JILA and Department of Physics, University of Colorado , Boulder, Colorado 80309-0440, United States.
Intel Corp., 2501 NW 229th Avenue, Hillsboro, Oregon 97124, United States.
Nano Lett. 2017 Apr 12;17(4):2178-2183. doi: 10.1021/acs.nanolett.6b04635. Epub 2017 Mar 1.
Precise characterization of the mechanical properties of ultrathin films is of paramount importance for both a fundamental understanding of nanoscale materials and for continued scaling and improvement of nanotechnology. In this work, we use coherent extreme ultraviolet beams to characterize the full elastic tensor of isotropic ultrathin films down to 11 nm in thickness. We simultaneously extract the Young's modulus and Poisson's ratio of low-k a-SiC:H films with varying degrees of hardness and average network connectivity in a single measurement. Contrary to past assumptions, we find that the Poisson's ratio of such films is not constant but rather can significantly increase from 0.25 to >0.4 for a network connectivity below a critical value of ∼2.5. Physically, the strong hydrogenation required to decrease the dielectric constant k results in bond breaking, lowering the network connectivity, and Young's modulus of the material but also decreases the compressibility of the film. This new understanding of ultrathin films demonstrates that coherent EUV beams present a new nanometrology capability that can probe a wide range of novel complex materials not accessible using traditional approaches.
准确描述超薄薄膜的力学性能对于理解纳米尺度材料的基本原理以及纳米技术的持续扩展和改进都至关重要。在这项工作中，我们使用相干极紫外光束来表征各向同性超薄薄膜的完整弹性张量，薄膜厚度低至 11nm。我们在单次测量中同时提取了具有不同硬度和平均网络连接度的低 k a-SiC:H 薄膜的杨氏模量和泊松比。与过去的假设相反，我们发现这些薄膜的泊松比不是常数，而是可以从 0.25 显著增加到 >0.4，当网络连接度低于约 2.5 时。从物理上讲，降低介电常数 k 所需的强烈氢化导致键断裂，降低了材料的网络连接度和杨氏模量，但也降低了薄膜的可压缩性。对超薄薄膜的这种新认识表明，相干极紫外光束提供了一种新的纳米计量能力，可以探测到使用传统方法无法探测的广泛的新型复杂材料。
