Atomic Layer Deposition of Cobalt Carbide Thin Films from Cobalt Amidinate and Hydrogen Plasma

Abstract

Atomic layer deposition (ALD) of cobalt carbide thin films is reported by using bis­( N , N ′-diisopropyl­acetamidinato)­cobalt­(II) (Co­(amd)2) and H2 plasma. The process shows a good self-limiting ALD film growth behavior for a fairly wide temperature range from 70 to 160 °C, and the growth rate is 0.066 nm/cycle for the deposition within the temperature range. The deposited cobalt carbide thin films are generally smooth and pure, and the film composition is approximately Co3C0.7 for the deposition at 80–200 °C. Notably, all the carbon in the as-deposited films forms cobalt carbide, and no carbon–carbon bonds are detected by X-ray photoelectron spectroscopy. Raman spectroscopy also confirms the absence of graphite or amorphous carbon in the as-deposited films. The films are nano-polycrystalline as deposited, and the crystal structure is the hexagonal Co3C structure. The films can decompose into hcp-Co metal and amorphous carbon upon the thermal annealing in N2 at 400 °C. The resistivity and magnetization of the as-deposited films are also characterized. It is further shown that by use of this plasma-assisted ALD process highly conformal cobalt carbide films can be deposited into the trench structures with a high aspect ratio of 20:1. In the last, the ALD growth chemistry is studied by using the in situ quartz crystal microbalance (QCM) technique, and the QCM results suggest that the structure of the amidinate ligand in the Co­(amd)2 precursor largely falls apart upon its reaction with the surface during the ALD.

Atomic Layer Deposition of FeSe2, CoSe2, and NiSe2

“…In the following, we further investigated the related mechanisms for these ALD processes. Since the M­(amd) 2 precursors have been used in a number of other ALD processes and their reaction mechanisms have been understood reasonably well, ,− the mechanism study herein was focused on the effect of the plasma. To this end, in situ quadrupole mass spectrometry (QMS) was employed to investigate the plasma effect on DEDSe.…”

Cobalt Metal ALD: Understanding the Mechanism and Role of Zinc Alkyl Precursors as Reductants for Low-Resistivity Co Thin Films

“…Intriguingly, a shift of the center of the C 1s signal from 284.8 to 283.6 eV was observed in the course of sputtering, which indicates the presence of different carbon species within the Co thin films. Component fitting shown in Figure S24 revealed the coexistence of carbidic carbon around 283.7 eV alongside graphitic carbon (284.6–284.8 eV) , in the film bulk. This is a remarkable finding, which contrasts, for example, a recent study by Fan and co-workers on PEALD grown cobalt carbide Co 3 C x thin films for which only carbidic carbon species were observed by XPS …”

“…This is a remarkable finding, which contrasts, for example, a recent study by Fan and co-workers on PEALD grown cobalt carbide Co 3 C x thin films for which only carbidic carbon species were observed by XPS. 58 Resistivity Measurements. To determine the electrical resistivity of ALD-deposited Co films, several ∼22 nm thick films were grown on Si substrates coated with 200 nm thermal SiO 2 .…”

Fabrication of iron carbide by plasma-enhanced atomic layer deposition

“…When H 2 plasma exposure time is shorter than 5 s, an increasing trend in the growth rate is achieved with increasing H 2 plasma pulse length. However, a saturated growth rate of 0.04 nm/cycle is obtained with an H 2 plasma exposure time of $5 s. To investigate the effect of H 2 purging pulse length on the growth rate of the deposited films, we vary the purging pulse from 2 [22,37]. It is believed that the higher input power is able to produce more energetic electrons, which cause a higher density of reactive intermediates beneficial to the generation of the iron carbide.…”

“…Commonly used methods for the production of bulk and amorphous iron carbides include solution chemistry method [15], ball milling [16], physical vapor deposition [17], and chemical vapor deposition [18]. Among them, atomic layer deposition (ALD) has recently attracted much attention for being able to fabricate high-quality nanomaterials [19,20,21,22,23]. ALD is a powerful thin-film deposition technique, which is able to control film thickness precisely on complex 3D structured morphologies and large substrates.…”