Some Insights into Atomic Layer Deposition of MoN_x Using Mo(CO)₆ and NH₃ and Its Diffusion Barrier Application

Abstract

Deposition providing precise control of the film thickness, low deposition temperature, and noncorrosive byproducts is essential for the efficient fabrication of barrier layers in semiconductor devices. Here, molybdenum nitride (MoN x ) is deposited for Cu diffusion barrier application at a relatively low temperature (180−300 °C) by atomic layer deposition (ALD) using molybdenum hexacarbonyl [Mo-(CO) 6 ] and ammonia gas (NH 3 ). The density functional theory calculations indicate favorable thermodynamics during the chemisorption of Mo(CO) 6 on −NH 2 -terminated Si clusters at 200 °C, confirming the suitability of Mo(CO) 6 for ALD. However, the films deposited beyond the ALD temperature window are of similar importance though decomposition-induced growth of the film is evident; nevertheless, other advantages exist (e.g., higher growth rate and improved film characteristics). Furthermore, a few experiments using NH 3 plasma as a reactant show further scope for this process. The as-grown MoN x film using thermal ALD is mostly amorphous with significant O impurity. Poorly structured nanocrystalline h-MoN and cubic Mo 2 N phase are formed in the film above 225 °C. These phases are converted into the crystalline cubic Mo 2 N phase upon annealing at higher temperature (500−700 °C) in a hydrogen atmosphere. The resistivity of the MoN x films decreases sharply with deposition temperature and is significantly reduced further upon post-annealing. The properties of the as-deposited and annealed films are characterized in detail by secondary-ion mass spectroscopy and X-ray photoelectron spectroscopy. The barrier properties against Cu diffusion for the asdeposited thin films (less than 10 nm) grown at 225 and 275 °C are analyzed using ex situ X-ray diffraction (XRD) and electrical impedance spectroscopy (EIS). EIS helps to determine the failure of the MoN x barrier layer qualitatively by comparing different EIS spectra obtained after annealing at different temperatures. Both XRD and EIS analyses show that the ALD-MoN x film deposited at the higher ALD temperature makes a better Cu diffusion barrier layer. This could be attributed to the higher density of the ALD MoN x film grown at 275 °C compared with that deposited at 225 °C.

Hydrogen Evolution Reaction by Atomic Layer‐Deposited MoNx on Porous Carbon Substrates: The Effects of Porosity and Annealing on Catalyst Activity and Stability

“…This observation was in good agreement with MoN x films that were deposited under similar conditions on either SiO 2 /Si or Ni-foam substrates. [21][22][23] Furthermore, the annealing in a H 2 atmosphere at 400 8C had a minimal influence on the phase of ALD-MoN x . However, the minor hump observed at 35-408 (Mo 2 N 111) was much clearer and apparent.…”

“…The ALD technique is extensively used to grow various active compounds on different substrates for applications such as Cu diffusion barrier, energy storage devices, and electrocatalysis. [21][22][23][24][25][26][27][28] Recently, ALD has been explored as a fabrication technique for the preparation of various active materials on a highly porous substrate for application in fields such as Li-ion batteries and supercapacitor. [29][30][31][32][33] However, the deposition of MoN x on CC or NCCC has not been reported and studied as a catalyst for HER.…”

“…The self-limiting growth kinetics, the linearity of growth with ALD cycles and the temperature window for ALD-MoN x using Mo(CO) 6 and NH 3 has been previously established by our group: The results indicated that the ideal ALD conditions occurs only in a very narrow temperature range of 200-215 8C on a SiO 2 /Si substrate. [21][22][23] The number of ALD cycles for the coating of a MoN x thin film on CC and NCCC substrates was chosen to be 700 cycles to obtain a uniform thin film with a thickness of approximately 25-30 nm based on our previous study. [21][22][23] A schematic representation of the synthesis of the electrode is shown in Figure S1 (Supporting Information), and the conditions used during NCCC preparation, ALD-MoN x coating, and heat-treatment are tabulated in Table S1.…”

“…The ALD-growth kinetics, growth rate, and the composition of the ALD-MoN x film have been extensively investigated and are described in our previous work. [21][22][23] The structure and phase of the as-deposited MoN x film on NC-powder-coated carbon cloth (MoN x /NCCC), and that of the sample annealed in a hydrogen atmosphere at 400 8C (MoN x /NCCC-400) and 600 8C (MoN x /NCCC-600) were analyzed by XRD spectroscopy (Figure 2 a). The post-annealing temperatures were chosen according to two important criteria; the Mo 2 C formation temperature (by the reaction of carbon and molybdenum compounds, which is ca.…”

“…The challenges associated with the synthesis of high-surface-area and porous molybdenum-based carbide and nitride electrodes can be overcome by using atomic layer deposition (ALD), which can effectively coat a thin film with excellent uniformity and conformality on a high-surface-area porous substrate at relatively low temperatures. [21][22][23] Furthermore, ALD can be used for precise control of the thickness of the coating, which is beneficial for electrode fabrication because an unnecessarily thicker active material not only adversely effects the electrical conductivity of the electrode but might also influences the catalytic activity as the electrocatalytic process is a surface-restricted phenomenon. Therefore, ALD is beneficial for the fabrication of free-standing large area electrodes for practical implementation.…”