The purpose of this paper is to define standard methods for effective and efficient image-based dimensional metrology for microlithography applications in the manufacture of integrated circuits. This paper represents a consensual view of the co-authors, not necessarily in total agreement across all subjects, but in complete agreement on the fundamentals of dimensional metrology in this application. Fundamental expectations in the conventional comparison-based metrology of width are reviewed, with its reliance on calibration and standards, and how it is different from metrology of pitch and image placement. We discuss the wealth of a priori information in an image of a feature on a mask or a wafer. We define the estimates of deviations from these expectations and their applications to effective detection and identification of the measurement errors attributable to the measurement procedure or the metrology tool, as well as to the sample and the process o fits manufacture. Although many individuals and organizations already use such efficient methods, industry-wide standard methods do not exist today. This group of professionals expects that, by placing de facto standard meth-odologies into public domain, we can help reduce waste and risks inherent in a "spontaneous" technology build-out, thereby enabling a seamless proliferation of these methods by equipment vendors and users of dimensional metrology. Progress in this key technology, with the new dimensional metrology capabilities enabled, leads to improved perform-ance and yield of IC products, as well as increased automation and manufacturing efficiency, ensuring the long-term health of our industry.
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.
Critical dimension scanning electron microscope metrology attempts to relate the electron intensity signal of the SEM tool to the actual size and shape of the feature measured. This intensity signal is frequently visualized and manipulated as a profile or waveform. A measurement of the size of a futuro involves the extraction of edge positions from this waveform. Traditional line width metrology ignores much of the effect of the variation of the shape of the feature measured on the waveform to be analyzed. Deducing the shape of a feature from the waveform requires interpretation of the shape of the waveform. Analysis of the CD SEM intensity signal allows one to not only measure the specific width of a feature but it also allows a better estimate as to the actual shape of the feature. Both photo and etch production process drift can be monitored, resulting in improved process and quality control before gross failures in metrology occur.
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