Optics: measuring and testing – Inspection of flaws or impurities – Surface condition
Reexamination Certificate
2002-06-13
2004-09-14
Font, Frank G. (Department: 2877)
Optics: measuring and testing
Inspection of flaws or impurities
Surface condition
C356S237100, C250S559280
Reexamination Certificate
active
06791681
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and method for optically determining a range in which a foreign substance attached to a surface of an object, such as dirt, dust, an oil film, a fingerprint, a scratch, flaws, or the like, exists.
2. Description of the Related Art
In recent years, in the field of recording mediums, such as optical discs, magnetic discs, magnetic tapes, etc., in the field of color filters for a liquid crystal display and organic EL display, and in the field of electronic devices, such as semiconductor integrated circuit, or the like, the size of a component incorporated in a product has been reduced to a very small size. As already known in the above fields, along with a significant reduction in the component size, a foreign substance, such as dirt, dust, scratches, etc., attached to an electronic device, which did not cause a significant problem before, brings about a greater adverse influence on the production yield and performance during operation of the electronic device. Thus, an apparatus and method for detecting a foreign substance with high accuracy has heightened in demand. Conventionally, various proposals have been made for such an apparatus and method. One known example of such is a foreign substance detection apparatus disclosed in Japanese Laid-Open Publication No. 6-223384.
FIG. 15
shows a structure of a conventional foreign substance detection apparatus
1500
for use with an optical disc. The foreign substance detection apparatus
1500
includes: a light source
91
; an objective lens
92
; a quarter waveplate
94
; a polarized beam splitter
95
; a light receiving element
96
; an I-V conversion section
97
; and a sum signal generation circuit
98
. The light source
91
is, for example, a semiconductor laser. The light receiving element
96
is separated into a first light receiving element
96
A and a second light receiving element
96
B. The I-V conversion section
97
includes a first I-V conversion circuit
97
A and a second I-V conversion circuit
97
B.
Next, an operation of the foreign substance detection apparatus
1500
for detecting a foreign substance which is present on an optical disc
93
is described.
The light source
91
emits a light beam toward the optical disc
93
. The emitted light beam passes through the polarized beam splitter
95
and the quarter waveplate
94
. Then, the light beam is converged by the objective lens
92
on the surface of the optical disc
93
so as to form a light spot thereon. The light beam reflected by the surface of the optical disc
93
passes through the objective lens
92
and the quarter waveplate
94
again, whereby the phase of the light beam is changed. The light beam with the changed phase is reflected by the polarized beam splitter
95
so as to enter the first light receiving element
96
A and the second light receiving element
96
B. The first light receiving element
96
A and the second light receiving element
96
B respectively generate a first electric current signal I
A
and a second electric current signal I
B
, each of which indicates the quantity of the received light beam. The first electric current signal I
A
and the second electric current signal I
B
are transmitted to the first I-V conversion circuit
97
A and the second I-V conversion circuit
97
B, respectively.
The first I-V conversion circuit
97
A and the second I-V conversion circuit
97
B convert the respective first electric current signal I
A
and the second electric current signal I
B
into a first voltage signal V
A
and a second voltage signal V
B
, respectively. The first voltage signal V
A
and the second voltage signal V
B
are transmitted to the sum signal generation circuit
98
.
The sum signal generation circuit
98
sums up the first voltage signal V
A
and the second voltage signal V
B
to generate a sum voltage signal V
A
+V
B
. The sum signal generation circuit
98
compares the generated sum voltage signal V
A
+V
B
with a reference voltage signal V
ref
. The reference voltage signal V
ref
is a voltage signal which indicates the quantity of light calculated from the theoretical reflectance of the optical disc
93
on which no foreign substance is attached.
If the relationship between the reference voltage signal V
ref
and the sum voltage signal V
A
+V
B
is V
ref
<V
A
+V
B
or V
ref
>V
A
+V
B
, the foreign substance detection apparatus
1500
determines that there is a foreign substance present. If the relationship between the reference voltage signal V
ref
and the sum voltage signal V
A
+V
B
is V
ref
=V
A
+V
B
, the foreign substance detection apparatus
1500
determines that there is no foreign substance present.
The foreign substance detection apparatus
1500
has two light receiving elements (the first light receiving element
96
A and the second light receiving element
96
B), but may have a single light receiving element.
The above described foreign substance detection apparatus
1500
mainly has the two problems (1) and (2) described below.
(1) In the case where the difference between the reflectance of an object (object to be examined) and that of a foreign substance is small, the foreign substance on the object sometimes cannot be accurately detected. Such applies especially to the case of a foreign substance, such as an oil film, a fingerprint, or the like. In this case, a large difference does not occur between the quantity of light reflected by a portion of the object on which the foreign substance exists and the quantity of light reflected by a portion of the object on which the foreign substance does not exist (i.e., a large difference does not occur between the sum voltage signal obtained from the quantity of light reflected by a portion of the object on which the foreign substance exists and the reference voltage signal obtained from the quantity of light reflected by a portion of the object on which the foreign substance does not exist). Accordingly, it is impossible to accurately detect the foreign substance.
Thus, in order to accurately detect such a foreign substance, it is necessary to stabilize the sum voltage signal with high accuracy. However, under a normal environment for using such a detection apparatus, the quantity of light readily varies due to a variation with time, and a variation due to temperature of a light source, a light receiving element, a signal processing circuit, or the like, or due to dust attached to an optical lens, a light receiving element, or the like. Thus, it is difficult to stabilize the sum voltage signal which is generated in a subsequent component. From experimentation conducted by the present inventors, it was confirmed that the sum voltage signal can vary by about 50% under a normal environment.
The sum voltage signal can be stabilized to some extent by using the foreign substance detection apparatus in a clean room, by incorporating a high-precision, complicated control apparatus, by periodically performing maintenance activities, or the like. However, in such cases, the cost efficiency is decreased.
(2) In the conventional foreign substance detection apparatus
1500
, the reference voltage signal V
ref
used for determining the presence/absence of a foreign substance is a fixed voltage signal which indicates, for example, the quantity of light calculated from the theoretical reflectance of an object on which no foreign substance is attached. However, as described above, under an actual environment for using the detection apparatus, the quantity of light reflected by the surface of the object readily varies. Accordingly, the quantity of light reflected by a portion of the object on which no foreign substance is attached, which is measured under the normal environment, is sometimes different from the quantity of light calculated from the theoretical reflectance of the object. As a result, accuracy in detection of a foreign substance decreases.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, an appara
Gotoh Yasuhiro
Nishiwaki Seiji
Font Frank G.
Matsushita Electric - Industrial Co., Ltd.
Nguyen Sang H.
Snell & Wilmer LLP
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