Reaction–diffusion in high-k dielectrics on Si

Thinning of the gate dielectric as required by scaling rules is currently inhibiting the so far outstanding evolution of the silicon age, owing to unacceptably high gate current (leakage current) arising from electron tunneling through the gate dielectric ultrathin layer. One possible solution is to use an alternative material to SiO2, which would interrupt more than 40 years of successful microelectronics technology based on Si and SiO2. This article discusses atomic scale investigation on the underlying difficulties of introducing ultrathin films of metal oxides, silicates, and oxynitrosilicates having dielectric constants much higher than that of SiO2—called high-k dielectrics—as gate dielectrics in advanced, Si-based metal-oxide–semiconductor field-effect transistor (MOSFET) fabrication. More specifically, we address atomic transport and chemical reaction processes generating instabilities in high-k dielectric films during different thermal processing fabrication steps following their deposition on (i) single-crystalline Si substrates or (ii) single-crystalline Si substrates on which SiO2, SiNx, or SiOxNy ultrathin films were either unintentionally formed during deposition or intentionally grown previously to high-k film deposition. A most typical reaction–diffusion situation is established in near-surface, bulk, and near-interface regions of this large family of amorphous ultrathin films deposited on Si, whose phenomenology, mathematical modeling, and atomic scale understanding constitute the subject of this article.