Polyimide surface treatment by atmospheric pressure plasma for metal adhesion

The surface of polyimide (PI) films before/after plasma surface treatment using a remote-type modified dielectric barrier discharge was investigated to improve the adhesion between the PI substrate and the metal thin film. Among the plasma treatments of the PI substrate surface using various gas mixtures, the surface treated with the N₂ /He/S F₆ / O₂ plasma showed the lowest contact angle value due to the high CO bondings formed on the PI surface, while that treated with N₂ /He/S F₆ showed the highest contact angle value due to the high C- Fx chemical bondings on the PI surface. Specifically, when the O₂ gas flow was varied from 0 to 2.0 slm in the N₂ (40 slm) /He (1 slm) /S F₆ (1.2 slm) / O₂ (x slm) gas composition, the lowest contact angle value of about 9.3° was obtained at an O₂ gas flow of 0.9 slm. And it was due to the high content of oxygen radicals in the plasma, which leads to the formation of the highest CO bondings on the PI surface. When the interfacial adhesion strength between the Ag film and PI substrate was measured after the treatment with N₂ (40 slm) /He (1 slm) /S F₆ (1.2 slm) / O₂ (0.9 slm) followed by the deposition of Ag, a peel strength of 111 gf/mm was observed, which is close to the adhesion strength between a metal and the PI treated by a low pressure plasma.