FORMATION OF ULTRATHIN COSI2 FILMS USING A 2-STEP LIMITED REACTION PROCESS

The formation of ultrathin (less-than-or-equal-to 20 nm) and smooth Co Si2 layers on c-Si substrates has been studied by using a one- and a t wo-step RTP silicidation method. Pinhole-free silicide layers with a t hickness down to approximately 10-12 nm were formed on n-, n+, and pcrystalline Si substrates in the one-step RTP process by sputtering of Co films as thin as 4 nm and subsequent silicidation at 750-degrees-C for 5 or 30 s. The two-step RTP silicidation method is based on the c onsumption of only a small fraction of a thick sputtered Co film to fo rm Co2Si or CoSi during a first RTP step at 400-500-degrees-C. A selec tive etch follows to remove the unreacted Co film. During a second, hi gher temperature, RTP step CoSi2 is formed. Pinhole-free and smooth Co Si2 films with a thickness down to 20 nm were formed in this way on bo th n+ and p+ monocrystalline Si substrates.