Electronic Packaging Science and Technology

10Electromigration

10.1 Introduction

In a Si chip of the size of our finger nail, there are billions of transistors, and the total length of Cu interconnects is over 10 kilometers in order to connect all the transistors to form the very‐large‐scale integration of circuits. So far, electromigration has been the most serious and persistent reliability problem in the interconnect technology. This is because typically a current density of 10⁵ to 10⁶ A/cm² is conducted by the Cu line. Under such a high current density, atomic diffusion and rearrangement are enhanced, leading to void formation (open) in the cathode and extrusion formation (short) in the anode of the interconnect. As the trend of device miniaturization demands smaller and smaller components, the cross‐section of nanoscale interconnect keeps shrinking and the current density keeps increasing, so does the probability of circuit failure induced by electromigration. This is why electromigration remains the most important reliability subject, which has attracted much attention.

For comparison, no electromigration occurs in an ordinary extension cord used at home and in laboratories. The electric current density in the cord is low, about 10² A/cm², and also the ambient temperature is too low for atomic diffusion to occur in Cu wire in a cord coated with rubber. However, because Si itself is an excellent thermal conductor, the Joule heating can be conducted away, so the current density in the Cu interconnect can go up to ...