Semiconductor industry is the application direction of silicon carbide material with the greatest development potential and the highest industrial added value.
Since the 1990s, the United States, Japan, Europe and other developed countries in order to maintain aerospace, military and technical advantages, the development of silicon carbide semiconductor technology in a very important strategic position, have invested a lot of manpower and capital to silicon carbide materials and device technology for extensive and in-depth research, aimed at improving the ability of their equipment system and reducing the volume of components. Major breakthroughs have been made.
An overview of silicon carbide
Silicon carbide (SiC) also called emery, density is 3.2g/cm3, natural silicon carbide is very rare, mainly through artificial synthesis. According to the different classification of crystal structure, silicon carbide can be divided into two main categories: αSiC and βSiC.
Silicon carbide material has excellent thermodynamic and electrochemical properties.
In terms of thermodynamics, silicon carbide hardness at 20℃ up to Mohs 9.2-9.3, is one of the hardest substances, can be used to cut ruby; The thermal conductivity is more than copper metal, is 3 times Si, GaAs 8-10 times, and its high thermal stability, can not be melted at atmospheric pressure
In terms of electrochemistry, silicon carbide has the characteristics of wide band gap and breakdown resistance.
Its band gap is 3 times that of Si, and its breakdown electric field is 10 times that of Si. And its strong corrosion resistance, at room temperature can be immune to all known caustics.
Silicon carbide semiconductor industry chain
Semiconductor material is one of the most promising application fields of silicon carbide. Silicon carbide is the most mature third generation semiconductor material at present. With the reduction of production cost, SiC semiconductor is gradually replacing the first and second generation semiconductor.
Silicon carbide semiconductor industry chain mainly includes silicon carbide high purity powder, single crystal substrate, epitaxial sheet, power devices, module packaging and terminal applications.
1. High purity silicon carbide powder
Silicon carbide high purity powder is a raw material for growing silicon carbide single crystal by PVT method. Its product purity directly affects the growth quality and electrical properties of silicon carbide single crystal.
There are many ways to synthesize SIC powder, including solid phase, liquid phase and gas phase. The solid phase method includes carbonthermal reduction method, self-propagating high temperature synthesis method and mechanical crushing method. Liquid phase method includes sol-gel method and polymer thermal decomposition method; The gas phase method includes chemical vapor deposition, plasma and laser induction.
2. Single crystal substrate
Single crystal substrate is a semiconductor supporting material, conductive material and epitaxial growth substrate. The growth of single crystal is the key step in the production of silicon carbide single crystal substrate. It 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 crystal include physical vapor transfer method (PVT method), liquid phase method (LPE method), high temperature chemical vapor deposition (HTCVD method) and so on.
3. Epitaxial sheet
Silicon carbide epitaxial film refers to a silicon carbide wafer grown on a silicon carbide substrate with certain requirements, and the substrate to the same single crystal film (epitaxial layer). In practice, wide band gap semiconductor devices are almost made on the epitaxial layer, silicon carbide wafer itself only as the substrate, including GaN epitaxial layer substrate.
At present, the preparation of SiC films on silicon carbide single crystal substrate mainly includes chemical vapor deposition (CVD), liquid phase method (LPE), sublimation method, sputtering method, MBE method and so on.
4. Power device
The wide band gap power device made of SIC material has the characteristics of high temperature resistance, high frequency and high efficiency. According to the device working form, SiC power device mainly includes power diode and power switch tube. SiC power devices and silicon - based power devices are fabricated by microelectronic technology.
From the perspective of SIC crystal materials, 4H-SiC and 6H-SiC are the most widely used in the semiconductor field, among which 4H-SiC is mainly used in the preparation of high frequency, high temperature, high power devices, and 6H-SiC is mainly used in the production of optoelectronic power devices.
5. Module encapsulation
At present, the packaging type of related power devices in the mass production stage basically uses silicon power devices. TO220 is the most commonly used packaging type of silicon carbide diode, TO247-3 is the most commonly used packaging type of silicon carbide MOSFET, and a few use TO247-4, D2PAK and other new packaging methods.
6. Terminal application
In third-generation semiconductor applications, silicon carbide semiconductor has the advantage of being complementary to gallium nitride semiconductor. Gallium nitride semiconductor materials market applications are concentrated in the lower than 1000V, and tend to the low and medium voltage range. Currently, commercial silicon carbide semiconductor products have voltage grades of 600-1700V.
Due to the advantages of SiC devices such as high conversion efficiency, low heating characteristics and lightweight, the downstream industry demand continues to increase, there is a trend to replace SiO2 devices.