Oxynitride-dioxide composite gate dielectric process for MOS manufacture

Claim 1

Method for making an MOS integrated circuit of the kind in which at least one transistor has a composite gate dielectric comprising a substantially silicon dioxide layer overlain by a silicon oxynitride layer, the method comprising: a) forming a dielectric layer on a principal surface of a silicon substrate; b) depositing a gate electrode layer over the dielectric layer; c) patterning the gate electrode layer, thereby to define at least one gate contact; and d) doping a source region and a drain region in substrate portions that lie adjacent the gate contact, characterized in that the step of forming a dielectric layer further comprises: e) forming a silicon oxynitride layer having a thickness in the range 30Å-100Å; and f) then subjecting the substrate to an oxidizing atmosphere such that chemical species comprising oxygen migrate through the oxynitride layer to a surface layer of the substrate and react therewith, resulting in the growth of a substantially silicon dioxide layer having a thickness in the range 5 Å-30 Å adjacent and underlying the silicon oxynitride layer, thereby to form said composite gate dielectric.