Formation of cobalt silicides as a buried layer in silicon using high energy heavy ion irradiation

Abstract

A multilayer heterostructure of Si(50 nm)/Co(50 nm)/Si(50 nm)/Si⟨ 100⟩ was prepared by an e-beam evaporation technique under UHV conditions and it was then subjected to irradiation by 120 MeV Au+ ions with fluence varying between 1013 and 1014 ions cm−2. No external thermal treatments were used. Secondary ion mass spectrometry was used in the depth profile mode, which indicated a monotonic increase in the mixing width with fluence at the first interface of Si/Co. Depth profile analysis suggested major changes in the preferential sputtering rates of Co at the interface indicating formation of silicides. Further investigation by x-ray diffraction confirmed the formation of different phases of cobalt silicides, Co2Si, CoSi and CoSi2, as a buried layer, while the Raman spectroscopy showed broad peaks near 325 and 725 cm−1, which are characteristic of the CoSi2 phase. The above work suggests that swift heavy ion irradiation can be advantageously used for interconnect related buried layer silicide formation at room temperature avoiding thermal annealing.