Scanning electron micrographs of microfabricated strained silicon substrates for epitaxial growth. The silicon nitride thin film stressing the template layer is visible as raised regions. The areas labeled as Si refer to the SOI template layer.
(a) Synchrotron x-ray microdiffraction measurements of the strain and bending in the bridge structure used a reflection geometry for the (004) x-ray reflection and a transmission geometry for the (220) reflection. (b) A rotation of the (004) planes rotates the x-ray reflection through an angle . A change in the lattice spacing can change the angle of the reflection.
The misorientation of Si (220) planes as a function of position along the bridge measured using x-ray microdiffraction in a transmission geometry (circles). Measurements using the surface-normal (004) reflection (squares) show the same trend across the exposed portion of the bridge and a reversal in the curvature under the silicon nitride stressor. The orientation of the handle wafer (220) planes is independent of position (diamonds).
The angular width of the Si (220) diffraction spot in the direction of the conventional angle depends on the position of the x-ray beam along the bridge. The handle wafer reflection (a) serves as a benchmark. The x-ray reflections from the bridge, both at from the notch and at the notch, (b) and (c), respectively, are broadened in the direction due to the variation of the (220) spacing through the thickness of the bridge. The width of the (220) x-ray reflection varies along the length of the bridge, (d), and reaches a maximum at the notch (e). The dip at is an artifact arising from the coincidental alignment of handle wafer and bridge reflections at that location.
Estimates of the strain derived from the bending of the bridge and from the excess angular width of the diffraction spot.
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