RBS characterization of the iridium diffusion in silicon

In this work, the Ir diffusion in Si has been studied in the high concentration regime. Si (1 0 0) samples were preamorphized by Si implantation and implanted with Ir with a peak concentration of 8x1021 cm-3, below the minimum necessary to the formation of a continuous layer of iridium silicide. The amorphized region of the substrate was regrown by solid phase epitaxy at 550 deg. C. This procedure eliminates the effect of the end of range region of the Ir implant on the diffusion process. After regrowth, the samples were annealed at temperatures in the 800-1000 deg. C range for different times. The Ir concentration profiles and the crystal quality were determined from random and aligned RBS spectra. Annealing at high temperatures causes a snow plow effect of Ir toward the surface of the sample, with a segregation coefficient close to 1. An Ir diffusion mechanism through the defect-free region of the Si substrate is also clearly identified, and a constant value of the diffusion coefficient D is derived for each temperature. The values of D follow an Arrhenius behavior with an activation energy Ea=3.3±0.2 eV. This value agrees with the typical ones found in vacancy assisted diffusion mechanisms reported for other species. Comparison of these results with the previously reported activation energy Ea=1.3 eV for Ir diffusion from the vapour phase at low concentrations shows that the diffusion mechanism is dependent on the concentration level. The values of D at high concentrations are 6 to 7 orders of magnitude lower than the ones reported for low concentrations