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 mechan ical adhesion of thick microstructures to the substrate. The interfacial bo nd 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 hav e been investigated. A mechanical type of adhesion was promoted by modifyin g the morphology of surfaces. Ti or Cu were microroughened by chemical oxid ation and acrylic resist sheets thermally processed. The largest increase i n adhesion was obtained with a combination of both substrate and resist tre atments. The use of Novolak resists as interfacial layers enhanced adhesion , independently of the nature of the substrates. Severalfold increases in b ond strengths were also obtained using various primers, such as 3-aminoprop yl-triethoxysilane on Au and Cu substrates. (C) 1998 American Vacuum Societ y. [S0734-211X(98)06306-9].