Silicon carbide (SIC) is a compound composed of silicon (SI) and carbon (c) by covalent bond. Its basic unit is Si-C tetrahedron, in which Si atoms are located in the center and surrounded by C atoms. All the structures of SiC are composed of Si-C tetrahedron in different stacking ways. At present, there are more than 200 kinds of SiC heteromorphic crystal structures. Among them, the hexagonal 4H SiC (4h SiC) has the advantages of high critical breakdown electric field and high electron mobility. It is an excellent semiconductor material for manufacturing high voltage, high temperature and radiation resistant power semiconductor devices, and is also the third generation semiconductor material with the best comprehensive performance, the highest commercialization degree and the most mature technology It has: (1) the critical breakdown electric field strength is nearly 10 times of that of silicon material; (2) the thermal conductivity is high, which is more than 3 times of that of silicon material; (3) the saturated electron drift velocity is high, which is twice as high as that of silicon material; (4) it has good radiation resistance and chemical stability; (5) like silicon material, silicon dioxide insulation layer can be directly grown on the surface by thermal oxidation process. Pure SiC is colorless. Industrial silicon carbide is brown to black because of its iron content. The iridescent luster of SiC crystal is caused by the passivation layer of silica on the surface.
The development of power semiconductor has experienced the following development process: the first generation of semiconductor materials represented by single crystal materials such as germanium and silicon, the second generation of semiconductor materials represented by gallium arsenide and indium phosphide, and the third generation of semiconductor materials represented by silicon carbide and gallium nitride.
Development of semiconductor materials
In recent years, with the rapid development of semiconductor technology, the performance of traditional Si based devices has approached the theoretical limit in terms of low energy consumption, high energy efficiency and miniaturization. Compared with Si based semiconductor materials, SiC has attracted much attention because of its low energy consumption, high efficiency and miniaturization. SiC MOSFET has become one of the most rapidly developing power semiconductor devices because of its low on resistance, good thermal stability, fast switching speed and high blocking voltage.
Infineon produces SiC devices for Tesla inverters (24 SiC MOSFET modules)
Development status of silicon carbide industry
Since the 1990s, the United States, Japan, Europe and other countries have invested a lot of money and manpower in-depth research on silicon carbide materials and devices, and made major breakthroughs in the performance improvement and volume reduction of devices. In this regard, China has also invested a lot of money and technology, and has made good achievements. For example, in the aspect of substrate, 8-inch substrate has been achieved internationally, and 6-inch substrate can also be achieved in China. 8-inch substrate is also under development, and the gap between us and the international leading level is gradually narrowing.
Silicon carbide production process
Silicon carbide power semiconductor industry chain mainly includes single crystal materials, epitaxial materials, devices, modules and applications. Among them, single crystal material is the foundation of silicon carbide power semiconductor technology and industry, epitaxial material is the key to realize device manufacturing, device is the core of the whole industry chain, module is the bridge to realize device application, application is the source power of silicon carbide power semiconductor device and industrial development.
Growth method of SiC single crystal
1. PVT (physical vapor transport)
High purity SiC powder is placed at the bottom of the graphite crucible as the growth source, and the seed crystal is fixed on the top of the graphite crucible. The SiC polycrystalline powder is heated and decomposed into gas phase materials such as Si atom, si2c molecule and sic2 molecule at high temperature above 2000 ℃. Under the driving of temperature gradient, these gaseous materials will be transported to the lower temperature SiC seed crystal to form specific SiC crystal 。 SiC crystals can be formed by controlling PVT temperature field, gas flow and other process parameters. There are two main types of silicon carbide substrate. Silicon carbide with high quality and large size is the primary problem to be solved in the development of silicon carbide technology. Continuous increase of wafer size and reduction of defect density (microtubule, dislocation, stacking fault, etc.) are the key development directions.
2. High temperature chemical vapor deposition (htcvd)
In a closed reactor, SiH4 and C2H4 carried by H2 or he were introduced into the reactor with appropriate reaction temperature (2000-2300 ℃) and pressure (40kpa). The reaction gas decomposes into SiC at high temperature and adheres to the surface of substrate material, and grows along the material surface. The optimal process conditions were obtained by controlling the reaction volume, reaction temperature, pressure and gas composition.
The main reaction occurred in the furnace: 2sih4 + C2H4 = 2sic + 6H2
Schematic diagram of htcvd
SiC epitaxial materials
Different from the traditional silicon power device manufacturing process, SiC power devices must grow high-quality epitaxial materials on the conductive single-crystal substrate, and make all kinds of devices on the epitaxial layer. The main epitaxial technology is chemical vapor deposition (CVD), which can realize the epitaxial material with certain thickness and doping by step flow growth. In terms of industrialization, the product level of SiC epitaxial materials with thickness of 20 μ m and below is close to the international advanced level; in the aspect of R & D, China has developed 100 μ m thick epitaxial materials, which is far behind the international advanced level in defect control of thick epitaxial materials.
Silicon carbide power devices
Silicon carbide power semiconductor devices mainly include junction barrier Schottky Power Diode (JBS), pin power diode and hybrid pin Schottky diode (MPS); metal oxide semiconductor field effect transistor (MOSFET), bipolar transistor (BJT), junction field effect transistor (JFET), insulated gate bipolar transistor (IGBT) and gate turn off thyristor (GTO), etc.
Silicon carbide power module
In order to further improve the current capacity of silicon carbide power devices, the module packaging method is usually used to integrate multiple chips in parallel. Silicon carbide power module is developed from the hybrid power module product which is composed of silicon IGBT chip and SiC JBS diode chip. Based on the mature packaging technology and industry of silicon-based power modules in China, the industrialization level of silicon carbide power modules in China closely follows the international advanced level.
Schematic diagram of SiC semiconductor industry chain
According to the market demand, Haoyue technology continuously develops and improves the technology, and introduces sintering equipment with excellent performance to assist the domestic semiconductor packaging market. It provides various atmosphere sintering furnaces, hot pressing sintering furnaces and spark plasma sintering furnaces, providing perfect heat treatment solutions for the sintering process of semiconductor packaging enterprises.
Haoyue technology is a high-tech enterprise integrating R & D, production and sales of electric furnace. The company has been focusing on advanced ceramics and composite materials, semiconductor materials, carbon materials, lithium batteries and new energy materials equipment four major fields, has rich industry experience and professional technology, wholeheartedly serves customers and provides perfect integrated industrial solutions.