Fabrication of three-dimensional silicon structures by means of doping-selective etching (DSE)

Abstract

Despite its early discovery, doping-selective etching (DSE) of silicon sensor and actuator structures has not been widely used. The potential advantages of DSE are IC compatibility, new degrees of freedom in three-dimensional micromachining and full exploitation of the excellent mechanical properties of silicon. The mechanisms of DSE are both chemical and electrochemical in nature, and can be described as a ‘race’ between dissolution and passivation of the reaction products. The process has been monitored by studying the current-voltage characteristics of homogeneous silicon wafers. Model experiments on basic sensor structures, such as thin membranes and cantilever beams, have been performed. It is shown that the sequence in patterning the structures is crucial in determining the detailed geometry. This is partly expected due to the well-known anisotropy of alkaline etchants. Some as yet unreported effects of anisotropy will be subject to further investigations. Conclusively, DSE offers new and interesting possibilities in the fabrication of sensor and actuator elements.