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Publication Citation: Test of CD-SEM Shape-Sensitive Linewidth Measurement

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Author(s): John S. Villarrubia; Andras Vladar; Michael T. Postek;
Title: Test of CD-SEM Shape-Sensitive Linewidth Measurement
Published: July 01, 2004
Abstract: In a model-based library (MBL) approach to scanning electron microscope (SEM) linewidth measurement, a library of simulation results for a range of lineshapes is searched for a match to the measured image of the unknown line. Compared to standard algorithms, MBL provides more information since it gives shape parameters in addition to linewidth. Because it is based upon a physical model of the electron scattering process in the line or gate, it is potentially more accurate than the standard methods. In previous measurements performed at NIST with a laboratory SEM, MBL showed good agreement with cross section measurements and improved repeatability compared to methods in common use today. We report here on results of a project to test the method on an industrial CD-SEM operating at International SEMATECH s fabrication facility.For this study CD-SEM images were obtained from polysilicon linewidth test patterns at several sites representing varying focus. The test patterns were also imaged in cross-section. The CD-SEM images were analyzed at NIST using the MBL method. This analysis produced a line profile (width and sidewall angles) from the CD-SEM images. These profiles were compared to the profiles obtained from cross-section images. In this first test of MBL for use with the CD-SEM, agreement for the sidewall angles was within about 1 degree, for linewidths within about 6 nm. Given the 2 nm pixel size of the cross-section images, this amount of disagreement represents 1 to 3 image pixels, a good level of agreement given the difficulty of insuring that cross section and top-down measurements were performed on the same part of the line. (7 references)
Citation: Test of CD-SEM Shape-Sensitive Linewidth Measurement
Volume: 5375
Keywords: critical dimension (CD),linewidth,model-based metrology,scanning electron microscopy (SEM)
Research Areas: Manufacturing, Metrology