Laser annealing studies on ion implanted iron in silicon

Abstract

The annealing effect of laser pulses from ruby and neodymium glass lasers on ion implanted 57Fe in silicon is investigated by Mossbauer conversion electron spectroscopy. For light pulses (≈ 70 ns duration time) from a ruby laser with a power density of 1.5 J/cm2, the Mossbauer spectrum changes drastically upon irradiation. After the irradiation, a quadrupole doublet is observed. This is interpreted to be due to the precipitation of FeSi compounds of approximately FeSi2 composition. From anodic stripping of surface layers it is found that these precipitates are formed in a shallow surface layer of ⪅ 200 A. The results are explained by the assumption that a surface layer of the silicon is molten. For light pulses from a Nd laser (≈ 100 ns duration time), the same result as for a ruby laser is obtained for power densities ⪆ 10 J/cm2. For lower power densities the Mossbauer spectra change only slightly but the implant with an average depth of ≈ 650 A is found to move towards the surface to an average depth of ≈ 300 A.