Jun-ichi Chikawa

Solid-Phase Epitaxy with X-Ray Irradiation to Grow Dislocation-Free Silicon Films at Low Temperatures

Amorphous silicon films with a thickness of 300 nm were deposited on silicon wafers. They were irradiated on a water-cooled specimen holder by X-rays using synchrotron radiation. The irradiation effect was investigated by Raman spectroscopy and electron microscopy. It was found that the irradiation at room temperature greatly enhanced homogeneous nucleation in post-annealing at 600°C. X-ray irradiation with a 54-pole wiggler heated the films up to about 500°C, and dislocation-free films were grown epitaxially within 10 min. This irradiation effect on crystal growth is explained by assuming that vacancy-interstitial pairs are formed with X-ray irradiation by Auger processes.

Invited) Swirl Defects in Silicon Crystals

The current understanding of microdefects in a striated distribution (swirls) in dislocation-free crystals is reviewed with focusing on their formation mechanism. In float-zoned crystals, their formation is due to clustering of self-interstitials and/or impurity segregation which depend upon both growth conditions and cooling processes. A model for the origin of self-interstitials is proposed which is based on the in-situ X-ray topographic observation that liquid drops are formed inside of crystals by superheating and microdefects are generated by their solidification. A systematic presentation of the swirl formation is attempted in the basis of this model, in contrast with other models of the non-equilibrium incorporation of interstitials at the growth interface and the predominant equilibrium existence of interstitials near the melting point. For Czochralski-grown crystals, the nucleation center of oxygen precipitates is discussed in comparison with the swirl formation of float-zoned crystals.

Photochemical etching of GaAs using synchrotron radiation

The photochemical etching of gallium arsenide by chlorine was investigated using synchrotron radiation. At the substrate temperatures above 25°C, both the irradiated and nonirradiated regions were uniformly etched. In case of substrate temperatures below -25°C, highly selective etching was observed in the irradiated region. We considered that at low temperatures, etching reaction caused by gas-phase excitation is suppressed and photochemical surface reaction becomes dominant.

Microdefects and Impurities in Dislocation-Free Silicon Crystals

Microdefects in striated (swirl defects) and nonstriated distribution (D-defects) have been observed in float-zoned crystals doped with various impurities by x-ray topography following copper decoration. A new type of defects were found to be present in swirl-free and D-defect-free regions and to become invisible by doping gallium. This gallium effect led to the conclusion that they are microprecipitates produced from residual oxygen impurity in FZ crystals. Effects of various impurities on defect formation indicate that D-defects are of vacancy agglomerates. It was observed that swirl defects are formed when the temperature gradient near the interface is high, and that their formation is suppressed by doping nitrogen. Formation processes of microprecipitates, swirls, and D-defects are discussed on the basis of observation of their mutual interaction and the impurity effects.

Pulsed laser annealing of GaAs in a high-pressure argon gas ambience

Abstract Pulsed laser annealing was carried out for n-type semiconducting GaAs in air, 1 bar nitrogen, 1 bar argon, and 100 bar argon gas ambiences. Depth profiles of the atomic ratio As Ga measured by SIMS indicate that pulse annealing in air results in As loss and penetration of oxygen into the crystal, both of which affect dopant redistribution and deteriorate electrical properties of the annealed layer. High electrical activity (100%) and electron mobilities were achieved for high-dose implants of Si + (1 × 10 15 cm −2 ) by pulsed laser annealing in the high-pressure ambience.

Solid Solubilities of Group-III and Group-V Dopants in Pulsed Laser-Annealed Silicon

Surfaces, {211} and {111}, of single crystal silicon uniformly doped with phosphorus were melted by laser irradiation. The interface segregation coefficients k*s were obtained from the redistributed impurity profile as determined by secondary-ion mass spectrometry. It was found that k*=k0 for {211} surfaces and k*<k0 for {111} surfaces in the dilute range of impurity concentration, where k0 is the equilibrium segregation coefficient. The maximum solid solubility of B, Al, Ga, P, As, or Sb in silicon is explained quantitatively by assuming that atoms in the liquid phase ordering at interface are frozen during rapid solidification.

Crystal growth of silicon from X-ray excited states of the solid

Abstract Amorphous silicon films were irradiated on a water-cooled specimen holder by X-rays using synchrotron radiation. The irradiation effect was investigated by Raman spectroscopy and electron microscopy. It was found that the irradiation at room temperature greatly enhanced homogeneous nucleation in post-annealing at 600°C, whereas X-ray irradiation with a 54-pole wiggler heated the films up to about 500°C, and dislocation-free films with a thickness of 300 nm were grown epitaxially within 10 min. When dose rates exceeded the growth threshold, the growth rate depended on dose rates and weakly on growth temperature. A growth rate of 10-5 cm/s at 500°C was achieved by the X-ray irradiation which was 3 orders of magnitude higher than that of thermal solid-phase growth at the same temperature. Impurity segregation at the growth interface took place as observed in the melt growth. The irradiation effect is non-thermal and leads to crystal growth from an “excited structure” which is considered to have vacancies and self-interstitials at very high densities formed by inner-shell excitation of silicon.

Impurity Incorporation at Melt-Crystal Interfaces in Pulsed Laser Annealing of Silicon

Segregation of P, C, and Fe impurities in laser annealed crystals was observed by secondary-ion mass spectrometry. By assuming that the interface segregation coefficients k* are equal to the equilibrium coefficients k0 even at a growth rate of V=200cm/s (for Fe, 0.01<k*<0.07), the diffusion coefficients of these melt impurities took the same value of 3×10-4 cm2/s, which agrees with the widely accepted values. The dwell time of Si atoms on the interface was found to be of the order of 10-10 s, far smaller than that postulated previously to explain the orientation-dependence of k* at a low V. The difference between laser annealing and usual crystal growth is discussed.

Solid phase epitaxy with x‐ray irradiation using a compact synchrotron radiation source AURORA

Solid phase epitaxy from the 0.2‐μm‐thick amorphous Si films, which were made by As ion implantation, was achieved by exposure to synchrotron radiation at a distance of 0.75 m from a compact synchrotron radiation source AURORA. The substrate temperature during this process was below 430 °C, not enough for thermal crystallization. We found the photon flux threshold for this x‐ray assisted crystallization to be 5×1015 photons/s mm2. The threshold may be due to the transition from the diffusion‐limited rate to the reaction‐limited rate for the annihilation of the vacancies to form the crystal. The L‐shell excitation may play a more important role than the K‐shell excitation in this case.

Low Temperature Nucleation of Silicon Crystal in Amorphous Phase with Synchrotron Radiation

Amorphous silicon filns sith a thickness of 300nn were nade by electron cycrotron resonance plasma enhanced chemical vapor deposition at hish temperatures. Raman spectroscopy revealed that micro-crystal s can be forned in these films with X-ray irradiation from synchrotron radiation at much lorer temperatures ( around 50oC ) than arb used in thermal anneal int. El ect ron spin resonance measurements shored that defects are al so introduced into amorphous phase with X-ray irradiation. Lor temperature nucleation is discussed in consideration of these defects.