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Film Deposition: Dielectric, Polysilicon and Metallization
Published in Kumar Shubham, Ankaj Gupta, Integrated Circuit Fabrication, 2021
Polysilicon can be doped by adding phosphine, arsine, or diborane to the reactants (in-situ doping). Adding diborane causes a large increase in the deposition rate because diborane forms borane radicals, BH3, that catalyze gas-phase reactions and increase the deposition rate. In contrast, adding phosphine or arsine causes a rapid reduction in the deposition rate, because phosphine or arsine is strongly adsorbed on the silicon substrate surface thereby inhibiting the dissociative chemisorption of SiH4. Despite the poorer thickness uniformity across a wafer when dopants are incorporated, uniformity can be maintained by controlling precisely the flow of reactant gases around the samples.
Synthesis and characterization of Cp*Ir-dithiolene-o-carborane phosphine complexes: A continuous investigation of B−H⋯π interaction
Published in Molecular Physics, 2019
Hou-ji Cao, Huimin Dai, Xiaolei Zhang, Hong Yan, Changsheng Lu
Weak non-covalent interactions, such as X−H⋯π (X = C, N, O, S) hydrogen bonds are extensively studied owing to their important roles in biological systems and molecular engineering [1–11]. However, B−H⋯π interaction between a boron−hydrogen bond and π-electrons of an aromatic ring seems a challenging experimental proposal, given that less studies have been reported [12–23]. Indeed, the electropositive character of boron (χ(B) = 2.04 vs χ(H) = 2.20 [24]) suggests repulsive property of B−H⋯π interactions. To realise such interactions, the polarities of B and H should be reversed. This can be achieved in B2H6⋯benzene system, where two-electron-three-centre (2e–3c) bonds lead to positively charged bridging hydrogen in B2H6 [14]. However, negatively charged terminal hydrogens in B2H6 are reluctant to form stable B−H⋯π interaction. Besides simple boron hydrides, polyhedral boranes contain terminal boron−hydrogen (B−H) bonds as well. Recently, icosahedral carborane clusters exhibit extensive applications in medicinal researches [25–30], materials [31–37], and coordination/organometallic chemistry [38–64]. However, the non-covalent interactions between the carborane cage and neighbouring molecular moieties remain less known, although the dihydrogen interactions (Hδ-⋯Hδ+) between B−H bonds of carborane and the proton donors in biomolecules has been applied in new drug design [65–69]. In the study of B−H⋯π interaction, factors that can enforce B−H⋯aryl interactions have been pursued starting from 16e half-sandwich Ir dithiolene complexes containing o-carboranyl dithiolate ligands [14].