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ABSTRACT: We present a new absolute position measurement method using a single track binary code where an absolute position code is encoded by changing the phase of one binary state representation. It can be decoded efficiently using structural property of the binary code, and its sub-division is possible by detecting the relative positions of the binary state representation used for the absolute position encoding. Therefore, the absolute position encoding does not interfere with the sub-division process and so any pseudo-random sequence can be used as the absolute position code. Because the proposed method does not require additional sensing part for the sub-division, it can be realized with a simple configuration and efficient data processing. To verify and evaluate the proposed method, an absolute position measurement system was setup using a binary code scale, a microscopic imaging system, and a CCD camera. In the comparison results with a laser interferometer, the measurement system shows the resolution of less than 50 nm and the nonlinearity error of less than ±60 nm after compensation.
The Review of scientific instruments 11/2012; 83(11):115115. · 1.52 Impact Factor
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ABSTRACT: We developed a metrological atomic force microscope (MAFM) using a large range scanning dual stage and evaluated the performance
in the measurement of lateral dimension. AFMs are widely used in nanotechnology for very high spatial resolution, but the
limitation in measurement range should be overcome to expand its application in nanometrology. Therefore, we constructed new
MAFM having a large measurement of 200 mm × 200 mm by using a dual stage and an AFM head module. The dual stage is composed
of a coarse and a fine stage to obtain large scanning range and high resolution simultaneously. Precision surfaces and PTFE
sliding pads guide the motion of coarse stage, drove by a fine pitch screw and DC motors. Flexure hinges and PZT actuators
are utilized for the fine stage. Multi-axis interferometers measure the five degrees of freedom motion of the dual stage for
the position control and the compensation of parasitic angular motions. The vertical displacement of AFM tip is measured by
a built-in capacitive sensor in the AFM head module within the range of 38 µm. The performance of the dual stage was evaluated
and the expanded uncertainty (k = 2) in the measurements of 1-D displacement L was estimated as $
U(L) = \sqrt {(2.8nm)^2 + (3.0 \times 10^{ - 7} \times L)^2 }
$
U(L) = \sqrt {(2.8nm)^2 + (3.0 \times 10^{ - 7} \times L)^2 }
. The relative uncertainty in pitch measurement was less than 0.02 % and the improvement of accuracy was verified by comparing
with other MAFM, which are mostly due to the expansion of scan range and the compensation of angular motion. To enhance the
performance, we will reduce the vibration and examine the motion of stage in the vertical direction during a long range scan.
International Journal of Precision Engineering and Manufacturing 04/2012; 10(5):11-17. · 1.14 Impact Factor
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ABSTRACT: We have proposed and demonstrated a novel method to measure depths of through silicon vias (TSVs) at high speed. TSVs are fine and deep holes fabricated in silicon wafers for 3D semiconductors; they are used for electrical connections between vertically stacked wafers. Because the high-aspect ratio hole of the TSV makes it difficult for light to reach the bottom surface, conventional optical methods using visible lights cannot determine the depth value. By adopting an optical comb of a femtosecond pulse laser in the infra-red range as a light source, the depths of TSVs having aspect ratio of about 7 were measured. This measurement was done at high speed based on spectral resolved interferometry. The proposed method is expected to be an alternative method for depth inspection of TSVs.
Optics Express 02/2012; 20(5):5011-6. · 3.59 Impact Factor
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ABSTRACT: We present an angle generator with high resolution and accuracy, which uses multiple ultrasonic motors and a self-calibratable encoder. A cylindrical air bearing guides a rotational motion, and the ultrasonic motors achieve high resolution over the full circle range with a simple configuration. The self-calibratable encoder can compensate the scale error of a divided circle (signal period: 20") effectively by applying the equal-division-averaged method. The angle generator configures a position feedback control loop using the readout of the encoder. By combining the ac and dc operation mode, the angle generator produced stepwise angular motion with 0.005" resolution. We also evaluated the performance of the angle generator using a precision angle encoder and an autocollimator. The expanded uncertainty (k = 2) in the angle generation was estimated less than 0.03", which included the calibrated scale error and the nonlinearity error.
The Review of scientific instruments 11/2011; 82(11):116108. · 1.52 Impact Factor
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ABSTRACT: We present a high speed optical profiler (HSOP) using frequency-scanning lasers for three-dimensional profile measurements of microscopic structures. To improve upon previous techniques for implementing the HSOP, we developed frequency-scanning lasers and a compact microscopic interferometer. The controller of the HSOP was also modified to generate proper phase-shifting steps. For measurements of step height specimens, the HSOP showed results comparable with a commercial optical profiler, even with much higher measurement speeds (up to 30 Hz). The typical repeatability of step height measurement was less than 1 nm. We also present measurements of microscopic structures to verify the HSOP's ability to perform high speed inline inspection for the semiconductor and flat-panel display industries.
The Review of scientific instruments 08/2011; 82(8):086111. · 1.52 Impact Factor
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ABSTRACT: A calibration system for linear-dimension artefacts was developed, which employed a multi-axis laser interferometer for direct metrological traceability and active compensation of angular motion errors. It can calibrate various end and line standards by changing probes (contact and optical probe). We designed the system as a moving probe type with a cantilever structure to reduce overall size and increase efficiency in calibration. A stage part including a two-axis tilt stage provides precise linear motion of a probing part over the range of 2000 mm with nanometric resolution. The three-axis interferometer measuring linear and rotational motions of the stage enables us to obtain probing position and compensate angular motion errors precisely. It was also arranged to minimize the Abbe offset, and so the Abbe error can be reduced remarkably combining the active compensation of angular motion errors. The overall system was installed in a temperature-controlled chamber to decrease thermal variation during measurements. The measurement uncertainty of the calibration system was analysed by considering the performance of the main components. We measured several long gauge blocks and a precision line scale, and compared the measured values with the reference ones and also checked their stabilities. Their deviations were less than 100 nm and existed within the expanded measurement uncertainty (k = 2).
Measurement Science and Technology 06/2011; 22(7):075304. · 1.49 Impact Factor
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ABSTRACT: High-speed two-wavelength phase-shifting interferometry is presented. The technique is aimed at high-speed in-line inspection of spacers in liquid crystal display panels or wafer bumps where the measuring range is well determined and high-speed measurements are essential. With our test setup, the measuring range is extended to 10 μm by using two injection locked frequency scanning lasers that offer fast and equidistant phase shifting of interference fringes. A technique to determine the unwrapped phase map in a frequency scanning phase-shifting interferometry without the ordinary phase-unwrapping process is proposed.
Applied Optics 04/2011; 50(11):1541-7. · 1.41 Impact Factor
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ABSTRACT: We propose and demonstrate a novel method to enhance the visibility of an optical interferometer when measuring low reflective materials. Because of scattering from a rough surface or its own low reflectivity, the visibility of the obtained interference signal is seriously deteriorated. By amplifying the weak light coming from the sample based on an injection-locking technique, the visibility can be enhanced. As a feasibility test, even with a sample having a reflectivity of 0.6%, we obtained almost the same visibility as a metal coated mirror. The suggested visibility enhanced interferometer can be widely used for measuring low reflective materials.
Optics Express 11/2010; 18(23):23517-22. · 3.59 Impact Factor
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ABSTRACT: We have proposed and demonstrated a novel method that can determine both the geometrical thickness and refractive index of a silicon wafer at the same time using an optical comb. The geometrical thickness and refractive index of a silicon wafer was determined from the optical thickness using phase information obtained in the spectral domain. In a feasibility test, the geometrical thickness and refractive index of a wafer were measured to be 334.85 microm and 3.50, respectively. The measurement uncertainty for the geometrical thickness was evaluated as 0.95 microm (k = 1) using a preliminary setup.
Optics Express 08/2010; 18(17):18339-46. · 3.59 Impact Factor
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ABSTRACT: We developed an Abbe-type comparator using a laser interferometer and a linear variable differential transformer (LVDT) probe as displacement sensors, which can measure the diameter of ring and plug gauges up to 300 mm. The measurement system is configured according to the Abbe principle, and consists of translation stages, a laser interferometer, an LVDT probe and an electronic controller. The main translation stage is made by using a precision ceramic guide and air bearing pads, and is driven by a backlash-free lead screw and a micro-stepping motor. The laser interferometer measures the displacement of a moving mirror aligned with the probe coaxially. The environmental effect is corrected automatically during the measurement. The effective diameter of the probe ball is calibrated using a reference gauge block. The performance of each component was evaluated through experiments and the measurement uncertainty of the overall system was analyzed. We measured three diameter artifacts, which are 11.95 mm and 100 mm ring gauges and a 98.5 mm plug gauge, and compared the measured values with the calibrated ones. They were consistent with each other within 0.3 µm, which is less than the expanded measurement uncertainty (k = 2).
Measurement Science and Technology 06/2010; 21(7):075109. · 1.49 Impact Factor
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ABSTRACT: This study presents an analysis of the nonlinearity resulting from polarization crosstalk at a polarizing beam splitter (PBS) and a wave plate (WP) in a homodyne interferometer. From a theoretical approach, a new compensation method involving a realignment of the axes of WPs to some specific angles according to the characteristics of the PBS is introduced. This method suppresses the nonlinearity in a homodyne interferometer to 0.36 nm, which would be 3.75 nm with conventional alignment methods of WPs.
Optics Express 12/2009; 17(25):23299-308. · 3.59 Impact Factor
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ABSTRACT: An interferometer having fourteen times higher resolution than a conventional single-pass interferometer has been developed by making multiple-pass optical path. To embody the multiple-pass optical configuration, a two-dimensional corner cube array block was designed, and its symmetric structure minimized the measurement error. The effect from the alignment error and the imperfection of corner cube is calculated as picometer level. An experiment proves that the suggested interferometer has about 45 nm of optical resolution and its nonlinearity is about 0.5 nm in peak-to-valley.
Optics Express 11/2009; 17(23):21042-9. · 3.59 Impact Factor
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ABSTRACT: We present a high speed phase shifting interferometer which utilizes the self injection locking of a frequency tunable laser diode. By using a confocal Fabry-Perot cavity made of ultra low expansion glass, and linearly modulating the laser diode current, the laser frequency could be injection locked to the resonant modes of the Fabry-Perot cavity consecutively. It provided equal phase steps to the interferograms which are ideal to be analyzed by the Carré algorithm. The phase step error was evaluated to be about 3 MHz which corresponds to 0.2 nm in length measurement. With this technique, profile measurements are insensitive to external vibration since four 640x480 pixels images can be acquired within 4 ms. Difference of two profile measurements, each made with and without vibration isolation, respectively, was evaluated to be 0.5 nm (rms).
Optics Express 03/2009; 17(3):1442-6. · 3.59 Impact Factor
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ABSTRACT: This note presents a digital signal processing module for the real-time nonlinearity compensation of a homodyne interferometer. The nonlinearity is corrected by using the parameter values describing two phase-quadrature signals, through simple arithmetic calculation of the quadrature signals at specific phases, which are multiples of π/4. A field-programmable gate array was employed for the real-time implementation of a processing module since it has reconfigurable input/output and high precision synchronization. The developed module has a minimum loop time of 4.4 µs and can compensate the nonlinearity error less than ±0.5 nm, which is comparable with the elliptical fitting method. We also proved the performance of the module by examining the convergence and the stability of parameter values under various operational conditions.
Measurement Science and Technology 11/2008; 20(1):017003. · 1.49 Impact Factor
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ABSTRACT: A phase-encoding electronics capable of compensating for the nonlinearity error in a heterodyne laser interferometer is described. The system consists of the phase demodulating electronics and the nonlinearity compensating electronics. For phase demodulation, we use the phase-quadrature mixing technique. For nonlinearity compensation, the offsets, the amplitudes and the phase of two output signals from the demodulator are adjusted electrically so that their Lissajous figure is a circle. As a result, the correct phase can be obtained. An analysis of the nonlinearity in the heterodyne interferometer and the design of the phase-encoding electronics are presented. The experiment was performed in a Michelson-type interferometer using a transverse Zeeman stabilized He–Ne laser. We demonstrate that this method can encode the phase of a heterodyne interferometer with sub-nanometer accuracy.
Measurement Science and Technology 06/2008; 19(7):075302. · 1.49 Impact Factor
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ABSTRACT: A 50 m linear measuring interferometer, consisting of a precision laser
interferometer, a 51 m long guide rail, a moving carriage, an optical
microscope with a CCD camera and an image processor, is described here.
The system is designed for the automatic calibration of surveying tapes.
The carriage can move up to 50 m along the guide rail. The dc servo
motor, which is fixed on the carriage, drives the carriage and its speed
is controlled by a computer through wireless communication. The CCD
camera captures the image of tape lines through the microscope fixed on
the stage, and the image is wireless transferred to the image processor
installed in the computer. The image processor calculates the deviation
between the center of the line and the field-of-view of the CCD camera,
and the laser interferometer measures the displacement of the carriage
simultaneously. Finally, the intervals between lines are determined
using the deviation and the reading of the laser interferometer. The
calibration process is performed automatically after the installation of
the tape. The estimated expanded uncertainty of the steel tape
measurement is \sqrt {(24\;\mu m)^2 + (6.6 \times 10^{ - 6} )^2 \times
L^2 } at the confidence level of approximately 95%.
Measurement Science and Technology 12/2007; 19(1):7003. · 1.49 Impact Factor
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ABSTRACT: We report on a novel compact interferometery system for measuring parasitic motions of a precision stage. It is a combination of a Michelson interferometer with an auto-collimator, of which full physical dimension is mere 70 mm x80 mm x35 mm (WxLxH) including optical components, photo-detectors, and electronic circuits. Since the beams, which measure displacement and angle, can be directed at the same position on the moving mirror, the system is applicable for testing small nano-stages where commercial interferometers are not able to be used. And thus, errors from nano-scale deformation of the moving mirror can be minimized. We find that the residual errors of linear and angular motion measurements are 2.5 nm in peak-to-peak and 0.2'', respectively.
Optics Express 12/2007; 15(24):15759-66. · 3.59 Impact Factor
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ABSTRACT: A 50 m linear measuring interferometer, consisting of a precision laser interferometer, a 51 m long guide rail, a moving carriage, an optical microscope with a CCD camera and an image processor, is described here. The system is designed for the automatic calibration of surveying tapes. The carriage can move up to 50 m along the guide rail. The dc servo motor, which is fixed on the carriage, drives the carriage and its speed is controlled by a computer through wireless communication. The CCD camera captures the image of tape lines through the microscope fixed on the stage, and the image is wireless transferred to the image processor installed in the computer. The image processor calculates the deviation between the center of the line and the field-of-view of the CCD camera, and the laser interferometer measures the displacement of the carriage simultaneously. Finally, the intervals between lines are determined using the deviation and the reading of the laser interferometer. The calibration process is performed automatically after the installation of the tape. The estimated expanded uncertainty of the steel tape measurement is at the confidence level of approximately 95%.
Measurement Science and Technology 11/2007; 19(1):017003. · 1.49 Impact Factor
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ABSTRACT: Microscope calibration standards in nanometrology were calibrated using a metrological atomic force microscope (metrological AFM) and the validity of calibrated values was shown. The metrological AFM was developed through the modification of a commercial AFM, which replaced the PZT tube scanner with flexure hinge scanners and displacement sensors. These modifications improved the traceability of measured values to metrological primary standards. The grating pitch and step height specimens, which are typical standard artefacts for the calibration of lateral and vertical magnifications of microscopes, were measured using the metrological AFM. The expanded uncertainties (k = 2) of calibrated values were estimated considering the characteristics of the calibration process and were less than 1 nm. The measurement results were compared with those obtained by other metrological methods or the certified values and their consistency was verified by checking the En numbers. These experimental results show that the metrological AFM can be used effectively for the measurements of microscope calibration standards in nanometrology.
Measurement Science and Technology 06/2006; 17(7):1792. · 1.49 Impact Factor
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ABSTRACT: Precision actuators, such as pick-up actuators for HDDs or CD-ROMs, mostly show multidimensional motion. So, to evaluate them more completely, multidimensional measurement is required. Through structural variation and optimization of the design index, the performance of a measurement system can be improved to satisfy the requirement of this application, and so the resolution of each axis is higher than 0.1 μm for translation and 0.5 arcsec for rotation. Using this measurement system, the multidimensional motion and frequency transfer functions of a bimorph-type piezoelectric actuator are obtained. © 2001 American Institute of Physics.
Review of Scientific Instruments 08/2001; 72(9):3731-3733. · 1.37 Impact Factor
