Hiromitsu Takase

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.

Analysis of carbon deposition on multilayer mirrors by using two different beamlines

It is very important to mitigate oxidation of multilayer mirrors (MLMs) and carbon deposition onto MLMs to extend the lifetime of EUV exposure tool. In order to estimate the lifetime, we have to figure out scaling law. Previous results at EUVA have shown that carbon deposition rate on MLMs is not proportional to every hydrocarbon partial pressure and every EUV intensity3-4. In this study we focused on carbon deposition on Si-capped multilayer mirror. We made experiments of EUV irradiation to the MLMs using two different apparatuses. One is connected to a beamline (SBL-2) of synchrotron radiation facility Super-ALIS in the NTT Atsugi research and development center, and the other is connected to a beamline (BL9) of synchrotron radiation facility New SUBARU in the University of Hyogo. As the result of experiments, we found that different carbon deposition rate occurred on the different beamlines, although they have the same average EUV intensity. We present differences of carbon deposition rate on MLMs between two different beamlines and estimation of carbon deposition rate on EUV tool analyzing dependences of carbon deposition rate on characteristics of EUV source.

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.

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.

Effect of residual gas atmosphere on lifetime of Ru-capped EUVL projection optics mirror

Reflectance changes during the EUV irradiation were in-situ measured using two different experimental systems. One system consisted of slight high hydrocarbon (HC) content chamber and the other consisted of low HC content chamber. Distribution maps of the reflectance changes were quite different from each other. Especially, the reflectance change at the center of the EUV irradiation area was suppressed when the high HC content system was used. The surface analysis using XPS was performed. According to the analysis, it was found that two reflectance changes were arising from different reasons. It would seem that the origin of the different reasons were difference of the residual gas atmosphere.

New contamination experimental equipment in the NewSUBARU and evaluation of Si-capped multilayer mirrors using it

New experimental equipment was installed in the NewSUBARU synchrotron radiation facility in order to investigate the contamination inhibition mechanism of projection optics for extreme ultraviolet lithography (EUVL). The equipment consisted of two all-metal sealed chambers, and the atmosphere was accurately controlled a over the wider degree of vacuum compared to the previous experimental equipment. The light source was the long undulator (LU) which can irradiate a sample with high EUV flux density of about 200 mW/mm2. Reflectivity and its distribution of an irradiated sample can be measured in situ. NEXAFS spectrum of the sample can be also obtained in situ utilizing the beam-line monochromator, which is a useful method for surface analysis. Using this equipment, EUV irradiation, reflectance measurement, and surface analysis were carried out for Si-capped Mo/Si multilayer (ML) samples. A wavelength dependence of photoemission current was changed at the irradiated area, which suggested that the phase change of standing wave at the ML surface occurred from contamination.