Elastic relaxation in an ultrathin strained silicon-on-insulator structure

Coherent x-ray diffraction was used to study the relaxation in single ultrathin strained silicon structures with nanoscale accuracy. The investigated structure was patterned from 20 nm thick strained silicon-on-insulator substrate with an initial biaxial tensile strain of 0.6%. Two-dimensional maps of the post-patterning relaxation were obtained for single 1 × 1 μm2 structures. We found that the relaxation is localized near the edges, which undergo a significant contraction due to the formation of free surfaces. The relaxation extent decreases exponentially towards the center with a decay length of 50 nm. Three-dimensional simulations confirmed that over-etching is needed to explain the relaxation behavior.