Optics: measuring and testing – Inspection of flaws or impurities
Reexamination Certificate
2003-03-27
2004-09-28
Pham, Hoa Q. (Department: 2877)
Optics: measuring and testing
Inspection of flaws or impurities
C356S237500, C250S559360
Reexamination Certificate
active
06798503
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an edge flaw inspection device that optically inspects flaws in inspected edges, and more particularly, to a device that detects flaws in components formed into the shape of plates such as silicon wafers and semiconductor wafers.
2. Background Art
Edge flaw inspection devices that detect edge flaws such as cracks, chips or polishing marks in long, narrow edges such as the outer edges of silicon wafers have a structure described in, for example, Japanese Patent No. 2999712 (Japanese Patent Application, First Publication No. Hei 9-269298).
As shown in
FIG. 6
, this edge flaw inspection device
20
is provided with an elliptical mirror
23
in the form of a concave mirror that is severed near the midpoint of a first focal point
21
and a second focal point
22
, a light source
24
that radiates laser light towards first focal point
21
of elliptical mirror
23
, a photo detector
25
arranged at second focal point
22
, and a douser
26
arranged between first focal point
21
and light source
24
. A slit
27
is formed along a horizontal plane that contains two focal points
21
and
22
(the direction of this plane is hereinafter to be the horizontal direction) in the apex of elliptical mirror
23
. Reference symbol
30
in the drawing indicates a lens.
Slit
27
has a width that is slightly larger than the thickness of a silicon wafer
28
, and a portion of silicon wafer
28
can be inserted within elliptical mirror
23
from outside elliptical mirror
23
. Silicon wafer
28
that has been inserted into elliptical mirror
23
from slit
27
is held so that its outer peripheral edge does not pass first focal point
21
. In addition, silicon wafer
28
is rotatably held about a vertical axis, and the outer peripheral edge arranged at first focal point
21
can be continuously changed in the peripheral direction.
Through hole
29
is formed in douser
26
on the light path that connects light source
24
and first focal point
21
. Laser light emitted from light source
24
passes through through hole
29
of douser
26
, and reaches the outer peripheral edge of silicon wafer
28
arranged at first focal point
21
where it is then reflected.
In the case of viewing silicon wafer
28
with its edge facing towards the front, there is a flaw in its edge as shown in
FIG. 7
, and if this flaw is a vertical flaw
31
that extends in the vertical direction, laser light radiated onto the edge is typically strongly scattered to the left and right. On the other hand, if a flaw that has occurred in the edge is a horizontal flaw
32
, laser light radiated onto the edge is typically strongly scattered up and down.
This reflected light scattered at the peripheral edge of silicon wafer
28
at first focal point
21
is scattered three-dimensionally, reaches the mirrored surface of elliptical mirror
23
, and is then reflected there after which it converges at second focal point
22
. Since photo detector
25
is arranged at second focal point
22
, the converted scattered and reflected light is detected by photo detector
25
.
Since this scattered reflected light has different frequency components depending on the type of defect present in the peripheral edge of silicon wafer, its surface roughness and so forth, by detecting this light and analyzing its frequency components, the type of defect, surface roughness and so forth can be detected. In addition, as a result of rotating silicon wafer
28
about a vertical axis, its peripheral edge can be detected for flaws over its entire circumference.
On the other hand, light reflected from the surface other than the location of a flaw in the outer peripheral edge of silicon wafer
28
is in the form of low order diffracted light such as so-called regular reflected light. For example, regular reflected light from the outer peripheral edge of silicon wafer
28
arranged along the horizontal direction is predominantly light that is reflected in the vertical plane that contains first focal point
21
and second focal point
22
or its vicinity. However, since this low order diffracted light is light reflected by a surface other than that containing a flaw, and does not contain information necessary for detecting a flaw in the outer peripheral surface, it is preferable that it not be detected by photo detector
25
.
In an edge flaw detection device
20
of the prior art, a douser
26
is provided in the form of a strip that extends in the vertical direction in the space between light source
24
and first focal point
21
, which either prevents regular reflected light and other low order diffracted light from reaching the mirrored surface of elliptical mirror
23
, or blocks low order diffracted light that has reached the mirrored surface of elliptical mirror
23
from reaching the second focal point after it has been reflected there.
However, in the case of a douser
26
arranged in the space between a light source and a first focal point as was previously described, the problem arises in which not only low order diffracted light such as regular reflected light, but also all diffracted light that attempts to pass through the space in which douser
26
is arranged ends up being blocked.
Namely, all diffracted light reflected by the outer peripheral edge of silicon wafer
28
is three-dimensionally scattered at first focal point
21
, and proceeds through the plane that contains the scattering direction vector and the first and second focal points
21
and
22
. However, in a device of the prior art in which douser
26
is arranged in the space between light source
24
and first focal point
21
, even in the case of scattered diffracted light scattered by an edge flaw in the outer peripheral edge of silicon wafer
28
, if the scattering direction vector is facing in a direction at an angle that is shallower than the vertical plane as in the manner of scattered diffracted light produced by a horizontal flaw, the plane through which the scattered diffracted light proceeds ends up intersecting with douser
26
, thereby resulting in the problem of the scattered diffracted light being blocked by douser
26
.
In this case, since diffracted light containing effective information relating to edge flaws cannot be detected by photo detector
25
, there were cases in which it was difficult to judge the presence and types of defects.
In addition, as indicated in Japanese Unexamined Patent Application, First Publication No. 11-351850, although a method has been proposed in which regular reflected light is blocked and scattered diffracted light produced by a horizontal flaw is detected by arranging a light receiving element array in the vicinity of a first focal point, since the light receiving element array arranged in the space inside an elliptical mirror blocks scattered diffracted light effective for flaw detection, there was the problem of a decrease in the amount of information detected by a photo detector in the same manner as described above.
In consideration of the above circumstances, an object of the present invention is to provide an edge flaw inspection device that effectively eliminates low order diffracted light such as regular reflected light, but detects high order diffracted light such as scattered diffracted light in a photo detector without blocking that light.
SUMMARY OF THE INVENTION
An edge flaw inspection device of the present invention comprises: an elliptical mirror having a first focal point and a second focal points; a light source that radiates coherent light towards an inspected edge arranged near the first focal point of the elliptical mirror; a light blocking member that blocks diffracted light of a low order that is radiated from the light source and reflected by the inspected edge; and a photo detector arranged at the second focal point of the elliptical mirror; and the light blocking member comprising a light absorbing member arranged on the mirrored surface of the elliptical mirror reached by the low order diffracted right.
According to the
Hiramoto Kazuyuki
Kanno Takashi
Pham Hoa Q.
Raytex Corporation
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