Conformal Coating of Organic Dielectric Film on Gold Electrodes in Microelectromechanical System Devices by Electrodeposition

Abstract

This paper describes a technology to prevent sticking between actuator and control electrode during microelectromechanical system device operation. The technology involves the electrodeposition of organic dielectric film on the gold electrode. The focus is on solving the problems found on gold surfaces that have passed through many fabrication-process steps, which are an incubation period and two types of anomalous growth (selectivity loss and skirt growth). Two pre-treatments and one post-treatment solve each problems, respectively. The incubation period is eliminated by dipping in hydrochloric acid as a pre-treatment, which dissolves gold oxides formed during the oxygen plasma exposure used for surface cleaning or sacrificial layer ashing. The anomalous growth is suppressed by adding a hydrofluoric acid dip as a pre-treatment to improve the selectivity and by annealing the films below the glass-transition temperature as a post-treatment to suppress large film reflow. The fabricated cantilever structure with the electrode coated using this technology exhibits a conformal coating with excellent isolation between the cantilever and the electrode.