TRANSMISSION ELECTRON-MICROSCOPY INVESTIGATION OF THE CRYSTAL-AMORPHOUS-POLYCRYSTAL TRANSITION IN SILICON DURING BISMUTH ROOM-TEMPERATURE ION-IMPLANTATION

Transmission electron microscopy and related diffraction techniques ar e applied to characterize the structural modifications induced in a (1 0 0) silicon substrate by a bismuth ion implantation at room temperat ure. Calculations were performed to provide a theoretical support to t he observations. It is shown that a 50 keV-10 mu A cm(-2) Bi+ implanta tion successively induces: a complete silicon substrate amorphization - a clustering phenomenon inside the amorphous layer - an amorphous to polycrystal (a-p) transition, Combining the experimental measurements of the extension of the amorphous layer for increasing doses with con cepts arising from the ''critical damage energy density'' model leads to a value of about 5 eV at.(-1) for the crystal to amorphous transiti on to occur. Then, the clusters band formation at the center of the am orphous layer is attributed, by use of the calculated ion concentratio n profile, to the formation of Bi precipitates around the concentratio n peak. The calculated substrate temperature increase suggests that th e Pi precipitates finally melt inside the amorphous silicon. These liq uid Bi precipitates finally induce the a-p transition as a result of s ilicon crystallites nucleation at the droplets' sides and bismuth crys tallites formation during the implanted sample cooling. (C) 1997 Publi shed by Elsevier Science B.V.