The integration of CMOS with plasma-enhanced micromachining

The integration of micromechanical devices in a microsystem with microelectronic circuitry seems to be one of the most interesting and promising directions of the development of silicon technology. Basically, surface micromachining, which uses a specific sequence of deposition and etching processes is more compatible with high-volume CMOS technology. However, high-temperature annealing, which is necessary to relax stress in thick CVD layers, could affect the performance of a microelectronic device if the IC is fabricated first, followed by the fabrication of the micromachined device. The reverse of this process would damage the already created micromechanical structures. In bulk micromachining, no such annealing is required, and thus, using carefully selected and optimized etching processes and adequately chosen masking materials, the integration of micromachining and CMOS can be performed. In this paper, micromachining techniques and the possibility of their integration with CMOS are discussed. The applicability of various possible integration schemes is considered. It is shown that thorough use of the plasma etching technique enables the integration of bulk micromachining with CMOS. The technique is demonstrated using an AFM sensor as an example. (C) 1997 Elsevier Science S.A.