Science and technology of thin films and interfacial layers in ferroelectric and high-dielectric constant heterostructures and application to devices

Abstract

The fabrication of the next generation of complex oxide thin film-based micro and nanoscale devices, such as, for example, low and high density nonvolatile ferroelectric random access memories (FeRAMS), high-dielectric constant (K) high-frequency devices, and the next generation of complimentary metal oxide semiconductor (CMOS) nanoscale devices based on high-K dielectrics, require understanding and control of film growth and interface processes as well as development of materials integration strategies with atomic scale control. In recent years, we developed and applied a unique combination of integrated film synthesis / in situ characterization and ex situ analytical techniques capable of providing information about thin film surface and interface processes at the atomic scale as required for the development of the devices mentioned above. These techniques are also useful for establishing composition-microstructure-property relationships critical for the integration of oxide thin films with semiconductor device platforms for the development of a whole new generation of micro and nanodevices based on film technologies beyond semiconductors and specifically silicon. Our recent work has been focused on developing diffusion barrier layers and heterostructured bottom electrodes that play a critical role in high-density FeRAM integration. We demonstrated that TiAl layers can be used as a material with a double diffusion barrier/bottom electrode functionality for integration of ferroelectric capacitors CMOS devices for fabrication of FeRAMs. We also demonstrated that control of interfaces is critical to the integration of high-K dielectric films with appropriate substrates for the fabrication of high-performance high-frequency devices, and here again a diffusion barrier such as the TiAl layer developed by our group is critical for such integration. These studies revealed that when properly oxidized, nanoscale thick amorphous Ti-Al-O layers exhibit properties that make them strong candidates for application as gate dielectric in the next generation of nanoscale CMOS devices. We discuss here results from systematic studies designed to understand film growth and interface processes and their effect on materials integrations and composition-microstructure-property relationships and oxidation processes using sputter-deposition in conjunction with complementary in situ atomic layer-resolution mass spectroscopy of recoil ion (MSRI) and surface sensitive x-ray photoelectron spectroscopy (XPS) and ex situ transmission electron microscopy and electrical characterization. The unique combination of films synthesis and in situ/ex situ analytical techniques provides a powerful platform for the fundamental and applied materials science needed for the development of the next generation of multifunctional micro and nanoscale devices. A common theme in this article is the science and technology a TiAl layer that exhibit multifunctional characteristics as diffusion barrier and bottom electrode for integration of ferroelectric and high-dielectric constant (K) thing films with appropriate platform substrates for FeRAMs and high-frequency devices, and as a promising high-K dielectric layer for the next generation of nanoscale CMOS gates, flash memories, and other micro and nanodevices that require high-K layers in the device architecture.