(Invited) A Wet Process of Copper Wiring on Surface Modified Polyimide Film By Aminosilanes

Polyimide (PI) film is widely used in several applications especially in the electronics industry, e.g., as a base material for flexible printed wiring assembly, because of its excellent mechanical and thermal stability and a low dielectric constant. Our group proposed an all-wet process to fabricate the diffusion barrier layer and Cu wiring by using an organosilane layer as an adhesive/catalyst layer as shown in fig. 1 [1, 2]. Additionally, wet processes offer relatively simple procedures and tools, and usually are cost effective.

In previous study, an immobilized aminosilane film on polyimide works as an adhesion layer and a catalyst supporting layer for electroless deposition (ELD) of NiB. Adhesion of NiB-ELD film on ultra-smooth polyimide is a particular need for realizing a high-density printed circuit board [3]. We have reported that an induction time of NiB-ELD was changed by the number of amino groups in aminosilane, and a shorter induction time was found in the aminosilane having two or three amino groups as compared with that having single.

Our recent critical problem is in the step of Cu deposition onto NiB-ELD: a low reduction rate of cupric ion in sulfuric acid, or if the reduction proceeded, the film peeling was observed. We therefore used the alkaline electrolytes developed by Japanese company or it’s improved to fabricate Cu wiring, and examined thermal annealing effect on the electronic conductivity, crystallinity.

References

[1] T. Osaka, M. Yoshino, “New Formation Process of Plating Thin Films on Several Substrates by Means of SAM (Self-Assembled Monolayer) Process”, Electrochim. Acta, 53, 271 (2007).

[2] M. Yoshino, T. Masuda, T. Yokoshima, J. Sasano, Y. Shacham-Dimand, I.Matsuda, T. Osaka, A. Hashimoto, Y. Hagiwara, I. Sato, “Electroless Diffusion Barrier Process Using SAM on Low-k Dielectrics”, J. Electrochem. Soc, 154, D122 (2007)

[2] T. Osaka, S. Wakatsuki, T. Masuda, M. Yoshino, N. Yamachika, J. Sasano, I. Matsuda, Y. Okinaka, “A Wet Process for Forming an Adhesive Copper Layer on Polyimide Film”, Electrochemistry, 76, 191 (2008).