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

Abstract

The suppression of oxygen precipitation in Czochralski silicon (Cz-Si) using the ultrahigh-temperature rapid thermal oxidation (ultrahigh-temperature RTO) technique was investigated by infrared (IR) tomography. The oxygen precipitate nuclei generated during crystal growth were completely dissolved, and the formation of new nuclei due to ultrahigh-temperature RTO was also restrained by controlled slowing of the cooling rate. The ultrahigh-temperature RTO technique is demonstrated to effectively control the oxygen precipitate nucleus formation to yield either uniformly distributed precipitates or completely suppressed precipitation. Our results indicate the flexible and precise control of oxygen precipitation nucleus using ultrahigh-temperature RTO technique is beneficial for device fabrication. Oxygen precipitates in Czochralski Silicon (Cz-Si) wafers effectively act as getter sites for heavy metal impurities in semiconductor devices, 1,2 and they also increase the mechanical strength of the wafer by precipitation hardening.3 Both these roles are important for stable device manufacturing, but oxygen precipitates are also responsible for decreasing the mechanical strength of the wafers if their size and density are not appropriately controlled. 4 In addition, when oxygen precipitates remain in the device formation region, they can result in failure due to current leakage. 5 For this reason, oxygen precipitation must sometimes be suppressed depending on the kind, structure, and process conditions of a semiconductor device. In particular, because of current advances in device structures such as scaling and threedimensional chip integration, precise control of oxygen precipitation will become more significant as the stress induced in Si wafers during device fabrication becomes increasingly crucial.6-8 Therefore, an effective method that can be used for either promoting or suppressing oxygen precipitation in Cz-Si crystals is needed.Many studies have been performed on methods for achieving such precise control of oxygen precipitation. However, maintaining the stability of the growing crystal both in the pulling and radial directions still remains difficult. Thus, both local and widespread nonuniformity often exists in the grown crystal. 9,10 To address this very important problem, we have proposed rapid thermal oxidation (RTO) at ultrahigh temperature (ultrahigh-temperature RTO).11 Our results obviously demonstrated that the oxygen precipitates generated during the crystal growth were dissipated entirely, and dense oxygen precipitate nuclei were formed uniformly in the radial direction during RTO at temperatures over 1350• C. We believed that the newly formed oxygen precipitates in the wafers that had been subjected to ultrahigh-temperature RTO were closely related to preserved vacancies. In particular, each oxygen precipitate nucleus is thought to consist of an oxygen-vacancy complex (for example, O 2 V). 12Ultrahigh-temperature annealing using rapid thermal processing (RTP) has great advantages in terms of uniformit...

Near‐Surface Defect Control by Vacancy Injecting/Out‐Diffusing Rapid Thermal Annealing

“…The inclusion of a pre‐step at temperatures >1210 °C in an Ar/O 2 ambient before nitriding is useful as the wafer can further homogenize and increase the BMD‐denuded zone, as small grown‐in BMDs (≤12 nm) are dissolved near the surface and in the bulk. This dissolution of BMD nuclei starts lower in temperature as described by Sudo et al and Araki et al, respectively …”

“…This dissolution of BMD nuclei starts lower in temperature as described by Sudo et al [17,18] and Araki et al, respectively. [14,15]…”

“…Recently, the oxygen precipitation behavior and defect annihilation of grown-in voids were studied above 1300 C by Araki et al [14,15] They found that even under these oxidizing ambient the BMD formation occurred and in parallel void formation was possible. The complex interplay of interstitial supersaturation and in parallel oxygen precipitate nuclei formation by vacancies was simulated and the needed thermal conditions for nucleation and void dissolution were simulated by Sudo and co-workers.…”

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

“…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.…”

“…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.…”