K. L. Brower

29Si hyperfine structure of unpaired spins at the Si/SiO2 interface

The hyperfine spectrum associated with unpaired electrons at the (111) Si/SiO2 interface (Pb centers) is reported for the first time. Electron paramagnetic resonance measurements indicate that the hyperfine interaction S↘⋅A⋅I↘ arises from the 29Si isotope and is characterized by A∥=146.(±5.)×10−4 cm−1 and A⊥=85.(±8.)×10−4 cm−1. An analysis of this hyperfine interaction firmly establishes many of the details in the structure of this interface defect.

Chemical kinetics of hydrogen and (111) Si‐SiO2 interface defects

Electron paramagnetic resonance (EPR) measurements and theoretical considerations have yielded a unified model for the hydrogen chemistry of silicon dangling bond Pb defects at the (111)  Si‐SiO2 interface. Previous EPR measurements indicated that passivation of Pb centers with H2 proceeds by the reaction H2+Pb→HPb+H with an activation energy of 1.66±0.06 eV. New EPR studies reported here show that HPb centers dissociate by the reaction HPb→Pb+H with an activation energy of 2.56±0.06 eV. When combined, these two reactions yield H2→H+H, which in vacuum requires an energy input of 4.52 eV. Comparison of these energies indicates that the reverse reactions H+HPb→Pb+H2 and H+Pb→HPb occur with essentially no energy barrier and are controlled by the local availability of atomic hydrogen.

Defects and impurities in thermal oxides on silicon

Oxides grown at 1100 °C in dry oxygen for 60 min to a thickness of 1350 A on silicon with and without subsequent forming gas anneals were 60Co γ irradiated at 4 K with doses up to 106 rad (Si). In situ electron paramagnetic resonance measurements at 10 K revealed ≊3×1017 atomic hydrogen/cm3 and ∼1017 oxygen‐hole centers/cm3 in the oxide. The paramagnetic dangling bond on the silicon side of the Si/SiO2 interface (Pb center) was also observed. The (relative) concentration of these centers was measured as a function of isochronal annealing between 10 and 300 K.

Electron paramagnetic resonance of the lattice damage in oxygen‐implanted silicon

The nature of the lattice damage produced at room temperature in ion‐implanted intrinsic and n‐type silicon has been studied as a function of 160‐keV O+ ion fluence using electron paramagnetic resonance (EPR). The known EPR spectra observed were the negative divacancy (Si‐G7), the neutral vacancy‐oxygen (Si‐S1), the neutral 4‐vacancy (Si‐P3), and the isotropic resonance at g = 2.0055 which is indicative of amorphous silicon. In addition, a new spectrum, labeled Si‐S2, was observed which may be the negative 4‐vacancy. Concentrations (number/cm2) for the various paramagnetic defects were determined as a function of ion fluence for fluences ranging from 1010 to 1017 O+/cm2. From these measurements we conclude that the lattice damage produced in crystalline silicon by individual ions whose maximum calculated energy density into atomic processes is ≲ 15 eV/A ion consists of simple defects such as observed in electron‐ and neutron‐irradiated silicon. Furthermore, overlap effects in the lattice damage produced b...

Radiation-Induced Trivalent Silicon Defect Buildup at the Si-SiO2 Interface in MOS Structures

Electron spin resonance and capacitance versus voltage measurements demonstrate approximately a one-to-one correspondence between the density of radiation-induced trivalent silicon defects at the (111) Si-SiO2 interface and the density of radiation induced electronic interface states.

Passivation of paramagnetic Si‐SiO2 interface states with molecular hydrogen

Dry thermal oxides were grown on (111) silicon substrates at 850 °C. The Pb centers associated with this (111) Si‐SiO2 interface were observed with electron paramagnetic resonance to be stable under subsequent annealing in vacuum up to at least 850 °C. The rate of passivation of Pb centers with H2 was observed to be proportional to the concentration of H2 in the oxide and the density of Pb centers. The forward reaction rate constant kf is temperature dependent and obeys the Arrhenius relationship having an activation energy Ef of 1.66±0.06 eV and a pre‐exponential factor k0f of 1.94 (+2./−1.)×10−6 cm3 /s for temperatures at least between 230 and 260 °C. The linear H2 pressure dependence in the rate of passivation and the magnitude of k0f are reasonably consistent with a model in which the H2 molecule reacts directly with Pb centers during its diffusional motion among the interstices of the SiO2 network and the reaction site at Pb centers.

ELECTRON PARAMAGNETIC RESONANCE OF DEFECTS IN ION‐IMPLANTED SILICON

The first EPR measurements of the identity of defects in an ion‐implanted layer (< 15 000 A) are reported. The Si–P3 center is the dominant paramagnetic defect produced at room temperature by 400‐keV O+ implantation in Al‐ and B‐doped Lopex Si, and it anneals below 200°C. The Si–P1 center is the dominant defect remaining above 200°C, and it anneals near 350°C. Interstitial Al++ (Si–G18) are observed in the Al‐doped sample; their number indicate that Si interstitials do not migrate over large distances into the unirradiated Si. Comparison of EPR and infrared data indicates that the Si divacancy is produced in the diamagnetic neutral charge state.

DEPTH DISTRIBUTION OF EPR CENTERS IN 400‐keV O+ ION‐IMPLANTED SILICON

The depth distribution of Si‐P3 centers in 400‐keV O+ ion‐implanted silicon was determined using EPR measurements in conjunction with anodization and stripping of the implanted layer. The depth distribution of the EPR centers compares favorably to theoretical calculations by Brice for the depth distribution of the energy deposited into atomic processes and with infrared absorption measurements of the depth distribution of divacancies by Stein, Vook, and Borders. The combined EPR and infrared measurements indicate that the Fermi level in the damaged layer lies between Ec − 0.21 eV and Ev + 0.25 eV.

Dangling bonds and the Urbach tail in silicon

Electron spin resonance (ESR) and highly sensitive optical‐absorption measurements have been performed on plastically deformed silicon, polycrystalline silicon, and high interface state density, oxidized silicon samples. In the first two cases, the response of the Urbach‐like subgap optical absorption and the ‘‘dangling bond’’ ESR signal following thermal and atomic hydrogen anneals is found to be distinctly different from that reported previously for polycrystalline silicon. These data suggest that transitions of the dangling bond are not responsible for this Urbach‐like behavior. In addition, we find that removal of the interfacial silicon dangling bond by oxide stripping results in no measurable sample absorptance decreases, implying a considerably lower optical cross section than has been previously estimated for dangling bonds in the bulk.

ELECTRON PARAMAGNETIC RESONANCE OF ION‐IMPLANTED DONORS IN SILICON

The EPR of As75, Sb121, and Sb123 substitutional donors implanted in silicon have been observed. The Si‐P3 and Si‐P1 center resonances associated with the damage were also observed. Samples were implanted at room temperature to fluences of ∼ 1013 ions/cm2, and the EPR spectra associated with the damage and the implanted impurities were monitored as the samples were isochronally annealed to 970 °C. The spectra of the implanted donors were observed after the 400 °C anneal with illumination and following the 600 °C anneal without illumination. After the anneal at ∼ 900 °C, the proportion of implanted antimony that is observed by EPR to be substitutional is significantly larger than for the implanted arsenic.