Formation of nickel suicide layer on strained-Si_0.83Ge _0.17/Si(001) using a sacrificial Si layer and its morphological instability

Nickel suicide was formed on strained-Si_0.83Ge _0.17/Si(001) using a sacrificial Si capping (cap-Si) layer and its morphological characteristics were investigated. Nickel silicide layers were grown by rapid thermal annealing of the samples with the structure of Ni (≅ 14 nm)/cap-Si (≅ 26 nm)/Si_0.83Ge_0.17/Si(001) at the annealing temperature (T_A) range of 400-800°C. The phase formation, surface and interfacial morphologies, and electrical properties of the resulting samples were characterized by various measurement techniques, including X-ray diffraction, atomic force microscopy, scanning electron microscopy, Auger electron spectroscopy, cross-sectional transmission electron microscopy, and the four-point probe method. The results showed the formation of a uniform layer nickel monosilicide (NiSi) with a thickness of ≅30 nm at 400-550°C and sheet resistance values of 6.5-7.9Ω/□, The sheet resistance values of the samples annealed at T_A ≥ 600°C were found to be increased, however, and this is attributed to the agglomeration of nickel monosilicide leading to discrete large-size NiSi grains. Microstructural and chemical analyses of the samples annealed at elevated temperature, T _A ≥ 750°C, indicated the formation of large agglomerated NiSi grains penetrating into the Si_0.83Ge_0.17/Si(001) structure and the conversion of the cap-Si layer situated in between the nickel suicide grains into an Si_1-uGe_u layer (u ≅ 0.01-0.03, due to the out-diffusion of Ge from the SiGe layer during agglomeration. However, no NiSii phase was observed at these elevated annealing temperatures.