Application prospects of silicon carbide

Whether it is low voltage or medium high voltage, power devices are closely related to our lives. Almost all electrical equipment needs to control and manage electrical energy through power devices, which are widely used in many fields such as new energy vehicles, communications, and industrial automation. Li Hui stated that silicon is currently the most widely used power semiconductor material, but the third-generation semiconductor silicon carbide, as a strategic electronic information material, has more significant physical performance advantages, with higher breakdown electric field (10 times that of Si), higher saturation electron drift rate (2 times that of Si), higher thermal conductivity (3 times that of Si and 10 times that of GaAs), and excellent performance in high temperature, high frequency, high voltage resistance, miniaturization, and other aspects.

Li Hui introduced that power devices made of silicon carbide have greater advantages. "Its blocking voltage is higher, the thickness of the device is about 1/10 of silicon, and the forward conduction resistance is lower. Therefore, at 300V-4.5kV, SiC devices are expected to replace Si based devices. Above 4.5kV, SiC based devices have an absolute advantage She pointed out that new energy vehicles are an important application scenario for silicon carbide and also the main driving force for silicon carbide, promoting the rapid development of the entire industry chain from semiconductor epitaxy to devices.

She is very optimistic about the development prospects of silicon carbide based power devices, especially with the development of rail transit and DC transmission networks. In the future, silicon carbide will develop towards higher power density, greater blocking voltage, and greater current, requiring the development of new silicon carbide single crystals, such as P-type silicon carbide single crystals, to prepare IGBT devices. According to Yole's forecast data, the market size of silicon carbide based power devices will exceed $10 billion by 2029, with a compound annual growth rate of approximately 25% from 2023 to 2029.

The industrial chain of silicon carbide power devices is very long, involving upstream silicon carbide single crystals and silicon carbide epitaxy, midstream chips, devices, modules, as well as downstream systems and applications. In the entire industry chain of silicon carbide power devices, the cost of silicon carbide single crystal substrate and epitaxy accounts for approximately 60%. Therefore, Li Hui pointed out that reducing the cost of silicon carbide single crystals and epitaxy is a very important link in reducing the overall cost of silicon carbide power devices, and it is also a prerequisite for improving the market penetration rate of silicon carbide power devices.

SiC Power Device Challenge

Although SiC power devices have many technological advantages, their preparation faces various challenges. Among them, SiC is a hard material that grows slowly and requires high temperatures (over 2000 degrees Celsius), resulting in long production cycles and high costs. In addition, the processing of SiC substrates is complex and prone to various defects.

At present, the preparation techniques for silicon carbide substrates include PVT method (physical vapor transfer method), liquid-phase method, and high-temperature vapor chemical deposition method. Li Hui stated that currently, the PVT method is mainly used for large-scale growth of silicon carbide single crystals in the industry. However, this preparation method presents great challenges in producing silicon carbide single crystals. Firstly, silicon carbide has more than 200 crystal forms, and the difference in free energy between different crystal forms is very small. Therefore, phase transition is easy to occur during the PVT method for growing silicon carbide single crystals, which can lead to low yield. In addition, compared to the growth rate of silicon pulled single crystal silicon, the growth rate of silicon carbide single crystal is very slow, resulting in a more expensive silicon carbide single crystal substrate.

The second reason is that the temperature for growing silicon carbide single crystals using PVT method is higher than 2000 degrees Celsius, which makes it impossible to accurately measure the temperature. In this growth system, it's like a black box, and we can't directly test the growth process of silicon carbide. This is also one of the reasons why it's difficult to grow silicon carbide single crystals

Thirdly, the sublimation of raw materials with different compositions results in a low growth rate.

Fourthly, PVT method cannot grow high-quality p-4H SiC and 3C SiC single crystals.

Li Hui pointed out that due to the reliability, stability, and low lifespan defects of 4H SiC MOSFETs, China currently relies on imports for 90% of its automotive grade main drive MOSFET devices. To overcome the defects of silicon carbide power devices and improve market penetration, several measures can be taken: firstly, reducing growth costs.

The second is to grow larger crystal sizes, resulting in a higher number of chips on a single crystal size. This is also the reason why 8-inch silicon carbide single crystal substrates have experienced rapid development in recent years.

The third is to develop new processing technologies, such as laser cutting technology.

The fourth is to produce P-4H silicon carbide single crystals to achieve higher blocking voltage and larger current.

The fifth is to improve the current problems of poor reliability, stability, and low lifespan of MOSFET devices from the material end.

The Application Prospects of Liquid Phase Method Technology

So, why develop liquid-phase technology? Li Hui stated that growing n-type 4H silicon carbide single crystals (for new energy vehicles, etc.) cannot grow p-type 4H SiC single crystals and 3C SiC single crystals. And p-type 4H SiC single crystal will be the basis for preparing IGBT materials in the future, which will be applied to high blocking voltage, high current IGBT, such as rail transit and smart grid applications. 3C SiC will solve the technical bottleneck of 4H SiC and MOSFET devices.

She also introduced that "from a comprehensive perspective of cost, energy consumption, etc., the cost of high-temperature liquid-phase method will be lower, expected to be reduced by 30% compared to PVT growth method. If raw material recovery is added, this cost will be further reduced." In addition, liquid-phase growth of silicon carbide is a growth method close to thermodynamic equilibrium, and the defect density of the grown crystal will be lower, making it easy to achieve diameter expansion and obtain P-type crystals.

Li Hui also introduced the progress of liquid phase silicon carbide growth in the Institute of Physics of the Chinese Academy of Sciences under the leadership of Chen Xiaolong. Unlike silicon, silicon carbide sublimates before being heated to melt. Therefore, a suitable cosolvent system is the basis for liquid-phase growth of silicon carbide single crystals, which mainly requires three aspects: first, a large ability to dissolve carbon; Secondly, there is no second phase in the liquid phase region; The third is the appropriate solid-liquid interface energy to regulate whether the desired growth is p-type silicon carbide single crystal or 3C silicon carbide single crystal.

The research team searched for some suitable co solvent systems through phase diagram calculations and experimental methods, in order to further grow the required silicon carbide single crystals. At present, the main challenges of PVT method are non-uniformity, poor quality, difficulty in controlling a single crystal structure, high resistance, and difficulty in obtaining high-quality P-4H-SiC single crystals. Therefore, Li Hui's research team used liquid-phase method to produce P-4H SiC single crystals and studied the key factor affecting the growth rate - interface energy. By optimizing the growth technology parameters, high-quality crystals without pore defects were obtained, with a resistivity of 0.1 Ω· cm and no giant step coalescence.

Li Hui introduced that the research team has recently grown 6-inch and 8-inch P-4H-SiC single crystals using liquid-phase method. Among them,

The thickness of the 8-inch P-4H-SiC single crystal reaches 8 millimeters. We have jointly developed with the Beijing lattice field and have achieved small-scale sales of P-type 6-inch 4H silicon carbide single crystals. We have studied its defects and found that the defect size grown by liquid-phase method is 1/10 of the size of silicon carbide single crystals grown by PVT method

In terms of 3C SiC growth, the Institute of Physics of the Chinese Academy of Sciences obtained 3C SiC single crystal for the first time in the world through high-temperature liquid phase method, achieving a breakthrough from 0 to 1. She said, "In the early stage, we achieved solid-liquid interface energy control by adjusting the composition and ratio of the co solvent, thus growing for the first time in the world 2 to 6 inches of 3C silicon carbide single crystals without phase transition, and the crystal quality is very high

Li Hui also stated that a series of studies have shown that the liquid-phase method has significant advantages in growing P-type 4H SiC single crystals and 3C SiC single crystals. With the continuous development of technology, especially with the participation of scientific research institutions and enterprises such as the Institute of Physics of the Chinese Academy of Sciences, Beijing Lattice Field Semiconductor Co., Ltd., Shandong Tianyue, Meishan Boya, Changzhou Zhenjing Semiconductor, Liancheng CNC, Hangzhou Science and Technology Innovation Center, Yunnan University, Tianjin University of Technology and other scientific research institutions and enterprises in the research of liquid phase growth of silicon carbide single crystals, P-type 4H SiC single crystals and 3C SiC single crystals will also gradually mature.