Why Yttrium Oxide (Y₂O₃) Is Used for  Semiconductor Plasma-Etching Environment

With the rapid expansion and technological maturity of the semiconductor and display industries, plasma etching processes are increasingly demanding in terms of materials performance. In etching chambers, critical components made from aluminum alloys, quartz, and ceramics are continuously exposed to high-density plasma and aggressive corrosive gases. Plasma bombardment and chemical corrosion lead to surface erosion and particle generation, which directly causes wafer defects and yield loss.

Plasma Etching Environment and Challenges

Typical etching processes employ highly reactive gases such as CF₄, SF₆, O₂, Cl₂, and HBr. Under high-density plasma conditions, materials must simultaneously withstand:

• Intense ion bombardment (physical sputtering)

• Strong chemical corrosion by halogen species

• Extremely strict particle contamination requirements

Any particles released from chamber surfaces can redeposit onto wafers, leading to critical defects and scrapped devices. Therefore, improving the plasma corrosion resistance of chamber components is essential.

Limitations of Conventional Protective Coatings

Traditional protection methods, such as anodized aluminum (Al₂O₃) coatings, offer limited resistance to plasma erosion. In fluorine- or chlorine-based plasmas, anodized layers react to form volatile by-products (e.g., AlF₃, AlCl₃), resulting in rapid material loss, surface roughening, and particle generation. Quartz and conventional oxide ceramics suffer from similar limitations due to high etch rates and unstable reaction products.

Advantages of Yttrium Oxide Coatings

Yttrium oxide (Y₂O₃) has become the most widely adopted plasma-resistant material for etching equipment due to its unique combination of chemical and physical properties:

1. Extremely Low Plasma Etch Rate
   In fluorine-containing plasmas, Y₂O₃ forms yttrium fluoride (YF₃), a stable compound with high melting point and low vapor pressure. This results in a dense, protective surface layer that significantly suppresses further chemical erosion.

2. Minimal Particle Generation
   The non-volatile reaction products and dense microstructure of Y₂O₃ coatings reduce surface degradation and particle release, directly improving wafer yield.

3. Excellent Thermal Stability
   With a melting point above 2400 °C, Y₂O₃ maintains structural and chemical stability under high-power plasma and elevated operating temperatures.

4. Proven Thermal Spray Processability
   Yttrium oxide powders are well suited for plasma spraying and related thermal spray techniques, enabling dense coatings with thicknesses of ~0.15 mm or greater. These coatings adhere well to aluminum alloys and steel substrates, making them practical for large-scale industrial deployment.

Performance Benefits in Etching Equipment

Applying a ~0.15 mm Y₂O₃ thermal spray coating to etching chamber inner walls effectively prevents substrate-derived contamination of silicon wafers. In industrial practice, such coatings can extend chamber overhaul intervals from approximately 15 days to up to 6 months, significantly reducing downtime and maintenance costs while improving process stability.

Extended Applications

Beyond semiconductor etching, Y₂O₃ coatings are also used in high-temperature and harsh-environment applications, such as protective layers for graphite components in hard-metal processing and thermal insulation coatings, owing to their excellent heat resistance and chemical inertness.

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