Methods for forming dielectric layers over polysilicon substrates, useful
in the construction of capacitors and other semiconductor circuit
components are provided. A self-limiting nitric oxide (NO) anneal of a
polysilicon layer such as an HSG polysilicon capacitor electrode, at less
than 800.degree. C., is utilized to grow a thin oxide (oxynitride) layer
of about 40 angstroms or less over the polysilicon layer. The NO anneal
provides a nitrogen layer at the polysilicon-oxide interface that limits
further oxidation of the polysilicon layer and growth of the oxide layer.
The oxide layer is exposed to a nitrogen-containing gas to nitridize the
surface of the oxide layer and reduce the effective dielectric constant
of the oxide layer. The process is particularly useful in forming high K
dielectric insulating layers such as tantalum pentoxide over polysilicon.
The nitridized oxynitride layer inhibits oxidation of the underlying
polysilicon layer in a post-treatment oxidizing anneal of the high K
dielectric, thus maintaining the oxide layer as a thin layer over the