Adsorption dynamics and angular dependency of contaminants on Ru mirror surfaces

Abstract

A real time contamination of the Ru surface and corresponding effect on its work function were studied using extreme ultraviolet photoelectron spectroscopy with a 13.5-nm wavelength of light. The change in work function indicates formation of molecular dipoles, oriented outward from the Ru surface. X-ray photoelectron spectroscopy investigations suggest variation in electromagnetic interaction with the components of the adsorbed foreign species when the emission angle from the target surface was changed from 0 to 50 ; H 2 O and C-O n show a strong coupling at lower angles and OH dominates at higher angles, whereas carbon is found in the mid-range peaking at 30 .In order to continue the steady growth of the semiconductor industry, next generation computer chips are required to have features as small as 20 nm. To meet this goal, next generation photolithography systems are looking to employ extreme ultraviolet (EUV) radiation at a wavelength of 13.5 nm. The mirrors to be used in these systems consist of alternating layers of Mo and Si. 1 Because there are concerns about potential oxidation of the surface Si layer, a thin Ru protective layer has often been used on the top Si layer. 1 A Mo/Si multilayer mirror with a Ru capping layer can reflect up to 70% of the EUV light 2 near normal incidence. 3 Ruthenium films can also reflect 92 eV photons at a grazing angle. 4 Since short wavelengths can be attenuated by most materials 5 and even by background gases, 1 an EUV lithography system requires a vacuum chamber. Now, the issue is how to keep the optics clean, as carbonaceous and/or oxidized Ru surfaces are often formed during EUV exposure and, as a consequence, degrade the overall reflectivity of Mo/Si mirrors. Several cleaning processes 1 have been proposed to circumvent and mitigate this problem. In fact, a large number of groups have been working on understanding the processes involved to mitigate the oxidation and/or carbonization of the top Ru layer (Ref. 6 and references therein). 6 It has so far been established that the secondary electrons from the Ru surface mainly take part in dissociating hydrocarbons and/or water molecules under EUV radiation, 6 creating chemically active fragments on the Ru surface. 7 Although several reports are available in the literature that deal with EUV radiation-induced growth of contaminants on Ru surfaces, 8 knowledge of the adsorption dynamics and of the emission angle (h from the target surface) dependency are still scarce. In fact, detailed analyses of the latter will help to figure out which of the components of the adsorbed species are mainly responsible for degrading the mirror performance.In this communication, we show real time contamination of the Ru surface in the presence of a 13.5-nm wavelength of light using EUV photoelectron spectroscopy (EUPS). This approach is extremely surface sensitive due to low photoelectron escape depth. 9 Using the measured cutoff energy shift, we show the formation of dipoles on the Ru surface. The in situ angular-resolved x-ray photoelectro...

Tracking electron-induced carbon contamination and cleaning of Ru surfaces by Auger electron spectroscopy

“…7 However, we observed an increase in d with EUV exposure. 21 Independent of primary electron energy 30 and 92 eV photons, 5 as d of a typical MLM was found to decrease drastically with increasing carbon coverage, the observed increase in SEs under EUV exposure only 21 indicates the dominant role of water molecules on Ru for supplying free O atoms, 11 which in turn take part in cleaning a fraction of C. A recent observation of a gradual decrease in SEs with eEUV radiation, 17 however, can change the scenario, indicating more hydrocarbons to dissociate than water molecules in the presence of additional PEs that take control of C growth and O desorption ( Fig. 1) and so the EUVR (Fig.…”

“…The experiments were performed at the materials characterization laboratory IMPACT at CMUXE that hosts an ultrahigh vacuum (UHV) chamber equipped with in situ diagnostic tools such as XPS, AES, EUVR, etc.. 17,21 To create a chamber condition similar to a EUVL system, 6 we did not bake the UHV chamber, giving a base pressure of $1.8 Â 10 À8 Torr. Since the residual gases in the chamber are known to control the growth of carbon and oxidation of the target surface, 22 a residual gas analyzer (RGA-100) was used to identify the gaseous components.…”

Probing temporal evolution of extreme ultraviolet assisted contamination on Ru mirror by x-ray photoelectron spectroscopy

“…The samples were sputter cleaned by 2 keV Ar þ for 15 min (beam current of $590 nA) in a mildly baked ultra high vacuum (UHV) chamber (base pressure $1.4 Â 10 À8 Torr) at the materials characterization laboratory IMPACT at Purdue University. 15 This UHV system is equipped with a suite of in situ diagnostic tools for surface analysis including XPS, EUV photoelectron spectroscopy, Auger electron spectroscopy, ion scattering spectroscopy, and EUVR. 15 The XPS measurements were performed using an Al Ka radiation source (h ¼ 1486.6 eV), where photoelectrons emitted at 45 from the sample surface were analyzed with a PHOIBOS-100 hemispherical electron analyzer (energy resolution of 0.8 eV).…”

“…15 This UHV system is equipped with a suite of in situ diagnostic tools for surface analysis including XPS, EUV photoelectron spectroscopy, Auger electron spectroscopy, ion scattering spectroscopy, and EUVR. 15 The XPS measurements were performed using an Al Ka radiation source (h ¼ 1486.6 eV), where photoelectrons emitted at 45 from the sample surface were analyzed with a PHOIBOS-100 hemispherical electron analyzer (energy resolution of 0.8 eV). Calibration of binding energy (BE) scale with respect to the measured kinetic energy was made using the silver Fermi edge.…”

Time dependent changes in extreme ultraviolet reflectivity of Ru mirrors from electron-induced surface chemistry

“…Next generation processes have been targeted in the extreme ultraviolet (EUV) regime, e.g., 13.5 nm wavelength (due to the existence of reflective mirrors), 2 and thus experimental campaigns to develop such sources 3 and understand the performance of related optics are currently underway worldwide. Both single-and multi-layer mirrors are being considered for EUV optics, where Ru is an excellent candidate either as a primary mirror [4][5][6] or as a capping layer for multi-layer Mo/Si mirrors. 2 Research suggests that mirror performance and lifetime depend on several variables, such as radiation, chemical exposure, morphology, temperature, etc.…”