Directional-rolling method for strained SiGe/Si films and its application to fabrication of hollow needles

A method enabling stress-driven directional rolling of patterned SiGe/Si films released from selectively etched Si substrates, is presented. Selective orientation-dependent etching of sacrificial single-crystal Si substrates is shown to permit: i) robust rolling of SiGe/Si films, released from substrates, in directions along which the lateral etch rate of the substrates is maximal; and ii) suppression of detrimental rolling of the films on pattern edges where vertical walls bounded by {111} stopping planes self-form during the etching. Efficiency of the method is demonstrated with the example of controlled directional rolling of SiGe/Si films, lithographically defined on (110) Si substrates as long narrow strips, in free-standing precise-diameter microtubes-needles. A technique making it possible to obtain chips with tubes protruding over substrate edges is introduced, which incorporates through-etching of (110) Si substrates in KOH : H2O solution, followed by subsequent cleaving of the substrates with SiGe/Si rolled tubes along cleavage planes.