Mechanisms of Stress and Structure Evolution During Processing of Polycrystalline Thin Films

多晶薄膜广泛应用于微纳米器件和系统中，其应力状态和晶粒结构深刻地影响着其性能、性能和可靠性。在薄膜形成和随后的加工过程中，应力和结构演化是强耦合的。应力演化的原位测量揭示了一系列复杂的现象，包括拉应力和压应力状态之间的演化，以及生长中断期间明显可逆的应力变化。非原位和原位的晶粒结构和表面形貌表征也揭示了岛屿聚并过程中晶粒生长和织构演化、岛屿聚并过程中网状结构的形成、晶界深沟的保留以及薄膜岛屿聚并过程中表面形貌的变化等复杂过程。这种现象学在目前对应力和结构演化之间联系的理解中没有考虑到。在这个程序中，应力演化将研究一系列材料在一系列条件下沉积的过程。使用不同的材料和沉积温度将允许观察到那些已经成为先前研究重点的中间行为。使用具有较高熔化温度的材料也将允许淬火表面和晶粒结构以进行非原位表征。利用光散射技术，在沉积过程和沉积中断期间监测表面形貌。原子沉积通量的入射角也会发生变化，以可控地提高不同程度的表面粗糙度。形成薄膜的初始岛屿的大小和间距也将使用模板脱湿技术来改变。通过这些研究，我们将进一步了解多晶薄膜的结构和性能，以及基于多晶薄膜的微/纳米结构。为我们的手机、电脑和互联网供电的电子设备和集成电路是用非常薄的金属层和半导体制成的，这些金属层和半导体是在硅等材料的平面上形成的。然后在这些薄膜上制作极小的图案，以创建数百万个连接在一起的设备电路。有时，这些设备的部件在工作时可以移动。不同材料的层或薄膜通常是通过将原子喷射到平面上制成的。一旦原子到达表面，它们就会四处移动形成小晶体，这些晶体会不断生长，直到它们相互碰撞形成连续的薄膜。这些晶体形成和生长的方式可能会有很大的不同，这取决于原子是如何喷射的，以及使用了哪些原子。这些变化强烈地影响着薄膜的性质，包括电子穿过薄膜的容易程度或运动部件的容易程度。这使得制造复杂的集成电路变得非常困难，并限制了可以制造的东西。这个研究项目的重点是理解为什么会发生这些变化，以及如何控制它们，以便制造新的设备和电路。为了做到这一点，研究人员将改变原子喷射的方式，并测量薄膜在形成过程中性能和结构的变化。

TECHNICAL SUMMARY Polycrystalline films are used in a wide range of micro- and nano-scale devices and systems in which their stress state and grain structure profoundly affect their performance, properties and reliability. Stress and structure evolution during film formation and subsequent processing are known to be strongly coupled. In-situ measurements of stress evolution have revealed a complex range of phenomenology, including evolution between tensile and compressive stress states, and apparently reversible stress changes during growth interruptions. Both ex-situ and in-situ characterization of grain structures and surface topography have also revealed complex processes that include grain growth and texture evolution during and after island coalescence, network formation during island coalescence, retention of deep trenches at grain boundaries, and changes of surface topography during and after film island coalescence. This phenomenology is not accounted for in current understandings of the linkage between stress and structure evolution. In this program, stress evolution will be studied during deposition of a range of materials under a range of conditions. Use of different materials and deposition temperatures will allow observations of behavior that are intermediate to those that have been the focus of prior studies. Use of materials with higher melting temperatures will also allow quenching of surface and grain structures for ex-situ characterization. Surface topography will be monitored during deposition, and during interruptions of depositions, using light scattering techniques. The angle of incidence of the atomic deposition flux will also be varied in order to controllably promote different levels of surface roughness. The size and spacing of the initial islands from which films are formed will also be varied using templated dewetting techniques. Through these studies, understandings will be developed that will allow application-specific engineering of structures and properties of polycrystalline thin films and the micro/nanostructures patterned from them. NON-TECHNICAL SUMMARY The electrical devices and integrated circuits that power our cell phones, computers, and the Internet are created using very thin layers of metals and semiconductors that are formed on flat surfaces of materials like silicon. Extremely small patterns are then made in these films to create millions of devices that are connected to make circuits of devices. Sometimes the devices have parts that physically move as they work. Layers, or films, of different materials are usually made by essentially spraying atoms onto a flat surface. Once the atoms arrive on the surface, they move around to form small crystals and these crystals grow until they run into each other to form a continuous film. The way these crystals form and grow can vary tremendously, depending on how the atoms are sprayed and on which atoms are used. These variations strongly affect the properties of a film, including how easily electrons can move through them or how easily the moving parts can be moved. This makes it very difficult to make complex integrated circuits and limits what can be made. This research program focuses on understanding why these variations occur and on how they can be controlled, so that new devices and circuits can be made. To do this, the researchers will change the way the atoms are sprayed and measure how the properties and structure of films change, while they are being formed.