Submicrometer patterning of epitaxial CoSi 2/Si(111) by local oxidation

Abstract

We have investigated the thermal oxidation of epitaxial CoSi 2 on Si(111). The epitaxial layers were grown by molecular beam allotaxy with thicknesses ranging from 30 to 40 nm. Similar to the well established technology for local oxidation of silicon (LOCOS), the silicide layer was capped by 20 nm SiO 2 followed by 200 nm Si 3N 4. The nitride was patterned by optical lithography and dry etching. Wet thermal oxidation was used in a temperature range from 850 to 1000°C. On the unprotected regions SiO 2 formed on top of the silicide. During this process Co atoms diffused from the SiO 2/CoSi 2 interface through the silicide layer to the CoSi 2/Si interface to form CoSi 2, leading to a shift of the silicide layer into the Si substrate. Near the edges of the nitride mask the silicide layer thinned and finally separated. Two metallic layers electrically separated by Si and SiO 2 with a small gap of about 300–500 nm were produced this way. We have observed a strong temperature dependence of the separation process in the investigated temperature range of 850°C and 1000°C. We attribute this behavior to the distinctly different activation energies of the Co diffusion and the silicide oxidation. We will show that the lateral uniformity of the separation process is related to the crystal symmetry of the Si(111) wafer.