Transmission electron microscopy and X-ray diffraction investigation of phase formation and transition between Pd 2Si and PdSi in Pd thin films on (111)Si

Abstract

Phase formation and transition between Pd 2Si and PdSi in Pd thin films on (111)Si has been investigated by X-ray diffraction and transmission electron microscopy. In as-deposited and 200 °C/1 h annealed Pd(30nm)/(lll)Si samples, epitaxial Pd 2Si was found to coexist with the unreacted Pd layer. In samples annealed at 250–800 °C, epitaxial Pd 2Si is the only suicide phase present. PdSi was found to form along with Pd 2Si in samples annealed at 850 °C. Pd 2Si was found to be the predominant phase along with PdSi in samples annealed at 900–1000 °C. Pd 2Si and PdSi were found to be the stable phases at 300–800 and 850–875 °C, respectively. The phase transition between Pd 2Si and PdSi is reversible. In samples annealed at 900 °C, epitaxial Pd 2Si is initially the only suicide phase present; then polycrystalline PdSi becomes the dominant phase. After annealing for more than 240 s, polycrystalline Pd 2Si predominates over PdSi. The peculiar Pd 2Si to PdSi, then back to Pd 2Si phase transition behavior is correlated with the formation of PdSi islands, which is thought to alter the order of the total energy of the system.