Study of a vibrating fiber probing system for 3-D micro-structures: performance improvement

Abstract

This paper presents a system for measuring 3D micro-structures that uses an optical fiber probe equipped with a piezo element that causes the probe to vibrate. The optical fiber probe consists of a stylus shaft with a diameter of 3 µm and a glass ball with a diameter of 5 µm attached to the tip. The stylus is vibrated in a circular motion in a single plane. The vibrator mechanism is introduced to prevent adhesion of the stylus tip to the surface being measured. This adhesion, which adversely affects the accuracy and time of the measurement, is caused by intermolecular, electrostatic, and liquid bridge forces. The measuring principle involves monitoring the vibrational amplitude of the stylus shaft that is required to prevent the adhesion of the stylus tip to the surface being measured, this amplitude being measured optically. In our previous report (Murakami et al 2012 Key Eng. Mater. 523–524 907–12), we found that the stylus shaft actually moves in an elliptical motion when it is set to describe a circular motion in the X-Y plane. Therefore, when a measurement is taken, it is necessary to adjust the motion of the piezoelectric tube to compensate for the difference between the diameter of the perfect circle and the actual elliptical motion of the stylus shaft displacement. In this study, the stylus characteristics were examined and the motion of the stylus shaft was then corrected to attain the desired circular motion. Next, the expansion of the measuring area by using a line laser was investigated. Finally, an experiment involving the measurement of a micro-hole was performed to demonstrate the practicality of the vibrating fiber probe. As a result, it was shown that the displacement between the diameter of the perfect circle and the actual elliptical motion of the stylus tip was about 0.034 µm after compensation. In addition, it was confirmed that the measurement area can be expanded by using an optical slit, but the standard deviation of the repeatability of the point measurement with the slit decreases to about half of that without the slit. In addition, the practicality of this system was confirmed by measuring the shape of a 100 µm diameter micro-hole.