Photolithography Wavelength Light Source 365nm 248nm 193nm EUV
A photolithography light source is the illumination system that generates the UV or EUV light used to project a chip's circuit pattern onto the photoresist-coated wafer — and the wavelength it produces directly sets the smallest feature a fab can print, via the Rayleigh resolution criterion: CD = k₁ · λ / NA. Shrink the wavelength, and every node generation below it becomes possible.
Why the light source is the limiting ingredient. Everything else in a scanner — the lens, the mask, the resist chemistry — gets engineered around whatever wavelength the source can deliver. Mercury-arc lamps could only ever push so far because they emit a handful of fixed spectral lines (g-line at 436nm, i-line at 365nm); once nodes needed sub-350nm resolution, the industry had no choice but to switch to excimer lasers, which generate light through stimulated emission from a noble-gas/halogen plasma rather than heating a filament.
The four generations that got us to today's nodes:
| Source | Wavelength | Mechanism | Era / nodes enabled |
|---|---|---|---|
| Hg arc lamp (g/i-line) | 436nm / 365nm | Mercury vapor discharge | 1970s–90s, >350nm |
| KrF excimer laser | 248nm | Krypton-fluoride gas discharge | late 1990s, 250–130nm |
| ArF excimer (dry + immersion) | 193nm | Argon-fluoride gas discharge | 2000s–2010s, 90–7nm |
| EUV (laser-produced plasma) | 13.5nm | Tin droplets vaporized by a CO₂ laser, emitting EUV plasma | 2019–present, 7nm–2nm |
EUV is a different kind of machine, not just a shorter laser. At 13.5nm, light is absorbed by essentially everything — air, glass, water — so there's no refractive lens, no immersion fluid, and no transmissive mask. An EUV source fires a high-power CO₂ laser at a free-falling droplet of molten tin roughly 30 micrometers across, 50,000 times a second, vaporizing it into a plasma hot enough to emit 13.5nm light. That light is then collected and relayed entirely with multilayer mirrors, because EUV has no transparent material to pass through. It's arguably the most complex light source ever deployed in mass manufacturing — a single EUV scanner costs more than $150 million, largely because of what it takes to generate and collect that light reliably enough to run a fab 24/7.
The next step is already named: High-NA EUV (0.55 NA, vs. 0.33 today) doesn't change the wavelength — it uses a larger, more precisely figured mirror system to raise the NA term in the Rayleigh equation instead, buying another generation of resolution out of the same 13.5nm source before anyone has to solve the much harder problem of going shorter than EUV.