Concentration Of Nitrogen Atoms Research Articles

Measurements by optical and mass spectrometry of the density of active species in the flowing afterglow of a N2/(10−4–10−3)CH4 plasma

Abstract The influence of small quantities of methane on the behaviour of the active species N, N 2 (A) and N + 2 (B) has been studied by emission and mass spectrometry. The nitrogen atom concentration [N] is in the (0.1–4)×10 15 particles cm −3 range under the experimental conditions investigated. For a N 2 –0.01%CH 4 mixture, [N] is twice as high as for pure N 2 . The metastable N 2 (A) concentration is approximately 10 11 particles cm −3 , i.e. it varies from 3 to 6 times lower than in pure N 2 as the pressure decreases from 25 to 12.5 mbar, and the excited ion density [N + 2 (B)] is 5×10 4 –2×10 6 particles cm −3 , i.e. 100–1000 times lower than in pure N 2 .

Experimental Observations of the Redistribution of Implanted Nitrogen at the Si-SiO2 Interface During RTA Processing

ABSTRACTThe redistribution of nitrogen from silicon to the Si-SiO2 interface due to thermal processing is investigated by Secondary Ion Mass Spectroscopy (SIMS) using Metal-Oxide-Semiconductor (MOS) capacitors. SIMS profiles of implanted atomic nitrogen concentration indicate a significant redistribution of the nitrogen, from the silicon to the oxide layer in response to variations of the steady state time and temperature parameters of Rapid Thermal Anneal (RTA) processing. RTA treatment, in N2 ambient, over a temperature range of 750°C - 1100°C, results in a measured increase of the integrated nitrogen peak at the interface. High Frequency Capacitance Voltage (HFCV) measurements of an implanted (N/ 5 × 1014 cm2/s / 26keV) and annealed (900°C / 10s) sample is compared with a control (without N implant) sample to determine the relative nitrogen abundance at the interface. This value corresponds to the increase in fixed oxide charge Q that produces a negative shift in the flat band voltage Vo under negative gate bias conditions.

Influence of the field frequency on the nitrogen atom yield in the remote plasma of an high frequency discharge

An discharge sustained by an electromagnetic surface wave is investigated in order to develop an efficient nitrogen atom source. We take advantage of the flexibility of surface-wave discharges (SWDs) in terms of operating frequency to examine the influence of the field frequency (f = 13.56, 40.68, 440 and 2450 MHz) on the nitrogen atom concentration in the discharge spatial afterglow. The effects of absorbed power (up to 200 W), pressure p (1 to 8 Torr) and discharge tube diameter (4.5 and 15 mm) are also considered. The N atom concentration is determined through emission spectroscopy from the afterglow following validation by NO titration. We find that: (i) the N atom concentration increases with but saturates past a certain power, the value of which decreases with increasing f, (ii) the N atom saturation concentration is at 2450 MHz but only at ; (iii) the vibrational `temperature' of the state in the discharge varies in the same way as the N atom concentration with respect to f and ; (iv) whatever f, saturation of the N atom concentration occurs at a threshold value -600 K of the molecule rotational `temperature' in the discharge, suggesting that too high a gas temperature is the limiting factor of the N atom yield (v) the N atom concentration increases with increasing p and decreasing .

Properties of thin Ta–N films reactively sputtered on Cu/SiO 2/Si substrates

This work studied the thin film properties of 200 Å Ta and Ta–N films reactively sputtered on the Cu/SiO 2/Si substrates. The nitrogen atomic concentration in the Ta–N film was found to saturate at about 30%. Excessive sputtering gas flow, especially the N 2 gas, caused surface damage to the sputter deposited films. Thermal annealing in N 2 ambient at temperatures up to 700°C did not change the atomic concentrations and the chemical states of Ta and N in the Ta and Ta–N films. The thermal annealing resulted in the grain growth and the healing of sputter damage, but it also induced new defects in the Ta–N films due to thermal stress. This presents a reliability problem in process application involving high temperature thermal cycle.

Carbon nitride films deposited by reactive laser ablation

Carbon nitride films were deposited at 20, 250 and 500°C on 〈111〉 Si substrates by XeCl laser ablation of graphite in low pressure (1–50 Pa) N 2 atmosphere at fluences of 12 and 16 J/cm 2. Different diagnostic techniques (SEM, TEM, RBS, XPS, XRD) were used to characterize the deposited films. Films resulted plane and well adhesive to their substrates. N/C atomic ratios up to 0.7 were inferred from RBS measurements in films deposited at 20°C and 16 J/cm 2. Nitrogen concentration increases with increasing ambient pressure and laser fluence. The N 1s peak of the XPS spectra indicate two different bonding states of nitrogen atoms to C atoms, while the C 1s peak, apart from the two bonding states to nitrogen atoms, indicates one bonding state with regard to carbon atoms. XRD and TEM analyses point to an oriented microcrystalline structure of the films. Heating of the substrate results in a lower nitrogen concentration in respect of films deposited at 20°C in otherwise identical experimental conditions. Optical emission studies of the laser plasma plume indicate a correlation between the emission intensity of the CN radicals in the plume and the nitrogen atom concentration in the films.

Study of matrix isolation of nitrogen atoms in solid N2

The process of matrix isolation of nitrogen atoms in solid N2 is studied by the method of condensation from the gaseous phase. In order to vary the flow rates of nitrogen atoms and molecules at the sample surface over a wide range, N2–He mixtures of various compositions have been passed through the gas discharge zone. It is found that the EPR line width for N atoms in N2 increases upon a decrease in the nitrogen flow rate from the discharge zone to a cold substrate. It is shown that this increase is due to an increase in the concentration of atomic nitrogen in the matrix leading to an enhancement of the dipole–dipole interaction between atoms. It is established that a decrease in the intensity of recombination of atoms in the course of diffusion at the sample surface due to a decrease in the surface density of these atoms plays a decisive role in the growth of the concentration of matrix-isolated atoms in the experiments. It is found that for a constant flow rate of atoms from the discharge, their concentration in the matrix increases and attains saturation upon an increase in the discharge intensity. The dependence of concentration on the discharge intensity is attributed to a change in the degree of dissociation of molecular nitrogen in the discharge.

Ion Capacity of Siliceous Sorbents with Surface Polymer Layers Composed of Different Dextran—Triethylenetetraamine Mixtures (Ion Capacity of Sorbents with Surface Polymer Layers)

The formation of a polymer layer on the surface of a siliceous support employed for chromatography is one of the methods available for protecting the silica skeleton from dissolution in the mobile alkaline phase and for eliminating the negative influence of silanol groups on separated molecules. A polysaccharide-polyimine copolymer can play the role of the surface layer, especially in siliceous materials, for high performance affinity chromatography. The results presented here demonstrate the utility of the material with such a copolymer layer as a sorbent for metal ions. The ion capacity of sorbents with a copolymer layer composed of triethylenetetraamine-dextran can be changed both by the composition of the mixture and by the amount of crosslinking agent present. The presence of a transition layer on the polymer layer surface explains the distinctions between the ion capacity of sorbents and the concentration of electron-donor nitrogen atoms existing in the material.

Sub-surface modifications induced by nitrogen ion implantation in stainless steel (SS316L). Correlation between microstructure and nanoindentation results

The surface of SS316L was modified through nitrogen ion implantation at high fluences. Multiple energy ion implantations at decreasing energy (180, 100, 50 and 20 keV) were performed on the same samples in order to obtain nearly flat depth-profiles over a thickness of about 250 nm. The doses were chosen with help of a Monte Carlo simulation method (TRIM90) in order to obtain three different nitrogen atomic concentrations: 20%, 30% and 40%. The SIMS measurements show that the nitrogen profiles are nearly flat with a significant nitrogen diffusion toward the bulk in case of highest doses, which increases the thickness of the nitrided layers and limits the concentration to a saturation value. The grazing angle X-ray diffraction experiments show that for the 20% N sample, the austenitic unit cells are strongly expanded and form a nitrogen solid solution of γ-structure. For the 30% and 40% samples, besides the solid solution, one part of the austenite is transformed in iron nitride ε-Fe 2–3N and another part in an α-Fe phase. The nanoindentation study shows that the formation of the solid solution induces an important increase in hardness from 5.5 GPa for the non-implanted sample to 15 GPa for the 20% N implanted one (values at 50 nm depth). In the 30% and 40% N samples, the hardness remains about the same as for the 20% N implanted sample, but over a higher thickness, which confirms the nitrogen diffusion towards the bulk.

Nitrogen-induced modifications in microstructure and wear durability of ultrathin amorphous-carbon films

A systematic experimental investigation was carried out to understand the effects of nitrogenation on the microstructure and wear durability of thin amorphous-carbon films. The films were fabricated with 0%, 10%, 15%, 20%, 30%, 40%, and 50% N2 in the sputter gas. Microstructure properties were characterized using Rutherford backscattering spectroscopy, electrical resistance, Raman spectroscopy, and x-ray photoelectron spectroscopy. Nanohardness and scratch wear resistance of the films were studied with an atomic force microscope equipped with a diamond tip. The head–disk interface tribological properties of the films were tested with industrial standard contact–start–stop wear instrumentation. The results indicate that the introduction of nitrogen into the carbon film increases the film lattice disorder and allows for the formation of carbon–nitrogen single, double, and triple bonds. The nitrogen atomic concentration in the film, electrical resistance, and the ratio of carbon–nitrogen bonds to carbon–carbon bonds increase with increasing N2 in the sputter gas. A significant addition in C≡N bond percentage is observed when the N2 exceeds 30% in the sputter gas. Both the nanohardness and scratch wear resistance of the carbon film can be significantly improved by incorporating an optimized nitrogen concentration in the film. In this study, the film processed with 30% N2 showed the highest nanohardness and wear resistance. The degraded nanowear resistance for the films processed with 40% and 50% N2 is attributed to the significant addition of C≡N bonds. Within a wide process range (15%–30% N2), the films exhibit excellent tribological performances at the head–disk interface. The wear mechanisms from the contact–start–stop wear tests are interpreted based on the understanding of film structures and film mechanical properties.

XPS and SIMS characterisation of segmented polyether polyurethanes containing two different soft segments

Angle dependent X-ray photoelectron spectroscopy (XPS) and static secondary ion mass spectrometry (SSIMS) were used to study the surface composition of two polyether polyurethane block copolymers. Both were synthesised with 2,4-toluene diisocyanate and ethylene diamine as the hard segment, but different soft-segment compositions were used. In one case, the soft segment was polytetramethylene oxide (PTMO) while, in the other case, it was a mixture of PTMO and polyethyleneoxide (PEO). The selection of the two oligomers for the soft segments allowed for an investigation of the influence of an elastomer's polar character on the nature of chemical groups detected at the surface. By following the C1s signal and the atomic concentration of nitrogen with respect to take off angle, it was shown that the surface of the films were depleted in nitrogen containing hard segments. The study also showed that the sample having both PTMO and PEO soft segments displayed a tendency for the PTMO to segregate from the PEO and migrate to the top surface, resulting in a depletion of the top layer in PEO. Static SIMS of this sample confirmed this observation.

Remote plasma-enhanced CVD of silicon nitride films: effects of diluting nitrogen with argon. Part I: effect on nitrogen plasma parameters studied by emission spectroscopy

In a series of two papers we describe the effect of argon dilution of the nitrogen passed through the RF discharge region on the plasma composition, growth rate and some characteristics of silicon nitride films deposited by remove PECVD. In this part we report the results of an emission spectroscopic study of the plasma obtained in an SiH4–N2–Ar mixture. It is shown that argon in metastable electronic excited states plays an important role during the RPECVD of silicon nitride films by providing a high concentration of atomic nitrogen which is necessary for the promotion of film growth. In Part II the influence of argon dilution on the growth rate, composition and some properties of silicon nitride films deposited by capacitively and inductively coupled remote PECVD is discussed. © 1998 John Wiley & Sons, Ltd.

Remote plasma‐enhanced CVD of silicon nitride films: effects of diluting nitrogen with argon. Part I: effect on nitrogen plasma parameters studied by emission spectroscopy

In a series of two papers we describe the effect of argon dilution of the nitrogen passed through the RF discharge region on the plasma composition, growth rate and some characteristics of silicon nitride films deposited by remove PECVD. In this part we report the results of an emission spectroscopic study of the plasma obtained in an SiH4–N2–Ar mixture. It is shown that argon in metastable electronic excited states plays an important role during the RPECVD of silicon nitride films by providing a high concentration of atomic nitrogen which is necessary for the promotion of film growth. In Part II the influence of argon dilution on the growth rate, composition and some properties of silicon nitride films deposited by capacitively and inductively coupled remote PECVD is discussed. © 1998 John Wiley & Sons, Ltd.

Remote plasma-enhanced CVD of silicon nitride films: effects of diluting nitrogen with argon. Part II: effect of nitrogen plasma parameters on layer characteristics

In Part I we reported the results of an emission spectroscopic study of the plasma obtained in an SiH4–N2–Ar mixture. It was shown that argon in metastable electronic excited states provides a high concentration of atomic nitrogen. In this part we report the results of a study of the influence of argon dilution on the growth rate, composition and properties of silicon nitride films. The exact influence of nitrogen dilution with argon depends on the process parameters and on the method of coupling of the RF power, but it is found in general that a high concentration of atomic nitrogen leads to changes in the relative amounts of Si–Hj and N–Hi bonds and in the Si/N ratio of deposited films. In particular, it is shown that hydrogen incorporation can be reduced and improved stoichiometry can be obtained. © 1998 John Wiley & Sons, Ltd.

An arc discharge nitrogen atom source

An intense nitrogen atom beam source of simple construction, with easy handling and maintenance was built and tested. Nitrogen atom beams with an intensity estimated to be 1019 atom/sr s and with an average kinetic energy of 0.8–2 eV in the forward direction were obtained. This novel atom source can be successfully ignited using pure nitrogen gas and operated stably during several hours of continuous performance. The temperature-rise effect of calorimetric sensors due to the bombardment of the N atom beam was used to analyze the intensities and kinetic energies of nitrogen atom beams. The emission spectra from the arc also show that a high concentration of atomic nitrogen was produced using this source. Experiments such as the nitrogen atom beams interacting with substrates to form a TiON film and a carbon nitride film indicate the high concentration of atomic nitrogen in the beam.

Homoepitaxial SiC Growth by Molecular Beam Epitaxy

The homoepitaxial growth of SiC thin films by solid- and gas-source molecular beam epitaxy is reviewed and discussed. Our recent results regarding the homoepitaxial growth of single crystal 3C-SiC(111) and 6H-SiC(0001) thin films are also presented. The 3C-SiC(111) films were grown on both vicinal and on-axis 6H-SiC(0001) substrates at temperatures between 1000 and 1500 °C using SiH4 and C2H4. They contained double positioning boundaries and stacking faults and the surface morphology and growth rate depended strongly on temperature. Films of 6H-SiC(0001) with low defect densities were deposited at high growth rates on vicinal 6H-SiC(0001) substrates by adding H2 to the reactant mixture at temperatures between 1350 and 1500 °C. At temperatures below 1350 °C, only the cubic phase was formed. A kinetic analysis of the SiC deposition process is also presented. The SiC films were resistive with an n-type character and a lower N concentration than the p-type CVD-grown epilayers of the substrate. Undoped 6H-SiC films with the lowest atomic nitrogen and electron concentration had a mobility of 434 cm2 V—1 s—1, the highest room temperature value ever reported for this polytype. Both the 6H-SiC(0001) and the 3C-SiC(111) epilayers were controllably doped using a NH3/H2 mixture (for lighly n-doped films), pure N2 (for heavily n-doped SiC epilayers) and Al evaporated from a standard effusion cell (for p-type doping).

Impact of nitrogen concentration profile in silicon oxynitride films on stress-induced leakage current

Stress-induced leakage currents of silicon oxynitride films (9 nm thick) with different nitrogen concentration profiles have been investigated. We found that leakage current at a gate electric field of approximately 6 MV/cm after electron injection (0.1-1.0 C/cm 2 is reduced upon the incorporation of approximately 0.75 at% of nitrogen atoms near the oxynitride/Si interface. However, stress-induced leakage current increases with increasing nitrogen atom concentration at a depth of 1.5 nm in silicon oxynitride films. The optimum nitrogen atom concentration profile in silicon oxynitride films can decrease the number of tunneling sites and lead to small stress-induced leakage current at low electric field.

Homoepitaxial layer from ion-implanted diamond

Homoepitaxial tetrahedral amorphous carbon layer (ta-C) has been formed on synthetic diamond (type Ib) using molecular hydrogen ion implantation with 40 keV and dose range of 10 15–10 17 Hcm −2 at 100 K. For the modified layer, the deduced optical gap and its dose dependence were measured by a position-sensitive micro-spectrophotometer. And this method has also been applied to the characterization of the optical inhomogeneity caused by the concentration of nitrogen atoms in type Ib diamond at λ = 430 nm.

Stability of rapidly annealed reactive sputter deposited nitrided silicon dioxide

The effect of incorporation of nitrogen atoms into the structure of reactively sputtered SiO2 was examined. It was determined that the presence of a controlled concentration of nitrogen atoms improves the electrical properties of the oxide. This could be achieved at partial pres-sure of nitrogen of about 10%. High temperature annealing improved the oxide properties. The nitrided oxides showed a better resistance to high current stress.

Formation and etching of thin nitride layers on GaAs using atomic nitrogen and hydrogen

This paper reports on the nitridation of (001) GaAs using atomic nitrogen and the etching characteristics of the nitride layers formed using atomic hydrogen. Nitrogen and hydrogen molecules were cracked by a hot W filament to produce atomic nitrogen and hydrogen. After nitridation and etching, GaAs cap layers were grown by molecular beam epitaxy to form GaAs/GaN/GaAs structures. We determine the sheet nitrogen atom concentration for these structures by secondary ion mass spectrometry analysis. As the nitridation temperature decreases, the etched nitrogen atom concentration increases. The NAs bonds might be responsible for this increased concentration. The etching rate also depends on the substrate temperature.

Blue-green laser diode grown by photo-assisted MOCVD

Operation of the first blue-green laser diode grown by metalorganic chemical vapor deposition has been demonstrated at 77 K under pulsed current injection. The precursors were dimethylzinc, dimethylcadmium, diethylsulfide, bismethyl-cyclopentadienyl-magnesium, and dimethylselenide. Diisopropylamine and ethyliodide were used for a p-type and n-type doping under irradiation with ultraviolet light generated by a high-pressure mercury lamp, respectively. A 1 × 10 18 cm −3 nitrogen-atom concentration, which was measured by secondary ion mass spectroscopy, was obtained in the p-ZnSe contact layer. The 4.2 K photoluminescence spectrum was dominated by strong donor-acceptor pair emission and the net acceptor concentration was 1.4 × 10 16 cm −3 .