The Effect of D-Defect in Silicon Single Crystal on Oxygen Precipitation
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THE EFFECT OF D-DEFECT IN SILICON SINGLE CRYSTAL ON OXYGEN PRECIPITATION
I. FUSEGAWA, N. FUJIMAKI AND H. YAMAGISHI Isobe R&D Center Shin-Etsu Handotai Co., Annaka, Gunma 379-01, Japan
Ltd.,
Isobe 2-13-1,
ABSTRACT of D-defect in CZ silicon We investigated the effect single crystals on the oxygen precipitation by two-step thermal treatments consisting of the first annealing in nitrogen ambient at 1073K and the second annealing in dry oxygen ambient at 1273K. The density of D-defect was measured by counting "flow patterns" using an optical microscope after preferential etching in Secco's solution for 30 minutes. It was found that the amount of oxygen precipitation along the growth axis was not affected by D-defect. The predominant factor of the oxygen precipitation after the two-step thermal process is the nuclei of oxygen precipitation generated around 723K during CZ crystal growth. INTRODUCTION We reported that a distribution profile of precipitated oxygen concentration ([AOi]) along a growth axis of CZ silicon single crystal could be made uniform by adding a preannealing at 723K for several hours [1]. However, there is a possibility that point defects such as vacancies in silicon single crystals enhance the oxygen precipitation according to the following reaction; 2Si + 201 + Vacancy
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SiO2 + Siinterst.
(1)
Roksnoer et al [2] and Abe et al [3] showed that an uniform D-defect was generated in a FZ crystal when its growth rate was fast. Harada et al showed that D-defect was also generated in a CZ crystal [4]. Abe investigated such defects in detail by a technic involving inner diffusions of vacancies or of interstitial silicon atoms after annealing in various kinds of ambient [5]. He reported that D-defect contained a vacancy agglomerate. Recently, we developed a preferential chemical etching technic for revealing D-defect [6]. We could recognize wedge shaped "flow patterns" only in D region both of FZ crystal and of CZ one, using the same crystals as Abe et al [3] or as Harada et al [4], respectively. The density of these "flow patterns" [FPD] had strong dependency on the growth rate and reduced according to the decreasing of the growth rate, as the same results by a copper recognition technic [2][3]. These patterns became invisible all over a wafer after annealing at 1473K for 2 hrs in oxygen ambient. A gate oxide integrity was improved when [FPD] became lower. These phenomena were observed both in FZ and in CZ crystals. Therefore, we considered that Ddefect could be distinguished by this technic and the density of D-defect could be measured relatively by counting [FPD] using an optical microscope. Mat. Res. Soc. Symp. Proc. Vol. 262. ©1992 Materials Research Society
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In this paper we investigated the effect of D-defect on the oxygen precipitation, using this revealing technic. EXPERIMENTAL We grew four types of oriented silicon single crystals of 6" diameter, as shown in Table 1. Their ingot length was 50 cm or 90 cm to obtain different thermal history during CZ crystal growth. Their growth rates were
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