Speaking of silicon carbide wafers, everyone may feel very strange. But in the well-known electric vehicles and 5G communications, it plays a pivotal role. The reason why 5G is fast is because it has a very powerful heart, which depends on a thin silicon carbide wafer. As the world's most advanced third-generation semiconductor material, silicon carbide wafers have many advantages that other materials do not have. They are ideal substrates for manufacturing high-temperature, high-frequency, high-power semiconductor devices. In addition to electric vehicles and 5G communications, silicon carbide wafers also have broad application prospects in defense, aerospace and other fields. Its research and application are of strategic significance and have irreplaceable advantages. They are regarded as the new generation of national information technology. An important support for core competitiveness.
On May 12, General Secretary Xi Jinping visited the ZGDK silicon carbide material production base located in the demonstration zone. This will be the largest silicon carbide material production base in China.
From long-term dependence on imports, to mastering advanced mass production technology and achieving complete independent supply, in recent years, China's silicon carbide research and production has achieved outstanding 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?
Every electric car produced must consume at least one piece of silicon carbide
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 similar to that of a CD. Such a thin wafer is a silicon carbide wafer. It is such a slice, but the market price is about 2,000 US dollars, and it is often "it is difficult 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 has shown great application potential in the fields of new energy vehicles, smart grids, rail transit, industrial motors, and 5G communications. It has important application value in many strategic industries. Compared with ordinary silicon, the pressure resistance of silicon carbide devices is 10 times that of equivalent silicon devices. At the same time, silicon carbide materials have extremely low energy consumption for electricity and are an ideal energy-saving material. If calculated according to the annual output of 400,000 silicon carbide wafers, if it is only used in the field of lighting, the energy consumption reduced every year is equivalent to saving 26 million tons of standard coal.
Currently, silicon carbide wafers are mainly used in two ways. One is used as a substrate for making RF devices, such as 5G base station construction, intercity high-speed railways, and charging stations for new energy vehicles. As far as the construction of 5G base stations is concerned, the reason why 5G has a fast transmission speed is because it has a powerful 5G chip. The silicon carbide wafer is the ideal substrate for 5G chips.
Another role of silicon carbide wafers is to manufacture power electronic devices, such as transistors, and the main application area is electric vehicles. Wei Rusheng said: "At present, the battery life of electric vehicles is still a problem. If you use silicon carbide wafers, you can increase the battery's battery life by about 10% without changing the battery. Although silicon carbide is used in electric vehicles The application is just in its infancy and is still under development, but for every electric car produced, at least one piece of silicon carbide must be consumed, so the development prospects are broad."
In addition to its powerful functions, another important reason why silicon carbide wafers are so precious is that silicon carbide devices have high process requirements. Among them, the high stability of the long crystal process technology is its core. It was originally only controlled by a few developed countries such as the United States, and only a handful of companies in the world can be commercially mass-produced. China's silicon carbide crystal research started late, and it has just begun in the late 1990s. However, in recent years, China has been struggling to catch up in the field of silicon carbide wafers. Starting from basic principles research and basic experiments, it has gradually mastered the technology of silicon carbide wafers, step by step, from the laboratory to industrialization.
In 2018, after 11 years of technical development, ZGDK Silicon Carbide Research Institute took the lead in completing the engineering of 4-inch high-purity semi-insulating silicon carbide single crystal substrate materials and the development of 6-inch high-purity semi-insulating silicon carbide single crystal substrates in China. Break through the long-term blockade of China's silicon carbide crystal growth technology abroad. Today, China has achieved the development of 6-inch silicon carbide wafers and epitaxial wafers, and the crystal quality has reached or even surpassed the international advanced level.
Where is the difficulty of wafer manufacturing?
"Silicon carbide has very stable characteristics, so it can still work stably in some harsh environments. It is precisely because of stable chemical bonds that the technical threshold for silicon carbide production is very high." Talking about the difficulty of developing silicon carbide wafers, 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 relatively Unstable; limited by the size of the wafer growth furnace, which restricts the size of the ingot; silicon carbide is a hard and brittle material, the hardness is second only to diamond, the cutting difficulty is difficult, and the grinding accuracy is difficult to control."
To produce high-quality silicon carbide wafers, these technical difficulties must be overcome. The technical director of ZGDK introduced the complicated production process of silicon carbide wafers. "Put high-purity silicon carbide powder into a crystal growth furnace and heat it to more than 2000 degrees Celsius to let the particles vaporize directly, and then control it to recrystallize, and grow into a diameter of 4 inch or 6 inch wafer-shaped ingots. After that, we use a lot of diamond wires with a diameter of only 0.18 microns and cut them at the same time to cut the ingots into pieces. Each piece is put into the grinding equipment Here, the two sides are smoothed and finally polished to obtain a wafer like a transparent glass sheet."
At present, the two key technologies for producing 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 when the quality of the substrate is improved and the cost reduced, can downstream scientific research institutions or enterprises no longer have to deal with problems and have more opportunities to do more device-level research.
The reporter learned that a 4-inch wafer can be made into 1000 chips at a time, and a 6-inch wafer can be made into 3000 chips at a time, so a wafer with a larger diameter is more advantageous. From 2 inches to 6 inches, the key is crystal expansion technology. "Silicon carbide wafers are grown layer by layer from a seed, from 2 inches to 3 inches to 6 inches. During this growth process, the crystal is prone to defects." Mao Kaili, ZGDK production director, said, "Our One indicator is called microtubules, which is a tubular hole that appears in the crystal only about a few tenths of the hair. The eye cannot see it. Once the microtubule appears, the entire crystal is unqualified. Because the temperature is too high, There is no manual intervention, so the entire growth process is like'blindfolded embroidery', which is precisely the core technology of the wafer. 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 of the wafer is required to have a surface fluctuation of less than 0.1 nanometers. China is now using a combination of chemical and mechanical polishing. "Technically speaking, if one of our wafers is cut, it may be 700-800 microns thick, and the final product requires 500 microns, so it is equivalent to grinding away hundreds of microns. Now we have improved through technology and cut It’s about 550 microns, and it’s only about 50 microns, so the entire production cost has been greatly reduced.”
What are the prospects for mass production of chips?
600 crystal growth furnaces, 180,000 pieces of annual output, completely get rid of import dependence
In March this year, the ZGDK silicon carbide material industrial base was officially put into operation in the Shanxi 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 4-6 inch N-type silicon carbide single crystal wafers and 50,000 4-6 inch high-purity semi-insulating carbonization The production capacity of silicon single crystal wafers is currently the largest domestic silicon carbide material industrial base. The launch of this base will completely break the blockade of silicon carbide from abroad and achieve complete independent supply of silicon carbide.
In the silicon carbide production workshop at 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 furnace we use are all domestically produced equipment that we have developed and produced ourselves. The supporting products and functional components of the equipment can meet long-term, stable and reliable use. Requirements, at the same time, it has good energy-saving effect, high stability and good accuracy of continuous work."
For the domestic semiconductor field, the scale effect of industrialization not only reduces the cost of silicon carbide wafers, but also continuously promotes the quality of silicon carbide wafers. According to Li Bin, at present, the highest pass rate of silicon carbide wafers in the world is 70%-80%, while the pass rate of silicon carbide wafers produced by domestic laboratories is only 30%. But in the silicon carbide industrial base, this pass rate can reach 65%.
At present, the base has realized mass production of 4-inch wafers, and 6-inch high-purity semi-insulating silicon carbide single crystal substrates have also begun engineering verification to provide customers with small batches of product trials. It is expected to reach industrial application and international level by the end of the year. quite. "In the field of silicon carbide, we must keep up with the international pace, because the gap between China and the third-generation semiconductor materials is relatively small at present, and we must ensure that we cannot fall behind. Now we are carrying out rapid research and development while further developing the volume The entire project will reach an annual production capacity of 180,000 wafers in three years. In addition, we are currently conducting research on 8-inch wafers, and hope that after three years, we will have 8-inch samples. Because the wafers are the entire silicon carbide industry chain Upstream, we must go to the front of device research."