Narrow CoSi₂ line formation on SiO₂ by focused ion beam

We propose a technique for formation of CoSi₂ line structures on SiO₂ films, which utilizes irradiation with 40 keV Si²⁺ FIB to the Co (14 nm)/Si (50 nm)/SiO₂ (20 nm) stacked layer structures. Ion irradiation was performed at room temperature (RT) in order to prevent the thermal formation of cobalt silicide in regions without irradiation. After ion irradiation, unreacted Co layers remaining on the surfaces were removed by dipping the samples into the solution of HNO₃:H₂O₂ = 1:3, and unreacted Si layers were removed by H₃PO₄ at 160 °C. The hot H₃PO₄ removes the deposited Si without etching the irradiated regions or SiO₂ films. After the etching, the samples were heat treated at 700 and 900 °C for 20 min. As a result, cobalt silicide line structures were formed. The resistivity evaluated for samples heat treated at 700 and 900 °C was in agreement with that of CoSi and CoSi₂, respectively. CoSi₂ line structures with less than 200 nm width can be made by the procedure.