Optics: measuring and testing – Inspection of flaws or impurities – Transparent or translucent material
Reexamination Certificate
1998-12-09
2002-06-04
Font, Frank G. (Department: 2877)
Optics: measuring and testing
Inspection of flaws or impurities
Transparent or translucent material
Reexamination Certificate
active
06400455
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an observation apparatus, and in particular to an observation apparatus for observing patterns such as circuits and characters formed in the surface or near the surface of semiconductor wafers and insulation substrates such as glass, ceramic and the like.
2. Description of the Prior Art
Up to now, during the manufacturing process of semiconductor integrated circuits, observation of patterns such as numbers, characters and circuits provided on the surface of semiconductor wafers (hereinafter referred to simply as “wafer”), liquid crystal substrates, glass, ceramic or resin have been carried out by direct visual inspection or by the use of a camera or microscope. For example, during the manufacturing process, the identification code provided on a wafer are read, and then a predetermined process is carried out in accordance with such identification code.
In observation devices known in the prior art, light source of a fluorescent lamp, fiber optics illumination or a parallel light source through a lens is used to illuminate an observation object in order to perform observation.
In this connection, the present inventor previously proposed (in Japanese Laid-Open Patent Application No. HEI-8-327554) an illumination device for obtaining a high-contrast image, in which light from a light emitting portion is shone by means of an optical element onto an observation object, with the light emitting portion being movable with respect to the optical element in order to make it possible to adjust the illumination angle of the light shining onto the observation object.
SUMMARY OF THE INVENTION
With the invention described above, remarkable results were obtained when the light emission portion was moved to obtain optimum illumination, but it isn't always clear which way the light emission portion should be moved to obtain optimum illumination. Thus, it is an object of the present invention to provide a light source arrangement which makes it easy to obtain an optimum illumination.
In this connection,
FIG. 1
shows the principle of the observation apparatus according to the present invention for overcoming the problems described above. As shown in this drawing, the observation apparatus shines light from a light source through an optical element (converging lens
11
) and onto an observation object
3
a,
and a light source portion
13
is equipped with a first light-emitting body
13
a,
second light-emitting bodies
13
b,
third light-emitting bodies
13
c
and
13
d
and fourth light-emitting bodies
13
e,
and all these light-emitting bodies are arranged at or near the optical axis
11
b
of the converging lens
11
within a light source plane
110
a
arranged at or near the front focal position of the converging lens
11
. Further, the light-emitting bodies
13
a
~
13
e
are selectively activated to illuminate the observation object
3
a,
and the light reflected from or passing through the observation object is received by a light-receiving portion
7
a
to be used in observing the observation object
3
a.
If the light emitted from any one of the light-emitting bodies strikes the observation object
3
a
at an incidence angle &phgr; with respect to the optical axis
11
b,
then the incidence angle &phgr; will become larger as the distance between the light-emitting body and the optical axis
11
b
increases. In this regard, the incidence angle &phgr; is easily measured based on the focal point distance of the converging lens
11
and the position of the light-emitting body.
The first light-emitting body
13
a
is arranged on the optical axis
11
b,
and the second, third and fourth light-emitting bodies are arranged at increasing distances away from the optical axis
11
b
in that respective order. In this connection,
FIG. 2
is a series of drawings showing the relationship between light source images
14
a
~
14
e
of each of the light-emitting bodies and the light-receiver portion
7
a
and the image of the observation object
3
a
formed on the light-receiver portion
7
a.
Namely, the light source images
14
a,
14
b,
14
c,
14
d
and
14
e
correspond respectively to the light source images of the light-emitting bodies
13
a,
13
b,
13
c,
13
d
and
13
e.
In this regard, each of the light-emitting bodies carries out the following illumination.
(1) In general, in bright field illumination, if the observation object
3
a
and the observation plane were a plane mirror, the light from the light-emitting body arranged on the optical axis of the converging lens would reflect off such plane mirror and pass through an image-forming lens
17
at the light-receiving side along a direction aligned with the optical axis of the image-forming lens
17
, whereby the light source image will illuminate the entire surface of the light-receiving portion. In the present invention, the first light-emitting body
13
a
carries out this type of illumination, and the light source image at such time is like that shown in FIG.
2
A. Now, in the case where this type of illumination is to be used for characters formed in a wafer by laser etching or the like, if there is no image noise, such characters will generally be observed as dark forms in the shining light source image. However, if there are slight irregularities on the wafer or resist, it is possible for such irregularities to be observed as dark lines (image noise).
(2) By moving the light source to a position slightly away from the optical axis without changing the state in which the light source image covers the entire surface of the light-receiving portion, the present inventor discovered that it is possible to eliminate the dark lines (image noise) due to the above-mentioned irregularities. In the present invention, the second light-emitting bodies
13
b
carry out this type of illumination, with a light source image being formed as shown in FIG.
2
B. In this way, there is also a bright field illumination state in which the light source is positioned slightly away from the optical axis, and it was confirmed that this type of illumination makes it possible to eliminate image noise. The incidence angle &phgr; of this illumination depends on many conditions of the optical system, but a value around &phgr;=20° serves as a good example.
(3) The third light-emitting bodies
13
c
and
13
d
are positioned farther away from the optical axis than the light-emitting bodies
13
b,
with the light-emitting bodies
13
d
being positioned farther away from the optical axis than the light-emitting bodies
13
c,
and the incidence angles of the light emitted from the light-emitting bodies
13
c
and
13
d
cause their respective light source images 14c and
14
d
to cover only a partial portion of the light-receiving portion
7
a,
as shown in
FIGS. 2C and 2D
. As for the difference between the illumination of the light-emitting bodies
13
c
and the light-emitting bodies
13
d,
it should be noted that illumination by the light-emitting bodies
13
c
involves light from the light source striking the observation object
3
a
(hereinafter referred to as “incomplete bright field illumination”; see FIG.
2
C), and illumination by the light-emitting bodies
13
d
involves light from the light source not striking the observation object
3
a
(hereinafter referred to as “incomplete dark field illumination”; see FIG.
2
D). In this connection, either of these types of illumination were not used in the prior art because they were considered as incomplete illumination. However, the present inventor confirmed that even with these types of incomplete illumination, it is possible to obtain optimum contrast depending on the properties of the observation object and the incidence angle from the light source. The incidence angle &phgr; of these types of illumination depend on many conditions of the optical system, but a value around &phgr;=5° serves as a good example for the case of incomplete bright field illumination (light-emitting bodies
13
c
), and a value arou
Kobayashi Kenji
Kurokawa Shuji
Font Frank G.
Lintec Corporation
Marger & Johnson & McCollom, P.C.
Stafira Michael P.
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