Evaluation of thin Ta(N) film integrity deposited on porous glasses

Porous glasses are widely used in microelectronics as inter-metal dielectrics with low dielectric constant (so-called low-k dielectrics). At the same time copper is used as a metal because of its low resistivity. Combination of Cu and low-k requires a barrier to prevent Cu diffusion into a low-k dielectric. Integrity of such a barrier becomes an issue when porous glass is used as a low-k dielectric. The barrier should be as thin as possible and fully dense at the same time. Using solvent (toluene) penetration through a barrier (tantalum nitride in our case, which is non-stoichiometric, hence denoted as Ta(N)) and adsorption in porous glass as a barrier integrity probe, we show that barrier integrity depends not only on porous structure of the glass, but also on its chemical composition (namely on carbon content). Glasses with high carbon content are easier to seal with Ta(N) barrier. With help of Monte Carlo simulations, we speculate that different chemical composition of the porous glass results in different surface diffusion during barrier deposition. Different surface diffusion, in turn, results in different integrity of the porous barrier.