What Is Extreme Ultraviolet Lithography?

Extreme Ultraviolet Lithography (EUVL) is a photolithographic patterning technology that uses 13.5 nm wavelength light to print features on semiconductor wafers at dimensions below 10 nanometers. Because the wavelength is roughly 14 times shorter than the 193 nm deep-ultraviolet light used in the preceding ArF immersion systems, EUV enables finer resolution without the complex multi-patterning sequences that ArF requires, reducing process steps and overlay error accumulation. The technology draws on plasma physics, precision optics, photoresist chemistry, and vacuum engineering, and it has become the enabling technique for manufacturing logic and memory chips at the 5 nm, 3 nm, and 2 nm process nodes.

EUV Light Source

Generating usable EUV light requires a laser-produced plasma source. A high-power carbon-dioxide laser fires pulses at tin droplets, roughly 30 micrometers in diameter, at a rate of 50,000 droplets per second. A first, lower-power prepulse deforms each droplet into a disk, maximizing the surface area that the main pulse vaporizes into a plasma. The plasma radiates across a broad spectrum, but optical elements with multilayer reflective coatings select the 13.5 nm emission from excited tin ions. Because EUV light is strongly absorbed by all gases, the entire optical path from source to wafer must be maintained under near-vacuum conditions. ASML, the sole commercial manufacturer of EUV lithography systems, describes the engineering of these laser-plasma sources in detail on the ASML EUV lithography systems product page, where current-generation scanners operate at source powers above 250 watts and achieve throughputs of more than 170 wafers per hour.

Reflective Optics and Mask Technology

Unlike deep-ultraviolet systems, which use refractive glass lenses, EUV systems rely entirely on multilayer reflective mirrors because glass is opaque at 13.5 nm. Each mirror consists of alternating nanometer-thick layers of molybdenum and silicon deposited on a polished substrate, tuned to reflect roughly 67% of incident EUV radiation at the design wavelength. A six-mirror illumination and projection system reduces the mask image onto the wafer with a demagnification ratio of 4:1. The mask itself is a reflective reticle with a patterned absorber layer on top of the same multilayer coating, and any particle contamination on the mask surface prints as a defect. Pellicles, thin membranes stretched across the mask to intercept airborne particles, were a critical engineering challenge before commercially viable EUV pellicle materials were developed in the early 2020s. The precision requirements for EUV mirrors, with figure errors held to tens of picometers, represent some of the tightest manufacturing tolerances in any commercial product. NIST has contributed to this effort through metrology programs that characterize EUV reflectance and surface figure to the accuracy levels required for qualification of production optics, as described in NIST's EUV metrology research.

Resolution, Overlay, and High-NA EUV

At the 13.5 nm wavelength, a numerical aperture of 0.33 (the value used in current production scanners) yields a single-exposure resolution around 13 nm in half-pitch. The next generation, High-NA EUV with a numerical aperture of 0.55, is designed to extend single-patterning resolution below 8 nm half-pitch, enabling 2 nm and 1.4 nm node production. High-NA systems require a new anamorphic 8:1 demagnification scheme and taller reticles, demanding redesigned mask infrastructure. Intel and TSMC have each received early High-NA evaluation units from ASML. The International Roadmap for Devices and Systems published through IEEE's roadmapping activities places High-NA EUV as the primary patterning path for logic scaling through the late 2020s.

Applications

Extreme Ultraviolet Lithography has applications in a wide range of disciplines, including:

• High-volume logic chip manufacturing at 5 nm, 3 nm, and 2 nm process nodes
• DRAM and NAND flash memory patterning at advanced pitch dimensions
• Foundry fabrication of AI accelerators and mobile application processors
• Photomask and photoresist materials research aligned to sub-10 nm feature requirements
• Metrology and inspection tool development for EUV-patterned defect detection