Stepwise mechanism and H(2)O-assisted hydrolysis in atomic layer deposition of SiO(2) without a catalyst

Atomic layer deposition (ALD) is a powerful deposition technique for constructing uniform, conformal, and ultrathin films in microelectronics, photovoltaics, catalysis, energy storage, and conversion. The possible pathways for silicon dioxide (SiO(2)) ALD using silicon tetrachloride (SiCl(4)) and water (H(2)O) without a catalyst have been investigated by means of density functional theory calculations. The results show that the SiCl(4) half-reaction is a rate-determining step of SiO(2) ALD. It may proceed through a stepwise pathway, first forming a Si-O bond and then breaking Si-Cl/O-H bonds and forming a H-Cl bond. The H(2)O half-reaction may undergo hydrolysis and condensation processes, which are similar to conventional SiO(2) chemical vapor deposition (CVD). In the H(2)O half-reaction, there are massive H(2)O molecules adsorbed on the surface, which can result in H(2)O-assisted hydrolysis of the Cl-terminated surface and accelerate the H(2)O half-reaction. These findings may be used to improve methods for the preparation of SiO(2) ALD and H(2)O-based ALD of other oxides, such as Al(2)O(3), TiO(2), ZrO(2), and HfO(2).