Small angle neutron scattering from oxygen precipitates in silicon

Abstract

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...

Effect of annealing atmosphere on oxygen precipitation and formation of denuded zone in Czochralski silicon wafer

“…where Oi denotes an interstitial oxygen atom, V a vacancy, Si I a silicon self-interstitial and 2 SiO an oxygen precipitate. Therefore, it is evident that the point defects are actively involved in oxygen precipitation.…”

“…It has been proved that oxygen precipitation in silicon can be affected by initial oxygen contents [2], other impurities [3][4][5], annealing temperature [6], thermal history [7], point defects [8][9][10], and annealing atmosphere [9][10][11]. Hu has reported that the oxidizing atmosphere strongly retard oxygen precipitation in comparison with the inert gas atmosphere and attibuted this phenomenon to the excess silicon self-interstitials generated during thermal oxidation [9].…”

Effect of Nitrogen Doping on Oxygen Precipitate Profiles in Czochralski Silicon Wafer

“…The supersaturated oxygen in CZ silicon wafers can form oxygen precipitates, which act as effective gettering sites for heavy metals during semiconductor device manufacturing processes. 1,2) In past decades, oxygen precipitation in silicon can been influenced by oxygen content, 3,4) other impurities, [5][6][7] point defects 8,9) and thermal circles 10) has been investigated intensively. Recently, due to nitrogen's special properties in silicon, its effect on oxygen precipitation in CZ silicon has been receiving attention, along with the increasing diameter of CZ crystals.…”

Oxygen precipitation in neutron‐irradiated Czochralski silicon annealed at elevated temperature

“…In Czochralski (CZ) silicon, oxygen precipitates are used as effective gettering sites for heavy metals during device processes [1,2]. It is well known that oxygen precipitation in CZ silicon can be influenced by oxygen content [3], impurities [4,5], annealing temperature [6], and point defects [7][8][9][10]. Voronkov et al [10] have suggested that the vacancies incorporated in CZ silicon during crystal growth hardly affect oxygen precipitation at temperatures above the void onset temperature (around 1070 °C), but they could interact with oxygen atoms to form O 2 V species at lower temperature, which will enhance oxygen precipitation following the void formation.…”