We have developed a new atomic force microscope with differential laser interferometers (DLI-AFM), carried out test measurements of the prototype 1D-grating standards with pitches of 100, 80, 60 and 50 nm using the DLI-AFM and evaluated the uncertainty in the pitch measurements. In the procedures of the pitch calculation, two types of definitions of the peak positions, ‘the centre of gravity method’, and ‘the zero-crossing method’, were compared. The zero-crossing method was adopted in this study since the standard deviation of pitches by the zero-crossing method was smaller than that by the centre of gravity method. The expanded uncertainty (k = 2) was approximately 0.20 nm and was only 0.4% for the nominal pitch of 50 nm. We propose a design of usable 1D-grating standards as certified reference materials.
The cyclic error of a homodyne interferometer is caused mainly by phase mixing due to the imperfection of polarizing optical components such as polarizing beam splitters. In Appl. Opt. 43, 2443 (2004), we concentrated on the relationship between these imperfect optical characteristics and the cyclic error and found the preamplifier-gains condition for removing the cyclic error. Here we demonstrate the cyclic error correction method experimentally and show that the method can be applied in real time. We obtained 0.04-nm cyclic errors, with a standard deviation above 5 microm.
Most homodyne interferometers have a quadrature detector system that includes two polarizing beam splitters that cause nonlinearity of the order of a few nanometers by phase mixing. Detectors should have the same gains to reduce nonlinearity under the assumption that there is no loss in optical components. However, optical components exhibit some loss. We show that nonlinearity can be reduced to an order of 0.01 nm when the detector gains are adjusted by simulation to include the optical characteristics. The compensated nonlinearity is 18 times smaller than that when the four detector gains are set to be equal.
By present, the calibration of dimensions in nano scale is being paid more and more attentions. One-dimensional grating standard with pitches in nano-scale is being proposed by the CCL-WGDM 7 to be one of the five key comparison parameters in the emerging field of nanometrology. In the pitch calibration of grating standard, Gravity Center Method and Zero-Cross Points Method are proposed. The two methods are analyzed and simulated under different conditions. Based on the actual measurement data obtained by AFM, the two methods are used and the best value is determined. The results in the paper are useful to pitch calibration in nano scale.
Optical beam deflection detection is one of the main techniques used to detect the vibrating amplitude of dynamic mode atomic force microscope cantilevers. Due to the limitations of optical beam deflection detection systems and cantilevers, light leakage of the incident laser beam around the cantilevers can occur. An interference effect between the reflected beam from the cantilever and some scattered light from the specimen surface occurs, and an interference error in the probe tip–specimen approaching curve arises from this effect. In this paper, the interference effect in a dynamic atomic force microscope is analysed and observed in different conditions, and the micro-profile measurement error caused by the optical interference is deduced and calculated mathematically. The influence of the interference effect on a grating pattern measurement is then simulated.
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