Masahiko Okui

Formation Behavior of Infrared Light Scattering Defects in Silicon during Czochralski Crystal Growth

The formation behavior of grown-in defects which are considered to be oxygen precipitates formed during CZ-Si crystal growth, was investigated by means of infrared light scattering tomography. The following results were obtained. (i) The density of the IR light scattering defects decreases with a reduction in the crystal pulling rate. (ii) The defects are not formed just after solidification, but they grow to a size detectable by LST during cooling to about 1100°C. (iii) The defect density decreases by slow cooling in the temperature range from to 1500 to 1000°C, while their size increases. The formation mechanism of the defects was qualitatively discussed from the point of view of the interaction between oxygen atoms and point defects by a consideration of the free energy change and the critical radii of nuclei for oxygen precipitation. It was suggested that the formation of the defects depends on the vacancy concentration. In the case of a constant vacancy concentration, their density and size are determined by the cooling rate in the temperature range from 1150 to 1000°C.

Effect of Rapid Thermal Annealing on Oxygen Precipitation Behavior in Silicon Wafers

The effect of rapid thermal annealing (RTA) on oxygen precipitation behavior in Czochralski silicon wafers was investigated with an emphasis on the RTA ambient, temperature and cooling rate. It was found that (i) anomalous oxygen precipitation (AOP) was observed in the case of RTA temperature at 1240°C with cooling rates of 25°C/s in Ar and in the case of RTA temperature at 1200°C with cooling rates of 5°C/s in N2, while AOP was not observed in O2, (ii) an M-like depth profile of precipitate density appeared for the cooling rates of 50°C/s in Ar, and 25°C/s in N2, and (iii) the width of the precipitate denuded zone was larger than the width of outdiffused oxygen in the case of RTA in Ar. The relationships of thermal equilibrium concentrations CJ* and diffusion constants DJ were estimated to be CI* DV (I: interstitial, V: vacancy) from the experimental results of RTA in Ar and the calculated results using the Voronkov model.

A Model for the Formation of Oxidation-Induced Stacking Faults in Czochralski Silicon

The mechanism of oxidation-induced stacking fault (OSF) formation in Czochralski silicon (CZ-Si) crystals was investigated by transmission electron microscopy observations of the initial stages of OSF growth. OSFs were observed to be always generated at one of the edges of platelet oxygen precipitates. We observed previously that these platelet oxygen precititates had an expansive strain field in the direction parallel to the precipitate plate and a compressive strain field normal to the plate. Silicon self-interstitials having compressive strain are probably attracted to the expansive strain field of the precipitates, and condense to form stacking faults. A new model for OSF generation is presented taking into consideration the strain field around self-interstitials and oxygen precipitates.

Effect of rapid thermal annealing on oxide precipitation behavior in silicon crystal

Abstract Oxide precipitation behavior after rapid thermal annealing (RTA) in Ar, N2 or O2 ambient was investigated. Lightly boron-, nitrogen- or carbon-doped p-CZ silicon wafers with a diameter of 200 mm ( [ O i ]=11.5–13.9×10 17 atoms / cm 3 (old ASTM)) were prepared as samples. RTA temperature and cooling rate were changed between 1280 and 1200 °C, and between 70 and 5 °C/s, respectively. From the result of in Ar ambient, it was found that (1) M-like depth profile of precipitate density was observed in the lightly boron-doped wafer, (2) width of precipitate denuded zone (DZ) was decreased in the nitrogen-doped wafer compared with the lightly boron-doped wafer and (3) DZ width in the carbon-doped wafer was comparable to lightly boron-doped wafer. From the calculated result of the depth profile of vacancy (V) and silicon interstitial (I) concentrations, CV and CI, it was clarified that the relationships of thermal equilibrium concentration and the diffusion constant of point defects are to be C V ∗ >C I ∗ and DV

Determination of the criteria for nucleation of ring-OSF from small as-grown oxygen precipitates in CZ-Si crystals

The behaviour of small as-grown platelet-type oxygen precipitates, known to nucleate ring-like distributed oxidation induced stacking faults (ring-OSF), was studied in CZ-Si crystals grown with modulating growth rates using IR light scattering tomography, μ-photoconductive decay lifetime analysis and preferential etching. It was found that although these oxygen precipitates were observed on the ring region, their OSF nucleation ability differed greatly depending on the crystal growth conditions. We propose that the OSF nucleation ability of an oxygen precipitate depends on its size, and in order for successful OSF nucleation, the precipitate size must lie within certain limits. Using the difference in the thermal histories of the crystals grown with modulating growth rates, we calculated that only platelet-type oxygen precipitates on the ring-OSF region having a length between 260 and 1350 A are capable of OSF nucleation.

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.