Extreme Ultraviolet (EUV) Lithography is the semiconductor patterning technology that uses 13.5 nm wavelength light to print circuit features below 7 nm — replacing the multiple patterning required by 193 nm ArF immersion lithography with single-exposure capability, while demanding extraordinary engineering of tin-plasma light sources producing 500W+ power, multilayer reflective optics, and defect-free reflective masks that together represent the most complex optical system ever manufactured.

Why 13.5 nm Wavelength

The resolution limit of optical lithography scales with wavelength: R ~ kλ/NA. At 193 nm (ArF), printing 20 nm features requires multiple patterning (SADP, SAQP) — quadrupling mask count and process complexity. At 13.5 nm (EUV), the same features can be printed in a single exposure. The 13.5 nm wavelength is chosen because multilayer Mo/Si mirrors have ~70% peak reflectivity at this wavelength.

EUV Source Technology

No material is transparent at 13.5 nm — the entire system operates in vacuum with reflective optics. The light source uses Laser-Produced Plasma (LPP): 1. A 20 kW CO₂ laser fires a pre-pulse to flatten a 25 μm tin droplet into a pancake shape. 2. A main pulse vaporizes and ionizes the tin, creating plasma at >500,000°C. 3. The Sn¹⁰⁺/Sn¹¹⁺ ions emit 13.5 nm photons. 4. A multilayer collector mirror (with >10,000 Mo/Si bilayer coating segments) focuses the EUV light. 5. Current source power: >500W at intermediate focus. High-volume manufacturing requires sustained power for >90% uptime.

Reflective Optics and Masks

EUV masks are fundamentally different from DUV transmissive masks:

• Substrate: Ultra-low thermal expansion material (ULE glass) with <50 nm flatness.
• Multilayer: 40-50 pairs of Mo/Si bilayers (~7 nm period) providing ~67% reflectivity.
• Absorber Pattern: TaN-based absorber deposited on the multilayer and patterned by e-beam lithography.
• Pellicle: A thin membrane (polysilicon or CNT-based) protecting the mask from particles during exposure. Must transmit >90% of EUV light and survive sustained radiation exposure — one of EUV's most challenging components.

High-NA EUV (0.55 NA)

The next generation increases the numerical aperture from 0.33 to 0.55:

• Resolution improves from ~13 nm to ~8 nm half-pitch.
• Anamorphic optics demagnify 4x in one direction and 8x in the other, requiring new mask formats.
• Larger optics with tighter tolerances — the projection optics module weighs several tons with sub-nanometer surface accuracy.
• Intel and TSMC are the lead customers for ASML's first High-NA (EXE:5000) systems.

Cost and Throughput

An EUV scanner costs >$350M; High-NA systems exceed $400M. Throughput: >160 wafers/hour at 0.33 NA. The scanner represents ~25% of a leading-edge fab's equipment cost, and EUV layers account for 30-40% of total wafer processing cost at advanced nodes.

EUV Lithography is the enabling technology for continued Moore's Law scaling below 7 nm — a $10+ billion engineering achievement that makes printing features at the atomic scale a routine manufacturing operation.