Optimization of low-pressure plasma reactor for high-speed surface treatment of polyimide substrate

Summary form only given. Poor adhesive property of polyimide (PI) films limits their application to the flexible substrate. Hydrophilicity of polymer films is caused by the scission of chemical bonds in the polymer´s backbones and the grafting of functional groups onto the polymer´s surface. Thus, the working gas and pressure, input power, and gas flow rate can influence the adhesion of polymer films. In this work, we tried to find the optimum operation parameter of low-pressure plasma reactor for high-speed adhesion improvement of a polyimide substrate. A shower-head type plasma reactor was designed and fabricated, and its surface treatment performance was evaluated in terms of water contact angle (WCA). By varying the plasma exposure time, the WCAs of PI film were measured for three gas mixtures, Ar-O₂, Ar-N₂, and Ar-NH₃. Under the fixed plasma exposure time, the WCAs of PI film were measured with changing the gas flow rate, input power, and working pressure. The changes in surface property of the PI film before and after plasma treatment were evaluated by using the X-ray photoelectron spectroscopy (XPS) and atomic force microscope (AFM). Finally, the optimum operation parameter for high-speed surface treatment of polyimide substrates was determined based on the experimental results.