Three-dimensional simulation of microstructure evolution in damascene interconnects: Effect of overburden thickness

Abstract

Microstructure in the damascene interconnects evolves with the overburden layer, an excessive metal layer over trenches. We present the results of three-dimensional simulation, which show the effects of overburden thickness on microstructure evolution in a trench. When the thickness of the overburden is less than half of the trench depth, for a trench with the aspect ratio of unity, the microstructure in the trench tends to evolve into a bamboo structure. This effect is discussed in terms of grain sizes in the trench and those in the overburden. The thinner overburden layer would have smaller grains, of which growth is limited by its thickness. Such small-sized grains in the overburden are not likely to grow into the trench, which hardly make grain boundaries in the trench. Meanwhile, the grains from the trench are able to continue growth inside the trench, resulting in a bamboo structure. Overburden thickness affects the reliability and the electrical performance of the damascene copper interconnects. Optimization of overburden thickness is required to minimize these effects.