Sidewall Texture and Microstructure of iPVD Copper Seed in Narrow Damascene Trenches

Impurities incorporated into copper during electrochemical deposition have long been postulated to inhibit grain growth in narrow interconnects. In this article we examine an alternative possible origin for the microstructural differences observed between narrow and wide lines. Specifically, the iPVD Cu seed layers in wide (1 μm) and narrow (70 nm) lines differ significantly in microstructure and texture, as analyzed by transmission electron microscopy and electron diffraction. The seed in the wide lines has a polycrystalline microstructure similar to that seen in blanket films, with strong 111 texture in the field and sidewalls, and 112 texture at the bottom of the trench. Although the field between the 70 nm lines is also strongly 111-textured, the seed on the sidewalls and bottom of the trenches are largely untextured and, in fact, not entirely crystalline. This results in a higher energy, metastable microstructure which can contribute an additional driving force for the rapid nucleation and recrystallization of polycrystalline copper in the trenches before the overburden can transform and force the creation of bamboo grains in the lines.