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Hydrogen passivation of silicon grain boundaries has been investigated by using deuterium as a readily identifiable isotope which duplicates hydrogen chemistry. Deuterium detection with high sensitivity was achieved with secondary-ion mass spectrometry. Diffusion of deuterium in single- crystal silicon and polycrystalline silicon thin films at low temperatures (e.g., 350 °C) clearly demonstrates enhanced diffusion along grain boundaries. Defects at grain boundaries were detected by electron-spin resonance and identified as silicon-dangling bonds. Deuterium passivation of grain boundaries is revealed by correlated deuterium diffusion and dangling-bond annihilation in polycrystalline silicon films.

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On unannealed, thermally oxidized silicon, electron spin resonance reveals an oriented interface defect which is termed the Pb center and identified as the trivalent silicon defect. Deep level transient spectroscopy (DLTS) reveals two broad characteristic peaks in the interface-state distribution: one ∼0.3 eV above the silicon valence-band maximum and a second ∼0.25 eV below the conduction band. Isochronal anneals of oxidized silicon, coated with aluminum, show that the spin density and the densities of the two DLTS peaks have the same annealing kinetics. On large-area, Al-gated capacitors the spin density can be modulated with an applied voltage; sweeping the silicon band gap at the interface through the Fermi level reveals that the spin density is approximately constant over the central region of the band gap but decreases near the band edges. The variation of the spin density with gate voltage identifies an amphoteric center with both electronic transitions in the band gap. Both the annealing behavior and the voltage dependence of the Pb center support the conclusion that these transitions correspond to the two characteristic peaks in the interface-state distribution. The ∼0.6 eV separation of the peaks is the effective correlation energy of the dangling orbital on a trivalent silicon defect at the Si-SiO2 interface. The similarity between the disordered interface and amorphous silicon is discussed.

It was recently proposed that hydrogen compensation of shallow-acceptor impurities in single-crystal silicon is due to the diffusion of both monatomic oxygen and hydrogen into silicon which combine at acceptor sites to form neutral acceptor-OH complexes. It is shown here that oxygen does not diffuse into silicon under the conditions of shallow-acceptor passivation. Boron-doped silicon was exposed to monatomic deuterium and mass 18 oxygen at elevated temperatures. Depth profiles of D and 18O were measured by secondary-ion mass spectrometry for comparison with the boron concentration. While D readily diffuses into silicon with the concentration nearly equal to that of the boron, no 18O was detectable above the background level. Deuterium profiles in both phosphorus-doped and boron-doped silicon further reveal high densities of deuterium, in excess of the boron concentration, which are ascribed to diffusing monatomic deuterium and deuterium that is immobilized through recombination and impurity trapping.

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Secondary-ion mass spectrometry (SIMS) has been used to measure depth profiles of deuterium in thermally grown films of SiO2 on Si. Deuterium is a readily traceable element which simulates hydrogen chemistry and thereby permits detection of effective changes in the hydrogen content of annealed oxides even in the presence of high background concentrations of hydrogen in the sputtering ambient or oxide layer. For oxidized silicon annealed in atomic deuterium, SIMS profiles clearly reveal an accumulation of deuterium at the Si-SiO2 interface. It is demonstrated that the pile-up of deuterium is not a consequence of ion migration (’’snow plowing’’) during ion sputtering.

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