Impact of vacancies and impurities on ferroelectricity in PVD- and ALD-grown HfO2 films

We investigate the emerging chemical states of TiN/HfO2/TiN capacitors and focus especially on the identification of vacancies and impurities in the ferroelectric HfO2 layers, which are produced either by physical vapor deposition (PVD) or atomic layer deposition (ALD). Depending on the specific growth conditions, we identify different mechanisms of oxygen vacancy formation. Corresponding spectral features are consistently observed for all HfO2- and TiN-related core levels by hard x-ray photoelectron spectroscopy (HAXPES). In ALD-grown samples, we find spectral signatures for the electronic interaction between oxygen vacancies and nitrogen impurities. By linking the HAXPES results to electric field cycling experiments on the TiN/HfO2/TiN capacitors, we discuss possible formation mechanisms and stabilization of the ferroelectric HfO2 phase directly related to specific PVD or ALD conditions.