Erosion and degradation of EUV lithography collector mirrors under particle bombardment

Abstract

In extreme ultraviolet lithography (EUVL) environments both laser produced plasma (LPP) and gas discharge produced plasma (GDPP) configurations face serious issues regarding components lifetime and performance under particle bombardment, in particular collector mirrors. For both configurations debris, fast ions, fast neutrals, and condensable EUV radiator fuels (Li, Sn) can affect collector mirrors. In addition, collector mirrors are exposed to impurities (H,C,O,N), off-band radiation (depositing heat) and highly-charged ions leading to their degradation and consequently limiting 13.5 nm light reflection intensity.The IMPACT (Interaction of Materials with charged Particles and Components Testing) experiment at Argonne studies radiation-induced, thermodynamic and kinetic mechanisms that affect the performance of optical mirror surfaces. Results of optical component interaction with singly-charged inert gases (Xe) and alternate radiators (e.g. Sn) are presented for glancing incidence mirrors (i.e., Ru, Pd) at bombarding energies between 100-1000 eV at room temperature. Measurements conducted include: In-situ surface analysis: Auger electron spectroscopy, X-ray photoelectron spectroscopy, direct recoil spectroscopy and low-energy ion scattering spectroscopy; Ex-situ surface analysis: X-ray reflectivity, X-ray diffraction, atomic force microscopy and at-wavelength EUV reflectivity (NIST-SURF).

Hydrogen mediated transport of Sn to Ru film surface

“…38͒ and of erosion of Rucoated glancing incidence mirrors. 39 Spectra recorded after ·H dose 4.2ϫ 10 20 cm −2 in the presence of Sn ͓Fig. 5͑b͔͒ show the same tendency: the raise of the Ru signal with He dose followed by saturation.…”

Mitigation of fast ions from laser-produced Sn plasma for an extreme ultraviolet lithography source

“…If the kinetic energy of the particles can be slowed down to around 100 eV, the sputtering rate could decrease more than an order of magnitude as compared with that of ions above 1 keV. 7 In addition, lower energy particles are easier to remove using conventional methods, such as ambient gas, electric field, and their combination. In very recent time, increasing efforts to reduce the ion kinetic energy have been carried out.…”

Extreme-ultraviolet spectral purity and magnetic ion debris mitigation by use of low-density tin targets

“…Controlling and mitigating the fast ions from the tin target is one of the bigger challenges to overcome in order to successfully implement such EUVL sources as they are expected to significantly damage the collector mirror 4 . The ion debris measurements were carried out in the presence and absence of magnetic field using a Faraday cup In conclusion, we report the effectiveness of the tin doped foam target for ion mitigation using a transverse magnetic field.…”

“…The biggest concern is the fast ions from the plasma that are expected to significantly damage the collector mirror by means of ion-induced mixing of multi-layer mirror (MLM), by etching and implantation of the MLM coating, which is located near the EUV light source 4 . Hence application of practical EUV sources without proper debris mitigation results in an EUVL tool with unacceptable operational lifetime.…”