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Anti Reflection Coatings

An antireflection of silicon nitride is typically deposited using chemical vapour deposition process (CVD). Precursor gases of silane (SiH4) and ammonia (NH3) are fed into a chamber and break down due to temperature (LPCVD) or due to a plasma enhancement (PECVD). Other systems use microwaves to cause the silane/ammonia reaction to take place. The complete reaction is:

3SiH4 + 4NH3 -> Si3N4 + 12H2

but the usual reaction to produce a non-stoichiometric film with the incoporation of large amounts of hydrogen (SixNy:H).

Older cell designs use titanium dioxide (TiO2), which provides a good antireflection coating and is simpler to apply but does not provide surface or bulk passivation.

Wafers being deposited with silicon nitride antireflection coating giving a blue color.

A full view of the anti-reflection coating machine from loading to unloading