Atomic layer deposition (ALD) Co was developed using bis(N,N'-diisopropylacetamidinato)cobalt(II) as a precursor and NH3 as a reactant, producing pure Co thin films with excellent conformality and nanoscale thickness controllability. In addition to NH3, the Co films were also deposited by using H-2 gas as a reactant. Compared to ALD Co using H-2, the Co thin films deposited by NH3 showed a higher film quality, a lower resistivity, and a higher density. The Co thermal ALD process was applied to area-selective ALD using an octadecyltrichlorosilane self-assembled monolayer as a blocking layer, which produced 3 mu m wide Co line patterns without an etching process. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3248002] All rights reserved.