AVS 51st International Symposium
    Thin Films Monday Sessions
       Session TF-MoM

Paper TF-MoM3
Effects of Surface Chemistry on ALD Ta(N) Barrier Formation on Low k Dielectrics

Monday, November 15, 2004, 9:00 am, Room 303C

Session: ALD and Applications
Presenter: J. Liu, University of Texas at Austin
Authors: J. Liu, University of Texas at Austin
J. Bao, University of Texas at Austin
M. Scharnberg, Technische Fakultat der Christian-Albrechts-Universitat, Germany
P.S. Ho, University of Texas at Austin
Correspondent: Click to Email
For atomic layer deposition (ALD) of ultra-thin Cu barrier layers, the initial chemisorption at the substrate surface is important in controlling the barrier uniformity and morphology. It is particularly important for organosilicate (OSG) low k dielectrics generally characterized by inactive surface bonds which have to be properly activated for sufficient ALD nucleation. In-situ x-ray photoelectron spectroscopy (XPS) was employed to study the effects of the surface chemistry on ALD Ta(N) barrier formation on two main types of low k surfaces, OSG and SiLK. The initial chemisorption was confirmed to be through formation of Ta-O bonding on OSG films and charge transfer complexes on the aromatic SiLK films. The evolution of the low k surface chemistry revealed an initial transient growth region controlled mainly by the substrate surface chemistry. Pre-treatment of the OSG low k surfaces with nitrogen and hydrogen radical beams, particularly with nitrogen radicals, was observed to enhance significantly the chemisorption of the TaCl@sub 5@ precursor on the OSG surfaces. The enhancement was attributed to the dissociation of the weakly bonded methyl groups from the low k surface followed by surface nitrogen enrichment. The improvement of the growth rate observed in this study illustrates the criticality of the surface coverage at saturation for a successful ALD process. In the subsequent linear growth region, atomic hydrogen species was able to reduce the chlorine content under appropriate temperature and with sufficient purge. The role of the atomic hydrogen in this process enhancement is discussed. In addition, precursor penetration was observed to be suppressed as a result of surface activation on the mesoporous OSG, suggesting a possible approach to pore sealing of porous OSG with halide ALD chemistry.