Optical: systems and elements – Prism – With reflecting surface
Reexamination Certificate
2002-10-16
2004-08-24
Robinson, Mark A. (Department: 2872)
Optical: systems and elements
Prism
With reflecting surface
C359S861000, C356S399000, C356S614000
Reexamination Certificate
active
06781775
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an apparatus for effecting the precise alignment of surfaces that are to be joined together. In particular, the invention relates to an optical system adapted for use in aligning an integrated circuit wafer or microchip with a patterned substrate.
BACKGROUND OF THE INVENTION
The development of apparatuses for the precise alignment of surfaces that are to be joined together continues to be active. This is particularly the case in the area of microelectronic fabrication, where the patterns that are to be aligned are microscopic or nearly microscopic in scale. One such pattern may be on a surface of an integrated circuit wafer or an individual microchip and may comprise a variety of connectors, such as metallic wires or ribbons, or tiny bumps of solder, conductive epoxy or indium, that are formed thereupon. The complementary pattern typically would be on a surface of a substrate and would comprise a pattern of tiny pads or conductors to provide electrical connections to the microchip or to another patterned substrate.
In the commercial production of microelectronic devices, a die may be attached to a substrate during an automated process. In some approaches, the patterns of the die and substrate are aligned directly with each other, or reference marks for guiding alignment may be provided on the components or component carriers. Accurate alignment of components or reference marks may be facilitated using an optical system that provides enlarged images of the components superimposed one upon the other. A typical optical system is illustrated in FIG.
1
. The optical system
1
includes an optical cube beam-splitter
2
and an image processor
3
, which may contain components such as one or more cameras, a video monitor, and circuitry for signal processing and control of the assembly process. A die
4
having connector bumps
5
a
,
5
b
is suspended above the beam-splitter
2
by means of a die carrier
6
. Suction applied through a port
8
holds the die
4
against the die carrier
6
during the assembly operations. A substrate
10
having electrical contacts
12
,
14
is positioned beneath the beam-splitter
2
on a substrate carrier
16
. Reference marks A, B are provided on the die
4
and reference marks A′, B′ are provided on the substrate
10
to facilitate the accurate alignment, and hence, attachment, of the bumps
5
a
,
5
b
with the electrical contacts
12
,
14
, respectively.
Still referring to
FIG. 1
, the beam-splitter
2
is provided with two similar triangular optical prisms
18
and
20
. The prism
18
has a transparent face
22
, a 100% reflective mirror face
24
and a hypotenuse face
26
, with the faces
22
,
24
being perpendicular to each other. The prism
20
has a transparent face
28
, a transparent face
30
and a hypotenuse face
32
, with the faces
28
,
30
being perpendicular to each other. Each prism
18
,
20
also has a 45° angle between the faces
24
,
30
and the respective hypotenuse faces
26
,
32
. The prisms
18
,
20
contact each other at their respective hypotenuse faces
26
,
32
, forming an interface
34
along the plane of contact. One or both of the hypotenuse faces
26
,
32
is coated with a reflective material, such as a metal or a reflective dielectric material. Typically, these coatings provide the interface
34
with a reflectance of 50%, i.e, half of the light striking the interface
34
will be reflected and half will pass through the interface
34
.
Light, provided by a source of illumination (e.g., a lamp) and striking the die
4
, is reflected as an image of the die
4
comprising light beams
36
a
,
36
b
which pass through the face
28
of the prism
20
and strike the interface
34
. A portion
38
a
,
38
b
of each light beam
36
a
,
36
b
is reflected by the interface
34
at a 90° angle of rotation. The reflected portions
38
a
,
38
b
exit the prism
20
through the face
30
and is received by the image processor
3
.
Light, provided by a source of illumination (e.g., a lamp) and striking the substrate
10
, is reflected as an image of the substrate
10
comprising light beams
41
a
,
41
b
which pass through the face
22
of the prism
18
and strike the interface
34
. A portion
43
a
,
43
b
of each light beam
41
a
,
41
b
is reflected by the interface
34
at a 90° angle of reflection and is reflected back to the interface
34
by the mirror face
24
, thereby being transmitted to the image processor
3
.
The resulting image, viewed at the face
30
of the prism
20
, comprises images of the die
4
and the substrate
10
superimposed upon each other. Image processing software can be used to determine the relative locations of the reference marks A, B relative to the reference marks A′, B′ respectively, and to signal an associated control system to move the die carrier
6
and/or the substrate carrier
16
until the reference marks A, B are accurately aligned with the reference marks A′, B′, respectively.
The alignment method described above has various disadvantages and shortcomings. For example, with reference to
FIG. 1
, portions
40
a
,
40
b
of the light beams
36
a
,
36
b
(i.e., the image of the die
4
) pass through the interface
34
, project an image of die
4
onto the substrate
10
, and are then reflected back to the beam splitter
2
from the substrate
10
. Similarly, portions
45
a
,
45
b
of the light beams
41
a
,
41
b
(i.e., the image of the substrate
10
) pass through the interface
34
, project an image of the substrate
10
onto the die
4
, and are then reflected back to the beam-splitter
2
from the die
4
. These reflected images create interference fringes or blurring of the image received by the image processor
3
. Such effects can increase the difficulty of accurately aligning the die
4
, and the substrate
10
with each other.
One approach to overcoming this problem is to generate separate images of the die
4
and substrate
10
, and combine the images digitally. For example, if the interface
34
were made to be 100% reflective, the image processor
3
would receive only the image of the die
4
at the face
30
of the prism
20
. A second image processor would be provided to capture the image of the substrate
10
at the face
24
of the prism
18
(which is made to be transparent), and the two images would be superimposed by digital manipulation (see, e.g., U.S. Pat. No. 4,899,921 to Bendat, et al.). Besides the increased cost of equipment to capture and combine two images, it would be necessary to carefully calibrate the image processors to accurately track the positions of the die carrier
6
and the substrate carrier
16
relative to each other.
SUMMARY OF THE INVENTION
The present invention overcomes the disadvantages and shortcomings of the prior art discussed above by providing a new and improved optical device adapted to superimpose the image of a die positioned at one side of the device and the image of a substrate positioned at an opposite side of the device. In one embodiment, the device comprises a plurality of reflective surfaces arranged so that the superposition of images takes place at a partially reflective surface within the probe. The superimposed image is displaced laterally from the die and the substrate. Neither the superimposed image nor the individual images of the die or the substrate is projected onto either component. Preferably, the optical device comprises a pair of right triangular prisms, each having a mirror hypotenuse face, a pentaprism having a pair of opposed inclined mirror faces, and an optical cube beam-splitter comprising the partially reflective surface.
In another embodiment, the optical device is a component of a single-camera optical probe for use in aligning the die with the substrate. The camera receives the superimposed image of the die and the substrate together that is produced at the partially reflective interface, and converts the image to a digital signal. The image received by the camera can, thereby, be monitored by
Bendat Zvi
Sokol Miroslaw
McCarter & English LLP
Robinson Mark A.
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