Surface micromachining is the fabrication of micromechanical structures by deposition and etching of thin structural and sacrificial films. Thus, simple microstructures like beams or membranes as well as complex structures like linkages or encapsulated resonators can be fabricated on top of a silicon substrate. A processing sequence using polysilicon as micro-structural material and silicon dioxide as sacrificial layer is significant part of this procedure.


The main features of the surface micro-machining technology are the small microstructure dimensions and the opportunity to integrate micromechanics and microelectronics on the same chip. By use of VLSI compatible batch processing, low cost microstructure fabrication can be achieved for high volume applications.


There are three key challenges in fabrication of microstructures using surface micromachining:

  • Control of stress and stress gradient in the structural layer to avoid bending or buckling of the released microstructure
  • High selectivity of the sacrificial layer etchant to functional layers
  • Avoidance of sticking of the released microstructure to the substrate

CVD and thermal silicon oxide films are used as sacrificial layer, which can be etched with high selectivity against silicon using hydroflouric acid. However, after wet-etching of the sacrificial layer, rinsing and drying the microstructures causes the structures to be pulled down and to stick to the substrate by capillary forces. Preventing this is a solvable task through surface modification and the choice of the right process.

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