Chemical Identity and Crystal Forms
Titanium disilicide, TiSi2, is an intermetallic compound of titanium and silicon with CAS Registry Number 12039-83-7. Its formula weight is 104.04 g/mol, from titanium 47.867 plus 2 x 28.085 (silicon). It is a dark grey solid with a density of about 4.02 g/cm³ and a melting point in the region of 1,540 °C, and it is supplied both as a powder and as a sputtering target. The compound is polymorphic. The C49 phase is base-centred orthorhombic and metastable, and it forms first when titanium reacts with silicon at moderate temperature. On further annealing it converts to the C54 face-centred orthorhombic phase, which is the low-resistivity form used in microelectronics. That phase transformation, rather than the chemistry itself, is what makes titanium disilicide technically interesting: the resistivity of the C54 phase is of the order of 15 micro-ohm-centimetre, low enough for interconnect and contact layers.
Why Titanium Disilicide Matters in Semiconductor Processing
In the self-aligned silicide process, a thin titanium film is deposited on a wafer, reacted with the exposed silicon of gates, sources and drains at a controlled temperature to form the C49 phase, and then annealed to convert it to C54. Unreacted titanium on the dielectric is removed selectively, so the silicide forms only where it touches silicon - the self-alignment that gives the process its name. The resulting low sheet resistance reduces contact and gate resistance, which became essential as device dimensions shrank. Silicon consumption is an important process parameter because the reaction consumes silicon from the active area, and the stability of the phase depends on line width, dopant level and the presence of alloying elements. Titanium disilicide remains a reference material for silicide study and for processes where thermal stability at high temperature is required.
Powder and Target Applications Outside Semiconductors
Outside microelectronics, TiSi2 powder is used in reactive sintering and powder metallurgy to produce silicide ceramics, electrodes and wear-resistant components, and as a conductive phase in composite materials where a combination of hardness, thermal stability and electrical conductivity is required. It is also used as an alloying addition in titanium- and silicon-based metallurgy, and as a starting material for sputtering targets employed to deposit silicide films for research and for thin-film devices. Powders designed for thermal spraying and for sintering are normally specified by particle-size distribution and oxygen content rather than by resistivity, because bulk properties are dominated by porosity and by the oxide layer on the particle surface.
Typical Specification and Test Methods
| Parameter | Typical commercial value |
|---|---|
| Assay (TiSi2) | 99.9% (3N) |
| Appearance | Dark grey powder |
| Oxygen content | 0.5% maximum |
| Carbon content | 0.1% maximum |
| Iron content | 0.1% maximum |
| Particle size | D50 agreed per application, typically 1 to 10 µm |
| Apparent density | ASTM B212 (Hall funnel) |
| Tap density | ASTM B527 |
| Particle size method | Light scattering ASTM B822 or air permeability ASTM B330 |
| Packing | 25 kg drum, sealed under dry inert gas |
Particle size must always be reported with the method used: light scattering under ASTM B822 and air permeability under ASTM B330 give systematically different values on the same powder, and comparing a D50 from one method with a D50 from the other is a frequent source of disagreement between buyer and supplier. Oxygen is the critical impurity for sintering and spraying, because surface oxide inhibits interparticle bonding and changes the chemistry of the final densified part.
Handling, Storage and Safety
Titanium disilicide powder is stable in air at room temperature, but fine fractions are a dust hazard and should be handled with local extraction and dust suppression. Containers must be kept sealed and dry, with an inert gas blanket for long storage, because moisture and oxygen degrade the surface of the particles. Do not allow the powder to contact hydrofluoric acid or strong alkalis, which attack silicides. Earthing and bonding are recommended wherever dry powder is transferred, and appropriate respiratory protection should be used when airborne dust cannot be controlled by engineering means. Bulk density data and sieve or laser results should be recorded on receipt so that a deviation can be traced to a specific lot.
Frequently Asked Questions
Q: What is titanium disilicide TiSi2?
A: It is an intermetallic compound of titanium and silicon with CAS 12039-83-7, formula TiSi2, formula weight 104.04 g/mol, density about 4.02 g/cm³ and a melting point near 1,540 °C.
Q: Why is TiSi2 used in semiconductor devices?
A: In the self-aligned silicide process it forms low-resistivity C54 phase contacts on gates, sources and drains, which lowers gate and contact resistance without an additional masking step.
Q: What is the difference between the C49 and C54 phases?
A: C49 is a metastable base-centred orthorhombic phase that forms first during reaction with silicon; annealing converts it to the stable C54 face-centred orthorhombic phase, which has the low resistivity required for interconnect use.
Q: How is TiSi2 powder particle size measured?
A: Either by light scattering under ASTM B822 or by air permeability under ASTM B330. The two methods are not interchangeable, so the method must be stated with the D50 value.
Q: Which impurity matters most in TiSi2 powder?
A: Oxygen. Surface oxide on the particles inhibits sintering and spraying behaviour, so powder grades are normally specified with an oxygen limit, commonly 0.5% maximum, alongside limits for carbon and iron.