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- Books and publications in the field of semiconductor lithography by Chris Mack
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Electron-beam lithography often abbreviated as e-beam lithography , EBL is the practice of scanning a focused beam of electrons to draw custom shapes on a surface covered with an electron-sensitive film called a resist exposing.
The purpose, as with photolithography , is to create very small structures in the resist that can subsequently be transferred to the substrate material, often by etching.
This form of maskless lithography has high resolution and low throughput, limiting its usage to photomask fabrication, low-volume production of semiconductor devices, and research and development. Electron-beam lithography systems can be classified according to both beam shape and beam deflection strategy.
Older systems used Gaussian-shaped beams and scanned these beams in a raster fashion. Newer systems use shaped beams, which may be deflected to various positions in the writing field this is also known as vector scan.
Lower-resolution systems can use thermionic sources, which are usually formed from lanthanum hexaboride. Thermal field emission sources are preferred over cold emission sources, in spite of the former's slightly larger beam size, because they offer better stability over typical writing times of several hours. Both electrostatic and magnetic lenses may be used. However, electrostatic lenses have more aberrations and so are not used for fine focusing.
There is currently [ when? Typically, for very small beam deflections electrostatic deflection "lenses" are used, larger beam deflections require electromagnetic scanning.
Larger patterns require stage moves. An accurate stage is critical for stitching tiling writing fields exactly against each other and pattern overlay aligning a pattern to a previously made one. The minimum time to expose a given area for a given dose is given by the following formula: . This minimum write time does not include time for the stage to move back and forth, as well as time for the beam to be blanked blocked from the wafer during deflection , as well as time for other possible beam corrections and adjustments in the middle of writing.
This is a factor of about 10 million times slower than current optical lithography tools. It is clear that throughput is a serious limitation for electron beam lithography, especially when writing dense patterns over a large area. E-beam lithography is not suitable for high-volume manufacturing because of its limited throughput. The stage moves in between field scans. Currently an optical maskless lithography tool  is much faster than an electron beam tool used at the same resolution for photomask patterning.
As features sizes shrink, the number of incident electrons at fixed dose also shrinks. With each successive process node, as the feature area is halved, the minimum dose must double to maintain the same noise level. Consequently, the tool throughput would be halved with each successive process node. Shot noise is a significant consideration even for mask fabrication.
Despite the high resolution of electron-beam lithography, the generation of defects during electron-beam lithography is often not considered by users.
Defects may be classified into two categories: data-related defects, and physical defects. Data-related defects may be classified further into two sub-categories. Blanking or deflection errors occur when the electron beam is not deflected properly when it is supposed to, while shaping errors occur in variable-shaped beam systems when the wrong shape is projected onto the sample.
These errors can originate either from the electron optical control hardware or the input data that was taped out. As might be expected, larger data files are more susceptible to data-related defects. Physical defects are more varied, and can include sample charging either negative or positive , backscattering calculation errors, dose errors, fogging long-range reflection of backscattered electrons , outgassing, contamination, beam drift and particles.
Since the write time for electron beam lithography can easily exceed a day, "randomly occurring" defects are more likely to occur. Here again, larger data files can present more opportunities for defects.
Photomask defects largely originate during the electron beam lithography used for pattern definition. The primary electrons in the incident beam lose energy upon entering a material through inelastic scattering or collisions with other electrons.
By using the same integration approach, but over the range 2E 0 to E , one obtains by comparing cross-sections that half of the inelastic collisions of the incident electrons produce electrons with kinetic energy greater than E 0. These secondary electrons are capable of breaking bonds with binding energy E 0 at some distance away from the original collision. Additionally, they can generate additional, lower energy electrons, resulting in an electron cascade.
Hence, it is important to recognize the significant contribution of secondary electrons to the spread of the energy deposition. In general, for a molecule AB: . This reaction, also known as "electron attachment" or "dissociative electron attachment" is most likely to occur after the electron has essentially slowed to a halt, since it is easiest to capture at that point.
The cross-section for electron attachment is inversely proportional to electron energy at high energies, but approaches a maximum limiting value at zero energy. With today's electron optics, electron beam widths can routinely go down to a few nanometers.
This is limited mainly by aberrations and space charge. However, the feature resolution limit is determined not by the beam size but by forward scattering or effective beam broadening in the resist , while the pitch resolution limit is determined by secondary electron travel in the resist.
The use of double patterning allowed the spacing between features to be wide enough for the secondary electron scattering to be significantly reduced. The forward scattering can be decreased by using higher energy electrons or thinner resist, but the generation of secondary electrons is inevitable. It is now recognized that for insulating materials like PMMA , low energy electrons can travel quite a far distance several nm is possible.
This is due to the fact that below the ionization potential the only energy loss mechanism is mainly through phonons and polarons. Furthermore dielectric breakdown discharge is possible. This leads to exposure of areas at a significant distance from the desired exposure location. For thicker resists, as the primary electrons move forward, they have an increasing opportunity to scatter laterally from the beam-defined location.
This scattering is called forward scattering. Sometimes the primary electrons are scattered at angles exceeding 90 degrees, i. These electrons are called backscattered electrons and have the same effect as long-range flare in optical projection systems. A large enough dose of backscattered electrons can lead to complete exposure of resist over an area much larger than defined by the beam spot.
The smallest features produced by electron-beam lithography have generally been isolated features, as nested features exacerbate the proximity effect , whereby electrons from exposure of an adjacent region spill over into the exposure of the currently written feature, effectively enlarging its image, and reducing its contrast, i.
Hence, nested feature resolution is harder to control. The proximity effect is also manifest by secondary electrons leaving the top surface of the resist and then returning some tens of nanometers distance away.
Proximity effects due to electron scattering can be addressed by solving the inverse problem and calculating the exposure function E x,y that leads to a dose distribution as close as possible to the desired dose D x,y when convolved by the scattering distribution point spread function PSF x,y.
However, it must be remembered that an error in the applied dose e. Since electrons are charged particles, they tend to charge the substrate negatively unless they can quickly gain access to a path to ground. For a high-energy beam incident on a silicon wafer, virtually all the electrons stop in the wafer where they can follow a path to ground. However, for a quartz substrate such as a photomask , the embedded electrons will take a much longer time to move to ground.
Often the negative charge acquired by a substrate can be compensated or even exceeded by a positive charge on the surface due to secondary electron emission into the vacuum. However, they are of limited use due to their high sheet resistance, which can lead to ineffective grounding. Hence, resist-substrate charging is not repeatable and is difficult to compensate consistently. Negative charging deflects the electron beam away from the charged area while positive charging deflects the electron beam toward the charged area.
Due to the scission efficiency generally being an order of magnitude higher than the crosslinking efficiency, most polymers used for positive-tone electron-beam lithography will crosslink and therefore become negative tone at doses an order of magnitude than doses used for positive tone exposure. The damage was manifest as a loss of material. In , a thiol-ene resist was developed that features native reactive surface groups, which allows the direct functionalization of the resist surface with biomolecules.
To get around the secondary electron generation, it will be imperative to use low-energy electrons as the primary radiation to expose resist. Ideally, these electrons should have energies on the order of not much more than several eV in order to expose the resist without generating any secondary electrons, since they will not have sufficient excess energy.
Such exposure has been demonstrated using a scanning tunneling microscope as the electron beam source. The drawback to using low energy electrons is that it is hard to prevent spreading of the electron beam in the resist.
This phenomenon has been observed frequently in transmission electron microscopy. As a result, it is a slow process, requiring much longer exposure times than conventional electron beam lithography. Also high energy beams always bring up the concern of substrate damage. Interference lithography using electron beams is another possible path for patterning arrays with nanometer-scale periods.
A key advantage of using electrons over photons in interferometry is the much shorter wavelength for the same energy. Despite the various intricacies and subtleties of electron beam lithography at different energies, it remains the most practical way to concentrate the most energy into the smallest area.
There has been significant interest in the development of multiple electron beam approaches to lithography in order to increase throughput. From Wikipedia, the free encyclopedia. Lithographic technique that uses a scanning beam of electrons.
Rooks Emerging Lithographic Technologies IV. Bibcode : SPIE. Kempsell et al. Sunaoshi et al. SPIE vol. Ugajin et al. Chen et al. Feldman; J. Mayer Fundamentals of Surface and Thin Film Analysis. January Slovenian Research Agency. European Space Foundation.
spie handbook of microlithography - optik.uni .spie handbook of microlithography, micromachining
Embed Size px x x x x Electron beam lithography EBL is a specialized technique for creating the extremely fine patterns much smaller than can be seen by the naked eye required by the modern electronics industry for integrated circuits. Derived from the early scanning electron microscopes, the technique in brief consists of scanning a beam of electrons across a surface covered with a resist film sensitive to those electrons, thus depositing energy in the desired pattern in the resist film. The process of forming the beam of electrons and scanning it across a surface is very similar to what happens inside the everyday television or CRT display, but EBL typically has three orders of magnitude better resolution. The main attributes of the technology are 1 it is capable of very high resolution, almost to the atomic level; 2 it is a flexible technique that can work with a variety of materials and an almost infinite number of patterns; 3 it is slow, being one or more orders of magnitude slower than optical lithography; and 4 it is expensive and complicated - electron beam lithography tools can cost many millions of dollars and require frequent service to stay properly maintained.
Ford, S. February 1, J Biomech Eng. February ; 1 : 13— Micromachining was performed in polymethylmethacrylate PMMA using X-ray lithography for the fabrication of miniaturized devices microchips for potential applications in chemical and genetic analyses.
Books and publications in the field of semiconductor lithography by Chris Mack
Electron-beam lithography often abbreviated as e-beam lithography , EBL is the practice of scanning a focused beam of electrons to draw custom shapes on a surface covered with an electron-sensitive film called a resist exposing. The purpose, as with photolithography , is to create very small structures in the resist that can subsequently be transferred to the substrate material, often by etching. This form of maskless lithography has high resolution and low throughput, limiting its usage to photomask fabrication, low-volume production of semiconductor devices, and research and development. Electron-beam lithography systems can be classified according to both beam shape and beam deflection strategy. Older systems used Gaussian-shaped beams and scanned these beams in a raster fashion.
Skip to search form Skip to main content You are currently offline. Some features of the site may not work correctly. DOI: Rai-Choudhury Published Materials Science. View PDF.
Chris A. M This text attempts a difficult task — to capture the fundamental principles of the incredibly fast-changing field of semiconductor microlithography in such a way that these principles may be effectively applied to past, present and future microfabrication technology generations.
Миллиард долларов. Мидж хмыкнула. - Кажется, чуточку дороговато, не правда. - Да уж, - застонал. - Чуточку.
Мне нужна твоя помощь. Сьюзан плохо его понимала. Ей показалось, что столь своевременная кончина Танкадо решила все проблемы. - Коммандер, - сказала она, - если власти говорят, что он умер от сердечного приступа, это значит, мы к его смерти не причастны. Его партнер поймет, что АНБ не несет за нее ответственности. - Не несет ответственности? - Глаза Стратмора расширились от изумления. - Некто шантажирует АНБ и через несколько дней умирает - и мы не несем ответственности.
Беккер стоял с закрытыми глазами, а человек в очках в металлической оправе приближался к. Где-то неподалеку зазвонил колокол. Беккер молча ждал выстрела, который должен оборвать его жизнь. ГЛАВА 89 Лучи утреннего солнца едва успели коснуться крыш Севильи и лабиринта узких улочек под. Колокола на башне Гиральда созывали людей на утреннюю мессу. Этой минуты ждали все жители города. Повсюду в старинных домах отворялись ворота, и люди целыми семьями выходили на улицы.
Включился звук, и послышался фоновой шум. - Установлена аудиосвязь.
ГЛАВА 29 Все еще нервничая из-за столкновения с Хейлом, Сьюзан вглядывалась в стеклянную стену Третьего узла. В шифровалке не было ни души. Хейл замолк, уставившись в свой компьютер. Она мечтала, чтобы он поскорее ушел. Сьюзан подумала, не позвонить ли ей Стратмору.
Если только компьютер понимает, взломал он шифр или. Сьюзан чуть не свалилась со стула. - Что. - Может случиться так, что компьютер, найдя нужный ключ, продолжает поиски, как бы не понимая, что нашел то, что искал. - Стратмор смотрел на нее отсутствующим взглядом.
И повернулась к Джаббе.