Atomic Layer Deposition of Hafnium Oxide on InAs: Insight from Time-Resolved in Situ Studies

Abstract

III−V semiconductors, such as InAs, with an ultrathin high-κ oxide layer have attracted a lot of interests in recent years as potential next-generation metal−oxide− semiconductor field-effect transistors, with increased speed and reduced power consumption. The deposition of the high-κ oxides is nowadays based on atomic layer deposition (ALD), which guarantees atomic precision and control over the dimensions. However, the chemistry and the reaction mechanism involved are still partially unknown. This study reports a detailed time-resolved analysis of the ALD of high-κ hafnium oxide (HfO x ) on InAs(100). We use ambient pressure X-ray photoemission spectroscopy and monitor the surface chemistry during the first ALD half-cycle, i.e., during the deposition of the metalorganic precursor. The removal of In and As native oxides, the adsorption of the Hf-containing precursor molecule, and the formation of HfO x are investigated simultaneously and quantitatively. In particular, we find that the generally used ligand exchange model has to be extended to a two-step model to properly describe the first half-cycle in ALD, which is crucial for the whole process. The observed reactions lead to a complete removal of the native oxide and the formation of a full monolayer of HfO x already during the first ALD half-cycle, with an interface consisting of In−O bonds. We demonstrate that a sufficiently long duration of the first half-cycle is essential for obtaining a high-quality InAs/HfO 2 interface.

Oxygen relocation during HfO2 ALD on InAs

“…Atomic layer deposition (ALD) is a deposition technique that potentially can provide a defect-free and conformal layer of HfO 2 over the entire surface of InAs; especially as it comes along with the so-called "self-cleaning" effect, which comprises the removal of the unwanted native oxide from InAs together with the deposition of the desired HfO 2 . This "self-cleaning" or "clean-up" effect has been reported for native oxides of typical III-V surfaces including InAs, GaAs, GaSb, and mixed alloys of these materials [8][9][10][11][12][13] upon the ALD of Al 2 O 3 and HfO 2 , performed with trimethylaluminum (TMA) and tetrakis(DMA -)hafnium (TDMAHf, where DMAstands for the dimethylamido ligands), respectively. However, many questions about the efficiency of the self-cleaning and the surface chemical reactions during the ALD process behind are still unsolved, leaving substantial room for improvement of the resulting III-V/high-κ interface.…”

“…The intensities were normalized to that of the As 3d bulk component. The thickness evaluation of the thermal oxide was carried out using an overlayer model explained elsewhere 8 . The cross sections, inelastic mean free paths, and atom densities were estimated from literature values 8 .…”

“…Hence, it is important to obtain better insight into the details of the initial ALD process, where the influence of the surface plays a significant role. Here, we investigate eight InAs samples prepared with varying oxide thickness ranging from a few Å to a few nanometres by ambient pressure X-ray photoelectron spectroscopy (AP-XPS), a method which allows the real-time monitoring of the deposition process 8,21,22 . We evaluate the influence of the surface on the composition and thickness of the overlayer of HfO 2 already formed during the first half cycle of ALD performed with TDMAHf.…”

Upgrade of the SPECIES beamline at the MAX IV Laboratory

“…APXPS is a very convenient tool for studying ALD processes since the pressure and temperature ranges needed for optimal growth are within the ranges of the typical AP cells in use at SPECIES. APXPS has been recently demonstrated as a very powerful tool for in situ and operando investigations into the first half-cycles of the ALD processes (Head et al, 2016;Timm et al, 2018;Temperton et al, 2019;D'Acunto et al, 2020).…”

Synchronizing gas injections and time-resolved data acquisition for perturbation-enhanced APXPS experiments

“…Thicknesses of these films can be controlled accurately and simply by the number of deposition cycles repeated. APXPS measurements have emerged as a valuable source of fundamental information about the surface reactions involved in ALD [58][59][60][61] . We have used the pulsed valve system together with the RPi electronics to automate the pulsing of the precursor gases in order to study ALD processes in-situ using APXPS.…”