Defect and Surfactant Mediated Growth of High Quality Single Crystal Metallic Thin Films

技术摘要：缺陷介导生长（DMG）和表面活性剂介导生长（SMG）是生产极高质量外延单晶金属材料的新型电化学沉积方法。 DMG 涉及与金属进行可逆共沉积，该金属将成为介体金属的外延覆盖层。这种介体（例如，Pb）作为亚单层重复沉积在薄膜表面上，然后在薄膜生长时通过电化学势的循环完全剥离。每个循环都会在生长薄膜的表面上产生新的核，从而添加到先前循环中形成的表面簇中。通过适当选择沉积通量和循环频率可以保持二维簇的高密度，从而在二维簇最终合并时形成单层薄膜材料。以这种方式，获得二维而非三维薄膜生长。 SMG 使用最多单层介体金属作为表面活性剂，在沉积过程中持续保持在表面，从而导致二维生长。使用这些方法，可以在环境温度下电沉积原子级平坦的单晶薄膜（不含介体金属），并且对于在环境温度沉积期间经常显示三维生长的系统，薄膜质量与通过分子束外延生长获得的薄膜质量相似。要研究的具体系统包括金上的铜、铜上的镍以及硅上的铜、银、镍和钴。这项工作的新特点是在 DMG 和 SMG 过程中实时原位监测薄膜应力的产生，并将应力行为与形态演化相关联。这在科学和技术上都很有趣，因为应力行为与生长的微观结构特征相关，如果要将 DMG 和 SMG 生产的系统用于技术应用（例如，用于互连的硅上铜），则表征应力非常重要。应力的实时监控还将用于优化生长条件并监控沉积过程中的薄膜质量。非技术摘要：为薄膜应用（例如微电子）生产高质量单晶材料的能力对于维护和推进许多重要技术至关重要。缺陷和表面介导的电化学生长是最近开发的以廉价方式生产此类材料的方法，并且是可以纳入现有和下一代技术的过程。该研究将研究具有科学和工业重要性的合成材料系统，包括用于质量表征和控制的实时应力监测。这将是这些合成方法中首次采用应力测量，并将大大增强将它们转化为技术上可行的工艺的潜力。这项工作将与亚利桑那州立大学 (ASU) 和 IBM Thomas J. Watson 研究中心的研究人员合作进行。与该项目相关的外展活动包括通过实地考察、指导和实践模块让中学生参与科学技术工程数学 (STEM) 教育。这些学生将来自巴尔的摩市公立学校，这些学校在 STEM 教育方面代表性不足且服务不足。

TECHNICAL SUMMARY:Defect mediated growth (DMG) and surfactant mediated growth (SMG) are novel electrochemical deposition methods of producing extremely high-quality epitaxial single-crystal metallic materials. DMG involves reversibly co-depositing with the metal that is to become the epitaxial overlayer a mediator metal. This mediator (e.g., Pb) is repeatedly deposited as a submonolayer on the film surface and then completely stripped by the cycling of the electrochemical potential as the film is grown. Each cycle creates new nuclei on the surface of the growing film, adding to the surface clusters that developed on previous cycles. A high density of two-dimensional clusters can be maintained by appropriately choosing the deposition flux and cycling frequency, resulting in a monolayer of the film material being completed when the two-dimensional clusters eventually coalesce. In this manner, two-dimensional rather than three-dimensional film growth is obtained. SMG uses up to a monolayer of the mediator metal acting as a surfactant that is continuously maintained at the surface during deposition, resulting in two-dimensional growth. Using these approaches, atomically flat single-crystal films (free of the mediator metal) can be electrodeposited at ambient temperature, and the film quality is similar to that obtained by molecular beam epitaxial growth for systems that often display three-dimensional growth during ambient temperature deposition. Specific systems to be studied include Cu on Au, Ni on Cu, and Cu, Ag, Ni, and Co on Si. New features of this work will be the in situ monitoring of the thin film stress generation in real time during DMG and SMG and correlating the stress behavior with the morphological evolution. This of interest both scientifically and technologically, as the stress behavior is associated with microstructural features of growth, and it is important to characterize the stress if DMG and SMG-produced systems are to be used in technological applications (e.g., Cu on Si for interconnects). Real-time monitoring of the stress will also be used to optimize growth conditions and to monitor film quality during deposition.NON-TECHNICAL SUMMARY:The ability to produce high-quality single-crystal materials for thin film applications (e.g., microelectronics) is critical for maintaining and advancing many important technologies. Defect and surface mediated electrochemical growth are recently developed methods of producing such materials in an inexpensive manner and are processes that can be incorporated into existing and next-generation technologies. The research will investigate synthesizing material systems of both scientific and industrial importance and includes real-time stress monitoring for quality characterization and control. This will be the first time stress measurements will be employed during these synthesis methods and will greatly enhance the potential of converting them into technologically viable processes. This work will be conducted in collaboration with researchers at Arizona State University (ASU) and at IBM Thomas J. Watson Research Center. Outreach activities associated with this project include engaging middle-school students in science-technology-engineering-mathematics (STEM) education through field trips, mentoring, and hands-on modules. The students will be from the Baltimore City Public Schools who are both underrepresented and underserved in STEM education.