Kazuhiro Hamamoto

Aerial Image Mask Inspection System for Extreme Ultraviolet Lithography

We constructed an extreme ultraviolet microscopy (EUVM) system for actinic mask inspection that consists of Schwarzschild optics and an X-ray zooming tube. Using this system, a finished extreme ultraviolet lithography (EUVL) mask and Mo/Si glass substrates were inspected. An EUVM image of a 100-nm-width pattern on a 6025 glass mask was clealy observed. The resolution was estimated to be 50 nm or less from this pattern. The programmed phase defect on the glass substrate was also used for inspection. By using the EUV microscope, a programmed phase defect with widths of 90, 100, and 110 nm, a bump of 5 nm and a length of 400 µm was observed finely. The programmed phase defect of a 100-nm-wide and 2-nm-deep pit was also observed. Thus, in this research, the observation of a programmed phase defect was advanced using the EUV microscope, which succeeded in observing a topological defect structure image of a multilayer film. These results show that it is possible to detect the internal reflectance distribution of a multilayer film under the EUV microscope, without depending on surface pertubation.

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.

Development of fiducial marks on EUV blanks for defect mitigation process

We have developed two types of fiducial marks (FMs) which are going to be used for defect mitigation process of EUV masks. Those FMs were prepared either on substrate by conventional lithography process or on multilayer (ML) by focused ion beam (FIB). The position accuracy of those FMs was evaluated in advanced electron beam writer, and the FMs prepared on ML showed excellent position repeatability of less than 2nm in 3sigma. Teron 610 blank inspection showed good position repeatability of defects lower than 100nm in maximum. We have developed FIB process for preparing FMs, which gives no defect adder being larger than 70nm. Thus, the fiducial mark process on ML by FIB would be preferable, and will be developed further.

Challenges for quality 15nm groove patterning with ZEP520A for a master fabrication for track pitch 50nm full-surface DTR-Media

Discrete Track Recording Media (DTR-Media) requires 50nm track pitch patterns and a mold as the start for 1 Tb/inch2 areal density, which is a quality 15nm groove (trench) and beyond. Last year, 14nm groove was achieved with a newly designed solvent developer for ZEP520A, we reported in PMJ 2009. But, we still need to pursue extreme high resolution such as 10nm groove or 12.5nm dot array for bit patterns with ZEP520A since no alternative was found so far. To improve ZEP520 resolution, we just keep trying to find a new developer with a lower development speed for ZEP520 than the previous one. Then, a Fluoro-Carbon was selected from various candidates. It was proved that ZEP520 and the Fluoro-Carbon developer provided 11nm groove resolution at an exposure dose of 1800μC/cm2. Furthermore, the mixture of the Fluoro-Carbon and Solvent B provided the same 11nm groove resolution at a higher sensitive, i.e. less exposure dose than the Fluoro-Carbon and even the Solvent B.

Improvement of defects and flatness on extreme ultraviolet mask blanks

Abstract. We have improved flatness and defects on an extreme ultraviolet (EUV) blank, which are critical issues for implementing EUV lithography. A high flatness of less than 30 nm on a glass substrate and low defects over 22 nm sphere-equivalent-volume-diameter (SEVD) on a multilayer (ML) blank are required for 22 nm half-pitch process. Flatness quality was improved to an average of around 50 nm and 30 nm as best, through more precise polishing process. Defect quality of single digit over 60 nm was achieved by improvement of fabrication process. New defect inspection was started for further defect reduction using a Teron Phasur. It was confirmed that there are lots of real phase defects with low height of less than 2 nm on a ML blank captured by the Teron. Small defects over 25 nm SEVD have been dramatically reduced to 20 defects mainly by various improvements of fabrication processes. A gap in flatness and defects between actual quality and the requirement is getting small, and both the qualities will be improved further for near future production.

Pattern inspection of EUV mask using an EUV microscope

It is proposed that at-wavelength EUV mask inspection system based on EUV microscope, which is the best way to observe the mask directly. Using this system, preliminary experiments to examine the pattern inspection of EUVL mask is carried out. EUV microscope has a capability to resolve 50 nm lithographic node finished EUVL mask. We confirmed that at-wavelength microscope rather than SEM is both powerful and useful for evaluating the mask fabrication process for EUVL. Furthermore, it is find out that the contrast of the mask images observed by EUVM influenced by the absorber material. As the result, important information of the finished EUVL mask can be obtained utilizing EUVM, which is very important tool for the finished EUVL mask inspection.

Resolution enhancement of EUV microscope using an EUV beam splitter

Extreme ultraviolet lithography (EUVL) has been proposed as a next generation lithography. In this paper, EUV phase-shift microscope was developed to detect phase defect in multilayer mask and EUV beam splitter is also developed, which is critical component of phase-shift inspection or resolution enhancement.

Development of optical component for EUV phase-shift microscopes

This paper is described about fabrication and evaluation of the beam splitter used in an EUV region. This beam splitter has to be as a free standing, stress control of multilayer is main subject. It is investigated that the dependence of the intrinsic stress between a RF (DC) sputtering power and an argon pressure during the thin film deposition processes. At the low argon pressure, molybdenum and silicon films showed both high compressive stress. However, at the high argon pressure, the molybdenum and silicon films showed low tensile stress and low compressive stress, respectively. Therefore, it was possible to fabricate a multilayer films with low tensile stress by optimizing the argon pressure and applied RF power during deposition. Conclusively, a free-standing semitrasparent multilayer film of 8x22 mm area was fabricated. It shows high reflectance and transmission of near 25% at the wavelength of EUV region.

Evaluation of finished EUVL masks using a Mirau interferometric microscope

We have developed an EUVL experimental exposure system and demonstrated fine pattern replication less than 60 nm. Using this system, we have evaluated the characteristics of chemical amplitude resists. Also a series of studies for evaluating different type of masks has been carried out to establish mask process, e.g. selection of absorber or buffer material, etching conditions and so on.