Comparative Study of Sheet Resistance Stability of Electro-Deposited Ni/Co - Alloy Thin Films

Abstract

Cu is conventionally used for interconnect material in most of high performance and high integration of logic devices because Cu has low conductivity as 1.7×10－8 Ω･m and also has excellent electromigration resistance. However, Cu requires a barrier layer for eliminating Cu diffusion into SiO2 or Si. Because of the limitation of the barrier layer thickness, the effective resistance of the wiring including the barrier layer greatly increases with decreasing of the width of Cu wiring less than 10 nm. Therefore, many researches have been reported about the development of barrier layer-free wiring technology using Co or Ru with low resistivity compared to Cu wiring system. Ni has similar physical properties e.g. resistivity, thermal expansion coefficient, diffusion coefficient, etc. like Co or Ru, however, few research on electrical properties has been done so far. In this study, Ni, Ni-Co alloys, and Co are deposited by electrodeposition and crystallographic structure and electrical properties were evaluated.A Ni or W (5 nm) seed layer were deposited onto thermally grown SiO2/Si(001) substrates (10 mm sq.) at R.T. by RF sputtering. After forming the seed layer, Ni or Ni-Co alloy or Co thin film (50 nm) was deposited. Table 1 shows the composition of electrodeposition bath. After the deposition, all samples were annealed in argon atmosphere (0.1 Torr) at 450°C for 30 minutes. Elemental analysis was done by Energy Dispersive X-ray spectrometry (EDX). The crystal structure, Chemical bonding state and electrical properties were evaluated by X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS) and 2-terminal Method, respectively, before and after annealing.Figure 1 shows the sheet resistance change of Ni, Ni-Co alloy, or Co films before and after 450°C - 30 minutes annealing using (a) Ni and (b) W as a seed layer. There was no significant difference in sheet resistance between the Ni or W seed layer samples. In the case of Ni or Ni-Co alloy films, the sheet resistance after annealing was very stable for both seed layers, Ni and W. On the other hand, the sheet resistance of Co films increased and they were considered to be oxidized by XPS and XRD results. Co film by electrodeposition was oxidized but Ni and Ni-Co alloy films were not oxidized by annealing, so they are better wiring metal than Co in terms of oxidation resistance. Figure 1