Reduction of Sheet Resistance and Low-Thermal-Budget Relaxation of Stress Gradients in Polysilicon Microcantilever Beams Using Nickel-Silicides

Nickel-silicide (Ni_xSiy) is formed by the reaction of nickel and silicon at the temperature of couple of hundred degrees Celsius. Nickel-silicide technology is employed for the purpose of application in polysilicon-based microelectromechanical systems (MEMS) devices to reduce sheet resistance as well as to control residual stress gradients of the structures. To improve the compatibility of nickel-silicide with MEMS micromachining, anticorrosion release method is developed using cathodic protection. In situ study of stress evolutions during the reaction of a nickel film with polysilicon is quantitatively investigated using wafer curvature measurements. The phase of nickel-silicide is validated by using X-ray diffraction. The stress developed during the silicidation is utilized to control the stress gradient in polysilicon microcantilever beams. The experimental results show that the sheet resistance changes from over 20 000 Omega/sq. (insulating material) to less than 10 Omega/sq. The stress gradient is relaxed by counterbalancing the tensile residual stress at the upper part of a cantilever with a built-up compressive stress when the annealing temperature is 290 degC