Silicon nitride can be obtained by direct chemical reaction with elemental silicon and nitrogen at 1300-1400°C. The chemical formula is as follows:
3Si(s) + 2N2(g) →Si3N4(s)
It can also be synthesized with diimine:
SiCl4(l) + 6NH3(g) →Si(NH)2(s) + 4NH4Cl(s) (at 0 °C)
3Si(NH)2(s) →Si3N4(s) +N2(g) + 3H2(g) (at 1000 °C)
Or use carbothermal reduction reaction to synthesize under a nitrogen atmosphere at 1400-1450°C:
3SiO2(s) + 6 C(s) + 2N2(g) →Si3N4(s) + 6 CO(g)
The synthetic method of nitriding elemental silicon powder was developed in the 1950s with the rediscovery of silicon nitride. It is also the first method for mass production of silicon nitride powder. However, if the purity of the silicon raw material used is low, the produced silicon nitride will contain impurity silicate and iron.
The silicon nitride synthesized by the diamine decomposition method is amorphous, and it needs to be further annealed under nitrogen at 1400-1500°C to convert it into crystalline powder. At present, the diamine decomposition method is only important in terms of The commercial production method of silicon nitride is second to the nitriding method.
The carbothermal reduction reaction is the easiest way to manufacture silicon nitride and it is also the most cost-effective way to manufacture silicon nitride powder in industry.
Electronic grade silicon nitride film is manufactured by chemical vapor deposition or plasma enhanced chemical vapor deposition technology:
3SiH4(g) + 4NH3(g) →Si3N4(s) + 12H2(g) 3SiCl4(g) + 4NH3(g) →Si3N4(s) + 12 HCl(g) 3SiCl2H2(g) + 4NH3(g) →Si3N4 (s) + 6 HCl(g) + 6H2(g)
If you want to deposit silicon nitride on a semiconductor substrate, there are two methods available:
1. Use low-pressure chemical vapor deposition technology at a relatively high temperature using a vertical or horizontal tube furnace.
2. Plasma-enhanced chemical vapor deposition technology is carried out under relatively low-temperature vacuum conditions.
The unit cell parameters of silicon nitride are different from that of elemental silicon. Therefore, depending on the deposition method, the generated silicon nitride film may generate tension or stress. Especially when using plasma-enhanced chemical vapor deposition technology, the tension can be reduced by adjusting the deposition parameters.
Firstly, silica is prepared by the sol-gel method, and then the silica gel containing ultra-fine carbon particles is processed by the carbothermal reduction method and nitridation at the same time to obtain silicon nitride nanowires. The ultra-fine carbon particles in silica gel are produced by the decomposition of glucose at 1200-1350°C. The reactions involved in the synthesis process may be:
SiO2(s) + C(s) → SiO(g) + CO(g) 3 SiO(g) + 2N2(g) + 3 CO(g) →Si3N4(s) + 3CO2(g) or 3 SiO(g) ) + 2N2(g) + 3 C(s) →Si3N4(s) + 3 CO(g)
Method for processing silicon nitride block
Silicon nitride as a granular material is difficult to process. It cannot be heated above its melting point of 1850°C, because silicon nitride will decompose into silicon and nitrogen above this temperature. Therefore, the traditional hot press sintering technology is not acceptable. The silicon nitride powder can be bonded together by adding some other substances such as sintering aids or binders to induce silicon nitride to undergo a certain degree of liquid phase sintering at a lower temperature and then bond into a bulk material. However, due to the need to add binders or sintering aids, this method will introduce impurities in the produced bulk material. The use of spark plasma sintering is another method that can prepare purer bulk materials. The compacted powder is pulsed in a very short time (in a few seconds). This method can be used at 1500-1700°C. Obtain compact and dense silicon nitride lumps at the temperature.
TRUNNANO (aka. Luoyang Tongrun Nano Technology Co. Ltd.) is a trusted global chemical material supplier & manufacturer with over 12 years’ experience in providing super high-quality chemicals and Nanomaterials. The silicon nitride produced by our company has high purity, fine particle size and impurity content. Please contact us if necessary. 
