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The production process of epitaxy sheet is very complicated. After the development of epitaxy sheet, nine points are randomly sampled from each epitaxy sheet for testing. Those that meet the requirements are good products, others are bad products (voltage deviation is large, wavelength is short or long, etc.). The epitaxy sheet of good products should be made into electrodes (P and N poles). Next, the epitaxy sheet is cut by laser, and then the percentage is picked up. According to the different voltage, wavelength and brightness, the automatic detection is carried out, that is to say, the formation of LED chip (square). Then we have to do visual inspection to pick up the ones with a little defect or wear on the electrodes. These are the latter crystals. At this time, there are wafers on the blue film that do not meet the normal delivery requirements, which naturally become sideslices or graphs. Epitaxy wafers of defective products (mainly some parameters do not meet the requirements) are not used to make square wafers. They are directly used as electrodes (P poles, N poles) and are not separated. That is to say, large LED wafers on the market at present (there are also good things, such as square wafers).

Semiconductor manufacturers mainly use polished silicon wafers (PW) and epitaxial silicon wafers as IC raw materials. Epitaxy wafers have been used since the early 1980s. They have some electrical properties that standard PW does not possess and eliminate many surface/near surface defects introduced in crystal growth and subsequent wafer processing.

Historically, epitaxy wafers have been manufactured by silicon wafer manufacturers and used for their own purposes. They are not used widely in IC. They need to deposit a thin layer of single crystal silicon on the surface of single crystal silicon wafers. Generally, the thickness of epitaxial layer is 2-20 micron, while the thickness of Si substrate is 610 micron (150 mm diameter wafer and 725 micron (200 mm wafer).

Epitaxial deposition can be used to process multiple or single sheets at one time. The single-chip reactor can produce the best quality epitaxial layer (thickness, uniformity of resistivity and few defects); the epitaxial sheet is used in the production of 150 mm "frontier" products and all important 200 mm products.

Augmented Product

Epitaxy products are used in four areas. CMOS complementary metal oxide semiconductors support cutting-edge processes requiring small device sizes. CMOS products are the largest application areas of epitaxy chips and are used by IC manufacturers in non-recoverable device processes, including microprocessors and logic chips, flash memory and DRAM (Dynamic Random Access Memory) for memory applications. Discrete semiconductors are used to fabricate components requiring precise Si characteristics. Exotic semiconductors include special products that use non-Si materials, many of which incorporate compound semiconductors into epitaxial layers. The buried layer semiconductor is physically isolated by the heavy doping region in the bipolar transistor element, which is also deposited in the epitaxy process.

At present, epitaxial wafers account for 1/3 of the 200 mm wafers. In 2000, including buried layer, CMOS for logic devices accounted for 69%, DRAM for 11%, and discrete devices for 20%. By 2005, CMOS logic will account for 55%, DRAM for 30%, and discrete devices for 15%

LED Epitaxy: Substrate Material

Substrate materials are the cornerstone of technology development in semiconductor lighting industry. Different substrate materials need different epitaxy growth technology, chip processing technology and device packaging technology. Substrate materials determine the development route of semiconductor lighting technology. The choice of substrates depends mainly on the following nine aspects:

1. Structural characteristics are good. The epitaxy material has the same or similar crystal structure with the substrate, the lattice constant mismatch is small, the crystallization performance is good, and the defect density is small.

2. The interfacial properties are good, which is conducive to the nucleation and adhesion of epitaxial materials.

3. It has good chemical stability and is not easy to decompose and corrode at the temperature and atmosphere of epitaxy growth.

4. Good thermal performance, including good thermal conductivity and low thermal mismatch;

5. It has good conductivity and can be made into upper and lower structures.

6. Optical performance is good. The light emitted by the device is absorbed by the substrate little.

7. It has good mechanical properties and is easy to process, including thinning, polishing and cutting.

8. Low price;

9. Large size, usually not less than 2 inches in diameter.

It is very difficult to choose a suitable substrate to satisfy the above nine aspects simultaneously. Therefore, at present, we can only adapt to the development and production of semiconductor light-emitting devices on different substrates through the modification of epitaxy growth technology and the adjustment of device processing technology. There are many substrates for GaN research, but there are only three kinds of substrates available for production, namely Sapphire Al2O3 and SiC substrates and Si substrates.

The following factors must be taken into account in evaluating substrate materials:

1. Structural matching of substrate and epitaxy film: the crystal structure of epitaxy material and substrate material is the same or similar, the lattice constant mismatch is small, the crystallization performance is good, the defect density is low;

2. Matching of thermal expansion coefficients between substrate and epitaxy film: Matching of thermal expansion coefficients is very important. Excessive difference of thermal expansion coefficients between epitaxy film and substrate material may not only reduce the quality of epitaxy film, but also cause device damage due to heating in the process of device operation.

3. The matching of chemical stability between substrate and epitaxy film: Substrate material should have good chemical stability. It is not easy to decompose and corrode in the temperature and atmosphere of epitaxy growth, and the quality of epitaxy film can not be degraded because of chemical reaction with epitaxy film.

4. The difficulty and cost of material preparation: Considering the need of industrial development, the preparation of substrate materials requires concise, and the cost should not be very high. Substrate sizes are generally no less than 2 inches.

At present, there are many substrates for GaN-based LED, but there are only three substrates available for commercialization, namely sapphire, silicon carbide and silicon substrates. Other substrates such as GaN and ZnO are still in the research and development stage, which is still a long way from industrialization.

Gallium nitride

The ideal substrate for GaN growth is GaN single crystal material, which can greatly improve the crystal quality of epitaxy film, reduce the dislocation density, improve the working life of devices, improve the luminescence efficiency and improve the working current density of devices. However, the preparation of GaN single crystal is very difficult, so far there is no effective method.

Zinc oxide

The reason why ZnO can be a candidate substrate for GaN epitaxy is that they have amazing similarities. Their crystal structures are the same, their lattice recognition is very small, and their band gap width is close to each other (the value of band discontinuity is small, and the contact barrier is small). However, the fatal weakness of ZnO as GaN epitaxy substrate is that it is easy to decompose and corrode in the temperature and atmosphere of GaN epitaxy growth. At present, ZnO semiconductor materials can not be used to manufacture optoelectronic devices or high temperature electronic devices, mainly because the quality of materials can not reach the device level and the problem of P-type doping has not been really solved, and the equipment suitable for the growth of ZnO-based semiconductor materials has not been developed successfully.

Sapphire

The most common substrate for GaN growth is Al2O3. Its advantages are good chemical stability, no absorption of visible light, moderate price and relatively mature manufacturing technology. Although the thermal conductivity is not obviously insufficient in the low current operation of power devices, the problem is very prominent in the high current operation of power devices.

silicon carbide

SiC is the second most widely used substrate material after sapphire. At present, Professor Jiang Fengyi of China has grown commercial LED epitaxy wafers on Si substrates. Si substrate is superior to sapphire in thermal conductivity and stability, and its price is much lower than sapphire. It is a very promising substrate. SiC substrates have good chemical stability, good conductivity, good thermal conductivity and no absorption of visible light, but their shortcomings are also prominent. For example, the price is too high, the crystal quality is difficult to reach that of Al2O3 and Si, and the mechanical processing performance is poor. In addition, SiC substrates absorb ultraviolet light below 380 nanometers, which is not suitable for the development of ultraviolet LED below 380 nanometers. Because of the beneficial conductivity and thermal conductivity of SiC substrate, it can solve the heat dissipation problem of power GaNLED devices, so it occupies an important position in the field of semiconductor lighting technology.

Compared with sapphire, the lattice matching of SiC and GaN epitaxial films is improved. In addition, SiC has blue luminescent properties and is a low resistance material. It can be used to fabricate electrodes, which makes it possible to test the epitaxial film completely before packaging, and enhances the competitiveness of SiC as a substrate material. Because the layered structure of SiC is easy to cleave, a high quality cleavage surface can be obtained between the substrate and the epitaxial film, which will greatly simplify the structure of the device. However, due to its layered structure, there are many steps that introduce defects to the epitaxial film on the surface of the substrate.

The goal of luminous efficiency depends on the LED of GaN substrates to achieve low cost. The realization of high efficiency, large area and high power of single lamp through GaN substrates, as well as the simplification of technology driven by GaN substrates and the great improvement of product rate are also required. Once semiconductor lighting becomes a reality, its significance is no less than Edison's invention of incandescent lamps. Once breakthroughs have been made in key technology areas such as substrates, the industrialization process will make considerable progress.

Yiwu Fuwei e-commerce firm (IACS Co., Limited) is a very professional Led manufacturer who produces high quality outdoor led light. Our popular products are solar led lights, UFO lights, underwater lights and so on. If you have any question about the led product, please feel free to contact us.