Journal of Micromechanics and Microengineering vol:20 issue:9
Polycrystalline silicon-germanium (poly-SiGe) has already been shown to be an excellent structural material for microelectromechanical systems. It also enables a monolithic integration with CMOS due to its deposition temperature similar to 450 degrees C. An important factor in the success of this monolithic integration is the electrical resistance between MEMS and CMOS. In this paper the contact resistance between a poly-SiGe MEMS electrode and an Al-top CMOS electrode was investigated using a stacked Greek cross structure. It was significantly reduced by the use of a combined soft sputter etch and a Ti-TiN interlayer. All parameters influencing the contact resistance were identified and taken into account to determine the specific contact resistivity using a simplified model. A very low specific contact resistivity of 3.15 x 10(-7) Omega cm(2) was achieved on combining an Ar soft sputter etch (20 nm) and a Ti-TiN (5-20 nm) interlayer. The resistivity achieved is better than previously reported values using a complex Ni-silicide process.