Atomic Concentration Profiles Research Articles

ARAS Measurements on the Thermal Decomposition of Silane

AbstractIn the present investigation the thermal dissociation of silane was measured behind reflected shock waves using the Atomic Resonance Absorption Spectroscopy (ARAS) for detecting Si, H, and O atoms. The experiments were performed at temperatures 1250 K ≤ T ≤ 2115 K and pressures between 0.7 and 1.5 bar. Initial mixtures of 0.15 to 5 ppm SiH4 diluted in Ar and 5 ppm SiH4 with 500 ppm O2 diluted in Ar were studied. The H atom measurements show formation rates, which are much less than the respective rates for Si atom formation. This indicates that the H atoms were formed by secondary reactions and are not primary dissociation products of silane or silylene. A reaction mechanism suitable to describe all measured H atom concentration profiles is given in this paper.Si atoms also measured during the silane thermal decomposition were found to be useful to understand the kinetics of this process. From the Si concentration profiles together with computer simulations rate coefficients for the reactionsSiH4 + M ⇋ SiH2 + H2 + M (1) SiH2 + M ⇋ Si2 + H2 + M (2) were derived, which can be summarized by the following Arrhenis expressions:k1 = 9.9×1015exp(−24000 K/T) cm3mol−1 s−1k2 = 9.1×1013exp(−15100 K/T) cm3mol−1 s−1.In the case of the SiH4/O2/Ar mixtures no detectable Si atom concentrations were found, while the observed O atom formation rates were identical to that of Si atoms in mixtures without O2 under comparable reaction conditions. This means that Si originating from the thermal decomposition of silane is directly converted into O by reaction with O2, i.e. O is in this system a measure of Si.

Observation of X-Ray Absorption Magnetic Circular Dichroism in well-Characterized Iron-Cobalt-Platinum Multilayers

ABSTRACTMagnetic circular dichroism in the Fe 2p x-ray absorption is observed in multilayers of (Fe9.5Å/Pt9.5Å)92. The Magnetization and helicity are both in the plane of this multilayer which is prepared by magnetron sputter deposition. This sample is part of a study to examine magnetization in the ternary multilayer system of FeCo/Pt. Lattice and layer pair spacings are measured using x-ray scattering. The atomic concentration profiles of the multilayer films are characterized using Auger electron spectroscopy coupled with depth profiling. Conventional and high resolution transmission electron microscopy are used to examine the thin film, growth morphology and atomic structure.

Direct free energy minimization methods: application to grain boundaries

A critical review is given of recently developed methods for determining the atomic structures and solute concentration profiles at defects in elemental solids and substitutional alloys as a function of temperature. Exact results are given for the effective force on an atom arising from the vibrational entropy in the quasiharmonic approximation and for the occupancy of a site in the pair potential approximation. An improved, approximate formula is given for the effective force arising from the vibrational entropy. The mean field approximation that is used in the alloy problem is compared with the auto-correlation approximation. It is shown that the better statistical averaging of the auto-correlation approximation leads to effective pair interactions that are temperature and concentration dependent.

Shock Tube Measurements on the Thermal Decomposition of COS

AbstractThe thermal decomposition of carbonyl sulfide was studied behind reflected shock waves by direct measurements of the time‐dependent S(3P) atom concentration using atomic resonance absorption spectroscopy (ARAS). The experiments were performed in highly diluted mixtures of Ar with relative concentrations of COS between 4 to 100 ppm in the temperature range 1750 K ≤ T ≤ 2990 K at pressures between 0.5 bar and 1.5 bar. In reaction systems with very low concentrations (4 – 30 ppm COS in Ar) the initial reaction magnified image was found to dominante the initial slope of the measured S(3P) atom concentration profiles. The rate coefficient obtained results in: magnified image In reaction systems with higher initial concentrations of 100 ppm COS the measured S(3P) atom concentration profiles were additionally affected by secondary reactions consuming sulfur atoms. The most probable reaction is magnified image which has an influence on S(3P) at later reaction times. A rate coefficient for reaction (R2) of magnified image was determined from the present experiments by fitting calculated S(3P) atom profiles to measured ones. The given mean value is to be valid for temperatures near 2000 K.

Electrochemical capacitance-voltage depth profiling of nanometer-scale layers fabricated by Ga+ focused ion beam implantation into silicon

The electrochemical capacitance-voltage (ECV) profiling technique is employed to measure the active carrier concentration in nanoscale layers fabricated by focused ion beam (FIB) implantation of 3 to 10 keV Ga+ ions into crystalline Si. The carrier concentration profiles obtained by ECV indicate the ability of this technique to probe depths as shallow as 2–3 nm and with a nanometer-scale depth resolution. The carrier concentration obtained by ECV matches well with the Ga atomic concentration profile detected by secondary-ion mass spectroscopy, but is almost an order of magnitude higher than that provided by the spreading resistance profile technique.

Modeling of the role of atomic hydrogen in heat transfer during hot filament assisted deposition of diamond

The temperature and atomic hydrogen concentration profiles in a hot filament type diamond deposition reactor were determined experimentally and theoretically to demonstrate that the reaction of atomic hydrogen on the substrate surface plays an important role in the heating of the substrate. For a given filament temperature, the substrate temperature in helium was significantly lower than that in either pure hydrogen or 1% methane-hydrogen atmospheres. The presence of small amounts of methane in hydrogen did not have any significant effect in influencing the shape of the atomic hydrogen concentration profile. In the space between the filament and the substrate, the concentration field is established mainly due to the diffusive mixing of the atomic hydrogen with the molecular hydrogen and other species in the gas phase. Homogeneous chemical reactions in the gas phase do not significantly affect the atomic hydrogen concentration distribution in this region.

Quantitative AES depth profiling of thin oxide films grown on stainless steels and aluminium

AbstractAES depth profiling was performed in passive overlayers grown on the surface of stainless steels and in alumina films formed on aluminium at 250°C in oxygen. Our quantitative approach is based on the sequential layer sputtering model proposed by Benninghoven and Hofmann for analysis of thin layers (<10 nm). A careful measurement of AES sensitivities in pure standards constituted by metallic elements (for the substrate) and their corresponding normal oxides (for the film) is needed to achieve the necessary conversion of AES sputter profiles into atomic concentration profiles. With the assumptions of (1) an oxide film and a metallic substrate assimilated to two distinct media separated by a step‐like interface and (2) a time‐invariant sputter rate, the method provides an available determination of the film thickness mainly dependent on an appropriate choice for attenuation lengths of Auger electrons. The usual approximations and results should therefore be discussed in the light of the determination of absolute oxygen film contents by means of nuclear reaction analysis (NRA).

Phosphorus diffusion into silicon from a spin-on source using rapid thermal processing

Diffusion of phosphorus into silicon from a doped spin-on glass source using rapid thermal processing is described. The structural and electrical characteristics of the resulting shallow junctions including atomic and carrier concentration profiles, sheet resistance, as well as the effects on bulk carrier transport properties were studied and compared to those resulting from the use of conventional furnace heating. The results show that sheet resistance as low as 15 Ω/⧠ and surface carrier concentration higher than 1 × 1020 cm−3 are obtained in the annealed samples. Furthermore, a gettering effect is observed as the minority-carrier diffusion length measured by the surface photovoltage technique is improved after processing.

Two-channel thermal decomposition of CH 3

The two-channel thermal decomposition of CH3 was investigated by time-resolved measurements of both H atom and CH radical concentrations using ARAS and ring dye laser spectroscopy respectively. As a source for methyl radicals, mixtures of a few ppm ethane diluted in argon were shock heated to temperatures between 2100 K and 3800 K and pressures between 1.1 bar and 1.8 bar. From the initial time histories of the measured H atom and CH radical concentration profiles the rate coefficients of the reaction channels.

Single particle diffusion into a disordered matrix: simulation of a metal-polymer interface

A sensitive radiotracer technique has recently been utilized to examine the diffusion of copper atoms from the surface into the bulk of thin copper-deposited polyimide films upon annealing. Characteristics of the metal atom concentration profile were discussed in connection with Monte Carlo simulation studies. The present paper describes the simulation model in some detail and focuses upon the formation of metal atom clusters in the region near the film surface. Qualitative aspects of the copper atom diffusion will be shown to be consistent with the results of the Monte Carlo study

Atomic hydrogen concentration profiles at filaments used for chemical vapor deposition of diamond

The quantitative determination of atomic hydrogen concentrations cH in the vicinity of hot filaments is performed with two-photon laser-induced fluorescence. The measurements yield atomic hydrogen concentration profiles up to 28 mm from the filament surface with a spatial resolution of about 0.5 mm. The nonequilibrium nature of the hydrogen dissociation on the filament surface results in a saturation of hydrogen concentration profiles cH(r) for gas pressures above 10 mbar. Atomic concentrations in immediate vicinity of the filament are significantly lower than expected from thermodynamical calculations and depend on the filament diameter. Addition of methane results in a decrease of cH by more than 30% near the filament and a steeper cH(r) dependence, demonstrating the accelerated consumption of H atoms by the presence of hydrocarbon species. H concentration profiles for Ta, Ir, and W filaments show a dependence on filament materials which might be taken into account when selecting filament materials for chemical vapor deposition of diamond.

The importance of free radical recombination reactions in CF4/O2 plasma etching of silicon

The importance of free radical recombination reactions of F in CF4/O2 plasma etching of Si is explored in a combined experimental and modeling study of a single wafer etcher. The F atom concentration profiles in the reactor, as well as the silicon etch rate profiles, are strongly influenced by the recombination reactions. The surface recombination reaction is more important than the gas phase recombination reactions in determining overall system behavior. The effects of the homogeneous as well as heterogeneous recombination reaction diminishes with increasing flow rate. This is due to combined residence time and transport effects.

Chemical Nature of Silicon Nitride‐Indium Phosphide Interface and Rapid Thermal Annealing for InP MISFETs

Rapid thermal annealing (RTA) of the ion implanted indium phosphide compound semiconductors in pure nitrogen or hydrogen was investigated for the fabrication of metal‐insulator‐semiconductor field‐effect transistors (MISFETs). was encapsulated during RTA by 500Å silicon nitride films made using PECVD at 300°C and 500 mtorr with a 13.56 MHz RF power density of 50 mW/cm2. A sequence of high‐resolution x‐ray photoelectron spectra were obtained at four depths through the silicon interfacial region for the In , P 2p, N 1s, Si 2p, and O 1s peaks to determine the chemical nature of the interface after encapsulated RTA. There was a component of the In peak consistent with , , or which increased after RTA. No phosphate was observed in the P 2p peak. A significant decrease of the N‐H or N‐N component of the N 1s peak occurred after RTA. Secondary ion mass spectrometry atomic concentration profiles of implanted with silicon at 150 keV to a dose of showed peak atomic concentrations of at 0.2 μ.m for RTA of 15, 30, or 60s at 700°C in pure or . The atomic concentration profiles showed no diffusion of the implanted silicon in the during RTA. A pure RTA at 700°C for 30s followed by a furnace anneal at 400°C for 2h in forming gas of the phosphorus oxide/silicon dioxide gate insulator was determined to be the optimum thermal process for the fabrication of MISFETs. The MISFETs had threshold voltages of +1V, transconductance of 27 mS/mm, peak channel mobility of 1200 cm2 V−1 s−1, and drain current drift of only 7%.

Atomic profiles and electrical characteristics of very high energy (8–20 MeV) Si implants in GaAs

High-energy Si implantation into GaAs is of interest for the fabrication of fully implanted, monolithic microwave integrated circuits. Atomic concentration profiles of 8, 12, 16, and 20 MeV Si have been measured using secondary ion mass spectroscopy (SIMS). The range and shape parameters have been determined for each energy. The theoretical atomic concentration profile for 12 MeV Si calculated using TRIM-88 corresponded to the SIMS experimental profile. No redistribution of the Si was observed for either furnace anneal, 825 °C, 15 min, or rapid thermal anneal, 1000 °C, 10 s. The activation of the Si improved when coimplanted with S. The coimplanted carrier concentration profiles did not show dopant diffusion. Peak carrier concentration of 2×1018/cm3 was obtained with a Si and S dose of 1.5×1014/cm2 each.

A review of the photochemistry of selected nightglow emissions from the mesopause

The substantial research activity of recent years on the photochemistry of the hydrogen‐oxygen family has improved our understanding of the production of nightglow emissions in the mesopause region of the atmosphere between 80 and 100 km; this work is reviewed with specific attention paid to the emissions of OH, the 557.7‐nm emission of O, and the atmospheric bands of O2(b 1Sg). These emissions are closely related to the O atom concentration profile and would provide a wealth of useful photochemical data in studies of noctilucent cloud displays. Ground‐based and rocket measurements of the OH nightglow show that the kinetics are well represented by the combination of the production reaction, H + O3 → OH(v′) + O2, with significant collisional deactivation by N2 and O2 for the higher vibrational levels of OH. In contrast, the perhydroxyl radical, HO2, plays a negligible role in the vibrational excitation of OH and the production of OH optical emission in the mesopause region. Atomic oxygen quenching is important for the lower vibrational states of OH(v′). Improved experimental determination of the electric dipole moment function of OH has resulted in a new set of transition probabilities that agrees well with the theoretical set published by Mies for low v rovibrational transitions of OH. The Mies values for the higher overtone transitions do not agree well with the empirical results derived from airglow intensities. Recent papers on the results of the sounding rocket campaign called Energy Transfer in the Oxygen Nightglow (ETON) have demonstrated the substantial progress made once the consequences of mesospheric dynamics are decoupled from the photochemistry of the mesopause region by in situ measurements of the atomic oxygen concentration. The work of recent years utilizing this approach has produced strong evidence for the deduction that the major source of several important oxygen metastable energy states is an intermediate metastable state formed in the first step of a two step reaction chain (known as the Barth process). Energy transfer and quenching reactions involving these metastable states complicate the analysis of the measurements. Continued progress requires laboratory experiments designed to explore the relationship of energy transfer processes to the vibrational development of the precursor species. The production of global maps of atomic oxygen concentration profiles becomes feasible once the details of the mesopause photochemical processes are fully understood.

A Process Simulation Model for Silicon Ion Implantation in Undoped, LEC‐Grown GaAs

The activation efficiency of implanted Si in LEC grown has been investigated experimentally. Atomic and carrier distributions of the implant have been obtained using SIMS, conventional, and step‐etch C‐V techniques, respectively. Based on these experimental observations, Si activation efficiency is found to be a strong function of the implantation fluence and annealing temperature, and a weak function of the implantation energy and annealing time. An activation efficiency model is also constructed as the result of these experimental evaluations. For simplicity the model ignores all the weak processing parameters in the computation of activation efficiency. A model reproducing the atomic concentration profile for a given implant has also been developed to use in the activation efficiency model.

The influence of catalytic activity on the gas phase ignition of boundary layer flows Part II. Oxygen atom measurements

The process of gas phase ignition in a fuel-air boundary layer overa heated catalytic surface has been investigated using two-photon laser-induced fluorescence (LIF) measurement of oxygen atoms. The boundary layer was formed by flowing fuel-air mixtures over hot catalytic (platinum) and noncatalytic (quartz) surfaces, and simulates the entrance region of a catalytically stabilized thermal (CST) combustor. A unique optical design was required in order to eliminate interference with the fluorescence signal caused by thermal radiation from the hot surface of the plate. The O atom concentration profile data demonstrate that the platinum catalyst acts to promote the formation of oxygen atoms in the region adjacent to the surface. This effect is most apparent at lean equivalence ratios (Φ < 0.3 for ethane) where we have observed promotion of gas phase ignition by the catalytic surface. At higher equivalence ratios the ignition of ethane in air is inhibited by the platinum surface because of fuel depletion at the surface due to the mass transfer-limited catalytic oxidation reaction.

Atomic and carrier profiles of 1-, 2-, 4-, and 6-MeV 30Si implanted into GaAs

3 0Si has been implanted in GaAs at energies of 1, 2, 4, and 6 MeV. We have measured atomic concentration profiles using secondary ion mass spectroscopy (SIMS) and carrier concentration profiles using an electrolytic capacitance-voltage procedure. Theoretical atomic profiles have been calculated using the computer code TRIM-86. The range statistics and profile shape factors: Rm, Rp, ΔRp, skewness (γ1), kurtosis (β2), and maximum Si density (Nmax) have been determined from the SIMS data. The first two moments (Rp and ΔRp) were also obtained from the carrier profiles and the theoretical profiles. The range and standard deviation obtained by the separate techniques have a maximum difference of only 15%, and the difference is usually less than 10%. This is less than the mutual experimental uncertainty of 17%. The samples were activated using a furnace anneal (800 °C, 15 min) with a Si3N4 cap and using rapid thermal anneal (1000 °C, 10 s) with and without a cap. No redistribution of Si was observed for any of the anneal conditions.

Rapid thermal annealing of arsenic-implanted poly-Si layers on insulator

Atomic and carrier concentration profiles in poly-Si on insulator structures implanted with arsenic ions after furnace and rapid thermal annealing (RTA) have been investigated by Rutherford backscattering (RBS) and Hall effect measurements. Arsenic atoms at and near the implanted peak region show slow diffusion, while those at the tail region show fast diffusion. The diffusivity for As in poly-Si on insulator is represented by D = 8.4 × 10 4 exp(−3.8/ kT) cm 2/s for the tail region and D = 1.7 × 10 3 exp(−3.8/ kT) cm 2/s for the peak region. Poly-Si layers after implantation and annealing were found to have tensile stresses of 1.7–3.7 kbar.

High temperature dissociation of CN

AbstractThe thermal decomposition of CN radicals has been measured behind reflected shock waves in the temperature range 4060 K ≤ T ≤ 6060 K. Very low initial concentrations of C2N2 highly diluted in argon were shock heated and the concentrations of N and C atoms were monitored in the post shock reaction zone by using Atomin Resonance Absorption Spectroscopy (ARAS). From the initial slope of the measured N and C atom concentration profiles, a rate coefficient for the reactionCN + M → C + N + M of (R2)k2 = 2.5 · 1014 exp(−71000 K/T cm3 mol−1 s−1could be directly determined. For the secondary reactionsCN + CN → C2 + C2 (R3)CN + C → C2 + N (R4)CN + N → R2 + C (R5)rate coefficients were obtained from best computer fits of the experimental results. The inferred values of these rate coefficients are given in this paper.