FRONTSIDE BULK SILICON MICROMACHINING USING POROUS-SILICON TECHNOLOGY

Porous-silicon technology is successfully used for frontside bulk sili con micromachining in a process which is fully C-MOS compatible. Porou s silicon is used as a sacrificial layer and it is removed by C-MOS-co mpatible chemicals, leaving a very smooth bottom surface and sidewalls . Deep trenches, bridges with suspended membranes and cantilevers are formed, which open new possibilities in monolithic integration of sens ors with electronics. Cavities as deep as similar to 120 mu m and susp ended polysilicon membranes with a flat surface as large as 230 mu m X 550 mu m have been fabricated by this process. Also other micromechan ical structures such as very flat polysilicon cantilevers of dimension s 150 mu m X 2 mu m X 2 mu m are easily obtained after optimization of the process in order to minimize the strain within the polysilicon fi lms. (C) 1998 Elsevier Science S.A.