Microstructure characterization of semiconducting iron disilicide thin films by using the HARECXS and the CBED methods

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In this study, epitaxial β-FeSi_2 films were prepared by sputtering on the flat and the patterned Si(001) substrates under various substrate temperatures (T_s) with deposition rates of Fe (V_<Fe>), and the microstructures of these films were characterized by transmission electron microscopy (TEM). The following results were obtained.(1)In the film deposited on the flat Si(001) substrate, precipitates of flat-bottom shaped β-FeSi_2 and those of round-bottom shaped α-FeSi2 are formed at T_s=500℃ and V_<Fe>=0.02 nm/s. The β-FeSi_2 adopts the epitaxy to (001)_<Si>, plane, while α-FeSi_2 selects the epitaxy to {111}_<Si>, planes inside the Si matrix. At T_s=350℃ and V_<Fe>=0.01 nm/s, a continuous β-FeSi_2 layer are formed epitaxially on the Si(001) substrate without forming α-FeSi_2. The lower temperature and the higher Fe-concentration suppress the formation of a-FeSi_2 and promote the formation of β-FeSi_2.(2)In the film deposited on the patterned Si(001) substrate, both β-and α-FeSi_2 precipitates are formed in the top-hills and the valleys of the patterned substrate, while only α-FeSi_2 precipitates are formed in the sidewalls. Not only the growth conditions but also geometric situations affect strongly the epitaxial growth of FeSi_2 precipitates.(3)In the film deposited on Cu-mediated Si(001) substrate, non-radiative recombination centers in the β-FeSi_2 grains and the hetero-interface are improved, and then PL intensity from the β-FeSi_2 grains can be increased significantly.(4)ALCHEMI (atom location by channeling enhanced microanalysis) method of electron diffraction was employed to study the atomic configuration of the β-FeSi_2 film grown on Cu-mediated Si(001) substrate. In the β-FeSi_2 film, Cu atoms tend to occupy the Fe-site.(5)Clear CBED (convergent beam electron diffraction) patterns from the β-FeSi_2 grain and the Si substrate were measured successfully, in order to estimate the lattice strain near the hetero-interface.