Debris and radiation-induced damage effects on EUV nanolithography source collector mirror optics performance

Abstract

Exposure of collector mirrors facing the hot, dense pinch plasma in plasma-based EUV light sources to debris (fast ions, neutrals, off-band radiation, droplets) remains one of the highest critical issues of source component lifetime and commercial feasibility of nanolithography at 13.5-nm. Typical radiators used at 13.5-nm include Xe and Sn. Fast particles emerging from the pinch region of the lamp are known to induce serious damage to nearby collector mirrors. Candidate collector configurations include either multi-layer mirrors (MLM) or single-layer mirrors (SLM) used at grazing incidence.Studies at Argonne have focused on understanding the underlying mechanisms that hinder collector mirror performance at 13.5-nm under fast Sn or Xe exposure. This is possible by a new state-of-the-art in-situ EUV reflectometry system that measures real time relative EUV reflectivity (15-degree incidence and 13.5-nm) variation during fast particle exposure. Intense EUV light and off-band radiation is also known to contribute to mirror damage. For example offband radiation can couple to the mirror and induce heating affecting the mirror's surface properties. In addition, intense EUV light can partially photo-ionize background gas (e.g., Ar or He) used for mitigation in the source device. This can lead to local weakly ionized plasma creating a sheath and accelerating charged gas particles to the mirror surface and inducing sputtering.In this paper we study several aspects of debris and radiation-induced damage to candidate EUVL source collector optics materials. The first study concerns the use of IMD simulations to study the effect of surface roughness on EUV reflectivity. The second studies the effect of fast particles on MLM reflectivity at 13.5-nm. And lastly the third studies the effect of multiple energetic sources with thermal Sn on 13.5-nm reflectivity. These studies focus on conditions that simulate the EUVL source environment in a controlled way.

Hydrogen mediated transport of Sn to Ru film surface

“…This is in contrast to the result reported for Ru͑0001͒ at 330 K. 17 Thermal deposition of Sn led to Stranski-Krastanov growth mode, i.e., island growth over the initial twodimensional ͑2D͒ layer. Another recent study 72 reports the results for vapor deposited Sn on thin Ru film protecting an optical structure. Their LEIS spectra are consistent with fractional surface occupation.…”

Growth and thermal oxidation of Ru and ZrO2 thin films as oxidation protective layers

“…The appearance of RuO2 nanocolumns on the Ru surface at temperatures above ~200°C (Chapter 3) showed that Ru thin films could undergo deterioration above these enhanced temperatures. This is relevant when Ru is used as capping material, since mirrors close to the collector might achieve similar, and even higher temperatures, 61 and their lifetime might be threatened due to this agglomeration phenomenon. An important information that can help to predict this lifetime, is the detection of the kinetics of diffusion of oxygen through the capping material.…”

“…However, not all these oxides are stable until 400°C (the typical maximum temperature for all considered applications). 22,47,61 Sb2O5 decomposes at about 300°C, 77 just before melting at 380°C (see d in Fig. 1.1), V2O3 slowly converts to V2O4 upon air exposure, 78 Re2O7 sublimates at 250°C (see s in Fig.…”

“…Thermally stable. During the processing steps involved in the fabrication of electronics, 22 photovoltaics, 45 and also during their functionality (including the EUVL optics functionality), 54,61 enhanced temperatures are achieved, where a thermally stable protective layer is required. For instance, in DRAMs and CMOS devices, the high-K dielectric protective layer should be thermodynamically stable on silicon upon annealing in oxidative environments.…”

“…45 Likewise, absorbed EUV radiation provides energy to the EUVL multilayer in the form of heat, which can reach elevated temperatures, depending on the mirror's geometrics and the cooling system. 61 This means that the protective layer, which is part of the mirror, should be thermally stable together with the multilayer stack.…”