Synthesis of β- and α-FeSi2 phases by Fe ion implantation into Si using metal vapor vacuum arc ion source

Abstract

High-current Fe ion implantation technique was employed to synthesize Fe-silicide layers on Si wafers, using a newly constructed metal vapor vacuum arc ion source. The Fe ions were extracted at a voltage of 40 kV with a varying ion current density from 65 to 152 μA/cm2 and a nominal ion dose varied from 3×1017 to 3×1018 Fe/cm2. At a fixed nominal dose of 4×1017 Fe/cm2, a semiconducting β-FeSi2 layer gradually grew on Si with increasing ion current density and a qualified β-FeSi2 layer with a relative sharp interface was obtained, when the ion current densities exceeded 115 μA/cm2. While implanting at a fixed ion current density of 152 μA/cm2 with varying ion dose, the β-FeSi2 phase began to form first at a nominal dose of 3×1017 Fe/cm2, and eventually transformed into a metallic α-FeSi2 phase when the nominal dose reached 3×1018 Fe/cm2. Further information of the formation of Fe disilicides was obtained by comparing the postannealing results of some of the implanted wafers with those observed immediately after implantation. The formation mechanism of the Fe disilicides is discussed in terms of the beam heating effect, which in turn resulted in a simultaneous thermal annealing during Fe ion implantation.