Controlling monolayer Si oxide at the HfO 2 /Si interface is a challenging issue in scaling the equivalent oxide thickness of HfO 2 /Si gate stack structures. A concept that the author proposes to control the Si oxide interface by using ultra-high vacuum electron-beam HfO 2 deposition is described in this review paper, which enables the so-called direct-contact HfO 2 /Si structures to be prepared. The electrical characteristics of the HfO 2 /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 HfO 2 /Si structures provide obvious evidence for the formation of dipoles at the HfO 2 /Si interfaces. The author proposes that one-monolayer Si-O bonds at the HfO 2 /Si interface naturally lead to a large potential difference, mainly due to the large dielectric constant of the HfO 2 . Dipole scattering is demonstrated to not be a major concern in the channel mobility of MOSFETs.
Miyata, N. (2012). Study of Direct-Contact HfO2/Si Interfaces. Materials, 5(12), 512–527. https://doi.org/10.3390/ma5030512