Improvement of the poly-SiGe electrode contact technology for MEMS

Abstract

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 ⩽450 °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 × 10−7 Ω cm2 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.