Ultra-thin oxides on silicon fabricated using ultra-slow multicharged ion beams

We have used ultra-slow multicharged ions in ultra-high vacuum with a low partial pressure of O₂ to grow ultra-thin layers (0.3 to 2.0 nm) of SiO₂ on silicon. The advantage of using ultra-slow ions is that they interact with the surface only through their potential energy, not their kinetic energy, so they do not penetrate below the surface, avoiding implanted-induced damages to the substrate. This paper presents several analysis we have performed to qualify these ultra-thin SiO₂ layers, such as Fourier transform infrared spectroscopy–attenuated total reflection, Auger electron spectroscopy, X-ray photoelectron spectroscopy, spectroscopic ellipsometry and surface charge analysis. The oxidation process was monitored in situ and in real time using visible light emitted during the irradiation, and the thickness of the SiO₂ layers could be controlled. We plan to used these ultra-thin SiO₂ layers in next generation MOS gate dielectric stack, as a buffer layer between the channel in silicon and a high-k dielectric.