Electroless-plated films have the desirable property of conformal deposition on dielectric under layers. Therefore, electroless plated (ELP) barrier metals are promising, for preventing Cu atom diffusion into SiO2 and Si in through-silicon vias (TSVs) used for three-dimensional (3D) integration. In this study, we evaluated Cu inter-diffusion properties after annealing at 400 °C for electroless-plated CoB and CoWB barrier layers with different W contents (0, 12.3, and 20.8%) formed on thin SiO2/Si substrate. The secondary ion mass spectrometry (SIMS) depth profile and cross-sectional TEM analysis of the TiN/Cu/ELP Co alloy/thin SiO2 (5 nm)/Si stacked films suggest that a CoWB film with a larger W content has a better effect on suppressing Cu inter-diffusion. It is demonstrated that ELP-CoWB having a large amount of W is a promising barrier layer for high-aspect TSVs used for 3D integration.

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For fabrication of through-silicon via (TSV) of 3-D integration, sputtering or ALD are used for the barrier and seed layers formation, however, high cost processes using high vacuum instruments have hindered wide application of 3-D integration technologies. We have studied formation of barrier and seed layers with electroless plating which enables significant reduction of fabrication cost [1, 2]. Use of Pd nanoparticle catalyst adsorbed on silane coupling agent at TSV sidewall [3] is very effective for a highly conformal film deposition in the high aspect ratio TSV holes. In this study, we formed electroless barrier films such as CoWP and NiWP on SiO2 at various bath conditions. We evaluated film characteristics such as electrical resistivity, crystalline structure, adhesion property, alloy composition, Cu diffusion barrier properties, etc. Figure 1 shows SEM cross-sectional images of the barrier films and XRD profiles before and after annealing (400 oC, 30min. in vacuum).The crystalline structure of the as deposited CoWP film was amorphous and it remained almost amorphous after heat-treatment. On the other hand, the crystal structure of the as deposited NiWP film was also amorphous, but several peaks of NiP alloy appeared after heat-treatment and it turned to poly crystal film. In addition, we formed Cu seed layer on the barrier metal by displacement plating and studied Cu inter- diffusion properties after annealing. Reference [1] F. Inoue, T. Shimizu, H. Miyake, R. Arima,T. Ito, H.Seki,Y. Shinozaki, T. Yamamoto, and S.Shingubara, Microelectronic Engineering, 106(2013) 164–167. [2] F.Inoue, T.Shimizu, T. Yokoyama, H. Miyake, K. Kondo, T. Saito, T. Hayashi, S. Tanaka, T. Terui and S. Shingubara, Electrochimica Acta, 56-17 ,6245-6250, (2011). [3]W. J. Dressick, C. D. Dukey, J. H. Georger. Jr, G. S. Carabrese, and J. M. Calvert, J Electrochem. Soc., 141 (1) 210 (1994) Figure 1