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 nanometers. This device can be applied for various types of microscopes such as optical and scanning probing microscopes, and useful as an important scaling device for the calibration of measurement systems.