Ti-Rich Barrier Layers Self-Formed on Porous Low-k Layers Using Cu(1 at.% Ti) Alloy Films

Abstract

To investigate the applicability of the technique of barrier self-formation using Cu(Ti) alloy films on porous low-k dielectric layers, Cu(1 at.% Ti) alloy films were deposited on porous SiOCH (low-k) dielectric layers in samples with and without ~6.5-nm-thick SiCN pore seals. Ti-rich barrier layers successfully self-formed on the porous low-k layer of both sample types after annealing in Ar for 2 h at 400°C to 600°C. The Ti-rich barrier layers consisted of amorphous Ti oxides and polycrystalline TiC for the samples without pore sealing, and amorphous TiN, TiC, and Ti oxides for the pore-sealed samples. The amorphous TiN originated from reaction of Ti atoms with the pore seal, and formed beneath the Cu alloy films. This may explain two peaks of Ti segregation at the interface that appeared in Rutherford backscattering spectroscopy (RBS) profiles, and suggests that the Ti-rich barrier layers self-formed by the reaction of Ti atoms with the pore seal and porous low-k layers separately. The total molar amount of Ti atoms segregated at the interface in the pore-sealed samples was larger than that in the samples without pore sealing, resulting in lower resistivity. On the other hand, resistivity of the Cu alloy films annealed on the porous low-k layers was lower than that annealed on the nonporous low-k layers. Coarser Cu columnar grains were observed in the Cu alloy films annealed on the porous low-k layers, although the molar amount of Ti atoms segregated at the interface was similar in both sample types after annealing. The cause could be faster reaction of the Ti atoms with the porous dielectric layers.