All-metal AFM probes fabricated from microstructurally tailored Cu–Hf thinfilms

Abstract

A growing number of atomic force microscope (AFM) applications make use ofmetal-coated probes. Probe metallization can cause adverse side-effects and disadvantagessuch as stress-induced cantilever bending, thermal expansion mismatch, increasedtip radius and limited device lifetime due to coating wear. In this study wedemonstrate how to overcome these limitations using microstructural design tocreate a metallic glass thin film alloy, from which monostructural all-metal AFMcantilevers are fabricated. A detailed compositional study of co-sputtered Cu–Hffilms is performed using x-ray diffraction (XRD), nanoindentation, four-pointprobe and in situ multi-beam optical stress sensing (MOSS). Metallic glassCu90Hf10 films are found to possess an optimal combination of electrical resistivity(96 µΩ cm), nanoindentation hardness (5.2 GPa), ductility and incremental stress. A continuum model isdeveloped which uses measured MOSS data to predict cantilever warping caused by stress gradientsgenerated during film growth. Subsequently, a microfabrication process is developed to createCu90Hf10 AFM probes. Uncurled,1 µm thick cantilevershaving lengths of 100–400 µm are fabricated, with tip radii ranging from 10 to 40 nm. As a proof of principle, theseall-metal Cu–Hf AFM probes are mounted in a commercial AFM and used to successfullyimage a known test structure.