In-situ XPS Study of ALD Ta(N) Barrier Formation on Organosilicate Dielectric Surface
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In-situ XPS Study of ALD Ta(N) Barrier Formation on Organosilicate Dielectric Surface Junjun Liu, Junjing Bao, Michael Scharnberg1, and Paul S. Ho Laboratory for Interconnect and Packaging, Microelectronic Research Center, the University of Texas at Austin, Austin, TX 78712-1063, USA 1 Lehrstuhl für Materuakverbunde, Technische Fakultät der Christian-Albrechts-Universität zu Kiel, Kaiserstr.2, D-24143 Kiel, Germany ABSTRACT Beams of nitrogen and hydrogen radicals were investigated as surface pre-treatment and process enhancement techniques for atomic layer deposition (ALD) of tantalum nitride barrier layer on a dense organosilicate (OSG) low k film. In-situ x-ray photoelectron spectroscopy (XPS) studies of 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 low k surface with radical beams, particularly with nitrogen radicals, was found to enhance significantly the chemisorption of the TaCl5 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 nitridation with the nitrogen radicals. 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. INTRODUCTION Atomic layer deposition (ALD) of ultra-thin barrier layers is a key process for implementation of Cu/low k interconnects. For ALD, the initial chemical reactions at the substrate surface are important in controlling the barrier uniformity and morphology. This is particularly important for low k dielectrics generally characterized by weak surface bonds which have to be properly activated for barrier formation. Plasma pre-treatments with O2, N2 and H2 have been applied to various low k dielectrics for ALD of nitride barrier layers.1,2,3 O2 and N2 plasma or downstream RIE treatments on CVD organosilicates were generally successful in enhancing chemisorption by activation of the low k surfaces with low energy ions and radicals, but only in some special cases, the underlying low k film retained its dielectric property. These studies have generated interests in applying plasma induced radicals for surface modification, but the effects on barrier formation on low k surfaces are not well understood, particularly regarding the surface bonds and the chemical reaction for initial barrier formation. Moreover, as porous OSG is being investigated as a candidate ultra low k for integration in sub-90nm technology nodes, pore sealing has become a critical issue. Various plasma pretreatments have been attempted on mesoporous OSG films without much success.4 An in-situ chemical analysis of the initial barrier formation process would provide information for better understanding of the issues in pore sealing. In this study, in-situ XPS was used to study the initial formation of Ta-based barriers by A
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