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Access Type

WSU Access

Date of Award

January 2020

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Chemistry

First Advisor

Charles H. Winter

Abstract

ABSTRACT

THERMAL ATOMIC LAYER DEPOSITION OF SILVER METAL FILMS: SYNTHESIS AND CHARACTERIZATION OF THERMALLY STABLE SILVER METAL PRECURSORS

by

HARSHANI JAYABAHU ARACHCHILAGE

August 2020

Advisor: Professor Charles H. Winter

Major: Chemistry (Inorganic)

Degree: Doctor of Philosophy

Traditional film deposition techniques such as PVD and CVD are widely used in the microelectronics industry. However, the lack of thickness control and conformality requirements limit these techniques for current and future applications. By contrast, ALD offers the deposition of ultra-thin conformal films with accurate thickness control due to the self-limiting growth behavior. Ag metal has the lowest resistivity (1.59 µΩ cm) of all metals and has applications in plasmonic devices. Growth by thermal atomic layer deposition (ALD) has been hampered by the low thermal stabilities of virtually all Ag precursors. The synthesis of highly thermally stable Ag metal precursors is very challenging due to the positive electrochemical potential of the Ag(I) ion. The focus of this dissertation is given to the development of thermal ALD processes using highly thermally stable precursors and synthesis and characterization of thermally stable silver precursors. Trimeric silver pyrazolates were synthesized and characterized. These precursors are highly thermally stable, volatile, and reactive towards several reducing agents, which are the key properties that ALD precursors should have. The deposition of the silver metal thin films was attempted using [Ag(3,5-CF3)2Pz]3 and 1,1-dimethylhydrazine. Both the metal precursor and the reducing agent showed self-limited growth at 180 °C. Rather than a continuous film, silver nanoparticle growth was observed on the SiO2 substrate instead. New Ag pyrazolate and diketonate complexes were synthesized using saturated and unsaturated NHCs. Solid state structures of NHC-based Ag pyrazolates showed great diversity, including monomers, dimers, and a tetramer. Dimers have close Ag-Ag contacts, consistent with argentophilic interactions. These new Ag pyrazolate complexes are volatile between 110 and 140 °C at 0.2 Torr, and thermally decompose at temperatures between 160 and 293 °C. However, TGA traces and thermal decomposition temperatures suggest that trimers [Ag(3,5-CF3)pz]3 and [Ag(3-tBu,5-CF2CF2CF3)pz]3 still have better thermal stability than the NHC complexes. Most of the Ag(diketonate)(NHC) complexes are monomers with no close Ag-Ag contacts. The Ag diketonate complexes have volatilities that range from 100-124 °C at 0.2 Torr, and thermal decomposition temperatures that range from 141-188 °C. Carefully chosen anionic ligands with electron-withdrawing substituents are required to achieve the highest possible stabilities of the metal complex.

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