Small length measurement using regular crystalline lattice for reference (3rd report) - Suppression of thermal drift error and extension of measurement range to micrometers

Abstract

This paper describes a suppression of the thermal drift error and an extension of a measurement range to micrometers in the comparative length measurement using a regular crystalline lattice as a reference scale and a dual tunneling unit scanning microscope (DTU-STM) as a detector. A thermo-stabilized cell, in which the DTU-STM can be set, was developed to reduce the temperature fluctuation to less than 0.05 K. In order to assess the thermo-stabilized cell, direct length comparison between the certified scanning electron microscope (SEM) standard grating with a average pitch of 240 nm and highly oriented pyrolytic graphite (HOPG) lattice spacing, which is 0.246 nm, was performed using the DTU-STM, whose main body is made from Super-Invar. Images of the grating and the HOPG were simultaneously obtained in the range of 1 μm. To shorten the measurement time and thus reduce the thermal drift error, the lengths of 1 μm for the two samples were measured along the fast scanning axis. A new ultra-low thermally drifted DTU-STM, whose body is fabricated from ultra-low linear expansion glass, was also developed to extend a measurement range to micrometers in the comparative length measurement. Long atomic image of HOPG crystal over a 5-μm-long region along the fast scanning axis was obtained using the new DTU-STM in the thermostabilized cell. The experimental results show the possibility of the comparative length measurement in micrometers range with sub-nanometer resolution using the HOPG crystal and the DTU-STMs.