Abstract
In order to clarify the role of carbon regarding interstitial oxygen precipitation and secondary defect formation in a CZ silicon crystal, we performed various nucleating preanneals for carbon-doped (intentional) crystals and examined microdefect formation and the perfectness of the denuded zone by selective etching, TEM observation and spreading-resustance measurements following donor formation and angle lapping near the surface. In a high carbon content crystal many anomalies such as etch-pit density reduction, thermal-donor formation at 1000°C and large defect formation below the surface were observed. Carbon atoms acted as oxygen-precipitation nuclei, resulting the generation of a very small precipitate, which induced a low-density secondary defect and partly acted as a high-temperature donor. At an appropriate [Oi]/[C] ratio near the surface, large oxides were formed with secondary defects. The favorable carbon content for gettering site formation during a short time was estimated from these experiments.
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