Evaluation of Microdefects in As-Grown Silicon Crystals
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EVALUATION
OF
MICRODEFECTS
IN
AS-GROWN
SILICON
H. TAKENO, S. USHIO AND T. TAKENAKA SEH Isobe R&D Center, Shin-Etsu Handotai Co.,Ltd., Annaka-shi, Gunma 379-01, Japan
CRYSTALS
2-13-1 Isobe,
ABSTRACT Microdefects, revealed as "flow patterns" by preferential etching using Secco's etchant, in as-grown silicon crystals have been investigated by means of a transmission electron microscopy and a preferential etching. In as-grown CZ crystals, grown at the pulling speeds of 0.4 or 1.4 mm/min, dislocation loops and clusters were observed with TEM. The dislocation loops in both type. From a thermal behavior of flow crystals are interstitial patterns by heat treatments, we confirmed that the defects revealed as flow patterns in CZ crystals do not have a similar nature of that in D-defect region of FZ crystals. INTRODUCTION Microdefects in macroscopically dislocation-free silicon crystals have been extensively investigated for a long time. In the case of floating-zone(FZ) silicon crystals, mainly two types of microdefects have been well-known, i.e. striated A-defects and non-striated D-defects. A-defects were shown to be dislocation loops or loop clusters of interstitial type with the help of transmission electron microscope(TEM) [1,2]. On the other hand, D-defects have been presumed to be vacancy clusters (3-5], whereas D-defects of vacancy type have not ever been observed by TEM. So far only one observation result of D-defects by TEM was reported. The result showed that D-defects in FZ crystals grown at pulling speed of 6 mm/min were interstitial type [6]. Concerning the microdefects in Czochralski(CZ) silicon crystals, interstitial type dislocation loops(A-defects) and vacancy type precipitates(B-defects), which show striated distribution, have been observed (7]. It is believed that D-defects are not detected as any etch pit feature by means of preferential etching without metal decoration. However, recently it was reported that D-defects in silicon crystals are revealed by preferential etching using Secco's etchant, as a wedge shaped etched pattern named as "flow pattern" (8] . The flow pattern is a characteristic pattern appeared in D-defect region of FZ crystals, and this pattern also appears in CZ crystals grown at fast pulling speed. Moreover, flow pattern density depends on a crystal pulling speed. In this study, we characterized the microdefects revealed as flow pattern in as-grown CZ silicon crystals by means of TEM. In order to compare the natures of defects revealed as flow pattern in CZ crystals with those in FZ crystals, we studied their thermal behavior by heat treatments in dry oxygen or nitrogen ambients.
Mat. Res. Soc. Symp. Proc. Vol. 262. 01992 Materials Research Society
52
EXPERIMENTAL Boron-doped 10 ohm-cm, 4 inches in diameter and oriented CZ and FZ crystals were used in this experiment. CZ crystals were grown at the pulling speeds of 0.4 or 1.4 mm/min. The initial interstitial oxygen concentration of CZ crystals were around 7.1x10 1 7 atoms/cm3 (ASTM F121-80). FZ crystals, which contained A
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