Effect of Aminosilane Precursor and Surface Silanol Density on the Growth per Cycle during Atomic Layer Deposition of...

We report on the influence of the areal density of reactive surface sites and the growth temperature on the growth per cycle (GPC) during O₂-plasma-assisted atomic layer deposition (ALD) of SiO₂ using di-sec-butylaminosilane (DSBAS) and dimethylamino trimethylsilane (DMATMS) as precursors. The surface reactions during ALD were monitored using in situ attenuated total reflection Fourier transform infrared spectroscopy. ALD was performed on plasma-deposited SiO₂ films, and as the deposition temperature was increased from 100 to 500 °C, the areal density of isolated surface Si-OH groups decreased by a factor of ∼ 8. At 100 °C, ∼ 30% more surface Si-OH groups reacted with DMATMS than DSBAS. This shows that in the first ALD half-cycle, the initial aminosilane coverage is determined by the size of the aminosilane ligand, which reacts with surface Si-OH groups to form an alkylamine as the reaction product. However, in situ ellipsometry shows that the steady-state GPCs for DMATMS and DSBAS at 100 °C were ∼ 1.3 and ∼ 1.8 Å, respectively, which shows that the initial surface coverage of these precursors does not influence the GPC. As the plasma deposition and ALD temperatures were increased from 100 to 500 °C, the GPC for ALD of SiO₂ with DSBAS decreased from ∼ 1.8 to ∼ 1.0 Å due to a lower steady-state surface Si-OH density during ALD at higher temperatures. We further show that for DSBAS and DMATMS, a 500 °C preheat step did not influence the GPC. Finally, we attribute the higher GPC for ALD of SiO₂ with DSBAS versus DMATMS to a higher efficiency for the formation of surface Si-OH from surface -SiH₃ groups versus surface -Si(CH₃)₃ groups during O₂ plasma exposure.