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50-510: LIGA consists of three main processing steps: lithography, electroplating, and molding. There are two main LIGA-fabrication technologies, X-Ray LIGA , which uses X-rays produced by a synchrotron to create high-aspect-ratio structures, and UV LIGA , a more accessible method which uses ultraviolet light to create structures with relatively low aspect ratios. Notable characteristics of X-ray LIGA-fabricated structures include: X-Ray LIGA

100-407: A Cockcroft-Walton generator . Starting from an appropriate initial value determined by the injection energy, the field strength of the dipole magnets is then increased. If the high energy particles are emitted at the end of the acceleration procedure, e.g. to a target or to another accelerator, the field strength is again decreased to injection level, starting a new injection cycle . Depending on

150-405: A mercury lamp , to expose a polymer photoresist, typically SU-8 . Because heating and transmittance are not an issue in optical masks, a simple chromium mask can be substituted for the technically sophisticated X-ray mask. These reductions in complexity make UV LIGA much cheaper and more accessible than its X-ray counterpart. However, UV LIGA is not as effective at producing precision molds and

200-475: A base material on which processing is conducted. This surface could be used to produce new film or layers of material such as deposited coatings . It could be the base to which paint, adhesives, or adhesive tape is bonded. A typical substrate might be rigid such as metal , concrete , or glass , onto which a coating might be deposited. Flexible substrates are also used. Some substrates are anisotropic with surface properties being different depending on

250-469: A constant guiding magnetic field and a constant-frequency electromagnetic field (and is working in classical approximation ), its successor, the isochronous cyclotron , works by local variations of the guiding magnetic field, adapting to the increasing relativistic mass of particles during acceleration. In a synchrotron, this adaptation is done by variation of the magnetic field strength in time, rather than in space. For particles that are not close to

300-413: A cyclic accelerator can impart is typically limited by the maximum strength of the magnetic fields and the minimum radius (maximum curvature ) of the particle path. Thus one method for increasing the energy limit is to use superconducting magnets , these not being limited by magnetic saturation . Electron / positron accelerators may also be limited by the emission of synchrotron radiation , resulting in

350-409: A diameter of 100 mm to 150 mm , and smaller feature sizes. The starting material is a flat substrate , such as a silicon wafer or a polished disc of beryllium, copper, titanium, or other material. The substrate, if not already electrically conductive, is covered with a conductive plating base, typically through sputtering or evaporation . The fabrication of high-aspect-ratio structures requires

400-494: A fixed closed-loop path. The magnetic field which bends the particle beam into its closed path increases with time during the accelerating process, being synchronized to the increasing kinetic energy of the particles. The synchrotron is one of the first accelerator concepts to enable the construction of large-scale facilities, since bending, beam focusing and acceleration can be separated into different components. The most powerful modern particle accelerators use versions of

450-426: A given layout. After exposure, development, and electroplating, the resist is stripped. One method for removing the remaining PMMA is to flood-expose the substrate and use the developing solution to cleanly remove the resist. Alternatively, chemical solvents can be used. Stripping of a thick resist chemically is a lengthy process, taking two to three hours in acetone at room temperature. In multilayer structures, it

500-455: A large synchrotron) costs another two or three million dollars on average. These installations are mostly built by the science funding agencies of governments of developed countries, or by collaborations between several countries in a region, and operated as infrastructure facilities available to scientists from universities and research organisations throughout the country, region, or world. More compact models, however, have been developed, such as

550-469: A partial loss of the particle beam's kinetic energy. The limiting beam energy is reached when the energy lost to the lateral acceleration required to maintain the beam path in a circle equals the energy added each cycle. More powerful accelerators are built by using large radius paths and by using more numerous and more powerful microwave cavities. Lighter particles (such as electrons) lose a larger fraction of their energy when deflected. Practically speaking,

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600-524: A proper exposure. The exposure must be sufficient to meet the requirements of the bottom dose, the exposure under which a photoresist residue will remain, and the top dose, the exposure over which the photoresist will foam. The critical dose is the exposure at which unexposed resist begins to be attacked. Due to the insensitivity of PMMA, a typical exposure time for a 500-μm -thick PMMA is six hours. During exposure, secondary radiation effects such as Fresnel diffraction , mask and substrate fluorescence , and

650-474: A return to the linear accelerator , but with devices significantly longer than those currently in use. There is at present a major effort to design and build the International Linear Collider (ILC), which will consist of two opposing linear accelerators , one for electrons and one for positrons. These will collide at a total center of mass energy of 0.5 TeV . Synchrotron radiation also has

700-462: A synchrotron radiation source through a mask partly covered with a strong X-ray absorbing material. Chemical removal of exposed (or unexposed) photoresist results in a three-dimensional structure, which can be filled by the electrodeposition of metal. The resist is chemically stripped away to produce a metallic mold insert. The mold insert can be used to produce parts in polymers or ceramics through injection molding . The LIGA technique's unique value

750-863: A wide range of applications (see synchrotron light ) and many 2nd and 3rd generation synchrotrons have been built especially to harness it. The largest of those 3rd generation synchrotron light sources are the European Synchrotron Radiation Facility (ESRF) in Grenoble , France, the Advanced Photon Source ( APS ) near Chicago, United States, and SPring-8 in Japan , accelerating electrons up to 6, 7 and 8 GeV , respectively. Synchrotrons which are useful for cutting edge research are large machines, costing tens or hundreds of millions of dollars to construct, and each beamline (there may be 20 to 50 at

800-583: Is a fabrication process in microtechnology that was developed in the early 1980s by a team under the leadership of Erwin Willy Becker and Wolfgang Ehrfeld at the Institute for Nuclear Process Engineering ( Institut für Kernverfahrenstechnik, IKVT) at the Karlsruhe Nuclear Research Center, since renamed to the Institute for Microstructure Technology ( Institut für Mikrostrukturtechnik , IMT) at

850-432: Is common practice to protect metal layers against corrosion by backfilling the structure with a polymer-based encapsulant. At this stage, metal structures can be left on the substrate (e.g., microwave circuitry) or released as the final product (e.g., gears). After stripping, the released metallic components can be used for mass replication through standard means of replication such as stamping or injection molding . In

900-546: Is employed more broadly by several companies, such as Veco, Tecan, Temicon, and Mimotec in Switzerland, who supply the Swiss watch market with metal parts made of nickel and nickel-phosphorus. Below is a gallery of LIGA-fabricated structures arranged by date. Synchrotron A synchrotron is a particular type of cyclic particle accelerator , descended from the cyclotron , in which the accelerating particle beam travels around

950-419: Is that its closed particle path would be cut by a device that emits particles. Thus, schemes were developed to inject pre-accelerated particle beams into a synchrotron. The pre-acceleration can be realized by a chain of other accelerator structures like a linac , a microtron or another synchrotron; all of these in turn need to be fed by a particle source comprising a simple high voltage power supply, typically

1000-504: Is the plated photomask, which provides 3-μm resolution and can be outsourced at a cost on the order of $ 1000 per mask. The least expensive method is a direct photomask, which provides 15-μm resolution in resist 80 μm thick. In summary, masks can cost between $ 1000 and $ 20,000 and take between two weeks and three months for delivery. Due to the small size of the market, each LIGA group typically has its own mask-making capability. Future trends in mask creation include larger formats, from

1050-401: Is the precision obtained by the use of deep X-ray lithography (DXRL). The technique enables microstructures with high aspect ratios and high precision to be fabricated in a variety of materials (metals, plastics, and ceramics). Many of its practitioners and users are associated with, or are located close to, synchrotron facilities. UV LIGA utilizes an inexpensive ultraviolet light source, like

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1100-471: Is the synchrotron, capable of emitting high-power, highly- collimated X-rays. This high collimation permits relatively large distances between the mask and the substrate without the penumbral blurring that occurs from other X-ray sources. In the electron storage ring or synchrotron , a magnetic field constrains electrons to follow a circular path, and the radial acceleration of the electrons causes electromagnetic radiation to be emitted forward. The radiation

1150-494: Is then milled down to the precise height by a fly cutter prior to pattern transfer by X-ray exposure. Because the layer must be relatively free from stress, this glue-down process is preferred over alternative methods such as casting. Further, the cutting of the PMMA sheet by the fly cutter requires specific operating conditions and tools to avoid introducing any stress and crazing of the photoresist. A key enabling technology of LIGA

1200-485: Is thus strongly collimated in the forward direction and can be assumed to be parallel for lithographic purposes. Because of the much higher flux of usable collimated X-rays, shorter exposure times become possible. Photon energies for a LIGA exposure are approximately distributed between 2.5 and 15 keV . Unlike optical lithography, there are multiple exposure limits, identified as the top dose, bottom dose, and critical dose, whose values must be determined experimentally for

1250-502: Is thus used when cost must be kept low and very high aspect ratios are not required. X-ray masks are composed of a transparent low- Z carrier, a patterned high- Z absorber, and a metallic ring for alignment and heat removal. Due to extreme temperature variations induced by the X-ray exposure, carriers are fabricated from materials with high thermal conductivity to reduce thermal gradients. Currently, vitreous carbon and graphite are considered

1300-469: The Compact Light Source . Substrate (materials science) Substrate is a term used in materials science and engineering to describe the base material on which processing is conducted. Surfaces have different uses, including producing new film or layers of material and being a base to which another substance is bonded. In materials science and engineering , a substrate refers to

1350-485: The Karlsruhe Institute of Technology (KIT). LIGA was one of the first major techniques to allow on-demand manufacturing of high-aspect-ratio structures (structures that are much taller than wide) with lateral precision below one micrometer. In the process, an X-ray sensitive polymer photoresist, typically PMMA , bonded to an electrically conductive substrate, is exposed to parallel beams of high-energy X-rays from

1400-571: The 1990s, LIGA was a cutting-edge MEMS fabrication technology, resulting in the design of components showcasing the technique's unique versatility. Several companies that begin using the LIGA process later changed their business model (e.g., Steag microParts becoming Boehringer Ingelheim microParts, Mezzo Technologies). Currently, only two companies, HTmicro and microworks, continue their work in LIGA, benefiting from limitations of other competing fabrication technologies. UV LIGA, due to its lower production cost,

1450-599: The European Laboratory for High Energy Physics ( CERN ), has roughly seven times this energy (so proton-proton collisions occur at roughly 14 TeV). It is housed in the 27 km tunnel which formerly housed the Large Electron Positron ( LEP ) collider, so it will maintain the claim as the largest scientific device ever built. The LHC will also accelerate heavy ions (such as lead ) up to an energy of 1.15 PeV . The largest device of this type seriously proposed

1500-519: The adoption of the SI prefix giga- ). A number of transuranium elements , unseen in the natural world, were first created with this machine. This site is also the location of one of the first large bubble chambers used to examine the results of the atomic collisions produced here. Another early large synchrotron is the Cosmotron built at Brookhaven National Laboratory which reached 3.3 GeV in 1953. Among

1550-414: The anode. Difficulties associated with plating into PMMA molds include voids, where hydrogen bubbles nucleate on contaminants; chemical incompatibility, where the plating solution attacks the photoresist; and mechanical incompatibility, where film stress causes the plated layer to lose adhesion. These difficulties can be overcome through the empirical optimization of the plating chemistry and environment for

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1600-674: The best material, as their use significantly reduces side-wall roughness. Silicon , silicon nitride , titanium , and diamond are also used as carrier substrates but not preferred, as the required thin membranes are comparatively fragile and titanium masks tend to round sharp features due to edge fluorescence. Absorbers are gold, nickel, copper, tin, lead, and other X-ray-absorbing metals. Masks can be fabricated in several fashions. The most accurate and expensive masks are those created by electron-beam lithography , which provides resolutions as fine as 0.1 μm in resist 4 μm thick and 3 μm features in resist 20 μm thick. An intermediate method

1650-458: The complete separation of the accelerator into components with specialized functions along the particle path, shaping the path into a round-cornered polygon. Some important components are given by radio frequency cavities for direct acceleration, dipole magnets ( bending magnets ) for deflection of particles (to close the path), and quadrupole / sextupole magnets for beam focusing. The combination of time-dependent guiding magnetic fields and

1700-451: The direction: examples include wood and paper products. With all coating processes, the condition of the surface of the substrate can strongly affect the bond of subsequent layers. This can include cleanliness, smoothness, surface energy , moisture, etc. Coating can be by a variety of processes, including: In optics , glass may be used as a substrate for an optical coating —either an antireflection coating to reduce reflection, or

1750-422: The electroplating step, nickel, copper, or gold is plated upward from the metalized substrate into the voids left by the removed photoresist. Taking place in an electrolytic cell, the current density, temperature, and solution are carefully controlled to ensure proper plating. In the case of nickel deposition from NiCl 2 in a KCl solution, Ni is deposited on the cathode (metalized substrate) and Cl 2 evolves at

1800-477: The end of the Cold War resulted in a change of scientific funding priorities that contributed to its ultimate cancellation. However, the tunnel built for its placement still remains, although empty. While there is still potential for yet more powerful proton and heavy particle cyclic accelerators, it appears that the next step up in electron beam energy must avoid losses due to synchrotron radiation . This will require

1850-410: The energy of electron / positron accelerators is limited by this radiation loss, while this does not play a significant role in the dynamics of proton or ion accelerators. The energy of such accelerators is limited strictly by the strength of magnets and by the cost. Unlike in a cyclotron, synchrotrons are unable to accelerate particles from zero kinetic energy; one of the obvious reasons for this

1900-727: The few synchrotrons around the world, 16 are located in the United States. Many of them belong to national laboratories; few are located in universities. Until August 2008, the highest energy collider in the world was the Tevatron , at the Fermi National Accelerator Laboratory , in the United States . It accelerated protons and antiprotons to slightly less than 1 TeV of kinetic energy and collided them together. The Large Hadron Collider (LHC), which has been built at

1950-399: The generation of Auger electrons and photoelectrons can lead to overexposure. During exposure, the X-ray mask and the mask holder are heated directly by X-ray absorption and cooled by forced convection from nitrogen jets. Temperature rise in PMMA resist is mainly from heat conducted from the substrate backward into the resist and from the mask plate through the inner cavity air forward to

2000-524: The method of magnet control used, the time interval for one cycle can vary substantially between different installations. One of the early large synchrotrons, now retired, is the Bevatron , constructed in 1950 at the Lawrence Berkeley Laboratory . The name of this proton accelerator comes from its power, in the range of 6.3 GeV (then called BeV for billion electron volts ; the name predates

2050-405: The particles an initial acceleration, and a lower energy synchrotron which is sometimes called a booster to increase the energy of the particles before they are injected into the high energy synchrotron ring. Several specialized types of synchrotron machines are used today: The synchrotron evolved from the cyclotron , the first cyclic particle accelerator. While a classical cyclotron uses both

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2100-408: The required ratio of dissolution rates and reduces stress-related cracking from swelling in comparison to conventional PMMA developers. After development, the substrate is rinsed with deionized water and dried either in a vacuum or by spinning. At this stage, the PMMA structures can be released as the final product (e.g., optical components) or can be used as molds for subsequent metal deposition. In

2150-508: The resist, with X-ray absorption being tertiary. Thermal effects include chemistry variations due to resist heating and geometry-dependent mask deformation. For high-aspect-ratio structures, the resist-developer system is required to have a ratio of dissolution rates in the exposed and unexposed areas of 1000:1. The standard, empirically optimized developer is a mixture of tetrahydro-1,4-oxazine (20%), 2-aminoethanol-1 (5%), 2-(2-butoxyethoxy)ethanol (60%), and water (15%). This developer provides

2200-426: The speed of light , the frequency of the applied electromagnetic field may also change to follow their non-constant circulation time. By increasing these parameters accordingly as the particles gain energy, their circulation path can be held constant as they are accelerated. This allows the vacuum chamber for the particles to be a large thin torus , rather than a disk as in previous, compact accelerator designs. Also,

2250-463: The strong focusing principle enabled the design and operation of modern large-scale accelerator facilities like colliders and synchrotron light sources . The straight sections along the closed path in such facilities are not only required for radio frequency cavities, but also for particle detectors (in colliders) and photon generation devices such as wigglers and undulators (in third generation synchrotron light sources). The maximum energy that

2300-484: The synchrotron design. The largest synchrotron-type accelerator, also the largest particle accelerator in the world, is the 27-kilometre-circumference (17 mi) Large Hadron Collider (LHC) near Geneva, Switzerland, built in 2008 by the European Organization for Nuclear Research (CERN). It can accelerate beams of protons to an energy of 7 tera  electronvolts (TeV or 10 eV). The synchrotron principle

2350-412: The thin profile of the vacuum chamber allowed for a more efficient use of magnetic fields than in a cyclotron, enabling the cost-effective construction of larger synchrotrons. While the first synchrotrons and storage rings like the Cosmotron and ADA strictly used the toroid shape, the strong focusing principle independently discovered by Ernest Courant et al. and Nicholas Christofilos allowed

2400-424: The use of a photoresist able to form a mold with vertical sidewalls; thus, the photoresist must have a high selectivity and be relatively free from stress when applied in thick layers. The typical choice, poly(methyl methacrylate) ( PMMA ), is applied to the substrate by a glue-down process in which a precast, high-molecular-weight sheet of PMMA is attached to the plating base on the substrate. The applied photoresist

2450-522: Was invented by Vladimir Veksler in 1944. Edwin McMillan constructed the first electron synchrotron in 1945, arriving at the idea independently, having missed Veksler's publication (which was only available in a Soviet journal, although in English). The first proton synchrotron was designed by Sir Marcus Oliphant and built in 1952. Large synchrotrons usually have a linear accelerator (linac) to give

2500-566: Was the Superconducting Super Collider (SSC), which was to be built in the United States . This design, like others, used superconducting magnets which allow more intense magnetic fields to be created without the limitations of core saturation. While construction was begun, the project was cancelled in 1994, citing excessive budget overruns — this was due to naïve cost estimation and economic management issues rather than any basic engineering flaws. It can also be argued that

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