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The availability of thermochemical properties allows for the prediction of the equilibrium compositions of chemical reactions. The accurate prediction of these can be crucial for the design of new chemical synthesis routes. However, for new processes, these data are generally not completely available. A solution is the use of thermochemistry calculated from first-principles methods such as Density Functional Theory (DFT). Before this can be used reliably, it needs to be systematically benchmarked. Although various studies have examined the accuracy of DFT from an energetic point of view, few studies have considered its accuracy in predicting the temperature-dependent equilibrium composition. In this work, we collected 117 molecules for which experimental thermochemical data were available. From these, we constructed 2648 reactions. These experimentally constructed reactions were then benchmarked against DFT for 6 exchange–correlation functionals and 3 quality of basis sets. We show that, in reactions that do not show temperature dependence in the equilibrium composition below 1000 K, over 90% are predicted correctly. Temperature-dependent equilibrium compositions typically demonstrate correct qualitative behavior. Lastly, we show that the errors are equally caused by errors in the vibrational spectrum and the DFT electronic ground state energy. [ABSTRACT FROM AUTHOR]

The article focuses on the properties and technological application of two-dimensional (2D) crystals such as graphene and transition metal dichalcogenides. Topics include the capacity of graphene to serve as alternative to silicon (Si)-based transistors, its application on nano-based stacks materials composed of 2D materials such as insulators, metals and semiconductors, and the challenges related to 2D materials manufacturing processes such as gate engineering, patterning, and doping.

Abstract: The development of transistor manufacturing into the nanoscale regime is accompanied by a continuous awareness concern for contamination control. The ever-increasing demands for analysis sensitivity (in the sub-109 at/cm2 regime) combined with the introduction of new materials (i.e. non-silicon based) put severe challenges on the application of analytical techniques for atomic level contamination monitoring. Since many years, total reflection X-ray fluorescence spectrometry (TXRF) has developed as a preferred technique, ideally suitable due to the excellent reflectivity and flatness of the starting Si substrates. Driven by performance enhancement requirements, many new materials are being introduced at the substrate level (Ge, III/V compounds for higher mobility), gate stack (alternative dielectric materials and gate electrodes for capacitance scaling) and interconnect level (low-k and copper for faster switching). This paper reviews some recent developments in the state-of-the-art TXRF developments for semiconductor applications. Among the focus areas are the expansion of the elemental range (through multi-excitation line selection or multi-excitation source to excite low Z as well as high Z elements in one analysis sweep) and dynamic range (by pre-concentration techniques, synchrotron radiation analysis and detector developments). Further, emphasis is also focused towards quantification issues—whereby the three methodologies (micro-droplet, film and bulk type standards) are critically reviewed. Also, a recent development of sweeping TXRF, suitable for fast screening of large surface areas is being discussed. The applications of TXRF in a semiconductor environment are being reviewed. Finally, the performance of TXRF for the various semiconductor applications is assessed with respected to competitive techniques. [Copyright &y& Elsevier]

2D transition metal dichalcogenides (TMDs) for advanced logic transistor technologies are deposited by various modifications of the chemical vapor deposition (CVD) method using a wide variety of precursors. Being a major electrical performance limiter, the TMD crystal grain size strongly differs between the various CVD precursor chemistries from nano‐ to millimeter‐sized crystals. However, it remains unclear how the CVD precursor chemistry affects the nucleation density and resulting TMD crystal grain size. This work postulates guiding principles to design a CVD process for highly crystalline TMD deposition using a quantitative analytical model benchmarked against the literature. The TMD nucleation density reduces favorably under low supersaturation conditions where the metal precursor sorption on the starting surface is reversible and the corresponding metal precursor desorption rate exceeds the overall deposition rate. Such reversible precursor adsorption guarantees efficient long‐range gas‐phase lateral diffusion of precursor species in addition to short‐range surface diffusion, which vitally increases crystal grain size. The proposed model explains the large spread in experimentally observed TMD nucleation densities and crystal grain sizes for state‐of‐the‐art CVD chemistries. Ultimately, it empowers the reader to interpret and modulate precursor adsorption and diffusion reactions through designing CVD precursor chemistries. [ABSTRACT FROM AUTHOR]

• Interface properties are crucial to form dense ODT-SAM on Cu for ASD purposes. • ODT-SAM's ALD inhibition is superior if coating oxidized surfaces. • Selective cupric oxide etching is observed as Cu is coated with ODT-derived SAM. • SAM formation kinetic is hindered if Cu is treated with organic acids. Atomic layer deposition (ALD) combined with self-assembled monolayer (SAM) passivation allows selective deposition on patterned substrates at the nanoscale, enabling bottom-up material fabrication for various applications. Selective chemisorption of 1-octadecanethiol (ODT) on Cu over SiO 2 is exploited to achieve area selective deposition (ASD). Although the essential role played by SAM in preserving a confined material growth at higher ALD cycles is largely accepted, studies elucidating the influence of substrate properties on SAM's ALD inhibition are lacking. In this work, Cu is treated either with acids or oxidizing agents to produce a multiplicity of surfaces, which differ in terms of composition and morphology. Using water contact angle, atomic force microscopy, x-ray photoelectron spectroscopy and cyclic voltammetry measurements, Cu substrates are characterized before and upon ODT deposition. The ODT layers formed on Cu are tested as a passivation means towards Hf 3 N 4 ALD. The results stress the essential contribution of interface properties in forming dense thiol-SAM on metals, which is fundamental to a successful ASD process. It is here demonstrated that ODT on clean Cu cannot block Hf 3 N 4 ALD at 150 °C, whereas on oxidized Cu the same organic layer prevents up to 19 nm Hf 3 N 4 film growth before the Cu passivation is affected. [ABSTRACT FROM AUTHOR]

As the semiconductor manufacturing process is moving towards the 3 nm node, there is a crucial need to reduce the edge placement error (EPE) to ensure proper functioning of the integrated circuit (IC) devices. EPE is the most important metric that quantify the fidelity of fabricated patterns in multi-patterning processes, and it is the combination of overlay errors and critical dimension (CD) errors. Recent advances in machine learning have enabled many new possibilities to improve the performance and efficiency of EPE optimization techniques. In this paper, we conducted a survey of recent research work that applied machine learning/ deep learning techniques for the purposes of enhancing virtual overlay metrology, reducing overlay error, and improving mask optimization methods for EPE reduction. Thorough discussions about the objectives, datasets, input features, models, key findings, and limitations are provided. In general, the results of the review work show a great potential of machine learning techniques in aiding the improvement of EPE in the field of semiconductor manufacturing. [ABSTRACT FROM AUTHOR]

Ultralow energy (ULE) ion implantation is being increasingly applied to the modification of 2D materials, in particular, for substitutional doping and intercalation of graphene. Implantation-induced defects, whether desired or not, have a strong impact on the properties of graphene. Significant research has been devoted to vacancy-related defects however, disorder induced by ion irradiation in the ULE limit, that is, for energies below the vacancy-formation threshold, remains poorly understood. Here, we focus on that regime and report the formation of defects resulting from the breaking of C–C s p 2 bonds and formation of C-substrate bonds. As a model system we used epitaxial graphene grown on Cu(111) and on Pt(111), subsequently implanted with He, Ne and Ar at energies between 15 eV and 40 eV. The bond defect density is found to increase with increasing energy and atomic number of the implanted element. These findings significantly advance our understanding of disorder induced in graphene by ULE ion implantation, while simultaneously revealing the potential for exploiting such bond defects for physical or chemical functionalization. In particular, these bond defects can be generated with a high degree of selectivity since they occur in the low-energy limit (at least down to 15 eV), significantly below the energies required to form stable vacancies. [Display omitted] • Graphene was implanted at ultralow energies (15–40 eV) with He, Ne and Ar. • C–C bonds in graphene break at energies below the vacancy-formation threshold. • Bond defect density increases with energy and atomic number of implanted elements. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we have studied the effect of boric acid (H3BO3) on the nucleation of nickel (Ni) nanoparticles on titanium nitride (TiN). We linked the potential transients during galvanostatic deposition to the different regimes of Ni deposition. The two most important regimes, i.e. nucleation and growth regime, were found to depend on the H3BO3 concentration. Indeed, by lowering the amount of H3BO3 the particle density increased (nucleation), while it also resulted in an earlier growth termination. Based on these findings, we propose a growth-inhibited nucleation model to explain the impact of H3BO3 on the formation of Ni nanoparticles. During Ni nucleation the surface pH increases due to local H+ reduction, leading to the formation and adsorption of Ni(OH)2 on the Ni particles. As a result, the growth of the particles is inhibited and new nucleation is promoted. The formation of this inhibiting hydroxide is counteracted by the presence of H3BO3 as it buffers the surface pH. Therefore, a higher particle density is obtained at low H3BO3 concentrations. However, when the concentration of H3BO3 is too low, Ni(OH)2 is already formed in the diffusion layer during the nucleation regime as the onset of H2O reduction occurs sooner. This results in the termination of Ni deposition before the nucleation of Ni is complete yielding almost no deposited Ni at the surface at low H3BO3 concentrations. Therefore, an optimum H3BO3 concentration is needed where the degree of growth-inhibition is high while Ni is still deposited for a sufficient amount of time. [Copyright &y& Elsevier]

Hafnium-containing compounds are of great importance to the semiconductor industry as a high-κ gate dielectric to replace silicon oxynitrides. Here, the crystallization processes and chemistry of bulk hafnia powders are investigated, which will aid in interpretation of reactions and crystallization events occurring in thin films used as gate dielectrics. Amorphous hafnia powder was prepared via a sol-gel route using the precursor HfOCl2 .H2O. The powders were subjected to various heat treatments and analyzed using X-ray diffraction and thermal analysis techniques. A large change in the crystallization pathway was found to occur when the sample was heated in an inert environment compared with air. Instead of the expected monoclinic phase, tetragonal hafnia also formed under these conditions and was observed up to temperatures of ∼ 760°C. The tetragonal particles eventually transform into monoclinic hafnia on further heating. Possible mechanisms for the crystallization of tetragonal hafnia are discussed. It is proposed that, in an inert environment, tetragonal hafnia is stabilized due to the presence of oxygen vacancies, formed by the reduction of HfIV to HfIII. As the temperature increases the crystal grows until there are too few oxygen vacancies left in the structure to continue stabilizing the tetragonal phase, and hence transformation to monoclinic hafnia occurs. [ABSTRACT FROM AUTHOR]

2D materials offer a pathway for further scaling of CMOS technology. However, for this to become a reality, both n-MOS and p-MOS should be realized, ideally with the same (standard) material. In the specific case of MoS2 field effect transistors (FETs), ambipolar transport is seldom reported, primarily due to the phenomenon of Fermi level pinning (FLP). In this study we identify the possible sources of FLP in MoS2 FETs and resolve them individually. A novel contact transfer technique is used to transfer contacts on top of MoS2 flake devices that results in a significant increase in the hole branch of the transfer characteristics as compared to conventionally fabricated contacts. We hypothesize that the pinning not only comes from the contact-MoS2 interface, but also from the MoS2-substrate interface. We confirm this by shifting to an hBN substrate which leads to a 10 fold increase in the hole current compared to the SiO2 substrate. Furthermore, we analyse MoS2 FETs of different channel thickness on three different substrates, SiO2, hBN and Al2O3, by correlating the p-branch ION/IOFF to the position of oxide defect band in these substrates. FLP from the oxide is reduced in the case of Al2O3 which enables us to observe ambipolar transport in a bilayer MoS2 FET. These results highlight that MoS2 is indeed an ambipolar material, and the absence of ambipolar transport in MoS2 FETs is strongly correlated to its dielectric environment and processing conditions. [ABSTRACT FROM AUTHOR]

Extreme ultra-violet lithography (EUVL) is the leading-edge technology to produce advanced nanoelectronics. The further development of EUVL is heavily based on implementing the so-called high numerical aperture (NA) EUVL, which will enable even smaller pitches up to 8 nm half pitch (HP). In anticipation of this high NA technology, it is crucial to assess the readiness of the current resist materials for the high NA regime to comply with the demanding requirements of resolution, line-edge roughness, and sensitivity (RLS). The achievable tighter pitches require lower film thicknesses for both resist and underlying transfer layers. A concern that is tied to the thinning down is the potential change in resist properties and behavior due to the interaction with the underlayer. To increase the fundamental understanding of ultra-thin films for high NA EUVL, a method to investigate the interplay of reduced film thickness and different patterning-relevant underlayers is developed by looking at the glass transition temperature (Tg) of polymer-based resists. To minimize the ambiguity of the results due to resist additives (i.e., photoacid generator (PAG) and quencher), it was opted to move forward with polymer-only samples, the main component of the resist, at this stage of the investigation. By using dielectric response spectroscopy, the results obtained show that changing the protection group of the polymer, as well as altering the polymer film thickness impacts the dynamics of the polymer mobility, which can be assessed through the Tg of the system. Unexpectedly, changing the underlayer did not result in a clear change in the polymer mobility at the tested film thicknesses. [ABSTRACT FROM AUTHOR]

Assesses the compatibility of dielectric layers with conventional polysilicon gate electrodes. Use of standard processing equipment; Power capacity; Level of performance.

A strong polarity effect on the temperature dependence of the leakage current in TiN/HfO[sub 2]/SiO[sub 2]/Si capacitors is reported. A model is proposed to explain these experimental results that combines tunneling through the stack and Frenkel-Poole hopping in the HfO[sub 2] layer, depending on the value of the gate voltage. It is shown that the polarity effect most probably results from the anisotropy of the band diagram of the HfO[sub 2]/SiO[sub 2] stack, as well as from the location of the shallow traps with respect to the conduction band of the HfO[sub 2] layer. Comparison of the model with the experimental results allows an estimate of the trap depth to be between 0.5 and 0.8 eV. [ABSTRACT FROM AUTHOR]

Two-dimensional transition metal dichalcogenide (TMD) semiconductors have risen as an important material class for novel nanoelectronic applications. Molybdenum disulfide (MoS2) is the most representative TMD compound due to its superior stability and attractive properties for (opto-) electronic devices. However, the synthesis of single-crystalline and functional MoS2 across large-area substrates remains crucial for its successful integration in semiconductor industry platforms. Therefore, this work focuses on the study of MoS2 epitaxy via two well-established industry-compatible synthesis methods, promising for the large-area and single-crystalline integration of van der Waals (vdW) materials. These methods are molecular beam epitaxy (MBE) and metalorganic vapor phase epitaxy (MOVPE) and have studied MoS2 quasi-vdW heteroepitaxy on reconstructed sapphire substrates and MoS2 vdW homoepitaxy on exfoliated MoS2 flakes. By examining the MoS2 structural properties using diffraction and spectroscopy techniques, the epitaxial relation and crystal quality are assessed, which reveals insights into the prevalence of inter- and intragrain defects such as grain boundaries and sulfur vacancies. The MBE method yields superior epitaxial MoS2 registry on both sapphire and MoS2 surfaces as compared to MOVPE, although inferior defectivity arises from the typical lower MBE growth temperature and chalcogen partial pressure. Moreover, both synthesis methods generate high densities of twinned MoS2 grain boundaries, which hamper defect-free integration. As a result, this challenging integration might become an important bottleneck for industrial TMD-based applications with a low tolerance for material defects. [ABSTRACT FROM AUTHOR]

The spectra of optical constants, index of refraction (n), and extinction coefficient (k) of graphene and graphite are obtained in the wavelength range of 190–1000 nm (6.53–1.24 eV) using broadband optical spectrophotometry in conjunction with the Forouhi–Bloomer dispersion relations for n and k. Measurement is made possible by the use of a multilayer substrate consisting of bulk Si and a 3000 Å SiO2 film. The effect of multiple internal reflections between the Si/SiO2 and SiO2/graphene interfaces amplifies the attenuating effect of the graphene layer, thereby improving the sensitivity of the reflectance measurement by a factor of 27 in the deep ultraviolet region of the spectrum. Maximum sensitivity is observed in the deep ultraviolet region of the spectrum, where a strong peak in the spectrum of the extinction coefficient of graphene is identified. The proposed method enables fast nondestructive angstrom-level thickness measurements of graphene and graphite. In this work, layers ranging in thickness between 3.8 Å (graphene) and 792.8 Å are detected, measured, and characterized. Reflectance spectra of graphene and graphite on Ni, Co, and Fe substrates are calculated. Differences of 1.1%–2.0% between the bare substrate and the graphene on the substrate are predicted in the deep ultraviolet region of the spectrum, which makes graphene detectable and measurable on these substrates. [ABSTRACT FROM AUTHOR]

Atomic layer deposition (ALD) is used in applications where inorganic material layers with uniform thickness down to the nanometer range are required. For such thicknesses, the growth mode, defining how the material is arranged on the surface during the growth, is of critical importance. In this work, the growth mode of the zirconium tetrachloride/water and the trimethyl aluminum/water ALD process on hydrogen-terminated silicon was investigated by combining information on the total amount of material deposited with information on the surface fraction of the material. The total amount of material deposited was measured by Rutherford backscattering, x-ray fluorescence, and inductively coupled plasma–optical emission spectroscopy, and the surface fractions by low-energy ion scattering. Growth mode modeling was made assuming two-dimensional growth or random deposition (RD), with a “shower model” of RD recently developed for ALD. Experimental surface fractions of the ALD-grown zirconium oxide and aluminum oxide films were lower than the surface fractions calculated assuming RD, suggesting the occurrence of island growth. Island growth was confirmed with transmission electron microscopy (TEM) measurements, from which the island size and number of islands per unit surface area could also be estimated. The conclusion of island growth for the aluminum oxide deposition on hydrogen-terminated silicon contradicts earlier observations. In this work, physical aluminum oxide islands were observed in TEM after 15 ALD reaction cycles. Earlier, thicker aluminum oxide layers have been analyzed, where islands have not been observed because they have already coalesced to form a continuous film. The unreactivity of hydrogen-terminated silicon surface towards the ALD reactants, except for reactive defect areas, is proposed as the origin of island growth. Consequently, island growth can be regarded as “undesired surface-selective ALD.” [ABSTRACT FROM AUTHOR]

2-D material FETs hold the promise of excellent gate control, but the impact of nonidealities on their performance remains poorly understood. This is because of the need, so far, to use computationally intensive nonequilibrium Green’s function (NEGF) simulations. Here, we therefore use a semiclassical model to investigate the role of nonidealities in the scaling of back-gated (BG) and top-gated (TG) monolayer MoS2 FETs. We verify the electrostatics and transport of the semiclassical model with density functional theory-based NEGF simulations and calibrate nonidealities, such as interface traps (${D}_{\textsf {it}}$) and Schottky contact barrier height ($\phi _{\textsf {SB}}$) to experimental monolayer and bilayer MoS2 FETs. We find that among the nonidealities, ${D}_{\textsf {it}}$ has the strongest subthreshold swing impact with 70 mV/dec obtainable in BG devices for a ${D}_{\textsf {it}}$ of $5\times {10}^{11}$ cm−2eV $^{-1}$ , an equivalent oxide thickness (EOT) of 1 nm, and a channel length (${L}_{\textsf {ch}}$) of 5 nm. For scaled EOT, $\phi _{\textsf {SB}}$ only strongly impacts ${I}_{ \mathrm{\scriptscriptstyle ON}}$ for the TG case, as the overlapping gate thins the Schottky barriers in the BG case. We show in TG devices that a spacer of only 5 nm results in a 1000-fold drop in ${I}_{ \mathrm{\scriptscriptstyle ON}}$ because of the nonidealities. We propose positive spacer oxide charge as a solution and show that a charge density of above 1013 cm−2 is required to fully recover the device performance. [ABSTRACT FROM AUTHOR]

Extreme ultraviolet (EUV) lithography utilizes photons with 92 eV energy to ionize resists, generate secondary electrons, and enable electron driven reactions that produce acid in chemically amplified photoresists. Efficiently using the available photons is of key importance. To increase photon absorption, sensitizer molecules, containing highly absorbing elements, can be added to photoresist formulations. These sensitizers have gained growing attention in recent years, showing significant sensitivity improvement. Aside from an increasing absorption, adding metal salts into the resist formulation can induce other mechanisms, like higher secondary electron generation or acid yield, or modification of the dissolution rate that also can affect patterning performance. In this work, we used different sensitizers in chemically amplified resists. We measured experimentally the absorption of EUV light, the acid yield, the photoelectron emission, the dissolution rate, and the patterning performance of the resists. Addition of a sensitizer raised the acid yield even though a decrease in film absorbance occurred, suggesting an apparent increase in chemically resonant secondary electrons. While patterning results confirm a significant sensitivity improvement, it was at the cost of roughness degradation at higher sensitizer loading. This is hypothesized by the chemical distribution of the sensitizer in the resist combined with a modification of the dissolution contrast, as observed by dissolution rate monitor measurements. [ABSTRACT FROM AUTHOR]

Titania (TiO2) offers a high theoretical capacity of 336 mAh g-1 with the insertion of one Li per Ti unit. Unfortunately, the poor ionic and electronic conductivity of bulk TiO2 electrodes limits its practical implementation. Nanosizing titania below ~20 nm has shown to increase the rate performance and accessible capacity but still not more than 75% of the theoretical capacity at 1 C. In this work, we discovered that chlorine doping of amorphous TiO2 (TiO2-xCl2x) can achieve a high capacity without the need for nanosizing. By in situ doping during atomic layer deposition, an unprecedented 90% of the theoretical capacity was achieved at 1 C for 100 nm thick films. Even at a charging rate of 20 C, 40% of the maximum capacity was accessible for the film with highest Cl-content (x = 0.088). The capacity was found linearly dependent on the chloride content for a Cl/Ti atomic ratio from 0.06 to 0.09. The enhanced insertion kinetics are ascribed to enhanced electronic conductivity and facilitated Li+-ion diffusion as a result of Cl-doping. Furthermore, the potential of TiO2-xCl2x films as high rate anode were demonstrated on micropillar electrodes in a half-cell configuration using a liquid electrolyte solution, showing 10 times higher capacity at 10 C compared to the literature. [ABSTRACT FROM AUTHOR]

Defect generation in HfO[sub 2]/SiO[sub 2] gate dielectric stacks under constant voltage stress is investigated. It is found that the stress induced electrical degradation in HfO[sub 2]/SiO[sub 2] stacks is different than in the SiO[sub 2] layer. The variation of the gate leakage current with different polarities shows different degradation characteristics after stress. Positive charge generation is also observed under both negative and positive gate voltage polarities. These degradation phenomena are explained by the composite effect of three components: neutral trap generation, electron trapping, and positive charge generation in the gate stacks. [ABSTRACT FROM AUTHOR]

In situ characterization of the underwater stability of superhydrophobic micro- and nanostructured surfaces is important for the development of self-cleaning and antifouling materials. In this work, we demonstrate a novel attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy-based method for large-area wetting characterization of silicon nanopillars. When air is present in between the structures, as is characteristic of the Cassie-Baxter state, the relative intensities of the water bands in the absorption spectrum change because of the wavelength-dependent attenuation of the evanescent wave. This phenomenon enables unambiguous identification of the wetting state and assessment of liquid impalement. Using mixtures of isopropanol and water with different concentrations, the breakdown of superhydrophobic states and the wetting hysteresis effects are systematically studied on uniform arrays of silicon nanopillars. A transition from the Cassie-Baxter to Wenzel state is observed when the isopropanol concentration exceeds 2.8 mol %, corresponding to a critical surface tension of 39 mN/m. Spontaneous dewetting does not occur upon decreasing the isopropanol concentration, and pure water can be obtained in a stable Wenzel state on the originally superhydrophobic substrates. The developed ATR-FTIR method can be promising for real-time monitoring of the wetting kinetics on nanostructured surfaces. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) transition metal dichalcogenides are potential low dissipative semiconductor materials for nanoelectronic devices. Such applications require the deposition of these materials in their crystalline form and with controlled number of monolayers on large area substrates, preferably using deposition temperatures compatible with temperature sensitive structures. This paper presents a low temperature plasma-enhanced atomic layer deposition (PEALD) process for 2D WS2 based on a ternary reaction cycle consisting of consecutive WF6, H2 plasma, and H2S reactions. Strongly textured, nanocrystalline WS2 is grown at 300 °C. The composition and crystallinity of these layers depends on the PEALD process conditions, as understood by a model for the redox chemistry of this process. The H2 plasma is essential for the deposition of WS2 as it enables the reduction of -W6+Fx surface species. Nevertheless, the impact of subsurface reduction reactions needs to be minimized to obtain WS2 with well-controlled composition (S/W ratio of 2). [ABSTRACT FROM AUTHOR]

Graphene is considered as potential candidate for future nano-interconnects. In this respect we study the Brønsted acid doping effect of single layer graphene (SLG) and few layer graphene (FLG) synthesized by chemical vapor deposition (CVD). A sheet resistance reduction of 50% is achieved by HNO 3 doping of SLG, and the resulting resistivity of 9.1 μΩ·cm is comparable to alternative metals to copper (e.g. Ru). On the other hand, synthetic FLG shows higher sheet resistance due to higher defect density. Mobility degradation at increased carrier concentration is a main limiting factor for sheet resistance reduction of CVD graphene. [ABSTRACT FROM AUTHOR]

In this work we are electrically characterizing multilayer graphene ribbons as potential Cu replacement towards future interconnect applications. We are comparing their performance with single-layer ribbons and we are reporting on sheet resistance, mobility and mean free path. We are additionally characterizing the contact properties for Pd contacts in top and edge configuration. Our results show high current carrying capacity for the multilayer ribbons and lower sheet resistance. Edge contacts to multilayer ribbons seem a promising approach for the decrease of the contact resistivity. Values of sheet resistance Rs ~ 280 Ω and contact resistivity Rc*W ~ 325 Ω·μm are measured for multilayer samples and edge contacts. Although the calculated ribbon mean free path is high for single-layer graphene (MFP SLG ~ 60 nm), it is comparable with the MFP of Cu for the multilayer samples (MFP FLG ~ 30 nm). Intercalation is a potential approach for improvement of the multilayer wire properties. [ABSTRACT FROM AUTHOR]

For Cu/low-k interconnects, the reversed damascene is an alternative integration approach where the metal wires are patterned first and then the spacing filled with a flowable dielectric. In this paper, the replacement of a sacrificial template by gap-filling ultralow-k dielectrics is studied, focusing on yield and transport performance ("replacement dielectric" scheme). On non-passivated copper, the low-k curing processes induce severe damage to the metal lines, leading to the degraded electrical properties. This is confirmed by chemical inspection on the blanket Cu films and morphological inspection on patterned structures. In order to avoid Cu oxidation and out-diffusion at elevated temperature, Cu passivation by plasma-enhanced chemical vapor deposition SiCN is proposed and studied in detail. The inter-metal dielectric properties of replacement low-k are evaluated by resistance-capacitance and IV measurements using a Meander-Fork structure. By tuning the passivation layer thickness and ultraviolet curing time, high electrical yield is obtained with integrated porous low-k showing promising effective k-values (keff) and breakdown voltages (Ebd), confirming the interest of this specific integration scheme. [ABSTRACT FROM AUTHOR]

The use of sacrificial self-assembled monolayers (SAMs) to prepare clean n-type GaAs (100) surfaces without band bending in vacuo is demonstrated. GaAs surface passivation using octadecanethiol SAMs after HCl cleaning is shown to lead to an enhancement of the room-temperature photoluminescence intensity. Synchrotron-radiation photoelectron spectroscopy (SRPES) finds that the interfacial oxide between GaAs and the SAM remains below the detection limit. Evidence for both Ga-S and As-S bonds at the GaAs-thiolate interface is found. The limited thermal stability of the SAM allows the desorption of the alkyl chains by in situ thermal annealing at temperatures above 180 °C, leaving S bonded to Ga behind. The resulting surface contains only a very small amount of O (0.05 ML coverage) and C (about 3% of the SAM remaining) and shows no band bending with the surface Fermi level close to the conduction band. Atomic layer deposition of Al2O3 on this surface occurs via the formation of Al-S bonds without introducing any additional band bending. This indicates that the surface preparation of n-type GaAs (100) using sacrificial octadecanethiol SAMs followed by in situ thermal removal provides a route toward GaAs/oxide interfaces without interfacial oxides and without band bending. [ABSTRACT FROM AUTHOR]

[Display omitted] • Crystalline TiO 2 shows higher photocatalytic activity compared to amorphous. • Effective decomposition of SAM upon EUV exposure is a combined effect of EUV dose and photoactivity of the TiO 2 surface. • Promising selectivity of 0.85 achieved for ASD Ru hard mask target thickness of 1.6 nm. Patterning below 10 nm with conventional techniques such as Litho-etch (LE*), a subtractive self-aligned multiple patterning process, suffers from limitations due to edge placement errors, decreasing throughput, complexity, pattern collapse, photoresist non-uniformity. Bottom-up processes for fabrication of nano devices by means of Area selective deposition (ASD) are peaking up over top-down approaches to mitigate most of the above-mentioned problems. One of the ways to achieve ASD of an hardmask is by using extreme ultra-violet (EUV, λ-13.5 nm) lithography to single-step pattern self-assembled monolayers (SAM) on a photosensitive substrate (or layer) followed by atomic layer deposition (ALD). In this work, photo-catalytically active titanium oxide is considered as substrate for the deposition of organosilane SAMs of different chain length. Upon exposure to EUV, fragmentation of SAM's molecules is observed though a mechanism involving electron/hole pair exchange from TiO 2. This induces changes in the chemistry of the exposed area, allowing an ALD deposition in the SAM-cleared areas. [ABSTRACT FROM AUTHOR]

In this work, we evaluate the material properties of graphene and assess the potential application of graphene to replace copper wires in Back-End-Of-Line (BEOL) interconnects. Based on circuit and system-level simulations, high restrictions are imposed to graphene with respect to contact resistance and mean free path. Experimentally we evaluate single and multi-layer graphene wires and we measure carrier mean free paths (MFPs) above ~ 110 nm. However, contact engineering will be the key issue for integration of graphene as interconnect. [ABSTRACT FROM AUTHOR]

Continuing CMOS performance scaling requires developing MOSFETs of high-mobility semiconductors and InGaAs is a strong candidate for n-channel. InGaAs MOSFETs, however, suffer from high densities of border traps, and their origin and impact on device characteristics are poorly understood at present. In this paper, the border traps in nMOSFETs with an In0.53Ga0.47As channel and Al2O3 gate oxide are investigated using the discharging-based energy profiling technique. By analyzing the trap energy distributions after charging under different gate biases, two types of border traps together with their energy distributions are identified. Their different dependences on temperature and charging time support that they have different physical origins. The impact of channel thickness on them is also discussed. Identifying and understanding these different types of border traps can assist in the future process optimization. Moreover, border trap study can yield crucial information for long-term reliability modeling and device time-to-failure projection. [ABSTRACT FROM AUTHOR]

Achieving low resistance contacts to graphene is a common concern for graphene device performance and hybrid graphene/metal interconnects. In this work, we have used the circular Transfer Length Method (cTLM) to electrically characterize Ag, Au, Ni, Ti, and Pd as contact metals to graphene. The consistency of the obtained results was verified with the characterization of up to 72 cTLM structures per metal. Within our study, the noble metals Au, Ag and Pd, which form a weaker bond with graphene, are shown to result in lower contact resistance (Rc) values compared to the more reactive Ni and Ti. X-ray Photo Electron Spectroscopy and Transmission Electron Microscopy characterization for the latter have shown the formation of Ti and Ni carbides. Graphene/Pd contacts show a distinct intermediate behavior. The weak carbide formation signature and the low Rc values measured agree with theoretical predictions of an intermediate state of weak chemisorption of Pd on graphene. [ABSTRACT FROM AUTHOR]

Protein phosphatase-1 (PP1) is a major protein Ser/Thr phosphatase in eukaryotic cells. Its activity depends on two metal ions in the catalytic site, which were identified as manganese in the bacterially expressed phosphatase. However, the identity of the metal ions in native PP1 is unknown. In this study, total reflection X-ray fluorescence (TXRF) was used to detect iron and zinc in PP1 that was purified from rabbit skeletal muscle. Metal exchange experiments confirmed that the distinct substrate specificity of recombinant and native PP1 is determined by the nature of their associated metals. We also found that the iron level associated with native PP1 is decreased by incubation with inhibitor-2, consistent with a function of inhibitor-2 as a PP1 chaperone. [ABSTRACT FROM AUTHOR]

To meet the demands for sub-20 nm feature devices in the semiconductor industry, minimizing the line width roughness (LWR) is a critical concern for ultra-large scale integrated circuit manufacturing. Post-lithography treatments should reduce the LWR by at least 50% to meet the technology requirements, but the available post-lithography strategies come short. To support the delayed progress, an in depth understanding of the interaction of such post-lithography treatments with EUV-specific resist functionalities is required. In this article, we analyze the change in line widths and LWR's for 30-35 nm lines using EUV photoresists. In addition we study the effect of the chemical composition on the reduction of LWR after hydrogen plasma treatment using 'artificially' prepared reference resists. We highlight the effect of the fluorine unit, ester functionalities and photo acid generator/quencher loading on the LWR improvement and H2 plasma induced reflow. [ABSTRACT FROM AUTHOR]

As the semiconductor industry pursues Moore's law, the demand to obtain smaller features continues. Extreme ultraviolet (EUV) lithography remains one of the primary options for sub- 20 nm patterns. However, the technology struggles to meet the line width roughness (LWR) specifications. In this article, we present the significance of plasma treatment as a roughness smoothing technique. Two EUV photoresists with 22 nm lines are exposed to various plasma processes. We highlight the advantages of a hydrogen plasma treatment and its vacuum ultraviolet (VUV) emission as an optimal smoothing process and discuss the effect of photoresist thickness, initial LWR and the VUV plasma emission. Even though a H2 plasma treatment results in a successful reduction of LWR/LER, the target value of below 2nm is not yet achieved. [ABSTRACT FROM AUTHOR]

Aqueous solutions of oxalato- and citrato-VO2+ complexes are prepared, and their ligand exchange reaction is investigated as a function of the amount of citrate present in the aqueous solution via continuous-wave electron paramagnetic resonance (CW EPR) and hyperfine sublevel correlation (HYSCORE) spectroscopy. With a low amount of citrate, monomeric cis-oxalato-VO2+ complexes occur with a distorted square-pyramidal geometry. As the amount of citrate increases, oxalate is gradually exchanged for citrate. This leads to (i) an intermediate situation of monomeric VO2+ complexes with a mix of oxalate/citrate ligands and (ii) a final situation of both monomeric and dimeric complexes with exclusively citrato ligands. The monomeric citrato-VO2+ complexes dominate (abundance > 80%) and are characterized by a 6-fold chelation of the vanadium(IV) ion by 4 RCO2- ligands at the equatorial positions and a H2O/R-OH ligand at the axial position. The different redox stabilities of these complexes, relative to that of dissolved O2 in the aqueous solution, is analyzed via 51V NMR. It is shown that the oxidation rate is the highest for the oxalato-VO2+ complexes. In addition, the stability of the VO2+ complexes can be drastically improved by evacuation of the dissolved O2 from the solution and subsequent storage in a N2 ambient atmosphere. The vanadium oxide phase formation process, starting with the chemical solution deposition of the aqueous solutions and continuing with subsequent processing in an ambient 0.1% O2 atmosphere, differs for the two complexes. The oxalato-VO2+ complexes turn into the oxygen-deficient crystalline VO2 B at 400 °C, which then turns into crystalline V6O13 at 500 °C. In contrast, the citrato-VO2+ complexes form an amorphous film at 400 °C that crystallizes into VO2 M1 and V6O13 at 500 °C. [ABSTRACT FROM AUTHOR]

An aqueous precursor solution, containing citrato-VO2+ complexes, is synthesized for the formation of monoclinic VO2. With regard to the decomposition of the VO2+ complexes towards vanadium oxide formation, it is important to gain insights into the chemical structure and transformations of the precursor during synthesis and thermal treatment. Hence, the conversion of the cyclic [V4O12]4- ion to the VO2+ ion in aqueous solution, using oxalic acid as an acidifier and a reducing agent, is studied by 51Vanadium nuclear magnetic resonance spectroscopy. The citrate complexation of this VO2+ ion and the differentiation between a solution containing citrato-oxalato-VO2+ and citrato-VO2+ complexes are studied by electron paramagnetic resonance and Fourier transform infra-red spectroscopy. In both solutions, the VO2+ containing complex is mononuclear and has a distorted octahedral geometry with a fourfold R-CO2 - ligation at the equatorial positions and likely a fifth R-CO2- ligation at the axial position. Small differences in the thermal decomposition pathway between the gel containing citrato-oxalato-VO2+ complexes and the oxalate-free gel containing citrato-VO2+ complexes are observed between 150 and 200 °C in air and are assigned to the presence of (NH4)2C2O4 in the citrato-oxalato-VO2+ solution. Both precursor solutions are successfully used for the formation of crystalline vanadium oxide nanostructures on SiO2, after thermal annealing at 500 °C in a 0.1% O2 atmosphere. However, the citrato-oxalato-VO2+ and the oxalate-free citrato-VO2+ solution result in the formation of monoclinic V6O13 and monoclinic VO2, respectively. [ABSTRACT FROM AUTHOR]

Background: The chemically amplified resist (CAR) has been the workhorse of lithography for the past few decades. During the evolution of projection lithography to extreme ultraviolet lithography (EUVL), a continuous reduction in feature size is observed. Also, a reduction in resist film thickness (FT) is required to prevent large aspect ratios that lead to pattern collapse. A further reduction in resist FT, into an ultrathin film regime (<30 nm resist FT), is expected when advancing to high NA EUVL. This brings along associated challenges with (1) resist critical dimension scanning electron microscope (CDSEM) metrology and (2) resist patterning performance. Aim: Assessment of metrology challenges and patterning limits of a CAR working in this ultrathin film regime. Deconvoluting the metrology and patterning effect on the determination of the unbiased line width roughness (uLWR). Approach: Patterning a CAR at different nominal resist FTs on two different underlayers to quantify the changes in CDSEM image quality and resist patterning performance with the resulting uLWR changes. Results: The CDSEM image signal-to-noise ratio (SNR) depends on resist FT and the underlayer. The uLWR increases with a reduction in resist FT but scales differently on the two underlayers. Conclusions: A relationship between CDSEM image SNR and uLWR is found. The SNR and uLWR scaling difference on the two underlayers, as well as the uLWR dependency on SNR was determined to be a metrology effect. The general uLWR increase for a reduced resist FT was determined to be a patterning effect. [ABSTRACT FROM AUTHOR]

Highlights: [•] One MWCNT per contact hole meets ITRS conductivity requirement for sub-15nm DRAM contact technology. [•] Termination of CNT growth limits CNT length below 500°C. [•] Improved CNT contact resistance and yield across 200mm wafer upon adding ALD Al2O3. [•] Catalyst particle density close to 1012 cm− 2achieved on TiN. [ABSTRACT FROM AUTHOR]

In this paper, we show the electrochemicaldeposition of a subnanometerfilm of nickel (Ni) on top of titanium nitride (TiN). We exploit theconcept of cluster growth inhibition to enhance the nucleation ofnew nuclei on the TiN substrate. By deliberately using an unbufferedelectrolyte solution, the degree of nucleation is enhanced as growthis inhibited more strongly. This results in a very high particle densityand therefore an ultralow coalescence thickness. To prevent the terminationof Ni deposition that typically occurs in unbuffered solutions, theconcentration of Ni2+in solution was increased. We haveverified with RBS and ICP-MS that the deposition of Ni on the surfacein this case did not terminate. Furthermore, annealing experimentswere used to visualize the closed nature of the Ni film. The closureof the deposited film was also confirmed by TOF-SIMS measurementsand occurs when the film thickness is still in the subnanometer regime.The ultrathin Ni film was found to be an excellent catalyst for carbonnanotube growth on conductive substrates and can also be applied asa seed layer for bulk deposition of a smooth Ni film on TiN. [ABSTRACT FROM AUTHOR]

Abstract: Carbon nanotubes (CNTs) were integrated successfully into 150nm contact holes having a TiN underlayer and a Cu single damascene top contact module. All the integration steps for CNT integration, for patterning the Cu top contact and the mask-set used are compatible with 130nm device technologies on 200mm wafers. The first resistance yield plots for the CNT contacts on full wafer level are presented. For CNT grown at 540°C in contact holes with aspect ratio 1.3, a single CNT contact hole resistance of 3.4kΩ was achieved. The structure designed, the process flow presented here for CNT integration, and the automatic probing constitute a platform that allows benchmarking different recipes and process conditions. This constitutes a significant step forward towards the realization of a contact module with vertical CNT interconnects of superior quality. This is because the platform can speed up the learning cycle time for optimizing the CNT interconnect based on learning from the electrical performance. [Copyright &y& Elsevier]

Positive charges (PCs) in gate dielectric shift the threshold voltage and cause a time-dependent device variability. To assess their impact on circuits, it is useful to know their distribution for a wide energy range both within and beyond silicon bandgap. Such a distribution is still missing, and a technique for its extraction has not been demonstrated yet. The central objective of this paper is, for the first time, to develop a new fast technique and to demonstrate its capability for probing the energy distribution of PCs over such a wide energy range. Results show that PCs can vary significantly with energy level. The PCs in different energy regions clearly originate from different defects. The PCs below the valence band edge are as-grown hole traps that are insensitive to stress time and temperature, and substantially higher in thermal SiON. The PCs above the valence-band edge are from created defects. The PCs within the bandgap have a peak near Ev + 0.8 eV and saturate for either longer stress time or higher stress temperature. In contrast, the PCs above a conduction band edge, namely the antineutralization positive charges, do not saturate, and their generation is clearly thermally accelerated. [ABSTRACT FROM AUTHOR]

The surface chemistryand the interface formation during the initialstages of the atomic layer deposition (ALD) of Al2O3from trimethylaluminum (TMA) and H2O on InP(100)were studied by synchrotron radiation photoemission spectroscopy andscanning tunneling microscopy. The effect of the ex situ surface cleaningby either H2SO4or (NH4)2S was examined. It is shown that the native oxide on the InP surfaceconsisted mainly of indium hydrogen phosphates with a P enrichmentat the interface with InP. After a (NH4)2S treatment,S was present on the surface as a sulfide in both surface and subsurfacesites. Exposure to TMA led to the formation of a thin AlPO4layer, irrespective of the surface cleaning. The surface Fermi levelof p-type InP was found to be pinned close to midgap after H2SO4cleaning and moved only slightly further toward theconduction 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 InPclose to the conduction band edge. Hence, the InP surface was weaklyinverted, which can be attributed to surface doping by S donors. TMAexposure was found to remove surface S, which was accompanied by ashift 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 anydetectable changes of the AlPO4/InP interface and suggestedsimple overgrowth with Al2O3. [ABSTRACT FROM AUTHOR]

The article focuses on graphene transistors and photodetectors. It states that the graphene is a thin crystalline film that has unique electronic structure and strong electric field effect. It discusses the properties of single layer graphene based field effect transistor (FET). It also mentions the use and property of bilayer graphene (BLG) and features the operation principles of graphene photodetectors.

Defects in gate oxide cause breakdown and shorten device lifetime. Early works mainly focused on generation process that converts a precursor into a charged defect. Although it can be neutralized through “recovery,” the defect is still there and will recharge when resuming stress. Recently, we have shown that this is not always the case and some defects can be lost, but a detailed investigation is missing. The central objective of this work is to accurately define and extract the loss, separate it from slowdown, and evaluate their enhancement of device lifetime. Loss is defined as elimination of defects, while slowdown means that recharging a “hardened” precursor takes longer than charging a fresh one. Clear evidences show that losses originate from permanent components, i.e., generated interface states and antineutralization positive charges, while slowdown occurs to both permanent and recoverable components. Loss is thermally accelerated, but slowdown of recoverable component is not. This improved understanding adds slowdown and losses to the existing framework for defects. For the first time, we report that the losses and slowdown enhance device lifetime by a factor of 2.6–4.3, for an allowed threshold voltage shift of 20–45 mV. [ABSTRACT FROM AUTHOR]

Abstract: We propose an empirical law correlating the average number of walls and the average diameter in a population of multi-wall carbon nanotubes grown by catalytic chemical vapor deposition. The relationship and its dispersion are derived from the statistical analysis of a database of TEM images of nanotubes collected from more than 60 publications in literature and from our group in the last years. Considering the nanotubes were grown from independent sources in a variety of conditions and tools, it has general validity. The relationship may find applicability in a wide range of fields as it provides a simple model to quickly estimate the number of walls most likely present in a population of nanotubes from only the measure of their average diameter. [Copyright &y& Elsevier]

Interface states play an important role in the performance of MOSFETs, and previous works only addressed the states within band gap. The implicit assumption is that the states beyond band gap (SBBs) are negligible, but there is no experimental evidence supporting it. Because of a lack of techniques for characterizing SBBs, there is hardly any information available. The central objective of this paper is to develop a technique for evaluating SBBs and to show the impact of SBBs on mobility evaluation. For the first time, the pulse capacitance–voltage has been used to extract SBBs quantitatively. It is found that SBBs can reach the order of \10^13 \ \cm^-2\cdot\eV^-1 beyond both conduction- and valence-band edges on a fresh MOSFET. The conventional split C– V technique ignores the SBBs, and this can lead to an underestimation of carrier mobility over 30%. Using the newly developed technique as a tool, the impact of nitridation of Hf-based dielectric stacks on carrier mobility is assessed. As nitrogen density increases, the apparent reduction of carrier mobility observed by early works originates from the higher SBBs. Once SBBs are taken into account, nitridation does not degrade carrier mobility. The SBBs are sensitive to process conditions, and this paper opens the way for their minimization. [ABSTRACT FROM AUTHOR]

Graphene and carbon nanotubes (CNTs) are both carbon-based materials with remarkable optical and electronic properties which, among others, may find applications as transparent electrodes or as interconnects in microchips, respectively. This work reports on the formation of a hybrid structure composed of a graphitic carbon layer on top of vertical CNT in a single deposition process. The mechanism of deposition is explained according to the thickness of catalyst used and the atypical growth conditions. Key factors dictating the hybrid growth are the film thickness and the time dynamic through which the catalyst film dewets and transforms into nanoparticles. The results support the similarities between chemical vapor deposition processes for graphene, graphite, and CNT. [ABSTRACT FROM AUTHOR]

Abstract: We propose to use carbon nanotube (CNT)–CNT contacts instead of CNT–metal contacts as a route towards low resistance CNT horizontal interconnects. We characterize by electrical transport measurements and Kelvin probe force microscopy the contacts present in CNT horizontal interconnects grown by chemical vapor deposition between titanium nitride electrodes. When two CNTs with diameter around 30nm grow from opposing electrodes and touch each other with their outermost shells, typical contact resistances around 16kΩ are obtained. The corresponding contact resistivity of about 14Ωμm2 is one order of magnitude smaller than the contact resistivity of a CNT touching the TiN surface with its outermost shell. On the other hand, the contact resistance of a CNT grown from a nickel catalyst particle deposited on a TiN electrode is negligibly small when compared to the above mentioned contact resistances. Our results demonstrate that we are able to grow from opposing electrodes CNTs that touch each other with a corresponding high density (up to 1011 cm−2) of CNT–CNT contacts. This may offer an effective solution towards the growth of low resistance CNT horizontal interconnects. [Copyright &y& Elsevier]