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Fig. 5.Energy requirement, exergy loss and CO 2 emission for producing cold water of 1 GJ at 7°C for the heat supplying methods in cases 3-1 and 3-2.

The effect of ultrahigh temperature rapid thermal oxidation (RTO) on the behavior of oxygen precipitates in Czochralski silicon (Cz-Si) wafers was investigated using infrared (IR) tomography. Dense oxygen precipitate nuclei were formed in the bulk of the Cz-Si wafers when the treatment temperature was increased to 1350 • C. Furthermore, when ultrahigh-temperature RTO was combined with cooling rates of over 50 • C/s, the density of the oxygen precipitate along the radial direction exhibited significant uniformity. It is assumed that the tendency to form oxygen precipitates in Cz-Si wafers during RTO critically depends upon increasing the concentrations of vacancies that form under ultrahigh-temperature conditions and an oxygen atmosphere. Our results clearly indicate that highly dense oxygen precipitate nuclei can uniformly form along the radial direction of the Si wafer during rapid cooling after RTO at temperatures above 1350 • C.Oxygen precipitates in Czochralski silicon (Cz-Si) wafers, which effectively act as getter sites of impurities, are one of the most important characteristics that enable the fabrication of consistently stable devices. 1,2 However, they are also responsible for decreasing the mechanical strength of Cz-Si wafers if the size and density are not appropriately established. 3 For this reason, strict and highly accurate control of oxygen precipitates over the entire span of a Cz-Si wafer is necessary in order to develop advanced semiconductor devices. In particular, for semiconductor devices that require complicated structural enhancements such as scaling and three-dimensional chip integration, new technology for controlling oxygen precipitates will gain more significance, specifically because endurance against the stress induced in Si wafers during device fabrication is becoming increasingly crucial. [4][5][6] The behavior of oxygen precipitates in Cz-Si crystals is closely related to point defects such as vacancies and interstitial Si atoms. [7][8][9] Vacancies promote the formation of oxygen precipitates because their nucleus is formed as a complex between oxygen atoms (O) and vacancies (Va); for instance, in the form of O 2 Va. Therefore, controlling point defects during Cz-Si crystal growth has been extensively studied. 7-9 Maeda et al. 7 investigated the relation between the density of oxygen precipitate nuclei and the cooling rate used during CzSi crystal growth at approximately 1100 • C. Their results indicated the importance of vacancy survival by void aggregation during the cooling process, which results in the formation of oxygen precipitate nuclei. V/G (i.e., the ratio of the rate of crystal growth (V) to the axis temperature gradient (G) in the neighborhood of the growth interface) is suggested to be the key parameter that determines the excess number of point defects that form during Cz-Si crystal growth. 8 It has previously been reported that a whole defect-free domain can be formed in a Cz-Si crystal by appropriately structuring the hot zone in pulling furnace so that the distr...

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