Fumio Shimura

Role of Dislocations in Semi-Insulation Mechanism in Undoped LEC GaAs Crystal

For the undoped semi-insulating LEC GaAs crystal, microscopic inhomogeneity was investigated on the fixed position by using cathodoluminescence (CL), secondary ion mass spectrometry (SIMS), X-ray topography (XRT) and scanning leakage current measurement (IL). Microscale fluctuations observed in these measurements were attributed to the cellular dislocation structures. It was suggested that the impurity gettering effect of dislocation plays an important role in the semi-insulation mechanism in GaAs crystal. Carriers are inactive in the boundary region of cell structures but are active in the inner region of cell structures.

Octahedral precipitates in high temperature annealed Czochralski-grown silicon

Abstract Fine octahedral TEM images with thickness fringes were obtained for the first time in the Czochralski-grown silicon crystal annealed at 1150°C. The octahedra were investigated by means of electron diffraction and differential infrared absorption (DIR); as a result, they have been identified with amorphous SiO 2 precipitates generated by high temperature heat temperature heat treatment and the thickness fringes have been ascertained to be caused by electron diffraction effects in a matrix silicon negative crystal.

Crystal growth and fundamental properties of LiNb1−yTayyO3

Abstract LiNb1−yTayyO3 (LNT) crystals were grown by the Czochralski method under various conditions. Macroscopic defects such as cracks, bubbles and cellular structures appeared in some growing crystals. Cracks and bubbles generated in growing crystals largely depended on the pulling axis and the pulling rate, respectively. Fundamental properties, such as lattice constants, density, temperature dependence of dielectric constants and thermal expansion behavior, of LNT grown crystals were studied.

Heterogeneous distribution of interstitial oxygen in annealed Czochralski‐grown silicon crystals

It is shown that interstitial oxygen infrared (IR) absorption at 515 cm−1 decreases anomalously compared with the absorption at 1106 cm−1 in heat‐treated Czochralski‐grown silicon wafers. This phenomenon is described by the close correlation between the absorption coefficient ratio αr (α1106/α515), the half‐bandwidth of the 1106‐cm−1 peak, and the precipitated oxygen content during heat treatments. As a result, it is suggested that on the basis of IR absorption spectrum data interstitital oxygen atoms distribute heterogeneously in a silicon matrix as the forestage of Si‐0 complex precipitation.

Effect of Ultraviolet Light Irradiation on Noncontact Laser Microwave Lifetime Measurement

An ultraviolet (UV) irradiation effect on minority-carrier recombination lifetime measured by a noncontact laser/microwave (LM) method is investigated for silicon wafers with native oxide. After UV irradiation, the surface recombination velocity greatly decreased resulting in the increase in the effective recombination lifetime (τeff). The effect disappears rapidly with time after the irradiation, and τeff recovers to the initial value after several minutes at room temperature. Since the UV irradiation process is noncontact and nondestructive, the irradiation is proposed to minimize the surface effect of sample, in turn, to obtain the bulk lifetime (τb) with a noncontact LM lifetime measurement method.

Redissolution of precipitated oxygen in Czochralski‐grown silicon wafers

The redissolution behavior of precipitated oxygen in Czochralski‐grown silicon wafers during high‐temperature annealing (1230 °C) is investigated by means of infrared absorption and transmission electron microscopy. It is shown that the oxygen redissolution rate, which is 102∼103 larger than the precipitation rate, is highly dependent on the oxygen precipitation temperature which in turn determines the form of the precipitates. The dependence is described by the difference in the total surface area of precipitates and by the dislocation pinning effect.

Improved Intrinsic Gettering Technique for High-Temperature-Treated CZ Silicon Wafers

An improved intrinsic gettering (IG) technique for silicon wafers subjected to a high temperature of at least 1200°C is developed. It has been shown that multi-step annealing from low to high temperatures successively can enhance the IG effectiveness for high-temperature-annealed wafers. Moreover, this technique produces the IG ability even in a low oxygen wafer, ~11×1017 cm-3.

Dependence of Minority-Carrier Recombination Lifetime on Surface Microroughness in Silicon Wafers

The influence of silicon surface microroughness on the minority-carrier recombination life-time has been studied with a laser/microwave photoconductance technique. By means of an algorithm for separating the surface and bulk components, it has been shown that the microroughness considerably affects the surface recombination velocity, in turn the lifetime, of silicon wafers at elevated temperatures. It is found that the smoother results in the higher liletime.

Refractive indices of LiNb1−yTayO3 single crystals

The refractive indices of LiNb1−yTayO3 single crystals grown by the Czochralski method were determined in the wavelength range 5893 to 10600 A at 20 ± 0.5°C. The results indicate that a single crystal (0.95 < y < 0.96) has zero birefringence. Such composition is independent of the wavelength.

Microdefect Elimination in Reduced Pressure Epitaxy on Silicon Wafer by Back Damage ‐ Si3 N 4 Film Technique

A gettering technique which prevents microdefect formation during oxidation processes after the growth of reduced pressure Si epitaxial layer for bipolar devices is described. A gettering process which consists of protection of the back damage layer with film is proposed. A microdefect density in epi‐layers of ~102 cm−2 is obtained by back damage with the film coating technique, on the contrary, the microdefect density reaches ~106 cm−2without the film. The critical thickness of film to elminate microdefects in epi‐layers is obtained 2500 and 200A for substrates without and with back damage, respectively. It is found that the gettering action is closely correlated with induced defects in the back surface (OSF, dislocation, damage line, etc.) by sandblast‐damaging and/or film.