Crystalline lattice for metrology and positioning control

An important area in research on microelectromechanical systems (MEMS) is the introduction of a well-defined scale reference for measurements of fabricated objects and control of positioning. As an approach to high-accuracy measurements in the submicron region, the authors propose the use of regular lattice spacings of crystals as scale reference. A scanning tunneling microscope (STM) with two tunneling-units (dual tunneling-unit STM, or DTU STM) was developed to study the feasibility of comparison measurements with crystals. Measurement errors were found to be around 0.1%, which was evaluated through comparison of two highly oriented pyrolytic graphite (HOPG) chips with the DTU STM. As for the study of positioning control, an HOPG chip was attached to an XY table, and a probe tip was used to observe the lattice image of the chip. With this configuration, the HOPG chip can be used as a linear scale for displacement detection. Dither vibration (amplitude 70 pm (p-p), frequency 3.3 kHz) was applied to the XY table to implement positioning control. Experiments confirmed such functions as prolonged positioning of the XY table to the tip with sub-atomic resolution and relative stepping action of the XY table to the tip, where the step pitch is defined by the lattice spacing. Both functions were confirmed to be robust and practical.<>