Enhanced Ferroelectric Polarization in TiN/HfO₂/TiN Capacitors by Interface Design

The interface formation between ferroelectric HfO2 layers and TiN bottom electrodes was studied by hard X-ray photoelectron spectroscopy and directly correlated to the electric polarization characteristics of the TiN/HfO2/TiN capacitors. We consistently deduced the interface chemistry from HfO2- and TiN-related core levels, dependent on the oxygen flow ṁ supplied before and during physical vapor deposition (PVD) growth of HfO2. The results underline the critical, twofold impact of oxygen supply on HfO2 and interface properties. When supplied before growth, the supplied oxygen stabilizes the TiN/HfO2 interface by oxidation and formation of a self-limiting (noninsulating) TiO2 intralayer. When supplied during growth, on the other hand, oxygen flows above a critical threshold reduce the oxygen vacancy concentration within the HfO2 film. We reveal a direct relation between the maximum ferroelectric remanent polarization and a critical threshold PVD oxygen exposure flow rate. The results allow for advancement of the PVD growth process in terms of a more flexible design of the ferroelectric HfO2 films with chemically stable TiN interfaces.