NIST develops methods for elastic strain field mapping in semiconductor heterostructures. (General Developments).
NIST researchers are developing methods for detecting and quantifying, with high spatial resolution (sub 100 nm diameter), the elastic strains associated with selective wet oxidation of A1GaAs confined between GaAs layers. The AlGaAs to aluminum oxide transition is accompanied by volumetric compressive strains in excess of 6%, sometimes leading to detrimental stress relaxation in the form of delamination or dislocation formation. The industry need is to measure and control elastic strain development in such systems. Automated electron backscatter diffraction measurements have revealed both the extent of the elastic strain field in the neighborhood of an oxide growth front as well as the magnitude of elastic strain at any position in that field. The extent of the field is in the range of micrometers about the front, and becomes apparent through mappings of pattern sharpness. Researchers suggest that pattern sharpness, which is a measure of the distribution of lattice spacings, decreases as the magnitude of the localized elastic strain gradient increases within the sampling volume of the electron beam. The magnitude of elastic strain is measured by means of lattice spacing determinations from Kikuchi bandwidths, with a resolution approaching 0.1% strain.
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