Carbon In Silicon Research Articles

Mechanism of buried β-SiC formation by implanted carbon in silicon

The structure of silicon implanted with high doses of carbon ions in the range (0.35–1.3) × 10 18 C + cm −2 at implantation temperatures from 500 to 700 °C is studied by transmission electron microscopy. At an implantation temperature of 700 °C, cubiv (β-SiC) and hexagonal coherent or semicoherent precipitates are formed in the silicon overlayer. Only the cubic form is stable during high temperature annealing. At high implantation temperatures a thin discrete buried layer of β-SiC, with an epitaxial relationship to the silicon substrate, is formed. The quality of this layer is greatly improved after a high temperature annealing as revealed by the translation-type (111) Moiré pattern. The β-SiC epitaxial layer consists of adjoined grains on {111} and {100} planes without appreciable coalescence of these adjoining grains. The stability of the β-SiC precipitates is discussed and it is compared with the stability of SiO 2 precipitates which are formed in silicon implanted with oxygen.

EPR identification of the single-acceptor state of interstitial carbon in silicon.

An EPR center labeled Si-L6 is reported which is identified as arising from the singly ionized acceptor state of isolated interstitial carbon (${\mathrm{C}}_{\mathit{i}}^{\mathrm{\ensuremath{-}}}$) in electron-irradiated crystalline silicon. Correlated deep-level capacitance transient spectroscopy measurements locate the acceptor level at ${\mathit{E}}_{\mathit{c}}$-0.10 eV. The core structure of the defect is a 〈100〉 C-Si interstitialcy similar to that previously proposed for ${\mathrm{C}}_{\mathit{i}}^{+}$. The spin wave function is substantially more diffuse, however.

A Formation Mechanism of the Thermal Donors Related to Carbon in Silicon after an Extended Isochronal Anneal

The formation of thermal donors in silicon containing carbon at the concentration of was studied after a 100h isochronal anneal in the temperature range between 400° and 900°C. Two types of thermal donors were observed. The first type was identified as the oxygen thermal donors formed in the temperature range between 400° and 550°C. The second type that formed in the temperature range between 500° and 800°C is hypothesized to originate from an agglomerate consisting of interstitial carbons. Agglomerates of interstitial carbons dissolved during the subsequent 1050°C anneal. The dissolution of interstitial carbon caused the carbon atoms to return to their substitutional sites. Excess silicon interstitials which were released during the dissolution condensed into interstitial‐type dislocation loops.

Ab Initio Calculations of the Structure and Properties of Large Atomic Clusters

Abstract A discussion is given of the problems involved in computing the total energy, using local density functional methods, of a cluster of atoms with a real space basis set of Gaussian orbitals. Particular attention is given to the methods used to evaluate the Hartree and exhange-correlation energies and their potentials. Several applications are described: molecular structures and properties, the bond lengths and dynamic properties of bulk silicon and diamond, the local vibratory mode of carbon in silicon, and the structures of H and H related complexes in diamond and gallium arsenide.

Evidence for valence hole localization in the Auger decay and fragmentation of carbon and silicon tetrafluorides

Monochromatic synchrotron radiation was used to excite selectively core electrons of the carbon and fluorine atoms in carbon tetrafluoride and silicon and fluorine in silicon tetrafluoride. The fragmentation processes were examined using time-of-flight mass spectroscopy. The mass spectra show the distribution of ions collected in coincidence with low and high energy electrons. Distinct changes in the mass spectra with atomic site of excitation and photon energy are observed. The observation of F2+ ions following fluorine 1s excitation in SiF4 provides significant evidence for a ‘‘valence bond depopulation’’ mechanism involving the formation of a localized, two-hole final state that persists on the time scale of fragmentation. In contrast, no F2+ was observed for CF4, which indicates that fragmentation for this molecule is more characteristic of a delocalized two-hole state.

Impurity Gettering by Implanted Carbon in Silicon

AbstractWe have observed strong gold gettering by implanted carbon in silicon. It was found that the gettering agents in carbon implanted layers are point defects associated with singular carbon atoms. The positions of the gettered Au atoms were found to be distorted substitutional sites. A pointdefect gettering model is proposed to explain our findings.

Advances in the Understanding of Oxygen and Carbon in Silicon

Advances in the Understanding of Oxygen and Carbon in Silicon

Determination of traces of carbon in silicon, tantalum and titanium alloy by combustion-nonaqueous coulometric photometric titration.

Determination of traces of carbon in silicon, tantalum and titanium alloy by combustion-nonaqueous coulometric photometric titration.

Lattice distortions induced by carbon in silicon

Abstract X-ray double-crystal diffractometry has been used to investigate the lattice distortions in silicon crystals containing carbon impurities. Precise lattice-spacing measurements have been carried out with a double-source double-crystal transmission technique. A linear correlation between the absolute value of lattice spacing and the carbon concentration was observed. X-ray double-crystal reflection topography was used to measure residual minute lattice strains also as a function of the carbon atom number density. A similar relationship was found. A comparison of the results of the lattice-spacing measurements and of the topographic investigations indicates that the lattice consists of consecutive layers which are alternately more and less carbon enriched. The observed lattice deformations arise from the substitutional exchange of silicon and carbon atoms.

Gettering of gold and copper with implanted carbon in silicon

The gettering effects of implanted carbon for Au and Cu are studied and compared with the gettering effects of implanted oxygen, nitrogen, BF2, neon, and argon. It is demonstrated that implanted carbon forms strong gettering centers in silicon which are an order of magnitude more effective than implanted oxygen. The amount of gettered Au by implanted carbon is found to be approximately linear with dose in the range from 1015 to 1016 cm−2 and no thermal instability is observed with annealing up to 12 h at 1000 °C. It is found that the gettering effect of carbon is reduced by the addition of oxygen. This indicates that the strong gettering effect of carbon is not due to carbon-enhanced oxygen precipitation but a phenomenon of its own.

Complexing of nitrogen with carbon and oxygen in silicon: Photoluminescence studies

We study interactions of nitrogen with carbon and oxygen in crystalline silicon by photoluminescence spectroscopy. Such processes manifest themselves in five photoluminescence lines in the spectral region around 1.6 μm emerging after nitrogen and carbon implantations and furnace annealing with 550° C optimum temperature. Nitrogen and carbon isotope shifts of the lines confirm the incorporation of these atomic species in the optical defects. Nitrogen-oxygen interactions are demonstrated by differences in the lines’ appearance between oxygen-lean float-zone and oxygen-rich pulled silicon starting materials. The data suggests similar basic nitrogen-carbon units in all five defects.

Dielectric screening in semiconductors.

Intra-atomic and interatomic Coulomb interactions are incorporated into bond-orbital theory, based upon universal tight-binding parameters, in order to treat the effects of charge redistribution in semiconductor bonds. The dielectric function \ensuremath{\epsilon}(q) is obtained for wave numbers in a [100] direction. The screening of differences in average hybrid energy across a heterojunction is calculated in detail, indicating that the decay length for the potential depends upon the relative values of Madelung and intra-atomic Coulomb terms. The parameters used here predict an imaginary decay length and thus an oscillating potential near the interface. The same theory is applied to point defects by imbedding a cluster in a matrix lattice, taking charges in that lattice to be consistent with continuum theory. Illustrating the theory with a phosphorus impurity in silicon, it is seen that the impurity and its neighboring atoms have charges on the order of only one-tenth of an electronic charge, alternating in sign from neighbor to neighbor as for planar defects. Although there are shifts in the term values on the order of a volt, the difference in these shifts for neighboring atoms is much smaller so that the effect on the bonds is quite small. This behavior is analogous to the response of a dielectric continuum to a point charge: The medium is locally neutral except at the center of the cluster and there are slowly varying potentials ${e}^{2}$/\ensuremath{\epsilon}r. Because of this slow variation, free-atom term values should ordinarily suffice for the calculation of bond properties and bond lengths at impurities. Corrections are larger for homovalent substitutions such as carbon in silicon.

Valence Hole Localization in Molecular Auger Decay

ABSTRACTStudies of the unimolecular decay, following the excitation of core electrons of the carbon and fluorine atoms in carbon tetrafluoride and silicon and fluorine in silicon tetrafluoride by monochromatic, synchrotron radiation, provided evidence for a “valence bond depopulation” fragmentation mechanism. The fragmentation processes were examined using time-of flight mass spectroscopy. The mass spectra show the distribution of ions collected in coincidence with low and high energy electrons. Distinct changes in the mass spectra with atomic site of excitation and photon energy are observed. The observation of F2+ ions in the time-of-flight mass spectra following excitation of a fluorine is electron in SiF4 is significant because it provides direct evidence for the formation of a localized, two-hole, final valence state that persists on the time scale of fragmentation. In contrast, the lack of F2+ ions from CF4, indicates that the fragmentation occurs through a delocalized two-hole state.

Carbon in silicon: a cluster calculation

Cluster calculations of carbon in silicon using an ab-initio self-consistent method are presented. The clusters are saturated with hydrogens and are designed to simulate a-Si. From total energy analysis the probable configuration is found to be the high symetry one in the center of a tetrahedron of silicon atoms. The bond length between C and Si in the equilibrium position is 2.16 Å. The local density of states at the carbon site shows a three-peaked structure in the valence band, the lower energy band edge being s-like and the upper one p-like. The CSi bond is mainly covalent although charge density contours show a higher concentration of charge around the carbon atom.

Solid combustion synthesis of β SiC powders

A method of obtainment of β SiC powders under conditions of the self-propagating high-temperature synthesis (SHS), based on the exothermic reaction between silicon micropowders and active carbon substrates (carbon black and charcoal), has been developed. The method described in the paper is characterised by a low ignition temperature (1250–1300°C) and a short duration of synthesis (3–5 minutes). The product retains the morphology of the carbon substrates used what indicates the occurrence of a mechanism similar to the one suggested in the case of carbon fibres-silicon systems, namely the occurrence of alternating steps of solution of carbon in liquid silicon and crystallisation of SiC from supersaturated solution.

Grain boundary segregation of oxygen and carbon in polycrystalline silicon

The electrical activity of grain boundaries (GB’s) in polycrystalline silicon is strongly affected by heat treatments, which are known to induce the segregation of oxygen. The large, quantitative variations of the electrical activity of GB’s observed experimentally, which are a function not only of the heat treatments but also of the carbon and oxygen content of the specific sample examined, could not be explained however, without assuming that carbon and oxygen play a synergistic role. We demonstrate in this work, by using secondary ion mass spectrometry, that oxygen and carbon segregate simultaneously, albeit spatially resolved, at grain boundaries. This result appears to be of major importance when interpreting electron or light beam induced current profiles at grain boundaries in polycrystalline silicon.

Evaluation of the peak ratio method for determining high carbon impurity concentrations in solar grade silicon

Two methods for determining high concentrations of carbon in silicon are compared. The peak ratio method, ulitizing an arbitrarily chosen, fixed baseline is found to compare well with the standard ASTM method.

Recent Topics of Infrared Absorption of Oxygen and Carbon in Silicon

Recent Topics of Infrared Absorption of Oxygen and Carbon in Silicon

Mechanism of reactions in the Si l + C f system and the self-propagating high-temperature synthesis of silicon carbide

Using moderately and highly reactive carbon fibres and high-purity silicon powders, the kinetics and mechanism of reactions in the Si + C system have been investigated in order to explain the possibility of occurrence of the self-propagating high-temperature synthesis (SHS) in this system. After a review of conditions required for SHS in different C-containing systems, the experimentally found main parametrs of the Si + C reaction and the self-ignition temperature in the Si + C system are described and discussed. The high reaction enthalpy and the very high activation energy of the reaction found confirm that the requirements for SHS are satisfied in this system under certain experimental conditions. In order to explain the high reaction rate and the specific microstructure of the product in the first stages of the reaction, a mechanism of the reaction has been postulated in which repeating steps of solution of carbon in liquid silicon followed by precipitation of SiC from the liquid solution occur successively as the reaction front moves.

Determination of the Conversion Factor for Infrared Measurements of Carbon in Silicon

The carbon content of silicon single crystals and polycrystals has been measured by charged particle activation analysis (CPAA) and infrared absorption. We obtained a linear relationship between the absorption coefficient at 605 cm−1 and the carbon content obtained by CPAA. We obtained a conversion factor of for a 100% substitutional carbon.