Initial interface formation of Ta-based barriers on SiLK™ low dielectric constant films

Abstract

Tantalum and its nitride were deposited onto dense SiLK™ low dielectric constant (low-k) films with e-beam evaporation and atomic layer deposition (ALD). In situ x-ray photoelectron spectroscopy (XPS) studies revealed that the e-beam evaporated Ta formed charge-transfer complexes on the SiLK™ surface. Conventional thermal ALD process using TaCl5 chemistry had ready nucleation on the SiLK™ surface. Absence of “carbide”-like peak in C1s spectra throughout deposition suggested a similar interface formation mechanism. After an initial dielectric interface, the final nitride film was found to be metallic by e-beam evaporation but dielectric Ta3N5 by atomic layer deposition. XPS uptake curves indicated the thinnest interface for ALD Ta3N5 and the thickest interface for PVD Ta. This can be attributed to suppressed diffusion of Ta atoms in the presence of NH3 and limited diffusion of TaCl5 molecules in SiLK™.