The surface chemistry and the interface formation during the initial stages of the atomic layer deposition (ALD) of Al2O3 from trimethylaluminum (TMA) and H2O on InP(100) were studied by synchrotron radiation photoemission spectroscopy and scanning tunneling microscopy. The effect of the ex situ surface cleaning by either H2SO4 or (NH4)2S was examined. It is shown that the native oxide on the InP surface consisted mainly of indium hydrogen phosphates with a P enrichment at the interface with InP. After a (NH4)2S treatment, S was present on the surface as a sulfide in both surface and subsurface sites. Exposure to TMA led to the formation of a thin AlPO4 layer, irrespective of the surface cleaning. The surface Fermi level of p-type InP was found to be pinned close to midgap after H2SO4 cleaning and moved only slightly further toward the conduction band edge upon TMA exposure, indicating that the AlPO4/InP interface was rather defective. (NH4)2S passivation led to a Fermi level position of p-type InP close to the conduction band edge. Hence, the InP surface was weakly inverted, which can be attributed to surface doping by S donors. TMA exposure was found to remove surface S, which was accompanied by a shift of the Fermi level to midgap, consistent with the removal of (part of) the S donors in combination with a defective AlPO4/InP interface. Further TMA/H2O ALD did not lead to any detectable changes of the AlPO4/InP interface and suggested simple overgrowth with Al2O3.
The influence of different wet chemical treatments (HCl, H 2 SO 4 , NH 4 OH) on the composition of InP surfaces is studied by using synchrotron radiation photoemission spectroscopy (SRPES). It is shown that a significant amount of oxide remains present after immersion in a NH 4 OH solution which is ascribed to the insolubility of In 3+ at higher pH values. Acidic treatments efficiently remove the native oxide, although components like P 0 , In 0 and P (2± )+ suboxides are observed. Alternatively, the influence of a passivation step in (NH 4 ) 2 S solution on the surface composition was investigated. The InP surface after immersion into (NH 4 ) 2 S results in fewer surface components, without detection of P 0 and P (2± )+ suboxides. Finally, slight etching of InP surfaces in HCl/H 2 O 2 solution followed by a native oxide removal step, showed no significant effect on the surface composition.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 128.255.6.125 Downloaded on 2015-06-08 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 128.255.6.125 Downloaded on 2015-06-08 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 128.255.6.125 Downloaded on 2015-06-08 to IP
Three new volatile cobalt amidinate compounds were prepared: Co(tBuNC(R)NEt)2, R=Me, Et and n-Bu. They were characterized by elemental analysis, 1H NMR, X-ray structure analysis, melting point, vapor pressure, vaporization rate, thermal stability and chemical reactivity. They were found to evaporate cleanly without decomposition. Two of them are liquids at room temperature, allowing for more convenient preparation, handling and purification by distillation. They are highly reactive compounds that have been found to be suitable precursors for vapor deposition of cobalt metal, cobalt nitride and cobalt oxide. A new synthetic method allows for the facile and inexpensive preparation of large quantities of these compounds.
The wet chemical etching of InP and its native oxide has been studied in HCl and H 2 SO 4 solution to create oxide-free surfaces. The (100) InP surface is not etched in ≤2 M HCl and ≤6 M H 2 SO 4 . As the v etch <0.1 nm/min for these concentrations, the native oxide after OFOD treatment can be effectively removed without significantly etching the surface, as confirmed by contact angle measurements, ellipsometry and X-ray photoelectron spectroscopy. STM and AFM measurements showed that after OFOD treatment and subsequent oxide removal very smooth surfaces are achieved due to the creation of atomic terraces. The size of these terraces can be increased up to micron-size in 6 M H 2 SO 4 . Furthermore, it was shown that in presence of oxygen, n-type InP is photoetched/oxidized during wet processing. Last, the anisotropy in etching is discussed for InP in 2 M HCl and 2 M H 2 SO 4 .For the past and current technology node, transistors in integrated circuits are fabricated on silicon substrates, and in some cases, SiGe alloys are used. In order to meet the future requirements imposed by the scaling roadmap, the next generation of transistors (i.e. the 7 nm node and beyond) will be based on high mobility III-V compound semiconductors. 1,2 To be cost effective, the III-V materials will be integrated on Si substrates. In part A of this paper, we show a possible integration route for such a technology; a Quantum Well based III-V transistor using InP buffer and InGaAs channel layers. 3 The manufacture of transistors consists of many different processing steps, which involve multiple exposures to chemical solutions. The goal of these wet treatments is to obtain a well-defined surface, (i.e. free of contaminants and stoichiometric), essential for obtaining good interfacial properties and, consequently, device performance. 4 There are different ways of preparing III-V surfaces for subsequent processing steps: ion sputtering followed by high temperature annealing, atomic hydrogen cleaning, sulfur passivation, and wetchemical cleaning. 5 Wet-chemical cleaning offers an effective and practical cleaning method for semiconductor surfaces. 6 In the case of III-V compound semiconductors special care should be taken due to the possible formation of highly toxic hydrides during low pH processing. Additionally, anisotropy in etching may be expected, 7,8 which leads to significant surface roughening. In part A of this paper, we propose an oxide formation/oxide dissolution (OFOD) model that prevents hydride formation and allows for smooth etching. 3 In a first step the semiconductor is oxidized by a strong oxidizing agent in solution and, subsequently, the (hydr)oxides formed are dissolved by the acid. Due to the presence of a strong oxidizing agent in solution no dissolved hydrides are expected. This approach, was developed for cleaning of (100) oriented InP buffer layers after a chemo-mechanicalpolishing (CMP) step, and can, in principle, be used for other III-V semiconductors. After OFOD treatment a native oxide is present. In order to p...
The atomic layer deposition (ALD) of Ta2O5 and TaSiOx from TaCl5, SiCl4, and H2O is reported. Both processes are influenced by the concomitant etching of Ta2O5 and TaSiOx by TaCl5. The optimum deposition temperature is found to be 250 °C for both Ta2O5 and TaSiOx. For lower deposition temperatures, the large Cl contamination leads to poor dielectric properties of the films, whereas higher temperatures lead to poor within‐wafer (WiW) thickness non‐uniformity due to etching. Si incorporation is limited to Si/(Si + Ta) ∼ 0.65 because of the slow adsorption kinetics of SiCl4 on SiOH‐terminated surfaces. Under optimum conditions, amorphous films with good dielectric quality are obtained.
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