THE COMPOSITION AND STRUCTURE OF SIPOS - A HIGH-SPATIAL-RESOLUTION ELECTRON-MICROSCOPY STUDY

The nanostructure and chemical distribution in semi-insulating polycry stalline oxygen-doped silicon (SIPOS) deposited on (001) Si and its is othermal transformation behavior at 900-degrees-C were investigated by high resolution electron microscopy (HREM) and electron energy loss n anospectroscopy (EELS). The structure of the as-deposited film, which contained 15 at. % oxygen, was amorphous. No evidence for nanocrystall ine second phases was found. It was similar in appearance to amorphous silicon. After annealing for 30 min at 900-degrees-C in an inert envi ronment (N2), a dispersion of small nanocrystals, identified as silico n by imaging, diffraction and EELS, formed in the amorphous SIPOS matr ix, with a thin precipitate free zone (PFZ) adjacent to the Si substra te. The SIPOS matrix oxygen concentration increased to 36 at. % and th e matrix remained amorphous after annealing. No other phases were obse rved in annealed specimens. Changes in Si-L near edge fine structure a nd low loss peaks in EELS spectra from SIPOS with increasing oxygen co ncentration indicated that it is a solid solution supersaturated with silicon. Microstructures indicated that the Si nanocrystals formed dur ing a homogeneous precipitation reaction.