23 March 2009 CD-SEM parameter influence on image resolution and measurement accuracy
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Abstract
To determine scanning electron microscopy (SEM) image resolution, we processed a wafer-based sample that demonstrates directionally isotropic, yet high frequency, details after Fourier transformation [3],[4],[5]. We developed a new fully automatable method that outputs the SEM resolution, beam shape, and eccentricity as results. To verify the influence of further parameters (e.g., scanning conditions, acceleration voltage) on how the resolution influences critical dimension (CD) measurement accuracy, wafers with test structures of a wide range of nominal sizes of lines and contact holes were created. For all CD-SEM measurements, we used a calibrated CD-atomic force microscope (CD-AFM) as a reference [6]. CD-SEM measurements were done on different tool generations with variations in best achievable resolution. Experimental SEM resolution results will be shown, including influences of focus and stigmation. Both the wafer sample for resolution monitoring and a new Fourier-based evaluation method show significant sensitivity to variations in these parameters. By comparing the resolution results in the X and Y directions, astigmatism can be estimated. Even stigmation drifts less than normal daily variations can be observed. Differences in accuracy of less than 30nm to 500nm among different CD-SEM tool generations will be shown, which is revealing when trying to understand the quantitative influence of the SEM resolution on measurement accuracy.
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Benjamin Bunday, Uwe Kramer, "CD-SEM parameter influence on image resolution and measurement accuracy", Proc. SPIE 7272, Metrology, Inspection, and Process Control for Microlithography XXIII, 727204 (23 March 2009); doi: 10.1117/12.816251; https://doi.org/10.1117/12.816251
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