Formation of Ni(Ge1−xSnx) layers with solid-phase reaction in Ni/Ge1−xSnx/Ge systems

We have demonstrated the formation of Ni(Ge1−ySny) layers on Ge1−xSnx layers by using solid-phase reaction for samples with Sn contents ranging from 2.0% to 6.5%. We have also investigated solid-phase reaction products in Ni/Ge1−xSnx/Ge samples after annealing and the crystalline properties of nickel–tin–germanide layer/Ge1−xSnx contact structures. After annealing at temperatures ranging from 350 to 550 °C, the formation of polycrystalline Ni(Ge1−ySny) layers has been observed on epitaxial Ge1−xSnx layers with Sn contents ranging from 2.0% to 6.5%. We also observed anisotropic crystal deformation of NiGe with the incorporation of Sn atoms into substitutional sites in NiGe. In the case of the Ni/Ge1−xSnx/Ge sample with a Sn content of 3.6%, the formation of an epitaxial Ni2(Ge1−zSnz) layer on the Ge1−xSnx layer was found. The formation of β-Sn crystallites was observed after annealing at above 450 °C in samples with a high Sn content of 6.5%. This β-Sn formation is due to the precipitation of Sn atoms. In all samples annealed at 350 °C, the morphology of Ni–Ge–Sn layers is smooth and uniform. However, the surface roughness and interface roughness increase for an annealing temperature of 550 °C. In particular, in the sample with a Sn content of 6.5%, the temperature at which agglomeration noticeably occurs is as low as 450 °C.

Research highlights
► Formation of nickel-tin-germanide contacts for germanium-tin source/drain stressors.
► Reaction products after the solid phase reaction of Ni/Ge1−xSnx systems with various Sn contents.
► Sn precipitation from Ni(Ge1−xSnx) layers with annealing.
► Agglomeration behavior of Ni(Ge1−xSnx) layers on Ge1−xSnx layers.
► Strain behavior of Ge1−xSnx layers after the germanidation process for contact formation.