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Nanosensor Laboratory
Published in Vinod Kumar Khanna, Nanosensors, 2021
The photomask (an opaque plate with transparent regions that allow light to shine through in a defined pattern) used in photolithography is created by a photographic process and developed onto a glass substrate. Chrome (vernacular for chromium) on quartz glass is used for the high-resolution deep UV (electromagnetic radiation between violet light and X-rays, having wavelengths of 200–400 nm) lithography. Depending on the design of the photolithography machine, there are three options: (i) the mask may be in contact with the surface; (ii) very close to the surface; or (iii) it is used to project the image of the pattern on to the surface of the substrate. These methods are called, not surprisingly, contact, proximity, and projection, respectively. Figure 3.10 shows a schematic diagram of these methods. Option (i) provides good resolution but the mask is spoilt, sometimes excessively damaged, on repeated abrasion with the substrate. Option (ii) increases the life of the mask but the resolution is slightly sacrificed. Option (iii) is good for both the mask and the resolution, and hence is the best solution. Photolithographic techniques: (a) contact, (b) proximity, and (c) projection.
Data Acquisition and Intelligent Diagnosis
Published in Diego Galar, Uday Kumar, Dammika Seneviratne, Robots, Drones, UAVs and UGVs for Operation and Maintenance, 2020
Diego Galar, Uday Kumar, Dammika Seneviratne
As a result, UV imaging enables automated systems to detect scratches and digs on optical surfaces such as lenses or windows. In the semiconductor industry, photolithography requires inspection of photomasks with very fine lines and features to find defects that may be submicron in size. Confocal microscopes operating in the DUV band at 248 or 266 nm (laser wavelengths that can be generated by krypton fluoride and frequency-quadrupled Nd:YAG lasers, respectively) can be used to image these features with much greater clarity than in the visible band and can be used to find tiny defects in the silicon wafer starting material. Detection of these defects early in the production process can greatly improve yields and reduce waste.
Lithography
Published in Andrew Sarangan, Nanofabrication, 2016
Photolithography is a subset of lithography that uses photons to define the lateral structures. Additionally, there are also nonoptical lithography techniques that use charged beams such as electrons or ions to define the structures, but photolithography is the most widely used system today. In photolithography, a photomask is used to project an optical image onto a photosensitive film and permanently alter its chemical or mechanical properties. It is most commonly used as a sacrificial film and discarded after using it as stencil to pattern another underlying or overlying film. In a small number of cases, the photoresist is left as a structural film, and not discarded, such as the SU-8 photoresist.
Dual-field responsive polymer-dispersed liquid crystal films with polymer spacer columns and fluorescent properties
Published in Liquid Crystals, 2022
Xianliang Chen, Zemin He, Chunsheng Li, Zongcheng Miao, Dong Wang, Yi Luan, Yuzhan Li, Yuzhen Zhao
Photomasks, which have a wide range of applications in the Liquid Crystal Display (LCD) field due to their pattern transfer capability, are opaque plates used in the photolithography process. Wang et al. [37] proposed a method to fabricate reverse-mode PDLC films combining polymer wall technology with dynamic scattering state of ion-doped NLC molecules with negative Δε. It was found that the polymer wall plays the role of both the spacer and the locking of the ion-doped NLC materials in a confined area. In addition, Han et al. [38] fabricated a microlouver structure by using a designed photomask to pattern the dye-doped thiol-ene-based photopolymerisation resin. Therefore, a controllable anti-peeping device that can switch electrically between the wide viewing angle (WVA) and narrow viewing angle (NVA) mode was prepared by laminating the microlouver structure with PDLCs film.
Analysis and approximation for the performance of a workstation with various types of setups
Published in International Journal of Production Research, 2018
Photolithography machines (steppers and scanners) are the most expensive process tools in a semiconductor fab and are usually designed as the bottleneck of a production line. It transfers the pattern on a photomask to the photoresist on top of the wafer through light. Since different layers of a product require different masks, changeover setups occur frequently at photolithography machines. Different from CMP machines, the changeover times of different masks are about the same, and can be assumed to follow the same distribution. In this situation, the queue time for a station with the same changeover setup distribution can be approximated with Equation (7). The model is validated in this section with three cases with different changeover setups.