When the industry’s attention is fixed on EUV, an easily overlooked fact remains: the most numerous and highest-throughput lithography scanners in wafer fabs worldwide are still immersion DUV tools.
ArF immersion systems with a wavelength of 193 nm and a numerical aperture of 1.35 continue to expose a large share of critical layers in both advanced and mature processes, spanning advanced logic and memory manufacturing. What keeps pushing these “veterans” toward their limits is not a shorter-wavelength source or a larger NA, but computational lithography.
How does it actually achieve this? This article is organized around three questions: Where is the limit of DUV? What does ASML rely on to break through that limit? And how does an optimum computed in the digital world get realized on the tool itself?
Low-k1 process: the limiting challenge of DUV imaging
Lithographic resolution follows the Rayleigh equation: CD = k1 × λ / NA. For ArF immersion lithography, λ is fixed at 193 nm, and water immersion constrains NA to a maximum of 1.35. To shrink CD further, the only remaining lever is to reduce the process factor k1. That is precisely the core value of computational lithography, and a key reason treats it is treated as an integral part of its customer-facing total lithography solution.
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