Lattice strain in oxidized Si nanostructure arrays from X-ray measurements

Although lattice strains in oxidized wafers can be detected by optical and X-ray methods the measurement of strains in non-planar structures such as occur in Si devices is more difficult. We describe a novel technique for measuring such strains and report results for oxidized Si. In our work we have fabricated regular arrays of Si pillars on a Si(001) surface and measured the strain in the individual pillars induced by oxidation. The pillars have diameters of the order 100 nm and spacing of ~300 nm. With high resolution X-ray techniques this spacing is sufficiently small to allow the ‘superlattice’ diffracted beams from the fabricated structure to be well resolved. We measure the strain from the displacement of this superlattice diffraction pattern relative to the normal allowed bulk reflections. We report results for different combinations of Si pillar diameter and oxide thickness. Differential thermal contraction also contributes to the strain. The measured strains are of the order of 10 −4. Our results are in good agreement with simulations based on current models of Si oxidation.