As the device dimension decreases, the number of metal layers increases and the metal pitch decreases, Al dual damascene has been known to achieve low fabrication cost because the fabrication processes can be simplified by using Al sputter-filling technology and Al CMP. However, from the electrical characteristics and reliability point of view, it was not clear if the Al dual damascene is suitable for fine pitch metallization. In this paper, we compare via characteristics among W-plug, Al-plug and Al dual damascene for multilevel interconnects.
We investigated the via resistance and electomigration characteristics. Al dual damascene was formed by Al hot sputtering to fill via and trench, and by subsequent Al-CMP. The electromigration lifetime for via holes with misalignment between the 1st and 2nd Al for dual damascene is larger than that for conventional Al plug. On the dual damascene structure, via holes are opened first, then 2nd metal trench are patterned. Even misalignment between the 1st via and the 2nd Al occurs, contact area for dual damascene become large because of making contact at both of the via top and the side wall of the 2nd Al. The electromigration lifetime is longer for dual damascene with misalignment, in compared with that for Al plug and W plug with misalignment. Via resistance for dual damascene is almost the same as the via resistance for Al plug, which is lower than W plug. Via yield for dual damascene with misalignment is better than that for Al plug and W plug.
In conclusion, we compared W-plug, A plug and Al dual damascene for multilevel interconnects. Al dual damascene was found to be durable and reliable in structure and process against misalignment in terms of electromigtration lifetime and via resistance, as well as yield. Al dual damascene is the most promising technology for fine-pitch metallization.