Lithography technology has been one of the key enablers and drivers for the semiconductor industry for the past several decades. Improvements in lithography are responsible for roughly half of the improvement in cost per function in integrated circuit (IC) technology. The underlying reason for the driving force in semiconductor technology has been the ability to keep the cost for printing a silicon wafer roughly constant while dramatically increasing the number of transistors that can be printed per chip. ICs have always been printed optically with improvements in lens and imaging material technology along with decreases in wavelength used fueling the steady improvement of lithography technology. The end of optical lithography technology has been predicted by many and for many years. Many technologies have been proposed and developed to improve on the performance of optical lithography, but so far none has succeeded. This has been true largely because it has always been more economical to push incremental improvements in the existing optical technology rather than displace it with a new one. At some point in time, the costs for pushing optical lithography technology beyond previously conceived limits may exceed the cost of introducing new technologies. In this paper the author examines the limits of lithography and possible future technologies from both a technical and economic point of view.

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Limits of lithography

Written by a pioneer in the field, this text provides a complete introduction to X-ray microscopy, providing all of the technical background required to use, understand and even develop X-ray microscopes. Starting from the basics of X-ray physics and focusing optics, it goes on to cover imaging theory, tomography, chemical and elemental analysis, lensless imaging, computational methods, instrumentation, radiation damage, and cryomicroscopy, and includes a survey of recent scientific applications. Designed as a 'one-stop' text, it provides a unified notation, and shows how computational methods in different areas are linked with one another. Including numerous derivations, and illustrated with dozens of examples throughout, this is an essential text for academics and practitioners across engineering, the physical sciences and the life sciences who use X-ray microscopy to analyze their specimens, as well as those taking courses in X-ray microscopy.

X-ray Microscopy

The extreme ultraviolet lithography (EUVL) development effort in the United States, at universities, national laboratories, and semiconductor consortia, is focused on solving critical infrastructure issues in the mask, mask handling, source, optics, and resist areas. The current maturity of EUVL infrastructure will likely be sufficient to support the first full-field EUVL exposure tools that have been delivered in 2006. However, a significant effort is still required to make the EUVL infrastructure ready for EUVL manufacturing insertion later this decade. This paper reviews the current status of EUVL infrastructure development in the United States and reports recent progress in EUV mask blank development, EUV source collector and projection optics lifetime, and the evaluation of EUV resist performance.

https://iopscience.iop.org/article/10.1143/JJAP.46.6105/pdf

Extreme Ultraviolet Lithography Development in the United States

The need to print smaller features and tighter pitches drives the development of new photolithography technologies. Extreme Ultraviolet Lithography (EUVL) at 13.5 nm wavelength is expected to provide considerable resolution gain over the current technology based on 193 nm wavelength. In this paper we assess the current status of EUV photoresists and their readiness for EUVL insertion into High Volume Manufacturing (HVM). In addition, we discuss the requirements that EUV photoresists will need to satisfy in the near and long term future.

EUV resists: What's next?

Laser plasmas are intrinsically an attractive soft-x-ray source for projection lithography. Compact, flexible, and small enough to be dedicated to a single installation, they offer an alternative to costly multi-installation synchrotron sources. For laser plasmas to provide ideal sources of soft x rays for projection lithography, their properties must be tuned to optimize several critical parameters. High x-ray conversion in the spectral band relevant to projection lithography is obviously required and has already received the attention of several studies. However, other features, such as the spectral content and direction of the x-ray emission, the plasma and particulate emission, the technology of the target, and efficient laser design, must also be optimized. No systematic study of all these features specifically for projection lithography has yet been made. It is our purpose to optimize these parameters in a coordinated approach, which leads to the design of a source that satisfies all the demanding requirements of an operating lithographic installation. We make an initial investigation of the plasma and particle emission of plasmas that have previously been shown to be good x-ray converters to the 13-nm band. The importance of the results reported may well force new approaches to the design of laser plasma soft-x-ray sources for projection lithography.

O. R. Wood

Papers

Tenth micron lithography with a 10 Hz 37.2 nm sodium laser