Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Reexamination Certificate
2004-02-19
2004-11-30
Pyo, Kevin (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
C250S201200, C359S381000, C356S609000
Reexamination Certificate
active
06825454
ABSTRACT:
BACKGROUND OF THE INVENTION
a) Field of the Invention
The invention is directed to an autofocusing device for an optical instrument, in particular for a microscope.
b) Description of the Related Art
Autofocusing devices are used where there is a need for bringing an object that is to be observed or to be examined into a position that is as precise as possible relative to the observation instrument, in particular into the focal point of the observation instrument. A large number of commonly known autofocusing devices use their own illumination source, the light of which is directed onto the object and evaluated after interaction with the object for the purposes of determining a distance or a deviation from a reference position. When the distance or the deviation from the reference position is known, an automatic position correction can be carried out.
From the state of the art, autofocusing devices for optical instruments are known which essentially differ with regards to the following performance parameters:
Resolution in direction of the optical axis (subsequently referred to as the z-axis),
depth of the capture or working range,
whether generating a directional signal for a correcting adjusting movement is possible,
attainable measuring speed.
The triangulation methods often used for determining distances permit a relatively large capture range, but they are limited to values to the order of approximately 300 nm with regards to the resolution along the z-axis, and therefore unsuitable for the optical inspection of semiconductor components (wafers), since for these resolutions to values to the order of approximately 50 nm with a capture range of a several micrometers are necessary.
Autofocusing devices which are, for example, used in CD-players have a relatively large capture range and furthermore attain a high z-resolution, but only if the surface to be measured has very good reflective properties, since otherwise the z-resolution in particular drops off sharply.
The aforementioned autofocusing devices usually direct laser light onto the object that is to be examined, but if the wavelength spectrum of the main system differs a lot from the autofocusing system, systematic focusing errors result which amongst other things depend on the material properties and the microstructure, for example a surface coating, of the object to be examined.
OBJECT AND SUMMARY OF THE INVENTION
Based on this, it is the primary object of the invention to create an autofocusing device which permits high focusing precision and high focusing speed combined with simple construction.
For an autofocusing device for which the illuminating light is directed through imaging optics onto an object moving in a direction at least approximately vertical to the optical axis of the imaging optics, this object is met by arranging a diaphragm device in the illumination ray path between illumination source and imaging optics with at least one diaphragm opening which extends in a direction aligned with the direction of movement of the object; by arranging a receiving device in the measuring light ray path for the measuring light coming from a measuring location on the object, which receiving device has separate reception areas that can be evaluated individually and that are arranged in a row beside each other in a direction aligned with the direction of movement of the object; by inclining the diaphragm opening relative to the optical axis of the illumination ray path or the receiving areas arranged in a row beside each other relative to the optical axis of the measuring ray path by an angle such that 0 degrees<&agr;<90 degrees by means of which the image of the diaphragm opening is inclined relative to the receiving areas while the receiving device and the diaphragm opening are positioned relative to each other in such a way that characteristic measuring values are measured by the receiving areas when the measuring location is in or near the in-focus position; by the presence of a synchronous control which initializes the sequential reading of the measuring results in the receiving areas, wherein at the time (t
1
) of read-out the receiving device (e
1
) the measuring location is in a position (p
1
), at the time (t
2
) of read-out the receiving device (e
2
) the measuring location is in a position (p
2
) and so forth, and an evaluating device is provided which compares the measured values read from the receiving areas with desired values and from these generates signals for the optical instrument.
Preferably, the evaluation device is to be designed for the generation of adjusting signals for an adjusting device by means of which the direction of movement of the object into the focal plane of the imaging optics is initialized if there is a deviation between the read out measuring values and the stored desired values.
The imaging optics can nonetheless also be designed for the determination of other command signals for the optical instrument, for example for the activation of an image recording device and similar things.
Because of the inclination of the diaphragm device relative to the optical axis of the illuminating light or the inclination of the receiving device relative to the optical axis of the measuring light, an intensity distribution results on the receiving device which is aligned with the direction of movement of the object and which is characteristic for the position of the measuring location relative to the imaging optics.
The path of movement of the measuring location intersects with an imaginary plane the location of which is determined by the fact that if a mirror were to be inserted into the optical system in this location it would effect an optical conjugation of areas on the diaphragm device with assigned receiving areas and that the characteristic measuring values can be read out when the moving measuring location touches this imaginary plane.
By means of this, the autofocusing device according to the invention permits multiple measurements of the same measuring location on one object by means of one slit aperture or of a row of individual diaphragms, so that a set of data is available for the evaluation of the focal position. Such multiple measurements are particularly advantageous if the surface structure of the objects to be examined is highly fissured.
Advantageously, a device for the continuous advance of one or more objects can be present, which device is coupled to a synchronous control, wherein the direction of advance should be at right angles to the optical axis of the imaging optics.
The arrangement according to the invention described so far is more suited for the gathering of measuring values relating to the focal position of a moving object or of a measuring location; such an operating mode, where the imaging optics and the object are moving relative to each other, is here to be referred to as a “dynamic” operating mode, wherein the movement can, for example, be continuous or also a stepped advance movement of the object.
For a “static” operating mode, on the other hand, where the image information is to be gained about measuring locations on objects which are at rest relative to the imaging optics, the following arrangement according to the invention is better suited.
For this autofocusing device, the illuminating light is directed through imaging optics onto the surface of an object at rest; a diaphragm device is provided in the ray path between the illumination source and the imaging optics which has at least one diaphragm opening and extends in a preferred direction V; a receiving device for the measuring light coming from the measuring object is present which has receiving areas arranged in a row in a direction V′ corresponding to the preferred direction V and which can be evaluated individually; furthermore, the diaphragm opening and the optical axis of the illumination ray path or the receiving areas arranged in a row and the optical axis of the measuring ray path form an angle such that 0 degrees<&agr;<90 degrees, so that the image of the diaphragm device
Czarnetzki Norbert
Hagemann Eckard
Kurosawa Toshiro
Mack Stefan
Scheruebl Thomas
Carl Zeiss Microelectronic Systems GmbH
Pyo Kevin
Reed Smith LLP
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