Optical: systems and elements – Lens – With viewed object or viewed field illumination
Reexamination Certificate
2000-05-05
2002-03-12
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
With viewed object or viewed field illumination
C359S642000, C356S445000, C356S600000, C356S612000, C356S237200
Reexamination Certificate
active
06356399
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a light illuminating method, a surface examining method, and apparatuses for performing these methods.
BACKGROUND OF THE INVENTION
The applicant has already developed and filed an improved surface examining method and an improved apparatus for performing the method, as follows (U.S. Pat. No. 5,737,074).
The surface examining apparatus
10
comprises a light illuminating device
11
and an observation device
12
, as shown in FIG.
12
. The light illuminating device
11
comprises a light source
11
a
, an aperture stop
11
b
, a half mirror and a lens
11
d
for illumination. The light beam emitted out of the light source
11
a
is changed to a substantial point light source by the aperture stop
11
b
. The light beam from the point light source is reflected by the half mirror and is collimated through the lens
11
d
for illumination, to illuminate an object
13
to be measured. The observation device
12
comprises a lens system
12
a
for observation (the lens
11
d
for illumination also constitutes a part of the lens system
12
a
for observation), and an aperture stop
12
b
which is located at the position of a stop of the lens system
12
a
for observation. The light beam reflected by the object
13
to be measured forms an image on an image pickup part
14
through the observation lens system
12
a
and the aperture stop
12
b
. The observation lens system
12
a
and the aperture stop
12
b
constitutes an object-side telecentric optical system. In the specification, the meaning of the term “point light source” includes not only a light source which is considered to be a perfect point but also one having a size to a small degree.
In the surface examining apparatus
10
, if it is assumed that the light source is considered to be a perfect point one (i.e., the illumination angular aperture is approximately 0°) and the object-side angular aperture of the aperture stop
12
b
is also approximately 0°, when observing the object
13
to be measured having an approximate flat surface without inclining, the image of the flat surface of the object
13
to be measured comes to have a luminance of 100% and the image of the slope of an irregularity of the object
13
comes to have a luminance of 0%.
On the other hand, if it is assumed that the light source is considered to be a substantial point one and has a predetermined illumination angular aperture and the object-side angular aperture of the aperture stop
12
b
is also approximately 0°, the image of the slope of the irregularity of the object
13
comes to have a luminance which depends on the angle of the slope.
When observing the object
13
to be measured by inclining itself, it is possible to obtain the image of the slope of the irregularity of the object
13
having a luminance which depends on the angle of the slope by optionally changing the luminance of the flat surface of the object
13
, for example, to 0% or 50%.
Such an observation for the surface condition of the object
13
to be measured enables measurement of the presence or absence of irregularity and the condition of the irregularity on the basis of the luminance of the observed image.
However, as a result of observation for the surface condition of the object
13
to be measured, by using the above-described surface examining apparatus
10
, the existence of white or black portions (missing portion) from which portions of image were missed was recognized in a relatively wide range. Existence of such missing portions makes hard to examine the entirety of the surface of the object
13
to be measured, accurately.
The present invention was developed in view of the above-described problems. An object of the present invention is to provide a light illuminating method which is suited for, e.g., observation for the surface condition of the object to be measured and the like, to provide a surface examining method using the light illuminating method, and to provide apparatuses for performing these methods.
DISCLOSURE OF THE INVENTION
Generally, a lens has a spherical aberration. In practice, because of the spherical aberration, as shown in
FIG. 1
, after the light beams entered a lens
1
in parallel to the optical axis thereof and passed through the lens
1
, the light beams do not converge at a point. That is, the image formation points on the optical axis are shifted according to the heights of light beams entering the lens
1
. This is the longitudinal aberration caused by a spherical aberration. A longitudinal aberration view in the case is shown in the right portion of the Figure.
When using a lens which has a longitudinal aberration for an observation device, generally, a plurality of lenses are combined so as to have an aberration curve of the so-called full correction, as shown in
FIG. 2
, and an image pickup surface is set at a position of the optimal image point in the inside of the group of image formation points on the optical axis.
In a light illuminating device, although the lens therefor has no aberration curve of full correction, generally, a point light source is set at a position of the optimal image point, like the case of an observation device, instead of an image pickup surface.
FIG. 3
shows an example of such a light illuminating device. The right side in this Figure is a longitudinal aberration view in the light source side. The lens (lens for illumination)
2
shown in this figure has a characteristic with respect to a longitudinal aberration caused by a spherical aberration in the light source side, that the amount of shift from the paraxial image surface gradually decreases with an increase in height of light incidence into the lens
2
. In the light illuminating device, the point light source
3
is set at a position in the inside of the group of image formation points on the optical axis.
In the light illuminating device, by tracing back along the light beams after passing through the lens
2
, from the side of the point light source
3
, to study the change of inclination angle of the light beams with respect to the optical axis of the lens
2
in a direction perpendicular to the optical axis, it is understood that some points of inflection in the change of inclination angle of the lights, that is, points at which a plus sign or a minus sign of inclination of the lights is changed to the other, are created. When there is such a point of inflection in the change of inclination angle of the lights, the change of inclination angles of the lights reflected by an illuminated body (one having an approximately flat surface) comes also to have a point of inflection. In the case, the number of points of inflection in the change of inclination angle is the same as that of points of inflection in the change of reflection angle in a particular direction of the illuminated body.
When there are some points of inflection in the change of reflection angle of light beams in a particular direction of the illuminated body, an observation from a certain direction comes to give a noticeable unevenness of illumination. Therefore, existence of such a point of inflection is not preferable for a light illuminating device to which a uniform illumination on a surface to be illuminated is required. For a surface examining apparatus, unevenness of illumination on the surface to be illuminated leads to an inaccurate surface examination. Particularly, in a surface examining apparatus to observe the reflected light from an object to be measured through an aperture stop or an aperture, a phenomenon of partially missed image is often caused.
In such cases, when the number of points of inflection in the change of reflection angle in a particular direction of the illuminated body is one, it is possible to reduce unevenness of illumination or to optically cut the part of the image having unevenness of illumination, by changing the position of aperture in the light illuminating optical system or the observing optical system, or the like. However, when the number of points of inflection in the change of reflection angle i
Haga Kazumi
Sakai Motoshi
Ushiyama Zenta
Crowell & Moring LLP
NewCreation Co., Ltd.
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