New fabrication process for monolithic probes with integrated heaters for nanothermal machining

In this study, we developed a new fabrication process for a micromachined probe. The microprobe comprised a microcantilever, a nanotip and a supporting substrate, which are monolithically made of single-crystal silicon. The fabrication process started with a bilayer silicon wafer made up of a 20-μm-thick epitaxial Si layer with strong boron doping and a 400-μm-thick bulk Si substrate. The tip with a radius of curvature of 50 nm was formed by anisotropic etching followed by oxidation sharpening. Then a cantilever beam was released by the back etching of an etch-stop Si layer. The spring constants of cantilevers ranging from 0.03 to 0.4 N/m were determined by finite element analysis (FEA), static measurement using an atomic force microscope (AFM) system and dynamic measurement using a laser Doppler vibrometer (LDV) system. Most importantly, Young's modulus of thin-film materials could be confirmed using these methods. The developed probe was also equipped with a Pt heater to apply it to thermal machining on poly(methyl methacrylate) (PMMA) substrates. The cantilever tip was heated to above 120°C, and the successful machining of a cavity and a submicron-scale straight line was demonstrated. The development of the probes could be crucial for the submicron-scale machining of plastic materials.