Formation of ultra-thin Ta-based Cu diffusion barrier with atomic layer deposition
With in-situ x-ray photoelectron spectroscopy (XPS) monitoring of atomic layer deposition (ALD) of Ta-based Cu barriers, this dissertation work is aimed at providing definite information regarding the initial interface formation during ALD barrier growth on low dielectric constant (low k) dielectric surfaces. The ALD nucleation and the substrate effects on ALD growth were investigated on two main types of low k dielectrics using two representative chemistries. In-situ surface chemical analysis confirmed the existence of a growth initiation stage controlled mainly by the substrate surface chemistry. TaCl5 precursor can readily nucleate on SiLK™ through formation of charge transfer complexes on surface benzene groups, but has difficulties in nucleating on organosilicate (OSG) low k surfaces which are characterized by inactive surface methyl bonds. In contrast, a distinctively different nucleation and pore penetration behavior was observed with an organometallic precursor Pentakis-Dimethylamino Tantalum (PDMAT). This can be attributed to the low self-decomposition temperature and the higher sticking coefficient of PDMAT on the non-polar OSG surfaces. Beams of reactive sub-molecular radicals were employed to activate the inactive OSG surfaces. Pure radical beams, amine radicals in particular, were found to be effective in the surface activation. Atomic hydrogen beam were demonstrated to provide an effective technique for surface cleaning, which is essential for chemisorption. Additionally, other applications with radical beams in enhancing ALD barrier processes were examined, such as formation of metallic Ta/dielectric Ta3N5 bi-layer stack, and reduction of chlorine and oxygen impurity contents. As dielectric recovery and pore sealing may become a necessity for integration of ultra-low k porous OSG, the interactions between surface silylation and ALD barrier process were investigated. Tri-alkyl-substituted silylation agents were found to be detrimental to the initiation of the subsequent ALD barrier process. The surface activation with radical beams thus provides an effective, controllable and less destructive approach to improving ALD barrier formation following the surface silylation. On the other hand, as a preliminary attempt, alternative phenyl containing silylation agents were tested on porous OSG films damaged with O2 plasma for dielectric recovery while retaining the surface reactivity for ALD initiation.