ION-BEAM SYNTHESIS OF HETEROEPITAXIAL SI/COSI2/SI STRUCTURES

The formation of buried single crystalline CoSi2 layers within a monocrystalline Si substrate by high-dose ion implantation of Co has been studied. Comparison of measured Co distributions with profiles obtained from Monte Carlo calculations has revealed the two basic phenomena that are responsible for the formation of buried layers. The enhanced stopping due to the incorporation of high concentrations of Co into Si has been identified as the dominant effect in the ion beam synthesis of buried layers. The high stopping near the top of the implanted distribution causes accumulation of Co at this point, which promotes buried layer formation. Sputtering brings the entire Co profile closer to the surface. After implantation at a temperature of 450°C, Co is present in the form of coherent CoSi2 precipitates. Precipitates occur both in a twinned and an aligned orientation and are highly strained due to the lattice mismatch with Si. For high doses a buried monocrystalline and aligned CoSi2 layer forms within the Si lattice, during implantation. Annealing of the implanted structures results in the formation of a buried layer when, near the top of the implanted distribution, more than 50% of the Si is converted into CoSi2. These layers too are monocrystalline and have on aligned orientation. Cobalt diffusion in the Si lattice has been suggested to be the rate-determining step in the growth process of the buried layers. Finally, the electrical properties of these ion beam synthesized structures exhibit some unique features.