Reaction of amorphous Si with cobalt silicide before disilicide formation for reducing Si consumption in SIMOX

Abstract

A method is introduced to reduce the substrate Si consumption during the silicide process by supplying Si from an amorphous Si film where unsaturated silicide is converted into a disilicide phase. This technique is applied to SIMOX device fabrication. After the first annealing, the sheet resistance of cobalt silicide formed on 40–45 nm SIMOX silicon coated with a 3-nm Ti/20-nm Co film is about 58 Ω/sq. After depositing 47 nm of amorphous silicon and annealing at 850°C, the sheet resistance reduces to 4.5 Ω/sq. The remaining silicon on oxide and over spacer regions is removed in a plasma etch step. The consumption of amorphous silicon and the formation of disilicide can be monitored by observing the surface reflectivity change in the small features of patterned wafers. A functional metal oxide semiconductor (MOS) transistor has been fabricated using this technique.