EUV Source

EUV Light Source Technology covers the laser-produced plasma (LPP) source systems that generate 13.5nm extreme ultraviolet radiation for EUV lithography scanners — one of the most extreme engineering achievements in semiconductor manufacturing, requiring 50,000 droplets of molten tin per second to be vaporized by a CO₂ laser to create a plasma that emits EUV light collected by a multi-layer mirror, all operating continuously with industrial reliability.

LPP Source Architecture:

Droplet Generator → Tin droplets (25-30μm diameter, 50 kHz rate)
    ↓
Pre-Pulse Laser (PP) → Hits Sn droplet, flattens it into a disc (~300μm)
    ↓ (~1-2 μs delay)
Main CO₂ Laser Pulse (~20 kW average power) → Vaporizes Sn disc
    ↓
Tin Plasma (~30-50 eV, ~500,000°C)
    ↓ Emits EUV at 13.5nm (Sn¹⁰⁺ to Sn¹³⁺ ionic transitions)
Collector Mirror (Mo/Si multilayer, 5m² area)
    ↓ Focuses EUV to intermediate focus (IF)
Scanner illumination optics

Key Parameters:

The Conversion Efficiency Challenge:

Only ~5-6% of CO₂ laser energy converts to in-band 13.5nm EUV (within 2% bandwidth). The remaining ~95% becomes: out-of-band radiation (visible, IR), debris (Sn fragments, ions, atoms), and thermal load on the collector mirror. This extreme inefficiency means a 250W EUV source requires ~40kW of laser power, which generates enormous waste heat and debris management challenges.

Tin Debris Mitigation:

Sn debris from 50,000 plasma events per second threatens the collector mirror and other components:

• Hydrogen buffer gas: H₂ at ~100 Pa slows Sn ions and reacts with Sn to form volatile SnH₄ that pumps away
• Magnetic debris mitigation (MDB): Superconducting magnets deflect charged Sn ions away from the collector
• Collector cleaning: In-situ hydrogen radical cleaning removes Sn deposits. Collector replacement still needed every ~30-40 billion pulses (~6-12 months)
• Sn recycling: Excess tin is captured, purified, and recirculated to the droplet generator

Collector Mirror:

The collector is a massive Mo/Si multilayer-coated concave mirror (~5m² surface area) that reflects ~65% of incident 13.5nm EUV light. The multilayer must maintain reflectivity despite continuous bombardment by Sn atoms, ions, hydrogen radicals, and out-of-band radiation. A ruthenium capping layer protects the surface. Even with protection, gradual degradation requires periodic replacement at ~$1M+ per collector.

Pre-Pulse Technology:

The pre-pulse (initially a Nd:YAG laser, now a shaped CO₂ pre-pulse) transforms the spherical Sn droplet into a flat disc (pancake shape), increasing the interaction cross-section with the main CO₂ laser pulse by 10× and dramatically improving conversion efficiency. Double-pulse and advanced pre-pulse shaping are active R&D areas for further efficiency gains.

Laser Technology:

The CO₂ drive laser (10.6μm wavelength — chosen because CO₂ photons efficiently couple to Sn plasma) uses: a master oscillator power amplifier (MOPA) architecture, multi-stage RF-excited CO₂ amplifiers, and pulse shaping for optimal energy coupling. Trumpf (Germany) is the sole supplier of these industrial CO₂ lasers.

EUV source technology represents arguably the most extreme light source ever engineered for industrial use — generating reliable, high-power 13.5nm radiation from tin plasma 50,000 times per second, 24/7, with the precision and stability required to pattern the world's most advanced semiconductors.