- Titel
- Optimization of Sputtered Hafnium Zirconium Oxide Ferroelectrics for Memory Applications
- Zitierfähige Url:
- https://nbn-resolving.org/urn:nbn:de:bsz:14-qucosa2-990312
- Erstveröffentlichung
- 2025
- Datum der Einreichung
- 29.10.2024
- Datum der Verteidigung
- 14.08.2025
- Abstract (EN)
- Since the initial publication of ferroelectricity in HfO2 thin films in 2011, numerous theories and models have been proposed to elucidate the root of this phenomenon. It is widely accepted that the ferroelectricity in HfO2 arises from its polar orthorhombic crystal phase, which is metastable at room temperature and under standard atmospheric conditions. Therefore, sputtering, being a non-equilibrium process, can be advantageous in stabilizing the metastable crystal structure of HfO2 in thin film. With regard to the practical processing, the incorporation of ferroelectric (FE) HfO2 in the front-end-of-line (FEOL) requires complicated steps and significant cost. Consequently, the back-end-of-line (BEOL) integration of FE HfO2 is technically preferred. However, this straightforward integration is accompanied by a trade-off, which is the limited thermal budget to prevent the detrimental impact on the components finished in FEOL processes. According to existing research, sputtered HfO2 requires high temperature (> 600 °C) anneals to activate a proper FE switching. Thus, the primary objective of this study is to engineer the sputtered hafnium zirconium oxide (HZO) to be thermally compatible with BEOL processes (< 450 °C). Through the optimization process, the FE response of HZO is found to be highly dependent on the sputtering parameters. This indicates that distinct optimal sputtering processes must be employed in accordance with varying sputter target conditions. By summarizing the effects of the sputtering parameters, general models are proposed to guide the optimization of sputtered HZO. Moreover, the reproducibility of similar ferroelectricity is demonstrated on the sputter targets with different conditions and from various suppliers. Further enhancements in the ferroelectricity of the ferroelectric capacitor are achieved via electrode engineering. Based on the results of this work, sputtered HZO promises an expedient and straightforward BEOL integration of FEs.
- Freie Schlagwörter (EN)
- HfO2, HZO, ferroelectrics, sputtering
- Klassifikation (DDC)
- 621
- Klassifikation (RVK)
- ZN 3400
- GutachterIn
- Prof. Dr. Thomas Mikolajick
- Prof. Dr. Martin Ziegler
- Den akademischen Grad verleihende / prüfende Institution
- Technische Universität Dresden, Dresden
- Version / Begutachtungsstatus
- publizierte Version / Verlagsversion
- URN Qucosa
- urn:nbn:de:bsz:14-qucosa2-990312
- Veröffentlichungsdatum Qucosa
- 02.10.2025
- Dokumenttyp
- Dissertation
- Sprache des Dokumentes
- Englisch
- Lizenz / Rechtehinweis
CC BY 4.0- Inhaltsverzeichnis
Contents List of Figures vi List of Tables xiv List of Abbreviations xv List of Symbols xvii 1 Introduction 1 2 Theoretical Background 3 2.1 Ferroelectricity and Ferroelectric Memory Device 3 2.1.1 Basics of Ferroelectricity 3 2.1.2 Ferroelectric Field-Effect Transistor 5 2.1.3 Ferroelectric Random-Access Memory 6 2.2 Hafnium-oxide-based Ferroelectrics 8 2.2.1 Hafnium Oxide 8 2.2.2 Doped Hafnium Oxide 10 2.2.3 Zirconium-doped Hafnium Oxide 11 2.2.4 Role of the Electrode 12 2.3 Fabrication Technology for HfO2-based Ferroelectrics 13 2.3.1 Atomic Layer Deposition 13 2.3.2 Sputtering 15 3 Experimental Section 18 3.1 Fabrication 18 3.1.1 Capacitor Stack Deposition 18 3.1.2 Capacitor Annealing 20 3.1.3 Capacitor Patterning 20 3.2 Characterization 22 3.2.1 Structural and Chemical Analysis 22 3.2.2 Electrical Analysis 27 4 Path of Sputtered Hafnium-Zirconium Oxide to Back-End-of-Line Compatibility 33 4.1 Effect of Sputtering Parameters 33 4.1.1 Sputtering Power 33 4.1.2 Zirconium Oxide Content 39 4.1.3 Sputtering Pressure 45 4.1.4 Other Parameters 54 4.2 Towards Back-End-of-Line Compatibility 60 4.2.1 High Remanent Polarization after BEOL-compatible Annealing 60 4.2.2 General Model 62 5 Optimizing the Sputtered Hafnium-Zirconium Oxide Ferroelectric Capacitor 65 5.1 Titanium Nitride Electrode Engineering 65 5.1.1 Effect of Nitrogen Tuning on Titanium Nitride 65 5.1.2 Engineering Oxygen Scavenging 68 5.2 Tungsten Oxide Electrode Engineering 74 5.2.1 Effect of Oxygen Tuning on Tungsten Oxide 75 5.2.2 Engineering Oxygen Supply 79 6 Conclusions and Outlook 85 7 Bibliography 87