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Annaka, Japan

The main purpose of this paper is to confirm the conclusion of a previous manuscript that the generation of silicon interstitials is the result of the relaxation of the lattice strain induced due to the thermal gradient. In this paper, we consider the relaxation of the lattice strain from a different point of view due to impurity doping during FZ crystal growth. Doping with nitrogen molecules annihilates both the A and D defects, which are the secondary defects of silicon interstitial and vacancy, respectively. The first half of this paper describes such peculiar behavior of nitrogen molecules in crystals doped with both a high concentration of vacancies and nitrogen molecules. The following four important values: the estimated vacancy concentrations, the deep levels at 0.44 eV under the conduction band for n-type and at 0.66 eV over the valence band for p-type for pure vacancies and the diffusion coefficient of the silicon interstitials DI-FZ=1.3 exp(-4.5 eV/kT) are determined. The last half of the paper demonstrates how impurity doping is systematically correlated with the generation and annihilation of point defects. This phenomenon occurs in accordance with Vegards law as tested with seven kinds of impurities, which have covalent bonding radii that are smaller or larger than that of silicon. Silicon interstitials are generated by doping with impurities that have smaller covalent bonding radii than silicon to maintain the essential lattice constant of silicon at around 1300 °C, and vacancies are increased above the equilibrium concentration by doping with impurities that have larger covalent bonding radii than silicon. © 2011 Elsevier B.V. All rights reserved. Source


Abe T.,Isobe R and nter | Takahashi T.,Isobe R and nter | Shirai K.,Osaka University | Zhang X.W.,High Energy Accelerator Research Organization
Journal of Crystal Growth | Year: 2016

In conventional CZ crystal growth, since formation of a cone tail takes a long time, from such a crystal to have been subject the long heat treatment it is not possible to observe actual distribution of vacancies (Vs) and interstitial atoms (Is) in a straight body of a crystal during growth. This experiment attempted to observe point defect distribution frozen by rapidly cooling a crystal that had been detached from a melt during growth to eliminate the effect of the time delay. Comparison between the experimental results of these specimens and the defect distributions of a conventionally pulled crystals revealed that Vs are introduced at a growth interface and the concentration of the Vs does not depend on the pulling rate. In addition, when the pulling rate is low, Is are generated by thermal stress which increases with increasing thermal gradient G because the amount of heat transfer by mass transfer is decreased and the crystal surface near the growth interface is cooled for longer period. As a result, the generation of Is due to the increase of the thermal stress is observed in an area referred to as an interstitial generation area (IGA) located above the vacancy region on the growth interface, where the crystal temperature is 1300 °C or more. This paper describes the recombination (Rc) mechanism by which these Is created in the IGA are recombined with Vs transformed through the growth interface, thereby creating an observable Rc area at a location where no defect can be detected. © 2015 Elsevier B.V. All rights reserved. Source


Abe T.,Isobe R and nter | Takahashi T.,Isobe R and nter | Shirai K.,Osaka University
Journal of Crystal Growth | Year: 2016

The crystals were grown by a gradually decreased pulling rate method, a special crystal growing method, and detached from a melt during the growth so as to rapidly cool the grown crystal and then to observe the appearance and disappearance of point defects at the moment of the detachment. This observation - nearly in situ observation, as it were - revealed that vacancies (Vs) were introduced through a growth interface, and interstitials (Is) were generated at an interstitial generation area, an area at which the thermal stress was increased through the increased thermal gradient, above the growth interface. In the beginning of the gradually decreased pulling rate method, since the pulling rate was high, the Vs introduced through the growth interface remained in the crystal; as the pulling rate was decreased, the generation of the Is began from the interstitial generation area, and these interstitials were recombined with the Vs introduced through the growth interface, thereby forming a first recombination area. As the concentration of the Is increased due to a lower pulling rate, a dislocation loop region began to be formed. On the growth interface side of this dislocation loop region, a V region from the growth interface and a second recombination area were similarly formed. The formation of these two recombination areas proves that the growth interface was the V region. In this paper, the point defects and secondary defects thereof were observed by our three new observation methods and the etch-pit method used in product inspection. The results of these methods were consistent with all the above phenomenon. © 2015 Elsevier B.V. All rights reserved. Source


Abe T.,Isobe R and nter | Takahashi T.,Isobe R and nter
Journal of Crystal Growth | Year: 2011

During the growth of float-zoning (FZ) and Czochralski (CZ) Si crystals, the temperature distributions from the growth interface were measured using a two-color infrared thermometer for the FZ crystal surfaces and three thermocouples within the CZ bulk crystals. The results showed that the thermal gradient is a decreasing function of the growth rate, which forms the basis of this work. In a comparison of the shape variations in the growth interfaces observed in both FZ and CZ crystals of three different diameters, all of the results were in agreement with the above premise. In consideration of Stefans condition the premise above is discussed. One of the most important observations is that the region of increasing thermal gradient extends not only to the region grown before but also to the region afterward by stopping the pulling in FZ crystals or lowering the growth rate in CZ crystals. This phenomenon is termed the BA (before and after) effect. The growing CZ crystals are detached from the melt and rapidly cooled so that the point defects are frozen. Using the anomalous oxygen precipitation (AOP) phenomenon obtained by the above detaching, which demonstrates the existence of vacancies in the crystal, we found that the growth interface is always filled with vacancies. By increasing the thermal gradient, which can be controlled by lowering the growth rate, the vacancy (AOP) region is reduced, due to the generation of a silicon interstitial-rich region. The ratio of vacancies from the growth interface and silicon interstitials generated by the thermal gradient ultimately determines the nature of the bulk silicon crystal grown from the melt, i.e., with voids, defect-free or with dislocation loops. © 2011 Elsevier B.V. All rights reserved. Source


Abe T.,Isobe R and nter | Takahashi T.,Isobe R and nter
ECS Transactions | Year: 2010

During growth of a FZ crystal and a CZ crystal, the temperature distributions from growth interface are measured by a two color thermometer on FZ crystal surface and three thermocouples in CZ bulk crystals, respectively. Both results show that the thermal gradient is a decreasing function of growth rate which is the premise of this paper. From comparison of growth interface shape variations using three different diameter crystals of both FZ and CZ, all results do not contradict with the above premise. One of the most important facts is that the increased thermal gradient region extends not only in the already grown region but also further grown region by pulling stop in FZ and lowering growth rate in CZ crystal. In consideration of Stefan's condition the premise above is discussed. The growing CZ crystals are detached from a melt and cooled rapidly, so that the point defects are frozen. Using the AOP (anomalous oxygen precipitation) phenomenon which shows existence of vacancy in crystal, it is found that the growth interface is always filled with vacancy. By increasing of thermal gradient induced by lowering growth rate, the vacancy (AOP) region is shrunk due to generation of silicon interstitial region. The ratio between vacancies from the growth interface and the silicon interstitials generated by the thermal gradient determines the nature of the Si crystal: with void, defect-free or with dislocation-loops. ©The Electrochemical Society. Source

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