Early Increase in Resistance during Electromigration in AlCu-plugged Via Structures

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This paper reports on the electromigration(EM)failure mechanism in AlCu-plugged via holes. Based on an observed increase in the via chain resistance and cross-sectional analysis of the damaged vias, an early failure and a normal failure were identified during the EM tests. The early failure occurred in the Al plug at the cathode side, and was attributed to void growth in the Al plugs during EM. The normal failure occurred not in the Al plugs, but on the Al lines, and exhibited a three-stage increase in resistance. An early increase in resistance of about 5% was found in the normal failure during EM. Failure sites were observed around the terminated via using the optical-beam-induced resistance change(OBIRCH)method. At the failure sites, crystallization of CuAl_2 was observed at the anode via using transmission electron microscope(TEM). The early increase in resistance caused by CuAl_2 crystal formation at the anode was brought about by using the AlCu via plug. This resistance increase is a serious problem for the small AlCu via connected to long or wide AlCu interconnects.
社団法人応用物理学会の論文
2000-03-15