Formation of ultrathin CoSi2 films using a two-step limited reaction process

The formation of ultrathin (≤20 nm) and smooth CoSi2 layers on c–Si substrates has been studied by using a one- and a two-step RTP silicidation method. Pinhole-free silicide layers with a thickness down to ∼10–12 nm were formed on n−, n+, and p+ crystalline Si substrates in the one-step RTP process by sputtering of Co films as thin as 4 nm and subsequent silicidation at 750 °C for 5 or 30 s. The two-step RTP silicidation method is based on the consumption of only a small fraction of a thick sputtered Co film to form Co2Si or CoSi during a first RTP step at 400–500 °C. A selective etch follows to remove the unreacted Co film. During a second, higher temperature, RTP step CoSi2 is formed. Pinhole-free and smooth CoSi2 films with a thickness down to 20 nm were formed in this way on both n+ and p+ monocrystalline Si substrates.