Optical: systems and elements – Compound lens system – Microscope
Reexamination Certificate
1999-09-14
2001-03-20
Sikder, Mohammad Y. (Department: 2872)
Optical: systems and elements
Compound lens system
Microscope
C359S369000, C359S372000, C359S385000, C359S388000, C359S389000, C359S390000
Reexamination Certificate
active
06204962
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a confocal microscope having a focal point detecting function and, more particularly, to a scanning confocal microscope for observing the surface of an object such as, especially, a semiconductor wafer, a photomask, and a semiconductor integrated device for a liquid crystal display.
2. Description of the Related Art
FIG. 9
is a drawing showing the construction of a conventional confocal microscope. In the figure, reference numeral
91
denotes a point light source,
92
a beam splitter,
93
an objective lens,
95
a stage on which an object is placed or to be placed,
96
a diaphragm for allowing the passage of only a part of light split by the beam splitter that converges on or in the vicinity of a focal point of the light so split, and
97
a light detector.
In operation, irradiated light from the point light source
91
passes through the beam splitter
92
and is focussed on the surface of the object
94
by the objective lens
93
, and a part of light reflected from the surface of the object is split by the beam splitter
92
so as to pass through the diaphragm
96
, and light that has passed through the diaphragm
96
is focussed on a detecting portion of the light detector
97
. The surface of the object
94
is observed by moving the point light source
91
so as to scan the entire surface of the object
94
and repeating the aforementioned procedure.
In order for light from the point light source
91
to be focussed on the object
94
, the stage
95
on which the object
94
is placed needs to be moved by hand so as to adjust the position of the object
94
.
In the above prior art, if there are irregularities on the surface of the stage
95
on which the object
94
is placed, or if there are irregularities on the surface of the object, or if the surface of the stage or object is warped, every time such is found, the position of the stage
95
has to be manually adjusted, this making the operation of a confocal microscope complicated and troublesome.
SUMMARY OF THE INVENTION
The present invention was made in view of the problem inherent in the prior art, and an object thereof is to provide a confocal microscope that can automatically focus light from a point light source on the surface of an object.
In order to attain the above object, the present invention provides a confocal microscope comprising a light detector for detecting reflected light from an object, a beam splitter for splitting light from the object into two directions, and a light quantity difference detecting means for detecting a difference in the quantity of light split by the beam splitter into two directions, wherein the light quantity difference detecting means detects a predetermined quantity of light as a difference in quantity of light when reflected light from the object is focussed on the surface of the light detector while, when reflected light from the object is not focussed on the surface of the light detector, it detects a value different from the predetermined quantity as a difference in quantity of light, and wherein the position of the object is controlled such that an output from the light quantity difference detecting means becomes the predetermined quantity.
The light quantity difference detecting means is provided with a diaphragm and another light detector for detecting the quantity of light that has passed through the diaphragm for each of the two directions, and it is preferable that a difference between the quantity of light detected by the diaphragm and the detector for one of the two directions and that detected by the diaphragm and the detector for the other direction becomes the aforementioned difference in quantity of light.
To be more specific, provided in accordance with a first embodiment of the present invention, a confocal microscope comprising a second beam splitter is provided along an optical path between a first beam splitter and a first light detector which already exist, a third beam splitter provided along an optical path split by the second beam splitter, a second light detector for detecting the quantity of light that has been split by the third beam splitter and has passed through the second diaphragm, a third light detector for detecting light that has passed through the third beam splitter and then passed the third diaphragm, and a comparator for comparing the quantity of light detected by the second light detector with that detected by the third light detector. The layout relationship between the second beam splitter, the third beam splitter, the second light detector and the third light detector is such that a difference between the quantity of light detected by the second light detector and that detected by the third light detector becomes a predetermined quantity when light is focussed on the surface of the first light detector, while when light is not focussed on the surface of the first light detector, the layout relationship is such that a difference between the quantity of light detected by the second light detector and that detected by the third light detector becomes a quantity of light different from the predetermined quantity. The position of an object is automatically controlled such that an output from a comparator becomes the predetermined quantity.
With this construction, light from the point light source is automatically focussed on the object whether or not the stage is warped or there are irregularities on the surfaces of the stage and the object, and therefore this makes the operation of the confocal microscope markedly simple.
Preferably, the predetermined quantity is zero, but it may be a finite offset quantity.
According to a second embodiment of the present invention, a fourth beam splitter is provided along an optical path between the first beam splitter and the third beam splitter, and beam splitters and light detectors having constructions identical to those used in the first embodiment may be provided for light split by the fourth beam splitter and light that has passed through it.
This construction expands a positional range within which the object can be moved along the optical axis.
According to a third embodiment of the present invention, an optical system may be inserted between the first beam splitter and the third beam splitter of the first embodiment for altering the focal point of light.
This also expands the positional range within which the object can be moved along the optical axis.
REFERENCES:
patent: 4-350818 (1992-12-01), None
patent: 5-232370 (1993-09-01), None
patent: 6-051206 (1994-02-01), None
patent: 7-174962 (1995-07-01), None
patent: 8-043717 (1996-02-01), None
patent: 8-178623 (1996-07-01), None
patent: 8-220418 (1996-08-01), None
patent: 9-325277 (1997-12-01), None
Christie Parker & Hale LLP
Sikd-er Mohammad Y.
Tokyo Seimitsu Co. Ltd.
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