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Resist planarization is applied to trench first dual damascene process in order to enhance focus margin for via lithography after hard mask etch. As a planarization process, resist CMP is better than conventional resist etch back, However, hard mask (HM) erosion by resist CMP causes serious problem of lessened thickness of Cu. To solve it, the combination of CMP and etch back (C+E) is adopted. This method realizes enhancement of the focus margin and prevention from the hard mask erosion at the same time.

RuTa(N) film has been prepared by doping N in Ru-Ta alloy and investigated its use as a barrier layer against Cu diffusion in Cu interconnects. It was found that RuTa(N) has a poor barrier property against Cu in the BEOL process, since N in Ru-Ta alloy is desorbed and RuTa(N) is recrystallized by heat treatment. It was also shown that RuTa(N) has inferior reliability due to its poor wettability with Cu compared to RuTa. On the other hand, RuTa has both good barrier property and superior reliability performance. It is possible to apply RuTa single film as a barrier layer for Cu interconnects.

In order to control the characteristics of porogen-based porous SiOC film (k ≪ 2.5), we investigated its dependence on the wavelengths of ultraviolet (UV) light by using methods of FT-IR, TDS and nano-indentation. As a result, it was found that specific wavelengths of UV light strongly was effective to porous SiOC film production : porogen desorption, mechanical strength improvement, and reduction of the film damage. Vacuum ultraviolet (VUV) irradiation is necessary for porogen desorption. However, after porogen was removed from SiOC film, the energy of VUV irradiation was too high for porous SiOC film and this caused film damage. The energy of deep ultraviolet (DUV) irradiation was sufficient to improve mechanical strength. We propose that UV curing process should be a multi-step process consisting of VUV and DUV irradiation (Figure 1). The first step removes porogen using VUV irradiation. The second step forms robust porous SiOC film using DUV irradiation. A multi-step curing process was used to control the characteristics of porogen-based porous SiOC film.

In order to reduce the effective dielectric constant (keff) for the 32 nm technology node and beyond, Direct-CMP of a porous low-k film without a protective cap layer is required. However, the degradation of breakdown electric field (Ebd) has been one of critical issues. This study clarified that the Ebd degradation was caused by the pit defects on the surface of porous low-k film during Direct-CMP. In order to suppress the pit defects, we evaluated dependency of micro-pores density of CMP pads. As a result, we demonstrated that CMP pads with low-density micro-pores drastically reduced them and improved the Ebd degradation. In this paper, the mechanism for their reduction is also discussed.