Formation of buried CoSi 2 by ion implantation

Abstract

High dose 59Co + implantation into Si(111) and Si(100) substrates heated to 350°C and subsequent two-step annealing leads to the formation of buried, epitaxial CoSi 2 layers in Si. Ion channeling, sheet resistivity measurements and transmission electron microscopy were used to study the silicidation and the recrystallization processes. After annealing at 600°C low Omegaic silicide layers were obtained. For the formation of CoSi 2 during the first annealing step we determined an activation energy of 2.8 eV. The second annealing step at about 1000°C results in single crystalline, epitaxial CoSi 2 layers in full alignment with the Si matrix (A/A/A heterostructure). The low resistivity of 13 μΩ cm is indicative of the high quality and high purity of the layers. Due to the lattice mismatch the buried layer is elastically strained. Layers thicker than about 30 nm undergo strain relaxation by generating misfit dislocations. For the planarization of the silicide layer we obtained an activation energy of 3.6 eV. Planarization may occur via Ostwald ripening of isolated CoSi 2 precipitates, or it may occur by a coagulation process. The single crystalline Si layer on top was used as a templated for subsequent growth of epitaxial Si by MBE to bury the silicide deep in Si. Buried metallic lines with a width of several microns were fabricated by implantation using a SiO 2 mask.