Adhesion promotion between poly(methylmethacrylate) and metallic surfaces for LiGA evaluated by shear stress measurements

The fabrication of high-aspect-ratio microelectromechanical structures (HI-MEMS) using the LiGA process [German acronym for Lithography, Galvanoplasty, and molding (Abformung)] requires both sufficient lithographic and mechanical adhesion of thick microstructures to the substrate. The interfacial bond strength between poly(methylmethacrylate) and various metal surfaces (Ti, Cu, and Au), in the preliminary stages of the LiGA process, was evaluated by shear stress measurement. In addition, adhesion promotion processes have been investigated. A mechanical type of adhesion was promoted by modifying the morphology of surfaces. Ti or Cu were microroughened by chemical oxidation and acrylic resist sheets thermally processed. The largest increase in adhesion was obtained with a combination of both substrate and resist treatments. The use of Novolak resists as interfacial layers enhanced adhesion, independently of the nature of the substrates. Severalfold increases in bond strengths were also obtained using various primers, such as 3-aminopropyl-triethoxysilane on Au and Cu substrates. (C) 1998 American Vacuum Society. [S0734-211X(98)06306-9].