Electromigration performance of Al-Si-Cu filled vias with titanium glue layer

摘要

Electromigration performance of vias filled with high temperature (480degC) sputtered Al alloys on Ti glue layers was investigated in comparison with W-stud vias. Electromigration lifetime and failure mode are quite different according to via structures and kinds of Al alloys used. Electromigration lifetime of W-stud via chain and Al-Cu filled via chain depends on the via to via distances, while that of Al-Si-Cu filled via chain does not depend on the via to via distances. Failure model observations revealed that voids were formed only at a few locations in the test structure in Al-Si-Cu filled via chain while voids were formed at every via in W-stud via chains and Al-Cu filled via chains. It is supposed that Al moves through the Al-Si-Cu filled vias during electromigration test in spite of the existence of the Ti glue layer at the via bottom. The Al transportation, however, was prohibited at W-stud vias and Al-Cu filled vias. Glue Ti deposited at via bottom was converted to Al-Ti-Si alloy in Al-Si-Cu filled vias, while Al_3Ti alloy was formed at Al-Cu filled via bottom. It is speculated that Al transportation occurs through via bottom Al-Ti-Si alloy layer during electromigration test in the case of Al-Si-Cu filled vias.