Yukinobu Kakutani

Carbon deposition on multi-layer mirrors by extreme ultra violet ray irradiation

Organic gases cause carbon depositions on the multi-layer mirrors by Extreme Ultra Violet (EUV) light irradiations in EUV lithography tool. The dependences on organic gas species, organic gas pressure and EUV light intensity in the carbon deposition were researched in order to understand this reaction. EUV light was irradiated on a (Si/Mo) multilayer mirror sample injecting organic gas like buthane, buthanol, methyl propionate, hexane, perfluoro octane, decane, decanol, methyl nonanoate, diethyl benzene, dimethyl phthalate and hexadecane. X-ray photoelectron spectroscopy measurements revealed that organic gases with heavier molecule weight or higher boiling temperature caused faster carbon deposition rates. Carbon deposition rates increased linearly with organic gas pressures. Dependence on EUV light intensity was estimated from comparisons between an EUV light profile and carbon distributions on irradiated samples. Carbon deposition rates increased rapidly, but became saturated at higher EUV light intensities. Three chemical reactions, an adsorption, a desorption and a carbon deposition by EUV light irradiation, were taken into account to explain the behavior of the carbon deposition. Electron irradiation on a mirror sample revealed that photoelectrons emitting from the mirror surface played an important role in carbon deposition.

In situ x-ray absorption near-edge structure analysis for extreme ultraviolet lithography projection optics contamination

A contamination evaluation system for extreme ultraviolet (EUV) lithography projection optics was developed in the NewSUBARU SR facility, in which in situ surface analysis and elemental concentration mapping were carried out with the use of the x-ray absorption near-edge structure (XANES) method. For concentration mapping, the linearity between the x-ray absorption intensity and contamination thickness was confirmed by examining standard samples. The problem of quantitativity, which was caused by the antagonistic reaction of carbon deposition and surface oxidation on the mirror surface, was successfully solved by taking the ratio of intensities of the upper and lower sides of the absorption edge. Very useful information for protecting the surface of EUV lithography optics was obtained when the in situ XANES analysis was applied to the experiment of EUV irradiation with the introduction of ethanol gas to the vacuum atmosphere.

Long-term durability of a Ru capping layer for EUVL projection optics by introducing ethanol

The inhibition of contamination of Ru-capped Mo/Si multilayer mirrors was systematically investigated by introducing ethanol into a controlled vacuum that mainly consisted of water vapor. Water vapor was introduced up to several partial pressures of 1.0X10-7 to 3.8X10-5 Pa. At the lowest ethanol pressure, the same degree of reflectance degradation as in the water-only case was observed. However, reflectance degradation was suppressed at ethanol pressures higher than 2.0X10-6 Pa. In the condition of ethanol pressure of 2.0X10-6 Pa, the long-term durability of a Ru capping layer was investigated up to an EUV dose of 6000 J/mm2. This dose was corresponded to the 1-year use of a mirror which would be irradiated by the maximum power expected in actual EUVL tools. As a result of this investigation, it was found that reflectance degradation of a Ru capping layer was suppressed to less than 0.5% until 6000 J/mm2 by introducing ethanol.

New Extreme Ultraviolet Irradiation and Multilayer Evaluation System for Extreme Ultraviolet Lithography Mirror Contamination in the NewSUBARU

A new contamination evaluation system that can irradiate high-flux extreme ultraviolet (EUV) and measure, in situ, the reflectivity of multilayer mirrors for EUV lithography (EUVL) projection optics was constructed to develop a contamination inhibition mechanism at the NewSUBARU synchrotron radiation (SR) facility. The vacuum chambers of the systems are all metal sealed. All automatic stages in the system are driven by motors set outside the chambers. The optimum pressure of the chamber was 2 ×10-7 Pa, two orders of magnitude higher than that in the system reported last year. The partial pressure of the hydrocarbon components was also two orders of magnitude smaller than that in the previously reported system. In the first experiment using the system, the lifetime of Si-capped Mo/Si multilayer mirrors was evaluated as a function of water vapor pressure. The system can also be used to measure and map X-ray absorption near-edge structure (XANES) spectra in the irradiated area, which is very important for the in situ evaluation of the contamination mechanism.

Phenomenological analysis of carbon deposition rate on the multilayer mirror

It is very important to mitigate oxidation of multilayer mirrors (MLMs) and carbon deposition onto MLMs to extend the lifetime of EUV exposure tool. We focused on carbon deposition on Si-capped multilayer mirror. We made experiments of EUV irradiation to the multilayer mirrors using an EUV irradiation apparatus connected to a beam line (SBL -2) of synchrotron radiation facility Super-ALIS in the NTT Atsugi research and development center. Thickness of deposited carbon was obtained by using XPS. We investigated carbon deposition rates at various partial pressures of various organic species. Phenomenological analysis was applied to the obtained carbon deposition rate. Carbon deposition rate was proportional to the pressure at the proportional EUV intensity. Applying this normalization of the deposition rate and the EUV intensity, carbon deposition rate seems to behave according to each universal function for each hydrocarbon species.

Inhibition of carbon growth and removal of carbon deposits on extreme ultraviolet lithography mirrors by extreme ultraviolet irradiation in the presence of water, oxygen, or oxygen/ozone mixtures

Experiments involving the inhibition of carbon growth and removal of carbon deposits on extreme ultraviolet (EUV) lithography mirrors were carried out. First, a carbon film was deposited on a Ru-capped Mo/Si multilayer mirror by introducing n-decane gas at a pressure of 1.3×10−5 Pa into the vacuum chamber and irradiating this mirror with an EUV dose of 380 J/mm2. Following, the mirror was further exposed to EUV irradiation while introducing water vapor, oxygen, or oxygen/ozone mixtures at a gas pressure of 1.0×10−2 Pa into the chamber. The reflectivity of the mirror, which was decreased upon carbon-film growth, could be recovered by the introduction of oxygen or oxygen/ozone mixtures. In the inhibition experiment, EUV irradiation was carried out while introducing n-decane gas at a pressure of 1.3×10−5 Pa and, simultaneously, water vapor, oxygen, or oxygen/ozone mixtures with a pressure of about 1×10−2 Pa. No remarkable inhibition of carbon-film growth was observed for water vapor and oxygen gas. However, ...

Protection and reduction of surface oxidation of Mo∕Si multilayers for extreme ultraviolet lithography projection optics by control of hydrocarbon gas atmosphere

To protect the surface oxidation of Mo∕Si multilayer films by extreme ultraviolet (EUV) irradiation under a vacuum atmosphere with residual water, two experiments were carried out. One consisted of examining the oxidation protection effect for isopropyl alcohol (IPA) and n-decane gases. The reflectivity change of the Ru-capped multilayer film by EUV irradiation was investigated under a vacuum atmosphere with residual water vapor at a pressure of 1.3×10−5Pa, and, in addition, each hydrocarbon (HC) gas was introduced by changing its pressure. A protective effect against oxidation was observed in both gases when introduced at a pressure in the order of 10−6Pa. For IPA, no remarkable decrease in the reflectivity was observed even when the introductory pressure was raised to the order of 10−4Pa. However, for n-decane, the reflectivity decreased remarkably when pressure in the order of 10−5Pa was introduced. The other experiment consisted of examining the reduction effect of the oxidized surface by EUV irradiat...

Scaling law in acceleration test of extreme ultraviolet lithography projection optics mirror contamination

A model to describe surface physics in extreme ultraviolet lithography (EUVL) optics mirror contamination is proposed. Photon-induced desorption is a key process in determining the surface areal density of the related adsorbed gas species when irradiating power is high. Scaling law for acceleration test is analyzed and experiment was performed by using synchrotron undulator radiation. It appears that oxidation on a Si capping layer is almost anti-linearly dependent on photon intensity and acceleration test can be conducted by increasing the H2O pressure linearly with photon intensity increase. In contrast, it was found that carbon deposition does not linearly scale to photon intensity. Special care is necessary in understanding results conducted in accelerated conditions as well as under different pulse duty conditions.

Inhibition of Contamination of Ru-Capped Multilayer Mirrors for Extreme Ultraviolet Lithography Projection Optics by Ethanol

The inhibition of the contamination of Ru-capped Mo/Si multilayer mirrors was systematically investigated by introducing ethanol into a controlled vacuum that mainly consisted of water vapor. Water vapor was introduced at a pressure of up to 1.3×10-5 Pa, which is a typical pressure in extreme ultraviolet (EUV) lithography production tools. Additionally, ethanol was introduced at several partial pressures ranging from 1.0×10-7 to 3.8×10-5 Pa. At the lowest ethanol pressure, the same degree of reflectance degradation as in the water-only case was observed. However, reflectance degradation was suppressed at ethanol pressures higher than 2.0×10-6 Pa. As a result of surface analyses using X-ray photoelectron spectroscopy, we determined that the reflectance degradation was caused by oxidation. The inhibition of contamination may be caused by a mechanism of a self-limiting carbon layer from ethanol adsorption on a hydroxylated mirror surface. It was found that oxides at the mirror surface were deoxidized by introduced ethanol. Therefore, deoxidization of the Ru layer may be one of the mechanisms of the inhibition of contamination. The suppression of reflectance degradation was independent of the photon intensity and measured for up to 1200 J/mm2. This dose corresponds to about 3 months of operation for projection optics mirrors at the maximum power expected. Therefore, the introduction of ethanol was found to be a promising method for inhibiting the contamination of projection optics mirrors, which are irradiated by a wide range of EUV power.

Study of ruthenium-capped multilayer mirror for EUV irradiation durability

The changes of chemical state and multilayer structure of Ru capped multilayer mirrors (MLMs) by irradiation of extreme ultraviolet (EUV) from synchrotron radiation (SR) were investigated using Auger electron spectroscopy (AES). It was found that irradiation induced Si diffusion and Si oxidation. Calculation of temperature distribution showed that Si diffusion was less relevant to temperature during irradiation.