Defects at the Si(111)/SiO2interface investigated with low-energy electron diffraction

After removal of the oxide, defects at the Si/${\mathrm{SiO}}_2$ interface have been studied by a high-resolution low-energy-electron-diffraction (HR-LEED) system. Analyzing the profile of LEED spots, we are able to detect two different kinds of defects, one due to steps and the other due to inhomogeneities. The HR-LEED measurements enable us to determine the terrace length distribution and the size distribution of inhomogeneities with atomic resolution. Both are described by a geometric distribution. The investigated samples with a thin oxide layer (10 nm, dry oxidation) are characterized by very low step densities at the interface. The boundary between the silicon crystal and its oxide is extremely sharp; within the transfer width of the instrument (∼70 nm) the interface changes between only two silicon layers. Therefore, annealing cannot drastically improve the quality of the interface. On the other side there are many inhomogeneities in small patches. In contrast to the steps, they are drastically reduced by annealing of the wafers.