The semiconductor industry, as the foundation of the modern electronic information industry, is an important industry that supports the high-quality development of the national economy. The third generation of semiconductors refers to emerging semiconductor materials such as SiC, GaN, ZnO, diamond (C), AlN, etc. that have wide bandgap (Eg>2.3eV) characteristics. Silicon carbide is currently the most mature third-generation semiconductor material in development.
1、 Silicon carbide crystal structure
Silicon carbide (SiC) is composed of carbon (C) atoms and silicon (Si) atoms, with a density of 3.2g/cm ³， Natural silicon carbide is very rare and mainly synthesized through artificial means. Its crystal structure has the characteristic of homogeneous polytype, and the most common ones in the semiconductor field are 3C-SiC with cubic sphalerite structure and 4H-SiC and 6H-SiC with hexagonal wurtzite structure.
2、 Basic properties of silicon carbide
Silicon carbide has a hardness of up to 9.2 to 9.3 Mohs at 20 ℃, making it one of the hardest substances and can be used for cutting rubies;
The thermal conductivity exceeds that of metallic copper, which is 3 times that of Si and 8-10 times that of GaAs. Moreover, it has high thermal stability and cannot be melted under normal pressure;
Silicon carbide has the characteristics of wide bandgap and breakdown resistance, with a bandgap width of 3 times that of Si and a breakdown electric field of 10 times that of Si.
Material parameters of 4H SiC and 6H SiC
3、 The Development History of Silicon Carbide Materials
In 1824, the Swedish scientist Berzelius unexpectedly discovered silicon carbide in an experiment to synthesize diamond. However, due to the scarcity of silicon carbide in nature, it has not received sufficient attention.
In 1885, another chemist, Acheson, generated SiC crystals at high temperatures during the heating process of quartz sand mixed with carbon, marking the first time in human history that pure silicon carbide was prepared.
In 1959, a Dutch scientist proposed a method for single crystal growth through sublimation, which was later improved and optimized by Russian scientists in 1978.
In 1979, a blue light-emitting diode made mainly of silicon carbide was invented.
Until now, in the subsequent research and application process, silicon carbide has played a huge role in various forms and application methods in electronic information storage, transmission, and data communication related industries. With its stable chemical properties and excellent semiconductor material characteristics, it has obtained great development space in the field of semiconducting materials.
4、 Advantages of Silicon Carbide Semiconductor
Advantages of Silicon Carbide Crystal Material Application
5、 Silicon carbide semiconductor industry chain
The silicon carbide semiconductor industry chain mainly includes links such as "high purity silicon carbide single crystal substrate epitaxial wafer power device module packaging terminal application".
1. High purity silicon carbide powder
Silicon carbide high-purity powder is a raw material for growing silicon carbide single crystals using the PVT method, and its product purity directly affects the growth quality and electrical properties of silicon carbide single crystals.
There are various synthesis methods for silicon carbide powder, mainly including solid phase method, liquid phase method, and gas phase method. Among them, solid-phase method includes carbothermal reduction method, self-propagating high-temperature synthesis method, and mechanical crushing method; Liquid phase method includes sol gel method and polymer thermal decomposition method; Gas phase methods include chemical vapor deposition, plasma method, and laser induced method.
2. Single crystal substrate
Single crystal substrates are the supporting materials, conductive materials, and epitaxial growth substrates for semiconductors. The key step in producing silicon carbide single crystal substrates is the growth of single crystals, which is also the main technical difficulty in the application of silicon carbide semiconductor materials. It is a technology intensive and capital intensive link in the industrial chain. At present, the growth methods of SiC single crystals include physical vapor transport method (PVT method), liquid phase method (LPE method), high-temperature chemical vapor deposition method (HT-CVD method), and so on.
Comparison Table of Silicon Carbide Single Crystal Growth Methods
3. Epitaxial wafer
Silicon carbide epitaxial film refers to a silicon carbide film (epitaxial layer) grown on a silicon carbide substrate with certain requirements and the same crystal orientation as the substrate. In practical applications, wide bandgap semiconductor devices are almost always made on the epitaxial layer, and silicon carbide wafers themselves only serve as substrates, including GaN epitaxial layers.
At present, there are various methods for preparing SiC thin films on silicon carbide single crystal substrates, including chemical vapor deposition (CVD), liquid phase deposition (LPE), sublimation, sputtering, MBE, and so on. Among them, the CVD method is the main method for preparing high-quality silicon carbide crystal thin film materials and devices.
4. Power devices
The wide bandgap power device made of silicon carbide material has the characteristics of high temperature resistance, high frequency, and high efficiency.
According to the working form of the device, SiC power devices mainly include power diodes and power switches. SiC power devices, like silicon based power devices, are processed using microelectronic processes.
From the perspective of silicon carbide crystal materials, 4H-SiC and 6H-SiC are the most widely used in the semiconductor field, with 4H-SiC mainly used for preparing high-frequency, high-temperature, and high-power devices, while 6H-SiC is mainly used for producing power devices in the optoelectronic field.
5. Module packaging
Module packaging can optimize the performance and reliability of silicon carbide power devices during use, and flexibly combine power devices with different application solutions.
At present, the packaging types of related power devices in the mass production stage mainly use silicon power devices. The commonly used packaging types for silicon carbide diodes are TO220, while the commonly used packaging types for silicon carbide MOSFETs are TO247-3, with a few using new packaging methods such as TO247-4 and D2PAK.
6. Terminal applications
Silicon carbide devices have advantages such as small size, high power, high frequency, low energy consumption, low loss, and high voltage resistance. Current main application areas: various power supplies and servers, photovoltaic inverters, wind power inverters, on-board chargers for new energy vehicles, motor drive systems, DC charging piles, variable frequency air conditioning, rail transit, military industry, etc.
6、 Current problems in silicon carbide wide bandgap semiconductors
The preparation technology for large-sized SiC single crystal substrates is still immature.
At present, 8-inch SiC single crystal samples have been developed internationally, and the single crystal substrate size is still relatively small and the defect level is still high. And there is a lack of more efficient SiC single crystal substrate processing technology; The research and development of p-type substrate technology is relatively lagging behind.
The epitaxial growth technology of n-type SiC needs further improvement.
The market advantage of SiC power devices has not yet fully formed, and it cannot shake the current dominant position in the silicon power semiconductor device market.
International SiC device field: The development of SiC power devices towards high capacity is limited; The process technology level of SiC devices is relatively low; Lack of unified testing and evaluation standards.
There are three gaps in the field of SiC power devices in China:
(1) The research and development progress in SiCMOS FET devices is slow, with only a few units possessing independent research and development capabilities, and the level of industrialization is not optimistic.
(2) The main process equipment for SiC chips is basically monopolized by foreign companies, especially high-temperature ion implantation equipment, ultra-high temperature annealing equipment, and high-quality oxide layer growth equipment. The key equipment used for large-scale establishment of SiC process lines in China basically needs to be imported.
(3) The high-end testing equipment for SiC devices is monopolized by foreign countries.
4. The main problems with SiC power modules currently exist:
(1) Adopting a SiC power module with multiple chips in parallel will generate severe electromagnetic interference and additional losses, which cannot fully utilize the excellent performance of SiC devices; The SiC power module has large stray parameters and low reliability.
(2) The development of SiC power high-temperature packaging technology lags behind.
The driving technology of SiC power devices is not yet mature.
The application model of SiC devices cannot fully reflect the physical characteristics of SiC devices. Generally, it is only suitable for conventional industrial applications with low precision requirements.
7、 Application and advantages of SiC devices in various industries
Power supply/large server: used inside power supply and power factor corrector to reduce volume and weight, improve efficiency, and reduce losses.
Photovoltaic: Used in photovoltaic inverters, the current generated by photovoltaic power generation is direct current, which needs to be converted into alternating current through the inverter to achieve grid connection. The use of SiC power devices can reduce volume and weight; Improve the inverter conversion efficiency by about 2%, and achieve a comprehensive conversion efficiency of 98%; Reduce losses and improve the economic benefits of photovoltaic power stations; SiC material characteristics reduce failure rate.
Wind power: used for wind power rectifiers, inverters, and transformers. The AC power generated by wind power generation is easily affected by wind power, causing voltage and current instability. It needs to be rectified into DC power before being converted into AC power to achieve grid connection, improving efficiency and reducing losses. At the same time, the cost and quality are reduced by 50% and 25% respectively.
New energy vehicle on-board charger (OBC): reducing volume and weight, improving efficiency, and reducing losses.
New energy vehicle motor drive system: Utilizing SiC power module to reduce the volume by 1/3-2/3 compared to silicon-based modules, reducing volume and weight; Reduce power loss by 47%, switch loss by 85%, and improve power utilization efficiency; The switching frequency can reach more than 10 times that of silicon based IGBTs. Increasing the switching frequency will significantly reduce the volume and cost of peripheral components such as inductors and capacitors. Reduce volume and weight; The heat generation is only half of that of silicon devices, which has excellent high-temperature stability, easier heat dissipation treatment, reduced heat dissipation volume, and can reduce the volume of vehicle cooling systems by 60%, even eliminating secondary liquid cooling systems, reducing volume and weight; It can achieve the integration of inverter and motor, reducing volume and weight. It can comprehensively increase the range of new energy vehicles by about 5% to 10%.
DC charging pile for new energy vehicles: reducing volume and weight; Improve charging efficiency by at least 1% to achieve conversion efficiency of over 96%; Due to the low temperature dependence of SiC power devices, the efficiency of energy conversion during high summer temperatures is improved; Reduce electrical energy loss and improve the economic benefits of large charging stations; The cost of the charging station system is basically the same as that of silicon-based systems, with a high cost-effectiveness.
Air conditioning: Used in the power factor correction (PFC) power supply of the front-end of variable frequency air conditioning, the volume and mass are significantly reduced by more than half, the power consumption is reduced by 15%, and the overall cost is reduced by 10%.
Rail transit: By using SiC inverters, the power loss of the vehicle system can be reduced by more than 30%, the volume and mass of components can be reduced by 40%, and efficiency and speed can be improved.
Electromagnetic induction heating: reducing volume and weight, improving efficiency, and reducing losses.
Military industry: various power supply devices for vehicle, airborne, ship, and missile, reducing volume and weight, improving efficiency, and reducing losses.
epilogue
Silicon carbide has been widely used due to its excellent physical and chemical properties, quickly occupying half of the semiconductor material market. With the continuous decline in production costs, excellent performance has enabled silicon carbide to gradually replace silicon based semiconductors in the power device industry. Faced with the huge development potential of the silicon carbide semiconductor market worldwide, China needs to quickly enhance its research and development capabilities and improve the development system of silicon carbide semiconductors.
