Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1987-01-12
1988-07-19
Westin, Edward P.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
250235, 250561, 350 691, G03B 4100, G03F 900
Patent
active
047587318
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method and an arrangement for aligning, examining and/or measuring two-dimensional objects situated on a table of a measuring machine, which table is displaceable at least on two coordinate directions extending perpendicular to one another.
By means of methods and arrangements of this type, structures of masks or wafers are, for example, recorded, aligned, examined and/or measured.
In this connection, from patent application No. P 35 12 615.9 an arrangement is known, in which, in order to determine the position of the objects in terms of coordinates by scanning by means of a light spot, the light fluxes generated from an illuminating device in each coordinate direction are combined in a beam path and imaged by a beam-collecting system in a common intermediate image plane. Moreover, they are deflected by an optical element according to the coordinate directions assigned to them, and are projected by an imaging system onto the objects to be measured in each instance. The light fluxes reflected by the respective object are converted, by at least one photoelectric detector system, into electrical measurement signals, from which the quantities corresponding to the objects are determined in a computer, as a function of the deflection of the light spot and of the position of the table of the measuring machine.
The disadvantage of the described device is that the measurement in the individual coordinate directions can take place only in succession, and that, as a consequence of the light diffraction occurring in the case of the imaging of the very slender light spots, the position of the edges of the object can be determined only with limited accuracy.
In order to overcome these disadvantages, the object of the invention is accordingly to provide a method and an arrangement with which a simultaneous measurement can take place in both coordinate directions, the scanning accuracy is not detrimentally influenced by the imaging of very small light spots, and moreover a low thermal stressing of the object is assured.
The subject of the invention is a method of the initially mentioned type, in which light fluxes which are distinguishable according to associated coordinate directions are combined in a beam path, imaged in a common intermediate image plane and deflected by an optical element according to their coordinate directions, and are projected by an imaging system onto the object to be measured in each instance, and which is defined illumination of the respective object structures, beams, separated according to coordinate directions, on scanning means, in both coordinate directions, scanning of the object structure images by means of the scanning means into electrical measurement signals and recording, display, control and/or regulation.
The arrangement according to the invention for carrying out the method is defined by illuminating beam for each coordinate direction, which beam is conducted by means of deflecting means over the structures to be scanned, the imaging system and the deflecting means, causes imaging of the illuminated object structures which is separated according to coordinates, displacement of the image of the illuminated ohject structures in the two coordinate directions and by system for each coordinate direction and which converted light fluxes resulting from the scanning of the object structure images into electrical measurement signals.
Advantageous further developments of the method according to the invention and of the arrangement for carrying out the same are the subject of the subclaims.
The invention is schematically represented in an exemplary embodiment in the drawing and is described in greater detail below. In the drawing:
FIG. 1 shows a constructional diaqram of the arrangement according to the invention,
FIG. 2 shows a section through the arrangement along the line II--II in side elevation and
FIG. 3 shows a section through the arrangement according to the invention, along the line III--III.
In FIG. 1, an illumination slit is illuminated by the illuminatio
REFERENCES:
patent: 3865483 (1975-02-01), Wojcik
patent: 4165149 (1979-08-01), Suzuki et al.
patent: 4251160 (1981-02-01), Bouwhuis et al.
patent: 4647144 (1987-03-01), Finkel
Ernst Leitz Wetzlar GmbH
Westin Edward P.
Wieland Charles
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