Impact of Rapid Thermal Oxidation at Ultrahigh-Temperatures on Oxygen Precipitation Behavior in Czochralski-Silicon Crystals II

Abstract

Oxygen precipitates (OPs) in a Czochralski silicon (Cz-Si) wafer can degrade the performance of semiconductor devices if they are in the active region of the Si wafer, i.e., the surface layer. On the other hand, they can improve device fabrication yield through their ability to enhance impurity gettering and through mechanical strengthening, both of which are important characteristics for semiconductor device fabrication. 1,2 Thus, the OPs must be controlled in an appropriate manner depending on the structure of the intended semiconductor devices and the production process employed. More precise and uniform control of OPs in Si wafers will be a significant factor for future advanced semiconductor devices. To understand this very important issue, we previously investigated the re-formation effect of OP nuclei using ultrahigh-temperature rapid thermal oxidation (RTO), at over 1300 ◦ C, and achieved wide and precise controllability of new OP nuclei. 3 This technique also demonstrated a remarkable ability to eliminate heterogeneity effects such as OP nuclei or related defects in the grown crystal. Ultrahigh-temperature annealing using rapid thermal processing (RTP) has significant advantages in terms of excellent temperature uniformity in the radial direction of the Si wafer as compared to the Cz-Si crystal growth process. As mentioned above, ultrahigh-temperature RTO showed a remarkable ability to control the effects of the OP nuclei. The behavior of OP nuclei in Cz-Si crystals is strongly related to point defects such as vacancies and Si interstitials. 4 Vacancies promote the formation of OP nuclei because these nuclei are formed as a complex between oxygen atoms and vacancies. It is generally known that annealing in an oxygen atmosphere is not a practical way to increase vacancy concentration because Si interstitials are dominant in the Si wafer due to the injection of Si interstitials from the oxidized surface. However, as we previously reported, 3 the behavior of OP nuclei can be controlled by changing the dominant point defects from Si interstitials to vacancies depending on the difference of each thermal equilibrium concentration at ultrahigh temperatures, even though the oxidation atmosphere is used for RTP. Furthermore, in the case of ultrahigh-temperature RTO, it is expected that Si interstitials also exist at high concentration due to the Si surface oxidation even though the dominant point defects are vacancies. Interstitial Si point defects are expected to annihilate vacancy-related defects such as void defects when enough interstitial Si atoms exist. 5 The void defects also influence the semiconductor device performance; therefore, in addition to OP control, annihilating void defects is a very important goal. It is well known that RTP in a nitrogen or argon atmosphere does not effectively annihilate void defects under the surface of the Si wafer. 6‐8 Ultrahigh-temperature RTO would gain a further advantage over RTP in a nitrogen or argon atmosphere if annihilation of void defects is confirmed. In this study, the annihilation behaviors of void defects in the case of the ultrahigh-temperature RTO were evaluated in detail.