With a scaling trend of LSI interconnection, effective resistivity of Cu/barrier metal interconnect is expected to increase due to increasing electron scattering due to ultrafine dimension smaller than electron mean free path. Therefore, the trend is to substitute Co metal liner for Cu when the line width of LSI interconnect is 10 nm or less. While Chemical Vapor Deposition (CVD) or electrodeposition are discussed as formation method of Co mainly, we introduced electroless deposition (ELD) method. In electroless deposition of Co using Dimethylamine Borane (DMAB), B was incorporated in Co film, and the electric resistivity of the film after heat treatment (400℃ in vacuum, 30 minutes) was 68 µΩ∙cm. In this report, we introduced hydrazine monohydrate as a reducing agent for the purpose of forming ELD pure Co film. ELD Co bath contains cobalt chloride hexahydrate (CoCl2∙6H2O) as metal ion source and hydrazine monohydrate (N2H4∙H2O) as a reducing agent. In addition, some complexing agents were added to prevent Co hydroxide precipitation. Plating bath pH was adjusted to about 12.3 and the CVD-Co film (thickness: 20 nm) on SiO2 and Si was used as substrate for Co deposition. Obtained Co plated film were observed and analyzed by Scanning Electron Microscope (SEM), X-ray Photoelectron Spectroscopy (XPS) and X-Ray Diffraction (XRD). Furthermore, Co plating film was heat-treated at 400℃ in vacuum, and the electrical resistivity of Co film before and after the heat-treatment was measured by four-terminal method. The deposition rate of ELD cobalt bath was about 19 nm/min, and this cobalt film consisted of columnar crystals (Figure 1). If the film surface is rough, it may cause void formation during electroless Co plating in fine via. Regarding the properties of Co film, impurities derived from the reducing agent were not detected from XPS spectral analysis. Co film with few impurities leads to low resistivity because the probability of electron impurity scattering decrease. However, the resistivity of obtained and heat-treated Co film is 53 µΩ∙cm. It is necessary to form the smooth Co film to reduce the electrical resistivity. Figure 1
There is a serious problem of poor side wall coverage for the sputtered barrier metals in high aspect ratio TSVs. We have proposed electroless plated Co-alloy barrier metals for TSV. For this purpose, we prepared various CoB and CoWB alloys with different atomic compositions and crystalline structures. Furthermore, we evaluated interdiffusion properties of Cu/Co-alloy/Si stacked structure by SIMS analysis. It turned out that the electroless CoWB film containing larger amount of W has excellent diffusion barrier property than other CoWB films with smaller W content. We formed electroless barrier films of CoB and CoWB using Pd nanoparticle catalyst on SiO2/Si substrate [1]. For evaluation of Cu interdiffusion properties by SIMS, we deposited Cu and TiN thin films successively by sputtering on the barrier film. The ratio of the atomic composition was changed by adjusting the ratio of cobalt sulfate, tungstic acid, and some other contents of the plating bath. SIMS depth profiles of CoB (Fig.1-a) and CoWB films after annealing at 400 ℃ (Fig.1-b) are shown in Fig.1. There was a large interdiffusion between Cu and CoB after 400 ℃ annealing (Fig.1-a). Co-Silicide formation significantly occurred and Si atoms diffused into CoB layer. However, interdiffusion was significantly suppressed in the case of Co-20%W-B film (Fig.1-b). These results suggest that W atoms existed in CoWB have a strong effect of suppressing Cu diffusion in Co film, and CoWB with 20 atom % W showed a good diffusion barrier property. The present study suggests that the electroless plated CoWB having a larger W content has a high potential as a diffusion barrier film for the via last TSV process. [1] F. Inoue, T.Shimizu, F.Miyake, R.Arima, T.Ito, H.Seki, Y.Shinozaki, T.Yamamto, and S.Shingubara, Microelectronic Engineering, 106 (2013) 164–167. [2] T. Iseri, S.Shindo, Y.Miyachi, A.Hirate, S.Tanaka, T.Shimizu, T.Ito, S.Shingubara, Jpn. J. Appl. Phys. 57 (2018), 07MB02-1~6. Figure 1
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.