EUV Lithography
Why EUV was needed, 13.5nm wavelength, and the engineering marvel behind it
Why EUV Was Needed
Why EUV Was Needed
By the 7nm node, ArF immersion with multi-patterning required 4–5 exposures for a single critical layer, making it extremely expensive and complex. EUV lithography replaces these multiple exposures with a single exposure at 13.5 nm wavelength.
The jump from 193 nm to 13.5 nm — a 14× reduction in wavelength — was one of the most challenging engineering feats in history. It took over 20 years and $10+ billion in R&D.
Key Concept: Everything Changes at EUV
At 13.5 nm, everything absorbs EUV light — including air, glass lenses, and most materials. This means EUV systems must operate in a near-perfect vacuum, use reflective mirrors instead of lenses, and generate light from a tin plasma source.
How EUV Works
How EUV Works
An EUV scanner is arguably the most complex machine ever built:
- Light source: A high-power CO₂ laser hits tiny tin droplets (50,000 per second) at 50 km/s. Each droplet explodes into plasma that emits 13.5 nm EUV light. Conversion efficiency is only ~5%.
- Optics: 11 multilayer mirrors (alternating Mo/Si layers, ~40 pairs) collect and focus the light. Each mirror reflects only ~70% of incident EUV, so total optical efficiency is ~2%.
- Mask: Reflective mask (not transmissive) with absorber patterns on a Mo/Si multilayer substrate.
- Vacuum: The entire optical path operates in ultra-high vacuum (hydrogen environment for debris mitigation).
Despite all these losses, modern High-NA EUV scanners achieve 200+ wafers per hour throughput — a testament to the extraordinary source power (>500W at intermediate focus).
Knowledge Check
Knowledge Check
1 / 2Why must EUV systems operate in a vacuum?