Noriyuki Sakaya

Investigation of soft X-ray emission from a gas puff target irradiated with a Nd:YAG laser

Abstract Experiments investigating soft X-ray emission in the 1–22 nm wavelength range from plasmas produced using a gas puff target irradiated with a Nd:YAG laser are described. Gas puff targets were created by pulsed injection of high-density gas through a nozzle. The use of the gas puff targets eliminates the production of debris associated with solid targets. Laser pulses of either 0.9 ns or 10 ns time duration with energies up to 0.7 J were used to produce plasmas. X-ray emissions from laser-produced gas puff plasmas were characterized for various gases. The spectral measurements of the soft X-ray emission were performed with the use of grating spectrographs equipped with the back-illuminated CCD camera. The source size was measured using the Fresnel zone plate imaging system and the grating spectrograph equipped with a slit placed perpendicularly to the dispersion direction. The obtained results would allow to develop an efficient and debrisless laser-produced X-ray source to be useful for applications in various fields.

Improvement of total quality on EUV mask blanks toward volume production

Total quality on EUV mask blanks have to be improved toward future volume production. In this paper, progress in EUV blank development and improvement in flatness, bow and ML blank defects as critical issues on EUV blanks were reported. Steadily progress in flatness improvement was made in the past five years by improving polishing processes. A LTE substrate with a high flatness of 78 nm PV in 142 mm square area was achieved in average. Annealing process was developed to make small bow of less than 600 nm after ML coating. It was confirmed that annealed ML blank has stable performance in bow and centroid wavelength values through mask making process. Small bow of less than 300 nm was successfully demonstrated using annealing process and a CrN back side film with high compressive stress. Low defects of 0.05 defects/cm2 at 70 nm SiO2 sensitivity inspected by a Lasertec M1350 was demonstrated on a multilayer (ML) blank with a LTE substrate as best. Small defects over 50 nm in a M7360 were effectively reduced by improvement of polishing process consisting of local polish, touch polish and cleaning.

Mask defect inspection using an extreme ultraviolet microscope

A defect inspection technique on an extreme ultraviolet lithography mask is described. There are two kinds of defects, amplitude defects and phase defects due to the multilayer coating. The technique utilizes a microscope using the same 13.5 nm wavelength as the light used for exposure, and producing a magnified image of defects on a mask. Using this microscope, amplitude defects on practical masks and phase defects are observed. A phase defect was formed by a multilayer coated on a line pattern with a height of 5 nm and width of 90 nm on a glass substrate. Although the detected defect is made beforehand, it is detected by reflection of the light which penetrated inside of a multilayer. These results show that it is possible to detect the internal reflectivity distribution, without depending on surface perturbations.

Cleaning of extreme ultraviolet lithography optics and masks using 13.5nm and 172nm radiation

Under extreme ultraviolet (EUV) exposure, the surfaces of the imaging optics and mask, which are coated with a Mo∕Si multilayer, become contaminated with organic compounds. Thus, an efficient method of removing carbon contamination from masks and the imaging optics is required. Then, we propose two methods as a removal method of contamination: one is in situ cleaning method without heating a sample by synchrotron radiation irradiation that is mainly targeted at the imaging optics, and another is cleaning method without heating a sample using by 172nm light irradiation that is targeted at an EUV lithography finished mask. For in situ cleaning so called online cleaning, the contamination removal rate is 0.24nm∕min in the condition of O2-rich-vacuum environment at a pressure of 5.0×10−2Pa and an electron beam current of 130mA of 1.0GeV electron storage ring. For offline cleaning using 172nm light, the contamination removal rate is 2nm∕min in the O2-rich-vacuum environment at the pressure of 2×10−3Pa. Both tw...

Novel Evaluation System for Extreme Ultraviolet Lithography Resist in NewSUBARU

A standard assessment system for resist development with extreme ultraviolet (EUV) light was developed. The system for the evaluation of an EUV resist was installed at the BL3 beamline in the NewSUBARU synchrotron radiation facility. This optical system simulates a six-mirror imaging system. Incident light is reflected seven times in the chamber. The centroid wavelength is 13.57 nm. The beam size at the sample surface is 4×4 mm2 and we can take twelve shots for each sample by moving the sample in the lateral direction. Furthermore, a highly sensitive quadrupole mass spectrometer that can measure the mass numbers of ion species from 1 to 500 and is connected to a resist evaluation chamber is used for resist outgassing analysis under EUV irradiation. The main purpose of this whole system is to evaluate the basic physical and chemical properties of various EUV resists candidates, such as sensitivity and outgas characteristics.

Actinic Mask Inspection Using an EUV Microscope-Preparation of a Mirau Interferometer for Phase-Defect Detection-

This paper describes a mask defect inspection system using 13.5 nm light for extreme ultraviolet lithography (EUVL). The Schwarzschild optics which is employed as a microscope optics has a numerical aperture (NA) of 0.3 and a magnification of 30. Furthermore, it has a potential of detecting defects as small as 22 nm on a mask. In order to inspect defects with the phase change induced by swelling of the multilayer, a Mirau interferometer is employed. It is developed that the performance of the optical system, the focal position detection mechanism for image detection while scanning, and the driving mechanism of the reference mirror for the Mirau interference. Since the accuracy of the driving mechanism of the reference was found to be 0.1 nm, enough performance of the ring-shaped piezo actuator for interference measurement was confirmed. Moreover, examples of the mask inspection by this system are shown.

Resolution Enhancement of Extreme Ultraviolet Microscope Using an Extreme Ultraviolet Beam Splitter

We developed the extreme ultraviolet (EUV) beam splitter, which is a critical component for resolution enhancement, to achieve the uniform numerical aperture (NA) for all planar directions in the EUV microscope. In the fabrication of the EUV beam splitter, stress control of the Mo/Si multilayer is a necessary to achieve a self-standing membrane of the Mo/Si multilayer. We succeeded with the stress control by optimizing RF power, DC power, and argon working pressure during Mo/Si multilayer deposition. A large effective area of 8×10 mm2, reflectivity of 27%, and transmittance of 17% were achieved simultaneously. Furthermore, by installing the EUV beam splitter in stead of a turning mirror of Schwarzschild optics (SCO), the NA of the SCO became the same in the horizontal and vertical directions on a sample plane. Thus, the 300-nm line and space elbow pattern on an EUV mask for all planar directions was clearly resolved. We have developed an EUV microscope with an EUV beam splitter and succeeded in the highly precise pattern inspection.

Cleaning Characteristics of Contaminated Imaging Optics Using 172 nm Radiation

We evaluated the cleaning characteristics of a 172 nm excimer lamp. The 172 nm excimer lamp was used to irradiate contaminated samples under different conditions, such as various irradiance distances, irradiance environments and atmospheric O2 flow rates that enhance the removal rate. As results, we found the most suitable conditions, which are the absence of surface damage and increasing temperature by irradiation with the 172 nm excimer lamp. Using these conditions, we carried out the cleaning of the Schwarzchild optics used for extreme ultraviolet microscopes. Before cleaning, the total reflectivity of the Schwarzchild optics was only 2.5% because of the adhesion of contamination. However, it was restored to a reflectivity of more than 30% by cleaning. The reflectivity of the Schwarzchild optics was restored to its initial value. We found that 172 nm excimer lamps are very effective for the removal of contamination.

Fabrication of programmed phase defects on EUV multilayer blanks

Programmed phase defects, at desirably specified sizes and known locations, for EUV multilayer blanks were successfully fabricated by the following newly developed simple technique; depositing Cr film on a 6025 glass substrate or a Si wafer, generating Cr patterns of isolated lines and/or dots by EB lithography, and depositing Mo/Si multilayer of 40-bilayers by ion beam sputtering over the Cr patterns. Thereby, programmed bump defects were created on the multilayer surface over the Cr pattern at the bottom. The programmed defects were observed by TEM and AFM, of which images revealed behavior of the multilayer growth on the Cr patterns. The observed images show that height and full width at half maximum (FWHM) of the bump on the multilayer surface strongly depended on the Cr pattern in height and width, and also incident angle of the sputtered molecular flux to the substrate surface. The multilayer coating at near-normal (vertical) incidence provides a significant amount of smoothing near the Cr patterns. A bump phase defect of 2-nm height and 60-nm FWHM, as the result, was obtained on the multilayer surface using a 5-nm thick Cr pattern, which corresponded to a minimum killer defect for EUV lithography at 45-nm node. The multilayer blanks with the programmed phase defects can be effectively used as a standard for defect inspection tool development and defect printability study. This paper describes a simple fabrication process of the programmed phase defects on EUV multilayer blanks, evaluation results on the programmed phase defects, and growth behaviors of multilayer on various patterns (seed of the defects).

Experimental characterization of short-wavelength Ni-like soft-x-ray lasing toward the water window

We report experimental results of studies of Ni-like x-ray lasing at wavelengths as short as 4.5 nm. The performance of x-ray lasing pumped by various types of pulse train that were composed of 100-ps pulses was investigated with a double-slab target placed in series to double the gain length. Two opposing laser beams separated by an appropriate time difference irradiated the double targets for quasi-traveling-wave pumping. Well-collimated double-target amplification was successfully demonstrated for Yb and Hf lasing at 5.0 and 4.7 nm whose gain–length products were 11 and 6, respectively. The Ni-like lasing lines of Ta have also been observed at 4.5 nm.