Solid-state imaging device and method of production of the same

Details Solid-state imaging device and method of production of the same Solid-state imaging device and method of production of the same

2001-06-25

2002-10-29

Thompson, Craig (Department: 2813)

Semiconductor device manufacturing: process

Making device or circuit responsive to nonelectrical signal

Responsive to electromagnetic radiation

Reexamination Certificate

active

06472247

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to solid-state imaging devices which read an image by using solid-state image sensors, and relates to semiconductor packaging techniques which are applicable to the production of solid-state imaging devices used in copiers, image scanners, facsimiles, digital cameras, video cameras or the like.
2. Description of the Related Art
Conventionally, the dominant method of production of solid-state imaging device is to produce a package that contains a solid-state image sensor, such as CCD (charge-coupled device), the package typically made of a ceramic insulating substrate.
FIG. 6
shows a conventional solid-state imaging device.
As shown in
FIG. 6
, the conventional solid-state imaging device includes a ceramic package
802
having a plurality of external terminals
801
. The package
802
contains a solid-state image sensor
803
, the package
802
being made of a ceramic insulating substrate. Hereinafter, the package itself (or the ceramic insulating substrate) will be referred to as the ceramic package. The external terminals
801
are provided for the solid-state imaging device to output an electrical signal to an external device via the external terminals
801
.
The ceramic package
802
includes a recessed portion
802
a
at its upper surface, and the solid-state image sensor
803
is mounted on the recessed portion
802
a
of the ceramic package
802
. The solid-state image sensor
803
has an effective light-receiving region, and the solid-state image sensor
803
is placed with this light-receiving region in a face-up condition.
In the recessed portion
802
a
of the ceramic package
802
, electrodes
804
, which are connected to the external terminals
801
in the ceramic package, are provided at internal peripheral locations of the recessed portion
802
a
. The solid-state image sensor
803
also includes electrodes at peripheral locations of the upper surface of the image sensor. By performing a wire bonding, the electrodes
804
of the ceramic package
802
are electrically connected to the electrodes of the image sensor
803
by wires
805
. The wires
805
are made of, for example, aluminum (Al) or gold (Au). Further, in order to protect the solid-state image sensor
803
, a silica glass
806
is attached to the top of the recessed portion
802
a
of the ceramic package
802
as a sealing cover for protecting the image sensor
803
from mechanical damage and environmental influences.
During an operation of the imaging device of
FIG. 6
, incident light
807
, which is derived from an object to be imaged, passes through the silica glass
806
on the top of the recessed portion
802
of the ceramic package
802
, and reaches the solid-state image sensor
803
. The light-receiving region of the image sensor
803
for receiving the incident light
807
is formed with a large number of photodiodes (not shown). The number of photodiodes in one solid-state image sensor varies depending on the type of the image sensor, and the number of photodiodes in the image sensor
803
is typically in a range from 20,000 to 40,000. The image sensor
803
generates an electrical signal through the optoelectronic conversion of the received light, and the signal, output by the image sensor
803
, is processed as image data in an image reading unit (not shown).
In the case of a recent solid-state image sensor in which a larger number of tiny photodiodes are more densely provided, a micro-lens of a resin material is additionally formed on the light-receiving region of the image sensor for the purpose of increasing the sensitivity of the photodiodes to receiving light. In such a case, the incident light
807
passes through the silica glass
806
, and it is converted by the micro-lens into a convergent light, so that the convergent light reaches the light-receiving region of the solid-state image sensor
803
. Similarly, the image sensor
803
generates an electrical signal through the optoelectronic conversion of the received light, and the signal, output by the image sensor
803
, is processed as image data in an image reading unit.
FIG. 7A
, FIG.
7
B and
FIG. 7C
show a conventional method of production of the solid-state imaging device shown in FIG.
6
.
In a first step of the production method of the solid-state imaging device, the die bonding process as shown in
FIG. 7A
is performed. The solid-state image sensor
803
is placed into the recessed portion
802
a
of the ceramic package
802
with the light-receiving region of the image sensor
803
in a face-up condition. The ceramic package
802
is provided with the external terminals
801
. The image sensor
803
is bonded to the ceramic package
802
by using a die bonding machine. The die bonding process to bond the image sensor
803
onto the ceramic package
802
is performed by using a conductive adhesive agent, such as a thermosetting silver paste. The curing of the conductive adhesive agent, which is provided between the image sensor
803
and the ceramic package
802
, is attained by heating it to about 150 deg. C.
In a second step, the interconnecting process as shown in
FIG. 7B
is performed after the end of the die bonding process. The electrodes
804
at the internal peripheral locations of the recessed portion
802
a
are electrically connected to the electrodes at the peripheral locations of the upper surface of the image sensor
803
by the wires
805
of aluminum or gold. The interconnecting process to interconnect these electrodes is performed by using a wire bonding machine. The electrodes
804
are respectively connected to the external terminals
801
in the ceramic package
802
.
In a third step, the encapsulation process as shown in
FIG. 7C
is performed after the end of the interconnecting process. The silica glass
806
is attached to the top of the recessed portion
802
a
of the ceramic package
802
as a sealing cover that protects the image sensor
803
from mechanical damage and environmental influences. The conventional imaging device is thus produced. When the silica glass
806
is attached to the ceramic package
802
as the sealing cover, it is necessary to maintain the internal space between the silica glass
806
and the ceramic package
802
in a vacuum condition before and after the encapsulation process. The silica glass
806
must be bonded to the ceramic package
802
under a vacuum condition, and the bonding process to bond the silica glass
806
to the ceramic package
802
is performed by using a thermosetting adhesive agent.
In the above-described solid-state imaging device, the electrical connections of the package electrodes
804
and the image sensor electrodes are established by the wires
805
. In order to arrange the wires
805
at the peripheral locations of the upper surface of the image sensor
803
where the electrodes are provided, the ceramic package
802
requires a relatively wide area to form the electrodes
804
at the internal peripheral locations of the recessed portion
802
a
. Further, the internal space between the image sensor
803
and the silica glass
806
must be wide enough to accommodate the looped portions of the wires
805
therein. Therefore, it is difficult to develop a small-size, light-weight imaging device based on the structure of the conventional imaging device.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an improved solid-state imaging device in which the above-described problems are eliminated.
Another object of the present invention is to provide a solid-state imaging device which not only provides small-size, lightweight features but also provides reliable protection of the imaging performance against mechanical damage and environmental influences.
Another object of the present invention is to provide a method of production of a solid-state imaging device which not only provides small-size, light-weight features but also provides reliable protection of the imaging performance against mechanical damage and environmental influences.
T

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