Silicidation

Silicidation is the chemical process by which silicon reacts with a metal to form a metal silicide. In semiconductor technology, silicidation is used to create low-resistance contacts on silicon surfaces. The process typically involves depositing a metal on a silicon wafer or exposing silicon to a metal source, followed by annealing to drive diffusion and interfacial reaction that produces a silicide layer.

Common metal silicides include titanium silicide (TiSi2), cobalt silicide (CoSi2), nickel silicide (NiSi, NiSi2), platinum silicide (PtSi), and tungsten silicide (WSi2). The exact silicide phase formed depends on temperature, metal choice, and silicon orientation; diffusion can proceed through multiple phases, with certain phases offering lower resistivity and better thermal stability. For example, C54-TiSi2 is a low-resistivity phase preferred in many applications.

Process variants include salicide (self-aligned silicide), where metal is deposited over patterned silicon and annealed to form silicide only in exposed regions, followed by removal of unreacted metal. Silicidation is widely used to form contact layers to source/drain and gate regions and to create interconnects in integrated circuits, as well as to form contacts in solar cells.

Advantages of silicidation include reduced electrical resistivity at contacts, good thermal stability, and compatibility with standard silicon processing. Challenges involve precise control of phase formation, prevention of silicide agglomeration or excessive diffusion, stress from volume changes, and ensuring compatibility with subsequent processing steps such as oxidation, etching, or chemical-mechanical polishing.

Silicidation remains a fundamental technique in device metallurgy, with ongoing research aimed at expanding material choices, improving process control, and enhancing stability for advanced microelectronic applications.