MRF and the Silicon Carbide Industry
MRF has been specializing in manufacturing high-temperature vacuum furnaces since 1990 for both R&D and production purposes. With new discoveries in materials and applications being employed for mass production and enhancements in today’s fast-moving markets, the need for precision is even more important than ever. We have had the opportunity to be a part of many R&D breakthroughs and discoveries over the years. Bringing to market these new applications has allowed us to serve multiple industries even after the initial process has been defined or commercialized. Silicon carbide crystal growth has become an increasingly important area of study for multiple sectors within the global market in recent years. As we become more aware of our surroundings, creating more environmentally friendly products has become a priority for many manufacturers, and SiC seems to be the answer for multiple industries to achieve this goal. MRF is proud to be a part of this new trend within the SiC market and has helped many achieve their R&D expectations as well as provide solutions for new production lines within the silicon carbide markets.
While attempting to produce artificial diamonds in 1891, American inventor Edward G. Acheson (Figure 1) inadvertently discovered a new compound, Carborundum, otherwise known as Silicon Carbide (SiC). Naturally occurring SiC known as Moissanite was discovered in 1893 by a French scientist named Henri Moissan (Figure 2). This gemstone is said to be born from the stars as it is primarily found in or around craters on earth created by fallen meteorites that carry debris formed from the explosion of red giant stars.  Unfortunately, the natural supply of this mineral was nowhere near sufficient in any capacity and experts began their research into ways of creating synthetic moissanite in labs.
Figure 1. Edward G. Acheson 
Figure 2. Henri Moissan 
Experimentation with crystals from various substances in the early 20th century helped in the discovery of the ‘unsymmetrical passage of current’ or rectification as we would know it, that can occur in substances such as germanium, which later found uses in crystal radios.  Because of these early experimentations, it was discovered that SiC has a thermal conductivity 3.5 times better than silicon and can be heavily doped for high conductivity while still maintaining high electric field breakdown. Mechanically, it is very hard, inert, and has a very low coefficient of thermal expansion and high-temperature rating. SiC does not even melt – it sublimates at about 2700⁰C. 
Properties and Structures
Many compound materials exhibit polymorphism. Polytypism is a type of polymorphism in which a given element or compound can assume more than one crystal structure. These structures are then identified and distinguished by the variation of occupation sites along the c-axis by the way that individual layers are stacked within a crystal structure. Silicon carbide follows this domain of existence and the solid industrial mineral crystalline has the capability of existing in over 200 different structures. See Figure 4 for examples of SiC polytypes.
Figure 4. Structure diagram of several low-pressure polytypes of SiC as well as the high-pressure rock salt structure. The larger blue spheres represent the Si atoms while the smaller brown spheres represent the C atoms. Structures visualized using the program VESTA  with 3C from , 2H from , 6H from , and 21R from . 
The properties that make silicon carbide so versatile and popular include its ability to withstand high temperatures and thermal shock with decomposition starting at 2000°C. Its Mohs hardness rating of 9 makes it one of the hardest available material next to boron carbide (9.5) and diamond (10).  SiC robust crystal structure also exhibits the ability to resist corrosion when exposed to or boiled in acids (hydrochloric, sulphuric, or hydrofluoric acid) or bases (concentrated sodium hydroxides).  SiC in its purified form, manifests behaviors of an electrical insulator. By governing impurities, silicon carbides can exhibit the electrical properties of a semiconductor. Figure 5 shows a brief comparison of Si and SiC. Even though Si was previously the best choice for many industry processes and applications, SiC has now taken that place and become the material of choice for those same processes and applications.
Figure 5. Comparison of Si and SiC 
Black, Green, and Other Grades
Properties of silicon carbide depend upon its purity, polycrystalline type, and method of formation. Thus, values reported for commercial polycrystalline silicon carbide should not be interpreted as being representative of single-crystal silicon carbide. The examples in Figure 6 illustrate the wide variation in hardness for various grades of silicon carbide. 
Figure 6. Hardness of various grades of silicon carbide 
The 2 colors of SiC are attributed to its level of purity and hardness. Black SiC contains some free silicon and carbon and will range in purity from 97-99% pure, depending on grit size, and has a Mohs of 9.1. Green SiC is made from silica sand and coke and has 99% purity with 9.4 Mohs.  Because the green SiC is harder than the black, it is generally used in abrasive applications such as honing stones, blasting, compounds, lapping, and polishing.  Even though there are subtle variations between the black and green SiC, the real difference of purity and hardness only exists as a real difference for the processes of specific applications and uses.
Figure 7. Comparison of brilliance between a moissanite and a diamond 
As mentioned earlier, the supply of natural moissanite could not meet the demands that were put upon this element. In 1995, one of the principals involved with Cree founded a company, C3, which was to be later renamed, Charles and Colvard.  This new company and Cree had set to work on the research and development of a synthetic moissanite and in 1998 the consumer market saw the first “diamond substitute” being promoted. Over time, the marketing for this stone has shifted and has now been focused on helping the consumers see it as a precious stone on its own instead of an imitation of a diamond.
After their initial success, Charles & Colvard continued their strategic partnership with Cree and in 2012 they introduced a whiter form of moissanite, called Forever Brilliant. This stone is said to be comparable to diamonds of G-H color.
Cree’s patented process for developing micropipe-free SiC material enables the exclusive production of Charles & Colvard’s premium moissanite product, Forever One™ which was released in 2015.  This new stone is the whitest moissanite available on the market.  Although moissanite was initially marketed as a diamond substitute, it is now being categorized as a gem in its own right.
The chart in Figure 8 shows the comparison between moissanite and other precious gems. Because the weight of moissanite is about 15% less than diamonds there is no accurate comparison for pricing between the two. Diamonds are measured by carats while moissanites are priced by size in millimeters. Figure 9 is an estimated close comparison between the diamond and the corresponding size in moissanite.
Figure 8. Gemstone comparison 
Figure 9. The table above shows a comparison between diamonds in various carat weights and moissanite stones in roughly corresponding sizes. 
Other than the ability to look pretty, Silicon carbide’s robust crystal structure has other attributes that give it mechanical properties that are considered advantageous when developing high-quality technical grade ceramics and semiconductors. SiC can also act as an abrasive used in grinding, sandblasting, water-jet cutting, and other frictional purposes. Below are some of the top reasons SiC is so popular within the various fields of high-quality technical grade ceramics, semiconductors, and abrasives:
- Exceptional hardness
- High strength
- Low density
- High elastic modulus
- High thermal shock resistance
- Superior chemical inertness
- High thermal conductivity
- Low thermal expansion
Silicon carbide has become a key player in various markets. These include the automotive industry, electronics, industrial applications, medical, nuclear, aerospace, and defense are just a few of the sectors that utilize this element in their various applications and processes. But of all of these markets, perhaps the largest market for SiC is the one producing semiconductors.
SiC semiconductors are gaining ground over silicon because of its ability to withstand more, take more, and transfer more all while being smaller. Electronics have become a big part of the reason for the increased use of silicon carbide in semiconductors in the last few years. The reason for this is the wide bandgap in SiC semiconductors. Figure 10 shows some examples of semiconductors and the companies that make them.
In terms of electrical applications, one of its earliest uses was as a lightning arrester in a high-voltage power system where engineers and scientists recognized that silicon carbide performs well even in the presence of high voltages and high temperatures. More modern applications of silicon carbide in electronics include Schottky diodes, MOSFETs, and power electronics. Other than its applications in semiconducting, SiC is also used for products such as bulletproof vests, ceramic plates, thin filament pyrometry, foundry crucibles, and car clutches.
Wide Bandgap (WBG)
The energy required for electrons and holes to transition from the valence band to the conduction band is called a bandgap. See Figure 11 for an illustrated explanation. The bandgap of 4H-SiC is 3.26 eV, and the electric breakdown field is 2.8 × 106, which is a very large value compared with that of Si, 3 × 105.
Figure 11. Bandgap explained 
With a wider bandgap, the ability to operate at higher voltages, power levels, and frequencies are all possible without losing functionality. SiC components increase efficiency while decreasing in size. And because SiC can withstand higher temperatures with more effective heat distribution, elimination of fans and heat sinks is often possible. More challenging applications like hybrid and electric vehicles, renewable energy, power factor boost correction, uninterruptible power supplies, down-hole drilling for the petrochemical industry, and more have all benefited from the wide bandgap ability of the SiC.  Figure 12, shows a comparison of the properties between Si and the newer materials being used in semiconductors today.
Figure 12. Physical property constants of Si and main wide-band-gap semiconductors 
Silicon Carbide in EVs and HEVs
As we become more environmentally conscious, the need to reduce emissions becomes a priority. One major way to do this is through electric cars. It is estimated that the majority of SiC growth will come from the automotive industry. As internal combustion engines (ICEs) are slowly being phased out with many in the car industry agreeing to make major changes in the next 10 years, growth in electric vehicles (EVs) and hybrid electric vehicles (HEVs) are climbing. Figure 23 shows the estimated growth of Electromobility (or e-Mobility) in the next few years.
Figure 23. The above graph shows the strong growth opportunity at hand as emission standards drive a significant shift to battery electric vehicles. (Source: Yole and Cree estimates) 
In the past, high cost paired with the narrow range limited the acceptance of EVs and HEVs by most end users. But research into replacing silicon with silicon carbide has the automotive industry hopeful in the next generation of electric cars. Figure 24 shows the major components that can be replaced with the new more efficient SiC parts. These new components have currently reached a level of maturity that has allowed it to rapidly gain ground over Si for demanding applications, such as traction power electronics in EVs and HEVs. SiC has also helped optimize fast-charging processes for EVs by reducing overall system loss by almost 30%, increasing power density by 30%, and reducing the component count by 30%. And because of these positive increases and decreases, charging stations can be designed to be smaller, faster, and more cost-effective.
Figure 24. Major components that can be replaced with SIC based devices 
The US Department of Energy awarded a $1.5 million grant to the University of Arkansas in 2019 to target the development of next-generation SiC-based power modules designed for PHEVs and EVs. In Japan, the University of Tokyo has been working with Mitsubishi Electric Corporation to enhance the reliability of SiC semiconductor devices and had already introduced a new ultra-compact SiC inverter designed for hybrid vehicles in 2017.
Toyota has been working with Denso to a similar end for years, and since as far back as 2014 has been developing SiC-based power control units for hybrid electric vehicles. On December 9, 2020, Denso announced that mass production had begun on its latest model of booster power module*1 equipped with high-quality silicon carbide (SiC) power semiconductors and are now being used in Toyota’s new Mirai.
Bosch Semiconductors has also entered the automotive silicon carbide race. In 2019 the company announced that it would begin making silicon carbide (SiC) power semiconductors for automotive applications at its wafer fabrication facility in Reutlingen, Germany.
The race is on and many manufacturers of power modules and power inverters have already developed or increased production of SiC components in preparation for the increase in demand for EVs and HEVs in the next few years. Market forecasts by Yole see PHEV and BEV have a CAGR between 37.3% and 44% for 2020-2026 with the converter market for xEV worth more than US$28.8 billion in 2026 with a CAGR of 27.7% between 2020-2026. The market value for semiconductor power electronic devices for xEVs will reach US$5.6 billion in 2026 with a CAGR 2020-2026 of 25.9% as indicated by Figure 25 below.
Figure 25. The market value for semiconductor power electronic devices for xEVs. 
Silicon carbide has a large variety of atomic configurations both in the crystalline as well as in the amorphous phase. The structure and properties of silicon carbide depend on the preparation conditions. Amorphous SiC (a-SiC) can be easily prepared by low temperature (400 °C) chemical vapor deposition (CVD) from the SiH4/CH4 gas mixture, and hydrogen incorporation allows to decrease the defect density down to 1017 cm−3 and to obtain high luminescent yield material. At 900 °C solid phase epitaxy takes place on (1 1 2 0) and (0 0 0 1) substrates, and the residual disorder depends on the crystallographic orientation. At 1650 °C CVD at low pressure on a single crystal gives a free-of-defects layer (1014 cm−3) with high electron mobility up to for 4H substrate. High growth rate (1 mm/h) for SiC bulk is reached with a sublimation process at temperatures as high as 2400 °C, however, macroscopic defects as micropipes or polytype inclusions are present. Intrinsic defects, vacancy or interstitial-type, introduced during the growth or intentionally by kiloelectronvolt ion implantation, can be removed after a thermal treatment at 1500 °C. Good performance optical and electrical devices are already fabricated with amorphous and crystalline silicon carbide. 
As mentioned earlier SiC has over 200 different structures. Once a successful SiC has been produced and tested the exact formula and conditions must be replicated for re-creation and duplication to occur for large-scale productions. Traditional growth methods for silicon carbide usually involved sintering and hot pressing. However, over time other newer techniques such as reaction sintering or reaction bonding silicon carbide have emerged as an alternative process to creating the required structures of SiC.
The process for sintered SiC involves conventional ceramic forming processes in temperatures up to 2000°C in inert atmospheres with non-oxide sintering aids from pure SiC powder. Hot pressing, also called pressure-assisted densification, a ceramic significantly decreases the defects in the grain structure. This gives hot-pressed silicon carbide an extremely hard surface and high strength which is utilized in ballistic armor.  Reaction-bonded silicon carbide is produced by mixing SiC powder with powdered carbon and a plasticizer, forming the mixture into the desired shape, burning off the plasticizer, and then infusing the fired object with gaseous or molten silicon, which reacts with the carbon to form additional SiC. 
SiC semiconductor wafers are made out of silicon carbide crystal ingots. The ingots are usually produced by one of these three methods, sublimation PVT (physical vapor transport), HT-CVD (high-temperature chemical vapor deposition), and LPE (Liquid Phase Epitaxy). Other methods such as the modified PVT (M-PVT), continuous feed PVT (CFPVT), and halide CVD (H-CVD) shown in Figure 26, are evolutions of the original method and were modified to solve specific issues with the base process for particular applications.
Figure 26. Conventional and modified versions of growing silicon carbide crystal ingots. 
Sublimation PVT shown in Figure 27 is the most mainstream preparation method, and about 95% of silicon carbide ingots for commercial use are grown by the Physical Vapor Transport (PVT) also known as “seeded sublimation growth.” [30,34] Using inert gas and an inductively heated closed graphite crucible surrounded by thermal insulation running at temperatures above 2200°C, causes the SiC to sublimate and rise towards the cooler seed to form a single crystal.
Figure 27. Physical Vapor Transport (PVT), also referred to as “seeded sublimation growth” 
The highest quality crystals formed by the sublimation method are said to be those produced by a team from Toyota Central R&D Labs, Japan, using repeated a-face (RAF) growth shown in Figure 28. However, basal plane dislocations were still a part of the material. Nippon Steel and Sumitomo Metal Corporation and Toyota Motor Corporation have teamed up to find a solution to help eradicate the dislocations. This solution involves using a modified form of liquid phase growth to help in the production of ultra-high-quality SiC single crystals. Although more research is needed the results seem promising for them.
Figure 28. The SiC solution growth set-up used by engineers at Nippon Steel and Sumitomo Metal Corporation and Toyota Motor Corporation. The graphite crucible, which provides a container for the solvent and a carbon source, is directly heated by induction. Growth, typically at 2000°C, is conducted under atmospheric pressure in a mixture of helium and nitrogen gases. (b) Inside a crystal growth furnace. Suppressing solvent inclusions 
Major issues facing the SiC crystal market include the time-consuming growth cycle, the enlargement process, and the multiplication process of the SiC ingots shown in Figure 29. Quality of the seed is also a major factor in both the production and reproduction process. With over 200 forms possible, precise formulas and exact calculations are necessary in the replication of the original success of the test SiC for any company looking to produce their variation of SiC. The information for these processes is usually proprietary to the individual companies and so R&D can be a lot more trial and error during the beginning stages of creation of a specific run of SiC. With the increase in demand for SiC wafers, production facilities have continuously looked for ways to improve upon current innovations to overcome the challenges that seem to be faced by most industry leaders in this field.
Figure 29. Enlargement and multiplication of the SiC crystals.
In January of 2021 Nagoya Institute of Technology’s research into non-destructive ways to measure carrier lifetimes in silicon carbide devices has led them to advance upon one of the methods for measurement known as the time-resolved free-carrier absorption with intersectional lights (IL-TRFCA). Dr. Kato remarks, “Our non-destructive approach for measuring the distribution of carrier lifetimes allows one to determine the non-uniformity of a material without destroying the sample, which can then be used to fabricate devices, and research and develop bipolar SiC technology, such as high-voltage diodes and transistors.” 
The IL-TRFCA method essentially consists of excitation laser, which creates photoexcited carriers and a probe laser plus a detector, which measure their lifetime. By pointing both lasers at the edges of an objective lens (see Figure 1), they are made to converge at the surface of the sample with opposite incidence angles. Then, the sample is moved towards the lens in micrometric steps, which causes the excitation and probe lasers to intersect not at the surface of the sample, but at progressively deeper regions. In this way, the scientists managed to measure the distribution of carrier lifetimes within the sample without the need to cut it. 
Figure 30. In the proposed method, carrier lifetime measurements are made in the region where the excitation and probe lasers intersect, which progressively varies as the position of the sample is changed. 
Knowing the lifetime of carriers will allow engineers the ability to find the perfect balance of conduction modulation and low switching losses which could lead to a new generation of higher-performing SiC devices.  While the academics study ways to develop, create, and explore the other potentials that SiC holds in R&D, companies in the SiC industry are looking for ways to expand and improve on the current SiC structures and reproduction methods.
Vishay introduced 10 new 650 V silicon carbide (SiC) Schottky diodes in January of 2021. Featuring a merged PIN Schottky (MPS) design, the Vishay Semiconductors devices are designed to increase the efficiency of high-frequency applications by reducing switching losses, regardless of the effects from temperature variances — allowing the diodes to operate at higher temperatures. This is a crucial feature for designers working in certain areas of power electronics.
That same month, Cree presented its Wolfspeed WolfPACK power modules. This new power module was built using Wolfspeed SiC MOSFETs and was specially designed for engineers working in the mid-power range and for those designers struggling to integrate the right SiC solution because of the pitfalls of design complexity. According to the company, the goal of the product is to maximize power density while minimizing design complexity. Meant for applications such as EV fast charging and solar, this family of power modules is said to offer 1200 V operation with up to 105 A of forward current and an RDS(on) of 11 milliohms at 25°C. 
The global market for silicon carbide is estimated to reach USD 7.18 billion by 2027 with a CAGR of 16.1 % from 2020 to 2027.  The Silicon Carbide Wafer market alone is projected to reach USD 491.7 million by 2026, from USD 290 million in 2020, at a CAGR of 9.2% during 2021-2026 and, as mentioned earlier, semiconductor power electronic devices for xEVs are expected to reach US $5.6 billion in 2026.
This versatile material will be the beginning of many changes for multiple sectors within the various markets of the world. Major industries like aerospace & aviation, steel & energy, medical & healthcare, automotive, electronics & semiconductors, and military & defense will be major drivers for most of the research and development we are slated to see in the next few years. The Asia-Pacific as shown in Figure 31, has been predicted to dominate the SiC market due to the increasing demand for advance and upgraded technology from countries like China, India, and Japan. [39,40]
Figure 31. Predictions of the Global Silicon Carbide Market 
The future for SiC is looking extremely positive and with an abundance of attractive opportunities within multiple sectors of the global market, we are poised to see immense growth in the next few years. MRF is proud to be a part of this expanding industry by helping provide the furnaces necessary to grow the SiC crystal ingots, as well as help provide the furnaces necessary for the mass production process for the SiC market. For more information on how our furnaces can help you, please contact us.
Silicon Carbide Industry
Below is a list of global players in the silicon carbide, SiC semiconductor, and SiC Wafer industries. This is by no means an exhaustive list, but it does give an overview of some of the major players within the SiC market. As you can see, some of the companies on the list are involved in multiple sectors of the SiC market while others remain specialized in a particular field.
|Top manufactures in silicon carbide market:||Global Silicon Carbide Wafer market competition by top manufacturers:||Key players in the global Silicon Carbide (SiC) Semiconductor market:|
|AGSCO Corp||3C Inc.||Infineon Technologies AG|
|Cree Inc. (Wolfspeed)||Ascatron AB and||Renesas Electronic Corporation|
|Toshiba Corporation||Aym0nt Technology Inc.||Mitsubishi Electric Corporation|
|Pilegrowth Tech S.R.L.||Boostec||Rohm Co., Ltd|
|Silicon Carbide Products||CETC||Fuji Electric Co. Ltd|
|Graphensic AB||CoorsTek||ON Semiconductor Corporation|
|GE (GENERAL ELECTRIC)||Cree Inc. (Wolfspeed)||Broadcom Limited|
|ESK-SIC||Dow Corning||ST Microelectronics NV|
|CoorsTek||DuPont (Dow Corning)||Toshiba Corporation|
|Renesas Electronics Corporation||Fuji Electric Co., Ltd.,||NXP Semiconductor|
|CUMI EMD.||General Electric,||Cree Inc. (Wolfspeed)|
|Basic 3C, Inc.||Genesic Semiconductor Inc.,||Texas Instruments Inc.|
|SNAM Abrasives||Glenn Research Centere, NASA||Semikron International|
|United Silicon Carbide, Inc.||Graphensic AB.||Microchip Technology Inc.|
|Genesic Semiconductor Inc.||Hebei Synlight Crystal||Hitachi Power Semiconductor Device Ltd|
|Sanken Electric Co.,Ltd.||Hoya|
|ASUZAC||II-VI Advanced Materials|
|Bruckewell Technology Corporation||Infineon Technologies AG,|
|Central Semiconductor Corporation||Japan Fine Ceramics Company Limited|
|CeramTec||Monolith Semiconductor Inc.,|
|Dow Corning||MTI Corp|
|Rohm Semiconductor||Nippon Steel and Sumitomo Metal|
|Fuji Electric Co., Ltd||Norstel|
|Infineon Technologies||POCO Graphite|
|Microsemi Corporation||Renesas Electronics Corporation,|
|Henan Yicheng New Energy||Rohm Semiconductors|
|Miller and Company||Semiconductor Wafer, Inc.|
|Global Power Technologies Group||Showa Denko|
|Monolith Semiconductor Inc.||SICC|
|Xiamen Powerway Advanced Materials||STMicroelectroni|
|Saint-Gobain||Technologies and Devices International, Inc.|
|Ascatron||Xiamen Powerway Advanced Material Company Limited|
|Hongwu International Group|
|Tankeblue Semiconductor Co. Ltd.|
[55, 59, 53, 60, 39]
MRF also supplies parts and hot zones for other furnaces and can design and manufacture them to meet specific needs. One of our top-selling hot zones is graphite-based for the production of SiC and we are proud to supply these hot zones to some of the top manufacturers of SiC in the market today.
For more information on our parts and hot zones, please contact:
+1 (603) 419-5747
+1 (603) 455-4876
Who We Are…
MRF is a global leader in precision thermal systems essential for the research, development, and production of advanced materials. These advanced materials include ceramic matrix composites (CMCs), advanced ceramics, and SiC crystals. For decades, we have pioneered some of the world’s most innovative, customized furnace systems, with a focus on enabling the processing of materials at high temperatures in controlled atmospheres or vacuum. For additional information about MRF’s capabilities, please visit our products page by clicking on this link: mrf-furnaces.com.