With the silicon interface becoming increasingly scrutinized in high dielectric constant materials for SiO2replacement, fine distinctions in the quality of silicon cleaning can have a large impact on MOS parameters. One of the cleaning schemes that have potential to replace the industry standard RCA clean with HF/H2O etch is a modified version of the Shiraki clean. The evolution of Si (100) surface cleaned by the modified Shiraki method has been investigated by a conventional, single‐wave length ellipsometer. Using Low Energy Electron Diffraction (LEED), we have calibrated the ellipsometric measurement for the as‐cleaned silicon surface. It was found that a lower baseline of 0.7∼0.9 nm from ellipsometric measurements could be established as equivalent to a clean, hydrogen passivated surface. To verify the effect of the interfacial oxide thickness on the dielectric constant of the high‐k gate stack, thickness of the thin‐oxide grown under high vacuum condition was measured and correlated with the dielectric constant of the HfO2gate dielectric layer. © 2003 American Institute of Physics