Precise measurements of the wavefront aberrations of projection optics with 0.1 nm RMS accuracy are indispensable to
develop the extreme ultraviolet (EUV) lithography. In order to study measurement methods, we built the Experimental
EUV Interferometer (EEI) that has built-in Schwarzschild-type optics as test optics and was supplied with EUV
radiation of 13.5 nm in wavelength from a synchrotron radiation facility as a source light. The EEI can evaluate several
methods of EUV interferometory replacing optical parts easily. Those methods are dividable into two categories,
namely point diffraction interferometer (PDI) and lateral shearing interferometer (LSI) and those were experimentally
compared. Finally, 0.045nm RMS of reproducibility was achieved with PDI method and the residual systematic error
after removing specified errors was reduced to 0.064nm RMS excluding axial symmetrical aberrations. In addition, one
of LSI-type methods also proved to have almost enough accuracy for the assembly of the projection optics.
Comparisons between several at-wavelength metrological methods are reported. The comparisons are performed by measuring one test optic with several kinds of measurement methods from the viewpoints of accuracy, precision and practicality. According to our investigation, we found that the PDI, the LDI, and the CGLSI are the most suitable methods for evaluating optics for EUV lithography.
We present the experimental results of EUVA Absolute Point Diffraction Interferometer (ABSPDI) and Lateral Shearing Interferometer (LSI) for at-wavelength characterization of the projection lens for use in extreme-ultraviolet lithography (EUVL). The attained repeatability of either type of the interferometers is within 0.04nmRMS. The experimental results have shown good consistency between the LSI and ABSPDI. The reasons for the residual differences have been analyzed and we believed it is mainly due to the CCD tilt effect in the experimental system. After the CCD tilt effect was removed, a better consistency below 0.33nm RMS has been achieved.
A Calibration technology for double-grating lateral shearing interferometer1 (DLSI) and lateral shearing interferometer (LSI) is proposed in this paper. In this method, two measurements are used for calibration. One is the measurement by using the first- and zero-order diffraction beams of grating in the interferometer; the other one is the measurement by using the minus-first-order and zero-order diffraction beams. The phase distributions were calculated out from the two measurements. After shifted one phase distribution to superpose the other one, in the sum of the two phase distributions, the test wavefront is canceled. The system error caused by the grating diffraction and grating tilt can be calculated out from the sum of the superposed phase distributions. For calculating out the system errors, the sum of the two phase distributions is fitted to Zernike-Polynomials. From the coefficients of the Zernike-polynomials, the system error is calculated. This method is carried out to calibrate the system error of DLSI. We performed an experiment to verify the available of our calibration method.
We are developing an at-wavelength interferometer for EUV lithography systems. The goal is the measurement of the wavefront aberration for a six-aspherical mirror projection optic. Among the six methods that EEI can measure, we selected CGLSI and PDI for comparison. PDI is a method well-known for its high accuracy, while CGLSI is a simple measurement method. Our comparison of PDI and CGLSI methods, verified the precision of the CGLSI method. The results show a difference between the methods of 0.33nm RMS for terms Z5-36. CGLSI measurement wavefronts agree well with PDI for terms Z5-36, and it is thought of as a promising method. Using FFT analysis, we estimated and then removed the impact of flare on the wavefront. As a result of having removed the influence of flare, the difference between CGLSI and PDI improved to only 0.26nm RMS in Zernike 5-36 terms. We executed PDI wavefront retrieval with FFT, which has not been used till now. By confirming that the difference between methods using FFT and Phase shift is 0.035nm RMS for terms Z5-36, we have proven that PDI wavefront analysis with FFT is possible.
The recent experimental results of EUV wavefront metrology in EUVA are reported. EUV Experimental Interferometer (EEI) was built at the NewSUBARU synchrotron facility of University of Hyogo to develop the most suitable wavefront measuring method for EUV projection optics. The result is to be reflected on EWMS (EUV Wavefront Metrology System) that measures wavefront aberrations of a six-aspherical mirror projection optics of NA0.25, of a mass-production EUV lithography tool. The experimental results of Point Diffraction Interferometer (PDI) and Lateral Shearing Interferometer (LSI) are shown and the error factors and the sensitivity of astigmatism measurements of these methods are discussed. Furthermore, for reducing these kinds of errors, another type of shearing interferometer called DTI (Digital Talbot interferometer) is newly introduced.
An Experimental extreme ultraviolet (EUV) interferometer (EEI) using an undulator as a light source was installed in New SUBARU synchrotron facility at Himeji Institute of Technology (HIT). The EEI can evaluate the five metrology methods reported before. (1) A purpose of the EEI is to determine the most suitable method for measuring the projection optics of EUV lithography systems for mass production tools.
Point diffraction interferometry (PDI) is a promising candidate of the wavefront metrology for EUV lithographic projection optics. However, the pinhole used in the PDI is easily filled up with carbon contamination induced by EUV irradiation. We have evaluated the filling rate of pinholes by measuring decreasing rates of intensity of EUV radiation that passed through the pinholes. As a result, we found the filling rates of the pinholes depend on their materials and blowing of the oxygen. The filling rate was the slowest when the pinhole made of Ni was used and oxygen was blown.
An experimental extreme UV (EUV) interferometer (EEI) using an undulator light source was designed and constructed for the purpose of developing wavefront measurement technology with the exposure wavelength of the projection optics of EUV lithography systems. EEI has the capability of performing five different EUV wavefront metrology methods.
In the F2 laser lithography, it is essential to reduce the loss of the optical coatings deposited on calcium fluoride lenses. In order to make low loss optical coatings, we have developed measurement apparatus, evaluated the coatings with various analyses, and found a correlation with the optical constants. In this paper we describe the optical loss measurement apparatus and the evaluation results analyzed for either single layer coatings or multi-layer anti-reflection coatings.
A new Coblentz type scatterometer is developed for evaluation of 157-nm optical coatings. The Coblentz hemisphere has ellipsoidal design for higher sensitivity and stability. The scatterometer works under nitrogen atmosphere keeping away from the organic contamination. Some kind of antireflective coatings are obtained from several Japanese suppliers and evaluated by the scatterometer. Results of the scatter measurement are almost equal except one sample that includes Na3AlF6 layer as low refractive index material. Its extremely high scatter loss could be ascribed degradation by reaction to the water in the air.
ntroduction Super-resolution is the eternal dream of the researchers in the field of optics. It is almost surprising that many new techniques for super-resolution have come in the field of optical storage recently. In the case of optical disc systems, one can modify the recorded mark on the disc so as to give the optimum result to the detected signal. This feature of optical systems makes it relatively easier to come up with a new super-resolution technique in comparison with microscopy where the image must be similar to the object. In addition, it is a great advantage to use scanning optical systems for read-out because finite time is necessary to form a scanned image, which allows us to make ’trick of time’. Therefore, it is relatively easier to figure out a new super-resolution technique in the field of optical storage compared with that of optical lithography where scanning optical systems have not been applied. However, it is well worth trying to introduce good concepts for super-resolution from historical work of microscopy. Sometimes a gem is hidden among them.
In high NA imaging systems such as Solid Immersion Lens ,incident angle is so large, and the polarization of incident beam is disturbed by passing through the SIL surface and by diffraction from the recording medium. Previously (ISOM'98) we reported the influence of polarization disturbance to the readout signals in phase change medium^. Here the same problem on the embossed mark is studied.
We investigate the readout signal with near field SIL by using vector diffraction theory. Readout signal from phase-change medium and optical ROM is analyzed. Air gap dependence and polarization dependence is discussed.
We have modified drives of 2Gbyte/130 mm non-DOW MO disk to be drives of 2GByte/130 mm DOW-MO disk. We have demonstrated that we have already reached the practical stage showing that it is possible to produce 2 GByte/130 mm DOW-MO disk and drive.
In order to use Magneto-Optical (MO) media for multi media applications, it is necessary to achieve higher density, higher data transfer rate and lower cost technologies than current MO media. MO recording is thermo- magnetic recording. MO recordings makes use of temperature modulation caused by light intensity modulation from the laser diode for recording. So, it is important to realize high speed response to the light intensity modulation for high data transfer rate recording. The high speed response is also indispensable to make small magnetic domains. So, it is important for high density recording, too. We investigate the temperature response to the light intensity modulation on MO disk. consequently, we found that MO medium shows the high speed response when the laser spot scanning velocity is large.
In 1987, we presented a direct overwritable Magneto-Optical exchange coupled Multilayered (DOW) disk by laser power modulation recording. Since then two major improvements of DOW were announced, namely 3- layered and 4-layered DOW disks, based on the 2-layered DOW disk, From the view point of merits and demerits, we compare the DOW disk with other direct overwritable optical disks, magnetic field modulation recording type of MO disk and phase change type of optical disk. As a latest topic, the recording power margin of the DOW scheme is explained. Adding metal coat to the DOW MO thin films is effective to expand the recording power margin. We have achieved (+/- 10%)2 allowance for direct overwriting power margin of PH and PL. Perspectives of the DOW disk for the next generation MO disk memory system are mentioned.
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