Cobalt(III) Diazabutadiene Precursors for Metal Deposition: Nanoparticle and Thin Film Growth

Abstract

We report the synthesis and characterization of a family of cobalt(III) metal precursors, based around cyclopentadienyl and diazabutadiene ligands. The molecular structure of the complexes cyclopentadienyl-Cobalt(III)(N,N'-dicyclohexyl-diazabutadiene) (2c) and cyclopentadienyl-Cobalt(III)(N,N'-dimesityl-diazabutadiene) (2d) are described, as determined by single crystal X-ray diffraction analysis. Thermogravimetric analysis of the complexes highlighted the isopropyl derivative CpCo((i)Pr2-dab) (2a) as a possible cobalt metal chemical vapor deposition (CVD) precursor. Atmospheric pressure CVD (AP-CVD) was employed using precursor 2a to synthesize thin films of metallic cobalt on silicon substrates under an atmosphere of hydrogen (H2). Analysis of the thin films deposited at substrate temperatures of 250 °C, 275 °C, 300 °C, 325 °C, and 350 °C, respectively, by scanning electron microscopy (SEM) and atomic force microscopy (AFM) reveal temperature dependent growth features: films grown at 325 and 350 °C are continuous and pinhole free, whereas those films grown at substrate temperatures of 250 °C, 275 °C, and 300 °C consist of crystalline nanoparticles. Powder X-ray diffraction (PXRD) and X-ray photoelectron spectroscopy (XPS) all show the films to be high purity metallic cobalt. Raman spectroscopy has also been used to prove the absence of cobalt silicides at the substrate/thin film interface.

Editors' Choice—Review—Cobalt Thin Films: Trends in Processing Technologies and Emerging Applications

“…Hot-Wall Cross-Flow ALD Reactor Liners and caps in IC Cu interconnects, as seed film for CoSi 2 as IC contact material, and in magnetic memories A two-step ALD process that deposits CoO which is then subjected to a reduction process in forming gas to yield Co 42 Väyrynen et al (2018) Shower head type ALD system Amorphous metal alloys (metallic glasses) due to their uncommon properties, such as high hardness, soft magnetism and electrical behavior Co and TiN were grown via cyclic combination of ALD to form multilayered Co/TiN stacked structures 43 Nam (2018) Thermal ALD Thermal Pulsed-MOCVD Spintronic devices for nonvolatile magnetic random access memories (MRAM) and diluted magnetic semiconductors (DMS) ALD and pulsed MOCVD were performed using a variety of co-reactants, with no self-limiting growth behavior observed. It was determined that the precursors studied could not be used as pure ALD precursors, and were more appropriate for low-temperature MOCVD Co films 44 Lubitz 17 increased substrate temperature leads to longer surface diffusion distances, thus extending surface reaction times and potentially producing enhanced step coverage and reduced contaminant incorporation. However, Co film growth in thermal MOCVD proceeds as isolated islands or disconnected layers until a specific thickness is achieved which enables the islands or layers to connect and establish a continuous film.…”

“…10 r Isopropyl derivative CpCo( i Pr 2 -dab) (Co-302) with H 2 as coreactant at a substrate temperature above 325 • C (Co oxidation state: 3; key parameter: substrate temperature). 17 r Dicobalt hexacarbonyl bis(trimethylsilyl)acetylene (Co-005) with no co-reactant at a substrate temperature above 250 • C (Co oxidation state: 0; key parameters: type of precursor and substrate temperature). 29 r Dicobalt octacarbonyl [Co 2 (CO) 8 ] (Co-001) with no co-reactant at a substrate temperature above 125 • C (Co oxidation state: 0; key parameter: substrate temperature).…”

Classification of processes for the atomic layer deposition of metals based on mechanistic information from density functional theory calculations

“…The C− −C bond length can therefore be used to monitor the charge state of the ligand, as previously noted. 58 It is important to consider electronic spin for a complete description of bonding in DAD complexes. As an example, consider the M ii (DAD ) 2 case.…”

Controlled metal nanostructures: Fertile ground for coordination chemists

“…These could be the ability to be easily thermally decomposed or reduced in the presence of a reducing gas, without formation of pollutant by-products. Some of these complexes are valuable atomic sources for the formation of thin films by chemical vapor deposition (CVD) or atomic layer deposition (ALD) [24].…”