With PECVD deposited poly-SiGe and poly-Ge forming contacts between MEMS and electronics

As a structural layer for microelectromechanical systems, in situ doped polycrystalline silicon germanium (poly-SiGe) can be deposited directly through openings of the uppermost dielectric onto the underlying metal interconnects to achieve electronic connections to the CMOS electronics. Differently from the existing works where poly-SiGe was deposited with the low pressure chemical vapor deposition (LPCVD), the plasma enhanced chemical vapor deposition (PECVD) method to produce poly-SiGe films forming the structural layer and the electrical contacts has been deployed. Compared with the films deposited with LPCVD, the as-deposited PECVD films formed contacts yielding low resistivity without any extra processing, such as precleaning and annealing. To investigate the contact resistance of poly-SiGe and polycrystalline germanium (poly-Ge) on titanium, Kelvin structures were fabricated and characterized. The substrate temperatures during the deposition were as low as 375°C for poly-SiGe and 340°C for poly-Ge, and low specific contact resistances of 3.2 × 10−6 O cm2 and 8.0 × 10−6 O cm2 respectively. This is expected to arise from the additionally acquired activation energies of ions from the plasma during PECVD. It is possibly due to the additional energies from the plasma, a titanium germanosilicide interfacial layer between poly-SiGe (or poly-Ge) and titanium (Ti) can be generated without high temperature processes. A metal stack was employed, to ensure a good adhesion, to block the diffusion and serve as an anti-reflection layer at the lithography.