Silicon nitride

• SN
• SSN
• GPSSN
• HPSN
• HIPSN
• RBSN

Slightly beige solid

Fixed

3.44 g · cm -3

1900 ° C.

Insoluble in water

Attention

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Silicon nitride (also: silicon nitride) is a chemical compound that is used as part of technical material. It is composed of the elements silicon and nitrogen, has the formula belongs to the class of Si3N4 and nitrides.

Crystal structure

It occurs in three modifications ( α -Si3N4, β -Si3N4 and γ -Si3N4 ), which differ in their crystal structure.

• Nitrogen atoms are shown in blue, gray silicon atoms

Hexagonal β -Si3N4

Cubic γ -Si3N4

Technical silicon nitride is a non-oxide ceramic, which is usually made of β - silicon nitride crystals in a glassy solidified matrix. The glass phase content reduces the hardness of Si3N4 compared to silicon carbide, but permits the recrystallization of the β - columnar Siliciumnitridkristalle during the sintering process, which causes, compared to silicon carbide and boron carbide substantially increased fracture toughness.

Use

The high fracture toughness in combination with small defect sizes silicon nitride gives the highest strength among the engineering ceramic materials. The combination of high strength, low thermal expansion coefficient and a relatively small modulus of elasticity is Si3N4 ceramic is particularly suitable for thermal-shock- stressed components, and is used for example as an indexable insert for cast iron materials (including interrupted cuts ) or for handling aluminum smelting used. Silicon nitride ceramics are suitable at a suitable choice of refractory glass phase (for example by the addition of yttria ) for operating temperatures up to about 1300 ° C. The material used in motors, silicon nitride has high despite efforts in research and development in recent decades not been able to prevail. Silicon nitride is also used as a special material in storage technology for hybrid bearings ( Si3N4 rolling elements ) and full ceramic bearings ( rolling elements and raceways from Si3N4).

A particular application are measuring tips ( cantilever ) are resolved with those in atomic force microscopes samples up to the atomic level. They are made from silicon wafers and made ​​on its surface by a silicon nitride particularly resistant to mechanical wear.

Semiconductor Technology

In the semiconductor technology, silicon nitride is used as insulating or passivating material for the production of integrated circuits, charge-trapping in the dielectric storage layer serves as a storage for bound electric charges. In addition, it is used in many processes as a mask and stop material, such as in the local oxidation of silicon (LOCOS ) process or the chemical mechanical polishing. The advantage here is a different chemical behavior as compared with etchants compared to the standard material is silica, that is, one uses etchant, although silica but do not attack silicon nitride, or vice versa. Thus, silicon nitride is etched usually wet chemically with hot 85 per cent phosphoric acid. Two methods of chemical vapor deposition ( CVD ) can be used for the deposition of silicon nitride layers, in essence, the low-pressure CVD (LPCVD ) and plasma enhanced CVD (PECVD).

Since the lattice spacing of silicon and silicon nitride differ, there may be tension of the deposited silicon nitride, depending on deposition method. In particular, when using the PECVD technique can be minimized by adjusting the process parameters so bracing. Furthermore, silicon used in photovoltaics as antireflection and passivation. Due to the lower reflection losses, the efficiency of solar cells and modules is increased.

Synthesis

• Direct nitridation by reaction bonding:

• Carbothermal nitriding:

• Diimide synthesis:

• Chemical vapor deposition ( LPCVD or PECVD) in microtechnology: