Multilayer ono structure

Abstract

Dielectric structures of the type that might be used in DRAMs, other memory devices, and integrated thin film transistors include repeated silicon oxide/silicon nitride layers. For example, the dielectric structure may have a silicon oxide/silicon nitride/silicon oxide/silicon nitride/silicon oxide or 'ONONO' layer structure. Such repeated layer structures exhibit higher levels of breakdown voltage than more conventional 'ONO' structures. Most of the growth of the five layer ONONO or more complicated dielectric structure can be accomplished in a single furnace through a series of temperature steps performed under different gas ambients. A substrate having a polysilicon lower electrode is introduced to a furnace and a lowest layer of silicon oxide is grown on the polysilicon electrode in an ammonia ambient. A first silicon nitride layer is grown in NH.sub.3 and SiH.sub.2 Cl.sub.2 and then growth of the first silicon nitride layer is interrupted by first altering or stopping the flow of reaction gases and then growing an intermediate silicon oxide layer on the first silicon nitride layer, again in an ammonia ambient. A second silicon nitride layer is then formed by reintroducing the same combination of processing gases. Growth of the second silicon nitride layer is then interrupted, and either additional repetitions of the silicon oxide/silicon nitride layer structure are formed or a surface layer of silicon oxide is grown in a steam or wet oxygen ambient.