Radiant energy – Photocells; circuits and apparatus – With circuit for evaluating a web – strand – strip – or sheet
Patent
1997-02-07
1998-09-01
Le, Que
Radiant energy
Photocells; circuits and apparatus
With circuit for evaluating a web, strand, strip, or sheet
250237G, 356375, G01N 2186
Patent
active
058013903
ABSTRACT:
Methods and apparatus are disclosed for performing detection of the position of a substrate, such as used in photolithography, with high precision by zero Nth-order detection. Alignment marks (grating marks) on the substrate are illuminated by coherent light beams comprising multiple wavelength components. Reflected light forms diffraction patterns that are detected by appropriate detectors. At least one level-difference detection circuit and at least one detected-position-correction circuit are provided, the former detecting grating-mark positions grating mark positions .DELTA.Xn' at respective wavelengths from light-quantity signals produced from the detectors, and the latter calculating relative level differences .delta..sub.n for the respective wavelengths at each grating mark, based on changes in the light-quantity signals accompanying relative scanning and based on design data for the grating marks. The apparatus also comprises a third circuit that calculates "final" positions of the grating marks by applying a factor corresponding to a situation resulting in the least amount of positional error to the positional determination as would otherwise be affected by asymmetry or resist-thickness variations of the grating mark.
REFERENCES:
patent: 5004348 (1991-04-01), Magome
patent: 5488230 (1996-01-01), Mizutani et al.
Le Que
Nikon Corporation
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