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 TiO 2 via titanium tetrachloride (TiCl 4 ). In-situ STM revealed that DEZ does not discriminate between different surface sites, in contrast to TiCl 4 which shows a strong preference toward dangling or OH bonds. Continued deposition showed distinct island growth for TiO 2 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.

Electrical Properties of Ultrathin Platinum Films by Plasma-Enhanced Atomic Layer Deposition

“…The development of thermal atomic layer deposition (t-ALD) allows precise control of thickness and high conformality on complex 3D architectures. − However, even with t-ALD there are limits to the attainable film thickness because material-dependent nucleation difficulties prevent continuous films below a certain number of t-ALD cycles. − Pt is one of the materials known to present nucleation challenges with t-ALD . The high surface energy of Pt leads to Volmer–Weber (VW) growth, forming islands at the early stages of nucleation. , This growth behavior sets a lower limit on the minimum closed-film thickness, as these Pt islands must grow large enough to connect to neighboring islands before the film becomes continuous .…”

Cyclic Plasma Halogenation of Amorphous Carbon for Defect-Free Area-Selective Atomic Layer Deposition of Titanium Oxide

“…The growth on nontreated a-C:H is only slightly delayed, in clear contrast with the same layer exposed to a Cl 2 or CF 4 plasma. While the nucleation delay on halogenated a-C:H is captured by both RBS and AFM (Figure ), the latter provides more detailed information about the process selectivity . For example, the AFM grain maps shown in Figure a show the presence of TiO 2 at a sensitivity level where no Ti signal is detected by RBS yet.…”

“…While the nucleation delay on halogenated a-C:H is captured by both RBS and AFM (Figure 5), the latter provides more detailed information about the process selectivity. 51 For example, the AFM grain maps shown in Figure 5a show the presence of TiO 2 at a sensitivity level where no Ti signal is detected by RBS yet. In addition, the topography information in AFM enables monitoring TiO 2 nucleation quantitatively, as exemplified by Figure 5b showing that the number of nucleation defects is not fixed but continuously grows.…”

Investigating the Nucleation of AlOx and HfOx ALD on Polyimide: Influence of Plasma Activation

“…At the last stages of the nucleation, the growth mechanisms were dominated by the second mechanism of lateral growth on the already deposited Al 2 O 3 and HfO 2 , as the likelihood of reactive sites on the polyimide to be vacant or even physically available was rather low. These observations clearly pointed to a nucleating mechanism based on the adsorption of precursors at reactive sites of the polyimide and further lateral growth, commonly referred to as island-coalescence nucleation or growth [34,65,70,71,102,103]. Island growth of Al 2 O 3 on H-terminated Si was already observed by selective etching of SiOx through the "defects" of the nucleating Al 2 O 3 layer [104].…”

“…The nucleation of ALD processes has been commonly studied by characterization techniques such as Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), ellipsometry, quartz microbalance (QCM), both in and ex situ, but has also been investigated using other techniques such as atomic force microscopy (AFM), scanning tunneling microscopy (STM), X-ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS), Auger electron spectroscopy (AES), or low energy ion scattering (LEIS) [57][58][59][60][61][62][63][64][65][66][67][68][69][70][71]. Each technique has its own advantages and disadvantages.…”