Electromigration behavior of advanced metallization on the structural effects for memory devices

• EM behaviors depend on not only metal materials but also the structure of the interconnects.
• The Cu line fed with a W contact has a shorter lifetime than that of Cu fed with a Cu contact.
• Mean time-to-failure for Cu interconnects can be enhanced under AC and pulsed DC.
• Mean time-to-failure for Cu interconnects was independent of the frequency of the pulsed DC.
• Mean time-to-failure for Cu interconnects increased with the off-time period.

We investigated the kinetics of the electromigration (EM) phenomenon regarding not only metal line materials (Al, W, Cu) but also multiple structures of the Cu metal line under various electric conditions: direct current (DC), alternating current (AC) and pulsed DC. Under DC stressing, the W line had the longest EM failure lifetime, and the Al line had the weakest EM lifetime among Al, W and Cu materials due to the different diffusivity of the constitutional atoms. Lateral voids induced by joule heating were observed at the W contact of the Cu line fed with W, which decreased the lifetime compared with the Cu line fed with Cu. Although the mean time-to-failure was independent of the frequency of pulsed DC, the lifetime of the Cu line increased with the off-time of pulsed DC because the atomic migration was relaxed during the off-time period. This study provides guidelines for highly reliable memory devices with respect to multi-component structures under users' circumstances.

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