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Characterization of Direct-Contact Via Plug Formed by Using Selective Aluminum Chemical Vapor Deposition

A novel via plug structure, direct-contact via plug with a submicron diameter, has been realized by selective aluminum (Al)-chemical vapor deposition (CVD). In this structure, the Al plug is in direct contact with the lower and upper level Al interconnects. It was found to be essential to carry out all three processes continuously in a high vacuum: surface cleaning by reactive ion etching (RIE), plug formation by selective Al-CVD and sputter deposition of upper level Al film. The via structure has no heteromaterial interfaces along the current path. Electrical characteristics were evaluated and were compared with those of the conventional tungsten (W) plug. The via chain resistance in 0.5 µm diameter was 0.25 Ω/via, which was found to be 1/3 of that of a W-filled plug, and the interface resistance was estimated to be extremely low. Electromigration (EM) tolerance was also found to be better than that of a W plug. Our data demonstrated that the direct-contact Al-CVD plug was very suitable for realizing high-performance LSI with lower process cost.