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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]

Large‐area epitaxy of layered materials is one of the cornerstones for a successful exploitation of van der Waals (vdW) materials in the semiconductor industry. The formation of 60° twin stacking faults and 60° grain boundaries is of major concern for the defect‐free epitaxial growth. Although strategies to overcome the occurrence of these defects are being considered, more fundamental understanding on the origin of these defects is highly essential. This work focuses on understanding the formation of 60° twins in (quasi‐)vdW epitaxy of 2D chalcogenides. Molecular beam epitaxy (MBE) experiments reveal the striking difference in 60° twin occurrence between WSe2 and Bi2Se3 in both quasi‐vdW heteroepitaxy and vdW homoepitaxy. Density functional theory (DFT) calculations link this difference to the interlayer vdW coupling strength at the unit cell level. The stronger interlayer vdW coupling in Bi2Se3 unit cells compared to WSe2 unit cells is explained to result in a reduced twin occurrence. Hence, such compounds show significantly more promise for defect‐free epitaxial integration. This interesting aspect of (quasi‐)vdW epitaxy reveals that the strength of interlayer vdW coupling is key for workable 2D materials and opens perspectives for other strongly coupled vdW materials. [ABSTRACT FROM AUTHOR]

Defect characterization of 2D materials is a critical aspect for their successful integration in future electronic devices. Here, a simple characterization technique is proposed that opens a path for fast, non‐invasive, quality assessment of transition metal dichalcogenide layers, such as MoS2, and their interfaces. It relates to the correlation between substrate‐induced traps and the indirect‐to‐direct photoluminescence peak ratio. It is shown that the indirect peak is quenched when interfacial trap sites are present. A physical mechanism is proposed to explain the observations based on different recombination mechanisms. [ABSTRACT FROM AUTHOR]

Large area MoS2 films with tunable physical-chemical properties are grown on dielectric substrates by annealing of ultrathin Mo layers in the presence of a sulfur-containing gaseous precursor. Different growth conditions are found to have a significant impact on material properties, including chemical composition, roughness, and grain sizes, thus shedding light on critical parameters that govern sulfurization processes for the synthesis of large area 2D transition metal dichalcogenides. Optimized growth conditions in combination with the use of single crystal sapphire substrates with atomically flat interface result in the formation of oriented MoS2 films with improved quality and electrical performance. On the basis of this versatile synthesis technique, an original double-step process is presented for the synthesis of WS2/MoS2 vertical heterostructures. Good uniformity of layers over large area has enabled first isolation of defects by electron spin resonance spectroscopy with densities correlated with mobility degradation and the first experimental characterization of the band alignment at the interfaces of MoS2, WS2, and their vertical stacks with the underlying SiO2 insulator. [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]

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]