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.
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 concept of Extreme Ultra-Violet Lithography (EUVL) mask dual pods is proposed for use in both mask shipping and handling in exposure tools. The inner pod was specially designed to protect masks from particle contamination during shipping from mask houses to wafer factories. It can be installed in a load-lock chamber of
exposure tools and evacuated while holding the mask inside. The inner pod upper cover is removed just before the
mask is installed to a mask stage. Prototypes were manufactured and tested for shipping and for vacuum cycling.
We counted particle adders through these actions with a detectable level of 54 nm and up. The adder count was
close to zero, or we can say that the obtained result is within the noise level of our present evaluation environment.
This indicates that the present concept is highly feasible for EUVL mask shipping and handling in exposure tools.
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.
We have built a visible light point-diffraction interferometer with the purpose to characterize EUVL projection optics. The interferometer operates at the wavelength of 532 nm and utilizes two identical pinhole wavefront reference sources for generation of both signal and reference wavefronts. In the simple configuration of our interferometer, the main source of system error is the pinhole reference wavefronts. It is important that the reference wavefronts are calibrated and the calibration is stable. The calibration using our refractive test optic is reproducible to better than 0.1 nm RMS. The interferometer measured the wavefront of our refractive test optic with the repeatability of 0.1nm RMS. This paper will discuss the error sources and removal of the errors with experimental results.
The azimuthal Zernike coefficients for shells of Zernike functions with shell numbers n<N may be determined by making measurements at N equally spaced rotational positions. However, these measurements do not determine the coefficients of any of the purely radial Zernike functions. Label the circle that the azimuthal Zernikes are measured in as circle A. Suppose that the azimuthal Zernike coefficients for n<N are also measured in a smaller circle B which is inside circle A but offset so that it is tangent to circle A and so that it has the center of circle A just inside its circular boundary. The diameter of circle B is thus only slightly larger than half the diameter of circle A. From these two sets of measurements, all the Zernike coefficients may be determined for n<N. However, there are usually unknown small rigid body motions of the optic between measurements. Then all the Zernike coefficients for n<N except for piston, tilts, and focus may be determined. We describe the exact mathematical algorithm that does this and describe an interferometer which measures the complete wavefront from pinholes in pinhole aligners. These pinhole aligners are self-contained units which include a fiber optic, focusing optics, and a "pinhole mirror". These pinhole aligners can then be used in another interferometer so that its errors would then be known. Physically, the measurements in circles A and B are accomplished by rotating each pinhole aligner about an aligned axis, then about an oblique axis. Absolute measurement accuracies better than 0.2 nm were achieved.
We have built and calibrated a set of 532-nm wavelength wavefront reference sources that fill a numerical aperture of 0.3. Early data show that they have a measured departure from sphericity of less than 0.2 nm RMS (0.4 milliwaves) and a reproducibility of better than 0.05 nm rms. These devices are compact, portable, fiber-fed, and are intended as sources of measurement and reference waves in wavefront measuring interferometers used for metrology of EUVL optical elements and systems. Keys to wave front accuracy include fabrication of an 800-nm pinhole in a smooth reflecting surface as well as a calibration procedure capable of measuring axisymmetric and non-axisymmetric errors.
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.
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.
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.
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.
An extreme ultra-violet phase-shifting point diffraction interferometer (PS/PDI) was studied by using the NewSUBARU[1] undulator radiation. The beam line was equipped with a monochromator for PDI measurement. To improve the converging performance of the undulator radiation, a new beam line suitable for PDI was designed. From the examination of monochromaticity required for PDI, the 0th-order light of the monochromator was used in the experiment. The higher-order radiation of the undulator was eliminated by the reflection band of the Mo/Si multilayer mirrors. By means of improvements of the pre-alignment method and of the mask structure, a higher contrast than ever was achieved in the interference fringes.
We have been studying phase-shifting point diffraction interferometry (PSPDI) as a technique evaluating extreme-ultraviolet (EUV) lithographic optics at the working wavelengths. In the PSPDI, the wavefront error of the test optic affects the measurement itself. One of these effects is that flare of a spot focused onto a pinhole of a PSPDI mask is mixed with a test beam as an optical noise. To mitigate the flare effect, we changed the PSPDI mask design and replaced the convex mirror of a test optic. The other effect is reducing the contrast of the interference fringe. To reduce the misalignment of the test optic, we have improved the accuracy of the PSPDI using visible light. Since the residual wavefront error of the test optic is not small enough for at-wavelength PSPDI measurement, we obtained an at-wavelength wavefront using a rather large second pinhole. The obtained EUV wavefront qualitatively agreed with the visible one.
Extreme-ultraviolet phase-shifting point diffraction interferometer (PS/PDI) was studied by using the NewSUBARU undulator radiation. The wave-front error of a Schwarzchild test optics was measured. Since this is a common path PDI technique, optics pre-alignment is very important to receive enough power at the second pinhole. We carried out this pre-alignment by using the same common path PS/PDI system but by using a He-Ne laser. A temporal wave-front error attained by pre-alignment was 4.4 nm rms. We then studied band width requirement to carry out this PS/PDI in EUV. We found that the wavelength ((lambda) ) dependency of grating diffraction angle plays an important role in phase matching at the CCD camera location, although significant optical path difference exists at the edge of the fringe field. A 1 micrometers square double window experiment was carried out with (lambda) /(Delta) (lambda) is congruent to 30, and straight fringes were observed throughout the CCD field. A PDI experiment using larger pinholes compared with nominal sizes was also conducted, and various factors, which were posed onto the experimental results, were investigated.
The precise alignment of Extreme Ultra-Violet Lithography (EUVL) imaging system is necessary in order to achieve diffraction-limited performance. Interferometric testing at the exposure wavelength is needed to ensure proper alignment and to achieve an acceptable final wavefront. We have built a prototype at-wavelength interferometer at the NewSUBARU facility. This interferometer is a phase-shifting point diffraction interferometer (PS/PDI) testing specially constructed Schwarzschild optics. Preliminary experiments using visible light were performed in order to learn this PS/PDI. The Schwarzschild optics were aligned using visible wavefront measurements with the interferometer. The precision of the visible measurements was evaluated. Experiments using EUV radiation have been started.
This paper reviews both proximity X-ray and EUV lithography activities related to ASET. The PXL project was started in 1996, and an 8' stepper (XS-1) and 100 keV mask EB writer was built, aiming to study the applicability of PXL to 100 nm device generation. The CD control and overlay study by XS-1 gave promising results, showing that a key issue is high accuracy mask fabrication. The EB writer has been attaining high image placement accuracy of 10 - 20 nm, however, process- induced distortion of the same level has also been observed. The work is under way to further reduce these numbers. Application of PXL to several integration studies is also under way by collaborating with the ASET PXL member companies. The EUV project was started in October 1998, studying optics technology, mask process and wafer resist process. The main subjects are: mirror fabrication and figure evaluation by visible PDI; optics at-wavelength testing; mask substrate multi-layer coating; absorber patterning; and resist exposure characteristics. We collaborate with Himeji Institute of Technology to study the resist process and at-wavelength testing.
A cost of ownership (CoO) model is used to analyze the cost of the next generation lithography (NGL) technology which includes proximity x-ray, ion beam projection (IPL), EUV and SCALPEL. The model takes into account the equipment cost, throughput, resist/process cost and mask cost. The purpose of this paper is to propose a baseline to discuss on the NGL CoO issue. General conclusion is that x-ray appears to be most cost-effective. This is the case when plural steppers are installed to a storage ring. IPL has to use a certain extent of complementary mask mode which may increase the IPL total cost. EUV appears to require higher throughput to be cost-competitive to other technologies because of expected higher machine and mask costs. SCALPEL may have difficulty to attain competent throughput. The key feature in this case is the electron beam current and the width of a unit exposure field covered by electron beam scanning.
We fabricated photomasks by means of a surface imaging technique using electron beams. For this purpose, a bi-level resist process was used. The resist consisted of three- dimensional polysilphenylenesiloxane (TSPS), a negative resist containing silicon, at the top and sulfonated polyaniline (SPAn), an electrically conductive polymer film, at the bottom. TSPS is known to be sensitive to electron beams. It swells slightly during development and it is easily oxidized. These features together make TSPS a good top coat substance. It is also know that the bottom layer substance SPAn reduces substrate charging because it is electrically conductive. By taking advantage of this resist system, we used O2-RIE (oxygen reactive ion etching) for transferring surface images from the top to bottom layer. This paper discusses the performance of photomasks which we fabricated by combining this bi-level resist process with variable-shaped electron-beam lithography system (acceleration voltage of 20 keV and current density of 10 A/cm2). By using this process, we succeeded in obtaining 0.2 micrometer line/space patterns. In addition since the multilayer resist system could reduce proximity effect, it was possible to produce reticles for 1-Gbit DRAM devices without any data correction.
The 3D heat diffusion equation was numerically solved to determine the e-beam writing induced local and global heating and the corresponding distortion for optical and x-ray masks. The beam was 50 kV with maximum current I equals 4 (mu) A for optical masks, and I equals 0.3 (mu) A for x-ray masks. Calculations indicate that the distortion due to the localized temperature rise is negligible for both types of masks. The global distortion for optical masks is on the order of 0.04 micrometers (for I equals 4 (mu) A), and on the order of 0.007 micrometers for x-ray masks (for I equals 0.3 (mu) A) for a dose of 10 (mu) C/cm2 under dense-pattern mask writing conditions.
The possibilities of sub-quarter-micron pattern fabrication by e-beam lithography with single- layer resist was studied on 0.5 micrometers thick W x-ray mask absorber. Calculation was made to evaluate the parameters determining the e-beam dose profile in the resist. It was found that at the incident energy of 40 keV pattern contrast in the resist, whose thickness is 0.2 micrometers , is homogenized through the depth. The experimental result proved that 0.15 micrometers line/space can be resolved by using a high contrast resist with this thickness.
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