Submicron Roughness Determination at the Si-SiO 2 Interface and Correlations to Prccessing Steps and Electronic Properties

A newly developed optical surface characterization technique using the diffuse scattered light of two laser beams will be presented. The method determines root-mean-square roughness values (RMS) of surfaces down to 1 A and corresponding correlation lengths in the submicron area. Scanning Tunneling Microscopy (STM), Transmission Electron Microscopy (TEM) and Diffraction of Low Energy Electrons (LEED) provide local information with atomic resolution revealing even monoatomic steps. It is, however, very difficult to extrapolate the atomic information of these methods to correlation lengths in the submcron range. Our lightscattering method enables a quick measurement of the total wafer surface. The determined roughness data correlate with STM- and LEED-data. Two laser beams (λ= 632 nm and λ = 325 nm) hit the surface under fixed but independantly choosable angles. The penetration depth of the light can be varied by the use of different angles of incidence permitting a differentiation between surface and bulk related defects. Completing these measurements with Total-Integrated-Scattered (TIS) light measurements we can conclude that the perfect polished wafer surface exhibits RMS-values below 1 A. Wafer processing influences the microroughness at the Si–SiO2 interface. Oxidation increases the microroughness in any case. An oxidatxon in dry atmosphere leads to higher roughness compared to wet oxidation. The roughness is a function of oxide thickness, too. There is an influence of the cleaning procedure also, which controls the chemical state of the surface. Oxidation rate and therefore interface roughness depend on it. The influence of the microroughness induced by oxidation on dielectric breakdown measurements will be shown.