Quantitative studies of copper diffusion through Ultra-thin ALD tantalum nitride barrier films by high resolution-RBS

Abstract

Depth profiles of annealed Cu on TaxNy barrier films (10Å-30Å) deposited by Atomic Layer Deposition (ALD) were obtained by high-resolution Rutherford backscattering spectroscopy (HRBS). The HRBS facility at the Centre for Ion Beam Application (CIBA) employs a 5-axis goniometer within a UHV chamber and a detection system consisting of a 90° double focusing sector magnet and a 1D-MCP focal plane detector. This non-destructive analysis is able to accurately determine the absolute Cu concentration with respect to depth, providing a depth resolution in the sub-nm regime, hence verifying the barriers effectiveness as a function of barrier thickness. Atomic Force Microscopy (AFM), glancing angle X-ray Diffraction (XRD) 2θ scans and sheet resistance measurements were applied to characterize the thin film thermal stability and microstructural changes. The results show that 10Å-20Å thick barriers prevent Cu diffusion up to 150°C whereas the 30Å films could work well up to 350°C before diffusion sets in. In all cases, Cu traces were found in the TaN films although there was no breaching of the barrier at lower temperature. Surface Si was detected in the 10Å-30Å samples, suggesting that the TaN agglomerates during annealing due to insufficient thickness to maintain its structural stability. As the annealing temperature increases, traces of Ar were found to increase in the TaN film. © 2008 Materials Research Society.