(A) study on the ultra-thin copper film formation by chemical vapor deposition

Abstract

Copper interconnection has been used extensively in fabricating metal interconnections for large scale integrated circuits because of its favorable electrical conductivity 1.67 μΩcm and superior resistance to electromigration. Cu metallization requires a seed layer of Cu which should have a continuous and smooth film surface, to achieve the Cu superfilling without leaving any voids on dual-damascene structures. To overcome this issue, Cu seed layer deposition on glue layer is studied. Ultra-thin Cu seed layer was deposited by metal-organic chemical vapor deposition (MOCVD) on Ru layer using hexafluoro-acetylacetonate copper vinyltrimethyl-silane $(hfac)Cu^I(vtms)$. On Ru, the incubation time for Cu MOCVD was nonexistent. As compared with MOCVD Cu on TaN, the nuclei density of Cu was considerably increased on Ru and the wetting angle of Cu on Ru was small (22°). Therefore, the coalescence between Cu islands on Ru layer begins earlier by prohibiting the severe three-dimensional Cu growth that is generally observed on TaN layer. As a result, 10 nm thick continuous Cu film with 1.75 nm root-mean-squared surface roughness was easily prepared on 40 nm thick Ru at $150^\circ C$. To enhance the surface morphology properties of Cu film, Ir material is proposed. Film growth of MOCVD Cu on Ir substrate shows almost same behavior with that on Ru substrate. The surface roughness of Cu on Ir layer is measured only 2.39nm, which is much lower than the value of Cu on Ru layer 2.91nm at 30nm-thick Cu. The reason of a surface smoothness improving is due to the lattice misfit of Cu with underlayer. In 200nm-thick Cu specimen, Cu(111) area ratio of Cu surface deposited on Ir substrate is almost 95%. And the sheet resistance of Cu/Ir system is 0.12Ω/□ which is not increased after thermal annealing. As an application aspect of a Cu/Ru, and Cu/Ir interface, CVD Cu deposited on 3nm-thick Ru and Ir which is as thin as possible in this experimental reactor. On Ir layer, MOC...