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Abstract. Czochralski grown silicon crystals contain interstitially dissolved oxygen which diffuses on heating to form precipitates of silica. We have examined these precipitates by small angle neutron scattering (SANS) in the Q-range 0.05 A -1 < Q < 0.4 A -1. The obtained SANS patterns reveal pronounced anisotropic intensity distributions which resemble the symmetry of the host crystal. The SANS spectra show an anisotropic central peak at Q < 0.1A-1 due to the single particle shape and a number of weak intensities for larger Q-values. These weak side maxima are considered correlation peaks or quasi-elastic interference peaks. They show, however, an unexpected and distinct temperature dependence: with decreasing temperature below values of 220 K their intensity is lost slowly, but reversibly. At T = 50 K only the central peak from the single-particle scattering remains unchanged. Upon heating, the correlation peaks regain their former value of intensity and Q-position without any evidence of thermal hysteresis.

Abstract. The formation of silicon oxide precipitates from Czochralski grown silicon depends on the time and temperature of the heat treatment as well as on the initial content of interstitially dissolved oxygen. Samples containing between 5 x 1017 Oi/cm 3 and 13 x 1017 Oi/cm 3 have been heated at 750°C for 96 h. SiO2 precipitates of various shape and size have been obtained and investigated by means of small angle neutron scattering (SANS) in the Q-range 0.05 A-~ < Q < 0.2 A-1. The obtained SANS patterns reveal a typical anisotropy of their intensity distribution, which splits into a central peak at Q < 0.1 it -1 due to the shape of the individual particles and a number of weak intensities for larger Q-values, originating from a correlation between defects, possibly between the precipitates. While these correlation peaks in the SANS patterns are seen best for rather low values of about (5-7) × 1017 Oi/cm 3 oxygen content, the central peak anisotropy is most pronounced for higher values of ca 10 x 1017 Oi/cm 3. The integrated intensity of the central peak increases with increasing initial oxygen content. For comparison, untreated samples of the same initial oxygen content do not reveal any anisotropic SAN scattering or a broadened central peak beam. 61.12Dw, 72.10, 78.50G Czochralski grown silicon crystals always contain small amounts (some 1017 Oi/cm 3) of dissolved interstitial oxygen, which diffuses and agglomerates to form SiO2 clusters upon heat treatment at 750°C for several days. In general, some substitutional carbon atoms may occupy Si lattice sites as well [1]. It is obvious that the size and shape of the SiO2 precipitates depends on the heating time and temperature and, further, on the initial concentration of chemical impurities [1]. Our samples with 5.5, 10.0, and 13.0x 1017Oi/cm3 have been heated at 950 ° C for 2 h, rapidly quenched and then aged at 750 ° C for 96 h in an Ar atmosphere. Their carbon content has been found to be less than 0.2 x 1017 Cs/cm 3 by means of infrared absorption technique [2,3]. So-called untreated samples of each oxygen concentration have been subjected to the first heating cycle only. They have then been investigated for comparison purposes. The SiO2 precipitates of platelet-or rod-like shape align predominantly in the {100} planes of the Si host crystal [2,4]. The SANS investigations were performed at room temperature on the Dll spectrometer at ILL, Grenoble, using incident neutrons with a wavelength of 2 = 8 A at 1.1 m sample-to-detector distance. Thus the accessible Q-range was up to Q _< 0.22/~k -1. The samples were aligned with their (100) or (110) axis parallel to the incoming neutron beam. PACS:The SANS patterns obtained from the heat-treated samples always show a pronounced anisotropy of their intensity distribution. Detailed results about the anisotropy of the SANS patterns for our samples and of the temperature dependence were reported in a recent paper [5]. Most of the results have been obtained for a sample with 7.0 x 1017 Oi/cm 3, i.e. of intermediate oxyg...