Low-Temperature Atomic Layer Deposition of Highly Conformal Tin Nitride Thin Films for Energy Storage Devices

Abstract

We present an atomic layer deposition (ALD) process for the synthesis of tin nitride (SnN x ) thin films using tetrakis­(dimethylamino) tin (TDMASn, Sn­(NMe2)4) and ammonia (NH3) as the precursors at low deposition temperatures (70–200 °C). This newly developed ALD scheme exhibits ideal ALD features such as self-limited film growth at 150 °C. The growth per cycle (GPC) was found to be ∼0.21 nm/cycle at 70 °C, which decreased with increasing deposition temperature. Interestingly, when the deposition temperature was between 125 and 180 °C, the GPC remained almost constant at ∼0.10 nm/cycle, which suggests an ALD temperature window, whereas upon further increasing the temperature to 200 °C, the GPC considerably decreased to ∼0.04 nm/cycle. Thermodynamic analysis via density functional theory calculations showed that the self-saturation of TDMASn would occur on an NH2-terminated surface. Moreover, it also suggests that the condensation of a molecular precursor and the desorption of surface *NH2 moieties would occur at lower and higher temperatures outside the ALD window, respectively. Thanks to the characteristics of ALD, this process could be used to conformally and uniformly deposit SnN x onto an ultranarrow dual-trench Si structure (minimum width: 15 nm; aspect ratio: ∼6.3) with ∼100% step coverage. Several analysis tools such as transmission electron microscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy, Rutherford backscattering spectrometry, and secondary-ion mass spectrometry were used to characterize the film properties under different deposition conditions. XRD showed that a hexagonal SnN phase was obtained at a relatively low deposition temperature (100–150 °C), whereas cubic Sn3N4 was formed at a higher deposition temperature (175–200 °C). The stoichiometry of these thermally grown ALD-SnN x films (Sn-to-N ratio) deposited at 150 °C was determined to be ∼1:0.93 with negligible impurities. The optoelectronic properties of the SnN x films, such as the band gap, wavelength-dependent refractive index, extinction coefficient, carrier concentration, and mobility, were further evaluated via spectroscopic ellipsometry analysis. Finally, ALD-SnN x -coated Ni-foam (NF) and hollow carbon nanofibers were successfully used as free-standing electrodes in electrochemical supercapacitors and in Li-ion batteries, which showed a higher charge-storage time (about eight times greater than that of the uncoated NF) and a specific capacity of ∼520 mAh/g after 100 cycles at 0.1 A/g, respectively. This enhanced performance might be due to the uniform coverage of these substrates by ALD-SnN x , which ensures good electric contact and mechanical stability during electrochemical reactions.

Area-Selective Atomic Layer Deposition of Ruthenium Using a Novel Ru Precursor and H2O as a Reactant

“…Every desorption of a ligand from the adsorbed precursor is endothermic, and such reactions can be driven by the entropy gain from the release of gaseous molecules. 49 On both H−Si and OH−Si surfaces, removal of the hydrogenated enamine ligand (iv,v) is energetically preferred over removal of two CO molecules (vi,vii). It is noted that the protonated imido ligand prefers the enamine form while it is still coordinated to Ru atoms adsorbed to the surface as it can coordinate with two Ru atoms via both N and CC double bonds; on the other hand, the imine tautomeric form {N(tBu)C(H)C(H) 2 (iPr)} is preferred by 10.4 kJ/mol as the desorbed gas-phase byproduct.…”

“…The sequential removal of the ligands from the chemisorbed precursor is also considered (iv–vii). Every desorption of a ligand from the adsorbed precursor is endothermic, and such reactions can be driven by the entropy gain from the release of gaseous molecules . On both H–Si and OH–Si surfaces, removal of the hydrogenated enamine ligand (iv,v) is energetically preferred over removal of two CO molecules (vi,vii).…”

Adsorption of Titanium Halides on Nitride and Oxide Surfaces during Atomic Layer Deposition: A DFT Study

“…Their values were obtained by calculating the vibrational frequency according to the desired temperature, based on the optimized structure in the gas phase [35,36]. The rotational and translational degrees of freedom appearing in the entropy term were excluded from the calculations involving surface reactions on Si clusters [37,38]. In other words, only the vibrational degree of freedom was considered, and thus, the Gibbs free energy (G) was derived using the following thermodynamic Equation:…”

Critical Aspects of Various Techniques for Synthesizing Metal Oxides and Fabricating Their Composite-Based Supercapacitor Electrodes: A Review

“…ALD is a multistep chemical-vapor deposition wherein atomically thin films are grown on conducting substrates [ 160 , 161 ]. ALD is important for the cost-effective fabrication of large specific surface-area materials for applications to a wide range of energy-storage devices and optoelectronics [ 162 ], nanogenerators [ 163 ], LIBs [ 164 ], photovoltaics [ 165 ], microelectronics [ 166 ], and SCs [ 167 ]. In ALD, because films are grown on substrates through binary chain reactions, a film’s thickness, morphology, and chemical properties are atomically controlled.…”