Some time ago, J. D. Blevins of the U.S. Air Force Research Laboratory (AFRL) published a report introducing the development process of the U.S. SiC industry.

According to reports, North Carolina State University has been conducting research on SiC sublimation growth for a long time. With a number of key patents,Cree-Research was officially established in 1987.In 1991, it became the first company to provide commercial silicon carbide.

Figure 1. Cree25mm 6H-SiC substrate and 6H-SiC Lely wafer.

In addition to Cree-Research, in the early 1990s,Westinghouse Technology Center and Advanced Technology Materials Inc. (ATMI)They are also actively involved in SiC research and development.

but,Early research on SiC sublimation growth was full of ups and downs.There are various technical challenges that are difficult to overcome, including micropiping, doping, polytype control, diameter expansion, and crystal defects.

Cree-Research launched 25mm 6H SiC in 1991 and 50mm 4H SiC in 1998. Although there are multiple suppliers producing similar products,The prices are very expensive, and the density of microtubules exceeds 100cm-2 。

Figure 2. Early sublimation silicon carbide single crystal suppliers and specifications.

In order to promote wider commercialization of SiC, the U.S. Defense Production Act of 1999"Title III Plan"Providing much-needed start-up capital to the SiC industry, the U.S. Air Force has awarded "cost-share contracts" to 3 companies,Including Cree-Research, Sterling (ATMI) and Litton-Airtron,The goal is to expand the SiC substrate diameter to 75mm and improve crystal quality.

Beginning in 2002, the U.S. Defense Advanced Research Projects AgencyWBGS planAlso pays great attention to the development of wide bandgap semiconductor materials,Both Cree and Sterling were awarded relevant contracts,The goal is to expand N-type and semi-insulating SiC substrate diameters to 100mm and reduce microtube density to less than 1cm-2.

However, not all businesses that receive funding do well.

December 2000,Litton Industrieswas sold at a price of US$3.8 billion (approximately 24.5 billion yuan) or US$80 per share.Northrop Grummanacquisition. At the end of 2001, Litton-Airtron’s SiC R&D departmentAcquired by II-VI.

In 2002, just weeks after being awarded the DARPA contract,SterlingUniroyal Corporation, the parent company of Uniroyal Corporation, filed for bankruptcy, resulting in the outflow of key technical personnel.Dow Corning immediately acquired Sterling.

and,Early SiC technology development fell far short of contract plan goals.As you can see from the picture below, Cree's quality is significantly better than its competitors.

Figure 4. Cross-polarization images of Cree 75mm, DOW 75mm and II-VI 50mm 4HN SiC (top) and semi-insulating SiC (bottom), circa 2002.

In 2005, DARPA’s support for SiC substrates basically ended.Only Cree shows strong signs of accelerating the commercialization of SiC substrates. At that time, Dow Corning's research and development was still struggling, and II-VI's progress was also very slow.

Subsequently, DARPA focused its investment mainly on SiC power switches and GaN RF devices, from which Cree's substrate business benefited.

In the early 2000s, Cree continued to lead in the development and promotion of SiC substrate technology. Through vertical integration, they were able to directly drive improvements in material quality through internal use demand,But this also means that their substrate and epitaxy customers are also their main competitors.

The United States believes thatThere is only a single supplier of SiC substrates, which may hinder the development of the industry.Pure SiC substrate suppliers are critical to the long-term development and commercialization of SiC and GaN device technologies.

Therefore, from 2003 to 2017,AFRL has provided 4 large contracts to II-VI Company, totaling more than 350 million yuan.

The main goal of the first two contracts is to expand the diameter of 4HN SiC to 100 mm.However, at that time, II-VI’s 100 mm semi-insulating 6H SiC edge area was covered with formed grains and other defects,Microtubule density reaches 117cm-2(picture below).

Therefore, while supporting II-VI,AFRL also supports Intrinsic in developing SiC.Intrinsic is made bySAfter terling was acquiredof key personnel.

Intrinsic quickly and successfully demonstrated high-quality 100-mm SiC in less than two years.More importantly, in September 2005, Intrinsic took the lead in releasingZero Micropipes (ZMPTM) 4HN SiC(picture below).

But in July 2006,Cree acquires Intrinsic. In 2007, Cree released 100mm 4HN ZMPTM SiC, and 100 mm semi-insulating SiC.

FortunatelyThere is also progress in the research and development of II-VI,exist2003-2010During this period, II-VI expanded the crystal diameter from 50 mm to 100 mm, and also released 100 mm 4HNSiC and semi-insulating SiC.

Caption: II-VI 100-mm semi-insulating 6H SiC substrate (top) and100mm 4HN SiC substrate (bottom).

At the end of 2010, AFRL signed its largest contract with II-VI——More than 20 million US dollars (approximately 130 million yuan), with a focus on development and commercialization6-inch 4HN SiC and semi-insulating 6H SiC, as well as continued diameter expansion to 8 inches。

Since receiving the funding, II-VI has made significant investments in facilities and equipment, including expanding its New Jersey facility and establishing two manufacturing facilities in Mississippi.

Ultimately, II-VI relies on its exclusive patentedAdvanced Physical Vapor Transport (APVT) and Axial Gradient Transport (AGT)crystal growth technology,The goals of 6-inch and 8-inch SiC single crystals were achieved.

II-VI demonstrated microtube-free 100mm 6H semi-insulating and 150mm 4HN SiC in 2013 and 2014 respectively; July 2015,Became the first company to display 8-inch 4HN SiC.

In March 2017, AFRL awarded II-VI a fourth contract for five years,Government funding of US$12 million (approximately RMB 774.8 billion). This work focuses on improving manufacturing efficiency, reducing defects and reducing costs,To grow and fabricate 200mm of 4HN SiC and semi-insulating SiC.

These defect-free large-diameter crystals were grown using a new fully automated growth platform, and II-VI successfully reduced the dislocation density of 200mm 4HN SiC toReduced to 1881cm-2,ThatIncludes a screw density of 598 cm-2 and a base density of 272 cm-2.

In terms of semi-insulating silicon carbide, II-VI uses vanadium compensation to introduce deep energy levels within the band gap,We are the only market supplier of semi-insulating SiC doped with vanadium, with its reproducible and highly uniform resistivity exceeding 1011Ω·cm.

October 2019,II-VI demonstrated 200 mm 6H semi-insulating SiC for the first time in the industry.

Over the past 30 years,U.S. Department of Defense funds more than 100,000 dollars for wide-bandgap semiconductors1 billion US dollars (approximately 6.457 billion yuan), it can be said that a whole new industry was born.Companies such as Cree Research, Westinghouse, Northrop-Grumman, ATMI, Sterling, Litton-Airtron, Dow and Intrinsic, some have been acquired and some have disappeared.andWolfspeed-Cree, II-VI "Winner Takes All",The current combined global market share of the two companiesMore than 70%.

In recent years, as SiC commercial and military demand has grown rapidly, these two companies have also continued to expand production.In September 2019, Wolfspeed-Cree announced its commitment to investUS$1 billionBuilding the world’s largest SiC power and RF manufacturing facility.And II-VI continues to expand manufacturing capacity in New Jersey, Pennsylvania and Massachusetts.

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