Tantalum as a diffusion barrier between copper and silicon: Failure mechanism and effect of nitrogen additions

Abstract

The interaction of Cu with Si separated by thin (50 nm) layers of tantalum, Ta2N, and a nitrogen alloy of Ta has been investigated to determine the factors that affect the success of these materials as diffusion barriers to copper. Intermixing in these films was followed as a function of annealing temperature by in situ resistance measurements, Rutherford backscattering spectra, scanning electron microscopy, and cross-section transmission electron microscopy. Ta prevents Cu-silicon interaction up to 550 °C for 30 min in flowing purified He. At higher temperatures, copper penetration results in the formation of η″-Cu3Si precipitates at the Ta-Si interface. Local defect sites appear on the surface of the sample in the early stages of this reaction. The Ta subsequently reacts with the substrate at 650 °C to form a planar hexagonal-TaSi2 layer. Ta silicide formation, which does not occur until 700 °C in a Ta-Si binary reaction couple, is accelerated by the presence of Cu. Nitrogen-alloyed Ta is a very similar diffusion barrier to Ta. It was found that Ta2N is a more effective barrier to copper penetration, preventing Cu reaction with the substrate for temperatures up to at least 650 °C for 30 min. In this case, local Cu-Si reaction occurs along with the formation of a uniform Ta5Si3 layer at the Ta2N-Si interface.

Dielectric Barrier, Etch Stop, and Metal Capping Materials for State of the Art and beyond Metal Interconnects

“…[259][260][261][262][263][264] A number of Cu barrier performance tests have been reported in the literature. Most are based on forming an interface between Cu and the barrier material and using techniques such as secondary ion mass spectroscopy (SIMS) or Rutherford backscattering to monitor for Cu in-diffusion into the barrier and ILD material, 265,266 or X-ray diffraction to detect Cu diffusion into the underlying Si substrate and formation of CuSi x . 267,268 Various electrical [269][270][271][272][273] and electrochemical 274,275 tests have also been reported in the literature for evaluating the Cu diffusion resistance of barrier materials.…”

Voiding Phenomena in Copper-Copper Bonded Structures: Role of Creep

“…16 It is followed by a copper deposition of 1 μm by physical vapor deposition (PVD) without airbreak between deposition steps. An annealing of 2 hour at 400…”

Statistical Analysis of Electromigration Lifetimes and Void Evolution for Cu Interconnects

“…Best results were obtained using Ta-based barriers, such as pure Ta, Ta x N y and amorphous ternary alloys, for example Ta x Si y N z . [Kolawa 1991, Holloway 1992, Wang 1993, Nicolet 1995. Bilayers of these materials are being used as well.…”