RECORD ETCHING RATES FOR CONTROLLED ELECTROCHEMICAL ETCHING OF SILICON MICROSTRUCTURES WITH HIGH ASPECT RATIO

We report on the controlled electrochemical etching at room temperature of deep (up to 200 μm) silicon microstructures with aspect ratio ranging from 5 to 100, fabricated at etching rates from 7 to 3 μm min-1 by adding an inert oxidant, namely H2O2, to aqueous electrolytes with low hydrofluoric acid (HF) concentration (from 5 to 8% by vol.). Under anodic biasing, the presence of H2O2 reduces the dissolution valence of silicon to 1 (typical value of about 3) by opening a more efficient silicon dissolution path with respect to the well-known Gerischer mechanism. This makes the electrochemical dissolution of silicon more effective and allows etching rates to be significantly increased at both shorter and higher depths without losing control (i.e. accuracy, roughness) in microfabrication. This work sets a novel record for the high speed fabrication of microstructures with high-aspect-ratio in silicon, and allows silicon microfabrication technology to enter a region in the parameter space etching-rate vs aspect-ratio that was so far unreachable for both commercial and research technologies.