Anisotropic etching in KOH solution with electrochemical stopping is commonly used in formation of thin silicon membranes of sensitive elements in various MEMS devices. However, the data of investigating the process of electrochemical stop-etching of elements in various MEMS devices are absent. In the work the process of electrochemical stop etching in KOH solution for structures using the n-type silicon layers, formed by diffusion on the p -type silicon substrate with a smooth and relief surface, has been studied. It has been studied that when using a 2-electrode circuit with positive (relative to the solution) voltage, applied to an n-layer, for a structure with an n-layer, formed on a smooth surface, the etching stops at the pn -junction boundary and as the result, a membrane forms, uniform in thickness over the entire area of the plate. When using a 2-electrode circuit for a structure with a relief surface during etching the current density J is 70-100 times greater than in the case of a smooth surface, the etching is non-uniform across the plate and stops long before reaching the pn -junction. It has been found that for a structure with a relief surface when using a circuit with two voltage sources, with an additional negative (relative to the solution) voltage, applied to the p-substrate at U » -2.0 V, the etching stops at the pn -junction interface, and as the result, it is possible to obtain silicon membrane, fairly uniform in thickness over the entire area of the plate. The dependences of the current density J (between the n -layer of silicon and the solution) on the etching time t have been obtained for the structures with a smooth and relief surface, which makes it possible to determine the end of the etching process.
Andrey V. Novak
National Research University of Electronic Technology, Moscow, Russia; OJSC «Angstrem», Moscow, Russia
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