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Notes: Chemical bonding of H to displacement defects and internal surfaces in Si has been investigated by infrared-absorption and nuclear reaction analysis techniques. A He implantation/anneal sequence was used to produce faceted voids which are retained to at least 800 °C in a buried layer as revealed by transmission electron microscopy. Hydrogen was injected into void layers by three different methods: ion implantation, plasma exposure, and H2 gas exposure. Infrared absorption by Si-H stretch modes with frequencies characteristic of monohydrides on (100) and (111) surfaces are observed for all methods of H injection, consistent with bonding on faceted void surfaces. Thermal stability of Si-H is higher on void surfaces than on other trapping sites. Displacement defects produced by H-ion implantation trap H but release it upon annealing for retrapping on voids. The Si-H absorption bands with frequencies characteristic of monohydrides on (100) and (111) surfaces anneal in parallel between 600 and 800 °C and in coincidence with the loss of total H measured by nuclear reaction analysis. Moreover, densities comparable to the total H density are estimated for void surface states and for Si—H bonds on void surfaces. It is inferred from these results that bonding of H on the void surfaces is energetically favored over H2 formation in the voids, and it is concluded that the 2.5±0.2 eV determined in a separate study of H release from buried voids is the Si—H bond energy descriptive of both (111) and (100) surfaces.

Notes: Electrical transport properties of zone-melt-recrystallized Si films of Si-on-Insulator wafers were investigated using resistivity and Hall effect measurements between 77 and 300 K. Both graphite strip and cold cathode electron beam methods were used for zone melting which produced high resistivity ((approximately-greater-than)103 Ω cm at room temperature) recrystallized films. Phosphorus implantation into the silicon films to a dopant level of 1×1016 cm−3 and subsequent annealing at 1100 °C reduced the room-temperature resistivities to ∼1 Ω cm. Hall mobilities of 950 cm2/V s were observed at room temperature for both materials after the implant anneal sequence. However, for temperatures less than 150 K, the mobility is higher in graphite strip than in electron beam recrystallized films. This behavior is consistent with the relative crystalline qualities of the two films as determined by electron channeling and x-ray diffraction. It is noteworthy that a deep level was observed at 0.2 eV below the conduction band in the graphite strip recrystallized film but not in the electron beam recrystallized samples.

Notes: The formation and annihilation behaviors of thermal donors in 16O+-, 18O+-, or 16O++12C+-implanted float-zone silicon have been investigated with secondary ion mass spectrometry, spreading resistance probe, Hall effect, and transmission electron microscopy. Various oxygen or carbon+oxygen-implanted samples were laser annealed to remove implant damage and subjected to furnace annealing at 450 °C for up to 100 h to activate oxygen-related thermal donors. Oxygen concentrations at the peak of the implanted profiles exceed the maximum for Czochralski Si by an order of magnitude. It is found that the third to fourth power dependence of thermal donor formation on oxygen generally observed for Czochralski Si does not hold for the higher oxygen concentration in the implanted layer. Annihilation characteristics of thermal donors formed in the oxygen implanted layers were investigated by the rapid thermal annealing technique. A rapid thermal anneal at 1150 °C for 30 s was required to remove all the thermal donors. Based upon the annihilation kinetics data, it is tentatively concluded that both old and new thermal donors exist in the oxygen-implanted layer. For carbon+oxygen-coimplanted samples, the data have shown that carbon greatly increases the new thermal donor concentration in the implanted layer. Finally, precipitate morphologies for both oxygen-only- and carbon+oxygen-coimplanted samples after a 450 °C furnace annealing were investigated by high resolution electron microscopy. In the case of oxygen-implant-only samples, predominant precipitate morphologies are needlelike while platelet defects predominate for carbon+oxygen-coimplanted samples. Since carbon increases the formation rate of new thermal donors, it is unlikely that they are distinctly related to needlelike precipitates as claimed in previous studies.

Notes: The dissociative chemisorption probability of N2 on W(100) is found to proceed by way of two dynamically distinct channels. At low kinetic energies Ei, dissociation proceeds primarily by way of a precursor-mediated process, where the dissociation probability is found to fall with increasing Ei, reflecting the energy dependence of the trapping probability into this state. Dissociation at low energies is also strongly dependent on surface temperature Ts which effects the fraction of trapped species that desorb. For energies above about 0.45 eV, the dissociation probability is found to rise from a minimum of about 0.14 at Ts=800 K to over 0.45 at Ei=5 eV. Over this range we believe that kinetic energy enables the incident molecules to directly overcome a barrier in the reaction coordinate. Throughout the entire range of energies we observe only slight variations of the dissociation probability with the angle of incidence, with no discernible sensitivity for energies below ∼0.5 eV. For energies between 1 and 4 eV, associated with the "activated'' channel, we observe a slight preference for non-normal incidence, with a clear preference for normal incidence only for Ei〉5 eV.While the "precursor-mediated'' channel displays a considerable sensitively to surface temperature, results at high energy are found to be essentially independent of this parameter. Moreover, dissociation by way of the precursor-mediated channel is found to be insensitive to surface coverage, in contrast to a roughly linear decrease in the dissociation probability with surface coverage observed for dissociation via the activated process. In this latter case, we find that the saturation coverage remains approximately constant at about 0.6 atomic monolayers for all conditions, up to the highest incidence energies. This differs from previous observations for the dissociation of O2 and N2 on W(110), where the saturation coverage was found to rise with increasing Ei. Finally we find that the dissociation probability vs kinetic energy curve for the "direct'' dissociation case is qualitatively similar to that for the N2/W(110) system, but with a threshold that is ∼0.4 eV lower. We argue that the "precursor-mediated'' mechanism does not contribute significantly to dissociative chemisorption in the W(110) case and conclude that the primary difference between N2 dissociation on the W(110) and W(100) surfaces is that the barrier to dissociation is slightly higher in the W(110) case.

Notes: The dissociative chemisorption of N2 on W(100) is found to fall rapidly with increasing kinetic energy Ei in the range 26 to 450 meV. For a surface temperature Ts of 300 K, the initial dissociative chemisorption probability S0 falls from ∼0.8 at Ei=26 meV to 0.15 at 450 meV. Over this range of energies the dissociation probability is also found to fall rapidly with Ts, and to be relatively insensitive to surface coverage at low Ts, strongly suggesting that dissociation occurs in this system via a precursor under these conditions. This picture is supported by angular distribution measurements of the scattered molecules which are consistent with an appreciable cosine component, which also becomes smaller as Ei increases. Results are found to be surprisingly insensitive to the incidence angle over the range 0° to 70°, indicating that the trapping process scales quite closely with the total incidence energy.

Notes: We have studied the incorporation of heavily supersaturated C into Si using solid-phase epitaxy (SPE) of implanted amorphous layers. The strain in the Si1−xCx/Si heterostructures was measured using rocking curve x-ray diffraction. The microstructure and defect introduction were examined using ion channeling and transmission electron microscopy (TEM). The fraction of C located on substitutional lattice sites in the Si was monitored using Fourier transform infrared absorption spectroscopy and ion channeling at resonance energies. Carbon-depth profiles were monitored by secondary ion mass spectroscopy. The metastable solubility limit for the incorporation of C into Si by SPE was found to be 3.0–7.0×1020 atoms/cm3, which is over three orders of magnitude above the equilibrium solubility at the Si melting point. This limit was determined by the ability to regrow without the introduction of microtwins and stacking faults along {111} planes. We postulate the local bond deformation resulting from the atomic size difference between C and Si leads to the faceting of the amorphous–crystalline interface and allows defect introduction, thus limiting the C supersaturations achieved in Si by SPE. It was also found that the defect density in the regrown alloys could be reduced by higher SPE regrowth temperatures in rapid thermal anneal processing. © 1996 American Institute of Physics.

Notes: We have studied the thermal stability of Si1−yCy/Si (y=0.007 and 0.014) heterostructures formed by solid phase epitaxial regrowth of C implanted layers. The loss of substitutional C was monitored over a temperature range of 810–925 °C using Fourier transform infrared absorbance spectroscopy. Concurrent strain measurements were performed using rocking curve x-ray diffraction to correlate strain relaxation with the loss of substitutional C from the lattice. Loss of C from the lattice was initiated immediately without an incubation period, indicative of a low barrier to C clustering. The activation energy as calculated from a time to 50% completion analysis (3.3±5 eV) is near the activation energy for the diffusion of C in Si. Over the entire temperature range studied, annealing to complete loss of substitutional C resulted in the precipitation of C into β-SiC. The precipitates are nearly spherical with diameters of 2–4 nm. These precipitates have the same crystallographic orientation as the Si matrix but the interfaces between the Si and β-SiC precipitates are incoherent. During the initial stages of precipitation, however, C-rich clusters form which maintain coherency with the Si matrix so the biaxial strain in the heterostructure is partially retained.

Notes: Plasma hydrogenation of Czochralski Si has been performed to investigate the introduction of Si–O stretch modes and their correlation with thermal donor formation. Plasma hydrogenation at 275 °C introduces a well-resolved vibrational absorption band at 1005 cm−1, while absorption due to electronic excitations for thermal donors remains weak. We attribute this band to a Si–O precursor center for thermal donor formation, and suggest it is the oxygen dimer center discussed in other studies of oxygen in Si. Vibrational modes introduced at 990 and 1000 cm−1 during post-hydrogenation furnace annealing at 400 °C correlate with thermal donors TD2 and TD3, respectively. Stretch frequencies for Si–O in thermal donor centers are compared to those for oxygen aggregates in oxygen-implanted and electron-irradiated Si.

Notes: Hydrogen has been introduced from a rf plasma into Czochralski Si at 275 °C. Most of the hydrogen is trapped near the surface where it forms Si—H bonds, but a small fraction diffuses into the Si. This fraction enhances oxygen-related thermal donor (TD) formation rates in a diffusionlike profile during subsequent furnace anneals between 350 and 400 °C. A hydrogen concentration that is only a few percent of the oxygen concentration is sufficient to enhance the TD formation rate, indicative of a hydrogen-catalyzed process. Maximum concentrations for TDs after annealing at 400 °C exceed that for retained hydrogen. A mechanism of hydrogen diffusion through oxygen traps and correlated hydrogen-promoted oxygen diffusion is proposed to explain the enhanced TD formation rates.

Notes: A new absorption band at 2029 cm−1 has been observed in GaAs following implantation with hydrogen at 80 K. Association of the band with a vibrational mode of hydrogen is confirmed by substitution of deuterium. Tentative assignment is made to As-H bonds. The new band is unstable below room temperature and a previously identified Ga-H absorption band forms as the new band is removed by annealing near 200 K.