Semiconductor device manufacturing: process – Making device or circuit responsive to nonelectrical signal – Responsive to electromagnetic radiation
Reexamination Certificate
1999-03-23
2002-05-28
Lee, Eddie C. (Department: 2815)
Semiconductor device manufacturing: process
Making device or circuit responsive to nonelectrical signal
Responsive to electromagnetic radiation
C438S069000, C438S072000, C438S094000, C438S928000, C438S978000
Reexamination Certificate
active
06395577
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a photodetecting device for receiving light incident on a side surface of a semiconductor substrate. More particularly, it relates to a photodetecting device of side-surface illuminated type wherein a gradient surface for refracting or reflecting incident light is formed in a second principal surface in opposing relation to a first principal surface on which a light-receiving portion is formed, thereby changing the optical path of the incident light.
As a photodetecting device for fiber-optics communications that is sensitive to light in a long wavelength band of approximately 1.3 to 1.55 &mgr;m, there has widely been used a pin photodiode using an InGaAs/InP compound semiconductor as a material.
Typical pin photodiodes include a top-surface illuminated type for receiving light at the light-receiving portion side and a back-surface illuminated type for receiving light at the side opposite to the light-receiving portion, which are used selectively depending on the direction of connection to an optical fiber.
In recent years, there has been developed a photodetecting device for receiving light incident on a side surface of a semiconductor substrate. The photodetecting device of side-surface illuminated type is useful in the case where an optical fiber is attached to the photodetecting device in parallel relation to the mount surface of a flat package to which the photodetecting device has been bonded or where the photodetecting device is used to monitor light emitted backward from a semiconductor laser diode that has been bonded to the same mount surface as the photodetecting device.
As examples of the conventional photodetecting device of side-surface illuminated type, pin photodiodes each internally provided with means for changing an optical path by refraction or reflection will be described with reference to the drawings. FIGS.
13
(
a
) and
13
(
b
) show cross-sectional structures of the conventional pin photodiodes disclosed in Japanese Patent Application Laid-Open Publication No. 8-316506. As shown in FIG.
13
(
a
), a buffer layer
102
composed of n-type InP, a light absorbing layer
103
composed of intentionally undoped n-type InGaAs, and a window layer
104
composed of intentionally undoped n-type InP are formed sequentially on a first principal surface
101
a
of a semiconductor substrate
101
composed of n-type InP.
A p-type impurity such as Zn has been diffused into the window layer
104
to form an island pattern, in which first and second diffused regions
104
a
and
104
b
are formed at a specified interval. The portion of the light absorbing layer
103
underlying the first diffused region
104
a
serves as a light-receiving region
103
a
. What results is a pin junction formed by the p-type first diffused region
104
a
, the intentionally undoped n-type light-receiving region
103
a
, and the n-type buffer layer
102
.
A cathode
105
is formed on the first diffused region
104
a
, while an anode
106
is formed on the second diffused region
104
b.
A second principal surface
101
b
of the semiconductor substrate
101
in opposite relation to the first principal surface
101
a
is formed with gradient portions
101
c
having exposed surfaces located at the side edge portions of the semiconductor substrate
101
. If light
201
is incident on the gradient portion
101
c
in
10
parallel to the second principal surface
101
b
, the incident light
201
is refracted by the gradient portion
101
c
before reaching the light-receiving region
103
.
Thus, in the conventional photodetecting device, the gradient portion
101
b
provided in the second principal surface
101
b
refracts the light incident thereon in parallel to the second principal surface
101
b
and thereby changes the optical path of the incident light. According to the foregoing publication, a (111) plane orientation is used preferably such that an angle of 54.7° is formed between the gradient portion
101
c
and the second principal surface
101
b
. This is because the gradient portion
101
c
is required conditionally to form a specified angle with respect to the second principal surface
101
b
and have a flat and smooth surface.
To provide the semiconductor substrate with such a gradient portion
101
c
as to form a specified angle and have a flat and smooth surface (mirrored surface), it is the easiest to perform wet chancel etching whereby a specified crystal plane orientation is exposed. In manufacturing a photodetecting device, a semiconductor substrate using a (001) plane at a principal surface is normally employed so that, when wet chemical etching for exposing a crystal plane orientation is performed, a (111) plane is exposed in most cases.
If it is assumed that the same components as shown in FIG.
13
(
a
) are designated by similar reference numerals in FIG.
13
(
b
), the second principal surface
101
b
of the semiconductor substrate
101
is formed with gradient portions
101
d
having exposed surfaces located at the near center portion thereof. In this case, the gradient portion
101
d
provided in the second principal surface
101
b
reflects light incident thereon in parallel to the second principal surface
101
b
and thereby changes the optical path of the incident light. The foregoing publication suggests the use of a (111) plane also at the gradient portion
101
d.
However, the aforesaid conventional photodetecting device of side-surface illuminated type has the problem that the device is larger in chip size than the photodetecting device of top-surface or back-surface illuminated type.
Specifically, if a (111) plane forming an angle of 54.7° with respect to the second principal surface
101
b
is used at the gradient portion
101
c
of the photodetecting device shown in FIG.
13
(
a
), the angle formed between the light
202
incident on the side edge portion and the second principal surface
101
b
in the semiconductor substrate
101
becomes 25.7°. If the thickness of the semiconductor substrate
101
is assumed to be 200 &mgr;m, the incident light
201
should travel 416 &mgr;m in a direction parallel to the principal surface to reach the first principal surface
101
a.
This indicates that a distance of 416 &mgr;m is necessary between the plane of incidence and the center of the light-receiving region
103
a
regardless of the largeness of the light-receiving region
103
. The distance is extremely large considering that the typical chip size of a photodetecting device having a light-receiving region with a diameter of 80 &mgr;m is 300 &mgr;m square (the distance between the end face of incidence and the center of the light-receiving region is 150 &mgr;m) and that the chip size of a photodetecting device having a light-receiving region with a diameter of 300 &mgr;m is approximately 500 &mgr;m square (the distance between the end face of incidence and the center of the light-receiving region is 250 &mgr;m).
On the other hand, the direction of travel of the incident light
201
reflected by the gradient portion
101
d
is tilted by 19.4° from a normal to the second principal surface
101
b
in the photodetecting device shown in FIG.
13
(
b
). If the thickness of the semiconductor substrate
101
is assumed to be 200 &mgr;m, the distance traveled by the incident light
201
in a direction parallel to the principal surfaces till it reaches the first principal surface
101
a
is 70 &mgr;m.
According to the foregoing publication, a pattern provided on the mount on which the photodetecting device is to be mounted is aligned with the end face of the semiconductor substrate
101
formed with the photodetecting device. However, since the distance between the end face of the semiconductor substrate
101
and the light-receiving region
103
a
is determined not by the accuracy of photolithography, but by the accuracy of dicing, it is difficult to enhance the accuracy. This leads to the problems that the position at which the light is incident is controlled less accurately and that the efficiency with which the in
Lee Eddie C.
Matsushita Electric - Industrial Co., Ltd.
Nixon & Peabody LLP
Richards N. Drew
Robinson Eric J.
LandOfFree
Photodetecting device and method of manufacturing the same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Photodetecting device and method of manufacturing the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Photodetecting device and method of manufacturing the same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2906191