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Air gap (AG) interconnects, with an ideal dielectric constant k of 1, is a promising approach to reduce signal propagation delay. In this paper, a comparative study of AG and dielectric copper damascene interconnect structures is performed through Raphael™ electric field simulation to investigate the capacitance benefit of introducing AG when scaling to small dimensions. The variation in total capacitance as a function of half pitch is simulated for different AG integration schemes proposed in the literature. Ideal and practical cases of these different integration schemes are simulated and compared to assess whether interconnect structures using a low- k ( k = 2.3) dielectric are more suitable than AG interconnects at scaled dimensions. The effect of using an additional (SiC-based) stiff liner on the AG capacitance benefit is also investigated. Finally, we verify our simulations using sub-40 nm half pitch AG structures prepared using the conformal and non-conformal processes.

We report a method to improve the chemical stability and the mechanical properties of a plasma enhanced chemical vapour deposited ultra low-dielectric constant material. This enhancement in the properties was achieved through extended UV cure times using a broad band lamp, emitting light at wavelengths higher than 200nm. These longer cures also increased significantly the Young's modulus, but the dielectric constant did increase less than the experimental error. It is also demonstrated that this improved property depends on the chemical bonds present in the film, such as Si-CH"3, as well as on the density of the film. Films with a dielectric constant of 2.06, Young's modulus of 4.9GPa and perfect resistance against 0.5% HF for up to 300s, were obtained. Another type of UV cure, using a narrow band lamp with wavelength of 172nm, induced completely different chemical resistance characteristics of the resulting films.

Atomic layer deposition is a promising technique to deposit conformal, nm-thin metal barriers in high-aspect-ratio trenches. However, exactly because of its excellent conformality, the deposition can also occur inside the nanopores of the most advanced low-k materials. In this work, the mechanisms of atomic layer deposition on and in low-k, porous dielectric films were studied, using HfO"2 as a test material. Exhaustive analyses showed firstly that the HfCl"4 precursor penetrated uniformly in the pores throughout a 44nm thick low-k film. Secondly, it was shown that the pores were sealed as function of precursor size, i.e. there are conditions where the pores became inaccessible for HfCl"4, while the - smaller - H"2O molecules could still penetrate the pores. From these analyses, a deposition model was proposed.

The use of low-k materials is essential for improving the quality of integrated circuits. Subsequent process steps may however modify this film to the extent that the final result is unacceptable. Organosilicate-based low-k films, with a nominal k-value of 2.3, were exposed to different post-CMP cleaning plasmas used for copper reduction. The resulting plasma damage was investigated and is reported in this paper. All the studied plasmas increased the density of the low-k film. TOFSIMS and FTIR analyses showed that they all removed CH"3 groups from the bulk, leading to water incorporation. The carbon depletion was more pronounced and deeper (100nm) from a NH"3 plasma than from any other investigated plasma. N"2+H"2 plasma removed somewhat less carbon from the low-k film (83nm deep). The N"2 plasma removed carbon down to a depth of 60nm into the film, while a pure H"2 plasma removed the least carbon of all the investigated plasmas, to a depth of only 35nm. The combination of TOFSIMS and XPS indicated the incorporation of a significant amount of N in the films treated with the pure N"2 plasma. C-V measurements showed an increase of the dielectric constant, again mostly for the NH"3 plasmas. There was an intermediate and approximately equal increase of the dielectric constant for all N"2 containing plasmas, and the least increase was for the H"2 plasma. This increase of the dielectric constant was caused by the increase of density of the film, incorporation of water, and in the case of the N"2 plasma also the incorporation of N. This shows that the presence of N"2 in plasma may significantly damage low-k materials, and it should not therefore be treated as a mere carrier gas.