The peel strength of Cu thin film deposited on polyimide substrate is known to be reduced by heat treatment in atmosphere at 150°C. After such heat treatment, Cu
2O microparticles were found to have penetrated the polyimide substrate. In order to prevent the penetration of Cu
2O particles, several different interlayers were introduced at the interface between the Cu thin film and polyimide substrate. Ti and Co interlayers were found to be effective barrier materials against the penetration of Cu
2O particles. The quality of the interlayers was found to be important in achieving this effect. By annealing Co interlayers at 280°C for 1 hr in vacuum before sputter deposition of Cu thin film, we succeeded in maintaining the peel strength between Cu thin film and polyimide substrate above 0.1 N/m even after heat treatment at 150°C for 3 days.
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