Multicolor photolithography using visible light holds the promise of achieving wafer-scale patterning at pitches on the 10 nm scale. Although substantial progress has been made on multicolor techniques, a number of challenges remain to be met before the ultimate resolution of these methods can be reached. These challenges include the development of improved materials, creation of high-quality thin films, transitioning to exposure schemes that rely completely on linear absorption, scaling up to large-area patterning, and developing methods for effective pattern transfer. This paper discusses the state of the art in multicolor photolithography, presents some of the most recent advances in this field, and examines the prospects moving forward.
The demand to create ever finer features at ever tighter pitches has fueled the drive towards lithographic methods that use radiation with the shortest possible wavelength. This approach, however, faces a considerable number of technological challenges that need to be addressed. An alternative, cost-effective approach is multicolor lithography. Inspired by the technology for superresolution in optical microscopy, multicolor visible light approaches led to achieving features down to λ/20 using 3-D multiphoton absorption polymerization (MAP). Although these original efforts in the field involved the use of two colors of light, it has become apparent that 3-color approaches will be required to address the need to pack features together tightly. In this work, we present some of the latest progress in the benchmarking and development of three-color photoresist materials, and demonstrate how the addition of a third color in the exposure scheme can lead to substantial improvements in resolution.
Traditional approaches to improving photolithographic resolution rely on using shorter and shorter wavelengths of electromagnetic radiation. This approach faces ever greater challenges each time the operating wavelength is decreased. Recently, alternative approaches to nanoscale photolithography have been introduced that employ photoresists that are sensitive to multiple colors of visible light. One or more colors of light activate the photoresist, and one or more colors of light can subsequently deactivate it. By controlling the spatial patterns of the colors, it is possible to create features with sizes that are far below the diffraction limit. This approach has been demonstrated for laboratory-based fabrication using multiphoton-absorption-based fabrication, but with improvements in materials it shows great promise for semiconductor lithography as well. A number of approaches to two-color photolithography have been demonstrated. A next generation of schemes that involve a third color of light has the potential to improve the performance of multicolor lithography substantially. The basic premises of both two-color and three-color lithography are discussed, and experimental examples of each type of approach are presented.
Multiphoton absorption polymerization uses nonlinear absorption of laser light to expose a negative-tone photoresist locally, creating three-dimensional structures that can have feature sizes on the sub-100 nm scale. The resolution can be further improved using schemes in which a second beam of light prevents exposure of the photoresist. However, the feature pitch that can be achieved by two-color schemes is limited by the inability to deactivate the photoresist completely. One solution to this problem is to develop a method that instead employs three laser beams. Here we discuss the potential advantages of three-color lithographic schemes and demonstrate new materials that pave the way towards the demonstration of three-color lithography.
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