## 1 Introduction  
Recent advances in machining technology have increased demand for the microfabrication of micro molds, various nozzle holes, through silicon via (TSV) semiconductors, micro electro mechanical systems (MEMSs), micro components such as micromachines, optical communication devices, and medical devices [1; 2; 3]. However, it is extremely difficult to accurately measure microstructures such as micrometer-order small holes and grooves with a high aspect ratio. Various microstructure measurement system based on different principles have been proposed [4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15]. We have developed a system that uses an optical fiber as a stylus to measure microstructures with low contact force [16; 17; 18; 19; 20]. The measurement system detects contact using a laser to measure the amount of deflection of the stylus shaft when the stylus tip makes contact with the measured surface. A stylus with a diameter from one to several hundred micrometers can be used. When the diameter of the stylus tip is less than several tens of micrometers, surface forces such as van der Waals force, electrostatic force, and liquid bridge force generated between the measured surface and the stylus tip, become larger than the gravity of the stylus tip, causing the stylus tip to stick to the measured surface as shown in Figure 1.  
If the stylus tip adheres to the measured surface, the measurement time increases because the stylus tip must be pulled away from the measured surface. The distance required to pull the stylus tip away from the measured surface, \(\delta\), shown in Figure 1, varies depending on the ambient environment, such as temperature and humidity, and ranges from several micrometers to several hundred micrometers. Naturally, as the diameter of the stylus shaft (corresponding to the stiffness of the stylus shaft) increases, the distance, \(\delta\), decreases. In other words, the distance, \(\delta\), is determined by the relative relationship between the stiffness of the stylus shaft and the surface forces generated between the measured surface and the stylus tip. In addition, the measurement accuracy may deteriorate due to deflection when measuring in scanning mode [19]. As a countermeasure for this adhesion, we have developed a measurement system which prevents adhesion by vibrating the stylus in a circular motion [18]. This method uses circular vibration of the stylus tip; therefore, it can be used to measure 2.5-dimensional shapes such as holes and grooves. However, when measuring 3-dimensional shapes such as free-form surfaces, there is a problem that errors occur depending on the contact direction. Therefore, we have developed a system which enables measurements to be taken in a vacuum vessel, reducing the effects of adhesion due to surface forces by about 60% [21]. However, the size of the space inside the vacuum vessel is limited, making it impossible to measure large objects. In addition, it takes time to create a vacuum inside the vessel. In this study, we have developed a high-performance stylus with water-repellent and antistatic coatings applied to the stylus to reduce stylus tip adhesion to the measured surface due to surface forces such as van der Waals force, electrostatic force, and liquid bridge force generated between the measured surface and the stylus tip. A water-repellent coating on the stylus reduces the effect of liquid bridge forces. Styluses coated with a  
Figure 1: Effect of the surface force, \(F\), during measurement. water-repellent layer are assumed to be used in humid environments, where the influence of liquid bridge forces is greater. On the other hand, a stylus coated with an antistatic layer can reduce the effects of electrostatic force. The measured surfaces are more likely to be charged in low-humidity environments; therefore, a stylus with an antistatic coating is expected to be used.