One of the reasons why the principal gettering mechanism of copper at oxide precipitates is not yet clarified is that it was not possible to identify the presence and measure the copper concentration in the vicinity of oxide precipitates. To overcome the problem we used a 14.5 nm thick thermal oxide layer as a model system for an oxide precipitate to localize the place where the copper is collected. We also analyzed a plate-like oxide precipitate by EDX and EELS and compared the results with the analysis carried out on the oxide layer. It is demonstrated that both the interface between the oxide precipitate being SiO 2 and the silicon matrix and the interface between the thermal oxide and silicon consist of a 2-3 nm thick SiO layer. As the results of these experiments also show that copper segregates at the SiO interface layer of the thermal oxide it is concluded that gettering of copper by oxide precipitates is based on segregation of copper to the SiO interface layer.

We used STEM and FTIR to investigate the morphology and stoichiometry of oxygen precipitates in samples pre-treated by RTA at 1250°C subsequently annealed in the temperature range between 800°C and 1000°C. The morphology of the oxygen precipitates depends on the temperature of the subsequent annealing. Annealing at 800°C results first of all in the formation of three dimensional dendritic precipitates while during annealing at 900°C or 1000°C mainly plate-like and octahedral precipitates are formed. The absorption bands of the dendritic SiOx precipitates were identified and simulated based on effective medium theory. All regular plate-like and octahedral precipitates could be well fitted assuming x = 2.

In this work, we investigated the stoichiometry of oxygen precipitates in Czochralski silicon wafers. The thickness dependence of the Cliff–Lorimer sensitivity factor for the silicon/oxygen system was determined and applied for the investigation of the stoichiometry of oxygen precipitates by EDX. The results show that both plate‐like oxygen precipitates and a transitional form between plate‐like and octahedral precipi‐ tates consist of SiO2. This was confirmed by EELS low loss spectra where the typical spectrum for amorphous SiO2 was observed. Moreover, the absorption band of plate‐like precipitates at 1227 cm–1 was found in the low temperature FTIR spectrum. It was demonstrated that this band can only be simulated by the dielectric constants of amorphous SiO2. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)

Vacancy dependent nucleation curves were measured. They exhibit four maxima which all increase with increasing vacancy concentration. Even at 1000 °C considerable nucleation takes place for high vacancy concentrations. The analysis of nucleation based on classical nucleation theory has shown that nucleation of oxide precipitates takes place at heterogeneous nucleation sites. These sites contain oxygen atoms and vacancies and it is assumed that these sites are VO n complexes with 2

We investigated thermal oxide layers of different thickness on (100) and (111) silicon substrates by STEM/EELS to determine the stoichiometry profiles and compared these with stoichiometry profiles of plate-like and octahedral oxide precipitates in silicon. It was found that the stoichiometry of SiO x (x = 2) cannot be reached if the oxide layer thickness is lower than 10 nm for thermal oxides grown at 900 • C. This is due to an interface layer of equal maximum slope of x for all oxide layers. The slope of x is the change in stoichiometry with position and was obtained from fitting by sigmoid functions. Similar results were found for the oxide precipitates in silicon. However, there are arguments which question the slope determined via the low loss EEL spectra and the maximum x value could be closer to 2 in reality. On a sample with an oxide layer of 13.9 nm thickness we compared stoichiometry profiles obtained from the plasmon region and the Si-K 2,3 and O-K ionization edges. The width of the interface measured on stoichiometry profiles decreases with increasing energy loss and is lowest for the O-K ionization edge with a width of 1. In a previous work, we found that both the interface between an oxide precipitate and the surrounding silicon matrix and the interface between a silicon substrate and a thermal oxide layer are of the same nature.1 In both cases, between SiO 2 existing in the center of the precipitate and in the oxide layer and Si of the matrix and the substrate a suboxide region of 2-3 nm was found. These results were obtained by electron energy loss spectrometry (EELS) carried out by scanning transmission electron microscopy (STEM). In the low loss region, it is possible to distinguish between Si, SiO, and SiO 2 which all exhibit different maxima of the plasmon loss energy. By deconvolution, the local composition of the phase can be determined with the help of reference spectra of the three components.The stoichiometry of the oxide precipitates (SiO x ) was debated for a long time and application of different methods on different samples containing oxygen precipitates resulted in different values for x ranging from 1 to 2. Recently, it was demonstrated by applying several direct and indirect methods that the oxide precipitates consist of SiO 2 .2 Inspired by the results in Ref. 1 and 2, a layer model was proposed explaining the different experimental values for x for oxide precipitates of different geometry.3 Especially, for plate-like precipitates with a small aspect ratio the lower x values could be explained assuming that they consist of SiO 2 surrounded by a 2 nm SiO shell. However, neither is it known until now if all oxide precipitates consist of SiO 2 in the center nor is it known how thick the suboxide region for oxide precipitates grown at different temperature and time is. It needs to be mentioned that the suboxide region is not a layer of SiO composition but a profile of x increasing from the silicon matrix to the SiO 2 core. The impression of a layer just stems from the analysis of ele...