The salicide process begins with deposition of a thin
transition metal layer over fully formed and patterned semiconductor devices (e.g.
transistors). The
wafer is heated, allowing the transition metal to react with exposed silicon in the active regions of the semiconductor device (e.g., source, drain, gate) forming a low-resistance
transition metal silicide. The transition metal does not react with the
silicon dioxide nor the
silicon nitride insulators present on the wafer. Following the reaction, any remaining transition metal is removed by chemical etching, leaving silicide contacts in only the active regions of the device. A fully integrable manufacturing process may be more complex, involving additional anneals, surface treatments, or etch processes.
Chemistry Typical transition metals used or considered for use in salicide technology include
titanium,
cobalt,
nickel,
platinum, and
tungsten. One key challenge in developing a salicide process is controlling the specific phase (compound) formed by the metal-silicon reaction. Cobalt, for example, may react with silicon to form Co2Si, CoSi, CoSi2, and other compounds. However, only CoSi2 has a sufficiently low resistance to form an effective electrical contact. For some compounds, the desired high-resistance phase is not
thermodynamically stable, such as C49-
TiSi2, which is
metastable with respect to the low-resistance C54 phase. ==Other considerations==