A Novel Deep Silicon Etching for Bulk-Micromachined RF MEMS Devices

This paper describes a new micromachinig method for deep silicon etching. Deep silicon etching is used in the realization of bulk-micromachined transducers and RF MEMS devices. The specific aim is to establish a deep silicon etch process with minimum anisotropy suitable for bulk micromachined electrostatic RF switches. The work has basically been focused on three research components: recognition of challenging areas, searching for appropriate and inexpensive deep etching methods and running preliminary experiments. Uniformity, anisotropy, mask material defects and surfactants are of the factors studied in order to establishing a reliable deep silicon etching process. Reliability has a significant influence on the long-term performance of MEMS devices and also on the final yield. In this paper, wet etching has extensively been employed to establish a new deep etching method. For the wet etching methods factors like etching solution, solution concentration, etching temperature, and agitation have been under close investigation. This paper initially describes how uniform etching was achieved for up to 0.35 mm deep silicon etching by using a new concept of alternate etch and dry steps. Then, this new micromachining technique was used to etch a full-scale 4" wafer with a 2 mm-depth. Anisotropy was at a maximum lOum lateral etching.