Method of making a silicon nitride film that is transmissive to ultraviolet light
View Patent ↗A method for producing an ultraviolet light (UV) transmissive silicon nitride layer in a plasma enhanced chemical vapor deposition (PECVD) reactor is presented. The UV transmissive film is produced by reducing, in comparison to a standard silicon nitride process, a flow rate of the silane and ammonia gas precursors to the PECVD reactor, and significantly increasing a flow rate of nitrogen gas to the reactor. The process reduces the concentration of Si—H bonds in the silicon nitride film to provide UV transmissivity. Further, the amount of nitrogen in the film is greater than in a standard PECVD silicon nitride film, and as a percentage constitutes a greater part of the film than silicon. The film has excellent step coverage and a low number of pinhole defects. The film may be used as a passivation layer in a UV erasable memory integrated circuit.
1. A method for forming a ultra violet (UV) light transmissive silicon nitride film, comprising:
providing a plasma-enhanced chemical vapor deposition (PECVD) reactor with a semiconductor substrate therein;
flowing a gas mixture comprising silane, ammonia, and nitrogen into the PECVD reactor, wherein a flow rate of the silane is between about 130 sccm and about 180 sccm, and a flow rate ratio of the silane to nitrogen is at most 1:50; and
forming a plasma in the PECVD reactor, whereby the UV light transmissive silicon nitride film is deposited on the semiconductor substrate.
2. The method of claim 1 , wherein forming the plasma comprises simultaneously applying both a low frequency RF power and a high frequency RF power to the plasma reactor.
3. The method of claim 1 , wherein the UV light transmissive silicon nitride film has a density of Si—H bonds of about 2e21 bonds/cm 3 or less.
4. The method of claim 1 , wherein the UV light transmissive silicon nitride film has a greater stoichiometric amount of nitrogen than silicon therein.
5. The method of claim 1 , wherein a flow rate ratio of the silane to nitrogen is 1:100±10%.
6. A method for forming a ultra violet (UV) light transmissive silicon nitride film, comprising:
providing a plasma-enhanced chemical vapor deposition (PECVD) reactor with a semiconductor substrate therein;
flowing a gas mixture comprising silane and nitrogen into the PECVD reactor, wherein a flow rate of the silane is between about 130 sccm and about 180 sccm, and a flow rate ratio of the silane to nitrogen is at most 1:50;
forming a plasma in the PECVD reactor, whereby the UV light transmissive silicon nitride film is deposited on the semiconductor substrate, said UV light transmissive silicon nitride film having a stoichiometric composition comprising Si x N y H z , wherein y>x, and a UV transmissivity of at least 60%.
7. The method of claim 6 , wherein the gas mixture further comprises ammonia.
8. The method of claim 2 , wherein forming the plasma comprises simultaneously applying both a low frequency RE power and a high frequency RE power to the plasma reactor.
9. The method of claim 6 , wherein the UV light transmissive silicon nitride film has a density of Si—H bonds of about 2e21 bonds cm 3 or less.
10. The method of claim 6 , wherein a flow rate ratio of the silane to nitrogen is 1:100±10%.