Modern Silicon-based MEMS Technology

Abstract

The fabrication technology for Si-MEMS devices is mainly derived from the processes used for the realization of microelectronic devices. However, due to the specific demands for MEMS, there are special processes needed for MEMS devices. In this chapter, after reviewing general aspects of microtechnology some of the specific MEMS- processes will be discussed, e.g. bulk-micromachining, surface micromachining, DRIE and SOI-technology. The success of microelectronic is strongly related to fabrication aspects. Using advanced lithography processes and sophisticated physical and chemical methods for pattern transfer minimum feature size well below 0.25 µm is achieved in today's large scale production. The reduction of minimum feature size has improved the performance of the microelectronic devices (power consumption, driving voltage, delay time) and has increased the possible complexity (transistors per chip) while keeping costs per chip almost constant during the last decades. This is achieved by a "giant in one time concept" based on parallel pattern definition processes (e.g. billions of structures are defined with one lithography step) and batch processing of several wafers at one time (e.g. oxidation). Si-based MEMS, or more generally speaking, Si-based microsystems technology, is benefitting from the achievements in microtechnology. However, it is worth while keeping in mind also the differences between microelectronics and microsystems. First, the demands on miniaturization for microsystems are not as strong as for microelectronic devices. Especially in micromechanical devices (e.g. sensors) minimum feature sizes are often well above one micrometer. Even in monolithically integrated microsystems the corresponding microelectronic part does not demand for sub-micrometer features in most cases. Secondly, the degree of standardization and the