Access Type

Open Access Dissertation

Date of Award

January 2014

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Chemistry

First Advisor

Charles H. Winter

Abstract

As a result of the continuous miniaturization of microelectronics devices, atomic layer deposition (ALD) has gained much attention in the recent years. ALD allows the deposition of ultra-thin conformal films with accurate thickness control due to the self-limiting growth mechanism. The microelectronics industry requires the growth of metallic first row transition metal films by ALD. Due to the positive electrochemical potentials, the ALD growth of noble metal thin films has been well developed in the past. By contrast, the ALD growth of first row transition metal films remains poorly documented. The reasons for this scarcity include the lack of suitable metal precursors and powerful reducing co-reagents that can convert precursors in positive oxidation states to the metals. In this dissertation, the development of new transition metal precursors, solution phase reaction screening for powerful reducing agents, and ALD growth of transition metal thin films are discussed.

In this dissertation, five classes of new ALD precursors for Cr, Mn, Fe, Co, Ni, and Cu are discussed, namely, fÑ-imino alkoxides, fÑ-imino ketonates, fÑ-imino enolates, hydrazonates, and 1,2,5-triazapentadienyls. These precursors are volatile, thermally stable, and reactive toward reducing co-reagents, which are the key properties that ALD precursors must have. fÑ-Imino alkoxide, fÑ-imino ketonate, fÑ-imino enolate, hydrazonate, and 1,2,5-triazapentadienyl precursors have volatilities that range from 85f{160, 135−145, 110−165, 100−135, and 105−175 ¢XC at 0.05 Torr, respectively, and thermally stabilities that range from 183−270, 108−248, 190−295, 240−308, and 180−310 ¢XC, respectively. Solution screening of these precursors with commercially available reducing agents revealed high reactivity toward reducing agents. These solution screening reactions demonstrated that BH3(NHMe2) is a powerful reducing agent that can transfer Cr(II), Mn(II), Fe(II), Co(II), Ni(II), and Cu(II) centers to their metallic forms and, thereby, can be used in viable ALD processes.

Thermal ALD growth of late first row transition metal films was discussed. Cu ALD depositions were carried out with Cu(damp)2 and BH3(NHMe2). The deposited Cu films are smooth and continuous, even at thicknesses of 2 nm, and high purity and low resistivity were achieved. The deposition of Cr, Mn, Fe, Co, and Ni films was performed with the fÑ-imino alkoxide precursors and BH3(NHMe2). X-ray photoelectron spectroscopy (XPS) of these films suggests that the film surfaces are oxidized, however, the bulk of the films showed metals for all except Mn. Moreover, Cr thin films have never been deposited by ALD and this dissertation reports the first ALD growth of Cr films.

Considering the fact that limited precursors are available for the deposition of metastable Mo and W oxide films, this work also discusses the synthesis and complete characterization of Mo and W complexes containing amidate and carbohydrazide ligands. These new complexes are volatile between 120-170 ¢XC at 0.05 Torr, and thermally decompose temperatures between 193 ¢XC and 355 ¢XC, which should allow low temperature ALD of oxide films.

Ligands that are discussed herein have emerged as new classes of ligands that can form thermally stable metal precursors for ALD applications. Additionally, the selection of the ligands with proper substituents for desired metal ions was demonstrated toward the design of ideal ALD precursors with the best possible properties. Moreover, the ALD growth of late first row transition metals was demonstrated using the metal precursors with similar ligands and same reducing co-reagent that enable the late transition metal alloy film growth.

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