Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Electromagnetic or particle radiation
Reexamination Certificate
2002-12-17
2004-09-14
Flynn, Nathan J. (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Electromagnetic or particle radiation
C257S656000, C438S048000
Reexamination Certificate
active
06791153
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2002-63188, filed on Mar. 8, 2002, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical semiconductor device and a method for manufacturing the optical semiconductor device.
2. Related Background Art
A photodiode of a PIN structure is conventionally employed as a photo detector which converts an optical signal used in optical communication or a DVD and the like into an electrical signal.
The PIN-type photodiode has a structure in which a so-called i (intrinsic) layer consisting of a semiconductor having a relatively low impurity concentration is put between p and n semiconductors having relatively high impurity concentrations.
A bipolar transistor, a capacitor, a resistance, a MOSFET and the like are used as signal-processing circuit elements which process an electrical signal from the photo-detector.
An optical semiconductor device is conventionally formed by hybridizing a PIN photodiode and signal-processing circuit elements formed on different semiconductor substrates or semiconductor chips, respectively (such optical semiconductor device will be referred to as “hybrid-optical semiconductor device” hereinafter).
Further, there is known an optical semiconductor device which has a PIN photodiode and a signal-processing circuit formed on the same semiconductor substrate or semiconductor chip (such optical semiconductor device will be referred to as “single-substrate-type optical semiconductor device” hereinafter).
The single-substrate-type optical semiconductor device has fewer parts than those of the hybrid-optical semiconductor device in an assembly process and requires fewer steps in the assembly process. Therefore, the single-substrate-type optical semiconductor device can reduce manufacturing costs more than the hybrid-optical semiconductor device. Further, the single-substrate-type optical semiconductor device does not require a bonding wire that connects from a semiconductor chip on which a PIN photodiode is formed to a semiconductor chip on which a signal-processing circuit is formed. Therefore, the single-substrate-type optical semiconductor device can resist external electromagnetic noise better than the hybrid-optical semiconductor device. As a consequence, the single-substrate-type optical semiconductor device is more advantageous than the hybrid-optical semiconductor device.
FIG. 8
is a schematic enlarged cross-sectional view of a conventional single-substrate-type optical semiconductor device. As shown therein, a p
−
-type epitaxial layer
12
is formed on a p-type semiconductor substrate
10
. An n-type epitaxial layer
16
is formed on the epitaxial layer
12
. An insulating layer
18
, an insulating layer
20
, an electrode layer
22
, a passivation film
24
and a passivation film
26
are sequentially provided on the epitaxial layer
16
in this order.
On the epitaxial layers
12
and
16
, various diffused layers
14
,
40
,
42
and
44
are provided to form a photodiode section
50
and a signal-processing circuit section
60
. In addition, electrodes
28
and
29
connected to the diffused layers through the insulating layer
18
are formed on the epitaxial layers
16
.
The electrode layer
22
is a metal layer electrically connected to one of the electrodes formed on the epitaxial layer
16
and also functions as a light-shielding film which shields the signal-processing circuit section from light. Therefore, in the optical semiconductor device
200
, the electrode layer
22
is not formed in the photodiode section
50
and light is allowed to be incident only on this photodiode section
50
.
However, the insulating layers
18
and
20
and the passivation films
24
and
26
used to manufacture the signal-processing circuit section
60
, the electrode
28
and the like are formed on the surface of the epitaxial layer
16
in the photodiode section
50
. Because of the presence of the insulating layers
18
and
20
and the passivation films
24
and
26
, most of the incident light incident on the photodiode section
50
is reflected. As a result, the quantity of light incident on portions below the surface of epitaxial layer
16
is decreased. Due to this, the photo sensitivity of the optical semiconductor device
200
disadvantageously deteriorates.
Furthermore, the film formed on the surface of the epitaxial layer
16
in the photodiode section
50
is a multilayer film which consists of the insulating films
18
and
20
and the passivation films
24
and
26
different from one another in property and thickness. Since the respective films of this multilayer film are formed in different manufacturing steps from one another, the material, property and film thickness vary among these films. As a result, the reflectance of the incident light incident on the photodiode section
50
is not kept constant. Due to this, there occurs the problem that the photo sensitivity of the optical semiconductor device
200
has a disadvantageously large variation.
As stated above, the reflectance for reflecting the incident light incident on the photodiode section
50
is largely influenced by the materials, properties and thicknesses of the films covering the surface of the epitaxial layer
16
. However, it is difficult to form the films having different materials, properties and thicknesses on the epitaxial layer
16
so as to minimize reflectance in view of the refractive index of the epitaxial layer (e.g., the refractive index of silicon≈3.44) and the wavelength of the incident light.
In addition, Japanese Patent Application Publication No.4-271173 discloses an optical semiconductor device having a dielectric thin film and an antireflection film which have common properties and thickness, and which are manufactured in a common manufacturing step. The dielectric thin film is used between the electrodes of the capacitor of a peripheral circuit element. The antireflection film is used in a photo detector.
In the optical semiconductor device disclosed in Publication No. HEI4-271173 (1992), however, the thickness of the antireflection film is a factor that determines the capacitance of the capacitor. Therefore, the thickness of the antireflection film is limited by the capacitance of the capacitor. If the thickness of the antireflection film is set at an optimum thickness in accordance with the wavelength of incident light, the areas of the electrodes of the capacitor have to be changed so as to obtain a desired capacitance.
Furthermore, in the optical semiconductor device disclosed in Publication No. 4-271173, the antireflection film of the photo detector is formed when the dielectric thin film used between the electrodes of the capacitor is formed. Due to this, such films as passivation films are formed on the antireflection film of the photo detector. As a result, there occurs the problem that in order to control the reflectance in the photo detector, it is disadvantageously necessary to control not only the thickness of the antireflection film but also that of the passivation films on the antireflection film.
Therefore, it is desired to provide an optical semiconductor device which has a relatively high photo sensitivity and which can reduce the variation of photo sensitivity even if a photodetector and a circuit element are formed on the same semiconductor substrate, and to provide a method for manufacturing the optical semiconductor device.
It is also desired to provide an optical semiconductor device which can control a photo sensitivity relatively easily without influencing a circuit element even if a photo detector and a circuit element are formed on the same semiconductor substrate, and to provide a method for manufacturing the optical semiconductor device.
It is further desired to provide a method for manufacturing an optical semiconductor device which enables a photo detector and a circu
Flynn Nathan J.
Kabushiki Kaisha Toshiba
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Wilson Scott R
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