Three - dimensional coherent electron microdiffraction applied to oxygen precipitates in silicon

Abstract

The study of the atomic and electronic structure of oxygen precipitates in CZ silicon has a long history. After a long annealing treatment at 600-700°C, two kind of precipitate phases have been observed. One is rod-like defects which have been known as a crystalline silica phase,coesite. The other is small amorphous platelets similar, but smaller than those observed at higher temperatures. We have found new polyhedral shaped, crystalline precipitates with a size of 300A° to 650A° in CZ silicon (oxygen rich, low carbon) annealed for 256 hours at 635°C. Fig.l shows high resolution lattice images of a 300A° diameter particle obtained using a JEOL 200CX at 200kV. Four faces are parallel to the Si﹛111﹜ planes, and two are truncated in Si(100) as for the amorphous octahedral observed at 1100-1200°C. These particles give the diffraction patterns shown in Fig.2 (obtained on a Philips 400 STEM FEG) at 100kV with 50A° probe from a 650A° particle. Our experimental data calibrated using silicon discs and lattice images are consistent with the tetragonal keatite [012] zone axis pattern within the error ranges.