In situ x-ray photoelectron spectroscopy (XPS) was employed to study the effects of the substrate surface chemistry on atomic layer deposition (ALD) of Ta-based barrier layers on various low k surfaces. The initial chemisorption was found to be through formation of Ta-O bonding on organosilicates (OSG) and charge transfer complexes on aromatic SiLK (TM). ALD process nucleated very slowly on the OSG low-k films, in distinct contrast with its ready nucleation on SiLK (TM) films. The evolution of the low-k surface chemistry revealed an initial transient growth region controlled mainly by the substrate surface chemistry. Pretreatment of the low-k surfaces with nitrogen and hydrogen radical beams, particularly with nitrogen radicals, was observed to enhance significantly the chemisorption of the TaCl5 precursor on the OSG surfaces. The enhancement was attributed to dissociation of 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. (c) 2005 American Vacuum Society.