Defects Suppression of Ni-P thin Film on Polymer Substrate via catalyzation in Sc-CO_2 and Electroless Plating in Sc-CO_2 emulsion

摘要

The flexible and biocompatible properties of polymer make polymer MEMS promising candidates for the next generation of micro devices. Bio-medical micro devices such as intracortical electrode on polymer substrate for neural interface are envisioned[1-2]. Polyimide has many outstanding properties, including good thermal stability, low dielectric constants, low dissipation factors, and inherent surface inertness. In addition, the polyimide surface chemistry is amenable to modifications and preparations which allow a host of bioactive organic species to be either adsorbed or covalently bonded to its surface[3]. These properties are important for application in MEMS technology. The best way to improve the quality of the metallization on polymer will be to develop a novel micro-fabrication technique for plating metal onto polymer substrate. Electroless plating were widely used for making thin film on organic substrate. Yet polymer substrates are hydrophobic and respond poorly to the wetness of the electroplating solution. One way to achieve contact Pd catalyzation on polymer substrate under this condition is to change from a hydrophobic to a hydrophilic surface. Chromate treatment has been used for this purpose in conventional catalyzation, but the environmental affinity restricts the applicability[4]. To alleviate this problem, we proposed a novel technique which is carried out in Sc-CO_2 with organic Pd complex in catalyzation procedure and an electroless plating reaction are conducted in emulsion of Sc-CO_2 and electroless plating solution with surfactant[5]. In previous experiment, we obtained an Ni-P thin film with fewer pinholes and voids by catalyzing the polyimide using supercritical CO_2 and an electroless plating mixing emulsion. Moreover, we discussed Sc-CO_2 effect on nucleation and nuclei growth of catalyst for uniform and smooth metallization on polymer through quantitative microscopic method on the microscopic images of the catalyzed substrates and the plated films with comparison with conventional catalyzation[6-7]. However, the problems to solve which individual properties of Sc-CO_2 play a dominant role to suppress the defects are remained. If we are to use this method, we must clarify effects of Sc-CO_2 for suppression of voids on electroless plated thin metal film and improvement of interface stability between fabricated metal and polymer substrate. In this report, we discuss how transport properties of Sc-CO_2 and the affinity with substrate affect the suppression of the defects in Ni-P thin film on polyimide substrate.