of carbon nitride thin films prepared by electron cyclotron resonance plasma assisted pulsed laser deposition

Carbon nitride (CN x ) thin films with high nitrogen content were deposited on Si (100) substrates by using electron cyclotron resonance nitrogen plasma assisted pulsed laser deposition (ECR-PLD), and their thermal stability were studied by examining their composition and bonding behaviors upon post-deposition heat annealing in vacuum and in nitrogen ambient. The as-deposited films contain nitrogen content varying around 50 at.% and are primarily amorphous containing several bonding configurations between carbon and nitrogen atoms with different bond components depending on bias voltage applied to the substrates. In addition to the D, G and L Raman bands reported for most CN x thin films, three prominent Raman peaks were observed at 170, 260 and 616 cm − 1 from our as-deposited films. Composition analysis by Rutherford backscattering spectroscopy measurement and chemical structure characterization by Fourier Transform infrared spectroscopy and Raman scattering measurements showed that the ECR-PLD deposited CN x thin films are quite stable upon annealing in vacuum up to 750 °C. The CN x films exhibit even higher thermal stability in nitrogen ambient.

Growth of hexagonal GaN films on the nitridated β‐Ga2O3 substrates using RF‐MBE

AbstractThe growth of hexagonal GaN (h‐GaN) films on the nitridated β‐Ga2O3 substrates using radio‐frequency. molecular beam epitaxy (RF‐MBE) was investigated. The β‐Ga2O3 single crystal prepared by optical floating zone method was used to a substrate for GaN film growth, and nitridated by exposing to electron cyclotron resonance nitrogen plasma. It was found that h‐GaN layer is formed on the surface of β‐Ga2O3 substrates by controlling the nitridation condition, and homo‐epitaxial growth of h‐GaN films was succesfully achieved by optimizing the RF‐MBE growth condition. The observation of cross‐sectional high‐resolution transmission electron microscopy indicated that obtained GaN films grown on these nitridated β‐Ga2O3 substrates were of a high structural quality. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A-plane (110) InN growth on nitridatedR-plane (102) sapphire by ECR-MBE

A-plane (110) InN has been successfully grown on R-plane (102) sapphire substrate by electron cyclotron resonance (ECR) plasma-exited molecular beam epitaxy through substrate nitridation process. The substrate nitridation of R-plane sapphire by ECR nitrogen plasma was carried out at 430 °C for 10 and 15 min. The results of reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD), and scanning electron microscopy indicated the formation of A-plane InN on R-plane sapphire. Inclusion of cubic InN was also observed together with A-plane InN through RHEED and XRD measurements in case of A-plane InN layer grown on 10 min nitridated substrate. However, when the nitridation time of R-plane sapphire by ECR nitrogen plasma increased to 15 min, it is confirmed that formation of cubic InN was successfully suppressed. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Spectroscopic study on pulsed laser ablation of graphite target in ECR nitrogen plasma for carbon nitride film deposition

The influence of nitrogen plasma generated by electron cyclotron resonance (ECR) microwave discharge on deposition of carbon nitride films by means of ECR plasma assisted reactive pulsed laser deposition was investigated by a comparative study on the optical emission of the plume produced by pulsed laser ablation of a graphite target in ECR nitrogen plasma, in vacuum and in low-pressure nitrogen gas ambient. Spatial and temporal spectroscopic measurements show that in vacuum optical emission lines originating from carbon atoms and ions dominate the plume emission, while in low-pressure N 2 ambient weak CN emissions appear. In nitrogen plasma, the plume emission exhibits itself very differently. It evolves from consisting of emissions almost from mono-atomic carbon atoms and ions to being dominated by emissions from CN molecules. The presence of the reactive nitrogen plasma greatly enhanced the CN emissions and eliminated the emission lines from carbon atoms and ions. The appearance of the CN emissions occurs after the emissions from carbon atoms and ions have decayed considerably, indicating that the dominant mechanism for the formation of CN molecules is gaseous phase reaction. Carbon nitride films with nitrogen content of about 40 at.% were obtained. Possible processes for CN molecule formation in gaseous phase and mechanisms responsible for efficient nitrogen incorporation and carbon nitride film deposition were suggested.

Growth of c-GaN films on the nitridated β-Ga2O3 substrates using RF-MBE

Cubic GaN is successfully grown on β-Ga2O3 by molecular beam epitaxy for the first time. Prior nitridation of the (100) β-Ga2O3 single-crystal substrate by exposure to electron cyclotron resonance nitrogen plasma causes the formation of a surficial (001) c-GaN layer, upon which homo-epitaxial growth of c-GaN can be achieved by radio-frequency molecular beam epitaxy. The epitaxial relationship is confirmed by electron microscopy to be (001) c-GaN // (100) β-Ga2O3, [110] c-GaN // [010] β-Ga2O3, and [1-10] c-GaN // [001] β-Ga2O3.

Enhancement of reactive species density in nitrogen plasma by mixture of helium and nitridation experiment for silicon

In order to increase the electron plasma density and/or temperature in electron cyclotron resonance (ECR) nitrogen plasma, electron acceleration has to be enhanced by reducing the electron collision frequency. One method is to add gas species with a lower electron collision cross-section, compared with the case of nitrogen gas. For this purpose, the helium gas was added into the ECR nitrogen plasma, where the total gas pressure and the absorption power of microwave were kept the same. The emission intensities of nitrogen molecular ion and excited nitrogen molecular were measured as a function of the ratio of helium pressure to nitrogen gas pressure. The densities of both excited nitrogen molecular and nitrogen molecular ion showed maxima to the ratio of helium gas pressure to nitrogen gas pressure. Hence, the densities of such reactive species can be maximized by the addition of helium gas into nitrogen plasma. Based upon the present results, the nitridation experiment for silicon was conducted by changing the ratio of helium gas pressure. In this irradiation experiment, the substrate was negatively biased and the temperature was kept 900 K. The degree of nitridation well corresponded to the change of density of reactive species.

Use of an Auger parameter for characterizing the Mg chemical state in different materials

Metallic, oxide and hydroxide environments of magnesium are clearly identified by X-ray photoelectron spectroscopy from chemical shift of Mg 1s and Mg 2p photopeaks. Unfortunately, Mg 3 N 2 cannot be distinguished from MgO through these two peaks. In this work, we give evidence that it is possible to unambiguously identify magnesium nitride from magnesium oxide thanks to a Mg Auger parameter defined as the difference between the kinetic energy (KE) of the Mg K L L Auger peak and the KE of the Mg 1s peak. The value obtained for Mg 3 N 2 (1000.0 eV) is quite different from the one observed for MgO (998.6 eV). Values obtained for metallic Mg and for Mg(OH) 2 are, respectively, equal to 1004.2 and 997.5 eV. This parameter is then used in order to characterize the modification of the Mg chemical environment in the Al-5083 aluminum alloy (containing 4.5 at.% Mg) nitrided by a distributed electron cyclotron resonance nitrogen plasma.

Enhancement of reactive species density in nitrogen plasma by mixture of helium and nitridation experiment for silicon

In order to increase the electron plasma density and/or temperature in electron cyclotron resonance (ECR) nitrogen plasma, electron acceleration has to be enhanced by reducing the electron collision frequency. One method is to add gas species with a lower electron collision cross-section, compared with the case of nitrogen gas. For this purpose, the helium gas was added into the ECR nitrogen plasma, where the total gas pressure and the absorption power of microwave were kept the same. The emission intensities of nitrogen molecular ion and excited nitrogen molecular were measured as a function of the ratio of helium pressure to nitrogen gas pressure. The densities of both excited nitrogen molecular and nitrogen molecular ion showed maxima to the ratio of helium gas pressure to nitrogen gas pressure. Hence, the densities of such reactive species can be maximized by the addition of helium gas into nitrogen plasma. Based upon the present results, the nitridation experiment for silicon was conducted by changing the ratio of helium gas pressure. In this irradiation experiment, the substrate was negatively biased and the temperature was kept 900 K. The degree of nitridation well corresponded to the change of density of reactive species.

Use of an Auger parameter for characterizing the Mg chemical state in different materials

Metallic, oxide and hydroxide environments of magnesium are clearly identified by X-ray photoelectron spectroscopy from chemical shift of Mg 1s and Mg 2p photopeaks. Unfortunately, Mg 3N 2 cannot be distinguished from MgO through these two peaks. In this work, we give evidence that it is possible to unambiguously identify magnesium nitride from magnesium oxide thanks to a Mg Auger parameter defined as the difference between the kinetic energy (KE) of the Mg K L L Auger peak and the KE of the Mg 1s peak. The value obtained for Mg 3N 2 (1000.0 eV) is quite different from the one observed for MgO (998.6 eV). Values obtained for metallic Mg and for Mg(OH) 2 are, respectively, equal to 1004.2 and 997.5 eV. This parameter is then used in order to characterize the modification of the Mg chemical environment in the Al-5083 aluminum alloy (containing 4.5 at.% Mg) nitrided by a distributed electron cyclotron resonance nitrogen plasma.

Electron cyclotron resonance plasma-assisted pulsed laser deposition of boron carbon nitride films

Boron carbon nitride thin films have been prepared on Si (100) substrates by means of plasma-assisted pulsed laser deposition at low temperatures (<80 °C). In this method, a sintered boron carbide (B 4C) target was ablated by laser pulses in the environment of a nitrogen plasma, generated from electron cyclotron resonance (ECR) microwave discharge in pure nitrogen gas, while the growing film was simultaneously being bombarded by the plasma stream. The prepared films are composed of boron, carbon and nitrogen with an average atomic B/C/N ratio of 3:1:3.8 as revealed by X-ray photoelectron spectroscopy (XPS) analysis. XPS, Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy were used for structural characterization. The results suggested that the prepared BCN films contain several chemical bonds with BCN atomic hybridization rather than a simple mixture of BN, BC and CN phases. The BCN films were also found to show good adhesion to the substrates and have a high transparency in the near-infrared region. For comparison, we have also grown BC films in vacuum without plasma assistance. We have found that the assistance of the ECR nitrogen plasma facilitated nitrogen incorporation and film formation.

Mutual influence among inert nitrogen molecules, nitrogen radical atoms, nitrogen radical molecules and nitrogen molecular ions on growth process and crystal structure of GaN heteroepitaxial layers grown on Si(0 0 1) and Si(1 1 1) substrates by molecular-beam epitaxy assisted by electron cyclotron resonance

We have investigated the mutual influence among inert nitrogen molecules, nitrogen radical atoms, nitrogen radial molecules and nitrogen molecular ions on optical and crystallographic properties of GaN heteroepitaxial layers (heteroepilayers) grown on Si(0 0 1) and Si(1 1 1) substrates by molecular-beam epitaxy assisted by electron cyclotron resonance (ECR). The heteroepilayer characteristics are elementally governed by the effective V/III mole ratio corresponding to the ratio of the density of nitrogen radical molecules in inert nitrogen molecules to Ga atoms in ECR-plasma process. The inert nitrogen molecules in ECR nitrogen plasma do not much degrade the crystalline quality of GaN heteroepilayer though they change the effective V/III mole ratio and dramatically reduce the growth rate. However, the heavy incorporation of inert nitrogen molecules into the layer degrades the crystalline qualities of GaN heteroepilayers.

XPS investigation of aluminum and silicon surfaces nitrided by a distributed electron cyclotron resonance nitrogen plasma

Aluminum and silicon samples were nitrided by a distributed electron cyclotron resonance nitrogen plasma. The plasma conditions used for the treatment correspond to a maximum N2+ concentration in the sample position, determined by optical emission spectroscopy. The substrates were always polarized by a DC bias voltage at −120 V and were externally heated or not. Nitrided samples were characterized by X-ray photoelectron spectroscopy (XPS) after an exposure to ambient air. A depth profile of the treated substrates was achieved by Ar+ etching sequences in the XPS spectrometer. When the samples are polarized and heated at 500°C during the plasma treatment, the nitride layer (dense AlN or Si3N4 and diffusion layers) obtained on aluminum (∼0.3 μm) is much thicker than on silicon (∼30 Å).

Characteristics of Tunneling Nitride Grown by Electron Cyclotron Resonance Nitrogen-Plasma Nitridation and Its Application to Low-Voltage Electrical Erasable-Programmable Read-Only Memory

Characteristics of a tunneling-nitride insulator grown by low-temperature electron cyclotron resonance (ECR) nitrogen-plasma nitridation are presented. The ECR nitridation shows a very high growth rate at lower temperatures and the thickness is proportional to the growth time. For example, we obtain a thickness of 16 [nm] and a refractive index of 1.75 after the nitridation time of 80 [min] at 400°C. The barrier heights measured from the Fowler-Nordheim (F-N) tunneling current are 2.3 [eV] and 1.4 [eV] in the inversion and the accumulation modes, respectively. These lower heights allow us much faster programming and erasing times of an electrical erasable-programmable read-only memory (EEPROM) with the ECR nitride than those of the conventional EEPROM with the thermal oxide. A double-gate EEPROM with an ECR-nitride tunneling insulator was fabricated. Surprisingly, it does not show any threshold voltage (VTH) degradation even after 100,000 cycles of programming and erasing.