Advances in Microtube Density for SIC Industrial Wafers and
Manufactured microtube density values of 40% and 90% for different devices
The above picture shows that the current SIC materials and optoelectronic devices have met the requirements and are no longer affected by the quality of the materials. The industrial production yield and reliability of the devices also meet the requirements. High-frequency devices mainly include unipolar devices in MOSFETSCHOTTKY diodes. The microtube defect density of SIC material basically meets the requirements, and it only has a certain impact on the yield. It will take about two years for SIC materials for high voltage and high power devices to further improve material defect density. In short, no matter what difficulties are present and how semiconductors are developing, SIC is undoubtedly a promising material in the new century.
Introduction to the history of the most complete third-generation semiconductor industry (with analysis of research profiles of countries in the world)
The third generation semiconductor refers to a wide band gap semiconductor material represented by gallium nitride (GaN), silicon carbide (SiC), diamond, and zinc oxide (ZnO). The band gap energy of various semiconductor materials is shown in Table 1. Compared with the traditional 1st and 2nd generation semiconductor materials silicon (Si) and gallium arsenide (GaAs), the 3rd generation semiconductor has a large band gap, high breakdown electric field, large thermal conductivity, and electron saturation drift speed. The unique properties such as high dielectric constant and small dielectric constant make it show great potential in optoelectronic devices, power electronics, radio frequency microwave devices, lasers and detectors, etc., and it is a hot spot in the field of semiconductor research in various countries around the world.
Development overview of main application areas
At present, the third generation of semiconductor materials is causing a revolution in clean energy and next-generation electronic information technology. Whether it is lighting, home appliances, consumer electronics, new energy vehicles, smart grids, or military supplies, this high-performance semiconductor There is great demand for materials. According to the development of the third-generation semiconductor, its main applications are semiconductor lighting, power electronics, lasers and detectors, and four other fields, each of which has a different industry maturity.
Third-generation semiconductor materials
1.Silicon carbide single crystal material
In the field of wide band gap semiconductor materials, in terms of technological maturity, silicon carbide is the highest in this family of materials and is the core of wide band gap semiconductors. SiC material is a group IV-IV semiconductor compound, which has the characteristics of wide band gap (Eg: 3.2eV), high breakdown electric field (4 × 106V / cm), high thermal conductivity (4.9W / cm.k), and the like. Structurally speaking, SiC material is a close-packed structure of silicon-carbon atoms. It can be regarded as a close-packed silicon atom, with carbon atoms occupying its tetrahedral vacancies; As for the close-packed structure of silicon carbide, a variety of different crystal forms are produced by different unidirectional close-packing methods, and about 200 kinds have been found. Currently the most common and widely used are 4H and 6H crystal forms. 4H-SiC is particularly suitable for the microelectronics field, used to prepare high-frequency, high-temperature, high-power devices; 6H-SiC is particularly suitable for the optoelectronics field to achieve full-color display.
With the development of SiC technology, its electronic devices and circuits will lay a solid foundation for the system to solve the above challenges. Therefore, the development of SiC materials will directly affect the development of wide band gap technology.
SiC devices and circuits have superior performance and broad application prospects, so they have always been highly valued by the industry, basically forming a triad situation in the United States, Europe, and Japan. At present, the international companies that commercialize silicon carbide single crystal polishing wafers include Cree, Bandgap, DowDcorning, II-VI, and Instrinsic in the United States; Nippon and Sixon in Japan; Okmetic in Finland; Germany SiCrystal, et al. Among them, Cree and SiCrystal have a market share of more than 85%. Among all silicon carbide manufacturers, Cree is the strongest in the United States, and its technical level of silicon carbide single crystal materials can represent the international level. Experts predict that Cree will continue to lead the silicon carbide substrate market in the next few years. .
GaN material is a group III-Ⅴ compound semiconductor material synthesized by Johason et al. In 1928. Under atmospheric pressure, the GaN crystal generally has a hexagonal wurtzite structure. It has 4 atoms in a cell, and the atomic volume is about It is 1/2 of GaAs; its chemical properties are stable, it is insoluble in water, acid and alkali at normal temperature, but dissolves at a very slow rate in hot alkali solution; it shows unstable characteristics at high temperature under HCl or H2, and The most stable under N2. GaN materials have good electrical characteristics, wide band gap (3.39eV), high breakdown voltage (3 × 106V / cm), high electron mobility (1000cm2 / V · s at room temperature), and high heterojunction surface charge density (1 × 1013cm-2), etc., so it is considered to be the most preferred material for studying short-wavelength optoelectronic devices and high-temperature high-frequency high-power devices. Compared to silicon, gallium arsenide, germanium, and even silicon carbide devices, GaN devices can be used at higher frequencies, more High power, higher temperature operation. In addition, gallium nitride devices can be applied in the high-frequency band of 1 to 110 GHz, which covers mobile communication, wireless networks, point-to-point and point-to-multipoint microwave communications, and radar applications.
In recent years, the group III nitrides represented by GaN have received widespread attention due to their application prospects in the field of optoelectronics and microwave devices. As a semiconductor material with unique optoelectronic properties, the application of GaN can be divided into two parts: it can replace some silicon and other compound semiconductor materials with the excellent performance of GaN semiconductor materials under high temperature and high frequency and high power working conditions; with GaN The unique properties of semiconductor materials with wide band gaps and exciting blue light have led to the development of new optoelectronic applications. At present, GaN optoelectronic devices and electronic devices have obvious competitive advantages in applications such as optical storage, laser printing, high-brightness LEDs, and wireless base stations. Among them, high-brightness LEDs, blue light lasers, and power transistors are the most interesting and concerned in the current device manufacturing field. .
Foreign countries started earlier in the study of gallium nitride single crystal materials. Now the United States, Japan, and Europe have achieved certain results in the study of gallium nitride single crystal materials. All have emerged that they can produce gallium nitride single crystal materials. , The highest level of research in the United States and Japan.
Many universities, research institutions and companies in the United States have carried out research on the preparation of gallium nitride single crystals, and have been in a leading position. TDI, Kyma, ATMI, Cree, CPI and other companies have successfully produced gallium nitride single crystal linings. bottom. Kyma can now sell 1-inch, 2-inch, and 3-inch gallium nitride single crystal substrates, and has developed 4-inch gallium nitride single crystal substrates.
Japan also has a high level of research on GaN substrates. Among them, Sumitomo Electric (SEI) and Hitachi Cable have started mass production of GaN substrates. Nichia, Matsushita, Sony, Toshiba (Toshiba) and others also carried out related research. Hitachi Wire's gallium nitride substrate has a diameter of 2 inches and the dislocation density on the substrate reaches the level of 1 × 106 cm-2.
European gallium nitride body single crystal research mainly includes Poland's Top-GaN and France's Lumilog two companies. TopGaN produces GaN materials using the HVPE process, with a dislocation density of 1 × 107cm-2, a thickness of 0.1-2mm, and an area greater than 400mm2. In summary, foreign GaN single crystal substrate research has made great progress. Some companies have achieved commercialization of GaN single crystal substrates, and the technology is becoming mature. The next development direction is Large size, high integrity, low defect density, self-supporting substrate material.
3.Aluminum nitride material
AlN material is a group III nitride with a direct band gap of 0.7-3.4eV, which can be widely used in the field of optoelectronics. Compared with materials such as gallium arsenide, it covers a larger spectral bandwidth, which is especially suitable for applications from deep ultraviolet to blue light. At the same time, group III nitrides have good chemical stability, excellent thermal conductivity, high breakdown voltage, and dielectric constant. Compared with silicon, gallium arsenide, germanium, and even silicon carbide devices, III-nitride devices can work at higher frequencies, higher power, higher temperatures, and harsh environments. Similar semiconductor materials.
AlN materials have a wide band gap (6.2eV), high thermal conductivity (3.3W / cm · K), and are better matched to the lattice and thermal expansion coefficient of the AlGaN layer. Therefore, AlN is an advanced high power light emitting device (LED, LD), UV detector, and ideal substrate material for high-power high-frequency electronics.
In recent years, GaN-based blue, green LEDs, LDs, UV detectors, and high-power high-frequency HEMT devices have made great progress. In terms of AlGaN HEMT devices, AlN has higher thermal conductivity than GaN materials, and it is easier to achieve semi-insulation; compared with SiC, the lattice mismatch is smaller, which can greatly reduce the defect density in the device structure, which is effective Improve device performance. AlN is an ideal substrate for growing III-nitride epitaxial layers and device structures. Its advantages include: a small lattice mismatch and thermal expansion coefficient mismatch with GaN; compatible chemical properties; the same crystal structure, no faults Layer; also has a polarized surface; due to its high stability and the absence of other elements, there is little contamination due to the substrate. AlN material can improve device performance and device grade, and is the source and foundation of the development of electronic devices.
At present, in the development of AlN single crystal materials abroad, the development level of the United States and Japan is the highest. The TDI company in the United States is currently the only unit that fully masters the technology of preparing AlN substrates by the HVPE method and realizes industrialization. TDI's AlN substrate is a 10-30 μm electrically insulating AlN layer deposited on a <0001> SiC or sapphire substrate. It is mainly used as a low-defect electrical insulation substrate for making high-power AlGaN-based HEMTs. There are currently 2
3, 4, 6 inch products. Japan's AlN technology research units mainly include Tokyo University of Agriculture and Technology, Mie University, NGK Company, Mingcheng University, etc., which have achieved certain results, but no mature products have yet appeared. In addition, Russia's Yofie Institute and Sweden's Linköping University also have a certain level of research on AlN growth by HVPE method. Russia's NitrideCrystal has also developed PVTAlN single crystal samples with a diameter of 15mm. In China, the research on AlN is obviously lagging behind that in foreign countries. Some research institutes have also made preliminary explorations on the epitaxial growth of AlNMOCVD, but there have been no significant breakthroughs and results.
Diamond is a material whose carbon crystals have a cubic crystal structure. In this structure, each carbon atom is connected to four adjacent carbon atoms with a "strong" rigid chemical bond and forms a tetrahedron. In diamond crystals, the radius of carbon atoms is small, so the bond energy per unit volume is large, making it harder than other materials, and it is the hardest material known (Vickers hardness can reach 10400kg / mm2).
In addition, the diamond material also has a large band gap (5.5eV); high thermal conductivity, up to 120W / cm · K (-190 ° C), generally up to 20W / cm.K (20 ° C); the highest sound transmission speed Low dielectric constant and high dielectric strength. Diamond combines mechanical, electrical, thermal, acoustic, optical, corrosion resistance and other excellent properties in one, is currently the most promising semiconductor materials. According to the excellent characteristics of diamond, it is widely used. In addition to the traditional use of tool materials, it can also be used in the fields of electronic devices such as microelectronics, optoelectronics, acoustics, and sensing.
Zinc oxide (ZnO) is a semiconductor material of group II-Ⅵ wurtzite structure with a band gap of 3.37eV. In addition, its exciton binding energy (60meV) is much higher than materials such as GaN (24meV) and ZnS (39meV). Such a high exciton confinement makes it stable at room temperature and difficult to be excited (the thermal ionization energy is 26 meV at room temperature), which lowers the lasing threshold at room temperature and improves the excitation efficiency of ZnO materials. Based on these characteristics, ZnO material is both a wide band gap semiconductor and a multifunctional crystal with excellent optoelectronic and piezoelectric properties.
It is not only suitable for the production of high-efficiency blue, ultraviolet light and detectors, but also for the production of gas-sensitive devices, surface acoustic wave devices, transparent high-power electronic devices, window materials for light-emitting displays and solar cells, and rheostats, piezoelectric conversion器 等。 And other. Compared to GaN, ZnO has advantages in manufacturing LEDs and LDs. It is expected that the brightness of ZnO-based LEDs and LDs will be 10 times that of GaN-based LEDs and LDs, while the price and energy consumption are only 1/10 of the latter.
ZnO materials have been widely used for their superior characteristics, and have attracted great attention from various countries.
Developed countries such as Japan, the United States, and South Korea have invested huge amounts of money to support the research and development of ZnO materials, and set off a wave of world ZnO research. According to reports, Japan has grown high-quality ZnO single crystals up to 2 inches in diameter; China has grown ZnO single crystals with a diameter of 32 mm, a diameter of 45 mm, and a thickness of 4 mm by the CVT method. Advances in material technology have also guided and promoted the advancement of device technology. Japan has developed electroluminescent LEDs based on ZnO homogeneous PN junctions; China has also successfully produced the world's first homogeneous ZnO-LED prototype device, which achieves electricity at room temperature. Inject glow. The advancement of device preparation technology promotes the practical process of ZnO semiconductor materials. Due to its unique advantages, it will have very important applications in national defense construction and national economy, and has unlimited prospects.