Through-focus technique for grating linewidth analysis with nanometer sensitivity

Ku, Yi-Sha; Liu, An-Shun; Smith, Nigel

doi:10.1117/1.2404959

Cited by 4 publications

(1 citation statement)

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“…This method utilizes a set of throughfocus optical images obtained by a conventional bright field microscope for the linewidth analysis. From 2005 onward, independent investigators successfully applied the same through-focus methodology for the linewidth measurement, primarily based on empirical analysis [3][4][5]. In this paper we present a comprehensive theoretical and experimental analysis based on application of the FM signature method for the linewidth measurements.…”

Section: Introductionmentioning

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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Section: Introductionmentioning

confidence: 99%