Study of Direct-Contact HfO₂/Si Interfaces.

Controlling monolayer Si oxide at the HfO₂/Si interface is a challenging issue in scaling the equivalent oxide thickness of HfO₂/Si gate stack structures. A concept that the author proposes to control the Si oxide interface by using ultra-high vacuum electron-beam HfO₂ deposition is described in this review paper, which enables the so-called direct-contact HfO₂/Si structures to be prepared. The electrical characteristics of the HfO₂/Si metal-oxide-semiconductor capacitors are reviewed, which suggest a sufficiently low interface state density for the operation of metal-oxide-semiconductor field-effect-transistors (MOSFETs) but reveal the formation of an unexpected strong interface dipole. Kelvin probe measurements of the HfO₂/Si structures provide obvious evidence for the formation of dipoles at the HfO₂/Si interfaces. The author proposes that one-monolayer Si-O bonds at the HfO₂/Si interface naturally lead to a large potential difference, mainly due to the large dielectric constant of the HfO₂. Dipole scattering is demonstrated to not be a major concern in the channel mobility of MOSFETs.