Variable spot-size scanning apparatus
First Claim
1. An apparatus for scanning a patterned wafer of the type having periodic and non-periodic features comprising:
- means for providing a beam scanning the surface of a wafer, with a spot; and
means for varying the dimension of the spot with a first dimension for periodic features and a second dimension for non-periodic features.
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Accused Products
Abstract
An apparatus for both deflecting a beam of light illuminating a spot on a surface and varying the size of the spot, electronically, without changing any system components. The apparatus includes an acousto-optic deflector driven with a linear FM signal produced by a chirp signal generator. The linear FM signal is characterized with a dispersion rate, and the chirp signal generator includes a chirp dispersion selector to vary the dispersion rate. A beam of collimated light passes through the acousto-optic deflector and appropriate focusing optics image the beam onto a spot in a nominal focal plane. The chirp dispersion selector sets the dispersion rate in accord to a nominal rate, resulting in the beam illuminating a spot in the focal plane. Generally, the focal plane coincides with a wafer surface, of the type having periodic and non-periodic features on it. The spot size may be varied from that of a diffraction limited spot to a spot whose maximum size is system dependent. The spot size varies as a result of changing the dispersion rate of the chirp signal. The spot size may vary as it is scanned, or may remain fixed during the inspection of a wafer. In this manner, inspection by periodic feature comparison may be implemented when it proves advantageous. Alternatively, a larger spot may be obtained when periodic feature comparison would provide no benefit, and spatial filtering would achieve an enhanced signal/background.
186 Citations
36 Claims
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1. An apparatus for scanning a patterned wafer of the type having periodic and non-periodic features comprising:
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means for providing a beam scanning the surface of a wafer, with a spot; and means for varying the dimension of the spot with a first dimension for periodic features and a second dimension for non-periodic features. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. An apparatus for deflecting a beam of light illuminating a spot on a surface, of the type having periodic and non-periodic features, comprising:
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an acousto-optic deflector having an entrance aperture and an exit aperture, opposite the entrance aperture, a linear FM signal generator electronically coupled to said acousto-optic deflector, a chirp correction lens positioned proximate to said exit aperture, means, electronically coupled to said generator, for varying a dispersion rate of a linear FM signal in accord with the presence of periodic and non-periodic features, wherein the beam passes through the acousto-optic deflector from the entrance aperture to the exit aperture, illuminating a spot on the surface with the size of the spot varying in accordance with the dispersion rate. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15)
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16. An optical scanning system for defect and foreign matter detection on a surface comprising,
means for producing a beam of light, means for directing the beam onto a sample surface of the type having locations with periodic and non-periodic features, producing an illuminated spot, means for scanning the spot across the sample surface, means for varying the spot size in accord with the locations of the periodic and non-periodic features, and means for detecting light scattered from the surface and generating signals representing the light impinging thereon.
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26. A method for scanning a patterned wafer of the type having periodic and non-periodic features comprising:
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providing a beam scanning the surface of a wafer with a spot, and varying the dimension of the spot with a first dimension for periodic features and a second dimension for non-periodic features. - View Dependent Claims (27)
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28. A method for varying a size of a spot produced by a beam of light illuminating a surface comprising the steps of:
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providing an acousto-optic deflector, driving the acousto-optic deflector with a linear FM signal, and varying a dispersion rate of the linear FM signal. - View Dependent Claims (29, 30, 31)
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32. An optical scanning method for anomaly detection on a surface comprising,
directing a light beam onto a sample surface to produce an illuminated spot, passing the beam through and supplying a chirp signal to an acousto-optic deflector in order to scan the spot across the sample surface, and providing a control electrical signal for controlling the spot size by altering a dispersion rate of the chirp signal.
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33. A method for scanning a patterned surface of the type having periodicity characteristics, comprising:
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providing a light beam to illuminate the surface at a spot, scanning the beam to cause the spot to move across the surface, and varying a dimension of the spot with the periodicity characteristics of the surface. - View Dependent Claims (34)
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35. An apparatus for deflecting a beam of light illuminating a spot on a surface, comprising:
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an acousto-optic deflector, a chirp signal generator supplying a chirp signal to said acousto-optic deflector, means for varying a dispersion rate of the chirp signal. - View Dependent Claims (36)
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Specification