Plasma etching and cleaning processes are core steps in semiconductor manufacturing. As process nodes advance to 7nm, 5nm, and beyond, plasma energy density continues to increase, and the chemical activity of halogen gases (fluorine-based and chlorine-based) becomes increasingly aggressive. While etching wafers, these plasmas also indiscriminately and continuously corrode all exposed components inside the chamber, including the chamber walls, liners, focus rings, gas distribution plates, viewports, etc. This not only leads to surface roughening, material loss, and increased frequency of equipment downtime for maintenance, but also causes wafer contamination and yield loss due to detached particles. Therefore, the search for materials with higher resistance to plasma corrosion has become an urgent need in the field of semiconductor equipment materials. Yttrium oxide (Y₂O₃) plays an irreplaceable role in this domain.
Why is yttrium oxide irreplaceable in semiconductor equipment?
In semiconductor equipment, aluminum oxide (Al₂O₃) is the most commonly used structural ceramic material. It has a melting point of 2050°C, high mechanical strength, high wear resistance, excellent electrical insulation, and good chemical stability. However, the bond energy of the Al-O bond is about 498 kJ/mol. Although it resists most chemical attacks, under high-energy plasma conditions it readily reacts with fluorine to form a flaky, easily spalled fluoride layer (AlF₃). This layer deposits and crystallizes on the surface, creating particles that detach and contaminate wafers, while continuously consuming the protective layer.
In contrast, yttrium oxide (Y₂O₃) has a cubic crystal system and a melting point as high as 2430°C. In addition to excellent electrical insulation and optical transparency, its Y–O bond energy is as high as 780 kJ/mol. It exhibits extremely low chemical reactivity with halogens (especially F and Cl). When it reacts with fluorine, it forms a much more stable and dense YF₃ layer that is not prone to spalling. This not only greatly reduces particle generation but also effectively prevents further attack by fluorine plasma on equipment components (such as etching chamber walls, showerheads, etc.), extending component service life. In typical high-density fluorine-based or chlorine-based plasma environments, the etching rate of Y₂O₃ is typically only 1/20 to 1/50 that of Al₂O₃. Furthermore, Y₂O₃ has a melting point of 2430°C and can maintain structural integrity at high temperatures above 1750°C without volatilization or deformation, adapting to the extreme temperature conditions of plasma processes. Its volume resistivity exceeds 10¹² Ω·cm, with low dielectric loss, ensuring the stability of high-frequency RF fields and avoiding process deviations caused by poor dielectric properties of materials.
Applications of yttrium oxide in semiconductor equipment
Based on the core properties of yttrium oxide and combined with the specific requirements of different semiconductor equipment components, its applications in the semiconductor field are mainly divided into four categories:
01 Yttrium oxide coatings
Because yttrium oxide, as a rare earth material, is relatively expensive, most etching equipment chambers or components do not use pure Y₂O₃ ceramics. Instead, a dense Y₂O₃ coating with a thickness of about 100–300 μm is deposited on the surface of aluminum alloy or Al₂O₃ substrates (such as chamber liners, focus rings, gas distribution plates, etc.) using techniques like plasma spraying or physical vapor deposition (PVD). This is currently the most widely used form of yttrium oxide coating in semiconductor equipment. This approach balances the structural strength of the base material with the surface corrosion resistance of Y₂O₃, while reducing costs. In advanced process nodes of 7nm and below, yttrium oxide coatings have gradually become the industry standard protective configuration, extending the major maintenance cycle of etching equipment chambers from a few hundred hours to over a thousand hours, while reducing particle contamination and significantly improving equipment uptime and wafer yield.
02 Transparent yttrium oxide viewports
Viewports on semiconductor plasma equipment are critical components for monitoring process conditions and ensuring process accuracy. They require not only excellent plasma corrosion resistance but also good optical transparency to allow operators to clearly observe wafer processing inside the chamber. Traditional transparent materials like quartz glass and alumina are easily corroded in fluorine-based plasma environments, leading to surface roughening, reduced transmittance, and inability to meet long-term use requirements. Transparent yttrium oxide ceramics have a transmission range covering ultraviolet to infrared (0.29–8 μm), with about 80% linear transmittance even in the far-infrared region. Combined with their excellent plasma corrosion resistance, they maintain a clean surface and stable transparency even after long-term use in fluorine-based and chlorine-based plasma environments, producing no corrosive debris or crystalline impurities, thus ensuring both observation quality and avoiding wafer contamination.
03 Yttrium oxide composite ceramic components
Due to the relatively low mechanical strength, high sintering difficulty, and high cost of pure yttrium oxide ceramics, the industry mainly uses doped yttrium oxide-based composite ceramics to balance performance requirements and cost-effectiveness. For example, yttrium aluminum garnet (YAG), formed by doping yttrium oxide with a certain proportion of aluminum oxide, also has a cubic crystal structure and stable chemical properties. It does not readily undergo violent chemical reactions with active gases in plasmas (such as fluorine, chlorine, and other halogens). In fluorine-containing plasma environments, compared to materials like Al₂O₃, it produces fewer fluoride byproducts, effectively reducing particle contamination and surface corrosion. At the same time, compared to pure yttrium oxide ceramics, YAG has higher hardness (Mohs hardness 8–8.5) and excellent mechanical strength, making it suitable for components with certain mechanical strength requirements in etchers, and it can also be used as a transparent viewport.