Float zone silicon (FZ-Si) is typically assumed to be an extremely high quality material, with high minority carrier lifetimes and low concentrations of recombination active defects. However, minority carrier lifetime in FZ-Si has previously been shown to be unstable following thermal treatments between 450 and 700 °C, with a range of unidentified deep level states being linked to reduced carrier lifetime. There are suspicions that nitrogen doping, which occurs from the growth atmosphere, and intrinsic point defects play a role in the degradation. This study aims to address this by using deep level transient spectroscopy (DLTS), minority carrier transient spectroscopy, Laplace DLTS, and photoluminescence lifetime measurements to study recombination active defects in nitrogen-doped and nitrogen-lean n-type FZ-Si samples. We find that nitrogen-doped samples experience increased degradation due to higher concentrations of deep level defects during thermal treatments compared to nitrogen-lean samples. In an attempt to explain this difference, in-diffusion of nickel has been used as a marker to demonstrate the existence of higher vacancy concentrations in the nitrogen-doped samples. The origin of the recombination active defects responsible for the thermally induced lifetime degradation in FZ-Si crystals is discussed.
The characteristics of Cu precipitation on various types of defects associated with oxygen precipitation in Czochralski-grown silicon are investigated by transmission electron microscopy and the electron-beam-induced-current technique. Specimens containing dominantly either punched-out dislocations or bulk stacking faults were intentionally contaminated with Cu at various temperatures and cooled at three different rates. Colonies of Cu precipitates developed irrespective of cooling rate, apparently originating from punched-out dislocations developed around oxygen precipitates. In heavily contaminated specimens cooled fast from the contamination temperature, Cu also precipitates on Frank partial dislocations bounding stacking faults. During slow cooling, precipitation of Cu takes place on Frank partials only in lightly contaminated specimens but never in heavily contaminated specimens. Cu precipitates in colonies are thermally more stable than those formed on Frank partials. It is concluded that punched-out dislocations are more favorable precipitation sites for Cu than Frank partials.
Characteristics of oxygen precipitation in Czochralski-grown silicon (CZ-Si) intentionally contaminated with Cu or Fe are investigated by means of Fourier-transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), electron-beam-induced-current (EBIC) mapping and etch pit observation. It is found that oxygen precipitation is not influenced by the presence of Cu impurities, while it is enhanced significantly by the presence of Fe impurities even if the concentration of Fe is much lower than that of Cu. Precipitations of supersaturated Cu and O impurities are found to proceed independently of each other in Si crystals. Oxygen precipitates in an Fe-contaminated specimen are much denser and smaller than those in a noncontaminated specimen. Fe impurities seem to react with minute Si oxide particles which are present in as-grown CZ-Si crystals and reduce the nucleation barrier for oxygen precipitation.
A series of electric-dipole spin-resonance (EDSR) lines, termed Si-SC1 lines, are found to develop in Czochralski-grown Si crystals due to annealing at 650'C. Some of these lines are very close to Si-2E and Si-3E reported in a previous work. The experimental data are self-consistently explained by use of a model that shows that the EDSR signals are caused by additional electrons trapped by long quasi-onedimensional defects lying along the (110}directions. The localization length of the trapped electrons is determined to be of the order of 100 nm and their mobility to be rather high along the defects, suggesting that a quasi-one-dimensional energy band is associated with the straight part of the defect. Si-SC1 centers are attributed to the so-called rodlike defects that are developed in the Czochralski-grown Si crystals due to the above heat treatment.
The gettering of Cu and Ni impurities in intentionally contaminated SIMOX wafers have been studied by means of cross-sectional transmission electron microscopy, nanoprobe energy dispersive x-ray spectroscopy, secondary ion mass 12 11 spectrometry, and selective etching. The wafers with Cu or Ni surface concentrations ranged from about 10 up to 10 atom/cm 2 were annealed at various temperatures followed by slow cooling to room temperature. Single and multistep thermal treatments were applied. It has been found that the buried oxide does not prevent the diffusion of both Cu and Ni contaminants from the top silicon layer into the bulk substrate at the whole investigated temperature range from 600 to 950~ Moreover the effective gettering of Cu and Ni in the thin silicon substrate layer located just beneath the buried oxide has been observed and explained as being due to the heterogeneous impurity precipitation at stacking fault tetrahedra formed there during the SIMOX manufacturing. The gettering process has remained stable during the thermal simulation of CMOS device process of new generation ICs with 0.25 ~m feature size.
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