Four-mask process based on spacer technology for scaled-down lateral NEM electrostatic actuators

This paper presents a four-mask fabrication process of lateral nanoelectromechanical (NEM) electrostatic actuators based on spacer technology. Critical dimensions of the actuators, i.e., the beam width and the gap size between the movable and fixed electrodes can be made smaller than the lithographic resolution by creating nitride spacers on an oxide hardmask followed by selective etching of the oxide hardmask. The combined oxide hardmask, nitride spacer, and another mask (photoresist mask) is then transferred to an underlying polysilicon structural layer to create lateral NEM electrostatic actuators with narrow beam and narrow gap.