Access Type
Open Access Embargo
Date of Award
January 2023
Degree Type
Dissertation
Degree Name
Ph.D.
Department
Chemistry
First Advisor
Charles Winter
Abstract
This dissertation presents precursor development for cobalt (Co) and titanium (Ti) metal films, as well as thermal atomic layer deposition (ALD) of Co metal thin films. The end goal for developing precursors and thermal ALD processes of Co and Ti metal is to deposit amorphous CoTix (x = 18 to 83 at.%) alloy films by thermal ALD. Co-sputtered CoTix alloy films showed desirable properties for ultrathin liner and barrier materials. However, sputtering is a line-of-sight deposition and is problematic for the growth of conformal films in high aspect ratio features. Alternatively, ALD-deposited CoTix films could provide extremely conformal and uniform thin films with Angstrom level thickness precision. To date, Co and Ti metal ALD are understudied, and these materials are in fact hard to grow by thermal ALD. New precursors and ALD processes for these materials thus need to be developed. Subsequently, Co and Ti metal ALD processes could be combined to obtain CoTix films. New Co ALD precursors and co-reactants are needed for the development of new Co metal ALD processes. Different classes of Co(II) complexes were synthesized as potential ALD precursors. The volatility and thermal properties of these compounds were assessed by thermogravimetric analysis (TGA), melting points, and thermal decomposition temperatures. Co metal ALD studies were carried out with deposition temperatures from 200 to 400 °C using the new Co precursor and various co-reactants. The elemental composition of grown films on various substrates was first analyzed by X-ray fluorescence. Film thicknesses were measured by cross-sectional scanning electron microscopy, and the phases of the films were characterized by grazing incidence X-ray diffraction. X-ray photoelectron spectroscopy was also used primarily for film composition analyses. This Co process could be incorporated with a Ti metal process to afford CoTix alloy thin films. Thin films of Ti metal and Ti-based diffusion barrier materials such as titanium nitride are very important materials in microelectronics. These materials are deposited using halogenated or metalorganic Ti(IV) sources. Both types of precursors, however, have some disadvantages. Halogenated Ti precursors can generate corrosive gases, which can etch and damage other materials used in microfabrication. Most current Ti metalorganic precursors have low thermal stabilities (< 200 °C) and can leave impurities in films, which could negatively affect thin film properties. Besides, growing metallic Ti films by thermal ALD is demanding as a result of the highly negative electrochemical potential of Ti ion (Ti2+ ↔ Ti0, E° = -1.628 V), and a lack of proper precursors and strong reducing agents. Due to decreasing dimensions in nanoscale devices, new materials and ALD processes with better performance are in high demand. New chemistry and precursors for Ti metal ALD are thus required. Herein, this work reports the synthesis and characterization of new classes of Ti(III) complexes that contain monoanionic, bidentate ligands. These new complexes are promising ALD precursors. Challenges in the development of these Ti(III) precursors are to find ligands that confer both high thermal stability and good volatility for use in ALD processes. Also, the ligands should not undergo decomposition reactions with the low-valent Ti metal ions. Essentially, the thermal stabilities of these Ti(III) precursors should be very similar to those of the Co(II) precursors, since precursors for Ti and Co metal will be used together in the ALD growth of CoTix alloys. The precursor properties of these complexes will be determined by measuring sublimation temperatures, melting points, thermal decomposition temperatures, and TGA. These precursors may also be useful when combined with the Co metal ALD process described herein to obtain CoTix alloy thin films and/or ALD growth of Ti-containing films such as titanium silicide.
Recommended Citation
Linn, Nyi Myat Khine, "Thermal Atomic Layer Deposition Of Cobalt Metal And Precursors For Titanium Metal Thin Films" (2023). Wayne State University Dissertations. 3859.
https://digitalcommons.wayne.edu/oa_dissertations/3859