Impact of narrow trench geometries on copper film crystallography

Abstract

Crystallographic texture of copper in interconnect trenches after anneal and planarization has been mapped across 200 mm wafers by means of X-ray diffraction (XRD). Texture in trenches 70 nm and 100 nm wide with aspect ratios of 2–2.5 was found to have (1 1 1) planes parallel to wafer surface and the (1 1 0) orientation along the trench direction near the wafer center. Away from the wafer center a sidewall component to the texture was found. The strength of the (1 1 1) fiber texture originating from the sidewalls increased with the distance from the wafer center, and was particularly evident in trenches that were perpendicular to the radial direction. A sidewall texture component was also observed at wafers center with the deposition of a thinner barrier as well as a change of the Ta phase from α to β. β-Ta more strongly textures the PVD seed and lowers the annealing/recrystallization rate resulting in retention of the as-deposited texture on the sidewall. We also show that trenches oriented perpendicular to the radial direction have asymmetric distribution of grain orientations; the sidewall with greater coverage has a (1 1 0) orientation along the trench direction, the sidewall with lesser coverage producing the sidewall texture. An in-line XRD tool was shown to be able to detect the different texture types and rapidly map the texture variation in trenches across the wafer as well as quantify the barrier phase composition in the trenches.