Big energy behind small chips

Speaking of silicon carbide wafers, everyone may feel very unfamiliar. But it plays a pivotal role in electric vehicles and 5G communications as we know it. 5G is fast because it has a very powerful heart, which relies on a silicon carbide wafer as thin as paper. Although it is only a small wafer from the outside, as the most advanced third-generation semiconductor material in the world, silicon carbide wafer has many advantages that other materials do not have. It is an ideal substrate for manufacturing high-temperature, high-frequency, and high-power semiconductor devices. . In addition to electric vehicles and 5G communications, silicon carbide wafers also have broad application prospects in national defense, aerospace and other fields. Its research and application are of great strategic significance and irreplaceable advantages. It is regarded as a new generation of national information technology. An important support for core competitiveness. On May 12, General Secretary Xi Jinping came to the Reform and Innovation Exhibition Hall of the Government Affairs Service Center of the Shanxi Transformation and Comprehensive Reform Demonstration Zone to learn about the reform, innovation and development of the demonstration zone. The China Electric Power (Shanxi) Silicon Carbide Material Industrial Base located in the demonstration area is the largest silicon carbide production base in the country.
From long-term dependence on imports and being "stuck" by foreign countries, to mastering mass production technology and realizing completely independent supply, in recent years, China's silicon carbide research and production has achieved remarkable results. What innovative technologies are contained in this small chip? What superb processes are used in the R&D and manufacturing process? Let's find out.
What is the purpose of the chip?
For every electric car produced, at least one piece of silicon carbide is consumed
The thickness is 0.5 mm, which is about the thickness of 5 sheets of A4 paper; the diameter is 4 inches or 6 inches, which is about the same as a CD disc. Such a thin wafer is a silicon carbide wafer. But just such a thin slice, the market price is around 2,000 US dollars, and it is often "hard to find".
Why are silicon carbide wafers so popular? This also starts with the material of silicon carbide.
As a mature third-generation semiconductor material, silicon carbide material has natural advantages such as high temperature resistance, high power, and high frequency. It shows great application potential in new energy vehicles, smart grids, rail transit, industrial motors, 5G communications and other fields. , has important application value in many strategic industries. Compared with ordinary silicon, the voltage resistance of silicon carbide devices is 10 times that of equivalent silicon devices. At the same time, silicon carbide material has extremely low power consumption and is an ideal energy-saving material. If calculated according to the annual output of 400,000 silicon carbide wafers, only in the field of lighting, the annual power consumption reduction is equivalent to saving 26 million tons of standard coal.
The reporter learned that at present, wafers made of silicon carbide are mainly used in two aspects. One is used as a substrate to make radio frequency devices, such as the construction of 5G base stations, intercity high-speed railways, and new energy vehicle charging piles in the new infrastructure mentioned in this year's government work report. As far as the construction of 5G base stations is concerned, the reason why 5G has a fast transmission speed is that it has a powerful 5G chip. Silicon carbide wafers are the most ideal substrates for 5G chips. "Now we also have some small 5G routers at home, but it is only indoors, and the radiation distance is very short. The radiation range of 5G base stations must be at least several kilometers. With such high power, silicon carbide can be used instead of silicon as radio frequency devices. Making the equipment smaller can also reduce energy loss and increase the reliability of equipment in harsh environments." Wei Rusheng, Technical Director of China Electronics Technology Group Corporation (hereinafter referred to as CEC), a silicon carbide manufacturer in Shanxi introduced.
Another role of silicon carbide wafers is to manufacture power electronic devices, such as triodes, and the main application area is electric vehicles. Wei Rusheng said: "At present, the battery life of electric vehicles is still a problem. If silicon carbide chips are used, the battery life of the car can be increased by about 10%. Although silicon carbide is used in electric vehicles The application of silicon carbide has just started and is still under development, but at least one piece of silicon carbide is consumed for every electric vehicle produced, so the development prospect is broad."
In addition to its powerful functions, another more important reason why silicon carbide wafers are so precious is that silicon carbide devices have high process requirements. Among them, the high-stability crystal growth process technology is its core. It was only mastered by a few developed countries such as the United States, and only a few companies in the world can commercialize mass production. my country's silicon carbide crystal research started relatively late, and it just started in the late 1990s. However, in recent years, my country has been catching up in the field of silicon carbide wafers, starting from basic principle research and basic experiments, and gradually mastered the technology of silicon carbide wafers, step by step, from the laboratory to the industrialization. In 2018, after 11 years of hard work, CLP II took the lead in completing the engineering of 4-inch high-purity semi-insulating silicon carbide single crystal substrate materials and the research and development of 6-inch high-purity semi-insulating silicon carbide single crystal substrates in China. In one fell swoop, it broke through the long-term blockade of my country's silicon carbide crystal growth technology abroad. Today, the development of 6-inch silicon carbide wafers and epitaxial wafers has been achieved in China, and the crystal quality is close to the international level.
Where is the difficulty in chip manufacturing?
In the crystal, there are not even microtubules as thin as several tenths of a hair.
"Silicon carbide has very stable characteristics, so it can still work stably in some harsh environments. It is precisely because of the stable chemical bonds that the technical threshold for silicon carbide production is very high." Talking about the difficulty of silicon carbide wafer development, the Chinese Academy of Sciences Semiconductor Zhang Yun, deputy director of the institute, listed the following aspects, "The growth conditions of silicon carbide ingots are harsh, requiring high temperature (~2600℃) and high pressure (>350MPa) growth environment; the crystal growth rate is slow, the production capacity is limited, and the quality is also poor. Relatively unstable; the size of the ingot is limited by the size of the wafer growth furnace; silicon carbide is a hard and brittle material, and its hardness is second only to diamond, which is difficult to cut and difficult to control the grinding accuracy.”
In order to produce high-quality silicon carbide wafers, these technical difficulties must be overcome. "We have a domestic demand of 100,000 pieces of radio frequency devices a year, and foreign countries have blocked embargoes on such products. The core technology cannot be bought with money. Only by self-reliance can we completely solve the problem of being 'stuck in the neck'. problem." Li Bin, general manager of CLP, introduced the complex production process of silicon carbide wafers to reporters. "Put high-purity silicon carbide powder in a crystal growth furnace and heat it to more than 2,000 degrees Celsius, let the particles vaporize directly, and then control it. It is recrystallized and grown into a 4" or 6" diameter pie-shaped ingot. After that, we use a number of diamond wires of only 0.18 microns in diameter, which are cut at the same time, and the ingot is cut into pieces. A wafer is then placed in a grinding device, the two sides are ground flat, and finally polished to obtain a wafer that is like a transparent glass sheet."
At present, the two key technologies for the production of silicon carbide wafers are crystal growth and wafer cutting and polishing. Zhang Yun said that the size and quality of wafers produced by upstream companies will affect the performance, yield and cost of downstream silicon carbide devices. Only by improving the quality of the substrate and reducing the cost, can downstream scientific research institutions or enterprises no longer be tied, and have more opportunities to do more device-level research.
The reporter learned that a wafer with a diameter of 4 inches can be made into 1,000 chips at a time, while a wafer with a diameter of 6 inches can be made into 3,000 chips at a time, so a wafer with a larger diameter has more advantages. From 2 inches to 6 inches, the key is crystal expansion technology. "Silicon carbide wafers start from a seed and grow layer by layer, from 2 inches to 3 inches to 6 inches. During this growth process, the crystal is prone to defects," said Mao Kaili, production director of CLP. " One of our indicators is called microtubule, which is a tubular hole that is only a few tenths of a hair in the crystal, which is invisible to the eyes. Once a microtubule appears, the entire crystal is unqualified. Because the temperature is too high Gao, there is no way to intervene manually, so the entire growth process is like 'blindfolded embroidery', which is precisely the core technology of the chip. It took us seven or eight years to solve this technical problem."
The processing of silicon carbide wafers is also a difficult process. Mao Kaili said that the roughness requirement of the wafer is that the surface undulation is less than 0.1 nanometers, and domestic polishing is now carried out by a combination of chemical and mechanical methods. "Technically speaking, if one of our wafers was originally cut, it may be 700-800 microns thick, and the final product requirement is 500 microns, so it is equivalent to grinding off several hundred microns. Now we have improved technology and finished cutting. It is about 550 microns, and only about 50 microns need to be ground off, and the entire production cost has been greatly reduced."
What is the prospect of chip mass production?
600 crystal growth furnaces with an annual output of 180,000 pieces, completely getting rid of import dependence
In March this year, China Electric Power (Shanxi) Silicon Carbide Material Industrial Base was officially put into operation in the Shanxi Transformation Comprehensive Reform Demonstration Zone, and the first batch of equipment was officially launched. The first-phase project of the base can accommodate 600 silicon carbide single crystal growth furnaces. After the project is completed, it will have an annual output of 100,000 pieces of 4-6 inch N-type silicon carbide single crystal wafers, and 50,000 pieces of 4-6 inch high-purity semi-insulating carbide wafers. The production capacity of silicon single crystal wafers is currently the largest silicon carbide material industry base in China. The launch of this base will completely break the situation of foreign countries' blockade of silicon carbide in my country, and realize the completely independent supply of silicon carbide.
In the silicon carbide production workshop of the base, white crystal growth furnaces are lined up, and silicon carbide wafers are quietly growing inside. Li Bin introduced: "Now, the powder synthesis equipment and crystal growth furnaces we use are nationally produced equipment developed and produced by ourselves. The supporting products and functional components of the equipment can meet the requirements of long-term, stable and reliable use. requirements, and at the same time, the energy saving effect is good, and it has high stability of continuous operation and good precision retention.”
For the domestic semiconductor field, the scale effect of industrialization not only reduces the cost of silicon carbide wafers, but also continuously improves the quality of silicon carbide wafers. According to Li Bin, the highest pass rate of silicon carbide wafers in the world is currently 70%-80%, while the pass rate of silicon carbide wafers produced in domestic laboratories is only 30%. But in the silicon carbide industrial base, this pass rate can reach 65%.
To achieve such a high pass rate, one depends on advanced equipment and the other depends on management. Mao Kaili introduced: "We divided all the processes into several sections, adding a large number of front-line workers, each person only does one thing in each section, not only the efficiency will be improved, but the error rate will also be greatly reduced, because it turns out that one person has to participate in the front line. There are about thirty or forty processes before and after, which is not conducive to specialization, and the error rate will be very high.”
At present, the base has achieved mass production of 4-inch wafers, and the engineering verification of 6-inch high-purity semi-insulating silicon carbide single crystal substrates has also begun to provide customers with small batches of product trials. It is expected to reach the industrialized application and international level by the end of the year quite. Looking forward to the future, Li Bin said with confidence, "In the field of silicon carbide, we must keep up with the pace of the world, because the gap between my country and the world in third-generation semiconductor materials is relatively small, and we must ensure that we will not fall behind. President Xi Jinping The secretary said that the core technology cannot be achieved by alms. Great efforts should be made in key areas and areas where the neck is stuck. Now we are implementing rapid R&D and further mass production, and the entire project will reach 180,000 pieces within three years. Annual production capacity. In addition, we are currently conducting research on 8-inch wafers, and we hope that in three years, we can have 8-inch samples out. Because wafers are the upstream of the entire silicon carbide industry chain, we must go to the front of device research. "