Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – In combination with or also constituting light responsive...
Reexamination Certificate
2001-01-11
2003-07-29
Tran, Minh Loan (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
In combination with or also constituting light responsive...
C257S459000, C257S764000, C257S765000, C257S767000, C257S771000, C257S784000
Reexamination Certificate
active
06600174
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light receiving element and a semiconductor laser device, and more particularly to a configuration of a light receiving element utilized for a pickup or the like of an optical disk and to a semiconductor laser device including the light receiving element.
2. Description of the Background Art
A semiconductor laser device utilized for a pickup of an optical disk has conventionally been known. An example of such a semiconductor laser device is shown in FIG.
5
.
The semiconductor laser device shown in
FIG. 5
is disclosed in Japanese Patent Laying-Open No. 7-142813, and includes a stem platform
9
and a stem
11
fixed to stem platform
9
. A semiconductor laser chip
17
is attached to the side surface of stem
11
, a photodiode chip for detection is attached to the top surface, and a photodiode (light receiving element)
16
is attached onto stem platform
9
.
A cap
12
having a window
13
is fixed to stem platform
9
. Glass
10
is mounted on cap
12
and fixed to cap
12
by bonding resin
14
.
A vent hole
15
is provided on stem platform
9
, which allows emission of moisture even when the moisture is externally introduced into a space within cap
12
through bonding resin
14
.
However, the semiconductor laser device has a problem such that moisture entered into the space described above from vent hole
15
corrodes a metal portion unprotected by a surface protection film, such as a bonding pad portion of photodiode (light receiving element)
16
.
An example of a light receiving element capable of addressing such a problem is a light receiving element disclosed in Japanese Patent Laying-Open No. 9-97892. The light receiving element described in this publication is shown in FIG.
6
.
Referring to
FIG. 6
, the light receiving element includes a bonding pad portion
20
, a photodiode portion
21
and a signal processing circuit portion
22
. Bonding pad portion
20
electrically connects, for example, photodiode portion
21
and signal processing circuit portion
22
, photodiode portion
21
detecting received light, and signal processing circuit portion
22
processing a light signal.
The light receiving element further includes a semiconductor substrate
1
, and an oxide film
2
formed thereon. Semiconductor substrate
1
includes a p-type semiconductor substrate
1
a
and an n-type epitaxial layer
1
b
. Various impurity diffusion layers are formed, and a metal layer (an electrode) connected to a predetermined impurity diffusion layer is also formed within semiconductor substrate
1
.
Bonding pad portion
20
is constituted by a part of a metal layer
4
a
formed on oxide film
2
, a part of the surface of bonding pad portion
20
not being covered by a surface protection film
5
. A metal layer having corrosion resistance such as TiW layer
7
and Au layer
8
is formed on the part of the surface. Au layer
8
is formed in order to enhance the bonding property.
By forming the metal layer having corrosion resistance such as TiW layer
7
on bonding pad portion
20
as described above, corrosion of bonding pad portion
20
can be inhibited even if moisture enters into the space within cap
12
from vent hole
15
as described earlier.
However, the conventional example shown in
FIG. 6
also has a problem described below. This problem is described with reference to FIG.
7
.
FIG. 7
is an enlarged view of bonding pad portion
20
and portions adjacent thereto.
Referring to
FIG. 7
, a bonding wire
6
is formed on bonding pad portion
20
. If there is a projection on, for example, the surface of metal layer
4
a
, TiW layer
7
or Au layer
8
is damaged at the time of bonding of bonding wire
6
, so that metal layer
4
a
located underneath TiW layer
7
is corroded, and thus a corrosion region
18
is locally generated as shown in FIG.
7
. Corrosion region
18
is generated mainly at the periphery of bonding wire
6
, and if corrosion region
18
reaches interconnection portion
23
, a problem may be raised such that bonding wire
6
and an interconnection portion
23
are not electrically conducted. This problem may also occur if TiW layer
7
or the like is damaged by contacting a probe with TiW layer
7
in a product test.
SUMMARY OF THE INVENTION
The present invention is directed to solve the problems described above. It is an object of the present invention to enhance corrosion resistance of a light receiving element.
According to one aspect of the present invention, a light receiving element includes a bonding pad portion, an interconnection portion extending from the bonding pad portion, a corrosion-resistant conductive layer formed of a corrosion-resistant material and extending from the bonding pad portion to the interconnection portion, and a bonding wire formed on the bonding pad portion. The corrosion-resistant conductive layer herein typically represents a conductive layer formed of a material having low corrosiveness (hard-to-corrode property) to a corrosive factor such as moisture, compared to materials constituting the bonding pad portion and the interconnection portion.
By extending the corrosion-resistant conductive layer from the bonding pad portion to the interconnection portion as described above, the interconnection portion and the bonding wire can be electrically connected by the corrosion-resistant conductive layer even if the bonding pad portion located on the periphery of the bonding wire is corroded.
The light receiving element according to the present invention includes a protection film having an opening on the bonding pad portion and covering the interconnection portion, the corrosion-resistant conductive layer extending underneath the protection film.
By thus forming the corrosion-resistant conductive layer such that it extends to the underneath the protection film, the bonding pad portion and the interconnection portion can be electrically connected by the corrosion-resistant conductive layer, and hence the effect described above can be obtained.
Further, an additional corrosion-resistant conductive layer may be formed between the bonding pad portion and the bonding wire.
This can inhibit corrosion of the bonding pad portion itself located on the periphery of the bonding wire, and can further ensure connection between the interconnection portion and the bonding wire.
The bonding pad portion and the interconnection portion are formed on an insulating film, and a corrosion-resistant conductive layer is arranged to be in contact with the insulating film.
By thus arranging the corrosion-resistant conductive layer on the insulating film side, the corrosion-resistant conductive layer can be protected by the bonding pad portion. Further, adhesion strength between the insulating film and the corrosion-resistant conductive layer can be maintained even if the bonding pad portion located on the periphery of the bonding wire is corroded. As a result, defections of the bonding pad portion can effectively be inhibited.
According to another aspect of the present invention, a light receiving element includes an Al alloy layer formed on an insulating film, a protection film having an opening on a part of the surface of the Al alloy layer and covering the Al alloy layer, and a bonding wire formed on a part of the surface of the Al alloy layer. The Al alloy layer then includes a TiW layer extending from underneath the opening to underneath the protection film.
By extending the TiW layer, which is an example of a corrosion-resistant conductive layer, from underneath the opening to underneath the protection film as described above, the Al alloy layer located underneath the protection film and the bonding wire can be electrically connected by TiW layer, even if the Al alloy layer located underneath the opening is locally corroded. Further, an Al alloy usable as an interconnection material of a circuit portion in the light receiving element, and TiW usable as a barrier metal in the circuit portion are used, so that no further complicated processes are required. Thus,
Fukunaga Naoki
Kubo Masaru
Natsuaki Kazuhiro
Ohkubo Isamu
Sharp Kabushiki Kaisha
Tran Minh Loan
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