Hiroshi Yamada-Kaneta

Observation of Low-Temperature Elastic Softening due to Vacancy in Crystalline Silicon

In challenging a direct observation of the vacancy in crystalline silicon, we have carried out low-temperature ultrasonic measurements down to 20 mK. The longitudinal elastic constants of non-doped and B-doped crystalline silicons, which were grown by a floating zone (FZ) method in commercial base, reveal the elastic softening proportional to the reciprocal temperature below 20 K. The applied magnetic fields turn the elastic softening of the B-doped FZ silicon to a temperature-independent behavior, while the fields up to 16 T do not affect the elastic softening of the non-doped FZ silicon. We present a plausible scenario for this result. Namely the vacancy with the non-magnetic charge state V 0 in the non-doped silicon and the magnetic V + in the B-doped silicon is responsible for the low-temperature softening of the shear elastic constants ( C 11 - C 12 )/2 and C 44 , which can be described in terms of the quadrupole susceptibility due to the Jahn–Teller effect.

Gap states caused by oxygen precipitation in Czochralski silicon crystals

Deep level transient spectroscopy measurements have been made on both n- and p-type silicon crystals containing various types of the oxygen precipitates to investigate the associated gap states. A new signal in the gap-state density was observed at about Ec−0.25 eV, as well as the previously reported peak at about Ev+0.3 eV. Both peaks are attributed to a defect generated by oxygen precipitation. The observed distribution of the gap-state density is very similar to that of the well-known Pb center due to a dangling bond of a silicon atom at the interface between the silicon and silicon dioxide at the surface of the sample. The measured gap states could be passivated by hydrogen, as found for the Pb center.

Influence of Grown-in Hydrogen on Thermal Donor Formation and Oxygen Precipitation in Czochralski Silicon Crystals

Using hydrogen-enhanced thermal donor formation and hydrogen-enhanced oxygen precipitate nuclei formation, we confirmed the presence of hydrogen in as-grown Czochralski (CZ) silicon (Si) ingots. Hydrogen concentrations in as-grown ingots were very low at 2.5×1011 cm-3. We found that even such a small amount of hydrogen influences the quality of as-grown CZ Si crystals due to hydrogen-enhanced oxygen precipitate nuclei formation caused by in situ annealing during crystal growth. Reducing hydrogen contamination during crystal growth is important in obtaining high-quality CZ Si crystals.

Electron spin resonance centers associated with oxygen precipitates in Czochralski silicon crystals

We have previously concluded that the oxygen-precipitate-associated defects that we identified by the deep levels at Ev+0.30 eV and Ec−0.25 eV were the Pb centers generated in the interface between the oxygen precipitates and the surrounding silicon crystal lattice [M. Koizuka and H. Yamada-Kaneta, J. Appl. Phys. 84, 4255 (1998)]. In order to confirm this conclusion, we have made electron spin resonance (ESR) measurements on the Czochralski-grown silicon crystals containing the oxygen precipitates generated by the two-step anneals of 500 °C, 20 h+700 °C, 60 h. We have found the ESR lines whose g values well coincide with those of the Pb0 and Pb1 centers. Thus it has been clarified that the Pb0 and Pb1 centers are generated by the oxygen precipitation as well as by the thermal oxidation. The present successful application of the ESR method to the annealed silicon crystals suggests that it can be a useful tool to characterize the precipitation state of the oxygen in silicon.

ANNEALING BEHAVIOR AND ATOMIC COMPOSITION OF SUBSTITUTIONAL CARBON-OXYGEN COMPLEXES IN SILICON CRYSTALS

We investigated the annealing behavior of the infrared‐absorption peaks at 1052 and 1099 cm−1 due to C–OB complex, and those at 1112 and 1026 cm−1 due to C–OC complex. Similar to previous observations [Y. Shirakawa, H. Yamada‐Kaneta, and H. Mori, J. Appl. Phys. 77, 41 (1995)], the formation‐dissociation reaction of C–OB and C–OC complexes rapidly reaches the quasithermal‐equilibrium state at the onset of annealing. Based upon the mass action law, it is suggested that the formation of the C–OB and C–OC complexes involves one carbon atom and two and three oxygen atoms, respectively.

Annealing behavior of carbon‐oxygen complexes in silicon crystals observed by low‐temperature infrared absorption

A low‐temperature infrared‐absorption study has been performed to investigate the annealing behavior of the carbon‐oxygen complexes causing the peaks at 1104 cm−1 (C‐OA complex) and 1108 cm−1 (C‐OD complex). Upon annealing, the concentrations of the C‐OA and C‐OD complexes quickly reach the quasithermal‐equilibrium values described by the mass‐action law. The obtained formulas of this mass‐action law indicate that both of these two complexes involve a carbon atom and an oxygen atom. For the annealing temperatures higher than 800 °C, the quasithermal‐equilibrium concentration of the C‐OA complex increases with increasing temperature. A hypothetical explanation is proposed for this unusual temperature dependence.

Elastic calculation of the thermal strains and stresses of the multilayered plate

An elastic calculation has been carried out on the thermal deformation strains, and stresses of a multilayered plate (MLP) which is composed of a circular substrate and thin films on it. The MLP is assumed to be constructed with no initial stresses at a temperature T0, and to be given a temperature change ΔT. In the calculation, the variation method has been utilized in such a manner as to minimize the total Helmholtz‐free energy of the MLP by varying its shape of deformation. Without using the assumption of the plane stress state, a closed form solution has been obtained which determines the radius of curvature of the warpage, strains eij (i, j=x,y,z) and stresses τij in each layer by ΔT, αm the thermal expansion coefficient, Em the Young’s modulus, σm the Poisson’s ratio, and tm the thickness of each layer. The solution obtained has reproduced the plane stress state as an approximate description of the deformation. A solution in the case of the large radius MLP, where the effect of the shear strains has...

Vibrational energy levels of oxygen in silicon up to one-A2u-phonon plus one-A1g-phonon states

We have measured infrared absorptions by the Si-O-Si centers in the 600- and 1800-cm -1 regions. Besides the previously reported lines at 648.2 and ∼658 cm -1 , we observed the new lines at 668.0, 588.4, ∼580, and ∼571 cm -1 , and the silicon isotope lines at 643.2 and 638.5 cm -1 . We also found a new line at 1831.3 cm -1 . We assigned these lines to the transitions from the lower energy levels that had been fixed previously, to find two new groups of energy levels belonging to the one-A 1g -phonon state and the one-A 1g -phonon plus one-A 2u -phonon state, respectively. This indicates that the A 1g -mode coupling, as well as the A 2u -mode coupling, is essential for describing the total energy levels. The transitions causing the lines around 600 cm -1 create an A 1g phonon, exciting or deexciting the 30-cm -1 mode of the oxygen, and those causing the lines around 1800 cm -1 simultaneously excite the A 1g phonon, the A 2u phonon, and the 30-cm -1 mode.

Annealing Behavior of Interstitial Nitrogen Pair in Czochralski Silicon Observed by Infrared Absorption Method

Annealing behaviors of interstitial nitrogen pairs (N-N pairs) in Czochralski (CZ) silicon are investigated by infrared absorption measurement. The annealing processes at 1000°C and 1100°C decrease the intensity of the infrared absorption peak at 963 cm-1, which is caused by the N-N pairs. The 963 cm-1 peak disappears during the annealing processes at 1000°C and 1100°C for 90 min and 30 min, respectively. It is proposed that the N-N pairs aggregate on grown-in void defects and/or grown-in oxide precipitates during annealing.

Technique for determination of nitrogen concentration in Czochralski silicon by infrared absorption measurement

A new method is proposed for the determination of the nitrogen (N) concentration in Czochralski silicon by infrared absorption measurement. Two specimens for the determination are cut from the same N-doped Czochralski silicon (wafer). They are subjected to isothermal annealing at 600°C and 750°C for 2 h and quenched in air to hold the quasithermal-equilibrium state in the formation-dissociation reaction of N-related defects. The absorption coefficient of the infrared absorption peak in the differential spectrum between annealed samples is proportional to the total N concentration. The calibration curve between the absorption coefficient and total N concentration is obtained, which is expressed as N/cm3=4.07×1017/cm2 × absorption coefficient of the 963 cm-1 peak.