Step Arrays at the Si(001)-SiO sub 2 Interface

Grazing incidence x-ray diffraction has been used to study the arrangement of steps at the Si-SiO sub 2 interfaces on highly oriented Si(001) substrates (miscut 0.05degrees). Prior to room temperature oxidation, an epitaxial Si layer, 100-300nm thick, is deposited by molecular beam epitaxy. Diffraction peaks arising from a staircase of steps at the interface, separated by as much as 500nm, are clearly resolved. Several orders of diffraction are present, whose separation directly yields the step height. An analysis of the peak width and of the diffuse signal shows the necessity to take into account not only a distribution of terrace widths, but also to introduce long range (~3micron) correlations between steps. Several examples are given showing the dependence of the step distribution and of the epitaxial oxide structure on the sample preparation.