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, good interface characteristics, is conducive to nucleation of epitaxial materials 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 small thermal mismatch
5, good electrical conductivity, can be made up and down structure
6. The optical performance is good, and the light emitted by the fabricated device is absorbed by the substrate.
7, good mechanical properties, the device is easy to process, including thinning, polishing and cutting, etc.
8, low prices
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.
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