Investigation of growth behavior of Al-Cu intermetallic compounds in Cu wire bonding

摘要

In this work, we investigate the intermetallic compound formation in Cu wire bonded device. Voids near the Cu side at the bond interface are clearly seen. Nevertheless, these voids do not seem to interfere with the function of the unit. High temperature storage test (HTST) results show that there are Al_2Cu and AlCu in the damaged unit while Al_2Cu and Al_4Cu_9 appear in the good unit. The results clearly show that the Al layer is exhausted in the damaged unit while those with Al_4Cu_9 on the Cu side pass HTST with uncon-sumed Al. Theoretical calculations indicate that AlCu and Al_4Cu_9 are energetically more favorable than Al_2Cu, which is consistent with the reported IMC forming sequence. Formation energy of AlCu is compatible but slightly lower to that of AI4CU9, suggesting AlCu tends to be the most stable phase among all. The reason why the Al layer is completely consumed in one case and some Al layer remains in the other is due to the fact that the formation of AlCu requires more than twice the amount of Al than Al_4Cu_9 for the same amount of Cu consumed. The complete consumption of Al is proposed as the reason responsible for the failure of the damaged unit.