As chip manufacturing processes continue to advance toward more critical nodes, the performance requirements for semiconductor equipment materials are constantly increasing. In the field of etching equipment, a subtle shift is taking place: the long-widely used alumina (Al₂O₃) material is gradually being replaced by yttria (Y₂O₃).
This upgrade is not a simple material substitution, but an inevitable result of the higher demands for cleanliness, stability, and equipment lifetime imposed by advanced processes. So, what challenges does alumina face, and what advantages make yttria the new choice?
Why Are Ceramic Materials Indispensable in Etching Equipment?
Dry etching is one of the most critical processes in chip manufacturing. The etch chamber is typically filled with reactive gases such as CF₄, SF₆, Cl₂, and HBr, which form a highly active plasma environment under a radio frequency electric field.
During this process, high-energy ions continuously bombard the chamber walls and component surfaces, accompanied by complex chemical corrosion and thermal shock. For components such as chamber liners, showerheads, focus rings, and windows, the material must not only exhibit excellent resistance to corrosion and erosion, but also minimise particle release and contamination.
The reason is simple: if any particle falls onto the wafer surface, it can cause defects or even scrap the entire wafer. As process nodes become smaller, the cleanliness requirements for equipment materials become increasingly stringent.
What Are the Limitations of Alumina?
Thanks to its mature technology, low cost, and good mechanical properties, alumina has long been the dominant ceramic material in semiconductor equipment. However, as processes advance to more critical nodes, the limitations of alumina in plasma environments become apparent.
In fluorine-containing plasmas, alumina reacts with active fluorine species to form aluminium fluoride (AlF₃) and other products. These reaction by-products can deposit, flake off, and become sources of particle contamination. Meanwhile, the alumina itself is gradually eroded under long-term plasma bombardment, shortening component lifetime.
For mature process nodes, such issues can usually be controlled by shortening maintenance intervals. However, as device critical dimensions shrink, the tolerance for particle and metallic contamination drops significantly, and trace contaminants released from chamber materials can affect product yield.
Why Is Yttria Gaining Favour?
Among many candidate materials, yttria has gradually stood out. Compared with alumina, yttria offers better chemical stability in halogen-based plasmas. When it reacts with fluorine-containing plasmas, the resulting yttrium fluoride (YF₃) layer is quite stable and can form a protective coating that slows further corrosion.
In addition, yttria typically exhibits a lower plasma etch rate. Studies and industrial applications show that under the same conditions, the erosion rate of yttria is significantly lower than that of alumina, effectively extending component lifetime and reducing equipment maintenance frequency and downtime.
Moreover, yttria maintains good structural stability at high temperatures and does not easily crack or spall under long-term thermal cycling, which is also important for controlling particle contamination.
From Coatings to Bulk Ceramics: Two Application Routes for Yttria
At present, two main technical routes exist for applying yttria in semiconductor equipment. From an industrial development perspective, these routes are not mutually exclusive; they correspond to different application scenarios and cost requirements.
(1) Yttria coatings: A yttria layer is deposited on an aluminium alloy or alumina ceramic substrate by processes such as plasma spraying, thereby improving the plasma resistance of the component. This approach is relatively mature, can be applied to complex-shaped parts, and has manageable costs, making it the most widely used form today. Components such as chamber liners, showerheads, and baffles are often treated with such coatings.
(2) Bulk yttria ceramics: High-purity yttria powder is directly sintered to produce ceramic components without relying on other substrate materials. Compared with coatings, bulk yttria ceramics provide a more uniform microstructure and superior plasma resistance, but the sintering difficulty, processing complexity, and manufacturing cost are significantly higher.
Domestic Production of Yttria Still Faces Multiple Challenges
Although the advantages of yttria are widely recognised, its industrialisation faces high barriers. For spray applications, high-purity yttria powder is the core raw material. The product must achieve extremely high purity, stable particle size distribution, good sphericity, and consistent batch quality to meet the powder feeding and melting requirements for thermal spraying.
At the same time, the control of spraying parameters, coating porosity, bond strength optimisation, and subsequent surface finishing processes directly affect the final product performance.
In the field of bulk yttria ceramics, because the material itself is difficult to sinter and expensive to machine, higher demands are placed on powder preparation, forming, sintering, and precision processing capabilities.