Cu wetting and interfacial stability on clean and nitrided tungsten surfaces

Cu growth/nucleation behavior and thermal stability on clean and nitrided t ungsten foil have been characterized by Auger electron spectroscopy (AES) a nd thermal desorption spectroscopy (TDS) under controlled ultra high vacuum (UHV) conditions. At room temperature, Auger intensity ratio versus time p lots demonstrate layer by layer Cu growth for the clean tungsten surface (W ) and three-dimensional nucleation for the nitride overlayer (7.5-10 Angstr om, WNx/W). Auger intensity ratio versus temperature measurements for the C u (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 nitr ide overlayer demonstrate N-2 decomposition from 800-1400 K. The addition o f Cu (1 ML) to the nitride overlayer lowers the decomposition temperature r ange of 750-1350 K. The enhancement of N-2 recombination is attributed to t he perturbing effect of Cu on W-N bonding driven by a Cu-W surface alloy fo rmation. (C) 2001 Elsevier Science B.V. All rights reserved.