Miniaturized test specimens of single-crystal silicon, fabricated by lithography and deep reactive ion etching (DRIE), were used to measure deformation and fracture properties at the micro scale. Two specimen geometries, both in the form of a Greek letter (theta), were measured using an instrumented indentation testing system that places the central web of the theta specimen in tension by compressing the outer frame. The DRIE process generated two different surface structures leading to two strength distributions that were specimen geometry independent: One distribution, centered about 2.3 GPa, was controlled by the 35 nm surface roughness of scallops from the intended DRIE; the second distribution, centered about 1.4 GPa, was controlled by larger, 200 nm, pitting defects from an unintended DRIE process. In both cases, the inferred largest controlling flaw sizes were comparable to the surface roughness. Finite element analyses were used to convert measured loads into strengths and to account for processing-induced variations in web width; tensile elastic measurements were used to validate the analyses. Fractography was used to verify failure locations. The theta specimen and testing protocols are shown to be extremely effective at testing statistically-relevant (hundreds) numbers of samples to establish processing-structure-property relationships at ultra-small scales and for determining design parameters for components of microelectromechanical systems.
Citation: Journal of Materials Research
Pub Type: Journals
Silicon, Microfabrication, Strength