The production of epitaxial wafers is a highly complex process. Once the epitaxial layer is completed, nine random points on the wafer are selected for testing. If the results meet the required specifications, the wafer is considered good and proceeds to the next stage. Otherwise, it's classified as defective due to issues like voltage deviation, incorrect wavelength, or poor brightness. Good epitaxial wafers then undergo electrode formation (P and N poles), followed by laser cutting. A percentage of the material is collected based on voltage, wavelength, and brightness, and through fully automated inspection, this forms LED chips—typically square in shape. After that, a visual inspection is performed to identify any defects or damaged electrodes, separating out the lower-quality pieces. These remaining wafers, which don’t meet shipping standards, are often referred to as side films or second-grade materials. Defective epitaxial wafers, which fail to meet key parameters, are not used for square chips but instead directly serve as electrodes for LED circles sold in the market. Some of these may still contain usable squares or other good components. Historically, semiconductor manufacturers have primarily used polished silicon wafers (PW) and epitaxial silicon wafers as raw materials for integrated circuits (ICs). Epitaxial wafers were introduced in the early 1980s and offer unique electrical properties not found in standard PW wafers. They also help eliminate surface and near-surface defects that occur during crystal growth and subsequent processing. Epitaxial wafers have been produced by silicon wafer manufacturers for decades and are used in small quantities within ICs. The process involves depositing a thin, single-crystal silicon layer onto a single-crystal silicon wafer. Typically, the epitaxial layer ranges from 2 to 20 micrometers thick, while the underlying silicon substrate is around 610 micrometers for 150mm wafers and 725 micrometers for 200mm wafers. Epitaxial deposition can be done either in batch or on a single wafer basis. Monolithic reactors produce the highest quality epitaxial layers, with excellent thickness uniformity, resistivity control, and low defect density. These high-quality epitaxial wafers are essential for producing leading-edge 150mm products and all critical 200mm devices. Epitaxial products are widely used across four main areas. Complementary metal-oxide-semiconductor (CMOS) technology supports advanced processes requiring smaller device sizes. CMOS wafers represent the largest application area for epitaxial wafers, used in non-recoverable processes such as flash memory, DRAM, microprocessors, logic chips, and memory applications. Discrete semiconductors are employed for precision Si-based components, while "exotic" semiconductors use compound materials like GaN or InP in their epitaxial layers. Buried layers in bipolar transistors are also formed using epitaxial techniques. As of 2000, 200mm epitaxial wafers accounted for about one-third of total production. At that time, buried layers and CMOS for logic devices made up 69% of all epitaxial wafers, DRAM accounted for 11%, and discrete devices for 20%. By 2005, the distribution shifted to 55% for CMOS logic, 30% for DRAM, and 15% for discrete devices. When it comes to LED epitaxial wafers, the choice of substrate material is crucial. It serves as the foundation for the entire semiconductor lighting industry. Different substrates require specific epitaxial growth techniques, chip processing methods, and packaging solutions. The selection of the right substrate determines the technological path of semiconductor lighting development. Choosing an ideal substrate that meets all nine criteria is extremely challenging. Currently, there are three main types of substrates available for gallium nitride (GaN) research: sapphire (Al₂O₃), silicon carbide (SiC), and silicon (Si). Each has its own advantages and limitations, and the industry continues to explore new options to improve performance and reduce costs. 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