Thin Film Metal Surface Micromachining: a new enabling foundry technology

摘要

A new generation of products has been developed at research institutes needing a combination of thin film metal processing and surface micromachining. This especially applies to RF MEMS switches and related products that are now entering the market. These products are not only complex in architecture, they also feature relative thick metal layers. The thicknesses of the metal layers give rise to problems in the field of step coverage, dimension control and limited resistance to etching agents. Reliability and yield in production is therefore a major concern. To make robust, compact and reliable structures, combinations of electroplating and Chemical Mechanical Polishing are used. The combinations are not only new in this area; they are rather different from the standards in the semiconductor industry, where the technology was developed. The process modules are used in RF MEMS to create the thick signal lines, as well as the delicate switch and varactor structures. The basic processes, tried and tested in the production of magnetic heads, had to be modified to meet the special demands of RF MEMS. Also new processes had to be introduced to create free hanging membranes. Due to the fragility of the structures, a special technology is being developed in the backend processing: wafer scale packaging. This article gives an overview of the processes, the challenges met and the results of the work on RF MEMS at the OnStream MST foundry.