SANTA CLARA, Calif., August 15 - Coherent Inc. Announced it has completed its tender offer for the outstanding shares of its Lambda Physik AG subsidiary, based in Gottingen, Germany. The offer was made through Coherent’s German holding company, Coherent Holding GmbH, at 9.25 euros per share.A total of 93.95 percent of Lambda's registered share capital, inclusive of shares Coherent already owns, was acquired in the offer.Coherent said efforts are underway to acquire additional shares in order to achieve 95 percent ownership, which will call for a shareholders meeting to adopt a squeeze-out resolution to acquire 100 percent ownership.
Device provides location controlled, high resolution, high power silicon film treatment with low temperature process. It is available with Lambda Physik LPX(R).
For other uses of photolithography in printing, see. For the same process applied to metal, see.Photolithography, also called optical lithography or UV lithography, is a process used in to pattern parts of a or the bulk of a (also called a wafer). It uses light to transfer a from a (also called an optical mask) to a (that is, light-sensitive) chemical on the substrate. A series of then either the exposure pattern into the material or enables deposition of a new material in the desired pattern upon the material underneath the photoresist.
In complex, a wafer may go through the photolithographic cycle as many as 50 times.Photolithography shares some fundamental principles with in that the pattern in the photoresist etching is created by exposing it to, either directly (without using a mask) or with a projected image using a photomask. This procedure is comparable to a high precision version of the method used to make.
Subsequent stages in the process have more in common with etching than with. This method can create extremely small patterns, down to a few tens of in size. It provides precise control of the shape and size of the objects it creates and can create patterns over an entire surface cost-effectively. Its main disadvantages are that it requires a flat substrate to start with, it is not very effective at creating shapes that are not flat, and it can require extremely clean operating conditions.
Photolithography is the standard method of printed circuit board (PCB). Simplified illustration of dry etching using positive photoresist during a photolithography process in semiconductor microfabrication (not to scale).A single iteration of photolithography combines several steps in sequence. Modern cleanrooms use automated, wafer track systems to coordinate the process. The procedure described here omits some advanced treatments, such as thinning agents or edge-bead removal.
Cleaning If organic or inorganic contaminations are present on the wafer surface, they are usually removed by wet chemical treatment, e.g. The procedure based on solutions containing.
Other solutions made with trichloroethylene, acetone or methanol can also be used to clean. Preparation The wafer is initially heated to a temperature sufficient to drive off any moisture that may be present on the wafer surface; 150 °C for ten minutes is sufficient. Wafers that have been in storage must be chemically cleaned to remove. A or 'adhesion promoter', such as, is applied to promote adhesion of the photoresist to the wafer. The surface layer of silicon dioxide on the wafer reacts with HMDS to form tri-methylated silicon-dioxide, a highly water repellent layer not unlike the layer of wax on a car's paint. This water repellent layer prevents the aqueous developer from penetrating between the photoresist layer and the wafer's surface, thus preventing so-called lifting of small photoresist structures in the (developing) pattern. In order to ensure the development of the image, it is best covered and placed over a hot plate and let it dry while stabilizing the temperature at 120 °C.
Photoresist application The wafer is covered with. Thus, the top layer of resist is quickly ejected from the wafer's edge while the bottom layer still creeps slowly radially along the wafer. In this way, any 'bump' or 'ridge' of resist is removed, leaving a very flat layer.
Final thickness is also determined by the evaporation of liquid solvents from the resist. For very small, dense features (. Main article:In etching, a liquid ('wet') or ('dry') chemical agent removes the uppermost layer of the substrate in the areas that are not protected by photoresist. In, dry etching techniques are generally used, as they can be made, in order to avoid significant undercutting of the photoresist pattern. This is essential when the width of the features to be defined is similar to or less than the thickness of the material being etched (i.e. When the aspect ratio approaches unity). Wet etch processes are generally isotropic in nature, which is often indispensable for, where suspended structures must be 'released' from the underlying layer.The development of low-defectivity anisotropic dry-etch process has enabled the ever-smaller features defined photolithographically in the resist to be transferred to the substrate material.Photoresist removal After a photoresist is no longer needed, it must be removed from the substrate.
This usually requires a liquid 'resist stripper', which chemically alters the resist so that it no longer adheres to the substrate. Alternatively, photoresist may be removed by a plasma containing, which oxidizes it. This process is called, and resembles dry etching.
Use of solvent for photoresist is another method used to remove an image. When the resist has been dissolved, the solvent can be removed by heating to 80 °C without leaving any residue.
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Exposure ('printing') systems. The wafer track portion of an aligner that uses 365 nm ultraviolet lightExposure systems typically produce an image on the wafer using a.
The photomask blocks light in some areas and lets it pass in others. ( projects a precise beam directly onto the wafer without using a mask, but it is not widely used in commercial processes.) Exposure systems may be classified by the optics that transfer the image from the mask to the wafer.Photolithography produces better thin film transistor structures than, due to smoother printed layers, less wavy patterns, and more accurate drain-source electrode registration. Contact and proximity. Main article:A contact printer, the simplest exposure system, puts a photomask in direct contact with the wafer and exposes it to a uniform light. A proximity printer puts a small gap between the photomask and wafer. In both cases, the mask covers the entire wafer, and simultaneously patterns every die.Contact printing is liable to damage both the mask and the wafer, and this was the primary reason it was abandoned for high volume production. Both contact and proximity lithography require the light intensity to be uniform across an entire wafer, and the mask to align precisely to features already on the wafer.
As modern processes use increasingly large wafers, these conditions become increasingly difficult.Research and prototyping processes often use contact or proximity lithography, because it uses inexpensive hardware and can achieve high optical resolution. The resolution in proximity lithography is approximately the square root of the product of the wavelength and the gap distance. Hence, except for projection lithography (see below), contact printing offers the best resolution, because its gap distance is approximately zero (neglecting the thickness of the photoresist itself). In addition, may revive interest in this familiar technique, especially since the cost of ownership is expected to be low; however, the shortcomings of contact printing discussed above remain as challenges.Projection. Main article:The image for the mask originates from a computerized data file. This data file is converted to a series of polygons and written onto a square of substrate covered with a layer of using a photolithographic process.
A laser beam (laser writer) or a beam of electrons (e-beam writer) is used to expose the pattern defined by the data file and travels over the surface of the substrate in either a vector or raster scan manner. Where the photoresist on the mask is exposed, the chrome can be etched away, leaving a clear path for the illumination light in the stepper/scanner system to travel through.Resolution in projection systems. Stochastic effect on aerial image. Due to EUV doses generally being low, the statistical bounds on the image are noticeably large. An individual location within a large feature population could suffer a severe image distortion as depicted here.As light consists of, at low doses the image quality ultimately depends on the photon number. This affects the use of or EUVL, which is limited to the use of low doses on the order of 20 photons/nm 2.This is due to fewer photons for the same energy dose for a shorter wavelength (higher energy per photon).Light sources.
One of the evolutionary paths of lithography has been the use of shorter wavelengths. It is worth noting that the same light source may be used for several technology generations.Historically, photolithography has used ultraviolet light from using, sometimes in combination with such as. These lamps produce light across a broad spectrum with several strong peaks in the ultraviolet range. This spectrum is filtered to select a single. From the early 1960s through the mid-1980s, Hg lamps had been used in lithography for their spectral lines at 436 nm ('g-line'), 405 nm ('h-line') and 365 nm ('i-line').
However, with the semiconductor industry's need for both higher resolution (to produce denser and faster chips) and higher throughput (for lower costs), the lamp-based lithography tools were no longer able to meet the industry's high-end requirements.This challenge was overcome when in a pioneering development in 1982, lithography was proposed and demonstrated at I.B.M. By Kanti Jain, and now excimer laser lithography machines (steppers and scanners) are the primary tools used worldwide in microelectronics production. With phenomenal advances made in tool technology in the last two decades, it is the semiconductor industry view that excimer laser lithography has been a crucial factor in the continued advance of Moore's Law, enabling minimum features sizes in chip manufacturing to shrink from 0.5 micrometer in 1990 to 45 nanometers and below in 2010. This trend has continued into this decade for even denser chips, with minimum features reaching 10 nanometers in 2016.
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From an even broader scientific and technological perspective, in the 50-year history of the laser since its first demonstration in 1960, the invention and development of excimer laser lithography has been recognized as a major milestone.The commonly used deep ultraviolet in lithography systems are the laser at 248 nm wavelength and the at 193 nm wavelength. The primary manufacturers of excimer laser light sources in the 1980s were Lambda Physik (now part of Coherent, Inc.) and Lumonics. Since the mid-1990s has become the dominant supplier of excimer laser sources to the lithography equipment manufacturers, with as their closest rival. Generally, an excimer laser is designed to operate with a specific gas mixture; therefore, changing wavelength is not a trivial matter, as the method of generating the new wavelength is completely different, and the absorption characteristics of materials change. For example, air begins to absorb significantly around the 193 nm wavelength; moving to sub-193 nm wavelengths would require installing vacuum pump and purge equipment on the lithography tools (a significant challenge). An inert gas atmosphere can sometimes be used as a substitute for a vacuum, to avoid the need for hard plumbing. Furthermore, insulating materials such as, when exposed to photons with energy greater than the band gap, release free electrons and holes which subsequently cause adverse charging.Optical lithography has been extended to feature sizes below 50 nm using the 193 nm ArF excimer laser and liquid immersion techniques.
Also termed, this enables the use of optics with numerical apertures exceeding 1.0. The liquid used is typically ultra-pure, deionised water, which provides for a above that of the usual air gap between the lens and the wafer surface. The water is continually circulated to eliminate thermally-induced distortions. Water will only allow NA's of up to 1.4, but fluids with higher would allow the effective NA to be increased further. Changing the lithography wavelength is significantly limited by absorption.
Air absorbs below c. 185 nm.Experimental tools using the 157 nm wavelength from the F2 excimer laser in a manner similar to current exposure systems have been built. These were once targeted to succeed 193 nm lithography at the 65 nm feature size node but have now all but been eliminated by the introduction of immersion lithography. This was due to persistent technical problems with the 157 nm technology and economic considerations that provided strong incentives for the continued use of 193 nm excimer laser lithography technology.
High-index immersion lithography is the newest extension of 193 nm lithography to be considered. In 2006, features less than 30 nm were demonstrated by IBM using this technique.UV excimer lasers have been demonstrated to about 126 nm (for Ar 2.). Mercury arc lamps are designed to maintain a steady DC current of 50 to 150 Volts, however excimer lasers have a higher resolution. Excimer lasers are gas-based light systems that are usually filled with inert and halide gases (Kr, Ar, Xe, F and Cl) that are charged by an electric field. The higher the frequency, the greater the resolution of the image. KrF lasers are able to function at a frequency of 4 kHz.
In addition to running at a higher frequency, excimer lasers are compatible with more advanced machines than mercury arc lamps are. They are also able to operate from greater distances (up to 25 meters) and are able to maintain their accuracy with a series of mirrors and antireflective-coated lenses.
By setting up multiple lasers and mirrors, the amount of energy loss is minimized, also since the lenses are coated with antireflective material, the light intensity remains relatively the same from when it left the laser to when it hits the wafer.Lasers have been used to indirectly generate non-coherent extreme UV (EUV) light at 13.5 nm for. The EUV light is not emitted by the laser, but rather by a tin or xenon plasma which is excited by an excimer laser. Fabrication of feature sizes of 10 nm has been demonstrated in production environments, but not yet at rates needed for commercialization.
However, this is expected by 2016. This technique does not require a synchrotron, and EUV sources, as noted, do not produce coherent light. However vacuum systems and a number of novel technologies (including much higher EUV energies than are now produced) are needed to work with UV at the edge of the X-ray spectrum (which begins at 10 nm).Theoretically, an alternative light source for photolithography, especially if and when wavelengths continue to decrease to extreme UV or X-ray, is the (or one might say xaser for an X-ray device).
Free-electron lasers can produce high quality beams at arbitrary wavelengths.Visible and infrared femtosecond lasers were also applied for lithography. In that case photochemical reactions are initiated by multiphoton absorption. Usage of these light sources have a lot of benefits, including possibility to manufacture true 3D objects and process non-photosensitized (pure) glass-like materials with superb optical resiliency.
Experimental methods. See also: andPhotolithography has been defeating predictions of its demise for many years. For instance, by the early 1980s, many in the semiconductor industry had come to believe that features smaller than 1 micron could not be printed optically. Modern techniques using excimer laser lithography already print features with dimensions a fraction of the wavelength of light used – an amazing optical feat.
New tricks such as, dual-tone resist and continue to improve the resolution of 193 nm lithography. Meanwhile, current research is exploring alternatives to conventional UV, such as, and.See also., a macroscale process used to produce three-dimensional shapes.References.
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