Nanoscale Structure-Property Relationship in Amorphous Hydrogenated Boron Carbide for Low- k Dielectric Applications
Nanoscale Structure-Property Relationship in Amorphous Hydrogenated Boron Carbide for Low- k Dielectric Applications
复制标题
用于低 k 介电应用的非晶态氢化碳化硼的纳米级结构-性能关系
DOI：
10.1017/s1431927617008091
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发表时间：
2017
影响因子：
2.8
通讯作者：
Hwang, Jinwoo
中科院分区：
文献类型：
--
作者：
Im, Soohyun;Paquette, Michelle M.;Belhadj-Larbi, Mohammed;Rulis, Paul;Sakidja, Ridwan;Hwang, Jinwoo
未来集成电路规模化的主要挑战之一是需要新的低介电常数（低k）材料，其可以在系统级显著降低电阻-电容延迟。新的低k材料还必须克服机械性能的致命下降，称为低k死亡曲线，这通常与实现低k值所需的材料的低密度相关[1]。非晶氢化碳化硼（a-BC：H）结合了低k和其他优点，包括化学、热、电和机械可靠性，因此最近作为传统SiO2和SiOC：H/SiCO：H的高性能低k材料替代品而受到关注。我们的a-BC：H膜是使用分子邻碳硼烷的等离子体增强化学气相沉积合成的，其在沉积时转化为无定形聚合物[2]。该方法实现了结构和组成（aB xC：Hy）的高度变化，这允许通过控制其纳米级结构来调节材料的性质。例如，控制由二十面体BxC正碳硼烷簇的连接或聚集引起的中程有序度（MRO）（图1a）可以使得能够调节具有高柔性的材料的介电常数和其他重要性质。因此，了解的MRO结构的a-BC：H是至关重要的，但MRO的表征一直是困难的，因为传统的成像或衍射方法是不敏感的，这种有序由于其小尺寸和难以捉摸的natural. In，我们报告的a-BC：H的纳米级结构的表征使用波动显微镜了解的细节MRO和它如何与材料的重要性能。涨落显微镜基于电子纳米衍射，测量无序结构中纳米级MRO引起的结构涨落，提供有关MRO的大小、类型、程度和体积分数的信息（图1b和1c）[3]。它需要从样品的许多不同区域（例如，图1d至e），并计算这些衍射强度之间的强度方差V，作为散射矢量大小k的函数（图2a），它代表结构波动。例如，图2a显示了来自高密度和低密度a-BxC：H样品的V（k），它们彼此显著不同。来自高密度样品的V（k）示出许多峰，表明样品在其结构中包括显著程度的MRO，而低密度样品不包括。通过将实验V（k）与来自已知原子模型（诸如分子动力学（MD）生成的模型）的模拟V（k）进行比较，可以分析V（k）处的峰的纳米级结构起源的细节（图2b）。例如，V（k）中的第一个峰值匹配来自MD生成的模型的模拟V（k）峰值，该模型在二十面体簇的超聚类之间具有明显的分离。这意味着峰值包括关于这些超聚类的MRO域如何彼此分离的信息。另一方面，第二个峰与已知B4 C晶体的模拟V（k）相匹配（图2c）[2]，表明类似于B4 C晶体的MRO在结构中丰富。这种MRO结构和重要的电气/机械性能之间的详细关系将在本报告中讨论。
One of the main challenges in scaling of future integrated circuits is the need for new low dielectric constant (low-k) materials that can substantially reduce the resistance-capacitance delay at the system level. The new low-k material must also overcome the fatal falloff in the mechanical properties, known as the low-k death curve, that is typically associated with the low density of the material required to achieve low k values [1]. Amorphous hydrogenated boron carbide (a-BC: H) combines low k with other advantages, including chemical, thermal, electrical, and mechanical reliability, and therefore has recently gained attention as a high-performing low-k material alternative to conventional SiO2 and SiOC: H/SiCO: H. Our a-BC: H films are synthesized using plasma-enhanced chemical vapor deposition of molecular ortho-carborane, which converts into an amorphous polymer upon deposition [2]. The method enables a high degree of variation in structure and composition (aB xC: Hy), which allows for tuning the properties of the material by controlling its nanoscale structure. For example, controlling the degree of medium range order (MRO) arising from the connection or gathering of icosahedral BxC orthocarborane clusters (Fig. 1a) can enable tuning the dielectric constant and other important properties of the material with high flexibility. Understanding the MRO structure of a-BC: H is therefore crucial, but the characterization of MRO has been difficult because conventional imaging or diffraction methods are insensitive to such ordering due to its small size and elusive nature.Here we report the characterization of the nanoscale structure of a-BC: H using fluctuation microscopy to understand the details of MRO and how it relates to important properties of the material. Fluctuation microscopy is based on electron nanodiffraction, and measures the structural fluctuation caused by the nanoscale MRO in disordered structure, providing information on the size, type, degree, and volume fraction of MRO (Fig. 1b and 1c)[3]. It requires a few hundred to a thousand nanodiffraction patterns taken from many different areas of the sample (eg. Fig. 1d to e), and calculates the intensity variance, V, among those diffraction intensities, as a function of the scattering vector magnitude, k (Fig. 2a), which represents the structural fluctuation. For example, Fig. 2a shows the V (k) from high-and low-density a-BxC: H samples, which are significantly different from each other. V (k) from a high-density sample shows many peaks, indicating that the sample includes a significant degree of MRO in its structure, while the low-density sample does not. By comparing the experimental V (k) to the simulated V (k) from known atomistic models, such as molecular dynamics (MD) generated models, the details of the nanoscale structural origins of the peaks at V (k) can be analyzed (Fig. 2b). For example, the first peak in V (k) matches the simulated V (k) peak from an MD-generated model that has a clear separation between the super-clustering of the icosahedral clusters. This implies that the peak includes the information on how those superclustered MRO domains are separated from each other. The second peak, on the other hand, matches the simulated V (k) from the known B4C crystal (Fig. 2c)[2], suggesting that MRO that resembles that of the B4C crystal is abundant in the structure. The detailed relationship between such MRO structure and important electric/mechanical properties will be discussed in this presentation.