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

J. D. Ferguson, E. R. Smith, A. W. Weimer, S. M. George
2004 Journal of the Electrochemical Society  
Amine catalysts can reduce the high temperatures and long exposure times required for SiO 2 atomic layer deposition ͑ALD͒ using SiCl 4 and H 2 O 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 SiO 2 ALD on BaTiO 3 and ZrO 2 particles using alternating exposures of tetraethoxysilane ͑TEOS͒ and H 2 O at 300 K with NH 3 as the
more » ... K with NH 3 as the catalyst. The sequential surface chemistry was monitored in a vacuum chamber using in situ transmission Fourier transform infrared ͑FTIR͒ 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 ͑TEM͒. 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 Å 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.
doi:10.1149/1.1768548 fatcat:3u3e6gciazfolgastrekxdwnam