Structure, Oxygen Content and Electric Properties of Titanium Nitride Electrodes in TiN/La:HfO/TiN Stacks Grown by PEALD on SiO/Si.

This work reports experimental results of the quantitative determination of oxygen and band gap measurement in the TiN electrodes in planar TiN top/La:HfO/TiN bottom MIM stacks obtained by plasma enhanced atomic layer deposition on SiO. Methodological aspects of extracting structural and chemical information from (scanning) transmission electron microscopy imaging (bright field and high angular annular dark field), energy dispersive X-ray spectrometry and electron energy loss spectroscopy are thoroughly considered. The study shows that the oxygen concentration is higher in the TiNO bottom electrode (about 14.2 ± 0.1 at. %) compared to the TiNO top electrode (about 11.4 ± 0.5 at. %). The following average stoichiometric formulas are TiN.O. top and TiN.O. bottom for top and bottom electrodes, respectively. The amount of oxygen incorporated into TiN during PEALD because of oxygen impurities in the plasma is minor compared to that because of diffusion from SiO and HfO. This asymmetry, together with results on a sample grown on a Si substrate, shows that incorporating oxygen impurity from the plasma itself is a minor part compared to diffusion from the SiO substrate and HfO dielectric during the PEALD growth. We observe the presence of TiO at the interface between the Hf oxide layer and the Ti nitride electrodes as well as at the SiO interface. EELS analysis led to a band gap ranging from 2.2 to 2.5 eV for the bottom TiNO and 1.7-2.2 eV for the top TiNO, which is in fair agreement with results obtained on the top TiN electrode (1.6 ± 01 eV) using optical absorption spectra. Measurement of sheet resistance, resistivity and temperature coefficient of resistance by a four-point probe on the top TiNO electrode from 20 to 100 °C corresponds to the typical values for semiconductors.