Methodology for Studying Surface Chemistry and Evolution during the Nucleation Phase of Atomic Layer Deposition Using Scanning Tunneling Microscopy

Abstract

We study the nucleation stage and growth of atomic layer deposition (ALD) on hydrogen terminated silicon (Si:H) by in situ and ex situ scanning tunneling microscopy (STM). STM allows the in-depth study of surface chemistry and evolution during the ALD nucleation phase. Here, the ALD systems studied to demonstrate this technique are ZnO via diethyl zinc (DEZ) and TiO2 via titanium tetrachloride (TiCl4). In-situ STM revealed that DEZ does not discriminate between different surface sites, in contrast to TiCl4 which shows a strong preference toward dangling or OH bonds. Continued deposition showed distinct island growth for TiO2 deposition on Si:H, versus homogeneous growth for DEZ. ZnO ALD exhibited a delay of approximately 5 ALD cycles in transitioning from lateral to vertical growth and nominal physical film closure occurred after approximately 12–15 cycles. STM observations of these ALD chemistries demonstrated the strength of this technique in quantifying film closure and the effects of surface termination and defects on ALD growth mode. This technique can be applied to the study of a broad variety of ALD systems.