Structural analysis of HZO thin film and electrode using X-ray diffraction

Abstract: Since its discovery in 2011, the ferroelectricity of thin films based on HfO2 has been studied intensively. In particular, thin films with a 1:1 ratio of HfO2 and ZrO2 (HZO) has been of great interest. The ferroelectricity arises from a non-centrosymmetric orthorhombic (o) phase of HZO whose prevalence is dependent on the processing conditions. One of these processing conditions is the annealing temperature. While higher temperatures has been shown to better crystallize the o-phase, such temperatures will hinder device implementation since the interface with a semiconductor will be damaged. The texturing of TiN top electrodes has also been shown to impact the crystallization of HZO, with a (111) texturing resulting in a larger o-phase fraction. In this paper, the nanoprobe X-ray diffraction imaging of the NanoMAX beamline at the synchrotron radiation facility MAX IV, Lund, Sweden, is utilized in order to disclose any regional phenomena in a 370◦ C thermally annealed sample consisting of a TiN (10 nm) bottom electrode and a TiN/Au (10 nm/200 nm) top electrode with HZO (12 nm) sandwiched in between. This provides new insight into the uniformity of the sample, not made possible by typical XRD measurements which are on the mm-μm scale which does not allow for precise imaging. The results show peaks arising from the o-phase in all of the diffraction spectra of the different points in the sample, indicating that the sample preparation was successful in crystallizing all of the sample in the o-phase. The spatial investigation of the sample shows peak-shifting in a region, multiple potential contributions to this are discussed. Grain size analysis from the Scherrer equation shows a minimum grain size of τ ∼ 19 nm, which is larger than the film thickness itself. This behavior can not be explained but has been seen observed previously. For a real investigation of the grain size, other methods would have to be utilized. Finally, the TiN electrode peaks in the XRD spectrum exhibit (111) texturing, ideal for the crystallization in the o-phase. The work displays that HZO thin films can be studied using an X-ray nanoprobe, and a more optimized sample could be investigated further using the same method. This would provide deeper insight into the uniformity of HZO thin films.