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Synthesis Method of Silicon Nitride

wallpapers Industry 2020-10-10
Silicon nitride (Si3N4) has three crystal structures, namely α, β and γ three phases. The two steps of α and β are the most common types of Si3N4 and can be prepared under normal pressure. The γ phase can only be synthesized under high pressure and high temperature, and its hardness can reach 35GPa.
 
Hexagonal β-Si3N4 can be directly combined with elemental silicon and nitrogen at 1300-1400℃ to obtain silicon nitride:
3 Si(s) + 2 N2(g) → Si3N4(s)
Can also be synthesized with diimine
SiCl4(l) + 6 NH3(g) → Si(NH)2(s) + 4 NH4Cl(s) at 0 ℃
3 Si(NH)2(s) → Si3N4(s) + N2(g) + 3 H2(g) at 1000 ℃
Or use carbothermal reduction reaction to synthesize under nitrogen atmosphere at 1400-1450℃:
3 SiO2(s) + 6 C(s) + 2 N2(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℃ to convert it into a crystalline powder. The diamine decomposition method is second only to the importance of Nitriding is a commercial production method of silicon nitride. 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:
3 SiH4(g) + 4 NH3(g) → Si3N4(s) + 12 H2(g)
3 SiCl4(g) + 4 NH3(g) → Si3N4(s) + 12 HCl(g)
3 SiCl2H2(g) + 4 NH3(g) → Si3N4(s) + 6 HCl(g) + 6 H2(g)

If you want to deposit silicon nitride on a semiconductor substrate, there are two methods available:
Use low-pressure chemical vapor deposition technology at relatively high temperature using vertical or horizontal tube furnace.
The plasma-enhanced chemical vapour deposition technology is performed under vacuum conditions with relatively low temperatures.
The 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 vapour deposition technology, the tension can be reduced by adjusting the deposition parameters.
Firstly, silica is prepared by the sol-gel method. Then the silica gel containing ultra-fine carbon particles is processed by the carbothermal reduction method and nitridation simultaneously to obtain silicon nitride nanowires. The decomposition of glucose produces the ultra-fine carbon particles in the silica gel at 1200-1350°C. The reactions involved in the synthesis process may be:
SiO2(s) + C(s) → SiO(g) + CO(g)
3 SiO(g) + 2 N2(g) + 3 CO(g) → Si3N4(s) + 3 CO2(g) or
3 SiO(g) + 2 N2(g) + 3 C(s) → Si3N4(s) + 3 CO(g)
 
Except for hydrofluoric acid and hot phosphoric acid, it does not react with other inorganic acids and has strong corrosion resistance.


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Tag: Silicon Nitride