The production of epitaxial wafers is a highly complex process. Once the epitaxial layer is completed, the next wafer is randomly selected from nine different points for testing. Those that meet the required specifications are considered good products, while others—such as those with large voltage deviations, incorrect wavelengths, or inconsistent brightness—are classified as defective. Good epitaxial wafers then proceed to the electrode formation stage (P and N poles), followed by laser cutting. Afterward, they are inspected based on various parameters like voltage, wavelength, and brightness in a fully automated system, resulting in the formation of LED chips. A visual inspection is then conducted to identify any defects or damaged electrodes, which are separated out. These are referred to as "latter crystals." At this point, some wafers on the blue film may not meet shipping standards and could be considered side films or rejects. Defective epitaxial wafers, which often fail to meet specific electrical or optical criteria, are not processed into square chips but instead are directly used as electrodes, without sorting. These are commonly found as LED circles on the market, though they may still contain usable components such as square chips. Historically, epitaxial wafers have been produced and utilized by silicon wafer manufacturers, mainly in small quantities for integrated circuits. The process involves depositing a thin layer of single-crystal silicon onto a single-crystal silicon wafer. The epitaxial layer typically ranges from 2 to 20 micrometers thick, while the underlying silicon substrate is about 610 micrometers thick for 150mm diameter wafers, and 725 micrometers for 200mm diameter wafers. This technique allows for improved electrical properties and reduces surface and near-surface defects that can occur during crystal growth and subsequent processing. Epitaxial deposition can be carried out either on multiple wafers simultaneously or on individual ones. Monolithic reactors are known for producing high-quality epitaxial layers in terms of thickness uniformity, resistivity, and defect density. These high-quality epitaxial wafers are essential for the production of advanced 150mm and all key 200mm semiconductor devices. Epitaxial products find applications across four main areas. Complementary metal-oxide-semiconductor (CMOS) technology, which supports leading-edge processes requiring smaller device sizes, is the largest consumer of epitaxial wafers. CMOS is widely used in non-recoverable device processes, including flash memory, DRAM (Dynamic Random Access Memory), microprocessors, logic chips, and memory applications. Discrete semiconductors are used for components that require precise silicon characteristics. The so-called "exotic" semiconductor class includes specialty products made using non-silicon materials, many of which incorporate compound semiconductors within epitaxial layers. Buried-layer semiconductors use heavily doped regions within bipolar transistors, which are also formed during epitaxial processing. In 200mm wafers, epitaxial wafers account for approximately one-third of the total. In the year 2000, buried layers and CMOS for logic devices made up 69% of all epitaxial wafers, with DRAM at 11% and discrete devices at 20%. By 2005, the distribution shifted to 55% for CMOS logic, 30% for DRAM, and 15% for discrete devices. LED epitaxial wafers—substrate materials Substrate materials play a crucial role in the development of the semiconductor lighting industry. Different substrates require unique epitaxial growth techniques, chip processing methods, and packaging solutions. The choice of substrate material significantly influences the technological path of semiconductor lighting. Selecting an appropriate substrate involves considering nine key factors: 1. Excellent structural characteristics: the epitaxial material should have a similar or identical crystal structure to the substrate, with minimal lattice mismatch, good crystallization quality, and low defect density.
2. Superior interface characteristics: it should support the nucleation of the epitaxial layer and ensure strong adhesion.
3. Strong chemical stability: it must remain stable under the temperature and atmosphere conditions of epitaxial growth.
4. Good thermal performance: including high thermal conductivity and minimal thermal expansion mismatch.
5. Excellent electrical conductivity: enabling both top and bottom structures.
6. High optical performance: ensuring that light emitted by the device is not absorbed by the substrate.
7. Strong mechanical properties: making it easy to process, including thinning, polishing, and cutting.
8. Low cost: economically viable for mass production.
9. Large size: typically requiring a diameter of at least 2 inches. It is extremely challenging to find a single substrate that meets all these requirements. As a result, current development and production of semiconductor light-emitting devices rely on adapting epitaxial growth techniques and adjusting device fabrication processes depending on the chosen substrate. While there are numerous materials being researched for gallium nitride, only three are currently suitable for commercial production: sapphire (Al₂O₃), silicon carbide (SiC), and silicon (Si) substrates. End Mill For Graphite Machining End Mill For Graphite Machining,Carbide End Mills, Sdc Coating Mill,Roughing Milling Cutter JIANGYIN GOLD STAR INDUSTRY CO.,LTD , https://www.jygoldstarindustry.com