| Because of its mono-dispersed nano-scale pore size and ordered pore structure, the self-assembled nanoporous silica is a promising low-k material for the next generation of interlevel dielectrics in a semiconductor chip. To prevent the contamination adsorption on its internal pore surfaces during subsequent processings, the open pores at the surface must be sealed with a dense, conformal, and ultra-thin cap layer.; Atomic layer deposition (ALD) is the best way to make such coatings, but ordinary ALD will result in undesired deposition inside the internal nanopores thus increase the effective dielectric constant of the material. In this project, the concept of using plasma-assisted ALD (PA-ALD) is brought forward to resolve the issue mentioned above.; As a preparation of PA-ALD, the interaction between deposition plasma and the nanoporous silica needs to be understood. Therefore, regular plasma enhanced CVD was carried out on the nanoporous silica substrate and it was found that the plasma processing did not have significant impact on the properties of the underlying nanoporous silica. Both the ordered pore structure and the hydrophobic pore surface chemistry remained unchanged after the plasma processing.; As the other preparation of PA-ALD, the behavior of ordinary ALD on nanoporous silica substrate was studied. As expected, deposition occurred in the internal pores of the nanoporous silica. And under optimized conditions, conformal coating can be uniformly made on the walls of those internal pores, suggesting an approach to adjust nanopore/channel diameters, to modify nanopore surfaces and to make ordered functional material nano arrays by ALD with nanoporous silica as the template.; Then, a PA-ALD instrument was built up. The ion density profile as well as the radicals' concentration profile were roughly estimated in the remote plasma zone. By conducting plasma-assisted ALD on flat solid surfaces, the effects of various experiment conditions were studied.; With all the information above in hand, PA-ALD was performed on patterned nanoporous silica and the capping efficacy was investigated. It was found the SiO2 cap layer made by PA-ALD was conformal and as thin as 5 nm. It prevented contamination such as reactive gases from entering the nanoporous matrix. Also, no evident deposition was found in the internal pores and the low-k property of the capped nanoporous silica survived through the capping process, demonstrating that PA-ALD is an effective approach to make dense, conformal and ultra-thin cap layers. |
