Shigeru Umeno

Dependence of the Grown-in Defect Distribution on Growth Rates in Czochralski Silicon

As-grown defects in 6-inch-diameter Czochralski-silicon crystals grown under different crystal growth rate conditions (0.4, 0.7, 1.1 mm/min) were studied by means of preferential etching and IR light-scattering tomography (LST). Grown-in defect images were classified into four types as follows: (a) flow patterns (wedge-shaped etch pits), (b) IR-defect images observed by LST, (c) ringlike distributed small pits, and (d) large pits. It was found by secondary ion mass spectrometry that IR defects are oxygen precipitates. Large pit defects were identified by transmission electron microscopy as large dislocation loops with a length of about 30 µm. At growth rates from 0.7 mm/min to 1.1 mm/min, flow pattern defects and IR defects coexist inside a ringlike distributed oxidation-induced stacking fault (ring-OSF) region. However, at growth rates less than 0.7 mm/min, large pit defects were observed in the region outside the ring. Characteristic ringlike distributed small pit defects were observed on the outer periphery of the ring region. Flow pattern defects were annihilated during annealing at 1100°C, while IR defects were stable at 1250°C.

Defect Formation Behaviors in Heavily Doped Czochralski Silicon

To reveal a difference of defect formation behaviors, i.e. grown-in void formation during crystal growth and oxide precipitation in nand p-type silicon, we have investigated by using heavily boron-and arsenic-doped silicon crystals. The density of void defects in heavily boron doped silicon was decreased with a shrinking OSF-ring, but in arsenic doped silicon were increased with resistivities below 3.3mΩcm. On the other hand, for oxygen precipitation, the nucleation rate in boron doped silicon was enhanced with increasing resistivities, while decreased by one tenth in reference to lightly doped silicon for resistivities up to 4.4mΩcm in arsenic doped silicon. These contrastive phenomena between n- and p-type cannot be explained with a growth model of precipitates by an accelerated diffusion of oxygen in silicon. We believed that the nucleation rate of oxide precipitates related to a dependence of point defects on fermi level closely.

Axial Microscopic Distribution of Grown-in Defects in Czochralski-Grown Silicon Crystals

The axial microscopic distribution of grown-in defects in Czochralski silicon was studied by means of IR light scattering tomography (LST) and preferential etching. IR scattering defects (defects observed with LST) were found to degrade the gate oxide integrity yield, and the axial density distribution of IR scattering defects and flow patterns (wedge-shaped etch patterns) fluctuated with oxygen concentration fluctuations along the growth axis. However, the defect density did not depend directly on oxygen concentration. It is considered that the formation of IR scattering defects is related to the solid-liquid intertace temperature fluctuations.

Study of the Phase Transition in BaSm2Mn2O7

The existence of phase transition in BaSm2Mn2O7 was revealed by high temperature X-ray diffractometry to be near 520 K. The phase transition is largely affected by the oxygen nonstoichiometry of this compound. For stoichiometric composition this phase has an orthorhombic distortion due to Jahn-Teller effect of Mn3+ ion and is transformed into a tetragonal phase above the transition temperature. Structure of the high temperature phase is isotypic with that of the oxygen nonstoichiometric phase at room temperature; the latter has a Sr3Ti2O7-type crystal structure with double perovskite bloc.

Dependence of Grown-in Defect Behavior on Oxygen Concentration in Czochralski Silicon Crystals

The behavior of grown-in voids in the as-grown state and during annealing was investigated for Czochralski silicon wafers using an atomic force microscope, Secco etching and an optical precipitate profiler. In previous reports, most grown-in voids have been found to consist of two octahedrons. In this report, it was shown that the percentage of the voids which consist of one octahedron increased as the oxygen concentration decreased. The annealing behavior of the voids was summarized as follows. In the case of supersaturated oxygen concentration, growth of the oxide films within the voids occurred and this reduced their ability to form flow patterns during Secco etching. The growth of oxide films within the voids was enhanced by excess interstitial silicon atoms injected during annealing in an oxygen ambient. In the case of undersaturated oxygen concentration, the annihilation of the voids was also enhanced due to the injection of interstitial silicon atoms during annealing in an oxygen ambient. Interstitial silicon atoms contributed to both of these phenomena.

Transition temperature of BaEu2Mn2O7

Abstract The existence of a phase transition was confirmed near 560 K in BaEu 2 Mn 2 O 7 by high-temperature X-ray diffractometry. The orthorhombic phase which is stable below this temperature and for stoichiometric composition transforms into the tetragonal phase without any large change along the c -axis.

Relationship between Grown-in Defects in Czochralski Silicon Crystals.

The relationship between flow pattern defects (FPDs), Secco etch pit defects (SEPDs), defects detected by IR light scattering tomography (LSTDs) and defects detected by an optical precipitate profiler (OPP-defects) was investigated in the same area of as-grown and annealed wafers. It was concluded that the relationship between grown-in defects in as-grown Czochralski silicon crystals is expressed as LSTDs=OPP-defects=FPDs+SEPDs. FPDs were decreased after annealing, but LSTDs were still observed at the positions where the LSTDs were detected in the as-grown state. It was found that the origins of FPDs are not annihilated during annealing.