Depth Profiles Of Atoms Research Articles

Hydrogen Incorporation and Carrier Reduction in Hydrogenated n-GaAs:Si and p-GaAs:Zn Crystals

ABSTRACTHydrogen implantation into either n-GaAs:Si or p-GaAs:Zn crystals leads to a neutralization of charge carriers, primarily through induced crystal damage. The resulting decrease in carriers is useful in opto-electronics applications for confining electrical current or optical radiation. Exposure of the same crystal materials to a hydrogen plasma also leads to reduction of the charge carriers, but through a passivation mechanism involving hydrogen-dopant atom complexes. This technique may be useful for opto-electronics device processing but further details converning the physical mechanisms need to be established. Here we present the results of investigations aimed at correlating the changes in carrier concentration as determined by infrared reflectivity measurements with atomic depth profiles obtained from secondary ion mass spectrometry (SIMS). Differences between the use of hydrogen or deuterium plasmas are also reported.

Ultrashallow Si p+–n junction fabrication by low energy Ga+ focused ion beam implantation

The fabrication of ultrashallow Si p+–n junctions by low energy Ga+ focused ion beam implantation has been investigated at energies ranging from 5 to 15 keV. Post-implantation rapid thermal annealing was performed at 600 °C for 30 s to activate the implanted Ga and to regrow the implanted layer. Secondary ion mass spectroscopy (SIMS), spreading resistance profile (SRP), and cross-sectional transmission electron microscopy (TEM) have been employed to characterize the resulting Ga atomic concentration depth profile and the structure of the implanted layer. For 5 keV Ga+ implantation, the cross-sectional TEM (xTEM) measurement yielded an amorphous layer thickness of 9 nm and a line of end-of-range defects 16 nm below the surface [after rapid thermal annealing (RTA)]. The SIMS profiles indicate that only minor Ga channeling occurred during implantation. The SRP measurements give a junction depth of only 20 nm for the 5-keV Ga implants. Leakage current density of 20 nA/cm2 has been measured at 5 V reverse bias.

Carbon diffusion in undoped, n-type, and p-type GaAs

The effects of background doping, surface encapsulation, and As4 overpressure on carbon diffusion have been studied by annealing samples with 1000 Å p-type carbon doping spikes grown within 1 μm layers of undoped (n−), Se-doped (n+), and Mg-doped (p+) GaAs. The layers were grown by low-pressure metalorganic chemical vapor deposition using CCl4 as the carbon doping source. Two different As4 overpressure conditions were investigated: (1) the equilibrium pAs4 over GaAs (no excess As), and (2) pAs4 ∼2.5 atm. For each As4 overpressure condition, both capless and Si3N4-capped samples of the n−-, n+-, and p+-GaAs crystals were annealed simultaneously (825 °C, 24 h). Secondary-ion mass spectroscopy was used to measure the atomic carbon depth profiles. The carbon diffusion coefficient is always low, but depends on the background doping, being highest in Mg-doped (p+) GaAs and lowest in Se-doped (n+) GaAs. The influence of surface encapsulation (Si3N4) and pAs4 on carbon diffusion is minimal.

Thin-layer p–n junction fabrication using Ga and In focused ion beam implantation

The fabrication of shallow p–n junction impurity profiles using Ga and In focused ion beam (FIB) implantation in conjunction with rapid thermal annealing is reported. A 75-keV focused ion beam with 80 mA/cm2 current density and 0.5-μm beam diameter was used to implant Ga+ and In+ into (100) Si substrates at doses ranging from 1×1013 to 5×1015/cm2. The annealing temperature was varied from 600 to 1000 °C for various times, 10–30 s. Secondary ion mass spectrometry and spreading resistance profiling were used to measure the implanted species atomic and carrier concentration depth profiles. As compared to the conventional broad beam implantation, the FIB implanted Ga concentration depth profiles exhibit higher activation percentage in the end-of-range and tail region. This results in thicker layers and deeper p+–n junctions, but with lower sheet resistance and leakage current. A similar phenomenon is also observed in In FIB-implanted samples. The damage generated by the high dose rate implantation is possibly responsible for this phenomenon. p+–n diodes fabricated using Ga FIB doping exhibit very good diode electrical characteristics: ideality factor as low as 1.01, leakage current density below 1 nA/cm2 at −1 V reverse bias, and breakdown voltage of ∼35 V. Diodes fabrication with In generally exhibit shallower junctions, but higher leakage current. Bipolar transistors have been fabricated using FIB-implanted Ga and In thin base layers. Common emitter current gain of 70 and 10 were obtained for Ga and In FIB-implanted bipolar transistors, respectively.

クロム板への高濃度窒素イオン注入

A study has been made of the microstructure and mechanical properties of chromium subjected to high-dose nitrogen implantation. The substrate used was polycrystal chromium plates 1mm in thickness with a purity of 99.9%. The implantation of nitrogen (N+) ions was performed to doses of from 1×1017 to 1×1018 ions/cm2 at an energy of 100keV. The substrate temperature during N+-implantation was kept at approximately 20°C. The depth profiles of atoms in the implanted layers were estimated by Auger electron spectroscopy combined with Ar+ sputter etching. The identification of nitrides produced by implantation was practiced by X-ray diffraction. Near-surface hardness was measured by a Knoop hardness tester. Friction coefficients were measured using a Bowden-Leben type friction testing machine. The nitrogen depth profile for the highest-dose sample showed a quasi-rectangular distribution, and maximum concentration did not exceed about 50at%. The X-ray diffraction patterns revealed that various nitrides were formed at each dose, and the increase in hardness corresponded to the dose increase. The friction coefficient for the highest-dose sample was less owing to the formation of chromium nitrides. It is concluded that the formation of nitrides by high-dose nitrogen implantation is useful for improving the mechanical properties of chromium plate.

Rapid Thermal Annealing of Fib-Implanted Ga Shallow Impurity Profiles

ABSTRACTIn this paper, we present the results of a study to fabricate shallow p+ n junction using Ga FIB implantation in conjunction with rapid thermal annealing (RTA). A focused 75 KeV ion beam with BO mA/cm2 current density and 0.5 μm beam diameter was used to implant Ga into (100) Si substrates at the doses from 1E13 to 5E15/cm2. The annealing temperature is from 600 °C to 1000 °C for various times, 10–30 sec. Secondary ion mass spectrometry (SIMS) and spreading resistance profiling (SRP) were used to measure the implanted Ga atomic and carrier concentration depth profiles. As compared to the conventional broad beam (BB) implantation, the FIB implanted impurity concentration depth profile has a longer tail and thus a deeper p+n junction. The damage generated by the high dose rate implantation is possibly responsible for this phenomenon. The results of SRP measurements of the FIB as-implanted samples show no Scif-anneal ing occured during implantations. p+n diodes fabricated using FIB exhibit good junction properties: ideality factor of 1.1, reverse–bias leakage current of below 5 nA/cm2 at -IV, and breakdown voltage of about 35 V.

Rapid thermal anneal and furnace anneal of beryllium-implanted Ga0.47In0.53As

The activation efficiency of conventional furnace annealing (550–750 °C, 30 min, capless, AsH3/H2 ambient) and rapid thermal annealing (800 °C,∼1 s, SiO2 cap, N2 ambient) has been compared in Be-doped Ga0.47In0.53As by investigating the carrier profiles and the atomic profiles. Nearly complete activation (100%) occurs during both 750 °C furnace annealing and rapid thermal annealing for an implanted fluence of 6×1013 Be ions/cm2. At a fluence of 6×1014 Be ions/cm2 a significantly higher activation (>50%) is found after rapid thermal annealing as compared with furnace annealing (30%) mainly due to out-diffusion of Be during furnace annealing. Low-temperature photoluminescence (2 K) revealed that comparable recrystallization is achieved in both methods. A high diffusivity of Be is apparent in the atomic depth profiles after furnace annealing. However, only insignificant redistribution is noticeable after rapid thermal annealing, probably due to gettering of the diffusing Be by defects.

Synthesis of silicon dioxide layers by high dose ion implantation

Abstract Single crystal silicon was implanted with molecular oxygen with energies ranging from 80 to 240 keV in a non-channeling direction. Rutherford backscattering (RBS) analysis was used to obtain the oxygen/silicon atomic ratio depth profiles and the thickness of the buried oxide layer, for doses ranging from 1016 to 1. 5 × 1018 O2+/cm2. This work links the early low energy work and the more recent higher energy work, and generally excellent agreement has been obtained. The minimum energy for formation of buried silicon dioxide has been identified as 160 keV per oxygen molecule and corresponding oxygen dose of 6 × 1017 O2+/cm2.

Concentration-Independent Solute Segregation in Laser Annealing of Semiconductor Crystals

ABSTRACTAtomic processes at the interface in regrowth following laser induced melting were investigated by observing behavior of impurity segregation. The interfacial segregation coefficient k* was obtained from depth profiles of solute atoms redistributed by laser irradiation of uniformly doped Si, Ge, and GayAl1−yAs crystals. It was found that k*=k0 for B in Si, Ga in Ge ih the growth rate range of 1 m/s. It is concluded that rapid growth freezes a state of liquid monolayer adjacent to the interface which has the character of ideal solution from dilute to eutectic composition for dopant-silicon systems and in the entire range of composition for the mixed crystal.

Determination of three parameters of a depth profile of foreign atoms in bulk material using pixe analysis: Part II: Influence of the errors of theoretical quantities which are used in the evaluation procedure

The mean depth (a), the mean width (b) and the relative concentration (c) of an unknown distribution of foreign atoms in bulk material can be determined by relative X-ray yield measurements. It is shown by means of a set of case studies for rectangular distributions of foreign Cu-atoms in Ag-bulk to which extent errors in the theoretical description of the X-ray production process and the stopping of projectiles contribute to errors in the result. Errors of 1%, 6% and 7% for a, b, and c, respectively, arise from the uncertainty of the theoretical description of the ionization process provided that one uses corrections of the theoretical ionization cross section and corrects for energy loss straggling and small angle multiple scattering effects. However, an additional large uncertainty is brought into evaluation by the uncertainty of the stopping power. Measurements on AgCuAg sandwich targets are presented.

Determination of three parameters of a depth profile of foreign atoms in bulk material using pixe analysis: Part I: Influence of the errors of yield measurements

The mean depth, the mean width and the relative concentration of an unknown distribution of foreign atoms in bulk material can be determined by relative X-ray yield measurements. It is shown by means of a set of case studies for rectangular distributions of foreign Cu-atoms in Ag-bulk to which extent experimental X-ray yield errors contribute to errors of the result. A rule of thumb for selection of optimum proton impact energy combinations is suggested.

PHOTO AND ELECTROCHEMICAL DOPING IN Ge-BASED CHALCOGENIDES

Photo and electrochemical doping of obliquely deposited Ge-chalcogenide films have been studied by AES/XPS techniques. The effect of electrochemical adsorption and photodoping on the optical transmittance is presented. The atomic concentration depth profiles of Ag-sensitized amorphous Ge and Ge 0.25 Se 0.75 films have been established. The chemical state of Ag and the associated chemical changes in the chalcogenide brought about by photo and electrochemical doping processes have been identified. Some details of the built-in columnar structure and stresses in obliquely deposited films have been revealed by the present study.

Correlation of atomic distribution and implantation induced damage profiles in be-ion implanted Si

Abstract Atomic depth profiles from Be-implanted Si have been examined as a function of implant fluence and annealing, and the results have been correlated with theoretically calculated implantation induced damage profiles. The Be atomic depth profiles were obtained by secondary ion mass spectrometry (SIMS) techniques from samples implanted at 300 keV to fluences ranging from 2 × 1012 to 1015 cm−2. Subsequent to annealing at 600°C for 30 min, the Be SIMS profiles exhibited anomalous redistribution effects. The Be profiles obtained from the annealed samples had the same general features as the depth distribution of implant energy deposited into damage, based on Brice's1 calculations. The correlation of the SIMS atomic profiles and the theoretical damage profiles indicated that Be “decorates” the implantation induced damage regions while redistributing during the annealing process.

Using proton-induced X-rays to determine three parameters of the depth profile of foreign atoms in bulk material

Three parameters of an unknown distribution of foreign atoms in bulk material can be determined by relative X-ray yield measurements at three proton impact energies. A method of evaluation is presented and its reliability is demonstrated by analyzing AgCuAg sandwich targets.

Impurity Depth Profiles by Microanalysis Techniques

A method for determining the depth profile of aluminum atoms near the surface of SiO2 has been demonstrated by means of a sharp 27Al(p,7)28Si resonance. The proton beam from the NRL 5-MV Van de Graaff is passed through two beam-energy analyzers and allowed to fall upon the specimen located in the well of a sodium-iodide gamma-ray detector. The gamma-ray yield is measured as the beam energy is varied in small steps throughout a neighborhood in the vicinity of the resonance energy. The shape of the resulting yield curve depends upon the impurity (implanted) atom profile, the resonance shape, the beam energy distribution, the mean energy loss of the protons as they penetrate the specimen, and the fluctuations about this mean. All factors except the impurity atom concentration depth profile are assumed known and the concentration profile is extracted from the data by iterative syntheses of the yield curve shape and comparison by means of a computer. Depth resolution of the order of 100 A is practicable near the bombarded face of the specimen. The method is capable of an absolute measurement of the number of impurity atoms but that has not been demonstrated in this work. The tesults have been compared with those from a Cameca ion-beam mass spectrometer.