Fabrication of Microcomponents by Electrochemical Manufacturing: Advanced Feed-Through Metallisation on Silicon and Nickel Micromechanical Resonators

Electrochemical processes such as electroplating, wet selective etching (or controlled corrosion) and electroless plating are powerful tools for fabrication of MEMS (Micro ElectroMechanical Systems) products. Especially when the electrochemical processes are used in combination with UV-lithography, silicon substrates and other processes traditionally associated with microelectronics. By replacing ceramic materials, in some parts of a MEMS structure, with metal - and introducing electrochemical manufacturing - the production costs can be significantly reduced. This will be illustrated by two very different MEMS component examples: An example uses electrochemical manufacturing to form multiple feed-though wires of copper (similar to printed circuit boards, but much smaller and on tree-dimensional surfaces) from one side of a silicon wafer to the other. In this example tin bumps for flip-chip bonding, as well as nickel/gold pads for conductive adhesive bonding, are also deposited by electroplating. The second example is a simple, inexpensive, low-temperature electroplating process for fabrication of released, stress-free nickel comb resonators. Since the manufacturing sequence only involves low-temperature steps, it is well suited for post processing on CMOS devices. The resonators have been tested using optical readout, and quality factors of around 550 have been measured in an atmospheric ambient.