JPH09153604A - Optical semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical semiconductor device having a photodiode which reduces reflection of incident light and has its sensitivity improved. SOLUTION: An SiN film 7 as anti-reflective coating is provided between an N-type epitaxial layer 2 in a photodiode forming region 10 and an SinO2 film 17 located above the N-type epitaxial layer 2. This SiN film 7 has a refractive index (about 2.0) which is an intermediate value between the refractive index (about 3.4) of the epitaxial layer 2 and the refractive index (about 1.45) of the SiO2 film 17.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical semiconductor device, and more particularly to an optical semiconductor device having a photodiode which prevents reflection of light on an incident surface. In recent years, DVD (Digital Video Disk), CD (Compact Di
sk) There is an increasing demand for an optical semiconductor device in which a photodiode and its peripheral circuits are integrated on the same semiconductor substrate as a detection element used in a photodetection unit such as a ROM or MD (Mini Disk), and the light reception of these There is a demand for further improvement in the sensitivity of photodiodes used as elements.

[0002]

2. Description of the Related Art An optical semiconductor device in which a photodiode and its peripheral circuit are integrated on the same semiconductor substrate is small and lightweight, unlike a hybrid IC in which a light receiving element and a peripheral circuit are formed separately. It has the advantages that cost reduction can be expected and that it is strong against noise caused by an external electromagnetic field.

As this type of optical semiconductor device, for example, the structure disclosed in Japanese Patent Laid-Open No. 4-245478 is known. That is, as shown in FIG. 9, one N-type epitaxial layer (32) is formed on the P-type silicon substrate (31).
It is formed with a thickness of 0 to 12 μm. The epitaxial layer (32) is separated into a plurality of element regions such as a photodiode formation region (30) and an NPN transistor formation region (40) by an element isolation region (35). The element isolation region (35) includes a lower diffusion layer (33) formed by diffusing P-type impurities from the substrate (31) to the epitaxial layer (32), and the epitaxial layer (32).
And an upper diffusion layer (33) formed by diffusing a P-type impurity from the surface.

In the photodiode formation region (30), an N + type diffusion region (36) is formed on the surface of the epitaxial layer (32). In the NPN transistor formation region (40), an N + type buried layer (41) formed by introducing antimony (Sb) is provided between the substrate (31) and the epitaxial layer (32). An N type collector region (43) made of an epitaxial layer is formed on the buried layer (41). An N + type contact region (44) and a P type base region (45) are formed separately from each other on the surface of the N type collector region (43). And a P-type base region (45)
An N + type emitter region (46) is formed on the surface of the.

S is formed on the entire surface of the epitaxial layer (32).
An iO2 film (38) is formed, and the N + type diffusion region (36), the N + type contact region (44), the P type base region (45) and the N + type emitter region (46) are each a SiO2 film. It is electrically connected to the electrode (48) through the contact hole formed in (38). The SiO2 film (38) is covered with an epoxy package resin layer (49).

In the semiconductor device having the photodiode thus constructed, a reverse voltage is applied between the substrate (31) and the N + type diffusion region (36) via the electrode (48). The light reaching the epitaxial layer in this state flows through the holes generated thereby (or the light reaching the substrate (31) generates electrons) and is detected as light.

[0007]

However, the above-mentioned conventional optical semiconductor device is particularly difficult to use with the SiO2 film (38) and N2.
Since the reflectance of light at the interface with the + type diffusion region (36) is relatively high and the amount of light incident on the substrate or the epitaxial layer is small, there is a problem of low sensitivity. Hereinafter, the problem will be described in more detail.

As shown in FIG. 10, part of the light incident on the photodiode is absorbed by the package resin layer (49) and Si.
It is reflected at the interface between the O2 film (38) and the interface between the SiO2 film (38) and the epitaxial layer (32). In the case of normal incidence of light, assuming that the effect of the film thickness and the effect of multiple reflection are not considered, the reflectance R at the interface between the layer of the substance having the refractive index n1 and the layer of the substance having the refractive index n2 is represented by the following formula 1 Given in. (Equation 1) R = {(n2-n1) / (n2 + n1)} 2 * 100
(%) In the case of a normal photodiode, the package resin layer (4
Since the refractive index of 9) is about 1.55, the refractive index of the SiO2 film (38) is about 1.45, and the refractive index of the epitaxial layer (32) is about 3.4, the package resin layer (49) and Si
Although the reflectance R01 at the interface with the O2 film (38) is small at about 0.1%, the reflectance R01 at the interface between the SiO2 film (38) and the epitaxial layer (32) is as large as about 16.2%.
Therefore, in the conventional photodiode, the amount of light reaching the depletion layer is not sufficient and the sensitivity is low.

[0009]

The present invention has been made in view of the above-mentioned drawbacks of the prior art. As shown in FIG. 1, a semiconductor substrate of one conductivity type and a reverse conductivity semiconductor formed on the semiconductor substrate are provided. Type semiconductor layer, an antireflection film formed on the opposite conductivity type semiconductor layer, an insulating film formed on the antireflection film, and a package resin layer formed on the insulating film. An optical semiconductor device having a photodiode, wherein the antireflection film is made of a material having a refractive index between the refractive index of the insulating film and the refractive index of the opposite conductivity type semiconductor layer. Therefore, it is intended to reduce the reflection on the light receiving surface of the photodiode and improve the sensitivity.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION An optical semiconductor device according to an embodiment of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 is a sectional view showing the structure of an optical semiconductor device having a photodiode according to the first embodiment of the present invention.

An N type epitaxial layer (2) is formed on a P type silicon substrate (1). This epitaxial layer (2) has a plurality of device formation regions (5) such as a photodiode formation region (10) and an NPN transistor formation region (20) due to an element isolation region (5) reaching the substrate (1) from the surface of the epitaxial layer (2). It is separated into element regions. The element isolation region (5) is formed on the surface of the substrate (1) by introducing P-type impurities into the lower diffusion layer (3) formed by diffusing the impurities upward and the surface of the epitaxial layer (2). An upper diffusion layer (4) is formed by introducing a P-type impurity and diffusing the impurity downward.

Of the element regions separated by the element isolation region (5), in the photodiode formation region (10), an N + type diffusion region (6) is formed on the surface of the epitaxial layer (2). On the other hand, in the NPN transistor formation region (20), the N + type buried layer (11) is provided between the substrate (1) and the epitaxial layer (2). Further, an N + type contact region (13) and a P type base region (12) are formed separately from each other on the surface of the epitaxial layer (2) on the buried layer (11). And, on the surface of the P-type base region (12), N
A + type emitter region (14) is formed.

A first layer is formed on the entire surface of the epitaxial layer (2).
SiO2 film (16) is formed. This first S
The iO2 film (16) is formed on the photodiode formation region (1
0) and an SiN film (antireflection film) (7) is formed in the opening so as to extend slightly from the epitaxial layer (2) to the SiO2 film (16).

The first SiO2 film (16) and Si
A second SiO2 film (17) is formed on the N film (7). Then, an N + type diffusion region (6), an element isolation region (5) adjacent to the photodiode formation region (10),
N + type contact region (13), P type base region (1
2) and the N-type emitter region (14) are electrically connected to the electrode (15) through contact holes penetrating the first and second SiO2 films (16) and (17), respectively.

The SiO2 film (9) is covered with an epoxy type package resin layer (18). In the optical semiconductor device of the present embodiment configured as described above, the photodiode formation region (10) is provided via the electrode (15).
When a reverse voltage is applied between the substrate (1) and the epitaxial layer (2), a depletion layer spreads between the substrate (1) and the epitaxial layer (2). When light reaches this depletion layer,
An electron-hole pair is formed, and a current flows between the substrate (1) and the N + type diffusion region (6). This current is amplified by the NPN transistor formed in the element region adjacent to the photodiode formation region (10) and transmitted to the circuit in the subsequent stage.

At this time, as shown in FIG. 2, a part of the incident light is contained in the package resin layer (18) and the SiO2 film (17).
And the SiN film (7) and the SiN film (7) and the epitaxial layer (2). In this case, the package resin layer (18)
Has a refractive index of about 1.55, the SiO2 film (17) has a refractive index of about 1.45, the SiN film (7) has a refractive index of about 2.0, and the epitaxial layer (2) has a refractive index of about 3.4. Therefore, according to Equation 1, the reflectance R01 at the interface between the package resin (18) and the SiO2 film (17) is about 0.1%,
The reflectance R12 at the interface between the 2 film (17) and the SiN film (7)
Is about 2.5%, and the reflectance R23 at the interface between the SiN film (7) and the epitaxial layer (2) is about 6.7%.

That is, in the present embodiment, since the SiN film (7) having a refractive index between the epitaxial layer (2) and the SiO2 film (17) is interposed, the total reflectance is increased. Can be reduced. This increases the amount of light reaching the depletion layer and improves the sensitivity of the photodiode. Hereinafter, a method for manufacturing an optical semiconductor device having the above-mentioned photodiode will be described. First, as shown in FIG. 3, on a P-type silicon substrate (1),
A mask (not shown) is formed in which a portion corresponding to the region where the burying layer (11) is to be formed is formed, and antimony is used to form the burying layer (11) on the surface of the substrate (1) through the opening of the mask. (Sb) is ion-implanted. afterwards,
After removing the mask, a mask (not shown) having an opening corresponding to the lower diffusion layer (3) is formed on the substrate (1). Then, boron (B) which forms the lower diffusion layer (3) on the surface of the substrate (1) through the opening of this mask.
Is introduced. Then, the mask is removed.

Next, as shown in FIG. 4, an N type epitaxial layer (2) is formed on the substrate (1) to a thickness of 10 to 12 μm. At this time, the impurities introduced into the substrate (1) in the previous step are diffused into the epitaxial layer (2), and each impurity region is expanded. Next, as shown in FIG. 5, P-type impurities are selectively introduced into the upper diffusion layer (4) formation planned region and the base region (12) formation planned region of the surface of the epitaxial layer (2), and then the impurities are removed. Spread. By this diffusion, the upper diffusion layer (4) and the lower diffusion layer (3) are connected to each other to form an element isolation region (5).

Thereafter, as shown in FIG. 6, an N + type diffusion region (6) formation planned region, an N + type contact region (13) formation planned region and an emitter region (14) formation on the surface of the epitaxial layer (2). After introducing the N-type impurity into the predetermined region, the impurity is diffused. Next, after forming a SiO2 film (16) on the epitaxial layer (2), a photodiode forming region (1) is formed by photolithography.
The SiO2 film (16) on (0) is opened, and the SiN film (7) is formed on the epitaxial layer (2) in this opening. At this time, for example, when forming a SiN film which acts as a dielectric of the capacitive element in another region, the S
By simultaneously forming the iN film and the SiN film (17) in the photodiode formation region (10), an increase in the number of steps can be avoided.

Then, as shown in FIG.
After forming the 2 film (17), a contact hole is formed in this SiO 2 film (17) and N + is formed through this contact hole.
An electrode 15 connected to the type diffusion region (6), the contact region (13), the base region (12), the emitter region (14) and the element isolation region (5) is formed. Then, a package resin layer (18) is formed on the entire surface. This completes the manufacture of the optical semiconductor device of this embodiment.

In the above description, the case where the photodiode is integrated with the bipolar transistor has been described, but the present invention is not limited to this, and the photodiode is integrated with the MOS transistor or with the BiCMOS. It is also possible to integrate. (Second Embodiment) FIGS. 7 and 8 are a sectional view and a top view showing a photodiode portion of an optical semiconductor device according to a second embodiment of the present invention.

An N type epitaxial layer (2) is formed on a P type silicon substrate (1), and Si is formed on the surface of the epitaxial layer (2) in the photodiode formation region.
The O2 film (16) and the SiN film (2
7) are arranged in stripes. The SiN film (27) is formed on the surface of the epitaxial layer (2) from the Si surface.
It is formed so as to extend slightly above the O2 film (16). In addition, each Si on the surface of the epitaxial layer (2)
An N + type diffusion region (26) is formed in the region between the N films (27).
Are formed. In addition, SiO2 film (16) and Si
A SiO2 film (17) is formed on the N film (27). The SiO2 layer (17) is covered with the package resin layer (17). The N + type diffusion region (26) is electrically connected to an electrode (not shown) via a contact hole selectively formed in the SiO2 films (16) and (17).

By the way, the reflectance of light at the interface between the SiO2 film (17) and the SiN film (27) is
It is related to the thickness of 7). Assuming that the wavelength of light incident on the photodiode is λ, the thickness of the SiO2 film (17) is controlled with an accuracy of λ / 4 or less in order to reduce the variation in reflectance due to the thickness of the SiO2 film (17). Need to do. However, it is extremely difficult to control the film thickness of the SiO2 film (17) with such accuracy.

In the present embodiment, the N + type diffusion region (6)
The SiN film (27) is formed on the upper surface in a stripe shape, and as shown in FIG. 7, irregularities are formed on the surface of the SiO2 film (17). That is, a thick portion and a thin portion of the SiO2 film (17) are continuous on each SiN film (27). Therefore, in this embodiment, each SiN
On the film (27), there is always a portion having a low reflectance.
As a result, variations in the sensitivity of the photodiode can be suppressed, and the quality can be made uniform.
Also in this embodiment, as in the first embodiment, the SiN film (27) having a refractive index between the epitaxial layer (2) and the SiO2 film (17) is interposed between the epitaxial layer (2) and the SiO2 film (17). Therefore, a photodiode having good sensitivity can be obtained.

The photodiode of this embodiment also has
Similar to the first embodiment, it is possible to integrate the bipolar transistor, the MOS transistor and the like on the same semiconductor substrate.

[0026]

As described above, according to the optical semiconductor device of the present invention, the reverse conductivity type semiconductor layer formed on the one conductivity type semiconductor substrate and the insulating film on the reverse conductivity type semiconductor layer are formed. Since an antireflection film made of a material having a refractive index between the refractive index of the opposite conductivity type semiconductor layer and the refractive index of the insulating film is interposed therebetween, it is possible to reduce the reflectance of incident light. it can. As a result, the amount of light reaching the depletion layer of the photodiode is increased, and the sensitivity of the photodiode is improved.

Further, by forming the antireflection film in a stripe shape, variations in sensitivity due to variations in the thickness of the insulating film can be suppressed, and the quality can be made uniform. Play.

[Brief description of the drawings]

FIG. 1 is a sectional view illustrating a structure of an optical semiconductor device according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram illustrating reflection in a photodiode of the optical semiconductor device according to the first embodiment of the present invention.

FIG. 3 is a first cross-sectional view explaining the method of manufacturing the optical semiconductor device according to the first embodiment of the present invention.

FIG. 4 is a second cross-sectional view illustrating the method for manufacturing the optical semiconductor device according to the first embodiment of the present invention.

FIG. 5 is a third cross-sectional view illustrating the method for manufacturing the optical semiconductor device according to the first embodiment of the invention.

FIG. 6 is a fourth cross-sectional view illustrating the method for manufacturing the optical semiconductor device according to the first embodiment of the invention.

FIG. 7 is a cross-sectional view illustrating the structure of a photodiode of an optical semiconductor device according to a second embodiment of the present invention.

FIG. 8 is a top view illustrating the structure of the photodiode of the optical semiconductor device according to the second embodiment of the present invention.

FIG. 9 is a cross-sectional view illustrating the structure of an optical semiconductor device including a conventional photodiode.

FIG. 10 is a schematic diagram illustrating light reflection in a photodiode of a conventional optical semiconductor device.

Claims (3)

[Claims] 1. A one conductivity type semiconductor substrate, a reverse conductivity type semiconductor layer formed on the semiconductor substrate, an antireflection film formed on the reverse conductivity type semiconductor layer, and an antireflection film formed on the antireflection film. And a package resin layer formed on the insulating film, the antireflection film has a refractive index of the insulating film and a refractive index of the opposite conductivity type semiconductor layer. An optical semiconductor device, which is formed of a material having a refractive index between and. 2. The optical semiconductor device according to claim 1, wherein the antireflection film is made of silicon nitride, and the insulating film is made of silicon oxide. 3. The optical semiconductor device according to claim 1, wherein the antireflection film is formed in a stripe shape on the semiconductor layer of the opposite conductivity type.