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  • 1
    Electronic Resource
    Electronic Resource
    An investigation of point defects in silicon carbide (1995)
    Springer
    Applied physics 61 (1995), S. 55-58 
    Details
    ISSN: 1432-0630
    Keywords: PACS: 61.70; 68.55; 78.70
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract.  Positron lifetime measurements on bulk samples of single crystal SiC wafers have shown that both 6H and 4H polytypes exhibit a bulk lifetime of 150±2 ps. All samples contained a second, defect-related lifetime component, ranging in value from 250 to about 300 ps with rather low intensities. The defect structure exhibited by the nanocrystalline samples is, not unexpectedly, much more complex. Positron beam experiments on Electron Cyclotron Resonance Chemical Vapour Deposited (ECR-CVD) SiC thin films showed that the positrons are very sensitive to changes in important film parameters as a function of the deposition conditions. It was found that the film density is lower than expected, probably due to hydrogen incorporation; variations in composition among different films were detected through variations in the S parameters, and differences were observed in the electric field at the film–substrate interface due to hydrogen passivation of dangling bonds and different substrate resistivities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01538211
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  • 2
    Electronic Resource
    Electronic Resource
    Annealing of Si-implanted GaAs studied using variable-energy positrons (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 1799-1804 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Modification of GaAs by Si+-ion implantation is an important process for selective doping of the material. Defects caused by the implantation process often lead to incomplete electrical activation, and annealing procedures are used to recover the crystal quality. Results are presented of variable-energy positron (VEP) and cross-sectional transmission electron microscopy (XTEM) studies of a series of GaAs samples implanted with moderate to high fluences of 3×1013, 3×1014, and 1×1015 Si+ ions cm−2. Samples were irradiated at room temperature, and studied both before and after thermal annealing for one hour at 850 °C. In all cases XTEM results show a high density of small extrinsic dislocations after implantation, and VEP shows high concentrations of point (vacancy type) defects. Annealing leads to a decrease in the point-defect concentration in the lowest-fluence sample, but both XTEM and VEP confirm the formation of macroscopic (i.e., (approximately-greater-than)20 A(ring) diameter) voids following annealing. These data are discussed in the context of microscopic models for defect formation and migration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351650
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  • 3
    Electronic Resource
    Electronic Resource
    Early stages of void formation in Al-Cu lines studied using positron annihilation (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 52-54 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have applied positron annihilation spectroscopy to examine the formation of voids in SiO2-passivated 1 μm×1 μm Al-0.5 wt. % Cu lines. Samples were heat-treated both ex situ and in the positron beam to monitor void formation as a function of time and temperature. By measuring the fraction of 3-γ annihilations (a sensitive indicator of large open volume defects) we have established that voids are present at the interface between the Al alloy lines and the SiO2 passivation before heat treatment. The 3-γ fraction then grows to a maximum in less than 1 h at a temperature of 300 °C. Changes in the Doppler-broadening S parameter are also observed. Studies are underway to apply the same methodology to investigate electromigration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.113071
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  • 4
    Electronic Resource
    Electronic Resource
    Effect of annealing on the defect structure in a-SiC:H films (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 2216-2223 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The annealing behavior of amorphous, hydrogenated silicon carbide films in the range 400–900 °C was studied by optical characterization methods, 15N hydrogen profiling, and defect profiling using a variable energy positron beam. The films were deposited in an electron cyclotron resonance chemical vapor deposition system using ditertiary butyl silane [SiH2(C4H9)2] as the monosource for silicon and carbon. As-deposited films were found to contain large concentrations of hydrogen, both bonded and unbonded. Under rapid thermal annealing in a N2 atmosphere, the bonded hydrogen effuses giving rise to additional Si–C bond formation and to film densification. After annealing at high temperatures in N2, a marked decrease in the total hydrogen content is observed. After annealing in vacuum, however, the hydrogen effusion promotes void formation in the films. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363049
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  • 5
    Electronic Resource
    Electronic Resource
    Positron beam study of annealed silicon nitride films (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 2458-2462 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Positron annihilation spectroscopy has been used to study silicon nitride films grown by plasma-enhanced chemical vapor deposition and annealed at different temperatures. For both silicon-rich and nitrogen-rich films, the positron line shape (S) parameter increases after annealing for 15 min at temperatures up to 700–800 °C. This is understood in terms of the fact that removal of the hydrogen by annealing leads to the presence of unpassivated silicon dangling bond sites and vacancy complexes. Annealing at higher temperatures leads to a reduction in the S parameter, consistent with further hydrogen removal producing unpassivated N− sites. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361173
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  • 6
    Electronic Resource
    Electronic Resource
    Si ion implantation-induced damage in fused silica probed by variable-energy positrons (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 9022-9028 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Samples of synthetic fused silica have been implanted at room temperature with silicon ions of energy 1.5 MeV. Fluences ranged from 1011 to 1013 cm−2. Samples were probed using variable-energy positron annihilation spectroscopy. The Doppler-broadening S parameter corresponding to the implanted region decreased with increasing fluence and saturated at a fluence of 1013 cm−2. It is shown that the decrease in the S parameter is due to the suppression of positronium (Ps) which is formed in the preimplanted material, due to the competing process of implantation-induced trapping of positrons. In order to satisfactorily model the positron data it was necessary to account for positron trapping due to defects created by both electronic and nuclear stopping of the implanted ions. Annealing of the 1013 cm−2 sample resulted in measurable recovery of the preimplanted S parameter spectrum at 350 °C and complete recovery to the preimplanted condition at 600 °C. Volume compaction was also observed after implantation. Upon annealing, the compaction was seen to decrease by 75%. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362579
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  • 7
    Electronic Resource
    Electronic Resource
    Positron study of plasma-enhanced chemical vapor deposited silicon nitride films (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 2568-2574 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Positron annihilation spectroscopy has been combined with Auger electron depth profiling, elastic recoil detection, Fourier-transform infrared spectroscopy, and capacitance-voltage measurements to study silicon nitride films grown by plasma-enhanced chemical vapor deposition. For silicon-rich films the positron lineshape parameter is very close to that of undefected silicon, consistent with a strong hydrogen passivation effect. With increasing nitrogen content in the films, there is an increase in the number of unpassivated vacancy complexes available to trap positrons prior to annihilation. Detailed analysis gives a measure of the electric field induced in the silicon substrate by the presence of charge trapped in the silicon nitride near the interface. These results agree qualitatively with electrical measurements. Both the charge and the electric field are found to decrease with increasing nitrogen content. Incorporation of a small amount of oxygen in the films leads to a suppression of the feature in the positron spectrum associated with vacancy complexes in favor of a spectrum typical of oxygen related defects. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360115
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  • 8
    Electronic Resource
    Electronic Resource
    Assessment of the normalization procedure used for interlaboratory comparisons of positron beam measurements (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 342-345 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Variable-energy positron annihilation data from ion implanted and unirradiated Si and SiO2 were obtained at five separate laboratories. Line-shape analysis of the 511 keV annihilation γ rays yielded normalized S parameter signatures for radiation defect distributions in both types of samples. Laboratory-to-laboratory variations are found which, although small, lie outside the expected range of reproducibility. Large variations found in the extracted values for positron diffusion lengths L+ in silicon are identified and thought to arise from differences in sample surface conditions. Possible sources of the observed discrepancies are discussed, together with methods for reducing them. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370735
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  • 9
    Electronic Resource
    Electronic Resource
    Charge states of divacancies in self-implanted doped Si (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 5991-5996 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The charge states of divacancies induced by 5 MeV self-implantation of doped silicon were investigated by positron annihilation methods. For low doping concentrations, results were found to be in agreement with the predictions of Fermi statistics. For the case of heavily boron-doped silicon (nB=1×1019 cm−3) an anomalous single-negative divacancy charge state was detected. We attribute this to the introduction of new levels in the band gap, due to the capture of boron by divacancies, resulting in a boron-divacancy complex. Detailed analysis of positron annihilation spectra suggests that the boron does not reside on a nearest-neighbor site to the divacancy. Isothermal annealing experiments yield activation energy of 0.9±0.1 eV for migration of this defect. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1363682
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  • 10
    Electronic Resource
    Electronic Resource
    Positron annihilation study of defects in boron implanted silicon (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 7685-7691 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Defects and their annealing behavior in boron implanted silicon have been studied using positron annihilation spectroscopy (PAS), ion channeling, nuclear reaction analysis, and transmission electron microscopy. Silicon wafers were implanted with 80 keV boron ions to fluences from 1012 to 1015 cm−2. Furnace annealing or rapid thermal annealing (RTA) of the implanted Si samples was conducted to temperatures in the range 750–950 °C in a N2 ambient. For as-implanted samples, the defect profiles extracted from PAS spectra were found to extend beyond the implanted boron distribution given by TRIM calculations. The Sdefect/Sbulk values increased monotonically with increasing boron fluences. For boron fluences ≥1013 cm−2,Sdefect/Sbulk was found to be 〉1.04 (the characteristic value for divacancy), while Sdefect/Sbulk was found to be 〈1.04 for a boron fluence of 1012 cm−2. After annealing at 750 °C, all B-implanted samples had similar S-parameter values in the near-surface region, while in the deep region the S values for high B fluences (φ≥1014 cm−2) were found to be lower than those for low B fluences (φ≤1013 cm−2). Annealing at 950 °C did not change the S-parameter data for the lowest boron fluence (1012 cm−2), but caused a slight increase of the S parameters in the deep region for other boron fluences. RTA at 750 °C shows that major defects in B-implanted Si are annealed out within the first 3 s. An interesting transient annealing behavior is observed in which the S value decreases in the initial annealing stage, and then increases to a saturating value after prolonged annealing. Possible effects of electric fields resulting from the electrical activation of implanted boron on the behavior of positron annihilation line shapes after annealing are discussed. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373441
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