Characterization of Nanoscale Defects and Pores

0100009Gidley提出了一项跨学科研究计划，该计划将众所周知的正电子湮没寿命谱(PALS)的空穴-体积敏感性与最先进的正电子束技术相结合，以表征传统技术不适用的各种工程材料中的缺陷和气孔。孔隙率控制是纳米工程新兴领域的一个重要方面。在微电子“低K”电介质膜、薄聚合物渗透滤光片和催化膜中引入和设计孔隙率引起了人们的强烈研究兴趣。另一方面，防止界面缺陷孔洞是粘合剂、密封剂和复合材料等结构材料中的一个长期存在的问题。这些薄膜的无定形性质以及气孔/缺陷的纳米尺寸对传统的探头提出了挑战。PALS已被证明是表征这种亚微米薄膜系统中纳米级孔隙率的一种重要的新工具。由于之前的NSF-ECS赠款，束流PALS在帮助微电子工业开发下一代低K层间介质薄膜方面发挥着重要作用。PAL对1-100纳米孔的大小和相互连通性的敏感性已经被证明。发展了一种用于提取闭孔系统的孔径分布的方法。研究发现，PALS对铜在介质中的互扩散很敏感，因此也可以测试所需的扩散阻挡层完整性。这项提案将在这项工作的基础上进行扩展。金属互扩散和阻挡层完整性/热稳定性将根据Sematech的要求进行研究，重点是开发标准化的PALS测试程序。Sematech是一个主要由美国主要电子公司组成的研究联盟。将继续利用补充技术进行交叉校准实验，以表征孔隙度，如NIST的小角中子散射(SANS)和IMEC的溶剂吸收椭圆偏振测孔法。这样的研究有助于确定每种技术的独特优势和劣势。这项建议的第二个主要推动力将是对聚合物薄膜、表面和界面的研究。IBIS的研究建立在以前工作的基础上，其中BEAM-PALS被用来研究以硅片为约束的10微米聚合物薄膜的结构和动力学。研究发现，这种薄膜在硅的旁边有一层高度固定的“粘附层”，在表面有一层不受约束的“液体”层。将特别注意界面区域，以确定固定层对粘合失效和分层的开始的敏感性。如果失效是由于例如疲劳、热应力或腐蚀导致前驱体纳米空洞结合到更大的孔中，那么深度异形束-PAL应该是这个失效前启动阶段的非常强大的探头，否则是看不见的。具体地说，将研究缺陷孔洞在微电子封装中使用的聚合物密封剂和粘合剂失效中的作用。还将对化学放大光致抗蚀剂在紫外线曝光下显影时纳米结构的演变进行辅助研究。拟议的研究建立在密歇根大学物理系和材料科学与工程系之间强大的现有合作基础上。为了提供关键的指导和明确的相关性重点，PI与六家独立公司、NIST以及两个大型工业财团--美国的Sematech和欧洲的IMEC--建立了强有力的工作合作关系。

0100009GidleyAn interdisciplinary research program is proposed that combines the well-known void-volume sensitivity of positron annihilation lifetime spectroscopy (PALS) with state-of-the-art positron beam technology in order to characterize defects and pores in a wide range of engineering materials where traditional techniques are not adequate. Porosity control is an important aspect of the emerging field of nanoengineering. Introducing and engineering porosity in microelectronic "low-K" dielectric films, in thin polymeric permeation filters, and in catalytic films is attracting intense research interest. On the other hand, preventing interfacial defect porosity is a long-standing problem in structural materials such as adhesives, encapsulants, and composites. Traditional probes are challenged by the amorphous nature of these very thin films and by the nanoscale size of the pores/defects. PALS has been demonstrated to be an important new tool in characterizing nanoscale porosity in such sub-micron film systems.As a result of the previous NSF-ECS grant beam-PALS is playing an important role in helping the microelectronics industry develop next-generation, low-K interlayer dielectric films. The sensitivity of PALS to the size and interconnectivity of 1-100 nanometer pores has been demonstrated. A procedure for extracting pore size distributions for closed-pore systems has been developed. PALS is found to be sensitive to Cu interdiffusion into the dielectric and the consequently required diffusion barrier layer integrity can be tested as well. This proposal will expand upon this work. Metal interdiffusion and barrier integrity/thermal stability will be studied with particular attention focussed on developing a standardized PALS testing procedure as requested by Sematech, a research consortium primarily comprised of the major U.S. electronics corporations. Cross-calibration experiments with complementary techniques used to characterize porosity, such as small-angle neutron scattering (SANS) at NIST and solvent absorption ellipsometric porosimetry at IMEC, will be continued. Such studies help determine the unique strengths and weaknesses of each respective technique.A second major thrust of this proposal will be the study of polymer thin films, surfaces and interfaces. Ibis research builds upon previous work in which beam-PALS was used to study the structure and dynamics of thin 10 urn polymer films constrained on silicon wafers. Such films were found to have a highly immobile "adhesive" layer next to the silicon and an unconstrained "liquid" layer at the surface. Particular attention will be focussed on the interfacial regions in order to determine the sensitivity of the immobile layer to the onset of adhesion failure and delamination. If failure is due to the coalescence of precursor nano-voids into larger pores due, for example, to fatigue, thermal stress, or corrosion, depth-profiled beam-PALS should be a very powerful probe of this pre-failure initiation phase that is otherwise invisible. Specifically, the role of defect voids in the failure of polymer encapsulants and adhesives used in microelectronic packaging will be studied. An ancillary study of the evolution of nanostructure in a chemically amplified photo-resist as it develops under UV exposure will also be performed.The proposed research builds upon a strong existing collaboration between the University of Michigan Physics Department and the Materials Science and Engineering Department. To provide critical guidance and clear focus on relevance the PIs have developed strong working collaborations with six individual companies, NIST, and with two large industrial consortiums; Sematech in the U.S. and IMEC in Europe.