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Silicon nitride
Silicon nitride is a chemical compound of the elements silicon and nitrogen. Si
3N
4 (Trisilicon tetranitride) is the most thermodynamically stable and commercially important of the silicon nitrides, and the term ″Silicon nitride″ commonly refers to this specific composition. It is a white, high-melting-point solid that is relatively chemically inert, being attacked by dilute HF and hot H
3PO
4. It is very hard (8.5 on the mohs scale). It has a high thermal stability with strong optical nonlinearities for all-optical applications.
Silicon nitride is prepared by heating powdered silicon between 1300 °C and 1400 °C in a nitrogen atmosphere:
The silicon sample weight increases progressively due to the chemical combination of silicon and nitrogen. Without an iron catalyst, the reaction is complete after several hours (~7), when no further weight increase due to nitrogen absorption (per gram of silicon) is detected.[citation needed]
In addition to Si
3N
4, several other silicon nitride phases (with chemical formulas corresponding to varying degrees of nitridation/Si oxidation state) have been reported in the literature. These include the gaseous disilicon mononitride (Si
2N), silicon mononitride (SiN) and silicon sesquinitride (Si
2N
3), each of which are stoichiometric phases. As with other refractories, the products obtained in these high-temperature syntheses depends on the reaction conditions (e.g. time, temperature, and starting materials including the reactants and container materials), as well as the mode of purification. However, the existence of the sesquinitride has since come into question.
It can also be prepared by the diimide route:
Carbothermal reduction of silicon dioxide in a nitrogen atmosphere at 1400–1450 °C has also been examined:
The nitridation of silicon powder was developed in the 1950s, following the "rediscovery" of silicon nitride and was the first large-scale method for powder production. However, use of low-purity raw silicon caused contamination of silicon nitride by silicates and iron. The diimide decomposition results in amorphous silicon nitride, which needs further annealing under nitrogen at 1400–1500 °C to convert it to a crystalline powder; this is now the second-most-important route for commercial production. The carbothermal reduction was the earliest used method for silicon nitride production and is now considered as the most-cost-effective industrial route to high-purity silicon nitride powder.
Electronic-grade silicon nitride films are formed using chemical vapor deposition (CVD), or one of its variants, such as plasma-enhanced chemical vapor deposition (PECVD):
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Silicon nitride
Silicon nitride is a chemical compound of the elements silicon and nitrogen. Si
3N
4 (Trisilicon tetranitride) is the most thermodynamically stable and commercially important of the silicon nitrides, and the term ″Silicon nitride″ commonly refers to this specific composition. It is a white, high-melting-point solid that is relatively chemically inert, being attacked by dilute HF and hot H
3PO
4. It is very hard (8.5 on the mohs scale). It has a high thermal stability with strong optical nonlinearities for all-optical applications.
Silicon nitride is prepared by heating powdered silicon between 1300 °C and 1400 °C in a nitrogen atmosphere:
The silicon sample weight increases progressively due to the chemical combination of silicon and nitrogen. Without an iron catalyst, the reaction is complete after several hours (~7), when no further weight increase due to nitrogen absorption (per gram of silicon) is detected.[citation needed]
In addition to Si
3N
4, several other silicon nitride phases (with chemical formulas corresponding to varying degrees of nitridation/Si oxidation state) have been reported in the literature. These include the gaseous disilicon mononitride (Si
2N), silicon mononitride (SiN) and silicon sesquinitride (Si
2N
3), each of which are stoichiometric phases. As with other refractories, the products obtained in these high-temperature syntheses depends on the reaction conditions (e.g. time, temperature, and starting materials including the reactants and container materials), as well as the mode of purification. However, the existence of the sesquinitride has since come into question.
It can also be prepared by the diimide route:
Carbothermal reduction of silicon dioxide in a nitrogen atmosphere at 1400–1450 °C has also been examined:
The nitridation of silicon powder was developed in the 1950s, following the "rediscovery" of silicon nitride and was the first large-scale method for powder production. However, use of low-purity raw silicon caused contamination of silicon nitride by silicates and iron. The diimide decomposition results in amorphous silicon nitride, which needs further annealing under nitrogen at 1400–1500 °C to convert it to a crystalline powder; this is now the second-most-important route for commercial production. The carbothermal reduction was the earliest used method for silicon nitride production and is now considered as the most-cost-effective industrial route to high-purity silicon nitride powder.
Electronic-grade silicon nitride films are formed using chemical vapor deposition (CVD), or one of its variants, such as plasma-enhanced chemical vapor deposition (PECVD):