Thermal stability of electroplated copper thin-film interconnections

There were local distributions of the crystallinity and resistance in a test interconnection. The local resistance of the interconnection varied with the local crystallinity. The maximum temperature appeared in the local area with the minimum crystallinity, in other words, the area with the highest resistance under the application of high current density of 10 MA/cm². Thus, local high Joule heating occurred in the test interconnection due to the local variation of the crystallinity of the interconnection. The maximum temperature decreased from about 170°C to 140°C when the average crystallinity (IQ value which was obtained from EBSD analysis) increased from 3000 to 4100. This decrease of the maximum temperature can be explained by the decrease of Joule heating under the application of a fixed current density. This decrease of the maximum temperature increased the long-term reliability of the interconnections drastically.