The study of forming gas plasma on HSG-7000 silsesquioxane-based low-k dielectric film using X-ray photoelectron spectroscopy

HSG-7000 is a spin-on glass (SOG) low k dielectric material, manufactured by Hitachi Chemical and is silesquioxane (SSQ) based. The dielectric constant (k) of HSG-7000 is claimed to be 2.2. Cu diffusion through nanoporous structure of SSQ based material in Cu/Low k interconnects has been reported as a concern. Approaches to minimize Cu diffusion involve the implementation of a barrier layer between Cu and the low k dielectric material, or surface densification via plasma treatment. This paper discusses the effects of forming gas (93% N-2 + 7% H-2) plasma in an attempt to reduce Cu diffusion through the HSG-7000 film without significant increase in the dielectric constant (k). The FTIR and XPS results suggest a formation of C-N bonds due to the plasma treatment. The depth profile measurement of Cu using XPS confirms the reduction of Cu diffusion through the film with plasma treatment. Results show that plasma treatment of 30-40 s on HSG-7000 will provide a reasonable Cu diffusion resistance while ensuring the increase in k is below 2.4.