Mechanistic study of atomic layer deposition of Al_xSi_yO thin film via in-situ FTIR spectroscopy

A study of surface reaction mechanism on atomic layer deposition (ALD) of aluminum silicate (Al_xSi_yO) was conducted with trimethylaluminum (TMA) and tetraethoxysilane (TEOS) as precursors and H₂O as the oxidant. In-situ Fourier transform infrared spectroscopy (FTIR) was utilized to elucidate the underlying surface mechanism that enables the deposition of Al_xSi_yO by ALD. In-situ FTIR study revealed that ineffective hydroxylation of the surface ethoxy (–OCH₂CH₃) groups prohibits ALD of SiO₂ by TEOS/H₂O. In contrast, effective desorption of the surface ethoxy group was observed in TEOS/H₂O/TMA/H₂O chemistry. The presence of Al-OH* group in vicinity of partially hydroxylated ethoxy (–OCH₂CH₃) group was found to propagate disproportionation reaction, which results in ALD of Al_xSi_yO. The maximum thickness from incorporation of SiO_x from alternating exposures of TEOS/H₂O chemistry in Al_xSi_yO was found to be ∼2 Å, confirmed by high resolution transmission electron microscopy measurements