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.

Popular Abstract

The advancement of technology is often taken for granted. Our devices become smaller and smaller as well as faster and faster, but this is not something that happens on its own. Behind every advancement, like the new mobile phone you bought, lies countless hours of hard work and heavy investments. Research is always done into new materials in the search of new, interesting, properties. One such property is ferroelectricity, the less famous sibling to ferromagnetism which is how your fridge magnets actually stick to your fridge. You are probably aware of how you can turn a paper clip magnetic by exposing it to an external magnetic field in the form of a magnet, the paper clip ”remembers” its history even after it is
no longer in contact with the magnet. Ferroelectricity works in the same way with electricity, it ”remembers” the electric field it was exposed to even after it is no longer applied. This means that even if a ferroelectric component is not provided with electricity, it ”remembers” that it was: so called ”Non-volatile memory”. Through applying the external electric field in the opposite direction, the direction of the ferroelectric field also switches direction, and we have an opposite state. As computers work with binary ”0s” and ”1s”, the ability to have a material that can remember if it is a ”0” or a ”1” even after an electric field is no longer
applied is of great importance.

One such ferroelectric material is a thin film of HfO2 and ZrO2 (HZO) which, ever since its ferroelectric properties were discovered around 10 years ago, has been heavily studied. When hafnium oxide and zirconium oxide are combined under certain conditions, the resulting compound is ferroelectric. In this compound there can exist several different crystal structures of the atoms, and in one of these the atoms reorient in a special shape such that we get a positive charge that is separated from a negative charge which results in an electric field. While this effect averages out over the entire thin film, applying an external field aligns the negative and positive charges in the same direction over the whole sample such that when the
electric field is switched off, the effect will no longer average out. This is the same thing that happens to your paperclip with magnetism. The process described above is how ferroelectric HZO is created. The ferroelectric properties are therefore highly dependent on the structure of the HZO. To study the structure, synchrotron facilities like MAX IV in Lund, Sweden are ideal. In such facilities, an X-ray beam is directed at the sample and depending on the crystal structure of the sample, the X-rays are then reflected in different directions. Measuring the reflection pattern using a detector, the structural properties of the material can be studied.
In this paper the NanoMAX beamline at MAX IV was used to study the structural properties of HZO. Knowing that the desired property is the special ferroelectric crystal structure, the reflection off this structure is analyzed in order to get a measure on how prevalent it is in the sample. Different properties from different regions of the sample are investigated from this, as well as material properties. Since the HZO thin film is produced such that it is sandwiched between two TiN electrodes, which impact the creation of the ferroelectric shape, these electrodes will also be studied from the reflection pattern.

• author: Winsnes, Elliot
• supervisor: Jesper Wallentin; Megan Hill; Huaiyu Chen
• organization: Synchrotron Radiation Research; Department of Physics
• course: FYSK03 20232
• year: 2024
• type: M2 - Bachelor Degree
• subject: Physics and Astronomy
• keywords: HZO, hafnia, hafnium dioxide, zirconium dioxide, ferroelectricity, ferroelectric, synchrotron radiation, X-ray diffraction
• language: English
• id: 9148409
• date added to LUP: 2024-02-13 12:48:37
• date last changed: 2024-02-13 12:48:37