How Does Wafer Thickness Impact Device Performance?
Wafer thickness significantly influences the performance, durability, and manufacturing efficiency of semiconductor devices. Here’s how it impacts various aspects of device performance:
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Heat Dissipation:
- Thicker wafers have a larger volume to absorb and spread heat, which can improve heat dissipation in high-power devices. This helps prevent overheating and ensures the stability and longevity of the device.
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Electrical Resistance:
- Thinner wafers reduce the electrical path between components, which can decrease resistive losses. This is especially beneficial for high-speed electronic applications where lower resistance improves performance.
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Mechanical Strength:
- While thinner wafers are more flexible, they are also more fragile and susceptible to breakage during handling or processing. Thicker wafers, on the other hand, provide greater mechanical strength, reducing the likelihood of breakage in production.
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Material Cost and Yield:
- Thinner wafers use less material, making them cost-effective, especially in high-volume manufacturing. They also allow for more wafers per silicon ingot, increasing the yield and reducing overall costs.
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Device Miniaturization:
- As devices become smaller, thin wafers enable stacking and packaging techniques, such as 3D integration. These methods reduce device size and allow for more compact and advanced designs in mobile and wearable electronics.
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Light Absorption in Solar Cells:
- In photovoltaic applications, thinner wafers can be beneficial as they allow for better light absorption efficiency in certain materials. However, they must be carefully engineered to balance absorption with mechanical stability.
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Signal Integrity:
- In some high-frequency devices, thinner wafers minimize parasitic capacitance, which can improve signal integrity and reduce noise, enhancing overall device performance in applications like radio frequency (RF) devices.
Choosing the right wafer thickness depends on the specific application requirements and processing considerations, balancing performance, cost, and durability factors.
Determining the Optimal Silicon Wafer Thickness for Research Projects
Choosing the right silicon wafer thickness is crucial for the success of a research project. The selection process involves a combination of theoretical understanding, practical considerations, and sometimes trial and error. Here's a guideline on how a researcher can determine the appropriate silicon wafer thickness for their project:
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Define the Project's Objectives: Understand the goals of the research. Are you aiming to optimize device performance, test a new fabrication process, or perhaps explore novel applications like flexible electronics?
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Review Relevant Literature: Check existing literature for similar research or applications. Often, previous studies will provide insights into optimal wafer thicknesses or at least offer a starting point.
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Device Performance:
- Thermal Management: Thicker wafers can often handle heat better, which is essential for high-power devices.
- Electrical Properties: The thickness can affect parameters like resistance, capacitance, and electron mobility.
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Fabrication Process:
- Deposition: If you're depositing layers onto the wafer, you need to ensure the wafer can support the added weight and stress.
- Etching: Thinner wafers might be more susceptible to over-etching or damage.
- Doping: The diffusion of dopants might vary based on wafer thickness.
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Handling and Equipment: Extremely thin wafers can be fragile. Ensure that your lab's equipment can handle the chosen thickness without causing breakage.
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Cost Considerations: Thicker wafers generally cost more due to the increased amount of silicon. If the project has a tight budget, this might influence the decision.
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Iterative Testing: Sometimes, the best approach is iterative. Start with a commonly used thickness, test the results, and adjust as needed based on observations.
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Consultation: Discuss with experts, suppliers, or colleagues. They might provide insights from their experiences or point out considerations you might have missed.
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Future Scaling: If the research aims to be applied in an industrial setting, consider the scalability. Industries might prefer thinner wafers due to cost savings, even if slightly thicker wafers give marginally better performance in a lab setting.
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Special Applications: For unique applications like transparent electronics, wearables, or bio-integrated devices, the desired properties (e.g., flexibility, transparency) will heavily influence the thickness decision.
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Safety and Waste Management: Thinner wafers can be more prone to breakage, leading to increased waste. Consider the safety protocols and waste management processes in place.
In conclusion, determining the right silicon wafer thickness involves a multifaceted approach, considering both the scientific objectives and practical constraints. It's often a balance between performance, cost, and feasibility. Regular review and adaptation as the research progresses are also crucial.
Processes involved in making a silicon wafer
Creating silicon wafers involves many processes that require special care and attention. The finished wafers must be sturdy enough to handle diverse applications. They must also be polished to an exquisite mirror finish.
Silicon is the raw material for semiconductor chips. It is one of the most abundant elements in the universe. It is also easy to combine with other materials. The silicon ingot is grown into a large crystal and sliced into smaller blocks.
It is then etched to remove microscopic cracks. It is polished to a smooth surface that will make printing circuit layouts easier. It is also chemically cleaned, which helps remove microscopic defects. The resulting wafers are checked for corrosion and refractivity. They are then packaged and shipped to the next manufacturing operation.
Another important process involves the application of dopants to certain areas of the wafer. Dopants, which are elements from Groups 3 and 4 of the periodic table, alter the properties of the wafer material. These dopants are used to make certain semiconductors conduct electricity. Some of these dopants include Boron, Phosphorus, and Arsine. The amount of dopant that is used depends on the temperature and the amount of material that is absorbed in the wafer.
Another process is laser grinding, which is used to slice silicon wafers of a small diameter. It is also used to slice wafers of a large diameter.
Applications of Thick Silicon Wafers in Electronics
Thick silicon wafers have found use in various applications due to their inherent properties and the advantages they offer over thinner wafers in specific contexts. Here are some of the prominent applications of thick silicon wafers:
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Power Electronics:
- Thick wafers can handle higher currents and have better thermal management properties, making them ideal for power devices like high-voltage transistors, diodes, and thyristors.
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Microelectromechanical Systems (MEMS):
- Some MEMS devices, such as accelerometers, gyroscopes, and pressure sensors, benefit from thick wafers as they allow for more substantial structural elements, leading to improved robustness.
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Optoelectronics:
- Devices like LEDs and photodetectors sometimes use thick wafers to enhance light absorption or emission properties.
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High-Performance Computing:
- Thick wafers can offer better thermal properties, crucial for high-performance processors and GPUs that generate significant heat.
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Acoustic Devices:
- Thick silicon wafers are used in some bulk acoustic wave (BAW) and surface acoustic wave (SAW) devices due to their improved mechanical properties.
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Solar Cells:
- While there's a trend towards thinner wafers in the solar industry, some traditional crystalline silicon solar cells, especially early designs, used thicker wafers for enhanced durability and light absorption.
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Radiation Detectors:
- Thick wafers can be used in radiation detection applications where increased material thickness provides better interaction with ionizing radiation.
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Infrared Imaging:
- Thick silicon wafers can be used in infrared imaging applications due to their enhanced absorption properties in the infrared spectrum.
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Robust Sensor Platforms:
- In environments where sensors face mechanical stress or high temperatures, thick wafers can offer the required robustness.
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Research and Development:
- In some experimental setups, researchers may opt for thick wafers to test the limits of device performance or to explore novel fabrication techniques.
- Microfluidics:
- Thick wafers can be etched to create deep channels, making them suitable for certain microfluidic applications.
- Packaging and Integration:
- Thick wafers can be used as substrates or carriers in wafer-level packaging processes, especially in 3D integration where multiple device layers are stacked.
While thick silicon wafers offer several advantages, they also come with some challenges, such as increased material costs and potential difficulties in handling and processing. Nevertheless, for the applications mentioned above, the benefits of using thick wafers often outweigh the drawbacks.
Most Commonly Used Silicon Wafer Thickness in Device Fabrication
1. Introduction
Silicon wafers are pivotal in the semiconductor industry, serving as the substrate for microelectronic devices built in and over the wafer. The thickness of these wafers is a crucial parameter, impacting both the performance and cost of the final device. This report delves into the most commonly used silicon wafer thicknesses in device fabrication.
2. Historical Context
Historically, the semiconductor industry utilized thicker wafers. As technologies have advanced, there's been a push towards thinner wafers to achieve better performance, reduce costs, and minimize material wastage.
3. Current Trends
With advancements in technology and the miniaturization of electronic components, the industry has seen a trend towards the use of thinner wafers. The reasons for this include:
- Cost-efficiency: Less material is used per chip, reducing costs.
- Improved Performance: Thinner wafers can lead to faster electron movement and improved device performance.
- Flexibility: Thinner wafers can be more flexible, opening up new potential applications, especially in wearable electronics.
4. Most Common Thicknesses
Based on the latest industry data:
- 200mm Wafers: These are traditionally between 725 µm to 775 µm thick.
- 300mm Wafers: The common thickness is around 775 µm to 925 µm.
- Thin Wafers: For specific applications, especially in MEMS (MicroElectroMechanical Systems) devices, wafers as thin as 50 µm to 200 µm are used.
5. Factors Determining Thickness
Several factors determine the optimal thickness for a wafer:
- Device Application: High-power devices may require thicker wafers due to heat dissipation needs.
- Handling and Processing: Extremely thin wafers can be more fragile and may require specialized handling equipment.
- Cost: Thicker wafers might be more expensive due to the increased amount of silicon used.
6. Future Outlook
As the push for more efficient and compact devices continues, the industry is expected to lean further towards thinner wafers. Innovations in wafer handling and processing technologies will likely make it feasible to use even thinner wafers without compromising on device quality or yield.
7. Conclusion
While the optimal silicon wafer thickness varies depending on the specific application and technological requirements, there's a clear industry trend towards thinner wafers. This is driven by the dual objectives of improving device performance and reducing costs. However, the exact thickness used is a balance between these objectives and the practicalities of device fabrication and wafer handling.
References:
- Semiconductor Industry Association (SIA) Reports.
- "Silicon Wafer Processing" - John C. Bean, 1998.
- MEMS Industry Group publications.
- "Semiconductor Manufacturing Technology" - Michael Quirk and Julian Serda, 2001.
Note: The information provided in this report is a general overview based on available data as of the last update in January 2022. Specific figures and trends might vary based on the source and the rapidly changing nature of the semiconductor industry.
The average thickness of silicon wafers can vary based on the wafer diameter and the specific requirements of the semiconductor process for which they are intended. Below is a general overview of the average thicknesses for silicon wafers ranging in diameter from 25.4mm to 450mm:
Silicon Wafer Diameter vs. Average Thickness
It's important to note that the exact thickness can vary based on the manufacturer, the intended application, and specific customer requirements. As technology progresses, there may also be shifts in these averages to accommodate newer device designs and fabrication techniques. Always consult with a wafer manufacturer or specific technical documentation for precise measurements.
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25.4mm (1 inch):
- Average Thickness: 275-325 µm
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50.8mm (2 inches):
- Average Thickness: 250-350 µm
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76.2mm (3 inches):
- Average Thickness: 380-450 µm
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100mm (4 inches):
- Average Thickness: 525-625 µm
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125mm (5 inches):
- Average Thickness: 625-725 µm
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150mm (6 inches):
- Average Thickness: 675-775 µm
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200mm (8 inches):
- Average Thickness: 725-775 µm
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300mm (12 inches):
- Average Thickness: 775-925 µm
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450mm (18 inches):
- Average Thickness: As of my last update in January 2022, the 450mm wafer technology was still under development and standardization. Consequently, there isn't a universally accepted "average" thickness. However, initial specifications suggest a thickness in the range of 900-1,150 µm.
What is The Average Thickness of Silicon Used in Solar Wafers?
Solar wafers, which are used in the fabrication of photovoltaic (PV) solar cells, have specific requirements distinct from semiconductor wafers used in electronics. The efficiency, light absorption capability, and mechanical strength of the solar cell are some factors that influence the thickness of the solar wafer.
Traditionally, crystalline silicon solar wafers were quite thick due to technological limitations and concerns about mechanical stability. However, with advancements in wafer manufacturing and PV cell technologies, there has been a continuous drive to reduce the thickness of these wafers to save on material costs and improve solar cell performance.
As of the last update in January 2022:
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Monocrystalline Silicon Solar Wafers:
- Average Thickness: 160-200 µm
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Multicrystalline (or Polycrystalline) Silicon Solar Wafers:
- Average Thickness: 180-220 µm
It's worth noting that some advanced solar cell designs and manufacturing processes aim to use even thinner wafers, with figures as low as 100 µm being explored. However, the challenges of handling such thin wafers, along with ensuring they have sufficient mechanical strength and light absorption capability, mean that these are not yet the industry norm.
The drive to reduce thickness is motivated by the desire to reduce silicon material costs, which form a significant portion of the overall cost of solar cell production. However, any reduction in thickness must be balanced against the need for mechanical strength, especially given that solar panels are expected to have a lifespan of over 20 years in outdoor environments.
In conclusion, while there's a trend towards thinner wafers in the solar industry, the exact average thickness can vary based on the technology, manufacturer, and specific application. Always consult specific technical documentation or manufacturers for the most accurate and up-to-date information.
Materials used in solar cells
Several types of semiconductor materials are used for solar cells. Each has its own advantages and disadvantages. However, researchers have found some innovative design solutions to optimize solar cells. These include perovskites and organic materials. They also have improved the efficiency of solar cells. Despite these advances, there is still a lot of research to be done to make solar cells competitive with silicon.
Perovskites are materials that have unique electromagnetic properties. They can absorb solar energy efficiently and can be used in the absorption layer of solar cells. They also have excellent photoelectric conversion efficiency. They are composed of a layered structure, which includes a hole transport layer.
Perovskites are organic-inorganic metal halide compounds. They can crystallize in both 2D and 3D structures. They have high optical absorption coefficients and charge mobility. They also have high extinction coefficients.
These materials can be used as light-absorbing layers, electron-hole transport layers and as a hole transport channel. They also have unique thermal and electromagnetic properties. In addition, they have a large dielectric constant. They are also stable and can be easily dissolved in polar solvents.
A mesoporous material has high porosity and a large specific surface area. It can be made of glass, plastic or metal. Its specific surface area can be up to 1000 m2 per gram. It can also be used as an insulating support layer.
The majority of organic solar cell materials have a band gap of about two eV. This is an ideal band gap energy for a single junction solar cell.
Larger silicon wafers reduce the total cost of ICs
Increasing the size of a silicon wafer can have a positive impact on the total cost of ICs. This can be attributed to a number of factors, including the increased yields of the material used, the larger number of dies that can be fabricated on the wafer, and the economies of scale associated with larger wafers.
The size of a silicon wafer is one of the most important parameters in semiconductor manufacturing. It determines how many dies can be fabricated on the wafer, the cost of the dies, and the overall cost of the finished ICs.
The size of a silicon sag varies based on the number of layers. It is also important to note that the maximum throughput of a lithography tool is governed by etch time and the load/unload time of the wafer.
The largest commercial wafers are 300 mm in diameter. This is a significant improvement over the earlier 1 inch size wafers. This is primarily due to the fact that the cost of manufacturing a 300 mm wafer is lower than that of an 8 inch wafer.
The size of a silicon wafer can also have a positive impact on the cost of lithography. This is due to the lower cost of tools. Lithography is one of the largest costs of producing a chip. Lithography represented 20-35% of the chip cost when it was fabricated on a 6-inch wafer.
SiO2 substrates
Almost all deposited silicon dioxide is done using CVD methods. These techniques result in a smooth, low-flocculated surface.
However, the intrinsic performance of SiO2 may be limited by residual structural defects. We investigated the effect of surface contamination on SiO2 film properties. In particular, we examined the impact of oxygen plasma treatment on the surface of Si3N4 and SiO2 films. The oxygen plasma treatment is known to promote surface reactivity and surface cleaning. This resulted in an increase in the surface energy of the investigated surface. It was also observed that a higher surface energy would increase van der Waals bonding.
FDTD-calculated spectra showed B excitonic resonances at 440, 620, and 660 nm. These resonances were also observed on TEOS-SiO2 and HDP-SiO2 films. These resonances were attributed to the presence of functional groups.
We also measured the contact angle between a solid and a liquid. This angle is known as the Young equation. The angle is usually below 90 degrees for flat surfaces. However, it can be as high as 170 degrees. This is because the bond energy does not change much with the bond angle. The bond rotation is almost free.
The SiO2 films were deposited using different precursors and process parameters. These precursors include PDDA, Si3N4, and thermal-SiO2. These films showed similar receptivity towards oxygen plasma.
The oxygen plasma treatment caused the surface to be partially oxidized. However, this did not affect the Si-C peak.
Optical grading
Optical grading of silicon wafers is a process of determining the optimum thickness and crystallinity for a particular optical application. This requires a good knowledge of optical constants and their dependence on the thickness. This is done by measuring the optical constants and taking accurate measurements.
Silicon is one of the most widely used semiconductor materials. It is produced in polycrystalline and monocrystalline forms. Polycrystalline silicon is created through the float zone or Czochralski crystal growth process. This process is more economical than other methods.
Silicon wafers are used in the fabrication of semiconductor devices such as LEDs, light emitting diodes, photovoltaics, and solar cells. They are also used in optics and micro-optic devices. Silicon wafers are also used as substrates for conductor materials.
Optical grade silicon wafers have high spectral translucency and are ideal for photonic devices and solar cells. They are produced in monocrystalline form with good transmission properties from 1.2 um to 7 um. The wafers are generally flat or with a continuous taper region. They are light doped and meet SEMI standards.
Prime grade silicon wafers are the most expensive and considered the highest quality. These wafers are made from synthetic fused silica and are the best choice for photolithography and semiconductor fabrication. They have phonon absorption peaks in the range of 6.5 to 25 um. They also have a characteristic oxide backseal. They are used in the most advanced devices.
How Do You Measure Silicon Wafer Thickness?
Video: How to Measure Wafer Thicknes
Silicon Wafer Thicknesses
The thickness of the wafers ranges from 775 to 12 inches per wafer, and the thickness in the EOR (defect zone) can be defined as the minimum distance thickness that the implanted wafers have reached. [Sources: 2, 14]
A bare wafer with a thickness of 300 mm has an effective life of 300 msec, with the lowest value (130 msec) being the ribbon - silicon wafers with a thickness of 1.5 mm. This time interval is therefore an important factor that controls the thickness and type of silicon wafers, especially in systems with continuous growth. [Sources: 3, 14]
The R and S readings correspond to those of the solar cells used to measure the thermal conductivity of silicon wafers with a thickness of 1.5 mm. When measuring the resistance, which the device measures with four probes, the results are available in cm. The measured values of e and e are 1: 45 and 1: 35, respectively, with values in the range of 0.1 - 1 cm for a bare wafer or 2 - 3 cm and 3 - 5 cm respectively. [Sources: 0, 9]
SEMI specifies the physical properties of the surface that are required to designate silicon wafers as "True Prime Wafers" or "Prime." Prime Wafer, Prime is the highest possible quality of silicon wafers. However, there are a variety of Prime WAFers, and waffles that meet these specifications are rare and quite expensive. [Sources: 7]
The silicon wafers with column structure in the figure have an even thickness of about 50 mm, and the deviation in silicon wafer thickness remains below 2 mm [4]. The standard silicone wafer diameter is about 1.5 mm and the thickness is measured at five points on the silicon wafer. The dots along the same line are plotted at 220 mm intervals, and the deviation of 1 mm from the standard is 0.1 mm. [Sources: 0, 8, 10]
Capacity measurement can be used to measure the thickness of silicon wafers with column structure, as shown in Fig. [Sources: 13]
It is useful to measure the thickness of a silicon wafer in relation to the number of fractures in a single layer. If the initial crack can be calculated from the stress caused by the electrical deposition of the layer, it can then be predicted. A new equation was created to predict the thickening of flaking silicon wafers with respect to their thickness in terms of column structure. [Sources: 0, 12]
As shown in the illustrations, the thickness of a flaking silicon wafer is in the range of 20 - 70 mm. The figures show the load caused by the residual stress of the nickel layer as a function of the nickel thickness. Figure shows the number of fractures in a single layer of column-shaped thin silicone wafers in relation to their column structure, as shown in the figure. Figure shows an equation for the fracture rate of the silicon layer in relation to the amount of residual stresses on nickel layers. [Sources: 0]
The wafer thickness determines the mechanical strength of the material used and must therefore have an even thickness. The wafers must be strong enough to carry their own weight without tearing during handling. Specific thickness variations should be taken into account in the GBIR assessment. [Sources: 6, 9]
This is important to obtain epitaxial silicon wafers (121) with a high flatness. Therefore, the thickness of the column structures on a silicon wafer must be uniform. Therefore, this study aims to present a method for controlling the thickening of columns made of structured silicone wafer by growing them directly from silicon molten material. Obtaining a flat epitaxial silicon wafer is difficult because the growth of silicon wafer 121 must have such uneven deformation and the epitrixial layer is formed during the growth process. [Sources: 3, 9]
The purpose of this paper is to show that silicon wafers have a thickness range of 3N-4, which is actually 2-3% of the thickness of a wafer. [Sources: 1]
This is due to the fact that the thickness of the silicon wafer increases by a factor of 3 due to the chemical dilution of the Si wafers. [Sources: 14]
The standard memory (DRAM, 2D NAND) uses silicon wafers that are thicker than 200%, while 3D stacked DRAM moves up to 30% thinner than this. In addition, the silicon-based MOSFETs are used and the thickness of the material layer on the silicon wafer must be miniaturized, as we also need to ensure uniformity and repeatability in semiconductor manufacturing [4, 5]. The standard DRam, 2D NAND, uses a silicone wafer up to 200% thick - and it gets thicker and thicker as the DR AM 3D batch memory advances. [Sources: 4, 5, 15]
Sources:
[0]: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6339913/
[1]: https://www.science.gov/topicpages/n/n-type+silicon+wafer
[3]: https://www.hindawi.com/journals/ijp/2012/147250/
[4]: http://www.yole.fr/Thining_Equipment_Materials_BusinessOverview.aspx
[5]: https://www.spiedigitallibrary.org/conference-proceedings-of-spie/11381/113811E/Coating-thickness-estimation-in-silicon-wafer-using-ultrafast-ultrasonic-measurement/10.1117/12.2558380.full
[6]: https://en.wikipedia.org/wiki/Wafer_(electronics)
[7]: https://cleanroom.byu.edu/ew_wafer_specs
[9]: https://patents.google.com/patent/US7781313B2/en
[10]: https://onlinelibrary.wiley.com/doi/full/10.1002/inf2.12087
[11]: https://www.epj-pv.org/articles/epjpv/full_html/2010/01/epjpv100001/epjpv100001.html
[12]: https://www.renewableenergyworld.com/2011/05/19/implant-cleave-process-enables-ultra-thin-wafers-without-kerf-loss/
