In this study, the phase composition and crystallization kinetics of a Si-Mn heterosystem synthesized on single-crystal silicon substrates via hightemperature thermal vacuum diffusion were comprehensively investigated as a function of annealing temperature (600-1200o C) using X-ray diffraction (XRD) analysis. As the annealing temperature increased, the system progressed from initial partial amorphization of the host silicon lattice to the sequential nucleation of a cubic B20-type MnSi monophase, followed by the formation of the higher manganese silicide Mn4Si7 exhibiting tetragonal symmetry. At temperatures exceeding 950o C, thermal redistribution of manganese triggered the appearance of the Mn5Si3 phase along with restabilized MnSi. Using the Scherrer formulation, crystallite size growth from 30 nm up to 45 nm and the structural evolution of lattice-induced microstrains across interphase boundaries were quantitatively determined.