High-precision optical elements are used in various fields. Ultraprecise aspherical mirrors that offer nanofocusing and high coherence are used to concentrate high-brightness X-rays in developing third-generation synchrotron radiation facilities. In industry, extreme ultraviolet (wavelength: 13.5 nm) lithography, which is used to fabricate semiconductor devices, uses high-accuracy aspherical mirrors for its projection optical systems. The demand for rapid progress in nanomeasurement technologies is increasing because it is difficult to realize next-generation ultraprecise mirrors with the required precision by conventional processing. The measuring method itself requires superhigh precision. We developed an innovative nanoprofiler that can directly measure the figure of high-accuracy mirrors without using a reference surface. The principle of our measuring method is to determine the normal vectors by causing the optical paths of the incident and reflected light at the measurement point to coincide; it is based on the straightness of laser light and the accuracy of rotational goniometers. From the acquired normal vectors and their coordinates, the three-dimensional shape is calculated by a reconstruction algorithm. We measured concave spherical mirrors and compared the results with those using a Fizeau interferometer. The profiles of the mirrors were consistent within the range of error in their middle portions. In addition, we evaluated the performance of an airflow control unit by measuring a concave spherical mirror. This unit suppressed the influence of environmental change, and drastically improved the repeatability.
A new high-speed slope measuring instrument is currently under development for small-aperture aspheric lenses and
mirrors. In the present study, normal vectors at each point on the lens surface were determined using the reflected light
beam that follows the same path as the incident beam. The capability of the developed instrument to achieve submicroradian
surface slope metrology of a small-radius aspheric lens was verified. The paper also describes in detail the
design principle, aspheric lens measuring method, initial alignment and calibration procedure, shape determination
procedure developed from the measured slope metrology, and the high-speed slope measuring technique.
Ultraprecise aspherical mirrors that offer nanofocusing and high coherence are indispensable for developing third-generation
synchrotron radiation and X-ray free electron laser sources. In industry, the extreme ultraviolet
(wavelength: 13.5 nm) lithography used for high-accuracy aspheric mirrors is a promising technology for fabricating
semiconductor devices. In addition, ultraprecise mirrors with a radius of curvature of less than 10 mm are needed in
many digital video instruments. We developed a new type of nanoprofiler that traces the normal vector of a mirror’s
surface. The principle of our measuring method is that the normal vector at each point on the surface is determined
by making the incident light beam on the mirror surface and the reflected beam at that point coincide, using two sets
of two pairs of goniometers and one linear stage. From the acquired normal vectors and their coordinates, the three-dimensional
shape is calculated by a reconstruction algorithm. The characteristics of the measuring method are as
follows. The profiler uses the straightness of laser light without using a reference surface. Surfaces of any shape can
be measured, and there is no limit on the aperture size. We calibrated this nanoprofiler by considering the system
error resulting from the assembly error and encoder scale error, and evaluated the performance at the nanometer
scale. We suppressed the effect of random errors by maintaining the temperature in a constant-temperature room
within ±0.01°C. We measured a concave spherical mirror with a radius of curvature of 400 mm and a flat mirror,
and compared the results with those obtained using a Fizeau interferometer. The profiles of the mirrors were
consistent within the range of system errors.
A new high-speed nanoprofiler was developed in this study. This profiler measures normal vectors and their coordinates on the surface of a specimen. Each normal vector and coordinate is determined by making the incident light path and the reflected light path coincident using 5-axis controlled stages. This is ensured by output signal of quadrant photo diode (QPD). From the acquired normal vectors and their coordinates, the three-dimensional shape is calculated by a reconstruction algorithm based on least-squares. In this study, a concave spherical mirror with a 400 mm radius of curvature was measured. As a result, a peak of 30 nm PV was observed at the center of the mirror. Measurement repeatability was 1 nm. In addition, cross-comparison with a Fizeau interferometer was implemented and the results were consistent within 10 nm. In particular, the high spatial frequency profile was highly consistent, and any differences were considered to be caused by systematic errors.
A new concept profiler has been developed to measure items such as asymmetric and aspheric profiles with a small
radius curvature lens and mirrors. In this study, the normal vectors at each point on the surface are determined by a
reflected light beam that returns along exactly the same path as the incident beam. In order to measure a small radius
curvature, a compact measuring instrument was redesigned according to the above principle of the measuring method
employed. The instrument is 1200 mm (W) × 1000 mm (H) × 1500 mm (V). The measurement of normal vectors of a
spherical lens, which has a small f number such as a 25 mm radius curvature, has been demonstrated with a measuring
accuracy for the normal vector of 0.1 μrad. The surface gradient at each point is calculated from the normal vector, and
the surface profile is obtained by integrating the gradient. When integrating the gradient, measured position accuracy
should be in the order of 10 nm. They were obtained by self-calibration techniques that have already developed by the
authors. In this paper, we discuss methods of calculating absolute radius curvature and deviation from the ideal surface
profile.
A new ultra-precision profiler has been developed to measure items such as asymmetric and aspheric profiles. In the current study, the normal vectors at each point on the surface are determined by a reflected light beam that returns along exactly the same path as the incident beam. The surface gradients at each point are calculated from the normal vector, and the surface profile is obtained by integrating the gradient. At a previous meeting, we reported that normal vector measured points with submicron accuracy can be determined by a self-calibration method. In this paper, the self-calibration method has been tested and shown to have the capability for surface profile measurement accuracy of nanometer order, using a concave mirror with a radius curvature of 2000 mm. The precise surface profile obtained from a measured normal vector has been studied as a new data analysis method that applies Fourier series expansion with the least-square method. Future development will include the following: the elimination of error propagation due to data analysis from normal vector to surface profile, unique determination of profile from normal vector, and enabling random
measuring position of normal vector on the mirror.
A new ultra-precision profiler has been developed in order to measure such as asymmetric and aspheric profiles. In the
present study, the normal vectors at each points on the surface are determined by the reflected light beam goes back
exactly on the same path as the incident beam. The surface gradients at each point are calculated from the normal vector
and the surface profile is obtained by integrating the gradient. The measuring instrument was designed according to the
above principle of the measuring method. In the design, four
ultra-precision goniometers were applied to the adjustment
of the light axis for the normal vector measurement. In the measuring instrument, the angle-positioning resolution and
accuracy of each goniometer are respectively 1.8x10-8rad and 2x10-7rad. A coaxial with an off-axis parabolic mirror has
been developing for applying as an optical cavity. The most important engineering technique is to measure the profile of
the reflective surface with sub nanometer. The present measuring instrument is evaluating to have capability to the
surface measuring accuracy with nanometer for such parabolic mirror profile measurement. A coaxial off-axis parabolic
mirror with 150 mm focal length has been polished. The outside and inside diameter of the mirror is 360 mm and 258
mm respectively. The thickness of the coaxial direction is 50 mm. The focal point is located on the center of the coaxial
and the center of the coaxial direction of the mirror. The profile measurement such a mirror has been demonstrated.
Specially, self calibration method for increasing the measured position accuracy from measured data is discussed.
A new ultra-precision profiler has been developed in order to measure such as asymmetric and aspheric profiles. In the present study, the normal vectors at each points on the surface are determined by the reflected light beam goes back exactly on the same path as the incident beam. The surface gradients at each point are calculated from the normal vector and the surface profile is obtained by integrating the gradient. The measuring instrument was designed according to the above principle of the measuring method. In the design, four ultra-precision goniometers were applied to the adjustment of the light axis for the normal vector measurement. The angle positioning resolution and accuracy of each goniometer are respectively 0.018 μrad and 0.2 μrad. In the measuring instrument, the most important item is the measuring accuracy of the normal vectors by the goniometers. Therefore, the rotating angle positioning errors were measured and calibrated. Then the measurement of a concave mirror with 300 mm radius and 460mm, 1m long plane mirrors were measured. Then, The 3D surface profile of the mirror such 1m-long flat mirror, a concave mirror with 2000 mm radius and off-axis parabolic mirror are obtained by integrating the interpolated gradient.
A new ultra-precision profiler was developed to measure X-ray and EUV optics such as asymmetric and aspheric profiles. In the present study, the normal vectors at each point on the surface are determined by a reflected light beam that follows exactly the same path as the incident beam. The surface gradients at each point are calculated
from the normal vector and the surface profile is obtained by integrating the gradient. The measuring instrument was designed according to the above principles. In the design, four goniometers and three-axis movers were applied to adjust the light axis to search for the normal vector at each point on the surface. The angle-positioning resolution and accuracy of each goniometer are respectively 1.8 x 10-8 radian and 2 x 10-7 radian. A SiC flat mirror 25.4 mm in diameter and an elliptical profile mirror for nanometer hard X-ray focusing were measured using the present instrument and compared to the measured profile using a Zygo Mark IVxp phase-measuring interferometer.
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