Microfabricated silicon coaxial field sensors for near-field scanning optical and microwave microscopy

We report a comprehensive process for fabricating silicon-based near-field electromagnetic antennas that are used with scanning force microscopy (SFM), and we also present initial results from measurements made with these tips. We present processes to make coaxial and diode tips. In both processes, anisotropic reactive ion etching (RIE) is used to define the tip and special resist spinning protocols are used to create sub-micrometer openings. One process results in a shielded coaxial tip structure used for electric field imaging in the microwave regime. By varying a few steps, Schottky diode junctions are formed at the tips and can act as optical sensors. The resulting tip opening is in the range of 100 nm for photodiode tips and 500 nm for open-ended coaxial tips. We have integrated such tips with the appropriate cantilevers, chip bodies, electrical interfaces and probe station necessary for routine experimental application. We show experimental data using both types of tips.