Interfacial reactions of sputter-deposited Ta with a low dielectric constant Si-O-C-H material (SiCOH), and with surface-nitrided SiCOH (N-SiCOH) were investigated using X-ray photoelectron spectroscopy (XPS). The studies were carried out in a system containing a processing chamber attached to an XPS analysis chamber so that sample transport between deposition and analysis environments occurred under ultrahigh vacuum (UHV) conditions. Ta sputter deposition on unmodified SiCOH yielded an interfacial phase similar to 3 nm thick composed of Ta oxide/carbide (Ta-O-C), which is known to interact only weakly with Cu. Bombardment of the vicinal SiCOH surface by 500 eV Ar+ in the presence of NH3 resulted in carbon depletion and the self-limiting nitridation of the surface, with N attachment primarily at Si sites. Subsequent Ta sputter deposition yielded reduced Ta oxide and carbide formation, and formation of a Ta-rich nitride layer of 10 angstrom average thickness. Subsequent deposition resulted in metallic Ta formation. (C) 2009 Elsevier B.V. All rights reserved.