For the last four decades, the feature sizes of electronic devices for computers have been reduced by a factor of two roughly every 18 months. The result has been a tremendous increase in computational power and reduction in the cost of computing, as measured by cost per function, of nearly 30% annually, so that computations can be done for a billionth of the cost of using the technology of the 1950s. However, devices will soon be so small that the current technology used to produce them will have reached its limits, and the graininess of individual atoms will affect their behavior. This issue focuses on techniques to make tiny devices with dimensions under 45 nm (45 billionths of a meter) for the next generation of devices.Techniques start with coupling currently used 193-nm and 157-nm optical lithography with liquid immersion to reduce the effective wavelength. Other techniques include microprinting, self-assembly, templating, and using supercritical fluids to avoid the effects of surface tension while enabling solution-based processing at such small dimensions. The development of three-dimensional structures that are approaching this scale is also discussed.The methods presented will have an effect on many areas of technology, including, in addition to electronics, advanced sensor technology, energy conversion, catalysis, and nanoelectromechanical systems.

Optical lithography at ultraviolet (UV) wavelengths is the standard process for patterning 90-nm state-of-the-art devices in the semiconductor industry, and extensions to 45 nm and below are currently being explored. With such high resolution, the inherent high throughput of optical lithography will enable the development of a broad range of applications beyond semiconductor electronics. In this article, we will review progress toward nanopatterning with UV light in a variety of materials and geometries.The common thread is the use of short wavelengths, 193 nm or 157 nm, coupled with immersion to further reduce the effective wavelength. Densely spaced, 32-nm (and even smaller) features have been patterned, facilitating the future preparation of large-area, deeply scaled microelectronics, nanophotonics, nanobiology, and molecular-scale self-assembly.

Nanoimprint lithography is a potentially low-cost, high-resolution patterning technique, but most of the surrounding development work has been directed toward tool designs and processing techniques. There remains a tremendous opportunity and need to develop new materials for specific nanoimprint applications. This article provides an overview of relevant materials-related development work for nanoimprint lithographic applications. Material requirements for nanoimprint patterning for the sub-45-nm integrated-circuit regime are discussed, along with proposed nanoimprint applications such as imprintable dielectrics, conducting polymers, biocompatible materials, and materials for microfluidic devices. Polymers available for thermal nanoimprint processing and photocurable precursors for ultraviolet-assisted nanoimprint lithography are discussed.

As the size scale of device features becomes ever smaller, conventional lithographic processes become increasingly more difficult and expensive, especially at a minimum feature size of less than 45 nm. Consequently, to achieve higher-density circuits, storage devices, or displays, it is evident that alternative routes need to be developed to circumvent both cost and manufacturing issues.

An ideal process would be compatible with existing technological processes and manufacturing techniques; these strategies, together with novel materials, could allow significant advances to be made in meeting both short-term and long-term demands for higher-density, faster devices. The self-assembly of block copolymers (BCPs), two polymer chains covalently linked together at one end, provides a robust solution to these challenges. As thin films, immiscible BCPs self-assemble into a range of highly ordered morphologies where the size scale of the features is only limited by the size of the polymer chains and are, therefore, nanoscopic.

While self-assembly alone is sufficient for a number of applications in fabricating advanced microelectronics, directed, self-orienting, self-assembly processes are also required to produce complex devices with the required density and addressability of elements to meet future demands. Both strategies require the design and synthesis of polymers that have well-defined characteristics such that the necessary fine control over the morphology, interfacial properties, and simplicity of processes can be realized. By combining tailored self-assembly processes (a “bottom-up” approach) with microfabrication processes (a “top-down” approach), the ever-present thirst of the consumer for faster, better, and cheaper devices can be met in very simple, yet robust, ways. The integration of novel chemistries with the manipulation of self-assembly will be treated in this article.

Supercritical fluids including carbon dioxide offer a combination of properties that are uniquely suited for device fabrication at the nanoscale. Liquid-like densities, favorable transport properties, and the absence of surface tension enable solution-based processing in an environment that behaves much like a gas. These characteristics provide a means for extending “top-down” processing methods including metal deposition, cleaning, etching, and surface modification chemistries to the smallest device features. The interaction of carbon dioxide with polymeric materials also enables complete structural specification of nanostructured metal oxide films using a “bottom-up” approach in which deposition reactions are conducted within sacrificial, pre-organized templates dilated by the fluid. The result is high-fidelity replication of the template structure in a new material. In particular, block copolymer templates yield well-ordered porous silica and titania films containing spherical or vertically aligned pores that can serve as device substrates for applications in microelectronics, detection arrays, and energy conversion. Finally, the synthesis of nanoparticles and nanowires in supercritical fluids is developing rapidly and offers promise for the efficient production of well-defined materials. In this review, we summarize these developments and discuss their potential for nextgeneration device fabrication.

The controlled formation of submicrometer-scale structures in three dimensions is of increasing interest in many applications. Not intended to produce the smallest structures, but instead aimed at complex topographies, two-photon lithography is an intrinsic 3D lithography technique that enables the fabrication of structures difficult to access by conventional single-photon processes with far greater spatial resolution than other 3D microfabrication techniques. By tightly focusing a femtosecond laser beam into a resin, subsequent photo-induced reactions such as polymerization occur only in the close vicinity of the focal point, allowing the fabrication of a 3D structure by directly writing 3D patterns. The current research effort in two-photon lithography is largely devoted to the design and synthesis of high-efficiency photoinitiators and sensitizers, as well as the development of new materials and systems. This article provides an overview of the progress in two-photon processes for the formation of complex images and the development of patterned structures.