The limits of image-based optical metrology

Silver, Richard M.; Barnes, Brian M.; Attota, Ravikiran; Jun, Jau-Shi Jay; Filliben, James J.; Soto, Juan Carlos; Stocker, Michael T.; Lipscomb, Pete; Marx, Egon; Patrick, Heather J.; Dixson, Ronald G.; Larrabee, Robert D.

doi:10.1117/12.660289

Cited by 8 publications

(9 citation statements)

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“…Normal incidence illumination yielded only zero-order diffraction for those features, while oblique illumination lead to first-order diffraction which could be rocked into the collection optics. [5] Although the present overlay targets are fabricated with linewidths larger than found in the aforementioned arrays, the present features still were sensitive to the angular distribution of the illumination intensity. Figure 9 shows an idealized description of the Köhler illumination at the sample plane and its interaction with the overlay target.…”

Section: Discussionmentioning

confidence: 95%

“…For example, we have reported results from a set of techniques we refer to as scatterfield microscopy, essentially a combination of scatterometry and bright-field optical microscopy. [5][6][7] Freedom in target design can be coupled with engineered illumination to yield quantitative measurements of subwavelength dimensions. We have designed and constructed a new microscope at the National Institute of Standards and Technology (NIST) to investigate the illumination engineering required to bring in-chip overlay metrology to the 45 nm node and beyond.…”

Section: -mentioning

confidence: 99%

“…[5] As devices are already sized below the diffraction limit of visible light, overlay metrology is trending away from edge-based measurement techniques towards the characterization of unique diffractionbased signatures of sub-micrometer targets. For example, we have reported results from a set of techniques we refer to as scatterfield microscopy, essentially a combination of scatterometry and bright-field optical microscopy.…”

Section: -mentioning

confidence: 99%

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Illumination optimization for optical semiconductor metrology

2006

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Uniform sample illumination via Köhler 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.[1] 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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Section: Discussionmentioning

confidence: 95%

Section: -mentioning

confidence: 99%

Section: -mentioning

confidence: 99%

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Illumination optimization for optical semiconductor metrology

2006

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“…Subsequent to the study presented here, a major cause of this effective lower INA on the tool used in this work was identified as significant differences in the intensity transmission of the "s" and "p" polarized light at larger incident angles. For more information on this, refer to Silver et al [18].…”

Section: B Focus Metric Signature Experiments and The Simulations Comentioning

confidence: 99%

Linewidth measurement technique using through-focus optical images

2008

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We present a detailed experimental study of a new through-focus technique to measure critical dimension linewidth with nanometer sensitivity using a bright field optical microscope. This method relies on analyzing intensity gradients in optical images at different focus positions, here defined as the focus metric (FM) signature. The contrast of an optical image of a structured target, where a particular structure is repeated several times, varies greatly as it is moved through-focus if the spacing between the structures is such that the scattered field from the features interferes. Complex, distinguishable through-focus optical response occurs under this condition giving rise to the formation of several cyclic high and low contrast images. As a result it exhibits several FM signature peaks as opposed to a single FM peak for structures nearly isolated. This complex optical behavior is very sensitive to the dimensions of the target geometry. By appropriately analyzing the through-focus optical image, information can be obtained regarding the target. An array of lines is used as a structured target. Linewidth measurements were made by using experimental through-focus optical data obtained using a bright field microscope and simulated optical data. The optical results are compared with reference metrology tools such as a critical dimension atomic force microscope and critical dimension scanning electron microscope.

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“…These measurements were analyzed with rigorous electromagnetic scattering and regression methods, and uncertainties were calculated. Prior to these measurements, attempts were made to model images and line profiles acquired through focus [5,6]. This required modeling the complete threedimensional electromagnetic field as it was imaged as a function of focus position.…”

Section: Introductionmentioning

confidence: 99%

Fourier domain optical tool normalization for quantitative parametric image reconstruction

et al. 2013

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There has been much recent work in developing advanced optical metrology methods that use imaging optics for critical dimension measurements and defect detection. Sensitivity to nanometer-scale changes has been observed when measuring critical dimensions of subwavelength 20 nm features or when imaging defects below 15 nm using angle-resolved and focus-resolved optical data. However, these methods inherently involve complex imaging optics and analysis of complicated three-dimensional electromagnetic fields. This paper develops a new approach to enable the rigorous analysis of three-dimensional, through-focus, or angle-resolved optical images. We use rigorous electromagnetic simulation with enhanced Fourier optical techniques, an approach to optical tool normalization, and statistical methods to evaluate sensitivities and uncertainties in the measurement of subwavelength three-dimensional structures.

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The limits of image-based optical metrology

Cited by 8 publications

References 0 publications

Illumination optimization for optical semiconductor metrology

Illumination optimization for optical semiconductor metrology

Linewidth measurement technique using through-focus optical images

Fourier domain optical tool normalization for quantitative parametric image reconstruction

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