Effect of post-etch cleaning on Ru-capped extreme ultraviolet lithography photomask
TL;DR: In this article, the changes in RuCl 3 formation and surface roughness with various cleaning processes were investigated and it was confirmed that, during Cl 2 dry etching to remove the absorber layer, RuCl3 was formed on the Ru capping layer surface, and the surface roughs thereby deteriorated.
Abstract: Ru-capped extreme ultraviolet lithography photomasks require cleaning after patterning of the absorber layer. In this study, it was confirmed that, during Cl 2 dry etching to remove the absorber layer, RuCl 3 was formed on the Ru capping layer surface, and the surface roughness thereby deteriorated. Therefore, the changes in RuCl 3 formation and surface roughness with various cleaning processes were investigated. Among the treatments used, i . e ., sulfuric peroxide mixture, an ammonia peroxide mixture or ozonated water (DIO 3 ), DIO 3 exhibited the most effective Cl removal efficiency and surface roughness recovery. DIO 3 treatment successfully reduced the Cl-terminated Ru surface to its original state and decreased the surface roughness to the pre-Cl 2 -etched Ru value.
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TL;DR: In this paper, the roughness of a plane surface is related to its specular reflectance at normal incidence, and expressions for the case when the root mean square surface roughness is small compared to the wavelength of light are presented.
Abstract: Expressions relating the roughness of a plane surface to its specular reflectance at normal incidence are presented and are verified experimentally. The expressions are valid for the case when the root mean square surface roughness is small compared to the wavelength of light. If light of a sufficiently long wavelength is used, the decrease in measured specular reflectance due to surface roughness is a function only of the root mean square height of the surface irregularities. Long-wavelength specular reflectance measurements thus provide a simple and sensitive method for accurate measurement of surface finish. This method is particularly useful for surface finishes too fine to be measured accurately by conventional tracing instruments. Surface roughness must also be considered in precise optical measurements. For example, a non-negligible systematic error in specular reflectance measurements will be made even if the root mean square surface roughness is less than 0.01 wavelength. The roughness of even optically polished surfaces may thus be important for measurements in the visible and ultraviolet regions of the spectrum.
1,049 citations
TL;DR: In this paper, a broad range of topics, including history, tools, source, metrology, condenser and projection optics, resists, and masks, are thoroughly reviewed over a broad variety of topics.
Abstract: Extreme ultraviolet lithography (EUVL) was thoroughly reviewed over a broad range of topics, including history, tools, source, metrology, condenser and projection optics, resists, and masks. Since 1988, many studies on EUVL have been conducted in North America, Europe, and Japan, through state sponsored programs and industrial consortiums. To date, no “show stopper” has been identified, but challenges are present in almost all aspects of EUVL technology. Commercial alpha lithography step-and-scan tools are installed with full-field capability; however, EUVL power at intermediate focus (IF) has not yet met volume manufacturing requirements. Compared with the target of 180W IF power, current tools can supply only approximately 55–62W. EUV IF power has been improved gradually from xenon- to tin-discharge-produced plasma or laser-produced plasma. EUVL resist has improved significantly in the last few years, with 25nm 1:1 line/space resolution being produced with approximately 2.7nm (3σ) line edge roughness. A...
363 citations
DSM1
TL;DR: In this paper, a simple phenomenological rule is used to predict the evolution of covalence/ionicity in mixed oxides compared to the parent ones, and is also widely used to interpret the x-ray photoelectron spectroscopy (XPS) binding-energy shifts of the cations in terms of charge transfer.
Abstract: The degree of ionic/covalent character in oxides has a great influence on the electronic structure and the material's properties. A simple phenomenological rule is currently used to predict the evolution of covalence/ionicity in mixed oxides compared to the parent ones, and is also widely used to interpret the x-ray photoelectron spectroscopy (XPS) binding-energy shifts of the cations in terms of charge transfer. We test the validity of this simple rule and its application to XPS of mixed oxides with a prototypical system: zircon ${\mathrm{ZrSiO}}_{4}$ and parent oxides ${\mathrm{ZrO}}_{2}$ and ${\mathrm{SiO}}_{2}.$ The ionic charges on Si, Zr, and O were extracted from the density functional theory in the local density approximation calculations in the plane-wave formalism. In agreement with the predictions of the phenomenological rule, the most ionic cation (Zr) becomes more ionic in ${\mathrm{ZrSiO}}_{4}$ than in ${\mathrm{ZrO}}_{2},$ while the more covalent one (Si) experiences a corresponding increase in covalence with respect to ${\mathrm{SiO}}_{2}.$ The XPS chemical shifts of the O $1s,$ Si $2p,$ and Zr ${3d}_{5/2}$ photoelectron lines in the three oxides were measured and the respective contributions of charge transfer and electrostatic effects (initial state), as well as extra-atomic relaxation effects (final state) evaluated. The validity of the phenomenological rule of mixed oxides used in x-ray electron spectroscopy as well as the opportunity to use the $\mathrm{O}1s$ binding-energy shifts to derive a scale of covalence in silicates is discussed.
331 citations
TL;DR: In this paper, an interface-engineered Mo-Si multilayer with 70% reflectance and 049nm bandwidth at 127-nm wavelength was developed with 50 bilayers consisting of alternating Mo and Si layers separated by thin boron carbide layers.
Abstract: Commercial EUV lithographic systems require multilayers with higher reflectance and better stability than those published to date This work represents our effort to meet these specifications Interface-engineered Mo-Si multilayers with 70% reflectance and 0545-nm bandwidth at 135-nm wavelength and 71% reflectance with 049-nm bandwidth at 127-nm wavelength were developed These results were achieved with 50 bilayers These new multilayers consist of alternating Mo and Si layers separated by thin boron carbide layers Depositing boron carbide on the interfaces leads to reduction in molybdenum silicide formation of the Mo-on-Si interfaces Bilayer contraction is reduced by 30%, implying that there is less intermixing of Mo and Si to form silicide As a result, the Mo-on-Si interfaces are sharper in interface-engineered multilayers than in standard Mo-Si multilayers The optimum boron carbide thicknesses have been determined and appear to be different for the Mo-on-Si and Si-on-Mo interfaces The best results were obtained with 04-nm-thick boron carbide layers for the Mo-on-Si interfaces and 025-nm-thick boron carbide layers for the Si-on-Mo interfaces The increase in reflectance is consistent with multilayers having sharper and smoother interfaces A significant improvement in oxidation resistance of EUV multilayers has been achieved with ruthenium-terminated Mo-Si multilayers The best capping-layer design consists of a Ru layer separated from the top Si layer by a boron carbide diffusion barrier This design achieves high reflectance and the best oxidation resistance during EUV exposure in a water-vapor (oxidizing) environment Electron-beam exposures of 45 h (in an effort to simulate EUV exposure perturbation of the top layers) in the presence of 5×10 - 7 -Torr water-vapor partial pressure show no measurable reflectance loss and no increase in the oxide thickness of Ru-terminated multilayers
214 citations
TL;DR: In this article, the surface-enhanced Raman spectroscopy (SERS) was combined with X-ray photoelectron spectroscopic (XPS) to study the oxidation of ruthenium at ambient pressure (1 atm) and elevated temperatures (25-300°C) and the SERS probe provided in-situ vibrational information regarding surface oxide bonding.
Abstract: Surface-enhanced Raman spectroscopy (SERS) combined with X-ray photoelectron spectroscopy (XPS) has been utilized to study the oxidation of ruthenium at ambient pressure (1 atm) and elevated temperatures (25–300°C). The SERS probe provides in-situ vibrational information regarding surface oxide bonding. While the XPS probe necessarily involves ex-situ measurements (i.e., transfer to and from ultrahigh vacuum), it provides valuable complementary information on the metal and oxygen electronic states. Ruthenium surfaces were prepared by electrodepositing ultrathin films (about three monolayers) onto electrochemically roughened (i.e., SERS-active) gold substrates. Insight into the in-situ oxidation process was obtained by probing the changes of surface speciation by SERS upon heating Ru in flowing O 2 . A pair of SERS bands at 470 and 670 cm −1 appear in the spectrum acquired for a freshly electrodeposited film, which are assigned to different stretching modes of hydrated RuO 2 formed during sample transfer to the gas-phase reactor. However, a fully reduced Ru surface (i.e., devoid of oxide features) could be formed by adsorbing a protective CO adlayer in an electrochemical cell followed by heating to 200°C in vacuum so to thermally desorb the CO. While the initially oxidized (i.e., RuO 2 ) surface was stable to further oxidation upon heating in O 2 , adsorbed atomic oxygen was detected at 200°C from the appearance of a SERS band at 600 cm −1 and a XPS O(1 s ) peak at 531.7 eV. In contrast, the higher oxides RuO 4 and possibly RuO 3 were produced only upon thermal oxidation of the fully reduced Ru surface. Evidence for RuO 3 formation includes the appearance of a 800 cm −1 SERS band at 200°C which correlates with the advent of a Ru(3 d 5/2 ) peak at 282.6 eV. The surface was further oxidized to RuO 4 at 250°C, as deduced from the formation of a 875 cm −1 band and a Ru(3 d 5/2 ) peak at 283.3 eV. While RuO 3 and RuO 4 were exclusively formed at temperatures higher than 250°C, RuO 2 was produced upon cooling to room temperature, possibly via the decomposition of RuO 4 .
208 citations