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Nanosensor Laboratory
Published in Vinod Kumar Khanna, Nanosensors, 2021
Photolithography is the process of transferring geometric shapes or patterns on a mask to the surface of a silicon wafer coated with a photoresist. What is a photoresist? It is a light-sensitive material performing two basic functions, namely precise pattern formation and protection of the substrate from chemical attack during the etching process. Photolithography is the means by which the small-scale features of integrated circuits are created. The steps involved in the photolithographic process are wafer cleaning, barrier layer formation, photoresist application, soft baking (the step during which the solvents are removed from the photoresist), mask alignment, exposure and development, and hard baking (the step to harden the photoresist and improve adhesion of the photoresist to the wafer surface). A diffusion barrier layer is a layer of thermally grown silicon dioxide that blocks the entry of dopant impurities, like phosphorus and boron, into the silicon wafer so that these impurities enter only through the windows in the oxide layer etched after the photolithographic operation.
Multifunctional Printing
Published in Amit Bandyopadhyay, Susmita Bose, Additive Manufacturing, 2019
Dishit Paresh Parekh, Denis Cormier, Michael D. Dickey
Photolithography is the cornerstone process utilized to pattern the components in a computer chip. AM is effectively a patterning technique, and thus, it is prudent to briefly discuss photolithography as a basis for comparison. An example of the photolithographic process is shown in Figure 8.2.27 Photolithography utilizes patterns of light to chemically modify the solubility of thin polymer films coated on a surface. Photolithography is an inherently 2D process because the light used to expose the polymer has a single focal plane. This limitation, along with the need to coat, expose, and remove polymer, makes photolithography essentially incompatible with AM. Although academic research provides many unconventional approaches8,25,28–35 to pattern electronic materials to overcome some of the limitations of photolithography, it still remains the backbone of the semiconductor industry.
The Importance of Photolithography for Moore’s Law
Published in Lambrechts Wynand, Sinha Saurabh, Abdallah Jassem, Prinsloo Jaco, Extending Moore’s Law through Advanced Semiconductor Design and Processing Techniques, 2018
Lambrechts Wynand, Sinha Saurabh, Abdallah Jassem
Photoresist is a light-sensitive material used in photolithography to transfer images from a photomask onto a wafer; exposure to wavelength-specific UV changes its chemical properties and its solubility. Photoresist is divided into two primary categories: positive photoresist and negative photoresist. Photoresist (both positive and negative) is not only distinguished by its solubility, it is characterized and typically qualified by features such as Its ability to distinguish between light and dark portions of the photomask; therefore, its contrast.How fine a line the photoresist can reproduce from an aerial image; therefore, its resolution.How much incident energy the photoresist requires to change its solubility; therefore, its sensitivity.Its absorbance of the wavelength of the light source; therefore, its spectral response.Its ability to protect the underlying material from etchants and its thermal stability; therefore, its etch resistance.
An improved imperialist competitive algorithm based photolithography machines scheduling
Published in International Journal of Production Research, 2018
Peng Zhang, Youlong Lv, Jie Zhang
Semiconductor manufacturing system is among the world’s most complicated manufacturing systems. A huge capital investment is required for equipment purchasing and maintenance for wafer fabrication, resulting in a very high production cost. Semiconductor manufacturers strive to reduce the wafer’s cycle time to rapidly recycle the cost. Moreover, industrial studies (Lentz 2011) have shown that the cost per wafer will decreased by 0.7% once the cycle time is reduced by 1%. Therefore, manufactures control the cycle time strictly and try to continuously reduce it. The investment for Photolithography machines is the highest in semiconductor manufacturing system, and as such is often the bottleneck for processing wafers. Any reduction of photo cycle time will significantly decrease wafer’s overall cycle time. Meanwhile, photo cycle time is about 10% of wafer’s overall cycle time, i.e. reducing the cycle time in photo area by 1% can reduce the cost per wafer by 0.07% (Spierings 2013). Hence, mining the potential capacity and decreasing cycle time of photolithography machines is a common goal in semiconductor manufacturing system. And photolithography machines scheduling problem has also been the main area of concern for many researchers.
Image-Based Feedback Control Using Tensor Analysis
Published in Technometrics, 2023
Zhong Zhen, Kamran Paynabar, Jianjun (Jan) Shi
The photolithography process is a critical stage in semiconductor manufacturing and silicon wafer production. The main objective of the photolithography process is to carve the designed circuit pattern onto the wafer surface. During the lithography process, with the help of the optical system, the patterns on a mask will be projected onto a thin layer of photoresist material on the wafer. The photoresist material will quickly solidify when it is exposed to light. Then, the unexposed material is washed away. The entire wafer is comprised of m identical rectangular fields, on which the light exposure is performed layer by layer. After completing one layer, the procedure is repeated to print the subsequent layers.
Fabrication technology for light field reconstruction in glasses-free 3D display
Published in Journal of Information Display, 2023
Fengbin Zhou, Wen Qiao, Linsen Chen
Traditional photolithography utilizes single-photon absorption (usually UV light) of photoresist to create arbitrary 2D or 3D patterns [117]. Unlike the above-mentioned single-photon absorption-based techniques (Figure 10(a)), TPL takes advantage of the nonlinear dependence of material to light excitation (Figure 10(b)). Since the laser intensity exceeds the two-photon polymerization threshold only at the region of the focal spot, the minimum achievable volume size was proven to be λ/10 [118–120]. The main parameters that influence minimum achievable volume size include the energy of the laser, exposure time, numerical aperture of the focusing lens, and polarization of the illumination [121]. With a minimum feature size beyond the diffraction limit, TPL is one of the most versatile and precise additive manufacturing processes. Another distinguishing feature of TPL is that complex 3D structures can be fabricated directly from computer-aided-design (CAD) models [122]. The TPL and micromolding techniques were combined to produce dissolving and hydrogel-forming microneedle arrays [123]. Furthermore, freeform micro-optics were patterned by TPL for optical coherence tomography (OCT) fiber probes [124]. Leveraging on TPL, high-resolution light field print was created by fabricating microlenses and structural color pixels in one patterning step [125], as shown in Figure 10(c–e). The light field print features a spatial resolution of 29–45 µm and an angular resolution of ∼1.6°. As shown in Figure 10(c), the TPL-based light field print sets an example of how nanofabrication techniques advance 3D virtual imagery. Despite the outstanding performance in 3D structuring, TPL has been criticized for the limited fabrication rate attributed to the serial dot-by-dot patterning mode. Researchers have explored parallel processing methods [126,127]. Without doubt, TPL will continuously innovate the design and fabrication of functional devices in the future.