Fabrication of silicon electrodes used for micro electrochemical machining

In micro electrochemical machining (ECM), stray corrosion always causes undesired material dissolution and deteriorates the machining localization. Adopting sidewall insulating films on the electrode is proven to be an effective approach for reducing stray corrosion. Sidewall films with characteristics of good insulation, thin thickness, and excellent durability are required. In previous work, we proposed a heavily-doped silicon electrode, on which silicon-based films were prepared and acted as the insulating films. To fabricate silicon electrodes, this research investigates wet etching behavior of heavily doped Si (100) and then presents a fabrication process. Firstly, shapes of micro electrodes are designed on photomasks of lithography. Aiming at patterned profiles, effects of etchants on etch rate, dimension accuracy and surface integrity are investigated. Experimental results indicate that tetramethylammonium hydroxide (TMAH) leads to smoother electrode surfaces and fewer defects compared with potassium hydroxide. Then, insulation and durability performances of silicon-based films are investigated. 500 nm SiO2 and 300 nm Si3N4 composite film achieves more durable insulation and excellent compactness. Consequently, silicon electrodes with the dimension of 86 x 54 mu m are fabricated on the Si (100) wafer with 25 wt% TMAH etchant, on which SiO2 and Si3N4 film is deposited by low-pressure chemical vapor deposition. In ECM experiments, stray corrosion of the non-machined surface is significantly reduced, and the sidewall taper of the machined structure is reduced to 5.5 degrees. The validity and durability of silicon electrodes for micro ECM processes are verified.