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Systematic approaches are introduced for (i) oxygen precipitation behavior, which is important for internal gettering, and (ii) segregation induced gettering behaviors of p/p+ epitaxial wafers and Poly-Si Back Seal (PBS) wafers. (i) Oxygen precipitation behavior during a whole sequence of a thermal process is predicted by a practical computer simulation technique involving a novel empirical function. The predicted oxygen precipitation behavior agrees with the corresponding experimental results reasonably well. (ii) For a systematic description of Fe segregation gettering, explicit expressions of the Fe segregation coefficients are obtained as functions of temperature and time. Using the determined expressions of the segregation coefficients and introducing diffusion dynamics, one can predict [Fe] behavior as a function of process time during a whole sequence of a thermal process. For both behaviors of(i) oxygen precipitation and (ii) segregation induced gettering, experimentally observed characteristics of a high-temperature process and a low-temperature process are well understood by aids of those simulations. (iii) For a high-sensitivity detection of an important heavy metal impurity Cu, we present a novel bulk impurity collection technique using a room-temperature Cu drift phenomenon accelerated by Corona charge showering on a Si wafer surface
In this report, we proposed that complexes responsible for optical absorption lines in Si grown in a hydrogen (H) atmsophere were composed of interstitial Si and H atoms and then determined the formation energy of interstitial Si in Au-doped Si from the measurements of optical absorption due to H bound to interstitial Si. In the first experiment, specimens were grown in a hydrogen atmosphere. In the second experiment, Si crystals were doped with Au by a vapor method; namely, specimens were sealed in quartz capsules together with a piece of Au wire and then annealed at high temperature followed by quenching in water. Then the specimens were doped with H by annealing them in hydrogen atmosphere of 1 atm. followed by quenching. We measured optical absorption of those specimens. From the effect of impurity on the optical absorption spectra of Si grown in a hydrogen atmosphere, we concluded that those optical absorption lines, including 2223 cm−1line, were due to complexes of interstitial Si and H. From the temperature dependence of the intensity of 2223 cm−1line, the formation energy of interstitial Si in Au-doped Si was determined to be about 2.1 eV
R-OSF are known to appear in CZ silicon crystals, but their nuclei are not observable in the as-grown state, and as-such have been difficult to characterize. Using a crystal grown with modifications in its pulling rate, this paper used lifetime in particular, coupled with the OPP, to investigate as-grown OSF nuclei size and density distribution and to discuss further how R-OSF are formed and how their formation interacts with that of other defects. It was found that faster cooling in the temperature range where large voids are formed (1070°C-970°C), which resulted in a larger residual vacancy concentration, caused the OSF ring to become wider, and the OSF-nuclei to become larger than normal in this area, while fast cooling in the temperature range where OSF are formed (990°C-900°C) is thought to suppress their formation, which thus resulted in smaller OSF-nuclei
A new kind of silicon wafer and a new class of materials engineering techniques for silicon wafers is described. This wafer, called the “Magic Denuded Zone” or MDZ wafer, is produced through the manipulation of the vacancy concentration and, in particular, vacancy concentration depth profiles in the wafer prior to the development of oxygen precipitates in subsequent heat treatments. The result is a wafer with ideal oxygen precipitation behavior for use in all types of integrated circuit applications. The methods used to prepare such wafers combine Frenkel pair generation with injection and the use of surface sinks. Simulations of the vacancy profiles produced by these techniques are presented and discussed. It is shown that within the range of vacancy concentration accessible by these techniques (up to ca. 1013 cm−3) the rate and oxygen concentration dependence of oxygen clustering can be substantially modified. Such techniques can be used to precisely engineer unique and desirable oxygen-related defect performance in silicon wafers both in terms of distribution and rate of defect formation. One result of the application of such techniques is an ideally precipitating silicon wafer in which the resulting oxygen precipitate profile (denuded zone depth and bulk density of precipitates) is independent of the concentration of oxygen of the wafer, the details of the crystal growth process used to prepare the wafer and, to a very large extent, the details of thermal cycles used to process the wafer into an electronic device. Optimal, generic and reliable internal gettering performance is achieved in such a wafer
The defect formation during sublimation bulk crystal growth of silicon carbide (SiC) is discussed. SiC bulk crystals are produced by seeded sublimation growth (modified-Lely method), where SiC source powder sublimes and is recrystallized on a slightly cooled seed crystal at uncommonly high temperatures (≥2000°C). The crystals contain structural defects such as micropipes (hollow core dislocations), subgrain boundaries, stacking faults and glide dislocations in the basal plane. The type and density of the defects largely depend on the crystal growth direction, and many aspects are different between the growth parallel and perpendicular to the <0001> c-axis. Micropipes are characteristic defects to the c-axis growth, while a large number of stacking faults are introduced during growth perpendicular to the c-axis. We discuss the cause and mechanism of the defect formation
Electrical properties of iron-related defects (IRD) introduced in n-type floating zoned (FZ) and Czochralski (CZ)-grown silicon are studied by deep level transient spectroscopy and Hall effect. Electrically active IRD have been observed for the first time in n-type CZ silicon. Enthalpy and entropy factors of electron emission rate of IRD are equivalent between those observed in CZ and FZ silicon. In-diffusion process at 1160° and isothermal annealing process at 150° also indicate the identical nature of IRD between CZ and FZ silicon, which can be understood in terms of the consecutive progress of iron-related complex-formation reactions including interstitial iron atoms (Fei) in the silicon crystal. The IRD is independent of oxygen and phosphorus atoms. Only a small fraction of Fei forms electrically ionizable complexes
Beryllium-doped, non-stoichiometric GaAs grown by MBE at low temperatures appears superior to its undoped counterpart in several key areas vital to device manufacturing. X-ray diffraction studies have indicated that material grown above 275°C shows complete thermal stability to annealing at temperatures up to 600°C. This behavior is ascribed in part to strain compensation between the small beryllium atoms and the large arsenic antisites. Consequently, outdiffusion of excess arsenic from the non-stoichiometric material into neighboring layers upon annealing or subsequent high temperature growth is expected to be negligible. Short carrier lifetime (<1 psec) and high resistivity (>104 Ω-cm) have been observed in the same as-grown material. Sub-picosecond lifetimes have been measured previously in undoped material, but the low growth temperatures required produce a supersaturation of antisites allowing for significant hopping conductivity through the defect band in as-grown material, and significant arsenic outdiffusion upon annealing. Due to electrical compensation of antisites by beryllium acceptors, materials in which the ionized antisites represent a major fraction of a relatively small total antisite concentration are now made possible by proceeding to higher growth temperatures. Thus, nonstoichiometric GaAs having a beneficial combination of thermal stability, short carrier lifetime and high resistivity can be fabricated
The role of hydrogen (H) in carbon (C)-doped GaAs was examined by co-doping of C and H atoms using low-energy hydrocarbon (CH+ and CH3+) ions. Experiments were carried out using the combined ion beam and molecular beam epitaxy (CIBMBE) system. Samples were characterized by low-temperature photoluminescence at 2K and Hall effect measurements at room temperature. Results show that incorporated C atoms are optically and electrically activated as acceptors even by hydrocarbon ion impingement. The effect of H incorporation was found to be noticeable when impinged current density of CH3+ ion beam is high that produces equivalent net hole carrier concentration greater than ∼1018 cm−3
We propose materials design for the fabrication of low-resistivity p-type ZnSe crystals using a new doping method which involves simultaneous codoping of both n- and p-type dopants, based on the ab initio electronic band structure calculations. We have clarified that while doping of acceptor dopants, Lizn and Nse, leads to the destabilization of the ionic charge distributions in p-type ZnSe crystals, doping of donor dopants, Inzn, ClSe or ISe gives rise to n-type doped ZnSe with high donor concentration due to a large decrease in the Madelung energy. The codoping of the n- and p-type dopants (the ratio of their concentrations is 1:2) enhances the incorporation of the acceptors in p-type ZnSe crystals due to a decrease in the Madelung energy, resulting in the formation of the p-n-p complexes which occupy nearest-neighbor sites. It results in an increase in the net carrier densities and the hole mobility due to a change in the scattering mechanism from that caused by long-range Coulomb scatters to that by short-range dipole-like ones
Low-energy N2+ molecular-ions were irradiated during the epitaxial growth of GaAs. Ion acceleration energy and ion beam current density were varied in the range of 30-200 eV and 3-37 nA/cm2, respectively. GaAs growth rate was kept constant at 1µm/ h and the thickness of N-doped GaAs layer was about 1 µm. N concentration was obtained by using secondary ion mass spectroscopy. Strong N-related emissions were observed in the low-temperature photoluminescence spectra, which indicates that N atom is efficiently substituted at As site and is optically active as an isoelectronic impurity
In this article, we propose a new model to explain how heteroepitaxial layers grown on a twist-bonded thin layer may have a significantly reduced number of threading dislocations even if the strain in the epitaxial layers is relaxed. We first point out the deficiency in the existing compliant substrate theory by showing that all the synthesized “compliant substrates” fail to behave as “ideal” free-standing templates assumed by the current theory. Our new model is constructed on the base of stress field interactions between the heteroepitaxial layer and the embedded twist boundary. In the new model, the reduction in threading dislocation density originates from the extension of the dislocation half loops due to the effect of misfit dislocation pinning by the twist boundary. When the average size of the dislocation half loops increases substantially from micrometers to millimeters or even to the size of the wafer, the density of threading dislocations drops significantly. This model does not require any “macroscopic” motion between the bonded thin layer and the handle wafer as the current theory does, which makes it more agreeable with the experimental results
The use of compositionally graded buffer layers in the growth of fully relaxed epitaxial Si1−xGex alloy layers has led to a major improvement in crystalline quality. A considerable reduction in the density of the threading dislocations has become possible, facilitating point defect studies in these materials. The issues addressed in this review are inherent to the coupling between band gap engineering and defect-related levels. Among them, the pinning behaviour, charge state effects and their consequence upon the thermal stability of point defects are discussed together with the impact of the fluctuation in Ge distribution
InxGa1−xAs structures with compositionally graded buffers were grown by metal-organic vapor phase epitaxy (MOVPE) on GaAs substrates and characterized with plan-view and cross-sectional transmission electron microscopy (PV-TEM and X-TEM), atomic force microscopy (AFM), and x-ray diffraction (XRD). The results show that surface roughness experiences a maximum at growth temperatures where phase separation occurs in InxGa1−xAs. The strain energy due misfit dislocations in the graded buffer indirectly influences phase separation. At growth temperatures above and below this temperature, the surface roughness is decreased significantly; however, only growth temperatures above this regime ensure nearly complete relaxed graded buffers with the most uniform composition caps. With the optimum growth temperature for grading InxGa1−xAs determined to be 700°C, it was possible to produce In0.33Ga0.67As diode structures on GaAs with threading dislocation densities < 8.5 × 106/cm2
Due to the prohibitively high 4.1% lattice mismatch, direct growth of GaAs on Si invariably leads to very high dislocation densities (> 108/cm2) which have precluded its use in device applications despite numerous attempts. However, the growth of low threading dislocation density (∼2 × 106/cm2) relaxed graded Ge/GexSi1−x/Si heterostructures can bridge the gap between lattice constants by replacing the high mismatch GaAs/Si interface with a low mismatch (< 0.1%) GaAs/Ge interface. Although the lattice mismatch problem is thus eliminated, the heterovalent GaAs/Ge interface remains highly susceptible to antiphase disorder. Since antiphase boundaries (APBs) nucleated at the GaAs/Ge interface act as scattering and nonradiative recombination centers, growth of device quality GaAs on Ge/GexSi1−x/Si demands effective suppression of antiphase disorder. The current work investigates the sublattice location of GaAs on 6° offcut (001) Ge/GexSi1−x/Si substrates as a function of atmospheric pressure metal-organic chemical vapor deposition (MOCVD) growth initiation parameters. Two distinct GaAs phases are observed, one dominant at temperatures > 600°C and another at temperatures <500°C. Incomplete phase transitions during pre-growth thermal cycling account for the appearance of localized bands of anti-phase disorder where the polarity of the GaAs film switches. We suspect that background arsenic levels in the MOCVD system are largely responsible for inducing the observed phase transitions. The complete suppression of antiphase disorder under optimized growth conditions is demonstrated by transmission electron microscopy (TEM)
We report the photo modified growth of GaAs by chemical beam epitaxy at substrate temperatures in the range 335 to 670°C using triethygallium (TEG) and arsine. A mercury-xenon lamp (electrical power 200 W) provided the irradiation for the photoassisted growth. The growth was monitored in real time by laser reflectometry (LR) using a 670 nm semiconductor laser, and the optically determined growth rate agreed with that obtained from the layer thickness measured by cross sectional transmission electron microscopy. The observed photo-enhancement of the growth rate at low substrate temperatures and inhibition at high substrate temperatures is thermal in origin, consistent with raising the substrate temperature by 10±3°C. Cross sectional transmission electron microscopy showed that the photoassisted layers are essentially free from dislocations
Sb diffusion in strained Si1−xGex (x = 0.1 and 0.2) layers during nitridation (in NH3, 810 °C) and oxidation (in dry O2, 825 and 900 °C) of Si/Si1−xGex/Si heterostructures is measured and, subsequently, compared with that obtained for treatments in vacuum. An enhancement (ν) or retardation (η) of Sb diffusion in strained Si1−xGex after nitridation/oxidation anneals is detected. For example, 810 (NH3) and 900 °C (O2) anneals results in ν ∼ 2 and η ∼ 0.15 in strained Si0.9Ge0.1, respectively. The retardation of Sb diffusion is attributed to the injection of excess self-interstitials (I) and strongly indicating low interstitialcy fraction of Sb diffusion in strained Si1−xGex. The enhancement of Sb diffusion may be due to direct injection of vacancies (V), but only if the V diffusivities are significantly different in Si and Si1−xGex, or depletion of I in the strained Si1−xGex layers caused by the excess V concentration at the top surface of silicon layer
Using production scale AIXTRON MOCVD systems various heterointerfaces in the GaInN/GaN system have been studied in depth. GaInN single hetero layers were investigated to optimise photoluminescence properties. Several approaches of capping GaInN/GaN with another GaN layer to develop high quality double-hetero (DH) structures were presented. Using an optimised interfacing technique we obtain device quality DH structures with state of the art composition uniformity across a 2 inch wafer
To engineer high-quality Inx(AlyGa1−y)1−x P/Ga1−xP graded buffers, we have explored the effects of graded buffer design and MOVPE growth conditions on material quality. We demonstrate that surface roughness causes threading dislocation density (TDD) to increase with continued grading: dislocations and roughness interact in a recursive, escalating cycle to form pileups that cause increasing roughness and dislocation nucleation. Experiments show that V/III ratio, temperature, and grading rate can be used to control dislocation dynamics and surface roughness in InxGa1−xP graded buffers. Control of these parameters individually has resulted in x = 0.34 graded buffers with TDD = 5 × 106 cm−2and roughness = 15 nm and a simple optimization has resulted in TDD = 3 × 106 cm −2and roughness = 10 un. Our most recent work has focused on more sophisticated optimization and the incorporation of aluminum for x > 0.20 to keep the graded buffer completely transparent above 545 nm. Given our results, we expect to achieve transparent, device-quality Inx(AlyGa1−y)1−x P/GaP graded buffers with TDD < 106 cm−2
SiO2 films, 2-20 nm thick, were grown on passivated, ordered Si(100) to correlate electrical properties and oxidation rates with processing for ultra-thin gate oxides. Ordered Si(l 00) (1 × 1) stable in ambient air was obtained at room temperature by wet chemical cleaning. The thickest oxides were grown by Rapid Thermal Oxidation at 850°C, the thinnest at room temperature. O was detected by Ion Beam Analysis (IBA) using a combination of ion channeling with the 3.05 MeV 16O(α,α)16O nuclear resonance. It then becomes possible to measure order in thin SiO2 by comparing the total amount of O from rotating random spectra to disordered O detected by ion channeling, and detect the alignment of O with the atoms in Si(100)
Recent progress in crystal growth of wide bandgap group III nitrides on highly-mismatched substrates has enabled us to produce high-quality GaN, A1GaN, GaInN and quantum well structures. High-performance blue and green light-emitting diodes and room temperature operation of nitride-based laser diodes have also been realized. Today, steady progress is being made in the areas of crystal growth and device performance. However, much further advances are required in many areas of materials science and device fabrication of the nitrides