For a leading-edge lithography technology, EUV (extreme ultraviolet) lithography is still plagued by some fundamental issues. While stochastically occurring defects probably have been the most often discussed, other issues, such as image shifts and fading [1-5], are an intrinsic part of using reflective EUV optics. However,… Read More
Stochastic defects in EUV lithography have been studied over the last few years. For years, the Poisson noise from the low photon density of EUV had been suspected [1,2]. EUV distinguishes itself from DUV lithography with secondary electrons functioning as intermediary agents in generating reactions in the resist. Therefore,… Read More
The resolution of EUV lithography is commonly expected to benefit from the shorter wavelengths (13.2-13.8 nm) but in actuality the printing process needs to include Pde the consideration of the lower energy electrons released by the absorption of EUV photons. The EUV photon energy itself has a nominal energy range of 90-94 eV,… Read More
In spite of increasing usage of EUV lithography, stochastic defects have not gone away. What’s becoming clearer is that EUV doses must be managed to minimize the impact from such defects. The 2022 edition of the International Roadmap for Devices and Systems has updated its Lithography portion [1]. An upward trend with decreasing… Read More
The 3nm node is projected to feature around a 22 nm metal pitch [1,2]. This poses some new challenges for the use of EUV lithography. Some challenges are different for the 0.33NA vs. 0.55NA systems.
For 0.33 NA systems, 22 nm pitch can only be supported by illumination filling 4% of the pupil, well below the 20% lower limit for
As a consequence of having a ~13.5 nm wavelength, EUV photons transfer ~90% of their energy to ionized photoelectrons. Thus, EUV lithography is fundamentally mostly EUV photoelectron lithography. The actual resolution becomes dependent on photoelectron trajectories.
Photoelectron trajectories in EUV lithography were… Read More
The list of possible stochastic patterning issues for EUV lithography keeps growing longer: CD variation, edge roughness, placement error, defects [1]. The origins of stochastic behavior are now well-known. For a given EUV photon flux into the resist, a limited fraction are absorbed. Since the absorption is less than 5% affected… Read More
Stochastic defects continue to draw attention in the area of EUV lithography. It is now widely recognized that stochastic issues not only come from photon shot noise due to low (absorbed) EUV photon density, but also the resist material and process factors [1-4].
It stands to reason that resist absorption of EUV light, which is … Read More
As EUV lithography is being targeted towards pitches of 30 nm or less, fundamental differences from conventional DUV lithography become more and more obvious. A big difference is in the mask use. Unlike other photolithography masks, EUV masks are absorber patterns on a reflective multilayer rather than a transparent substrate.… Read More
In previous articles, I had looked at EUV stochastic behavior [1-2], primarily in terms of the low photon density resulting in shot noise, described by the Poisson distribution [3]. The role of blur to help combat the randomness of EUV photon absorption and secondary electron generation and migration was also recently considered… Read More
