On the failure mechanisms of titanium nitride/titanium silicide barrier contacts under high current stress

Structures with a single pair of titanium nitride/titanium silicide barrier contacts with connecting narrow diffusion widths (⩽3.0 μm) have been investigated for their electromigration resistance and reliability performance by applying current ramping and high current stress at different temperatures. Under a current ramping, the contact structures show a decrease in contact resistance after being virtually constant in the low-current regime and a steady increase of contact resistance toward the higher-current regime due to Joule heating in the diffusion region. The transition occurs when the temperature in the diffusion region reaches a value (the critical point) above which the intrinsic carriers become a dominant for conduction, especially for the region near the p-n junction. This point is followed by an unstable region in which the contact resistance continues to reduce. As the current rises further, a catastrophic structural failure, similar to a thermally initiated second breakdown in a transistor, is observed. The magnitude of the critical current is linearly proportional to the diffusion width and is independent of the type of impurity used to dope the diffusion region