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Register a new userEnhancing Interconnect Reliability and Performance by Converting Tantalum to 2D Layered Tantalum Sulfide at Low Temperature
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The interconnect half-pitch size will reach ~20 nm in the coming sub-5 nm technology node. Meanwhile, the TaN/Ta (barrier/liner) bilayer stack has to be > 4 nm to ensure acceptable liner and diffusion barrier properties. Since TaN/Ta occupy a significant portion of the interconnect cross-section and they are much more resistive than Cu, the effective conductance of an ultra-scaled interconnect will be compromised by the thick bilayer. Therefore, two dimensional (2D) layered materials have been explored as diffusion barrier alternatives. However, many of the proposed 2D barriers are prepared at too high temperatures to be compatible with the back-end-of-line (BEOL) technology. In addition, as important as the diffusion barrier properties, the liner properties of 2D materials must be evaluated, which has not yet been pursued. Here, a 2D layered tantalum sulfide (TaSx) with ~1.5 nm thickness is developed to replace the conventional TaN/Ta bilayer. The TaSx ultra-thin film is industry-friendly, BEOL-compatible, and can be directly prepared on dielectrics. Our results show superior barrier/liner properties of TaSx compared to the TaN/Ta bilayer. This single-stack material, serving as both a liner and a barrier, will enable continued scaling of interconnects beyond 5 nm node.
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Superconducting Tunnel Junctions (STJs) are currently being developed as photon detectors for a wide range of applications. Interest comes from their ability to cumulate photon counting with chromaticity (i.e. energy resolution) from the near infrared (2 $mu$m) to the X-rays wavelengths and good quantum efficiency up to 80%. Resolving power can exceed 10 in the visible wavelength range. Our main goal is to use STJs for astronomical observations at low light level in the near infrared. This paper put the emphasis on two main points: the improvement of the tantalum absorber epitaxy and the development of a new version of the fabrication process for making Ta/Al-AlOx-Al/Ta photon counting STJs. The main features of this process are that pixels have aligned electrodes and vias patterned through a protecting SiO2 layer. These vias are then used to contact the top electrode layer. We use a double thin aluminum trapping layer on top of a 150 nm thick Ta absorber grown epitaxially. Photon counting experiments with Ta junction array are presented at lambda = 0.78 $mu$m. Digital filtering methods are used to compute the photon counting data in order to minimize the effects of noise.
Compared with the semiconductors such as silicon and gallium arsenide which have been used widely for decades, semimetals have not received much attention in the field of condensed matter physics until very recently. The realization of electronic topological properties has motivated interest of investigations on Dirac semimetals and Weyl semimetals, which are predicted to show unprecedented features beyond the classical electronic theories of metals. In this letter for the first time we report the electric transport properties of a robust Weyl semimetal candidate proposed by recent theoretical calculations, TaAs. Our study shows that this bulk material manifests ultrahigh carrier mobility ($mathrm{5times10^5 cm^2/Vcdot{s}}$) accompanied by an extremely large, unsaturated linear magnetoresistance ($mathrm{MR}$), which reaches 5400 at 10 Kelvins in a magnetic field of 9 Teslas and 2.47$times$10$^4$ at 1.5 Kelvins in a magnetic field of 56 Teslas. We also observed strong Shubnikov-de Haas (SdH) oscillations associated with an extremely low quantum limit ($sim$8 Teslas). Further studies on TaAs, especially in the ultraquantum limit regime, will help to extend the realization of the topological properties of these exotic electrons.
Layered two-dimensional (2D) materials display great potential for a range of applications, particularly in electronics. We report the large-scale synthesis of thin films of platinum diselenide (PtSe2), a thus far scarcely investigated transition metal dichalcogenide. Importantly, the synthesis by thermal assisted conversion is performed at 400 {deg}C, representing a breakthrough for the direct integration of this novel material with silicon (Si) technology. Besides the thorough characterization of this new 2D material, we demonstrate its promise for applications in high-performance gas sensing with extremely short response and recovery times observed due to the 2D nature of the films. Furthermore, we realized vertically-stacked heterostructures of PtSe2 on Si which act as both photodiodes and photovoltaic cells. Thus this study establishes PtSe2 as a potential candidate for next-generation sensors and (opto-)electronic devices, using fabrication protocols compatible with established Si technologies.
Quasi-two-dimensional (quasi-2D) materials hold promise for future electronics because of their unique band structures that result in electronic and mechanical properties sensitive to crystal strains in all three dimensions. Quantifying crystal strain is a prerequisite to correlating it with the performance of the device, and calls for high resolution but spatially resolved rapid characterization methods. Here we show that using fly-scan nano X-ray diffraction we can accomplish a tensile strain sensitivity below 0.001% with a spatial resolution of better than 80 nm over a spatial extent of 100 $mu$m on quasi 2D flakes of 1T-TaS2. Coherent diffraction patterns were collected from a $sim$ 100 nm thick sheet of 1T-TaS2 by scanning 12keV focused X-ray beam across and rotating the sample. We demonstrate that the strain distribution around micron and sub-micron sized bubbles that are present in the sample may be reconstructed from these images. The experiments use state of the art synchrotron instrumentation, and will allow rapid and non-intrusive strain mapping of thin film samples and electronic devices based on quasi 2D materials.
The volume of tantalum versus pressure has been accurately measured up to 101 GPa by single-crystal x-ray diffraction, with helium as pressure transmitting medium. Slight deviation from previous static determinations is observed. Discrepancy with reduced shock-wave and ultrasonic data supports recent doubts about the calibration of the ruby pressure scale. Finally, first principle calculations of the literature show a positive curvature in $P(V)$ relative to the experimental data, even with a modified pressure scale.
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