The mechanisms of formation and migration of molten inclusions in silicon are described. Consideration of them is necessary for development of technological approaches to formation of conducting regions (characteristic sizes of 10 μm–30 nm) and doped conducting channels in silicon. The problem of formation of local conducting regions is topical, e.g., for single electronics. It is known that sizes of a “Coulomb island” (about 10 nm) present difficulties to modern technologies. That is why the development of alternative procedures to form a “Coulomb island” (in particular, those based on electromigration of molten regions in semiconductor bulk) is a topical problem. Besides, high heat loads on the “classical” silicon structures, owing to specific character of their work (operating current densities may be as high as j ~ 109–1010 A/m2), promote their active degradation. The appearing molten regions coagulate into drops and are displaced by a current along the electric field lines. Therefore, a detailed analysis of the mechanisms of inclusions formation and migration in silicon will make it possible to predict more accurately the “critical” modes of silicon structures operation (e.g., in power electronics). The main mechanisms of molten inclusions formation (contact melting in a metal-semiconductor system, decomposition of supersaturated solid solutions in heavily doped semiconductors) are considered, as well as the procedures to form and control mobility of such objects: electric current, temperature gradient, structural inhomogeneities, etc. The problems of molten inclusions migration in silicon single crystals occurring in electric field with contact melting electric transport of melt components and thermoelectric effects at interphase boundaries are considered in detail. The molten region is moving along the electric field lines, thus enabling to exert control over the trajectory of its motion. The results of author’s original investigations on formation and migration of molten silver- and aluminum-based inclusions in silicon are presented, as well as the experimental data by other authors. The main migration mechanisms related to melting-crystallization processes at interphase boundaries and components diffusion through the melt region are discussed in detail. The problems to defect formation in silicon after crystallization of inclusions are also considered.
Part of the book: New Research on Silicon