Everything about Salicide totally explained
The term
salicide refers to a technology used in the
microelectronics industry used to form electrical contacts between the semiconductor device and the supporting
interconnect structure. The salicide process involves the reaction of a thin metal film with
silicon in the active regions of the device, ultimately forming a metal
silicide contact through a series of annealing and/or etch processes. The term "
salicide" is a compaction of the phrase
self-
aligned si
licide. The description "self-aligned" suggests that the contact formation doesn't require lithographic patterning processes, as opposed to a non-aligned technology such as
polycide. The term salicide is also used to refer to the metal silicide formed by the contact formation process, such as "titanium salicide", although this usage is inconsistent with accepted naming conventions in
chemistry.
Contact Formation
The salicide process begins with deposition of a thin transition metal layer over fully formed and patterned semiconductor devices (for example transistors). The wafer is heated, allowing the transition metal to react with exposed silicon in the active regions of the semiconductor device (for example, source, drain, gate) forming a low-
resistance transition metal silicide. The transition metal doesn't react with the silicon oxide and or 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 Co
2Si, CoSi, CoSi
2, and other compounds. However, only CoSi
2 has a sufficiently low resistance to form an effective electrical contact. For some compounds, the desired low-resistance phase isn't
thermodynamically stable, such as C49-TiSi
2, which is metastable with respect to the high resistance C54 phase.
Other considerations
Another challenge facing successful process integration include lateral growth, especially underneath the gate, which will
short circuit the device.
Further Information
Get more info on 'Salicide'.
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