5 September 2006 Illumination optimization for optical semiconductor metrology
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Abstract
Uniform sample illumination via Kohler illumination is achieved by establishing a pair of conjugate focal planes; a light source is focused onto the condenser lens back focal plane while the image of the field aperture is focused at the plane of the specimen. Placement accuracy of these elements along the optical axis will determine the quality of the spatial homogeneity of the illumination in the sample plane. Imaging is therefore inherently sensitive to the tolerance of this alignment. Measuring three-dimensional features on semiconductor wafers has demonstrated an additional requirement for angular illumination homogeneity, as this is critical for robust matching between experimental results and numerically modeled results. We outline our techniques for aligning a custom-built microscope that features a 12 mm diameter conjugate back focal plane, beginning with the establishment of an optical axis based upon the objective lens. We then illustrate the techniques used to establish the quantitative degree of spatial and angular homogeneity through quantifying the resultant illumination while apertures are scanned across this conjugate back focal plane. Examples of the correlation between homogeneity and optical metrology are provided.
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Bryan M. Barnes, Bryan M. Barnes, Lowell P. Howard, Lowell P. Howard, Richard M. Silver, Richard M. Silver, } "Illumination optimization for optical semiconductor metrology", Proc. SPIE 6289, Novel Optical Systems Design and Optimization IX, 62890P (5 September 2006); doi: 10.1117/12.681064; https://doi.org/10.1117/12.681064
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