Kouji Toyoda

A laser tracking robot‐performance calibration system using ball‐seated bearing mechanisms and a spherically shaped cat’s‐eye retroreflector

A new robot‐performance calibration system based on tracking multilaser trilateration has been developed. To realize 1 μm coordinate accuracy, a beam‐deflecting tracking mechanism with both a ball‐seated bearing and a spherically shaped cat’s eye retroreflector whose refractive index is 2.0 has been developed. The coordinate error and the repeatability of a commercial industrial robot have been verified by the system we developed in a two‐dimensional plane.

Effects of phase changes on reflection and their wavelength dependence in optical profilometry

The method as well as an appropriate instrumentation for measuring phase changes of reflected light is described. The phase changes on samples of Au, Al, Ag, and Cr evaporated films are measured for five wavelengths (lambda) from 442 to 633 nm, with respect to the phase change at the glass-air interface, where it should be zero. The measured results for the Au film are in fairly good agreement with values calculated by use of optical constants from a handbook or the complex refractive index measured by an ellipsometer. The phase changes for Al and Ag films are different from calculated values by ~5 degrees or a shift length of 4.4 nm at lambda = 633 nm, while those of the Cr film show large shifts as high as 16 degrees or a shift length of 9.8 nm at lambda = 442 nm.

Speed control characteristics and digital servosystem of a circular traveling wave motor

The rotational speed control characteristics of a circular traveling wave motor are investigated. This motor is an ultrasonic motor driven by a specially designed piezoelectric vibrator. There are various parameters for controlling rotational speed due to the influence of friction and resonance between rotor and stator. In this paper the dependence of rotational speed on these parameters is explored by using an experimental instrument. A digital servosystem to control the rotational position of the motor is then assembled, using the experimental results as a guide. The angular resolution of the motor is 5.4’, sufficient as a driver of a standard rotary table.

A metrological electron microscope system for microfeatures of very large scale integrated circuits

An absolute linewidth measuring system, based on a scanning electron microscope (SEM), is developed to measure critical dimension (CD) of VLSIs (very large scale integrated circuits). The system employs two laser interferometers for the absolute scales of the X and Y axes, while the electron beam is used to detect microfeatures on the silicon chips. The resolutions of the interferometers are 0.8 nm for X and 20 nm for Y. An LaB6 filament is used for the electron gun and the system is operated under low acceleration voltages of around 1 kV for noncharging measurements. In this article, the principle of the measurements, the electron beam system, the scanning mechanism, and the laser interferometer are described including basic experimental results.

Critical dimension measurements by electron and optical beams for the establishment of linewidth standards

To establish traceability in sub-micrometer critical dimension measurements, a silicon reference artifact was manufactured. The measurement characteristics of the artifacts were examined by simulation and a metrological scanning electron microscope system. The possibility of linewidth indication by a peak-to-peak definition for isolated lines is described, and a pitch reference by a silicon grating was examined. A simulation based on a diffusion theory is described to predict the edge signal for the electron beam line scan on the artifact. It predicted narrower linewidth for isolated lines and showed good agreement with experimentally obtained critical dimensions.<<ETX>>

Piezodriven spindle for a specimen holder in the vacuum chamber of a scanning electron microscope

A rotating specimen holder device for use in the vacuum chamber of a SEM (scanning electron microscope) is developed by using a piezodriven mechanism. The mechanism consists of piezoelectric elements, clamps, and actuators that work as feeders to rotate the spindle. It is specially designed to eliminate the magnetic field influence of standard motors, and the holder can be placed just under the electron probe beam. In this article, the basic ideas, design, and instrumentation techniques are described. Then a servosystem is constructed for positioning the spindle. The angular resolution is 0.9° and the maximum rotation speed is 9.4 s/rotation.

A compact laser interferometer with a piezodriven scanner for metrological measurements in regular SEMs

A compact laser interferometer combined with a mechanical scanner has been developed for precise microlinewidth measurements in regular scanning electron microscopes (SEMs). Optical components and a piezodriven mechanical table are integrated on a small disk 130 mm in diameter. The device is so compact that it can be installed in the vacuum chamber of regular SEMs, and useful for accurate and precise measurements based on the laser wavelength—a practical length standard. An optical multipath technique and a differential arrangement of prisms in the interferometer, as well as electrical sensitized technique, realized a high resolution of 0.4 nm (λ/1600). By using the device and a SEM, an absolute linewidth measurement system has been constructed for microlinewidth measurements. To evaluate the system performance, a comparison has been made between a metrological SEM and the system by using a silicon test artifact. The result shows a good agreement between the two systems within an uncertainty of several na...

Measurement of phase change of light on reflection

A sample consisting of different metals in the same plane is fabricated, and its surface profile is measured by interferometry. In spite of the flat surface, a virtual step height (max. value equals 33 nm) is measured at the boundary of the two adjacent metals. The measured step height corresponds to the difference in the phase change of reflected light between the two metals. From the results, the effect of the phase change on surface profilometry is estimated.