Access Type
Open Access Dissertation
Date of Award
January 2022
Degree Type
Dissertation
Degree Name
Ph.D.
Department
Chemistry
First Advisor
Charles H. Winter
Abstract
ATOMIC LAYER DEPOSITION (ALD) OF LANTHANIDE OXIDE FILMS: SYNTHESIS, CHARACTERIZATION, AND PRECURSOR PROPERTY EVALUATION OF NEW CLASSES OF LANTHANIDE COMPLEXES AND THERMAL ALD OF ERBIUM OXIDE THIN FILMSby NAVODA AMALI JAYAKODIARACHCHI August 2022 Advisor: Prof. Charles H. Winter Major: Chemistry (Inorganic) Degree: Doctor of Philosophy Lanthanide oxide-containing thin films are groups of materials with high application potential in numerous fields, including microelectronic, photovoltaic, catalysis, and surface-coating applications. These oxides are refractory materials with high melting points and thermodynamic stabilities, hence, are useful as heat and corrosion-resistant coatings. Further, due to the high refractive indices of lanthanide oxides, they are widely used in optics and photovoltaics. Most importantly, with the continuous downscaling of semiconductor devices, search of alternative high-κ gate dielectric materials for gate oxides in transistors is ongoing. Owing to the high dielectric constants and large band gaps inherent to lanthanide oxides, they have gained increased attention as potential alternative candidates for gate dielectrics in transistors. Traditional vapor phase thin film deposition methods include PVD and CVD. PVD is a line-of-site technique and difficult to achieve conformal thin film growth in high-aspect ratio features. CVD has a better conformal coverage than PVD on planar substrates. However, both of these techniques lack the required precision for film growth in high aspect ratio nanoscale 3-dimensional architectures. By contrast, the ALD technique deposits films with perfect surface conformality and nanometer-scale thickness control on both planar and non-planar architectures and in high aspect ratio features. However, the lack of lanthanide precursors with desired ALD precursor properties that can react with mild oxidants has made the thermal ALD of lanthanide oxide films difficult. Moreover, several established ALD processes for lanthanide oxide ALD are plagued by low growth rates, lack of self-limited growth, impurity incorporation, high surface roughness, or the need for highly reactive oxygen sources. The research herein seeks to develop new ALD precursors and processes for lanthanide oxide thin film growth with the scope of increasing the applications of lanthanide-containing oxide thin films for future nanoscale technologies. Accordingly, two new precursor classes for lanthanide(III) ions were introduced employing hydrazonate and enaminolate ligand systems (Chapters 2 and 3). All of the complexes were synthesized using salt metathesis approaches and were purified by sublimation or solvent crystallizations. Diamagnetic lanthanide complexes (La3+, Lu3+, and Y3+) were fully characterized by 1H and 13C{1H} NMR and all of the complexes were characterized using IR spectroscopy, melting points, and CHN microanalyses. Variable temperature NMR spectra were obtained for selected diamagnetic complexes to understand the solution state behavior. Single crystal XRD studies were carried out for selected complexes to understand the solid-state structures. Volatility and thermal stability evaluation to determine the potential of these precursors for ALD was carried out using sublimation, TGA, melting point, thermal decomposition temperature analysis, and long-term thermal stability tests. All of the new complexes sublimed, demonstrating their volatile nature. Hydrazonate complexes showed lower volatilities compared to enaminolate complexes, which could be attributed to the large molecular weight of the tert-butyl hydrazonate ligand compared to the L1 and L2 enaminolate ligands. Hydrazonate complexes have acceptable thermal stabilities for use in ALD. The thermal stabilities of enaminolate complexes varied with the ligand substituents. L1 and L3 enaminolate complexes are predicted to have sufficient thermal stabilities to use in ALD. Smooth, continuous, and high-purity Er2O3 films were deposited successfully using the Er-enaminolate precursor, Er(L1)3 (Chapter 4). Water was used as the co-reactant. Films were characterized using several techniques such as SEM, GI-XRD, SE, XRR, AFM, and XPS. The plot of thickness versus the number of cycles was linear and slope this linear plot gave a growth rate of about 0.3 Å/cycle. Self-limited growth behavior was observed for both Er-precursor and water at ≥4 s and ≥0.2 s pulse lengths, respectively. Being able to find a precursor system that shows adequate reactivity toward a mild oxygen source is one of the greatest achievements in this work. This Er2O3 ALD process further demonstrates the potential of using other enaminolate complexes reported in Chapter 3 for the deposition of other lanthanide oxides as future work.
Recommended Citation
Jayakodiarachchi, Navoda Amali, "Atomic Layer Deposition (ald) Of Lanthanide Oxide Films: Synthesis, Characterization, And Precursor Property Evaluation Of New Classes Of Lanthanide Complexes And Thermal Ald Of Erbium Oxide Thin Films" (2022). Wayne State University Dissertations. 3734.
https://digitalcommons.wayne.edu/oa_dissertations/3734