The production process of the epitaxial wafer is very complicated. After the epitaxial wafer is finished, the next epitaxial wafer is randomly selected from nine points for testing. The products that meet the requirements are good products, and the others are defective products (the voltage deviation is large, the wavelength is short or Long, etc.). The epitaxial wafer of the good product will start to be the electrode (P pole, N pole), then the laser will be used to cut the epitaxial wafer, and then the percentage of æ¡, according to different voltage, wavelength, brightness, fully automated inspection, that is, formation LED chip (square chip). Then, visual inspection is carried out to separate the defects or the electrodes from wear and tear. These are the latter crystals. At this time, there are wafers on the blue film that do not meet the normal shipping requirements, and it naturally becomes a side piece or a piece of film. The epitaxial film of the defective product (mainly some parameters do not meet the requirements), it is not used for the square piece, it is directly used as the electrode (P pole, N pole), and does not do the sorting, which is the LED circle on the market. The film (there are also good things in it, such as squares, etc.).
Semiconductor manufacturers mainly use polished Si wafers (PW) and epitaxial Si wafers as raw materials for ICs. Epitaxial wafers were used in the early 1980s, which have certain electrical characteristics not found in standard PW and eliminate many surface/near surface defects introduced in crystal growth and subsequent wafer processing.
Historically, epitaxial wafers have been produced and used by Si wafer manufacturers and are used in small quantities in ICs. It requires deposition of a thin single crystal Si layer on the surface of a single crystal Si wafer. The thickness of the epitaxial layer is generally 2 to 20 μm, and the thickness of the substrate Si is 610 μm (150 mm diameter sheet and 725 μm (200 mm sheet).
Epitaxial deposition can be used to process multiple wafers at the same time, or to process a single wafer. The monolithic reactor produces the best quality epitaxial layers (thickness, uniformity of resistivity, and low defects); this epitaxial wafer is used in the production of 150mm "leading edge" products and all important 200mm products.
Epitaxial product
Epitaxial products are used in four areas, and CMOS complementary metal oxide semiconductors support leading edge processes that require small device sizes. CMOS products are the largest application area for epitaxial wafers and are used by IC manufacturers for non-recoverable device processes, including flash memory and DRAM (Dynamic Random Access Memory) for microprocessors and logic chips and memory applications. Discrete semiconductors are used to fabricate components that require precision Si characteristics. The "exotic" semiconductor class contains specialty products that use non-Si materials, many of which are incorporated into epitaxial layers using compound semiconductor materials. Buried layer semiconductors are physically isolated using heavily doped regions within the bipolar transistor elements, which are also deposited during epitaxial processing.
At present, in 200mm wafers, epitaxial wafers account for 1/3.2000 years, including burying layers, CMOS for logic devices accounted for 69% of all epitaxial wafers, DRAM accounted for 11%, and discrete devices accounted for 20%. By 2005, CMOS Logic will account for 55%, DRAM for 30%, and discrete devices for 15%.
LED epitaxial wafer: substrate material
Substrate materials are the cornerstone of the technological development of the semiconductor lighting industry. Different substrate materials require different epitaxial growth techniques, chip processing techniques, and device packaging techniques. Substrate materials determine the development path of semiconductor lighting technology. The choice of substrate material depends mainly on the following nine aspects:
1. Good structural characteristics, the crystal structure of the epitaxial material and the substrate are the same or similar, the lattice constant mismatch is small, the crystallization property is good, and the defect density is small;
2, the interface characteristics are good, which is beneficial to the nucleation of the epitaxial material and strong adhesion;
3, good chemical stability, not easy to decompose and corrode in the temperature and atmosphere of epitaxial growth;
4, good thermal performance, including good thermal conductivity and low thermal mismatch;
5, good electrical conductivity, can be made up and down structure;
6, the optical performance is good, the light emitted by the fabricated device is absorbed by the substrate is small;
7, good mechanical properties, the device is easy to process, including thinning, polishing and cutting;
8, the price is low;
9, large size, generally requires a diameter of not less than 2 inches.
It is very difficult to select the substrate to meet the above nine aspects at the same time. Therefore, at present, the development and production of semiconductor light-emitting devices on different substrates can only be adapted by changes in epitaxial growth technology and adjustment of device processing processes. There are many substrate materials for gallium nitride research, but there are currently only three types of substrates that can be used for production, namely sapphire Al2O3 and silicon carbide SiC substrates and Si substrates.
The following factors must be considered in the evaluation of the substrate material:
1. Structural matching of the substrate and the epitaxial film: the crystal structure of the epitaxial material and the substrate material are the same or similar, the lattice constant mismatch is small, the crystallization property is good, and the defect density is low;
2. Matching the thermal expansion coefficient of the substrate and the epitaxial film: the matching of the thermal expansion coefficient is very important. The difference between the thermal expansion coefficient of the epitaxial film and the substrate material may not only reduce the quality of the epitaxial film, but also cause heat during the operation of the device. And cause damage to the device;
3. The chemical stability of the substrate and the epitaxial film: the substrate material should have good chemical stability, and it is not easy to decompose and corrode in the temperature and atmosphere of epitaxial growth. The quality of the epitaxial film cannot be degraded due to the chemical reaction with the epitaxial film. ;
4. The difficulty of material preparation and the cost: In view of the needs of industrial development, the preparation of substrate materials is simple and the cost is not high. The substrate size is generally not less than 2 inches.
There are currently many substrate materials for GaN-based LEDs, but there are currently only three types of substrates that can be used for commercialization, namely sapphire and silicon carbide, and silicon substrates. Other substrates such as GaN and ZnO are still in the research and development stage, and there is still a long way to go from industrialization.
Gallium nitride
The most ideal substrate for GaN growth is GaN single crystal material, which can greatly improve the crystal quality of the epitaxial film, reduce the dislocation density, improve the working life of the device, improve the luminous efficiency, and improve the working current density of the device. However, it is very difficult to prepare a GaN bulk single crystal, and there has been no effective method so far.
Zinc oxide
ZnO is a candidate substrate for GaN epitaxy because of the striking similarities between the two. The crystal structure of the two is the same, the lattice recognition degree is very small, and the forbidden band width is close (the band gap is small and the contact barrier is small). However, the Achilles heel of ZnO as a GaN epitaxial substrate is easily decomposed and corroded in the temperature and atmosphere of GaN epitaxial growth. At present, ZnO semiconductor materials can not be used to manufacture optoelectronic devices or high-temperature electronic devices, mainly because the material quality is not up to the device level and the P-type doping problem has not been solved. The equipment suitable for the growth of ZnO-based semiconductor materials has not been successfully developed.
sapphire
The most common substrate for GaN growth is Al2O3. It has the advantages of good chemical stability, no absorption of visible light, moderate price, and relatively mature manufacturing technology. Although the thermal conductivity is poor, there is no obvious shortage of exposure in the small current operation of the device, but the problem is very prominent in the high current operation of the power device.
Silicon carbide
The application of SiC as a substrate material is second only to sapphire. At present, Professor Jiang Fengyi of China's Jingneng Optoelectronics has developed LED epitaxial wafers that can be used for commercialization on Si substrates. The Si substrate is superior to sapphire in terms of thermal conductivity and stability, and the price is far lower than that of sapphire. It is a very promising substrate. The SiC substrate has good chemical stability, good electrical conductivity, good thermal conductivity, and no absorption of visible light, but the shortage is also prominent. If the price is too high, the crystal quality is difficult to achieve as good as Al2O3 and Si, and the mechanical processing performance is poor. In addition, the SiC substrate absorbs ultraviolet light below 380 nm, which is not suitable for the development of ultraviolet LEDs below 380 nm. Due to the beneficial electrical and thermal conductivity of the SiC substrate, the heat dissipation problem of the power GaN LED device can be better solved. Therefore, it plays an important role in the field of semiconductor lighting technology.
Compared to sapphire, the lattice matching of SiC and GaN epitaxial films is improved. In addition, SiC has a blue light-emitting property and is a low-resistance material, and an electrode can be fabricated, which makes it possible to completely test the epitaxial film before packaging, and enhances the competitiveness of SiC as a substrate material. Since the layered structure of SiC is easy to be cleaved, a high-quality cleavage surface can be obtained between the substrate and the epitaxial film, which greatly simplifies the structure of the device; but at the same time, due to its layered structure, it is often given on the surface of the substrate. A step in which a large number of defects are introduced into the epitaxial film occurs.
The goal of achieving luminous efficiency is to hope for the LED of GaN substrate, to achieve low cost, and to achieve high efficiency, large area, single lamp and high power through GaN substrate, as well as the simplification of the driving process technology and the large yield. improve. Once semiconductor lighting becomes a reality, its significance is no less than Edison's invention of incandescent lamps. Once breakthroughs are made in key technology areas such as substrates, the industrialization process will achieve significant growth.
Led Underground Light have
many designs, such as fixed ground light, adjustable buried ground light and
contemporary recessed design.
Fixed ground lights, fixed buried ground uplighters for driveways and pathways.
Adjustable buried ground lights, ideal for uplighting walls, fences and
features. Recessed ground lights providing a great projected light source. LED
recessed uplighters ideal for lighting up features. In ground light fittings
great for uplighting.
Contemporary recessed ground lights, great effective uplighters for a variety
of lighting effects.
3W Led Underground Light,Led Underground,Led Underground Light,Led Underground Paving Light
ZHONGSHAN G-LIGHTS LIGHTING CO., LTD. , https://www.glightsled.com