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Silicon nitride is an important material for the microelectronic industry, it is used as a dielectric film or as a passivation layer. Silicon nitride is very hard and chemically inert. It is also a very good thermal shock and oxidation resistant material.
SVM produces stoichiometric and low stress LPCVD si3n4 wafer for use as a passivation layer or in other electronic or photonic applications. It is produced by plasma enhanced chemical vapour deposition (PECVD) from SiH4 and NH3 gasses. The deposition temperatures are chosen to allow dangling bonds in the SiNx layer to be saturated with hydrogen and thus chemically and mechanically stabilized. This makes the SiNx layer much less sensitive to HF etching than untreated silicon.
High quality stoichiometric Si3N4 with very little stress can be produced by using a very precise blend of the Si(x)N(y) compounds. This lowers the residual stress down to around 200MPa in tension. This allows the Si3N4 to be grown to thicknesses of 2 or 3um without cracking.
The stoichiometric Si3N4 is also much more stable against dry CMP polishing than untreated silicon or sputtered thermal oxide. This is mainly due to the fact that stoichiometric Si3N4 has a higher density and more smooth surface than untreated silicon. This results in better planarization efficiency and good within-die/within-wafer uniformity, especially at high polishing speeds. It also enables a lower process temperature, which reduces the risk of damage to metal contacts during etching. This is particularly important for advanced metal gate CMOS devices with very close contact proximity.