Recently, octahedron structures have been found in the Czochralski-silicon substrate surface layer just under the oxide defects. An attempt is made to characterize these structures by analysis with transmission electron microscopy and energy-dispersive x-ray spectroscopy. Several results indicate that the structure is full of vacancies. This is contrary to previously reported results suggesting that the octahedron structures found in Si bulk are filled with amorphous SiO2. A model for the formation of an octahedron structure with many vacancies is proposed.
We found octahedral void defects in the bulk of silicon wafers by using infrared tomography. These voids are often twin type and their sizes are about 100 nm. A 2-nm-thick layer exists on the side walls of the void defects. Our analysis suggests that the 2-nm-thick layer is SiOx. It is believed that the void structure is formed as a result of agglomeration of vacancies during Si–ingot growth.
Analysis by TEM-energy-dispersive-X-ray-spectroscopy indicates that the majority of the octahedral structure found just under the oxide defect with Czochralski Si is void. This is contrary to previously reported results suggesting that the octahedral structures found in Si bulk are filled with amorphous SiO2. We investigate three models to explain our results. The first model, which we think most probable, suggests that the void formation occurs during Si crystal growth. The second model indicates that octahedral structures full of SiO2 are formed during Si crystal growth and, after wafer slicing, much of the SiO2 is removed. The third model suggests that the void is formed during copper decoration. We show some experimental results that are inconsistent with the second and third models.
We examined the effect of thermal annealing in vacuum on the behavior of dual-type
octahedral void defects in Czochralski silicon. We found that the smaller void shrinks first at
about 1100°C and that during the shrinkage of the smaller void to extinction, the bigger void
maintains its structure and size. In addition, we found that shrinkage of the smaller void
begins from the adjacent region between the two voids. We believe that the effect of
minimizing the surface energy first takes place selectively in the smaller void and that after
the extinction of the smaller void, the effect of minimizing the surface energy takes place in
the bigger void.
Some preliminary results on the comparison of scintillation efficiencies of scintillators based on two white oils are described. It is shown that a new solvent, technical white oil, has a better scintillation efficiency than that of medicinal paraffin, A possible reason for this higher efficiency is discussed.
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