Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Patent
1992-05-11
1993-01-26
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
356401, G01N 2186
Patent
active
051824558
ABSTRACT:
A method, usable with a workpiece having a predetermined grating pattern and to be exposed to a particular pattern through a projection lens system and by use of an exposure beam of a predetermined wavelength, for detecting a positional error of the workpiece. The method includes the steps of: providing a reference plate having first and second grating marks; irradiating the first and second grating marks with a radiation beam of a wavelength different from the predetermined wavelength, so that the first grating mark produces a first diffraction beam while the second grating mark produces a second diffraction beam; superposing, through the projection lens system, the first diffraction beam and the second diffraction beam upon one another on the predetermined grating mark to form a beam spot thereat; and detecting the positional error of the workpiece, on the basis of any deviation of the predetermined grating pattern relative to the beam spot.
REFERENCES:
patent: 4251160 (1981-02-01), Bouwhuis et al.
patent: 4631416 (1986-12-01), Trutna
patent: 4779001 (1988-10-01), Makosch
patent: 4870289 (1989-09-01), Sato et al.
patent: 4902133 (1990-02-01), Tojo et al.
Canon Kabushiki Kaisha
Nelms David C.
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