A lens-testing system using a simple wavefront shearing interferometer is described. This simple cube interferometer has all the interferometric adjustments built in at manufacture. In contrast to most interferometric test systems, the wavefront shearing interferometer is inexpensive, portable, relatively insensitive to vibration, does not need laser illumination, and requires only a minimum of experimental time and operational expertise. Reading of the interferograms and subsequent data reduction require the major effort in testing with the wavefront shearing interferometer. However, with automatic scanning of the interferograms and a high-speed electronic computer to perform the analysis, the data reduction may be completely automated. Operation of the wavefront shearing interferometer is described together with the method of data reduction. Experimental results are also presented.
In the current linewidth-measurement program at the National Bureau of Standards, the primary measurement of micrometer -wide lines on black-chromium artifacts is made with an interferometer located in a scanning electron microscope (SEM). The data output consists of a line -image profile from the electron detector and a fringe pattern from the interferometer. A correlation between edge location and fringe location is made for both line edges to give the linewidth in units of the wavelength of a He -Ne laser.A model has been developed to describe the interaction of the electrons with the material line and thereby relate a threshold value on the SEM image profile to a selected point on the material line.An optical linewidth-measuring microscope is used to transfer the primary measurements to secondary measurement artifacts; these artifacts will be used to transfer the linewidth measurements to the integrated-circuit industry. Linewidth measurements from the SEM /interferometer system and the optical linewidth-measuring microscope are compared, and the level of measurement uncertainty for each system is discussed.
Precision Characteristics of Microscopes 7.2 Comparison of Linewidths Measured witJi Filar and Image-Shearing Eyepieces 8. Linewidth Calibration 8.1 Calibration Hierarchy 8.2 Preliminary Comparison of Linewidths Measured on SEM/Inferometer and Photometric Optical Microscope 8.3 Transfer of NBS Measurements to Industry 8.4 NBS/IC-Industry Collaborative Test 9.
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