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Single-wall carbon nanotubes (SWCNTs) have great potential to become the channel material for future high-speed transistor technology. However, to realize a carbon nanotube field effect transistor (CNTFET) with excellent gate control, the high-k dielectrics between the CNT and the metal gate must have superb electrical properties and extremely high uniformity. Thus it is essential to understand the interactions between high-k materials and the SWCNTs to effectively control the transistor characteristics. In this study, we investigate the effects of atomic layer deposited (ALD) high-k dielectrics (Al2O3 and HfO2) on SWCNTs using Raman spectroscopy. We subjected the SWCNTs to various ALD cycles and studied the nucleation and growth of ALD dielectrics at defect sites using scanning electron microscopy and transmission electron microscopy images. We analyzed these samples using Raman spectroscopy and x-ray photoelectron spectroscopy. The Raman peak shifts of the G-peak and the 2D (G0) peaks suggest doping and stress induced effects on the CNTs by the surrounding high-k oxide environment. Trends in the G-peak FWHM and G/D-peak ratios were identified and compared between Al2O3 and HfO2. We confirmed the ALD-deposited HfO2 is polycrystalline using x-ray diffraction and analyzed dielectric-CNT bonding states using XPS measurements. This study provides insights on the effects of ALD high-k materials on SWCNTs for future high-speed transistor applications. [ABSTRACT FROM AUTHOR]

Due to its high intrinsic mobility, germanium (Ge) is a promising candidate as a channel material (offering a mobility gain of approximately ×2 for electrons and ×4 for holes when compared to conventional Si channels). However, many issues still need to be addressed before Ge can be implemented in high-performance field-effect-transistor (FET) devices. One of the key issues is to provide a high-quality interfacial layer, which does not lead to substantial drive current degradation in both low equivalent oxide thickness and short channel regime. In recent years, a wide range of materials and processes have been investigated to obtain proper interfacial properties, including different methods for Ge surface passivation, various high-k dielectrics and metal gate materials and deposition methods, and different post-deposition annealing treatments. It is observed that each process step can significantly affect the overall metal-oxide-semiconductor (MOS)-FET device performance. In this review, we describe and compare combinations of the most commonly used Ge surface passivation methods (e.g. epi-Si passivation, surface oxidation and/or nitridation, and S-passivation) with various high-k dielectrics. In particular, plasma-based processes for surface passivation in combination with plasma-enhanced atomic layer deposition for high-k depositions are shown to result in high-quality MOS structures. To further improve properties, the gate stack can be annealed after deposition. The effects of annealing temperature and ambient on the electrical properties of the MOS structure are also discussed. [ABSTRACT FROM AUTHOR]

It has recently been reported that nitrogen oxide species (e.g., N2O5, NO2, NO3, and/or N2O) can have an impact on ozone based atomic layer deposition (ALD) of metal oxides when ozone is generated by dielectric barrier discharge (DBD) in O2/N2 mixtures. In this work, we further investigate the effect of the O2/N2 ratio in the DBD for HfO2 ALD using HfCl4 as metal precursor. Using O3 in the absence of nitrogen oxides, uniform HfO2 layers are obtained between 200 and 250°C in a hot wall cross flow reactor. The self-limiting nature of the O3 and HfCl4 reaction is demonstrated at 225°C and the growth-per-cycle is 0.12 nm. At higher temperature, O3 decomposes at the HfO2 coated reactor walls, resulting in a decreasing HfO2 thickness over Si substrates in the direction of the gas flow. Using O3 in combination with nitrogen oxides by DBD in N2/O2 mixtures, we obtained uniform HfO2 layers in the 200-300°C temperature range. At 300°C, the GPC is 0.14 nm and the HfO2 films show a low impurity content. Both processes produce high quality dielectric layers in Pt gated capacitors. [ABSTRACT FROM AUTHOR]

Hafnium titanate (HTO) films were deposited within a large Hf-Ti compositional range by atomic layer deposition using HfCl4/TiCI4/H2O precursors. The Hf content of the layers is well controlled by the precursor pulse ratio, as indicated by Rutherford backscattering. The saturation conditions of ternary HTOs are different compared to those of the binary oxides. First-principles simulation confirmed the enhancement of the Hf precursor reactivity in the presence of Ti-OH. Growth curves of HTOs showed a good linearity with the number of reaction cycles. A linear correlation between density, quantified by X-ray refiectometry, and composition was observed. X-ray diffraction indicated that the as-deposited films are amorphous up to 500-700°C, depending on the Hf/Ti ratio. The orthorhombic HfTiO4 diffraction lines in the samples (30-64% Hf) annealed at 850°C were observed. For a Hf content higher than 82%, a monoclinic HfO2-like structure was reported. The dielectric constant and leakage current depend on the Ti content, the film crystallinity, and the anneal atmosphere. The postdeposition anneal in O2 is found to have a drastic effect in leakage current density reduction and could be a key for further improvements of HTO electrical properties. [ABSTRACT FROM AUTHOR]

The role of moisture (H[sub2]O) in atomic-layer-deposited (ALD) HfO[sub2∙] and HfSiO[sub2∙] dielectrics on equivalent oxide thickness (EOT) scaling is investigated in gate-first devices with physical-vapor-deposited TaN gates. By reducing the amount of H[sub2]O present in the gate stack, the EOT increase during high-temperature (1030°C) spike annealing is reduced from 0.5 to0.25 nm. This was achieved by a premetallization degas at 350-550°C for 3 mm. The origin of this improvement lies in the elimination of H[sub2]O-related reoxidation of the interfacial SiO[sub2]. By means of temperature-programmed desorption measurements, it is found that the majority of the H[sub2]O is desorbed between 200 and 600°C with activation energies between ∼0.3 and -0.5 eV. Furthermore, the H[sub2]O concentration is dependent on the Hf concentration and nitridation. Non-nitrided HfSiO[sub2∙] with [Hf] = 40% adsorbs twice as much H[sub2]O as HfO[sub2∙]. Correspondingly, a significantly larger FOT increase is observed for HfSiO[sub2∙] with [Hf] 40% as compared to HfO[sub2∙]. In HfSiON, the desorbed H[sub2]O concentration is independent of [Hf]. Finally, a strong metal dependency on the EOT regrowth is observed. With ALD TiN, the EOT increase after thermal treatment is found to be independent of the degas condition at ∼0.2 nm. [ABSTRACT FROM AUTHOR]

A good dielectric layer on the GaAs substrate is one of the critical issues to be solved for introducing GaAs as a candidate to replace Si in semiconductor processing. In literature, promising results have been shown for Al[sub2]O[sub3] on GaAs substrates. Therefore, atomic layer deposition (ALD) of Al[sub2]O[sub3] has been studied on GaAs substrates. We have been investigating the influence of the ALD process (thermal vs plasma-enhanced ALD) as well as the influence of the starting surface (no clean vs partial removal of the native oxide). Ellipsometry and total X-ray reflection fluorescence were applied to study the growth of the ALD layers. Angle- resolved X-ray photoelectron spectroscopy was used to determine the composition of the interlayer. Both processes were shown to be roughly independent of the starting surface with a minor dependence for the thermal ALD. Thermally deposited ALD layers exhibited better electrical characteristics based on capacitance measurements. This could be linked to the thinner interlayer observed for thermally deposited Al[sub2]O[sub3]. However, the Fermi tevel was not unpinned in all cases, suggesting that more work needs to be done for passivating the interface between GaAs and the high-k layer. [ABSTRACT FROM AUTHOR]

To increase complementary metal oxide semiconductor (CMOS) device performance, new materials are introduced in the gate stack (high-k dielectrics and metal gates) and the transistor channel (Ge, Ill-V materials). In this work we study the atomic layer deposition (ALD) of hafnium oxide on Ge and GaAs substrates. Passivation layers are required to achieve a sufficiently low interface state density, but these might also influence the growth behavior and dielectric quality. Therefore, we investigate the effect of surface preparation, for example, native oxide, wet clean, thermal oxidation, and S-passivation. for the HfCI4/H2O and tetrakis diethylamino hafnium = ((C2H2)2N)2Hf (TDEAH)/H2O processes. The growth of HfO2 from initial submonolayer coverage to continuous HfO2 film is studied by means of Rutherford backscattering, static time-of-flight secondary ion mass spectroscopy, and X-ray photoelectron spectroscopy. HfCl4/H2O ALD depends on the surface preparation. The growth is enhanced on oxide surfaces (thermally grown GeO2, HF-cleaned Ge, and GaOx-AsOy) and inhibited on oxide-free substrates (HBr-cleaned Ge). The initial island growth regime is least pronounced on germanium oxide. In contrast, TDEAH/H2O ALD is independent of the surface preparation. The growth is inhibited in the first ∼20 cycles on native oxide and S-passivated GaAs [(NH4)2S treatment], but the initial island growth regime is quickly followed by the two-dimensional growth regime. [ABSTRACT FROM AUTHOR]