Silicon as known by all is the most common element that is found on Earth. It is a semi-conductor and thus excessively used in electronics. The process of manufacturing these silicon wafers is quite tricky which is explained in the article below but once these are formed, they serve for a lot of uses as a result of which their applications in the field of electronics widen.
They are quite abundant in nature and due to all the characteristics that they have in them, they are known to be one of the excellent products in the industry as they serve various purposes and bring along ease. Consumers are now enjoying this very useful product so much that their demand in the market has increased excessively and due to the increased demand, the production of silicon wafers has increased quite rapidly too.
Being the universe's 7th common element and earth's 2nd common element, silicon is the semiconductor that's utilized most commonly and most broadly in the sector of technology and electronics. Fabrication of silicon can take place in many different ways, for instance, the Czochralski pulling method, the vertical gradient freeze, the vertical Bridgeman method, the horizontal Bridgeman method, and the horizontal gradient freeze method.
During the growth process, some silicon dopants are capable of being introduced, for instance, indium, gallium, nitrogen, aluminum, and boron. The level at which the silicon dopes the semiconductor determines whether the silicon should be considered degenerate or extrinsic. Degenerate semiconductors are more like conductors due to the doping's high levels during the production, meanwhile, the extrinsic semiconductors are doped in light to moderate level.
In integrated circuits, one of the significant components is the Silicon wafers. Integrated circuits are a composite of numerous different electronic components that are organized to operate a particular function. For semiconductors, the principal platform is the Silicon. This semiconductor material's thin slice is a wafer, serving as the substrate for microelectronic devices built-in and over the wafer.
Almost every electric device in our surroundings has silicon wafers in it. When it comes to making semiconductors, it is a pretty famous material. A flat-disk having a surface that's like a mirror and polished looks similar to the silicon wafer. An irregularity-free surface improves the purity of the surface, therefore making it a perfect candidate for the semiconductor devices
The vertical Bridgeman method and Czochralski pulling method are the two popular methods for the fabrication of Silicon wafer. Now because of fewer defects and more purity, a huge amount of attention is gained by the newer methods, for instance, the Float Zone method. To produce microchips and chips for electronic devices, they are utilized in a broad range.
Properties of Silicon Wafers
Ranging from the diameter of 300 mm (11.8 inches) to 25.4 mm (1 inch), different silicon wafers are available. The wafer’s diameter is used to define the semiconductor fabrication plants, which are also called fabs. The wafers that are chosen are those that the fabs are designed to create. For lessening the cost and enhancing the throughput with the current state-of-the-art fab utilizing 300 mm, there is a gradual increase in the diameter, and with it is a proposal of adopting 450 mm. Despite serious complications, research was being separately conducted by Samsung, TSMC, and Intel for 450 mm "prototype" (research) fabs advent.
A. Why silicon wafers are important for the industry
If you're an information technology professional or scientist, you must have heard about the name, silicon wafer. In fields of chemistry, physics, and IT, a device of this type is very common. This device is technically a circular, thin disc that is utilized in manufacturing semiconductors and integrated circuits. Silicon on insulator (SOI) and Gallium Arsenide are the types which are utilized in electronics, needing a very careful way of bringing manufacture to confirm high levels of efficiency. Even experienced technicians handle the growth of silicon wafers with extreme care and their growth is completed in a very controlled environment.
Big jobs are being done by these small little wafers. Many manufacturers use it to make computer chips. Every electronic device has one of these at least in them. Before the completion of fabrication, there are many various things included in the composition. For distribution, they are packaged after being carefully handled. To make sure that the consistency of the wafers is not changed in any way, a special compound is used to clean the wafers. This special compound is a weak acid, it is used to eliminate the impurities and remove the issues that have occurred during the sawing process. The cost of a small factory and the cost of the machinery that is utilized for making these parts is the same. Silicon is the general composite because of the application in electricity but there are some other materials in the composition too. In today’s world, in different fields of electronics, these little pieces are utilized.
Without even knowing, we see these little microdevices in commercials every day for processors, computer chips, and microchips. You should know that in any of your electrical devices, the most common and important building material is the silicon wafer, although the consumers only think about the end product and not the building block.
B. What are the types of wafers?
A thin semiconductor material, silicon wafer, is utilized in electronic applications and integrated circuits. In common gadgets like computers, TVs, mobiles, etc. silicon wafer is a very significant component. Wafers are of different types, each having its specific properties. To know the best silicon wafer for a specific project, one should know the various types of silicon wafers and their suitability.
A silicon wafer, which is specifically polished from both sides for achieving a surface of the mirror. Superior characteristics like purity and flatness define this wafer the best.
Undoped Silicon Wafer
They are also known as the intrinsic silicon wafers. Such semiconductor is silicon’s pure crystalline form which throughout the whole wafer, does not have the presence of any dopant, therefore, making it an ideal and perfect semiconductor.
Doped Silicon Wafer
N-type and P-type are the doped silicon wafers’ two types.
- Arsenic or phosphorus are contained by the N-type doped silicon wafers. Broadly, it is utilized for manufacturing the advanced CMOS device.
- Boron dopes the P-type silicon wafer. Mostly, it is utilized to make printed circuits or for lithography.
Epitaxial wafers are traditional wafers, utilized for obtaining surface integrity. Epitaxial wafers are of two types, thick and thin.
- Multilayered Epi wafers and thick epitaxial wafers are utilized for regulating the device’s energy consumption and in the electric power control too.
- In remarkable MOS instruments, the usage of thin Epitaxial Wafers is commonly seen.
Such wafers are used for insulating a monocrystalline silicon’s fine layer electronically from the whole silicon wafer. In silicon photonics and applications of high-performance radio frequency, SOI wafer is used commonly. Also in lessening the parasitic device capacitance in the microelectronics, an SOI wafer is used, contributing to enhanced performance.
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C. What are their application areas?
Due to having so many significant purposes and usages in the everyday life for silicon wafers, categorizing the most important usage is a difficult task. Focusing on just one of its applications is not fair to the silicon wafers as they are used commonly and have many applications. Here, we will focus specifically on the silicon wafer's applications and usages in the sector of electronic devices. If you want to know more about silicon wafer's importance in your normal life, continue reading.
Due to silicon’s high temperatures and high mobility at room temperature, the most popular semiconductor is silicon although there are different usages of the other conductors in more particular applications. In electronic devices, it is a remarkable option as the electrical current passes faster through silicon semiconductors as compared to most the conductors
Silicon Wafers in Electronic Devices
Silicon wafers are the semiconductors that are utilized for manufacturing microchips and chips in electronic devices. Integrated circuits are built by these semiconductors due to the features of the current of electricity through silicon wafers. In different and numerous electronic devices, the integrated circuits are utilized as the commands for specific functions that are performed by the electronic devices.
Associating the silicon wafers with extremely technical and specific devices of technology is easier than one may think. Silicon wafers are also utilized in a smartphone, tire pressure sensor systems, mobile devices, and computers. Different technological advancements can be developed and created by the manufacturing of the silicon wafer.
Use in high-performance radio frequency (RF) applications
An SOI process technology started to develop in 1990 by Peregrine Semiconductor began through the usage of an improved sapphire substrate and a standard CMOS node of 0.5 μm. In RF applications of high performance, the patented silicon on sapphire (SOS) process is broadly utilized. High electro-static discharge (ESD) tolerance, high linearity, and high isolation are insulating sapphire’s substrate intrinsic benefits. In cellular radios and smartphones, SOI technology has been applied to successful RF applications by various companies.
Use in photonics
In silicon photonics, the SOI wafers are used broadly. Active or passive optical devices and optical waveguides can be fabricated by the crystalline silicon layer on the insulator (via appropriate implantations). Infrared light’s propagation in the silicon layer is enabled by the buried insulator based on total internal reflection. Silica makes up the cladding which covers the waveguides’ top surface as it can be either covered by that cladding or don’t get covered and get exposed to air.
D. What are their production methods?
Consumers gain a remarkable sensorial experience from wafers. Despite being lighter, they are indulgent too. The demands from consumers lead to the further growth of the wafer category. At times wafers are separately eaten and at times, they are mixed with components with a contrasting texture, for instance, ice cream or chocolate. The most-selling confectionery products can be manufactured with the usage of wafers as they are the intermediate components. Chocolate and soft cream contrast well with the lightness and crispness. The level of crispness and its retention over shelf life critically determines the quality of wafer-based confectionery products.
For decades, wafers are being produced and marketed successfully. For fulfilling the local needs, different minor modifications are made during this time. The flat wafer's architecture displays the dispersion of gas bubbles in a solid phase. A wafer is capable of being considered as anisotropic foam, as suggested by the gas cell's distribution, shape, and size nonhomogeneity. Its mechanical characteristics are determined by the arrangements of gas cells and solids in the solid foam like the wafer, thus influencing the sensory perception. Understanding the science and logic behind the formation of the structure during the baking process for varying and controlling the texture of the wafer is very important.
Essential factors in wafer structure formation
Dispersions of flour and wafer with sodium bicarbonate, salt, sugar, and fat in small amounts, which are then mixed and confined in preheated molds, forming wafers. Other than sodium bicarbonate, yeast is also utilized in its place. During baking, steam and gassing are generated, which forms pressure and leads to the falling of the battery's moisture content (50-60 %) to a low level. At the end of baking, the total loss is around 1 % typically.
During the baking process in wafers, the gas and solids cells can be arranged, significantly due to these three factors
Gassing agents – incorporation of gas phase
Consolidating the solid phase – starch gelatinization
Heat transfer – structure development and fixation
Dynamics of wafer baking process
In the baking process, at various stages, the microstructure's gradual formation in wafers is analyzed. During the starting 30 seconds, the changes that take place are considered as at that time, the microstructure is being developed in a phased manner.
The flat wafer baking process was hypothesized by Sundara et al within two heated plates as the competition between gassing and viscous gelatinized starch, leading to the progress of five-layers in a phased manner. On the hot plate, the battery is deposited, leading to the occurrence of the nucleate boiling at the contact between the battery and the hot plate. Because of the water vapour being pushed away, when the water comes from the battery for nucleate boiling, a dry skin, next to the metal will form.
In this process, the wafer is utilized in little quantity. Because of the proximity to the source of heat, the trapped gases at this contact point and gelatinized starch are likely to instantaneously dry. Acting as an insulating layer, the skin layer delays the heat transfer from the hot plate to the battery's center.
Following are the steps explained which are carried out while preparing the silicon wafers:
High quality and cheap wafers are produced by surface grinding. For grinding wire-sawn wafers, it is capable of replacing lapping, entirely or partially. Relatively, etched wafers can be grind by it via partial replacement of the rough polishing.
The wire-sawing operation has some complications, for instance, waviness. To reach complete potential, the process of elimination should be utilized.
Over time, slicing a silicon wafer has turned into a difficult process because of different reasons, including the monitoring of the crystallographic perfection, specific and particular mechanical tolerances, and high purity levels.
The cost of production is affected directly by slicing. Therefore, if the yield is expanded, the manufacturers of the semiconductor will be concerned because it is very hard to slice a 12-inch silicon wafer.
Despite being hard, silicon is brittle. Rounding is very important because rough areas are produced due to the easy breakage of the sawn wafer’s edges. A diamond disk is utilized for making the wafer edges smooth and eliminating any damages. The desired diameter is produced by rounding to meet the demands of the customers.
In this mechanical process, a slurry mixture and pads are used for polishing and flattening the wafer. Due to lapping, the extra silicon is gone and a dull grey and semi-reflective finish are given. The damage that the slicing process inflicts, is also removed by the lapping. Customized services are offered by single and double-size lapping tools.
A final touch is given by polishing to the silicon wafers, making them more flexible, reliable, and thin. Due to polishing, the surface of the wafers is now free of stress, therefore, averting warping and preventing the breakage of the wafer. Polishing makes the wafers dicing-ready too. When it comes to making flexible circuits for electronic devices, polishing is the ideal process.
Silicon wafers can be contaminated when exposed to air. To work right, the wafers should be clean but their fragile nature makes their cleaning a difficult process yet important. Cleaning processes are so many, including, mega sonic cleaning, ozone cleaning, pre-diffusion clean, RCA clean, and a few.
Any defect on the wafers can be detected by inspection. Now, this process is turning expensive and challenging as sophisticated designs and new materials are being introduced. Normally, in process of inspection, photos of two dies are taken and then they both are compared for detecting the defect. Two inspection technologies are electron-beam inspection and bright-field inspection.
Wafer-level and conventional are packing’s two types. In the conventional method, before the wafer is encapsulated, it is sliced into individual clips. In wafer-level packaging (WLP), the chip is not removed from the wafer and is packed. More reliability, bandwidth, and speed is offered by the WLP schemes. Also, less power is used in such schemes.
The primary concerns during shipping the wafers are safety and protection from contamination as the wafers need to be handled with care due to their fragile nature. Not all wafers have the same size. For shipping them securely, numerous different kinds of jars and canisters are available. To meet the requirements of the customers, many different companies customize their products.
E. Why it is hard to manufacturer wafers?
When it comes to yielding, a silicon wafer of 12-inch is very hard to slice. Despite being hard, silicon is also brittle. Rough areas are produced due to the easy breakage of the sawn wafers’ edges. A diamond disk is used for making the wafer’s edges smooth and for removing any damages. After cutting, silicon wafers chip easily as they have sharp edges now. The edge of the wafer is designed that way so it can eliminate brittle, sharp edges, and reduce the chance of slipping too. Due to the edge shaping operation, the wafer's diameter is adjusted, the wafer is round (after slicing, off-cut wafers are oval-shaped), and a notch or orientation flat(s) is made or dimensioned.
When it comes to MEMS applications, most of the time the SEMI standard profile is not ideal or appropriate. After processing, if the wafer is thinned, then the edge of the wafer is may be brittle and sharp, thus the asymmetric edge profile is capable of being utilized. Also, particular requirements are set by the wafer bonding for the shape of the edge of the wafer; typically, for bonding applications, to obtain a better bond up to the edge of the wafer, a more blunt profile is suggested. That is why manufacturing the wafers is hard.
Silicon is a common element and abundant in nature has been taken up to be used in the form of silicon wafers. The manufacturing process of these wafers is a little tricky and requires a lot of minute detailing and that is exactly why once it is prepared it serves a lot of good purposes. Their applications are the most in electronics hence providing ease for the consumers.
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