Formation of self-aligned cobalt silicide in normal flow nitrogen furnace

Abstract

Cobalt can be completely transformed into cobalt silicide during annealing in a normal flow nitrogen furnace above a certain temperature which depends on the thickness of the cobalt film deposited on the silicon substrate. For a 400 Å cobalt film this temperature is 500 °C and for a 1500 Å cobalt film it is 650 °C. Loading the wafer into the furnace tube is a critical step to prevent the cobalt from oxidation before silicidation in the annealing process. Lateral growth of silicide is not observed using this silicidation scheme. The cobalt oxide together with the underlying cobalt over the silicon oxide can be removed by hot 3HCl + H 2O 2 + 3H 2O solution if the annealing is performed at a temperature below 650 and 900 °C for a cobalt film thickness of 400 and 1500 Å respectively. The optimum condition for practical silicide formation is defined. The products and microstructure over the silicon and silicon oxide are characterized by X-ray diffraction spectra, Auger electron spectroscopy depth profiles, sheet resistance measurements and scanning electron microscopy inspection.