/pdf/new-approaches-to-nanofabrication-molding-printing-and-other-9d730ga5zp.pdf

New approaches to nanofabrication: molding, printing, and other techniques.

Lithography is a field in which advances proceed at a swift pace. This book was written to address several needs, and the revisions for the second edition were made with those original objectives in mind. Many new topics have been included in this text commensurate with the progress that has taken place during the past few years, and several subjects are discussed in more detail. This book is intended to serve as an introduction to the science of microlithography for people who are unfamiliar with the subject. Topics directly related to the tools used to manufacture integrated circuits are addressed in depth, including such topics as overlay, the stages of exposure, tools, and light sources. This text also contains numerous references for students who want to investigate particular topics in more detail, and they provide the experienced lithographer with lists of references by topic as well. It is expected that the reader of this book will have a foundation in basic physics and chemistry. No topics will require knowledge of mathematics beyond elementary calculus.

Principles of Lithography

Semiconductor nanowires have been the subject of intensive research investment over the past few decades. Their physical properties afford them applications in a vast network of active microelectronic research fields, including logic device scaling in very large scale integrated circuits, sensor devices, and energy harvesting. A range of routes to semiconductor nanowire production have opened up as a result of advances in nanowire fabrication techniques over the last number of decades. These nanowire fabrication routes can usually be categorized into one of two paradigms, bottom-up or top-down. Microelectronic systems typically rely on integrated device platforms, where each device and component thereof can be individually addressed. This requirement for precise addressability places significant demands on the mode of fabrication, specifically with regard to device definition, placement and density, which have typically been strengths of top-down fabrication processes. However, in recent years, advances i...

Semiconductor Nanowire Fabrication by Bottom-Up and Top-Down Paradigms

A series of baseline displacement measurements have been obtained using 2D Digital Image Correlation (2D-DIC) and images from Scanning Electron Microscopes (SEM). Direct correlation of subsets from a reference image to subsets in a series of uncorrected images is used to identify the presence of non-stationary step-changes in the measured displacements. Using image time integration and recently developed approaches to correct residual drift and spatial distortions in recorded images, results clearly indicate that the corrected SEM images can be used to extract deformations with displacement accuracy of ±0.02 pixels (1 nm at magnification of 10,000) and mean value strain measurements that are consistent with independent estimates and have point-to-point strain variability of ±1.5 × 10−4.

Scanning Electron Microscopy for Quantitative Small and Large Deformation Measurements Part I: SEM Imaging at Magnifications from 200 to 10,000

A direct, accurate and convenient procedure for calibrating the spring constants of probes used for force microscopy/spectroscopy is described. It amounts to deflecting an 'unknown' cantilever with a 'standard' lever, where the standard lever has been precalibrated. The absolute and relative accuracies of the procedure are ±20-30% and ±10-20%, respectively; the former is limited by uncertainties in the determination of the spring constant for the 'standard' lever, as well as that for the 'unknown'. The method differs from others of the static deflection variety by its exploitation of the routine features of current instruments. The technique is compared with other static and dynamic methods currently being used.

https://iopscience.iop.org/article/10.1088/0957-4484/7/3/014/pdf

Determination of the spring constants of probes for force microscopy/spectroscopy

This new understanding and demonstration of features printed by proximity x-ray lithography allows a revolutionary extension and simplification of otherwise established processes for microfabrication. The ability to produce fine features is controlled predominantly by diffraction and photoelectron blur. The diffraction manifests itself as feature bias. In the classical approach the bias is minimized. Bias optimization in terms of mask/wafer gap and resist processing allows the formation, on a wafer, of features smaller than those on the mask: thus producing local demagnification. This demagnification ( ? 3- ? 6) is achieved without lenses or mirrors, but it offers the same advantages as projection optical lithography in terms of critical dimension control. The photoelectron blur is more or less pronounced depending on exposure dose and development conditions. Resist exposure and process can be optimized to utilize a ~ 50% photoelectron energy loss range. In consequence proximity x-ray lithography is extensible to feature sizes below 25 nm, taking advantage of comparatively large mask features (> 100 nm) and large gaps (30-15 ? m). The method is demonstrated for demagnification values down to ? 3.5. To produce DRAM half-pitch fine features, techniques such as multiple exposures with a single development step are proposed.

https://iopscience.iop.org/article/10.1088/0022-3727/32/22/102/pdf

Demagnification in proximity x-ray lithography and extensibility to 25 nm by optimizing Fresnel diffraction

The soft X-ray region around 13 nm (Extreme Ultra Violet, EUV) has become very important for applications to nanopatterning. Typically, high-resolution patterning of less than 50 nm pitch lines and spaces requires optical systems that are complex and expensive. An appealing alternative is provided by interferometric patterning, whereby an EUV beam of relatively high degree of coherence is used to create a pattern by interfering two (or more) parts of the wavefront. Briefly, the radiation from a short undulator illuminates two gratings with pitch in the range of 40–100 nm. The first orders overlap, and in this region an interference pattern is generated with pitch half the original. This technique produces very high resolution 20–50 nm pitch patterns. Thus, in a collaborative effort involving CNTech and the SRC we have designed, constructed and tested a new beamline dedicated to nanopatterning using the radiation from a new undulator on the Aladdin storage ring. The beamline provides 210 mW/cm2 average in-band power flux to the endstation. We note that the beamline is designed to provide a relatively large area exposure, with good wavefront quality in intensity and phase. The endstation supports interferometric lithography techniques, with demonstrated patterning capability down to 40 nm pitch lines and spaces. In addition to nanopattering, a branch-line experimental station is designed for studying the photo-desorption from materials during exposure. The outgassing species are captured and transferred to a gas-chromatograph for off-line characterization. This paper describes the undulator source, the beamline, and the exposure stations.

A novel EUV exposure station for nanotechnology studies

Soft x-ray lithography technology has been applied to fabrication of phase shifting Fresnel Zone Plate (FZP's) for hard x-rays. Effects of the exposure conditions, developing system, and electroplating process parameters on line width and aspect ratio have been analyzed. The process has been optimized and an aspect ratio of 11 has been achieved for 110 nm outermost zone width. SEM and AFM have been used for preliminary metrology of the FZPs. The FZP optical performance was characterized at 8 keV photon energy at the 2-ID-D beam line at the Advanced Photon Source. Focusing efficiencies of 23% for FZPs apertures to 100 microns and 18% for 150-micron-diameter apertures have been obtained. The parameters of the fabricated FZP are in good agreement with the predicted values.

/pdf/progress-in-the-fabrication-of-high-aspect-ratio-zone-plates-43qq5sht6z.pdf

Progress in the fabrication of high-aspect-ratio zone plates by soft x-ray lithography

The successful application of x‐ray lithography to a manufacturing process requires a detailed understanding of the image formation process. In a series of articles, a theoretical study of the optical processes involved in the definition of the image in proximity printing has been presented. In addition to the diffraction process, it is included here that the image formation in the very near field (microgaps) due to the guiding effects in the absorber which alters the boundary condition for diffraction and thus changes the final image pattern. Also presented here is an experimental study designed to verify the predictions of the models of image formation. Preliminary result shows a very large depth‐of‐focus for 0.25 μm features.

Experimental and theoretical study of image bias in x‐ray lithography

The advent of high-brightness x-ray sources in the 10–40 keV region opens new possibilities of experiments with microbeams. Techniques to form these focused beams may be based on glancing mirrors, phase elements, or diffractive optics, in particular Fresnel zone plates (FZPs). Because of the long focal length and large acceptance, FZPs designed to work in the hard x-ray region tend to have quite large diameters and large numbers of zones. For instance, the zone plate described in this article has a 1860 μm diam, a focal length of f=3 m (for 8 keV), and 1860 zones. On a standard pattern generator, circular shapes are always approximated as simpler structures. The tolerance requirement for shape and positions of zones depends on the number of zones, and it is necessary to guarantee that the circular structures are approximated to the required degree of accuracy while keeping the size of the data structure to a reasonable size for processing by the exposure system. For instance, if polygons are used to appro...

/pdf/design-and-fabrication-of-fresnel-zone-plates-with-large-34egcr0c9e.pdf

Q. Leonard

Papers

Demagnification in proximity x-ray lithography and extensibility to 25 nm by optimizing Fresnel diffraction

A novel EUV exposure station for nanotechnology studies

Progress in the fabrication of high-aspect-ratio zone plates by soft x-ray lithography

Experimental and theoretical study of image bias in x‐ray lithography

Design and fabrication of Fresnel zone plates with large numbers of zones