Single-layer MoS2 is a direct-gap semiconductor whose electronic band structure strongly depends on the strain applied to its crystal lattice. While uniaxial strain can be easily applied in a controlled way, e.g., by bending of a flexible substrate with the atomically thin MoS2 layer on top, experimental realization of biaxial strain is more challenging. Here, we exploit the large mismatch between the thermal expansion coefficients of MoS2 and a silicone-based substrate to apply a controllable biaxial tensile strain by heating the substrate with a focused laser. The effect of this biaxial strain is directly observable in optical spectroscopy as a redshift of the MoS2 photoluminescence. We also demonstrate the potential of this method to engineer more complex strain patterns by employing highly absorptive features on the substrate to achieve non-uniform heat profiles. By comparison of the observed redshift to strain-dependent band structure calculations, we estimate the biaxial strain applied by the silicone-based substrate to be up to 0.2 percent, corresponding to a band gap modulation of 105 meV per percentage of biaxial tensile strain.

Control of biaxial strain in single-layer Molybdenite using local thermal expansion of the substrate

Over the past decade, the primary focus for improving the performance of nano-electronic metal interconnect structures has been to reduce the impact of resistance-capacitance (RC) delays via utilizing insulating dielectrics with ever lower values of dielectric permittivity. The integration and implementation of such low dielectric constant (i.e. low-k) materials has been fraught with numerous challenges. For intermetal and interlayer (ILD) low-k dielectrics, these challenges have been largely associated to integration with metal interconnect fabrication processes and well documented and reviewed in the literature. Although equally important, less attention has been given to other low-k dielectrics utilized in metal interconnect structures that are commonly referred to as low-k dielectric barriers (DB), etch stops (ES), and/or Cu capping layers (CCL). These materials present numerous challenges as well for integration into metal interconnect fabrication processes. However, they also have more stringent integrated functionality requirements relative to low-k ILD materials that serve only a basic purpose of electrically isolating adjacent metal lines. In this article, we review the integration challenges and associated integrated functionality requirements for low-k DB/ES/CCL materials with a focus on the current status and future direction needed for these materials to facilitate both Moore’s law (i.e. More Moore) and More than Moore scaling. © The Author(s) 2014. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is not changed in any way and is properly cited. For permission for commercial reuse, please email: oa@electrochem.org. [DOI: 10.1149/2.0051501jss] All rights reserved.

https://iopscience.iop.org/article/10.1149/2.0051501jss/pdf

Dielectric Barrier, Etch Stop, and Metal Capping Materials for State of the Art and beyond Metal Interconnects

JSS FOCUS ISSUE ON ADVANCED INTERCONNECTS :M ATERIALS ,P ROCESSING, AND RELIABILITY Dielectric Barrier, Etch Stop, and Metal Capping Materials for State of the Art and beyond Metal Interconnects

Challenges in the implementation of low-k dielectrics in the back-end of line

Two-dimensional composite materials made from aligned nano- and microwires hold great promise for various applications such as thermoelectric device. Similarly, two-dimensional composites made from aligned nanoscale pores are also very important for various technologies. Phonon transport along such composites primarily involves three nondimensional parameters based on the phonon mean paths in the host medium and the wire. The first of these is the ratio of interwire distance to the phonon mean free path in the host medium, the second is the ratio of the diameter of the wire to the phonon mean free path in the host medium, and the third is the ratio of the diameter of the wire to the phonon mean free path in the wire. We develop an analytical model for the thermal conductivity in the longitudinal direction of these composites by solving the phonon Boltzmann transport equation. The analytical model includes the dependences of all three parameters and is in excellent agreement with a recently reported numerical model [Yang et al., Phys. Rev. B 72, 125418 (2005)]. Our solution shows that the scattering of phonons in the host medium at the wire interface reduces the thermal conductivity of the host medium.

A. Delan

Papers

Thermal conductivity of ultra low- k dielectrics