Nitrogen mixed into silicon dioxide on Si(100) is used in the present, and maybe last, generation of silicon oxide-based complementary metal-oxide semiconductor (CMOS) components to improve various properties of the gate dielectric. A pure nitride layer could offer certain advantages, but has been found to be less optimal than oxide for Si(100). In this work, the growth of pure ultrathin $(<3\mathrm{nm})$ silicon nitride films directly on Si(111) is achieved in reactions between the Si surface and atomic N, in an isothermal process at low temperatures $(300°\mathrm{C}\text{to}800°\mathrm{C})$ using a remote, microwave-excited nitrogen plasma connected to an ultrahigh vacuum chamber through a pressure differential stage. For this system, recent results have shown the possibility of a good interface with epitaxial crystalline ${\mathrm{Si}}_3{\mathrm{N}}_4$. In the present work, attention is paid to understanding the conditions separating the growth of amorphous ultrathin silicon nitride from the growth of crystalline structures during this process because the amorphous, ultrathin silicon nitride might be the best substitute for silicon oxide since ultrathin crystalline films grown in this way are microcrystalline.

• Received 2 December 2004

DOI:https://doi.org/10.1103/PhysRevB.72.205323