Electrical characterization of conductive and non-conductive barrier layers for Cu-metallization

For application of copper in advanced multi-level metallization schemes it is indispensable to prevent Cu diffusion into the active area and into interlevel dielectrics by total encapsulation of Cu with barrier films. For that purpose the barrier properties of W/TiN/TiSi2 contact systems were evaluated using electrical measurements. It is shown that barrier stability up to 600–700°C can be obtained by optimizing the sputtering conditions for TiN films (N2 flow, temperature, collimator). Low frequency admittance measurements on Schottky diodes were shown to provide a very reliable and easy way to test the barrier stability. As a non-conductive barrier the Si3N4SiO2(50 nm) system was investigated for different thicknesses of Si3N4 (0–200 nm). After annealing up to 550°C the samples did not show any degradation of the capacitance-voltage (C-V) and breakdown voltage characteristics. Bias thermal stress (BTS) test conditions (1–3 MV/cm, 220°C) reduce significantly the SiO2 barrier lifetime, while 50 or 100 nm thin Si3N4 films improve the barrier mean time to failure by a factor of 25 or 100, respectively.