In November 2019, the 2019 China Switzerland industry university research development forum hosted by China Association for science and technology and Shenzhen Municipal People's government, and hosted by China Association for science and technology enterprise innovation service center, Guangdong science and Technology Association, Shenzhen Science and Technology Association and Nanshan District People's government, was successfully held in Shenzhen.
In order to implement the cooperation agreement between China and the Swedish Royal Academy of engineering, explore the innovation cooperation between China and Switzerland, and promote the rapid development of the third generation semiconductor industry in China, the forum held the sub forum of the third generation semiconductor industry summit forum with the theme of "focus on innovation and win-win cooperation". Li Zheyang, director of micro manufacturing and integration technology center of Nanjing University, delivered a wonderful speech on the theme of "research and development status of silicon carbide epitaxy technology".
Research background of silicon carbide
With the development of economy, people's living standard has been greatly improved. At the same time, the problem of high pollution, high energy consumption and global temperature cooling has become increasingly serious. In this case, how to improve the efficiency of power utilization is a very important topic. According to statistics, more than 50% of current loss occurs in the process of power conversion and drive, and the key role is power electronic devices. How to control energy consumption has become a global topic.
In this case, silicon carbide has been paid attention to. Its thermal conductivity is three times of that of silicon, and its breakdown field strength is about 10 times of that of silicon. When it is reflected on the chip, it can work at a higher temperature, and the loss should be reduced at the same time, so we can use a better cooling system to complete the work. At the same time, high switching frequency can bring the switching loss of the chip, higher switching frequency can be used, and the peripheral components can use fewer filters and passive components.
Consumer electronics includes future laptops and chargers, including white household appliances. There are a lot of SiC in the air conditioner of the home, which can be said to exist in areas related to the national economy and people's livelihood. For a simple example, for example, solar energy, now mainly uses polycrystalline silicon, which is very difficult to increase by 0.1 percentage point at this time. After the conversion of solar energy, it will be direct current. We need to turn it into alternating current. It is not easy to increase 0.1 when using polysilicon. For example, in the aircraft carrier accessories, the importance of the transformer has been reduced from 6 tons to 1.7 tons, and the volume has been reduced from 10 cubic meters to 2.7 cubic meters. Silicon carbide, including submarine, can save a lot of space.
Governments all over the world attach great importance to silicon carbide. For example, if you want to promote the research and development of the next generation of gallium nitride semiconductors, we can't do without our extension, including the United States, the European Union, Japan and other countries have also formulated relevant semiconductor industry policies.
Research on epitaxy Technology
The process of silicon carbide is to synthesize silicon carbide powder with high frequency carbon powder, and finally turn it into wafer. There is a very important link before it becomes a chip to be a device. That is to say, it needs to epitaxial one or more layers. If the thickness is different, it needs to be sliced and subpackaged after it is made into a chip. Epitaxy is essential in the whole process, and it needs epitaxy Technology to realize. High quality epitaxy is also the basis of realizing the device.
The rapid development of epitaxy also promotes the application of silicon carbide. Li Zheyang said that in the early days, he was mainly engaged in military affairs, and now his goal has shifted to power electronic devices, because there is a larger market in this area.
Step control principle in silicon carbide epitaxial growth. In 1987 and 1988, two research teams successively proposed how to epitaxial silicon carbide with deflection angle, how to grow a perfect silicon carbide surface epitaxial wafer, and made good contributions. This technology has been used to this day.
Li Zheyang said that there are two themes of silicon carbide epitaxy, one is the whole control defect, and the other is how to improve the uniformity. The early defects of SiC originated from the substrate, and there were many defects, including microtubules, various dislocations and inclusions. Some of these defects will extend into the epitaxial layer during the epitaxial growth process, which brings a lot of bad consequences to the chip. For example, the breakdown voltage will be greatly reduced, leading to failure.
Japan's research team has done some research on defects such as substrate. The total dislocation density is unchanged. By converting high-risk defects to low-risk defects, epitaxy can promote the conversion of high-risk defects to low-risk defects through process control. In the growth process, if a particle falls on the surface, it will grow out and form a hole, which is cleaned out in the cleaning process. There are also triangle defects. All triangle defects will reduce the chip voltage to below 50V, which means the chip is useless.
For the study of uniformity, there has been a rule in the early development. From 3-inch to 4-inch, now to 6-inch, it will be more difficult for the size to become larger. Scientists have discovered in the process of epitaxy that the principle of growth is linear. When rotation is introduced, the thickness of epitaxial layer will be very gentle and uniform, but it is not the same as that of growth depletion. The epitaxial plate produced by this way is in the shape of N and bowl. What should we do at this time? The carbon source is introduced at both ends of epitaxy to improve the carbon ratio. When there is more carbon, the probability of entry will be reduced.
Through the study of carbon process, it is found that the influence of carbon micro ratio on the inhomogeneous doping concentration is greater than the growth temperature and the main hydrogen flow rate. The primary and secondary order of the influence of process parameters on the thickness heterogeneity is that the hydrogen flow rate is greater than the growth temperature. Optimizing the main hydrogen flow rate can effectively improve the thickness uniformity.
The current situation of the whole extension industry at home and abroad
With the development of control principle around 1988, the epitaxial silicon carbide has become a reality. In different years, the thickness reaches some index parameters. In the whole process of extension development, equipment development is also very important. The earliest equipment is also being used now, but it can not meet the requirements of the industry.
According to the prediction of the international authoritative consulting agency, the market capacity of silicon carbide will reach 12 billion US dollars in 2027. In the future, the development trend of substrate technology, no matter how many, has larger size requirements. When will 8-inch products be commercialized? The answer was given in late last month, and the first 8-inch silicon carbide has been prepared. In addition, lower defect density and higher yield are required. For epitaxy, one is large-scale thick layer epitaxy, including tens of thousands of volts for grid applications in the future; the other is multi-layer structure epitaxy research, how to control the concentration, thickness, uniformity and epitaxial defects when the size becomes large, which is the constant theme.
At present, the era of silicon carbide module is coming, there are many applications want to use silicon carbide, but they may not have the ability of module design, so it needs someone to do module design, including the design of some internal circuits. Driving the growth of the whole silicon carbide application market, including rail transit, motor drive, electric vehicles and various converters, many manufacturers have made layout.
People in the industry are more optimistic about the silicon carbide market, and the capital is constantly surging. The strong are always strong. The layout of international giants is very strict. Many companies are doing "substrate epitaxy chip module". Asia's capital also dare not lag behind, such as Japan's Roma, which acquired sicrystal in 2009 to form a SiC whole industry chain from substrate to module; Japan's Showa electric announced to expand its extension capacity in June 2016, April 2018, September 2018 and February 2019 successively; South Korea's sk silon acquired DuPont's silicon carbide wafer business unit in November 2019 with us $450 million. At present, electric vehicles and rail transit are in the process of relay, which will usher in a larger application market.
(sorted out according to the shorthand materials of 2019 "China Switzerland industry university research development forum")