Two films grown by fast deposition of Mg on Si(111) surfaces with temperature distributions within 365-395 degrees C and 545-609 degrees C were studied by Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and atom force microscopy (AFM). The film grown at 365-395 degrees C contains crystalline textured Mg2Si. The mechanism of Mg2Si formation at high temperature is considered. The role of a Mg atom lifetime before evaporation from the Si surface at high temperatures is emphasized. The crucial requirement for the Mg2Si growth at high temperatures is a sufficiently high deposition rate providing condensation of Mg on the surface and further formation of the silicide.