Low-Expansion Glass Materials Powering Next-Gen Semiconductor Equipment

In semiconductor equipment, stability is everything. That’s why quartz (fused silica) and Zerodur (a lithium–aluminosilicate glass–ceramic from Schott) are the go-to materials when even the tiniest thermal shifts can ruin a wafer pattern.

Why these materials stand out

• Ultra-low thermal expansion: Fused silica’s coefficient of thermal expansion (CTE) is ~0.5×10⁻⁶/K, while Zerodur’s class-0 grade is essentially zero (0 ± 0.02×10⁻⁶/K). For comparison, steel sits around 10–12×10⁻⁶/K and aluminum at ~23×10⁻⁶/K. This near-zero expansion keeps optics and stages perfectly aligned even under rapid temperature changes.

• High optical purity: Both materials can be produced with exceptional homogeneity, allowing precision polishing with virtually no birefringence. Fused silica’s amorphous nature ensures optical uniformity, while Zerodur’s engineered microstructure guarantees stability across large blanks.

• UV transparency: Fused silica excels in deep-UV (193 nm) and even some extreme-UV applications, essential for DUV lenses and photomask substrates.

• Chemical durability: Resistant to most acids and solvents (except HF), these materials withstand aggressive cleaning and patterning processes without degrading.

• Dimensional precision and vacuum compatibility: Unlike polymers, metals, or composites, they show negligible creep or outgassing and are dielectric, non-contaminating, and suitable for ultra-high vacuum environments.

Applications in semiconductor tools

• Photolithography optics: In 193 nm DUV scanners, high-purity quartz forms the lenses and mask substrates. For EUV (13.5 nm), Zerodur mirrors maintain nanometer-level focus despite intense laser heating.

• Wafer and reticle stages: Moving stages in steppers use Zerodur for frames and footers. Its stiffness and zero-expansion properties preserve nanometer accuracy during high-speed motion.

• Metrology and alignment: Interferometers, overlay sensors, and reference flats rely on Zerodur or fused silica to maintain calibration despite temperature or vibration changes.

• Wafer handling systems: Quartz wafer boats, carriers, and vacuum chucks leverage chemical resistance and thermal stability to survive harsh process conditions.

Industry trends

As lithography pushes toward smaller nodes and EUV adoption rises, demand for low-expansion glass is surging. The global quartz photomask market alone is projected to grow from $5.29B in 2024 to $7.44B by 2032 (~5.1% CAGR). Equipment makers like ASML continue to expand EUV capacity, driving increased need for quartz and Zerodur components. Governments worldwide are investing in domestic supply chains, recognizing photomasks and precision optics as strategic assets.

Looking ahead

Materials science continues to push the limits. Ultra-low CTE variants of fused silica (e.g., Corning’s ULE) and tailored Zerodur grades tighten tolerances even further. Advanced bonding techniques, additive manufacturing, and optimized glass–ceramic composites are enabling complex, thermally stable assemblies. High-NA EUV lithography demands ever-greater precision, prompting innovations in coatings, material purity, and thermal control.

In short, near-zero expansion, optical purity, and chemical robustness will remain critical as semiconductor tools evolve. Quartz and Zerodur aren’t just materials—they’re the foundation for next-generation lithography and metrology.