Radiant energy – Photocells; circuits and apparatus – With circuit for evaluating a web – strand – strip – or sheet
Reexamination Certificate
2000-03-22
2003-04-29
Allen, Stephone B. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
With circuit for evaluating a web, strand, strip, or sheet
C250S559220, C250S559270, C356S602000, C356S608000, C356S612000
Reexamination Certificate
active
06555836
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a method and an apparatus for inspecting bumps provided on an object to be inspected. The present invention particularly relates to detecting height of bumps provided on a surface of a semiconductor chip or a wafer of a flip-chip bonding type or on a package, such as a BGA, provided with bumps serving as mounting terminals.
Recently, in order to realize high-density mounting of input/output terminals of LSI chips, there is a greater interest in technologies such as flip-chip bonding and a package provided with bumps serving as connection terminals.
However, such technologies have a certain drawback. That is, any variation of the size of the bumps produced during manufacturing of the bumps may result in a problematic aspect during mounting of the semiconductor chip or the package. That is to say, the neighboring bumps may be short-circuited or the chip and the package may be badly connected to the substrate.
In order to prevent such a problem, it is necessary to find any defects of the bumps before mounting the semiconductor chip or the package. However, the semiconductor chip may be provided with bumps amounting to several thousands or more, in which case visual inspection of the bumps is almost impossible. Thus, there is a need for an apparatus which can automatically inspect any defect of the bumps.
2. Description of the Related Art
FIG. 1
is a schematic diagram showing a bump inspection device of the related art. The bump inspection device includes a movable inspection stage
26
, a laser beam generator
10
, a scanner
11
, a first objective lens
12
, a second objective lens
13
and a PSD (Position Sensitive Detector)
14
. An object to be inspected is represented by a wafer
1
, which is placed on the movable inspection stage
26
, however, the object to be inspected can be any type of semiconductor device provided with bumps. In
FIG. 1
, for the sake of clarity, only one bump
2
is shown on the wafer
1
.
The laser beam generator
10
generates a laser beam which serves as an irradiation beam
3
. The scanner
11
scans the irradiation beam
3
in a fixed direction. The irradiation beam
3
is irradiated onto the bump
2
via the first objective leans
12
. The second objective lens
13
receives the beam reflected at the bump
2
. The PSD
14
receives the reflected beam
4
from the second objective lens and outputs information related to an imaging position and brightness of the reflected beam
4
in the form of electric signals.
Now an operation of the bump inspection device will be described with reference to FIG.
1
. The scanner
11
scans the irradiation beam
3
from the laser beam generator
10
in a direction perpendicular to the plane of drawing (main scanning direction). Then, the scanned beam is, via the first objective lens
12
, irradiated on a surface of the wafer
1
provided with the bump
2
. The beam reflected from the surface of the wafer
1
is imaged on the PSD
14
via the second objective lens
13
. The PSD
14
outputs electrical signals corresponding to the position and the brightness of a spot imaged thereon.
Also, for every scanning operation of the scanner
11
, the stage
26
is moved in a direction parallel to the plane of drawing (sub-scan direction). Thus, the irradiation beam
3
is scanned for an entire area to be inspected on the wafer
1
. Since the position of the spot of the reflected beam
4
imaged on the PSD
14
varies with the height of the bump
2
, the height of the bump
2
can be detected from the scanning position of the irradiation beam
3
and the output signals from the PSD
14
. Such technology, in which the size of the bump is measured by triangulation, is known from Japanese laid-open patent application No. 6-137825.
Referring to
FIGS. 2A and 2B
, the image from the PSD
14
and the height profile will be described for the case where the entire inspection area is scanned.
FIG. 2A
shows an image (reflection image) produced by sequentially storing the signals from the PSD
14
into a memory (not shown), which signals indicating the brightness of the reflected beam
4
. Here, for the sake of clarity, it is assumed that there is only one bump
2
as shown in FIG.
1
and no other bumps exist around the bump
2
. Also, the shadow
6
of the bump will in fact be narrow in the middle, but since the shape of the shadow does not affect essential aspects of the present invention, the shadow
6
is shown as an ellipse.
FIG. 2A
also shows a regular reflection region
5
which appears as a bright region. The regular reflection region
5
is a region in which a regularly reflected portion of the reflected beam
4
is imaged at the PSD
14
. The regularly reflected portion of the reflected beam
4
corresponds to a portion of the irradiation beam
3
regularly reflected near the apex of the bump
2
. The bump shadow
6
is a region where the reflected beam
4
does not reach the PSD. The region around the bump shadow
6
becomes a bright region due to a portion of the reflected beam
4
reflected at the surface of the wafer
1
.
It is to be noted that this reflection image is produced by the reflected beam
4
which originates from the irradiation beam
3
irradiated in an oblique direction with respect to the surface of the wafer
2
on which the bump
2
is provided. Therefore, in the reflected image, the reflected beam
4
regularly reflected near the apex of the bump
2
will appear in the bump shadow
6
at a position shifted towards the direction of travel of the irradiation beam
3
. The regular reflection region
5
represents such shifted position.
FIG. 2B
is a diagram showing a height profile along line a-a′ for the reflected image shown in FIG.
2
A. In the figure, the abscissa indicates the position and the ordinate indicates the height-profile. As has been described above, the height for each scanning point can be derived from the scanning position of the irradiation beam
3
and the position of the beam spot on the PSD
14
. The height profile is obtained by sequentially storing thus derived height data for each scanning position into the memory.
In
FIG. 2B
, it can be seen that the height profile shows a curve having a relatively high value at a position corresponding to the regular reflection region
5
. On the contrary, the curve has a relatively low value at parts corresponding to other region of the bump shadow
6
. However, in practice, the height profile does not exist for the region corresponding to the bump shadow
6
since no data can be obtained from such a region. That is to say, the region in the bump shadow
6
wherefrom the height data can be obtained is only the regular reflection region
5
where the reflected light
4
is imaged on the PSD
14
.
Referring now to
FIGS. 3A
to
6
, drawbacks of the related art will be described.
In case where only one bump is provided and no other bumps are provided around that bump, the reflection image will include one reflection region. Such a region is shown as the regular reflection region
5
in FIG.
2
A. Therefore, there is no problematic aspect when deriving the height of the bump
2
. However, a wafer or a package normally has a number of bumps provided at a predetermined pitch. Thus, the irradiation beam
3
will be reflected on the plurality of bumps in a multiple manner. Therefore, a number of reflection regions other than the regular reflection region will appear in the reflection image due to multiple reflection.
The multiple reflection occurs in a various patterns in dependence of the size and pitch of the bumps and the direction of the irradiation beam. The following description relates to a few typical patterns of the multiple reflection.
FIGS. 3A and 3B
are diagrams showing an example of multiple reflection.
FIG. 3A
shows the wafer
1
and bumps
2
a
to
2
c
. When the irradiation beam
3
a
is incident near the apex of the bump
2
b
, the beam will be reflected in a path shown as a reflected beam
4
a
. However, when the irradiati
Fuse Takashi
Nishiyama Youji
Oshima Yoshitaka
Takahashi Fumiyuki
Tsukahara Hiroyuki
Allen Stephone B.
Armstrong Westerman & Hattori, LLP.
Glass Christopher W.
LandOfFree
Method and apparatus for inspecting bumps and determining... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for inspecting bumps and determining..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for inspecting bumps and determining... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3064234