Tungsten-Ligand Bond Strengths for 2p Elements Including σ- and π-Bond Strength Components, A Density Functional Theory and ab Initio Study

Dielectric-on-Dielectric Achieved on SiO2 in Preference to W by Water-free Chemical Vapor Depositions with Aniline Passivation

Selective and smooth dielectric-on-dielectric was achieved by water-free single-precursor chemical vapor deposition (CVD) processes with the help of aniline passivation. Aniline selective passivation was demonstrated on W surfaces in preference to SiO₂ at 250, 300, and 330 °C. After aniline passivation, selective HfO₂, Al₂O₃, and TiO₂ were deposited only on the HF-cleaned SiO₂ surface by water-free single-precursor CVD using hafnium tert-butoxide Hf(O^tBu)₄, aluminum-tri-sec-butoxide (ATSB), and titanium isopropoxide Ti(OⁱPr)₄ as the precursor reactants, respectively. Hf(O^tBu)₄ and Ti(OⁱPr)₄ single-precursor CVD was carried out at 300 °C, while the ATSB CVD process was conducted at 330 °C. HfO₂ and Al₂O₃ nanoselectivity tests were performed on W/SiO₂ patterned samples. Transmission electron microscopy images of the W/SiO₂ patterned samples after deposition demonstrated nanoselectivity and low surface roughness of HfO₂ and Al₂O₃ deposition on the SiO₂ regions only.

Thermochemistry of Tungsten-3p Elements for Density Functional Theory, Caveat Lector!

There are two primary foci in this research on WE (E = Si, P, and S) bonds: prediction of their bond dissociation enthalpies (BDEs), including σ- and π-bond energy components, and assessing the uncertainty of these BDE predictions for levels of theory commonly used in the literature. The internal standards for computational accuracy include metal-element bond lengths (mean absolute error = 1.8 ± 1.2%), main group homolog BDEs versus higher levels of ab initio theory (W1U and G4 BDEs, R² = 0.98), and DLPNO-CCSD(T)/def2-QZVPP calculations for metal-ligand BDEs (R² = 0.88). The W═Si first π-bond is underreported for density functional theory (DFT)/MP2 methods versus DLPNO-CCSD(T), while the latter shows negligible strength for the W;Si second π-bond, consistent with the literature. This research highlights clear issues with the underlying assumptions required for the use of perturbation theory methods for the fragments derived from W-P homolysis. The difficulties associated with modeling the metal thermochemistry with DFT (and MP2) levels of theory are manifest in the broad standard deviations observed. However, the average BDEs found using 48 popular DFT and MP2 levels of theory are reliable, 10.8 ± 6.8% mean absolute error (with W-P removed) versus DLPNO-CCSD(T), with the caveat that the individual basis set/pseudopotential/valence basis set combination can vary wildly. Analysis of the absolute error percentages with respect to the level of theory indicates little benefit to going higher on Jacob's Ladder, as simpler methods have lower error versus high-level ab initio techniques such as G4 and DLPNO-CCSD(T).