Microfabricated AFM probe with tungsten cantilever and < 40 nm pyramidal tip

In the past, conducting AFM probes have been made by coating standard Si-cantilevers and tips with a thin film of e.g. tungsten (W). Here, we describe a new AFM probe made entirely out of tungsten. The fabrication involves microfabrication techniques such as surface moulding, thin-film structuring of W and high aspect-ratio SU-8 patterning. The metallic cantilever and tip are attached to a SU-8 photopolymer body. The free-standing 500-nm-thick cantilevers are obtained by a wafer-through etching. Cantilever resonance frequencies range between 35 kHz and 1 MHz as measured by optical interferometry, which corresponds well to theoretical values assuming Ew= 410 MPa, ρw= 19.3 g/cm^3. The AFM probes have been designed for conducting mode imaging at the nanoscale whereas W has been chosen for its excellent properties in electrical conductivity and wear. First characterization has demonstrated AFM imaging capability. A critical parameter is stress-induced cantilever bending which can be minimized by optimization of process parameters such as W sputtering and annealing.