Order selected overlay metrology
First Claim
1. An optical apparatus for measuring a characteristic of a semiconductor target, comprising:
- an illumination system for generating and directing illumination rays towards a semiconductor target via an illumination path; and
an imaging system for directing light scattered from the semiconductor target in response to the illumination rays, the imaging system comprising;
an image sensor for forming an image from scattered light;
one or more optical components that are arranged to direct the scattered light to the sensor via an imaging path; and
a tunable spatial modulation device for selectively directing specific diffraction orders of the scattered light towards the image sensor while blocking selected other diffraction orders of the scattered light from reaching the image sensor.
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Accused Products
Abstract
Disclosed are apparatus and methods for measuring a characteristic, such as overlay, of a semiconductor target. In general, order-selected imaging and/or illumination is performed while collecting an image from a target using a metrology system. In one implementation, tunable spatial modulation is provided only in the imaging path of the system. In other implementations, tunable spatial modulation is provided in both the illumination and imaging paths of the system. In a specific implementation, tunable spatial modulation is used to image side-by-side gratings with diffraction orders ±n. The side-by-side gratings may be in different layers or the same layer of a semiconductor wafer. The overlay between the structures is typically found by measuring the distance between centers symmetry of the gratings. In this embodiment, only orders ±n for a given choice of n (where n is an integer and not equal to zero) are selected, and the gratings are only imaged with these diffraction orders.
38 Citations
27 Claims
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1. An optical apparatus for measuring a characteristic of a semiconductor target, comprising:
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an illumination system for generating and directing illumination rays towards a semiconductor target via an illumination path; and an imaging system for directing light scattered from the semiconductor target in response to the illumination rays, the imaging system comprising; an image sensor for forming an image from scattered light; one or more optical components that are arranged to direct the scattered light to the sensor via an imaging path; and a tunable spatial modulation device for selectively directing specific diffraction orders of the scattered light towards the image sensor while blocking selected other diffraction orders of the scattered light from reaching the image sensor. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A method of measuring a characteristic of a semiconductor target, comprising:
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determining a set of diffraction orders to use for imaging the semiconductor target; configuring a metrology tool so as to image the target using the determined set of diffraction orders; collecting an image of the target that is formed from the determined set of diffraction orders; and determining and storing an overlay error based on the collected image. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
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22. At least one computer readable storage medium having computer program instructions stored thereon that are arranged to perform the following operations:
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determining a set of diffraction orders to use for imaging the semiconductor target; configuring a metrology tool so as to image the target using the determined set of diffraction orders; collecting an image of the target that is formed from the determined set of diffraction orders; and determining and storing an overlay error based on the collected image. - View Dependent Claims (23, 24, 25, 26)
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27. An optical apparatus for measuring a characteristic of a semiconductor target, comprising:
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an illumination system for generating and directing illumination rays towards a semiconductor target via an illumination path, wherein the illumination system includes a first tunable spatial modulation device for producing coherent modulated illumination rays that are directed towards the semiconductor target; and an imaging system for directing light scattered from the semiconductor target in response to the selectively modulated illumination rays, the imaging system comprising; an image sensor for forming an image from scattered light; one or more optical components that are arranged to direct the scattered light to the sensor via an imaging path; and a second tunable spatial modulation device positioned at a pupil of the imaging path for selectively directing specific diffraction orders of the scattered light towards the image sensor while blocking selected other diffraction orders of the scattered light from reaching the image sensor.
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Specification