Extreme ultraviolet lithography (EUVL, also known simply as EUV) is a technology used in the semiconductor industry for manufacturing integrated circuits (ICs).
It is a type of photolithography that uses 13.5 nm extreme ultraviolet (EUV) light from a laser-pulsed tin (Sn) plasma to create intricate patterns on semiconductor substrates.
The EUV wavelengths that are used in EUVL are near 13.5 nanometers (nm), using a laser-pulsed tin (Sn) droplet plasma to produce a pattern by using a reflective photomask to expose a substrate covered by photoresist.
[citation needed] In 1991, scientists at Bell Labs published a paper demonstrating the possibility of using a wavelength of 13.8 nm for the so-called soft X-ray projection lithography.
The results of this successful effort were disseminated via a public/private partnership Cooperative R&D Agreement (CRADA) with the invention and rights wholly owned by the US government, but licensed and distributed under approval by DOE and Congress.
[4] Intel, Canon, and Nikon (leaders in the field at the time), as well as the Dutch company ASML and Silicon Valley Group (SVG) all sought licensing.
[6] By 2018, ASML succeeded in deploying the intellectual property from the EUV-LLC after several decades of developmental research, with incorporation of European-funded EUCLIDES (Extreme UV Concept Lithography Development System) and long-standing partner German optics manufacturer ZEISS and synchrotron light source supplier Oxford Instruments.
The scanner uses Zeiss optics, which that company calls "the most precise mirrors in the world", produced by locating imperfections and then knocking off individual molecules with techniques such as ion beam figuring.
[8] This made the once small company ASML the world leader in the production of scanners and monopolist in this cutting-edge technology and resulted in a record turnover of 27.4 billion euros in 2021, dwarfing their competitors Canon and Nikon, who were denied IP access.
Because it is such a key technology for development in many fields, the United States licenser pressured Dutch authorities to not sell these machines to China.
Along with multiple patterning, EUV has paved the way for higher transistor densities, allowing the production of higher-performance processors.
This significant growth reflects the rising demand for miniaturized electronics in various sectors, including smartphones, artificial intelligence, and high-performance computing.
The combination of the off-axis asymmetry and the mask shadowing effect leads to a fundamental inability of two identical features even in close proximity to be in focus simultaneously.
Generally, the image shift is balanced out due to illumination source points being paired (each on opposite sides of the optical axis).
[89][90] Since the pupil imbalance changes with EUV collector mirror aging or contamination, such placement errors may not be stable over time.
[101] The rotating plane of incidence (azimuthal range within −25° to 25°) is confirmed in the SHARP actinic review microscope at CXRO which mimics the optics for EUV projection lithography systems.
[105] More generally, so-called "ring-field" systems reduce aberrations by relying on the rotational symmetry of an arc-shaped field derived from an off-axis annulus.
For pitches requiring dipole, quadrupole, or hexapole illumination, the rotation also causes mismatch with the same pattern layout at a different slit position, i.e., edge vs. center.
[115] On 0.33 NA systems, 30 nm pitch and lower already suffer sufficient reduction of pupil fill to significantly affect throughput.
[99] Besides the more complicated effects due to shadowing and pupil rotation, tilted edges are converted to stair shape, which may be distorted by OPC.
[118] Aberrations, originating from deviations of optical surfaces from subatomic (<0.1 nm) specifications[119] as well as thermal deformations[120][121] and possibly including polarized reflectance effects,[122] are also dependent on slit position,[123][121] as will be further discussed below, with regard to source-mask optimization (SMO).
Though the EUV spectrum is not completely monochromatic, nor even as spectrally pure as DUV laser sources, the working wavelength has generally been taken to be 13.5 nm.
Hydrogen also reacts with metal-containing compounds to reduce them to metal,[209] and diffuses through the silicon[210] and molybdenum[211] in the multilayer, eventually causing blistering.
[245] Heating of the EUV mask pellicle (film temperature up to 750 K for 80 W incident power) is a significant concern, due to the resulting deformation and transmission decrease.
The two issues of shot noise and EUV-released electrons point out two constraining factors: 1) keeping dose high enough to reduce shot noise to tolerable levels, but also 2) avoiding too high a dose due to the increased contribution of EUV-released photoelectrons and secondary electrons to the resist exposure process, increasing the edge blur and thereby limiting the resolution.
For chemically amplified resists, higher dose exposure also increases line edge roughness due to acid generator decomposition.
[281] Even with higher absorption at the same dose, EUV has a larger shot noise concern than the ArF (193 nm) wavelength, mainly because it is applied to thinner resists.
[302][303] While Samsung introduced its own 7 nm process with EUV single-patterning,[304] it encountered severe photon shot noise causing excessive line roughness, which required higher dose, resulting in lower throughput.
[321] Also, an anamorphic 0.52 NA tool has been found to exhibit too much CD and placement variability for 5 nm node single exposure and multi-patterning cutting.
[328] For sub-2nm nodes, high-NA EUV systems will be affected by a host of issues: throughput, new masks, polarization, thinner resists, and secondary electron blur and randomness.