Film Deposition of Silicon Nitride
What is Silicon nitride?
Silicon nitride is a chemical compound of the elements silicon and nitrogen. Si3N4 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, attacked by dilute HF and hot H3PO4. It is very hard (8.5 on the Mohs scale). It has 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: 3 Si + 2 N2 → Si3N4. 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. In addition to Si3N4, 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 (Si2N), silicon mononitride (SiN), and silicon sesquinitride (Si2N3), each of which is a stoichiometric phase. As with other refractories, the products obtained in these high-temperature syntheses depend on the reaction conditions (e.g., time, temperature, and starting materials, including the reactants and container materials) and the mode of purification. However, the existence of the sesquinitride has since come into question. 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, using 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 method for silicon nitride production and is now considered 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). Low-pressure chemical vapor deposition (LPCVD) technology works at rather high temperatures and is done in a vertical or horizontal tube furnace. Plasma-enhanced atomic layer chemical vapor deposition (PECVD) technology, which works at rather low temperatures (≤ 250 °C) and vacuum conditions. Examples include (bis diethylamino)silane as a silicon precursor and plasma of N2 as a reactant.
Price of Silicon nitride
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