Improvement on the stress migration in tungsten-plug via

In this paper, we develop a new via structure (FTV1), to study the reliability performance of SM (Stress Migration). FTV1 structure is different from the conventional Al-based interconnect technology. Here, the metal beneath the tungsten via is Cu (the conventional is Al), while the upper metal above the via is Al. The complex process of the FTV1(single via) combined with the interaction of the metal layer stresses results in that the SM resistance shift after 168hr baking has bi-modal issue. A new failure mechanism in W-plug via was reported in this paper. By changing the anneal step from before FTV1 photo to after passivation etch, the resistance shift becomes smaller than 2% versus the original 8%, which can meet industry specification.