ALD of SiO[sub 2] at Room Temperature Using TEOS and H[sub 2]O with NH[sub 3] as the Catalyst

Amine catalysts can reduce the high temperatures and long exposure times required for SiO 2 atomic layer deposition (ALD) using SiCl 4 and H 2 O reactants. One problem is that the reaction product, HCI, readily reacts with the amine catalysts to form a salt. Salt formation can be avoided by using organometallic silicon precursors. This study investigated catalyzed SiO 2 ALD on BaTiO 3 and ZrO 2 particles using alternating exposures of tetraethoxysilane (TEOS) and H 2 O 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/NH 3 and H 2 O/NH 3 exposures yielded Si(OCH 2 CH 3 ) x * and SiOH* surface species, respectively, that sequentially deposited silicon and oxygen. Repetition of the TEOS and H 2 O exposures in an ABAB... reaction sequence led to the appearance of bulk SiO 2 vibrational modes. The infrared absorbance of these bulk SiO 2 vibrational modes increased with the number of AB reaction cycles. After SiO 2 deposition, the BaTiO 3 and ZrO 2 particles were examined using transmission electron microscopy (TEM). The TEM images revealed extremely uniform and conformal SiO 2 films. The measured SiO 2 film thicknesses were consistent with SiO 2 ALD growth rates of 0.7-0.8 A per AB reaction cycle. The NH 3 catalysis mechanism was also explored by monitoring the FTIR spectra of hydroxylated SiO 2 particles vs. NH 3 pressure at constant temperature and vs. temperature at constant NH 3 pressure. The spectra revealed strong hydrogen bonding between NH 3 and SiOH* surface species that activates the oxygen in SiOH* for nucleophilic attack. Catalyzed SiO 2 at room temperature should be useful for deposition of inorganic and insulating films on thermally fragile organic, polymeric, or biological substrates.