초록 ▼

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 linea

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.

대표청구항 ▼

An apparatus for deflecting a beam of light illuminating a spot on a surface, of the type having periodic and non-periodic features, comprising: an acousto-optic deflector having an entrance aperture and an exit aperture, opposite the entrance aperture, a linear FM signal generator electronically co

An apparatus for deflecting a beam of light illuminating a spot on a surface, of the type having periodic and non-periodic features, comprising: 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.