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.
We investigated the protection of a Ru-capped Mo/Si multilayer from surface oxidation under exposure to EUV
radiation in the presence of water vapor and isopropyl alcohol (IPA). Degradation of the reflectance of the Ru-capped
Mo/Si multilayer by EUV irradiation was controlled by introducing IPA gas. We also investigated the reduction effect of
the oxide layer in a multilayer mirror by introducing ethanol and exposed EUV. The Ru-capped multilayer sample was
exposed to EUV radiation in the presence of only water vapor to oxidize its surface. The reflectance decreased by about
1.5%. Then the sample was exposed to EUV radiation in the presence of only ethanol vapor. The reflectivity of the
sample was recovered to +0.5%, and the atomic concentration of oxygen in the irradiated area was decreased by EUV
irradiation in the presence of ethanol.
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
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.
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.
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.
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.
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.
The effect of extreme ultraviolet (EUV) exposure on the chemical states of ruthenium (Ru) capped multilayer mirrors (MLM) and Silicon (Si) capped MLM with increasing water pressure were investigated by using X-ray Photoelectron Spectroscopy (XPS). Also, The capability of analyzing carbon on the Ru capped MLM was investigated by using Auger Electron Spectroscopy (AES), XPS and Secondary Ion Mass Spectroscopy (SIMS). It was demonstrated that ruthenium oxide was produced on the surface by EUV exposure under water pressure more than 1x10-5 Pa. The dependency of oxidation on water pressure of the Ru capped MLM was not noticeable in comparison with the Si capped MLM, while Mo was not oxidized even under 1x10-3 Pa of water pressure. As for the analysis of carbon on Ru capped MLM, raising the precision of peak separation between carbon and Ru was required in AES and XPS and the investigation for quantification was needed in SIMS.
For the development of chemical contamination control of extreme ultraviolet (EUV) lithography, especially to prolong the lifetime of optical elements, we had established and installed the experimental apparatus on Super-ALIS, a synchrotron facility beam-line, at NTT Atsugi laboratory, Japan. The apparatus is constructed with ultra high vacuum (UHV) components, then it is achieved that the residual gas pressure less than 5x10-7 Pa with no significant hydrocarbon contaminants. Using the setup, radiation-induced oxide formation and/or carbon deposition on EUVL optics mirror can be evaluated by EUV light irradiations and in-situ measurements of the reflectance under specified partial pressure of contaminants. Sub-system to introduce and control of pressure of water vapor in the irradiation chamber between 1x10-6 and 1x10-2 Pa is available. Preliminary results about dependency to water vapor partial pressure and EUV light intensity/dose indicate that the tendency that higher degree of oxidation of Mo/Si multi-layered mirror (MLM) surface is obtained from longer irradiation time and higher ambient water vapor pressure, whereas the Ru-capped mirrors maintains negligible oxidation if water pressure is 1x10-6 Pa. Electron-beam (EB) irradiation sub-system was also mounted for the accelerated and off-line oxidation and/or carbon deposition/cleaning evaluation. Vacuum ultraviolet (VUV) light (Xe2 excimer lamp: 172nm) irradiation sub-system with oxygen introduction is also available. Significant cleaning effect is obtained while oxidation of multi-layer mirror surface was observed. Estimated cleaning rate under the oxygen pressure of 100 Pa for sputtered carbon film is about 0.03 nm/min.
An EUV irradiation and reflectance measurement system using intense EUV radiation emitted from a long undulator at the NewSUBARU synchrotron radiation (SR) facility was developed.
The system can measure the real-time reflectance drop during intense EUV irradiation and reflectance mapping as well as the photoemission current after irradiation at a fixed energy for atom absorption.
The irradiated EUV beam was very intense, and the power density was about 400 mW/mm2. The reflectances of Si- and Ru-capped Mo/Si multilayer mirrors (MLMs) were measured under several conditions of EUV power, i.e., 120, 15, and 5 mW/mm2 for Si-capped MLMs, or of water vapor, i.e., 6.6x10-5 and 1.3x10-2 Pa for Ru-capped MLMs. Each reflectance was reduced as the dose was increased. The reflectance was significantly reduced at the higher partial pressure of water vapor. When the intensity of the beam flux was reduced using ND filters, the reflectance was significantly reduced under the same conditions of atmosphere and dose. Carbon cleaning and oxidation were progressed in the beam center although carbon deposition was much progressed in the beam fringe for Si-capped MLM. Ru-capped MLM was more resistant to radiation damage than Si-capped MLM at each partial pressure of water vapor. The results of X-ray photoelectron spectroscopy (XPS) for Ru-capped MLM showed that deposited and desorbed carbons were balanced at the beam center and carbon deposition occurred on the fringe of the beam.
Radiation damage to multilayer mirrors has been intently studied in the view of the EUV lithography (EUVL) application in recent years.
To investigate the radiation damage, a reflectance measurement system for EUVL mirrors was developed at beam line 9 at the NewSUBARU SR facility. This system can irradiate the mirror using EUV radiation from a long undulator (10.8 m) and simultaneously measure changes in reflectance caused by radiation damage. The actual measurement of the power density of the EUV radiation at the sample mirror was about 500 mW/mm2, which is sufficiently intense for quickly investigating radiation damage. The EUV wavelength, 13.5 nm, was selected from the undulator radiations by using a planar multilayer mirror with a maximum reflectance of 13.5 nm. The θ and 2 θ stages were adopted for reflectance measurements, making the system more valuable and flexible. Because the system is equipped with a removable pinhole to restrict the incident beam size and x-z automatic stages, it can also be used to measure the spatial distribution of the reflectance and photoemission current.
The ultimate vacuum was in the order of 10-5 Pa even though the automatic stages were moving. Some aspects, which depend on the atmospheres, capping layers on mirrors, and flux density of the irradiation beam, were measured. The photoemission current was also measured. These measurements provide important information about the extent of the radiation damage and whether or not it is proportional to the flux density.