To reduce resistivity of interconnect, to enhance electromigration life time, and to improve a step coverage of barrier layer, cobalt and cobalt-tungsten alloy film was deposited by chemical vapor deposition (CVD) or atomic layer deposition (ALD) using octacarbonyl dicobalt (Co 2 (CO) 8 ) and biscyclopentadienyl cobalt (Cp 2 Co) as precursors, respectively. We demonstrated to form conformal cobalt films on to trench pattern and we confirmed that CVD/ALD cobalt-tungsten films have good barrier properties against copper diffusion.
Cap layers for Cu interconnects in ultra-large-scale integrated devices (ULSIs), with a low dielectric constant (k-value) and strong barrier properties against Cu and moisture diffusion, are required for the future further scaling of ULSIs. There is a trade-off, however, between reducing the k-value and maintaining strong barrier properties. Using quantum mechanical simulations and other theoretical computations, we have designed ideal dielectrics: SiCH films with Si-C2H4-Si networks. Such films were estimated to have low porosity and low k; thus they are the key to realizing a cap layer with a low k and strong barrier properties against diffusion. For fabricating these ideal SiCH films, we designed four novel precursors: isobutyl trimethylsilane, diisobutyl dimethylsilane, 1, 1-divinylsilacyclopentane and 5-silaspiro [4,4] noname, based on quantum chemical calculations, because such fabrication is difficult by controlling only the process conditions in plasma-enhanced chemical vapor deposition (PECVD) using conventional precursors. We demonstrated that SiCH films prepared using these newly designed precursors had large amounts of Si-C2H4-Si networks and strong barrier properties. The pore structure of these films was then analyzed by positron annihilation spectroscopy, revealing that these SiCH films actually had low porosity, as we designed. These results validate our material and precursor design concepts for developing a PECVD process capable of fabricating a low-k cap layer.
ALD-Co(W) was found to have a potential to replace the conventional PVD-Ta/TaN bi-layer in further shrinking interconnects as a single-layered barrier/liner material. We could confirm good barrier property of CVD/ALD-Co(W) film by BTS-TVS method after 350°C annealing. ALD-Co(W) showed lower resistivity of 60 μΩ-cm and good adhesion to Cu. Complete trench filling with Co(W) followed by Cu seed deposition was demonstrated. These properties were confirmed to be derived from W stuffing into grain boundaries of oxygen-free ALD-Co(W) films. We would like to suggest ALD-Co(W) as a next-generation barrier/liner layer for future development.
Cobalt film with tungsten addition [Co(W)] has the potential to be an effective single-layered barrier/liner in interconnects awing to its good adhesion with Cu, a lower resistivity than TaN, and an improved barrier property with respect to cobalt films. Our previous study on chemical-vapor-deposited (CVD) Co(W) using carbonyl precursors clarified, however, that WO3 included in the films increased the resistivity. In this current study, to reduce the resistivity of Co(W), oxygen-free Co(W) films were fabricated from two oxygen-free precursors, bis(cyclopentadienyl)cobalt and bis(cyclopentadienyl)tungstendihydride, by atomic layer deposition (ALD) using NH2 radicals generated using a hot filament. Results revealed that (a) W concentration in ALD-Co(W) could be controlled by adjusting the gas-feed sequences, (b) W addition improved the barrier property of ALD-Co(W) against Cu diffusion, (c) diffusion of Cu into ALD-Co(W) had a high activation energy, 2.0 eV, indicating interstitial diffusion, and (d) ALD-Co(W) consisted mainly of an amorphous-like phase, which is consistent with the high activation energy of Cu diffusion.
Continuous, atomically ultra-thin smooth ruthenium (Ru) films were deposited via hot-wire-assisted atomic layer deposition (HW-ALD) of ruthenocene and NH3. The behavior was self-limiting and no incubation cycle was required. The films were relatively pure at all deposition temperatures; the lowest resistivity was 17 μΩ-cm for a 30.6-nm-thick film after post-annealing. The effective work function was 4.83 ± 0.05 eV, comparable to that of sputtered films. As HW-ALD does not induce plasma damage or oxidation of the underlayer, which is fatal when preparing thermal and plasma-enhanced ALDs, the technique enables highly reliable device fabrication coupled with high conformality.
Hot-dip galvanized bolts tend to crack during galvanizing at the under-head fillet or thread root on which stress is concentrated. In this study, we investigated the influence of the temperature of cooling water on the occurrence of cracking. We further examined the plating performances under different cooling conditions. The main results obtained are as follows.(1) Heating of cooling water to a higher temperature is found effective against cracking.(2) The shower-cooling method is effective against cracking, with almost no difference from the conventional cooling method in plating performance such as plating microstructure or cramping torque coefficient.
In the case of fixing the tower crane on the base at the building site, the fastening method where the frame is held down by a beam called "Kanzashi" and bolts are inserted in it is widely used. This "Kanzashi" often deflects because of insufficient rigidity when bolts are fastened. This paper describes the results of an experiment employed a crane frame model, derivation of a practical formula based on strength of materials and comparisons of the theoretical and experimental values. The results obtained are that the force radio became smaller and the bending force ratio became larger with decreasing the thickness or increasing the bolted distance. The theoretical values agreed well with the experimental values.
