Process for producing micromechanical structures by means of reactieve ion etching

A process for producing etched micromechanical structures is provided, using Reactive Ion Etching (RIE), wherein a substrate is etched with a silicon etch gas mixture to obtain an aspect ratio of at least 10. The process comprises the steps of: a) anisotropic etching using a first silicon etch gas to obtain a primary microstructure; b) depositing a halocarbon film on the walls of the primary microstructure; d) isotropic etching using a second silicon etch gas, to obtain a final microstructure; said steps being carried out in a single run. Optional further steps are: c) etching the floor of the primary microstructure using said first silicon etch gas; and e) depositing a halocarbon film on the surface of the final microstructure. The process may involve applying high pressure (5-30 Pa) and low energy (10-90 eV), and preferably the use of a sulphur hexafluoride/oxygen/trifluoromethane plasma. The process can be controlled by monitoring the blackening of a silicon test surface as a function of varying the process parameters.