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2 June 2000 Dimensional metrology system of shape and scale in pattern transfer
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Traditionally a single CD width parameter is expressed in a metrology measurement of an amplitude modulated waveform. The measurement is the result of a single and specific edge detection algorithm applied to the waveform. There is no distinction between scale and shape (profile). Feedback and feedforward use of metrology information requires such a distinction as well as some sense of how far to trust the data in making process decisions. Typical metrology waveforms are obtained from optical imaging (overlay, mask, end of line truncation), scanning mechanical probe, optical diffraction, ellipsometry and SEM tools. This system we describe separately determines shape and scale of linewidth metrology by combining an entire range of edge detection parameters in the space domain. It specifically is used to monitor scale and shape changes from a basic template derived from the process margin. It can also be used to determine what portion of the linewidth or profile has deviated from the template in a diagnostic sense. The method repeatedly measures all possible features from the 1D or 2D waveforms stored in memory. Derived values of characteristic features are determined from the string of data obtained from the edge detection parameters. (sidewall width and angle, footing, topping, space features, 2D roughness, inflection positions) First the data is analyzed to confirm that it is valid and supports the requirements of the technology and level. Only valid data of rated quality is utilized. The system output is a group of three values. Scale (nm), Quality Index (0-1), Descriptive Bin (Deviation of shape and scale denoted A-Z). The Quality Index is a weighted consideration of template deviation (Both shape and measure error). i.e. CD feature equals 0.23 micrometer, 0.67, F (footing) This paper describes our attempts to find ways of extracting the information needed to monitor the pattern transfer process from CD SEM waveforms. The basic idea however applies to all metrology waveforms that approximate the topographical contours of a feature. Multiple Parameter Characterization (MPC) in the space and frequency domain as well as whole, partial and derivative waveform correlation are the basic tools utilized for quality and shape determination. The core principle is that different physical features are more strongly expressed in different parts of the SEM intensity traces. Some of these physical features are more predictive of how the pattern transfer occurs than others. Modern linewidth metrology systems require that the distinction be made between scale and shape. Automated inspection systems require that this be carried out quickly and robustly for it to have any production impact. Metrologists have always made such distinctions in evaluating features by utilizing all manner of direct and indirect observation of the monitored process. Unfortunately the abilities of the metrologist are not yet available as a supported automated system running 24 X 7.
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John M. McIntosh, Brittin C. Kane, Erik C. Houge, Catherine B. Vartuli, and Xin Mei "Dimensional metrology system of shape and scale in pattern transfer", Proc. SPIE 3998, Metrology, Inspection, and Process Control for Microlithography XIV, (2 June 2000);

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