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Sustainable silicon precursors for ALD
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School of Chemical Engineering |
Master's thesis
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Authors
Israr, Fasiha
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Language
en
Pages
84
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Abstract
Silicon based thin films (SiO2, SiC, SiN and SiCN), fabricated via Atomic Layer deposition (ALD), are of great importance in semiconductor technology and worth $150 billion, but the rapid growth causes adverse environmental impact. In this thesis work, precursors for ALD were synthesized using green chemistry principles and characterized to minimize the environmental impact of semiconductor fabrication. Tris(dimethylamino)silane (TDMAS) and tris(diethylamino)silane (TDEAS) were selected as target compounds due to their high volatility and reactivity. The films derived from these precursors are prominent for possessing properties such as high dielectric permittivity, appropriate refractive index, and a suitable optical band gap, making them suitable precursors for thin film deposition. The Schlenk line synthesis setup was used. Trichlorosilane was as the silicon source and dimethylamine and diethylamine were as amine ligands. Magnesium was used to reduce the formation of salt byproducts. Characterization of the precursors was performed using NMR, XRD, FTIR, and GC-MS. 1H, 13C and 29Si NMR analyses revealed that TDMAS synthesis was unsuccessful, as evidenced by the absence of predicted peaks when compared to NMR data from commercially available samples. whereas distinct peaks of NMR-spectra confirmed the effective synthesis of TDEAS. FTIR data of the synthesized TDEAS showed distinctive absorptions between 1024 cm⁻¹ - 2158 cm⁻¹, proving the existence of Si–N and Si–H bonds. However, due of TDEAS’s moisture sensitivity, the product encountered partial decomposition which was indicated by split peaks at 2158 cm⁻¹ for Si-H and at 2243 cm⁻¹ for Si-OH occurring due to open air analysis. GC-MS analysis fragments also showed the partial decomposition of TDEAS occurred due to moisture, impurities and high temperature (>270∘C) inside the GC injector. The byproduct formation during the synthesis is confirmed by XRD analysis provided evidence of magnesium, amine salts, and SiO2 within samples of the filter cake and flask buildup. Vapor pressure measurements using the distillation method revealed that, at 48–50°C, TDMAS (commercial) exhibited a vapor pressure of 2.4 kPa, and at 138–140°C synthesized TDEAS exhibited a vapor pressure of 11.7 kPa. For future work, the application of TDEAS for depositing SiO2 thin films via ALD offers a novel research opportunity in this field.
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Supervisor
Karppinen, MaaritThesis advisor
Philip, AnishTiitta, Marja