Cu wetting and interfacial stability on clean and nitrided tungsten surfaces

Cu growth/nucleation behavior and thermal stability on clean and nitrided tungsten foil have been characterized by Auger electron spectroscopy (AES) and thermal desorption spectroscopy (TDS) under controlled ultra high vacuum (UHV) conditions. At room temperature, Auger intensity ratio versus time plots demonstrate layer by layer Cu growth for the clean tungsten surface (W) and three-dimensional nucleation for the nitride overlayer (7.5±10 A Ê , WNx/W). Auger intensity ratio versus temperature measurements for the Cu (1 monolayer)/W system indicate a stable interface up to 1000 K. For the Cu (1 ML)/WNx/W system, initial Cu diffusion into the nitride overlayer is observed at 550 K. Maximum diffusion of the Cu occurs at 750 K. The driving force for diffusion is due to an effective Cu±nitride repulsion and a more thermodynamically favorable Cu±W interaction. TDS measurements of the nitride overlayer demonstrate N2 decomposition from 800±1400 K. The addition of Cu (1 ML) to the nitride overlayer lowers the decomposition temperature range of 750±1350 K. The enhancement of N2 recombination is attributed to the perturbing effect of Cu on W±N bonding driven by a Cu±W surface alloy formation. # 2001 Elsevier Science B.V. All rights reserved