ALD of SiO2 at room temperature using TEOS and H2O with NH3 as the catalyst

Amine catalysts can reduce the high temperatures and long exposure times required for SiO2 atomic layer deposition (ALD) using SiCl4 and H2O reactants. One problem is that the reaction product, HCl, readily reacts with the amine catalysts to form a salt. Salt formation can be avoided by using organometallic silicon precursors. This study investigated catalyzed SiO2 ALD on BaTiO3 and ZrO2 particles using alternating exposures of tetraethoxysilane (TEOS) and H2O at 300 K with NH3 as the catalyst. The sequential surface chemistry was monitored in a vacuum chamber using in situ transmission Fourier transform infrared (FTIR) spectroscopy. Alternating TEOS/NH3 and H2O/ NH3 exposures yielded Si(OCH2CH3)(x)* and SiOH* surface species, respectively, that sequentially deposited silicon and oxygen. Repetition of the TEOS and H2O exposures in an ABAB... reaction sequence led to the appearance of bulk SiO2 vibrational modes. The infrared absorbance of these bulk SiO2 vibrational modes increased with the number of AB reaction cycles. After SiO2 deposition, the BaTiO3 and ZrO2 particles were examined using transmission electron microscopy (TEM). The TEM images revealed extremely uniform and conformal SiO2 films. The measured SiO2 film thicknesses were consistent with SiO2 ALD growth rates of 0.7- 0.8 Angstrom per AB reaction cycle. The NH3 catalysis mechanism was also explored by monitoring the FTIR spectra of hydroxylated SiO2 particles vs. NH3 pressure at constant temperature and vs. temperature at constant NH3 pressure. The spectra revealed strong hydrogen bonding between NH3 and SiOH* surface species that activates the oxygen in SiOH* for nucleophilic attack. Catalyzed SiO2 at room temperature should be useful for deposition of inorganic and insulating films on thermally fragile organic, polymeric, or biological substrates. (C) 2004 The Electrochemical Society.