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 (HfOx) 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 HfOx 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 HfOx 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/HfO2 interface. (Less)
Highlights
Prior to the atomic layer deposition (ALD) half-cycle, we modeled an overlayer of InAs native oxide with a thin hafnium oxide (HfOx) layer on top due to chamber contamination, and we obtained the thickness of InAs native oxide as 11.5 Å, with only 1.5 Å of HfO2, according to XPS data taken when the TDMA-Hf deposition is started
This result is of particular importance for ALD of high-κ oxides on III−V semiconductors and its future application in semiconductor industries: not all the InAs native oxide, which got removed during the reaction, has been converted into HfOx, which suggests that it is possible that part of it is released into the gas phase during the TDMA-Hf deposition
We have shown that HfOx is formed already during the first half cycle of ALD, as the metal precursor uses the oxygen of the native oxide as an oxidation source
Summary
Properties such as high charge carrier mobility and a large range of available band gap values are the reason why III−V semiconductors have become the source for a number of highperformance devices in the microelectronics industries.[1,2] InAs, in particular, has an electron mobility which is more than 20 times higher than that of Si,[3] which makes it an optimal material for a new generation of high-speed metal oxide semiconductor (MOS) transistors, especially for radio frequency applications.[1,4,5] unlike Si, which naturally includes a uniform native oxide and an almost perfect semiconductor-oxide interface, InAs comes along with a high interface trap density that limits the performance of the device.[6,7] A promising solution, which has revolutionized the fabrication of III−V MOS gate stacks, was to replace the unwanted native oxide with an ultrathin layer of a material with a high dielectric constant, a so-called high-κ material[8,9] such as Al2O3 or HfO2, using atomic layer deposition (ALD). High-resolution spectra acquired on a fresh, native oxide-covered InAs surface helped us to identify the spin−orbit splitting, branching ratio, and full width at half maximum of the In 4d core level peaks, which can be used to distinguish between In 4d and Hf 4f components during deposition.
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