NEW FITTING ALGORITHM FOR SHAPE-SENSITIVE LINEWIDTH METROLOGY.Is a scanning electron microscope scan·ning electron microscope n. Abbr. SEM An electron microscope that forms a three-dimensional image on a cathode-ray tube by moving a beam of focused electrons across an object and reading both the electrons scattered by the object and (SEM) image of a semiconductor line produced by a rectangular rec·tan·gu·lar adj. 1. Having the shape of a rectangle. 2. Having one or more right angles. 3. Designating a geometric coordinate system with mutually perpendicular axes. line of width w, or by a non-rectangular line of different width w'? When the lines are less than 100 nm wide and nanometer-scale accuracies are the goal, distinguishing between the different possibilities is crucial to linewidth metrology. NIST (National Institute of Standards & Technology, Washington, DC, www.nist.gov) The standards-defining agency of the U.S. government, formerly the National Bureau of Standards. It is one of three agencies that fall under the Technology Administration (www.technology. scientists are implementing a scheme to make distinctions that are based upon matching measured images to a library of images corresponding, as determined by Monte Carlo Monte Carlo (môNtā` kärlō`), town (1982 pop. 13,150), principality of Monaco, on the Mediterranean Sea and the French Riviera. model calculations, for a variety of line shapes and widths. Matching images to the library will be done in three parts: * a model function that computes the expected image for a given set of parameters that describe the state of the instrument and the width and shape of the line, * a residuals function that determines the difference between this model image and the one actually observed, and * a nonlinear A system in which the output is not a uniform relationship to the input. nonlinear - (Scientific computation) A property of a system whose output is not proportional to its input. least squares fitting algorithm that adjusts model parameters to determine the best match, as judged by minimizing the sum of squares of residuals. The new system has several improved capabilities compared to the system in place late last year: * It can fit entire images (not merely single line scans) in a single fitting operation. This allows one to realistically require instrument parameters to be fixed for the whole image, instead of varying from line to line. * It can fit any number of line features per line scan. This means it can handle the industrially important case of dense lines, instead of only isolated lines. * Parameters can be "pinned." A pinned parameter is given a fixed value that is not varied for fitting purposes. This provides a convenient way to use calibration calibration /cal·i·bra·tion/ (kal?i-bra´shun) determination of the accuracy of an instrument, usually by measurement of its variation from a standard, to ascertain necessary correction factors. data determined from an independent measurement. For example, if the instrument's beam diameter The beam diameter of an electromagnetic beam is the diameter along any specified line that is perpendicular to the beam axis and intersects it. For this purpose, the diameter is often defined as the distance between the two diametrically opposite points at which the irradiance is a , brightness, and contrast are known independently, these can be pinned to their known values, leaving sample geometry as the only thing that can be adjusted to produce a fit. |
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