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Photomask
A PHOTOMASK is an opaque plate with holes or transparencies that allow light to shine through in a defined pattern. They are commonly used in photolithography . CONTENTS * 1 Overview * 2 Mask Error Enhancement Factor (MEEF) * 3 Pellicles * 4 Leading commercial photomask manufacturers * 5 See also * 6 References OVERVIEW A simulated photomask. The thicker features are the integrated circuit that is desired to be printed on the wafer. The thinner features are assists that do not print themselves, but help the integrated circuit print better out-of-focus. The zig-zag appearance of the photomask is because optical proximity correction was applied to it to create a better print. Lithographic photomasks are typically transparent fused silica blanks covered with a pattern defined with a chrome metal-absorbing film. Photomasks are used at wavelengths of 365 nm , 248 nm, and 193 nm. Photomasks have also been developed for other forms of radiation such as 157 nm, 13.5 nm (EUV ), X-ray , electrons , and ions ; but these require entirely new materials for the substrate and the pattern film. A set of photomasks , each defining a pattern layer in integrated circuit fabrication , is fed into a photolithography stepper or scanner , and individually selected for exposure. In double patterning techniques, a photomask would correspond to a subset of the layer pattern
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Photolithography
PHOTOLITHOGRAPHY, also termed OPTICAL LITHOGRAPHY or UV LITHOGRAPHY, is a process used in microfabrication to pattern parts of a thin film or the bulk of a substrate . It uses light to transfer a geometric pattern from a photomask to a light-sensitive chemical "photoresist ", or simply "resist," on the substrate. A series of chemical treatments then either engraves the exposure pattern into, or enables deposition of a new material in the desired pattern upon the material underneath the photo resist. For example, in complex integrated circuits , a modern CMOS
CMOS
wafer will go through the photolithographic cycle up to 50 times. Photolithography
Photolithography
shares some fundamental principles with photography in that the pattern in the etching resist is created by exposing it to light , either directly (without using a mask) or with a projected image using an optical mask . This procedure is comparable to a high precision version of the method used to make printed circuit boards . Subsequent stages in the process have more in common with etching than with lithographic printing . It is used because it can create extremely small patterns (down to a few tens of nanometers in size), it affords exact control over the shape and size of the objects it creates, and because it can create patterns over an entire surface cost-effectively
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Optical Proximity Correction
OPTICAL PROXIMITY CORRECTION (OPC) is a photolithography enhancement technique commonly used to compensate for image errors due to diffraction or process effects. The need for OPC is seen mainly in the making of semiconductor devices and is due to the limitations of light to maintain the edge placement integrity of the original design, after processing, into the etched image on the silicon wafer. These projected images appear with irregularities such as line widths that are narrower or wider than designed, these are amenable to compensation by changing the pattern on the photomask used for imaging. Other distortions such as rounded corners are driven by the resolution of the optical imaging tool and are harder to compensate for. Such distortions, if not corrected for, may significantly alter the electrical properties of what was being fabricated. Optical proximity correction corrects these errors by moving edges or adding extra polygons to the pattern written on the photomask. This may be driven by pre-computed look-up tables based on width and spacing between features (known as rule based OPC) or by using compact models to dynamically simulate the final pattern and thereby drive the movement of edges, typically broken into sections, to find the best solution, (this is known as model based OPC). The objective is to reproduce in the silicon wafer, as well as possible, the original layout drawn by the designer
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Fused Silica
FUSED QUARTZ or FUSED SILICA is glass consisting of silica in amorphous (non-crystalline ) form. It differs from traditional glasses in containing no other ingredients, which are typically added to glass to lower the melt temperature. Although the terms quartz and fused silica are used interchangeably, the fundamental structures and creation of each glass differ. Fused silica, therefore, has high working and melting temperatures. The optical and thermal properties of fused quartz are superior to those of other types of glass due to its purity. For these reasons, it finds use in situations such as semiconductor fabrication and laboratory equipment. It transmits ultraviolet better than other glasses, so is used to make lenses and optics for the ultraviolet spectrum. Its low coefficient of thermal expansion also makes it a useful material for precision mirror substrates. CONTENTS * 1 Manufacture * 2 Fusion * 3 Product quality * 4 Applications * 4.1 Refractory material applications * 5 Physical properties * 6 Optical properties * 7 Typical properties of clear fused silica * 8 See also * 9 References * 10 External links MANUFACTURE Fused quartz is produced by fusing (melting) high-purity silica sand, which consists of quartz crystals
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Nanometer
The NANOMETRE (International spelling as used by the International Bureau of Weights and Measures ; SI symbol: NM) or NANOMETER (American spelling ) is a unit of length in the metric system , equal to one billionth of a metre (6991100000000000000♠0.000000001 m). The name combines the SI prefix
SI prefix
nano- (from the Ancient Greek
Ancient Greek
νάνος, nanos, "dwarf") with the parent unit name metre (from Greek μέτρον, metrοn, "unit of measurement"). It can be written in scientific notation as 6991100000000000000♠1×10−9 m, in engineering notation as 1 E−9 m, and is simply 1/7009100000000000000♠1000000000 metres. One nanometre equals ten ångströms . When used as a prefix for something other than a unit of measure (as in "nanoscience"), NANO refers to nanotechnology , or phenomena typically occurring on a scale of nanometres (see nanoscopic scale ). The nanometre is often used to express dimensions on an atomic scale: the diameter of a helium atom, for example, is about 0.1 nm, and that of a ribosome is about 20 nm. The nanometre is also commonly used to specify the wavelength of electromagnetic radiation near the visible part of the spectrum : visible light ranges from around 400 to 700 nm. The ångström, which is equal to 0.1 nm, was formerly used for these purposes, but is still used in other fields
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Extreme Ultraviolet Lithography
EXTREME ULTRAVIOLET LITHOGRAPHY (also known as EUV or EUVL) is a next-generation lithography technology using an extreme ultraviolet (EUV) wavelength, currently expected to be 13.5 nm. EUV is currently being developed for high volume use by 2020. CONTENTS* 1 Tool * 1.1 Resource requirements * 2 Light source power and throughput * 3 EUV-specific optical issues * 3.1 H-V asymmetry * 3.2 Asymmetries in sets of parallel lines * 3.3 Pattern shift from defocus (non-telecentricity) * 3.4 Line tip effects * 3.5 Slit position dependence * 4 Enhancements for EUV Patterning * 4.1 Assist features * 4.2 Source-mask optimization * 4.3 Optimum illumination vs. Pitch * 4.3.1 Outlook for Advanced Nodes * 5 Photoresist exposure * 5.1 Impact of photoelectron and secondary electron travel on resolution * 5.2 DUV Sensitivity * 5.3 Resist outgassing * 6 Contamination effects * 6.1 Membrane * 7 EUV Mask Defects * 7.1 Multilayer damage * 7.2 Pellicles * 7.3 Hydrogen
Hydrogen
bulging defects * 8 Throughput-scaling limits * 8.1 Reduced fields * 8.2 Shot noise: the statistical resolution limit * 9 Uptime and productivity * 10 Deployment History * 11 EUV and multiple patterning * 12 Single patterning extension: Anamorphic High-NA * 13 Beyond EUV wavelength * 14 References * 15 Further reading * 16 Related links TOOL EUVL tool, Lawrence Livermore National Laboratory
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X-ray
X-RADIATION (composed of X-RAYS) is a form of electromagnetic radiation . Most X-rays have a wavelength ranging from 0.01 to 10 nanometers , corresponding to frequencies in the range 30 petahertz to 30 exahertz (3×1016 Hz to 3×1019 Hz) and energies in the range 100 eV to 100 keV . X-ray wavelengths are shorter than those of UV rays and typically longer than those of gamma rays . In many languages, X-radiation is referred to with terms meaning RöNTGEN RADIATION, after the German scientist Wilhelm Röntgen , who usually is credited as its discoverer, and who had named it _X-radiation_ to signify an unknown type of radiation. Spelling of _X-ray(s)_ in the English language includes the variants _x-ray(s)_, _xray(s)_, and _X ray(s)_
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Electrons
The ELECTRON is a subatomic particle , symbol e− or β− , with a negative elementary electric charge . Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no known components or substructure. The electron has a mass that is approximately 1/1836 that of the proton . Quantum mechanical properties of the electron include an intrinsic angular momentum (spin ) of a half-integer value, expressed in units of the reduced Planck constant , _ħ_. As it is a fermion , no two electrons can occupy the same quantum state , in accordance with the Pauli exclusion principle . Like all elementary particles, electrons exhibit properties of both particles and waves : they can collide with other particles and can be diffracted like light. The wave properties of electrons are easier to observe with experiments than those of other particles like neutrons and protons because electrons have a lower mass and hence a longer De Broglie wavelength for a given energy. Electrons play an essential role in numerous physical phenomena, such as electricity , magnetism , and thermal conductivity , and they also participate in gravitational , electromagnetic and weak interactions . Since an electron has charge, it has a surrounding electric field , and if that electron is moving relative to an observer it will generate a magnetic field
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Ions
An ION (/ˈaɪən, -ɒn/ ) is an atom , or a molecule , in which the total number of electrons is not equal to the total number of protons , giving the atom or molecule a net positive or negative electrical charge . An atom, or molecule, with a net positive charge is a cation . An atom, or molecule, with a net negative charge is an anion . Because of their opposite electric charges, cations and anions attract each other and readily form ionic compounds , such as salts . Ions can be created by chemical means, such as the dissolution of a salt into water, or by physical means, such as passing a direct current through a conducting solution, which will dissolve the anode via ionization . Ions consisting of only a single atom are atomic or monatomic ions . If they consist of two or more atoms, then they are called either molecular ions , or polyatomic ions . In the case of physical ionization of a medium, such as a gas, what are known as "ion pairs" are created by ion impact, and each pair consists of a free electron and a positive ion
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Photomask Set
A MASK SET or a PHOTOMASK SET is a series of electronic data that define geometry for the photolithography steps of semiconductor fabrication. Each of the physical masks generated from this data is called a photomask . A mask set for a modern process typically contains as many as twenty or more masks, each of which defines a specific photolithographic step in the semiconductor fabrication process. Examples of masks include: * p-well * n-well * active * poly * p-select * n-select * contact * metal1, 2, 3...For more information, see photolithography and semiconductor manufacturing . REFERENCES* Saint, Christopher and Judy. (2002). IC Layout Basics. McGraw-Hill. ISBN 0-07-138625-4 Retrieved from "https://en.wikipedia.org/w/index.php?title=Mask_set additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy .® is a registered trademark of the Wikimedia Foundation, Inc
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Semiconductor Device Fabrication
SEMICONDUCTOR DEVICE FABRICATION is the process used to create the integrated circuits that are present in everyday electrical and electronic devices. It is a multiple-step sequence of photo lithographic and chemical processing steps during which electronic circuits are gradually created on a wafer made of pure semiconducting material. Silicon
Silicon
is almost always used, but various compound semiconductors are used for specialized applications. The entire manufacturing process, from start to packaged chips ready for shipment, takes six to eight weeks and is performed in highly specialized facilities referred to as fabs . CONTENTS * 1 History * 2 Wafers * 3 Processing * 3.1 Front-end-of-line (FEOL) processing * 3.1.1 Gate oxide and implants * 3.2 Back-end-of-line (BEOL) processing * 3.2.1 Metal layers * 3.2.2 Interconnect * 4 Wafer test * 5 Device test * 6 Die preparation
Die preparation
* 7 Packaging * 8 List of steps * 9 Hazardous materials * 10 See also * 11 References * 12 Further reading * 13 External links HISTORY Main article: Integrated circuit
Integrated circuit
When feature widths were far greater than about 10 micrometres , purity was not the issue that it is today in device manufacturing. As devices became more integrated, cleanrooms became even cleaner
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Stepper
A STEPPER is a device used in the manufacture of integrated circuits (ICs) that is similar in operation to a slide projector or a photographic enlarger . The term "stepper" is short for step-and-repeat camera. Steppers are an essential part of the complex process, called photolithography , that creates millions of microscopic circuit elements on the surface of tiny chips of silicon. These chips form the heart of ICs such as computer processors, memory chips, and many other devices. CONTENTS * 1 The stepper\'s role in photolithography * 2 Basic operation * 3 Major subassemblies * 4 Illumination and the challenges of improving resolution * 5 Scanners * 6 See also * 7 References THE STEPPER\'S ROLE IN PHOTOLITHOGRAPHYElements of the circuit to be created on the IC are reproduced in a pattern of transparent and opaque areas on the surface of a quartz plate called a photomask or reticle. The stepper passes light through the reticle, forming an image of the reticle pattern. The image is focused and reduced by a lens, and projected onto the surface of a silicon wafer that is coated with a photosensitive material called photoresist . After exposure in the stepper, the coated wafer is developed like photographic film, causing the photoresist to dissolve in certain areas according to the amount of light the areas received during exposure. These areas of photoresist and no photoresist reproduce the pattern on the reticle
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Double Patterning
MULTIPLE PATTERNING (or MULTI-PATTERNING) is a class of technologies for manufacturing integrated circuits (ICs), developed for photolithography to enhance the feature density. It is expected to be necessary for the upcoming 10 nm and 7 nm node semiconductor processes and beyond. The premise is that a single lithographic exposure may not be enough to provide sufficient resolution. Hence additional exposures would be needed, or else positioning patterns using etched feature sidewalls (using spacers) would be necessary. SELF-ALIGNED DOUBLE AND QUADRUPLE PATTERNING WITH BLOCKING. Above: Self-aligned double patterning (SADP) with a block mask is commonly used for 40-50 nm pitches. Below: An option for sub-40 nm pitch metal patterning (used by Intel) is to make use of self-aligned quadruple patterning (SAQP). In this example, two block patterns are used after SAQP. Although EUV has been projected to be the next-generation lithography of choice, it would still require more than one lithographic exposure, due to the foreseen need to first print a series of lines and then cut them; a single EUV exposure pattern has difficulty with line end-to-end spacing control. It is also likely more than one cut would be needed, even for EUV. Even for electron beam lithography, single exposure appears insufficient at ≈10 nm half-pitch, hence requiring double patterning
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Mass Production
MASS PRODUCTION, also known as flow production or continuous production, is the production of large amounts of standardized products, including and especially on assembly lines . Together with job production and batch production , it is one of the three main production methods. The term _mass production_ was popularized by a 1926 article in the _Encyclopædia Britannica_ supplement that was written based on correspondence with Ford Motor Company . The _New York Times_ used the term in the title of an article that appeared before publication of the _Britannica_ article. The concepts of mass production are applied to various kinds of products, from fluids and particulates handled in bulk (such as food , fuel , chemicals , and mined minerals ) to discrete solid parts (such as fasteners) to assemblies of such parts (such as household appliances and automobiles ). Mass production is a diverse field, but it can generally be contrasted with craft production or distributed manufacturing . Some mass production techniques, such as standardized sizes and production lines, predate the Industrial Revolution by many centuries; however, it was not until the introduction of machine tools and techniques to produce interchangeable parts were developed in the mid 19th century that modern mass production was possible
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Integrated Circuit
An INTEGRATED CIRCUIT or MONOLITHIC INTEGRATED CIRCUIT (also referred to as an IC, a CHIP, or a MICROCHIP) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material , normally silicon . The integration of large numbers of tiny transistors into a small chip results in circuits that are orders of magnitude smaller, cheaper, and faster than those constructed of discrete electronic components . The IC's mass production capability, reliability and building-block approach to circuit design has ensured the rapid adoption of standardized ICs in place of designs using discrete transistors. ICs are now used in virtually all electronic equipment and have revolutionized the world of electronics . Computers , mobile phones , and other digital home appliances and are now inextricable parts of the structure of modern societies, made possible by the small size and low cost of ICs. ICs were made possible by experimental discoveries showing that semiconductor devices could perform the functions of vacuum tubes , and by mid-20th-century technology advancements in semiconductor device fabrication . Since their origins in the 1960s, the size, speed, and capacity of chips have progressed enormously, driven by technical advances that allow more and more transistors on chips of the same size - a modern chip may have several billion transistors in an area the size of a human fingernail
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Phase-shift Mask
PHASE-SHIFT MASKS are photomasks that take advantage of the interference generated by phase differences to improve image resolution in photolithography . There exist ALTERNATING and ATTENUATED PHASE SHIFT MASKS. A phase-shift mask relies on the fact that light passing through a transparent media will undergo a phase change as a function of its optical thickness. CONTENTS * 1 Types and effects * 2 Application * 3 References * 4 Further reading * 5 External links TYPES AND EFFECTSA conventional photomask is a transparent plate with the same thickness everywhere, parts of which are covered with non-transmitting material in order to create a pattern on the semiconductor wafer when illuminated. In alternating phase-shift masks, certain transmitting regions are made thinner or thicker. That induces a phase-shift in the light traveling through those regions of the mask (see the illustration). When the thickness is suitably chosen, the interference of the phase-shifted light with the light coming from unmodified regions of the mask has the effect of improving the contrast on some parts of the wafer, which may ultimately increase the resolution on the wafer. The ideal case is a phase shift of 180 degrees, which results in all the incident light being scattered. However, even for smaller phase shifts, the amount of scattering is not negligible