DUV Systems

DUV System Components

A DUV (Deep Ultraviolet) immersion scanner consists of several major subsystems:

• ArF excimer laser: Generates 193 nm light by exciting argon fluoride gas. Modern lasers produce 90W+ at 6 kHz repetition rate with extremely narrow bandwidth (<0.35 pm).
• Illuminator: Shapes the laser beam into the desired angular distribution (conventional, annular, dipole, quadrupole) to optimize imaging for different pattern types.
• Projection optics: 30+ fused silica and CaF₂ lens elements, polished to sub-atomic surface roughness. Total weight: several tons. The last lens element sits just above the water puddle.
• Immersion system: Delivers and recovers ultra-pure water between the final lens and wafer, maintaining a stable meniscus at high scan speeds.
• Alignment system: Multiple sensors measure wafer position, tilt, and height at each die location before exposure.

ArF immersion scanners from ASML achieve high throughput at advanced nodes: the TWINSCAN NXT:2000i is rated at ~275 wafers/hour and the newer NXT:2050i reaches ~295 wafers/hour. List price is approximately $80–100 million per tool.

Immersion Fluid and Pellicles

193 nm ArF dry scanners topped out at NA ≈ 0.93. The jump to NA ≈ 1.35 required filling the gap between the final lens element and the wafer with ultra-pure water (n = 1.44 at 193 nm). The maximum NA equals roughly n × sin θ, so a higher index lets sharper rays pass through.

What the immersion module does

• Delivers a stable water meniscus between the lens and wafer
• Maintains water resistivity >18 MΩ·cm and degasses dissolved O₂/N₂ to suppress micro-bubbles
• Recovers and recycles ~99% of the water without leaving stains on the wafer
• Tracks the meniscus during fast stage scans (up to 500 mm/s) — no air entrainment allowed

Pellicles

A pellicle is a thin transparent membrane stretched a few millimeters above the reticle pattern. Particles that land on the pellicle are far out of focus and don't print on the wafer.

• DUV pellicles: organic polymer, ~0.8 µm thick, >99% transmission at 193 nm — standard for decades
• EUV pellicles: free-standing polysilicon or carbon nanotube membranes 30–80 nm thick, ~90% transmission at 13.5 nm — only recently shipping in production