The contact resistance (R C) between a Ru electrode and a TiN plug in a crystalline Ta2O5 capacitor using Ru electrodes was evaluated. The TiN plug was oxidized in TiO x to increase the R C to failure. Two origins of oxygen are determined by Auger electron spectroscopy (AES) analysis, namely, the seed step of Ru deposition and the initial step of Ta2O5 deposition. During Ta2O5 crystallization annealing at 700°C, the oxygen molecules from Ru diffused into the TiN plug, forming TiO x . Ru films with Ti exhibited a decreased R C below 1 kΩ/contact and an increased leakage current of a Ru/Ta2O5/Ru capacitor according to the applied voltage, compared with Ru films without Ti. The atomic layer deposition (ALD) Ru process including a H2 plasma treatment decreased the R C to 2.5 kΩ/contact on average. The fabrication scheme for the crystalline Ta2O5 capacitor using the Ru electrode for reducing RC between the Ru storage node and the TiN plug was proposed.
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Lim et al. (2005) studied this question.