Initial Stages of Atomic Layer Deposition of Tantalum Nitride on SiO2 and Porous Low-κ Substrates Modified by a Branched Interfacial Organic Layer: Chemisorption and the Transition to Steady-State Growth

We have examined the initial stages of atomic layer deposition (ALD) of TaN x on SiO 2, a porous low-κ SiO 2 -based material, and both of these substrates modified by a branched interfacial organic layer, using in situ X-ray photoelectron spectroscopy (XPS) as the primary analytical method. The interfacial organic layer examined was poly(ethylene imine) (PEI), a branched molecule with amine functionality. We find that PEI alters both the density and nature of the species formed after the chemisorption of Ta[N(CH 3 ) 2 ] 5, which represents the first half-cycle of ALD. In particular, PEI suppresses chemisorption of Ta[N(CH 3 ) 2 ] 5 on SiO 2 while enhancing it on low-κ. Results from XPS suggest that the Ta species on low-κ and both surfaces modified by PEI are formed in reduced concentrations while also retaining more N(CH 3 ) 2 ligands. From angle-resolved XPS, PEI acts as an effective barrier to Ta penetration of porous low-κ, even for exposures to Ta[N(CH 3 ) 2 ] 5 at many mTorr of partial pressure. Concerning ALD, growth on low-κ and both surfaces modified by PEI was attenuated, all to an extent that would be expected based on the reduction of Ta species formed in the first half-cycle. The evolution of the chemical states for both Ta and N with TaN x thin film thickness showed similar trajectories for growth on low-κ and both of the surfaces modified by PEI, indicating the occurrence of similar chemical transformations in these cases.