Reliability is a major concern regarding semiconductor devices. One particular area of concern is electromigration. As device features for transistors become smaller and operating speeds increase, the current density in a transistor's metal lines has increased. The increased current densities often lead to device failures, such as failures due to electromigration.
It has been established that for aluminum straight line via-to-via interconnect structures, there exists a critical current density and length product (jLcrit), below which electromigration ceases and the interconnect is considered “immortal” due to a balance between the electron wind force and the opposing back stress force. That is, the interconnect will not experience electromigration failure. This effect is known as the Blech effect.
Copper-based interconnects typically suffer from electromigration failure at high current density and operating temperature. The primary cause for electromigration failure is mass transport and depletion driven by electron wind, resulting in voids in the interconnect and therefore, increased resistance. Electromigration usually becomes worse with integration of materials having a low dielectric constant (K) value, such as K<3.