Solid phase reactions between Fe thin films and Si-Ge layers on Si

Solid phase reactions in Fe thin films on epi-Si_0.8Ge_0.2, poly-Si_0.7Ge_0.3, a-Si_0.8Ge_0.2, and a-Si_0.7Ge_0.3 layers on silicon have been investigated. The as-deposited samples were in situ annealed in the ultrahigh vacuum chamber at 400–800°C for 30 min. The island structure was found to cause the abrupt increase in the sheet resistance of the annealed Fe/SiGe samples at 700–800°C. The formation of FeSi islands containing a small amount of Ge is attributed to the preferential reactions of Fe with Si to Ge. As the annealing temperature was raised to 800°C, the Fe(Si_1-xGe_x) phase is the only phase found in the annealed Fe/epi-Si_0.8Ge_0.2 and Fe/poly-Si_0.7Ge_0.3 samples. On the other hand, at the annealing temperature above 700°C, the β-Fe(Si_1-xGe_x)₂ phase was observed in the annealed Fe/a-Si_0.8Ge_0.2 and Fe/a-Si_0.7Ge_0.3 but the Fe(Si_1-xGe_x) is still the dominant phase. The results indicate that the formation of Fe disilicide was retarded by the presence of Ge atoms.