![]() Then, using a method similar to that of DigitalMicrograph, ImageJ measured the silicon lattice spacings. The TEM image was rotated according to the calculated angles so that the (220) spacings were perpendicular to the x-axis. 1.52a and the fast Fourier transform pattern of the original TEM images. calculated the rotation angles of Si (220) spacings using ImageJ ver. Numerous researchers have utilized ImageJ, a software program developed by the National Institutes of Health, to measure lattice constants. The measured lattice constant was equal to the distance divided by the number of lattice spacings contained in the dotted box. The distance between the left and right sides of the dotted box was displayed automatically. Then, we moved the left and right sides of the dotted box in the pop-up window to the center of the lattice stripes. The corresponding profile in the rectangular frame was displayed in a pop-up window. First, we drew a rectangular frame perpendicular to the measured lattice spacings on the TEM image. 2: an HRTEM image of Si acquired at a magnification of 790 k with 2048 × 2048 pixels). Generally, the lattice spacings are manually measured using the TEM integrated software DigitalMicrograph (Fig. Although the basic measurement principle has been verified by domestic and foreign researchers, several factors affecting the measurement results need to be addressed.Īccording to the measurement principle, the measurement of lattice spacings is critical for the accuracy of CD values. It became recognized especially after the incorporation of the Si lattice parameter in the CD measurement of integrated circuits, the measurement technique has attracted increasing attention from research institutions. TEM is a distinguished CD measurement method. The existing model-based library in our laboratory is only suitable for Au-based CD structures and CD values exceeding 200 nm. However, for each sample material and CD value, a corresponding library needs to be produced, which is a huge project and inflexible in the actual measurement. The CD values can be obtained within the range of the library data. After acquiring an SEM image, one should identify the best fit between the measured and simulated lines. This method, which is based on Monte Carlo simulation, generates a set of simulated secondary electron lines according to the designed input parameters. The model-based library for CD determination, which was written as an international standard (ISO/DIS 21466.1) in 2019, is a mainstream method. After the image is obtained, an appropriate algorithm is needed to extract the line features from the intensity profile. SEM is also widely applied for CD measurement owing to its high resolution and efficiency. Consequently, it is difficult to reconstruct the true shape of a specimen from a distorted image via morphological operations of dilation and erosion. However, it is difficult to accurately estimate the tip geometry because the tip wears during AFM scanning. The image is the convolution result between the actual surface topography and the tip geometry used during scanning. AFM can generate three-dimensional line width images with near-atomic spatial resolution. As described in the International Technology Roadmap for Semiconductors, the measurement uncertainty of the physical CD needs to be reduced to 0.7 nm by 2024 .Ĭurrently, numerous techniques have been developed for CD measurement, including atomic force microscopy (AFM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). With continuous reduction of the line feature size, requirements for measurement accuracy continue to increase. The nano line width (i.e., critical dimension, CD) is a crucial parameter in integrated circuits. Through experiments, we demonstrate the efficiency of the proposed method, which can be conveniently applied to accurately measure CDs in practical applications. The silicon crystal lattice constant guarantees the accuracy and traceability of the CD value. Finally, we estimate the standard CD value according to the half-intensity method. Then, the pixel span of the lattice spacing is calculated through the centre of gravity method. Through the two-dimensional inverse discrete Fourier transform of the central spot and a pair of symmetrical diffraction spots, an image containing only a set of lattice spacings is obtained. We develop an automatic and accurate method based on a two-dimensional discrete Fourier transform for measuring the lattice spacings from high-resolution transmission electron microscopy images. To accurately control the CD in manufacturing, a reasonable CD measurement algorithm is required. Line width (i.e., critical dimension, CD) is a crucial parameter in integrated circuits. ![]()
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