Microstructure and Texture of Electroplated Copper in Damascene Structures

Abstract

The transition from Al to Cu for advanced ULSI interconnects involves changes in architecture and deposition technique that will influence the microstructure and texture of the metal. Cu interconnects are typically formed within the confines of pre-patterned trenches and vias using an electroplating process with a sputtered Cu conduction layer deposited over a refractory metalbased diffusion barrier layer. In this paper, we focus on the influence of the barrier layer (PVD Ti/TiN, Ta, TaN, CVD TiN) and the effect of a vacuum break between barrier and conduction layer depositions, on the texture of the Cu lines, as examined by X-ray diffraction pole figure analysis.A preferred (111) orientation was observed for all samples. The samples with no vacuum break between barrier and conduction layer deposition exhibited in plane anisotropy that was particularly pronounced for the Ta and TaN samples compared with the Ti/TiN sample. Focused ion beam images and transmission electron micrographs showed Cu grain size to be on the order of the trench width with a high degree of twinning, and no boundary could be distinguished between the PVD Cu conduction layer and the electroplated Cu.

X-ray diffraction pole figure evidence for (111) sidewall texture of electroplated Cu in submicron damascene trenches

“…The dominant central ͑111͒ components in all three figures exhibit the previously observed elongation in the direction across the trench ͑defined as the y direction͒. 15 This anisotropy in the central ͑111͒ peaks is quantified by the full widths at half maximum ͑FWHM͒ for samples A, B cold and B hot as 18.2°, 30.2°, and 18.8°in the y direction and 9.6°, 12.8°, and 10.2°in x direction ͑along the trench͒, respectively, as derived from line cuts in the pole figures. The asymmetry factors ͑ASF͒ for the central ͑111͒ peaks, defined as the ratio of the FWHM across versus along the direction of the trench, i.e., ASFϭFWHM͑Y͒/FWHM͑X), 15 are similar for A, B cold , and B hot ͑1.9, 2.4, and 1.8, respectively͒.…”

“…Although not fully understood at this moment, we associate this directional elongation of the central ͑111͒ peaks with the geometric influence of the trench that, in extreme cases, leads to a split of this peak into two peaks separated by as much as 29°. 15 Despite the similarities between A and B noted above, there is a striking difference in the overall intensity distributions in the pole figures. Whereas sample A ͓Fig.…”

“…15 This anisotropy in the central ͑111͒ peaks is quantified by the full widths at half maximum ͑FWHM͒ for samples A, B cold and B hot as 18.2°, 30.2°, and 18.8°in the y direction and 9.6°, 12.8°, and 10.2°in x direction ͑along the trench͒, respectively, as derived from line cuts in the pole figures. The asymmetry factors ͑ASF͒ for the central ͑111͒ peaks, defined as the ratio of the FWHM across versus along the direction of the trench, i.e., ASFϭFWHM͑Y͒/FWHM͑X), 15 are similar for A, B cold , and B hot ͑1.9, 2.4, and 1.8, respectively͒. Although not fully understood at this moment, we associate this directional elongation of the central ͑111͒ peaks with the geometric influence of the trench that, in extreme cases, leads to a split of this peak into two peaks separated by as much as 29°.…”

Increasing the mean grain size in copper films and features

“…The use of these additives in the electroplating chemistry can have a great influence on the properties of the deposited copper. For instance, the brightener additives tend to enhance the nucleation of new grains during the deposition, which will eventually lead to a reduction of the as-deposited grain size, a lower surface roughness, and consequently more reflective layers [81]. Unfortunately, the reduction in grain size also renders the deposit subcritical (~tens of nanometers for copper), leading to an inhomogeneous grain growth process which proceeds over a period of weeks, days or even hours and is characterized by selective growth of a few large grains at the expense of other normal grains.…”

Effect of encapsulation on electronic transport properties of nanoscale Cu(111) films

“…The models of ideal Cu thin film are constructed such that the atomic layers of the (111) crystal plane are perpendicular to the z -axis, and thus, there are two Cu (111) free surfaces. We considered (111) orientation because the formation energy for (111) surface is the lowest when compared to other crystallographic orientations and the (111) texture is often observed in electroplated Cu interconnects 17,18 . All atomic layers in the Cu film are optimized using DFT within VASP 19 .…”