Crystalline Aminoorganosilanes - Syntheses, Structures, Spectroscopic Properties: Crystalline Aminoorganosilanes

Enhancing silicon-nitride formation through ammonolysis of silanes with pseudo-halide substituents

Considering the challenges in reactivity, potential contamination, and substrate selectivity, the ammonolysis of traditional halosilanes in silicon nitride (SiN) thin film processing motivates the exploration of alternative precursors. In this pioneering study, we employed density functional theory calculations at the M06-2X/6-311++G(3df,2p) level to comprehensively screen potential pseudo-halide substituents on silane compounds as substitutes for conventional halosilanes. Initially, we investigated the ammonolysis mechanism of halosilanes, exploring factors influencing activation barriers, with the aid of frontier molecular orbital and charge density analyses. Subsequently, a systematic screening of silane substituents from group 14 to group 16 was conducted to identify pseudo-halides with low reaction barriers. Additionally, we examined the inductive effects on pseudohalide substituents. Using cluster models to represent the silicon surface validates the realistic prediction of ammonolysis barriers with a simplified model. Our findings indicate that pseudo-halide substituents from group 16, particularly those with electron-withdrawing groups, present as practical alternatives to traditional halosilanes in SiN thin film processing, including applications such as low-temperature atomic layer deposition (ALD) techniques.

Si⋯O proximity in imidosilanes – absence of orbital interactions

New N-silylated phthalimides, succinimides, and 1,8-napthalimides were synthesised by reactions of the alkali imides with chlorosilanes in THF. Six different mono-, di-, tri- and tetra-iminosilanes of the type (CH3)4–n Si(imide) n were obtained and the products analysed with 1H, 13C, 29Si NMR, and Raman spectroscopy. The molecular structures of four imidosilanes have been determined by single-crystal X-ray diffraction. A characteristic structural feature of the compounds is the fact that all intramolecular Si⋯O distances are significantly below the sum of the van-der-Waals radii of silicon and oxygen of 3.62 Å. Experimentally found values for Si⋯O distances range from 2.813 to 3.030 Å. However, there are no significant orbital interactions between silicon and oxygen atoms, as shown by quantum chemical analysis with AIM and NBO methods. The short Si⋯O distances in these molecules are caused by the geometry of the rigid imide group bound to the silicon atom, and there is no evidence for an increase of the coordination number of the Si atoms.

Syntheses and Molecular Structures of Liquid Pyrophoric Hydridosilanes

Trisilane, isotetrasilane, neopentasilane, and cyclohexasilane have been prepared in gram scale. In-situ cryo crystallization of these pyrophoric liquids in sealed capillaries on the diffractometer allows access to the single crystal structures of these compounds. Structural parameters are discussed and compared to gas-phase electron diffraction structures from literature and with the results from quantum chemical calculations. Significantly higher packing indices are found for the silanes compared to the corresponding alkanes. Radiation with ultraviolet light (365 nm) and parallel ESR (EPR) measurement shows that cyclohexasilane is easily split into radicals, which subsequently leads to the formation of branched and chain-like oligomers. The other compounds form no radicals under these conditions. NMR spectra of all four compounds have been recorded.

Insertion of phenyl isocyanate into mono- and diaminosilanes

The aminosilanes MenSi(NRR′)4−n (n=2,3) with NRR′=ethylamino (NHEt), n-propylamino (NH n Pr), sec-butylamino (NH s Bu), n-octylamino (NH n Oct), n-dodecylamino (NH n Dodec), allylamino (NHAll), tert-butylamino (NH t Bu), diethylamino (NEt2), and anilino (NHPh) were synthesized and their reactions with phenyl isocyanate were studied. In all cases of these silanes Me3SiNRR′ and Me2Si(NRR′)2 formal insertion of the –NCO group into their Si–N bonds was observed, i.e. formation of products with Si–N (rather than Si–O) bonds was found. In some cases, the products could be crystallized and their molecular structures have been elucidated with single-crystal X-ray diffraction analyses.