Direct length comparison between regular crystalline lattice and SEM standard grating using dual tunneling unit STM

This paper presents a potential image processing method for calibrating the in-plane geometrical distortion of a scanning tunneling microscope (STM) image using a regular crystalline lattice, describes the assessment evaluation of comparative length measurement in the range of about 1 micrometer using a regular crystalline lattice as a reference scale and a dual tunneling unit-STM (DTU-STM) as a detector, and shows the results of direct length comparison between a scanning tunneling microscope (SEM) standard grating, whose pitch is 240 nm, and a regular crystalline lattice using a DTU-STM. The method is based on two-dimensional fast Fourier transform (FFT) analysis. The DTU-STM with one X-Y stage and two tunneling units independently controlled in the Z-axis direction has been utilized for comparative length measurement. To improve the measurement accuracy, the present method is used to process the raw images obtained from the DTU-STM. The results of assessment experiments, in which the cleaved surface of highly oriented pyrolytic graphite (HOPG) is used as a reference scale for measurement of lengths on the order of 1 micrometer, demonstrate the feasibility of the present image processing method and the comparative length measurement with sub-nanometer resolution using the DTU-STM. The value of the SEM standard grating pitch, which obtained from the direct length comparison with HOPG lattice spacing using the DTU-STM, was coincided with the value obtained from the conventional diffraction method within a error of 2%. (C) 1998 Elsevier Science Ltd.