WSi2 and CoSi2 as diffusion sources for shallow‐junction formation in silicon

The redistribution of B and As ions implanted into thin layers of WSi2 and CoSi2 on poly‐ or monocrystalline Si and the outdiffusion into the Si substrate during furnace annealing (FA) and rapid thermal processing (RTP) were investigated by several analytical techniques. Shallow junctions (depth xj < 100 nm) with interface concentrations Cint close to the solid solubility of the respective dopant in Si (Cint≳3×1020 cm−3 for As; (Cint ≳ 8 × 1019 cm−3 for B) were obtained with RTP. For FA above 800 °C, the diffusion of B from CoSi2 into Si results in a drop of Cint < 2 × 1019 cm−3 because of strong B segregation and probably reactive loss at the SiO2/CoSi2 interface. No evidence on metal‐dopant‐compound formation could be found. The dopant redistribution is demonstrated to be a superposition of lattice and grain‐boundary diffusion, solubility limits, layer inhomogeneities, dopant segregation at the interface and grain boundaries, and probably phase transformation of the dopants segregated at the SiO2/silici...