Access Type

Open Access Embargo

Date of Award

January 2021

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Chemistry

First Advisor

Charles H. Winter

Abstract

Due to the continuous miniaturization of microelectronic devices, robust deposition techniques are required which can provide continuous and conformal thin films even in high aspect ratio structures. Atomic Layer Deposition (ALD) is an excellent choice of deposition technique as it is capable of providing perfect film coverage. Because of its self-limited growth mechanism, ALD can afford sub-nanometer thickness control. Precursors used in ALD should be volatile, thermally stable at the deposition temperature, and highly reactive towards the co-regent. Traditionally, ALD has been used to grow metal oxide films. However, the microelectronics industry now demands ALD for metals and metal nitrides. Titanium nitride (TiN) is widely used as adhesion layers, electrode material, and diffusion barriers. Halogenated precursors used in TiN ALD studies require high deposition temperatures and the corrosive byproducts can etch the substrates. Dialkylamido titanium precursors have low thermal stabilities, and hence, significant carbon incorporation arises in TiN ALD. Moreover, during the TiN depositions, current Ti(IV) precursors should reduce to Ti(III) and this reduction step is often incomplete. Hence, the synthesis of novel Ti(III) precursors which do not require reduction steps is needed. The research herein seeks to develop highly volatile and thermally stable Ti(III) and Ti(IV) precursors and to carry out TiN ALD with highly thermally stable titanium metal-organic precursors.ALD of TiN film was carried out using Ti(tBu2DAD)2 and 1,1-dimethylhydrazine. Ti(tBu2DAD)2 is highly volatile and thermally stable with a decomposition temperature ≥ 350 °C, which is much higher than commonly used metal-organic precursors. According to the plots of growth rate versus pulse length on SiO2 substrates, self-limited growth behavior was observed ≤ 3.0 s for Ti(tBu2DAD)2 and ≤ 0.1 s 1,1dimethylhydrazine with a saturative growth rate of 0.28 Å/cycle. An ALD window was observed from 325 to 350 °C, and a linear relationship was observed for a plot of thickness versus the number of cycles at a deposition temperature of 325 °C for TiN growth on SiO2 substrates. GI-XRD revealed the presence of nanocrystalline material on the films deposited at 350 and 400 °C. Atomic force microscopy of 30 nm thick films deposited at 325 and 350 °C showed RMS roughness values of 4.1% and 5.2% of the film thicknesses, respectively. X-ray photoelectron spectroscopy analyses were performed on films deposited within the ALD window. Both samples revealed TiOxNy upon argon ion sputtering. TiN ALD was attempted using Ti(iPr2DAD)3 and 1,1-dimethylhydrazine, but highly resistive, rough, and poor-quality films were obtained. Novel Ti(III) complexes containing pyrazolate and carbohydrazide ligands were synthesized and characterized. These complexes are non-volatile and thermally unstable. Hence, they are not viable candidates for the TiN ALD study. However, Ti(III) pyrazolate complexes unexpectedly were found to decompose thermally to afford Ti(IV) pyrazolates and possibly Ti metal. A disproportionation mechanism is proposed. This finding may be valuable for the development of Ti metal, TiN, and TiSi2 CVD and ALD precursors.

Available for download on Friday, January 06, 2023

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