Surface passivation of Cu cone bump by self-assembled-monolayer for room temperature Cu-Cu bonding

Abstract

Cu-Cu room temperature bonding is investigated using Cu cone bumps with SAM passivation. Effect of the SAM passivation for preventing the Cu oxidation is confirmed by AES and water contact angle measurements. The contact resistance at the bump interconnection is kept small even with 24 hours storage in air after the SAM passivation. Also, the die shear strength of the bonded chip is enough high to satisfy the criterion of MIL-STD. According to these findings, we can conclude that the Cu cone bump with the SAM passivation is promising candidate for room temperature Cu -Cu bump interconnections. Keywords-Chip on chip; Micro bump; SAM; Cu cone bump; Room temperature bonding II. EXPERIMENTAL A. SAM Passivation EffectBefore applying SAM passivation on Cu cone bumps, we investigated SAM passivation effect by using Cu plate. The purity and thickness of the Cu plate was 99.96 % Cu and 0.3 mm, respectively. The Cu surface was mirror-polished. To remove native oxide on the Cu plate, the Cu plate was dipped into a diluted sulfuric acid for 1 min and then rinsed in pure water for several seconds. Then immediately, the Cu plate was put into a SAM solution for 1 hour. The composition of the SAM solution was 1 mMol/L of l-Hexanethiol diluted in ethanol. After dipping into the SAM solution, the Cu plate was rinsed in an ethanol for 5 min.The SAM passivation effect was evaluated by AES and water contact angle measurements by taking storage time in air as the parameter. Change with post-deposition armealing was also investigated.