JPH05326917A - Optical semiconductor device - Google Patents

Abstract

PURPOSE:To perform degassing and light shielding at the same time by providing through hole 5 in an interlayer insulating film around a penetrating hole in a light shielding film, surrounding the peripheral part of the penetrating hole with the connecting part of the light shielding film and a second light shielding film, cutting a part of the connecting part so as to form a degassing path, and bending the path. CONSTITUTION:Through holes are provided around a penetrating hole 43 in a light shielding film 42. The peripheral part of the penetrating hole 43 is surrounded with a connecting part 45 of the light shielding film and a second light shielding film 44. A part of the connecting part 45 is cut so as to form a degassing path 46. The path 46 is bent and snaked. Thus, the gas generated in a polyimide resin is discharged to the outside by way of the path 46 and the penetrating hole 43. Meanwhile, a second light shielding film 44 is provided under the penetrating hole 43. Since the path is bent, light does not go out to the outside from the region surrounded with the connecting part 45 since the light has the rectilinear propagating property. In this way, the degassing and the light shielding can be made compatible at the same time.

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 in which a photodiode is integrated with a bipolar IC.

[0002]

2. Description of the Related Art An optical semiconductor device in which a light-receiving element and a peripheral circuit are integrated to form a monolithic device can be expected to reduce costs, unlike a hybrid IC in which a light-receiving element and a circuit element are separately formed. , It has a merit that it is strong against noise caused by an external electromagnetic field.

As a conventional structure of such an optical semiconductor device,
For example, as described in Japanese Patent Laid-Open No. 1-205564
Things are known. This is shown in FIG. In the figure
(1) is a P-type semiconductor substrate, and (2) is a P-type epitaxial substrate.
Axial layer, (3) is N type epitaxial layer, (4)
Is P⁺Mold separation area, (5) is N⁺Type diffusion region, (6) is N
⁺Type buried layer, (7) P type base region, (8) N type⁺
It is a mold emitter region. Photodiode (9) Is P-type
The epitaxial layer (2) and the N-type epitaxial layer (3)
PN junction of⁺Cathode type diffusion region (5)
With the take-out / separation area (4) as the anode take-out
is there. NPN transistor (10) Is P-type epitaxy
Buried at the boundary between the rule layer (2) and the N-type epitaxial layer (3)
The embedded layer (6) is provided, and the N-type epitaxial layer (3) is formed.
It was intended as a collector. And from the substrate (1)
The auto-doping layer (11) creates an accelerating electric field,
Easy movement of carriers generated in regions deeper than the depletion layer
It was done.

Since such a device needs to receive an optical signal, it is molded with a resin that allows passage of light having the wavelength of the optical signal. In addition, photo-generated carriers are also generated in the region of the NPN transistor ( 10 ) or the like due to the incidence of light, and this carrier causes a parasitic effect or malfunction. Therefore, it is necessary to provide the IC chip with a means for irradiating light only to the photodiode ( 9 ) portion.

The simplest method as the above means is to use an Al wiring layer using a multilayer wiring technique as a light shielding film. That is, after connecting elements with a single-layer or multi-layer structure, ICs are formed through an interlayer insulating film made of a polyimide resin.
An Al film is formed on the entire surface of the chip, and a photodiode ( 9 ) portion of this Al film is opened to form a window for light incidence.

[0006]

However, when the polyimide resin is coated with an Al film having a size larger than a certain area, heating (300 to 400) in the subsequent Al alloy process or the like is performed.
It is known that the phenomenon that the Al film swells due to (° C.). It is considered that this blister is caused by the fact that the polyimide-based resin is hygroscopic, so that water adheres to the resin and the water is evaporated by heat treatment.
Therefore, when covering with an Al film, it is necessary to provide a gas vent hole for each certain area (see Japanese Patent Publication No. 58-46853). On the other hand, if a gas vent hole is provided, light will naturally enter from there, and photo-generated carriers will be generated in unnecessary portions, resulting in a parasitic effect,
It may cause malfunction.

[0007]

The present invention has been made in view of the above-mentioned conventional drawbacks, and a through hole is provided around the through hole (43) of the light shielding film (42) to form the through hole (43).
Is surrounded by a connecting portion (45) between the light-shielding film (42) and the second light-shielding film (44), and a part of the connecting portion (45) is cut to form a degassing passage (46), By bending the passage (46), it is possible to provide a structure in which the shielding of the incident light and the degassing of the interlayer insulating film (41) are compatible with each other.

[0008]

According to the present invention, since the passage (46) is provided by cutting the connecting portion (45) surrounding the through hole (43), the gas generated by the polyimide resin passes through the passage (46) and the through hole (46). 43) is discharged to the outside. On the other hand, through holes (4
By providing the second light-shielding film (44) under 3) and bending the passage, the light has a straight traveling property.
There is no escape from the area surrounded by 5).

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will now be described with reference to the drawings.
Will be described in detail. First, the overall outline is explained using FIG.
To do. Figure 8 shows a photodiode (21) And NPN Transi
Star (22) Is a cross-sectional view of an integrated circuit (IC). Same figure
(23) is a P-type single crystal silicon semiconductor substrate
Plate, (24) is non-deposited on the substrate (23) by vapor phase epitaxy
First epitaxy with a thickness of 15-20 μ, laminated with dope
Layer (25) on the first epitaxial layer (24)
Thickness of 4 (P) doped by vapor phase epitaxy
˜6 μ second epitaxial layer. Board (23)
Has lower impurity concentration than that of general bipolar IC
Using the one with a specific resistance of 40-60 Ω · cm,
The axial layer (24) is a non-doped laminated layer.
Form a diffusion region of 1000 Ω · cm or more when laminated
200-1500 at the time of completion after heat treatment for
It has a specific resistance of Ω · cm. Second epitaxial layer
(25) is the phosphorus (P) 10 ¹⁵-10¹⁶cm^-3Hodo
The specific resistance of 0.5 to 3.0 Ω · cm by
Have.

First and second epitaxial layers (24)
(25) is P that completely penetrates both ⁺Mold separation area (Two
6) By a photodiode (21) Forming part and NPN
Transistor (22) Electrically separated from the forming part
It This separation area (26) Is above the substrate (23) surface
A first separation region (27) diffused downwardly,
Above and below the boundary between the two epitaxial layers (24) and (25)
Directionally diffused second isolation region (28) and a second epi region
Third separation region formed from the surface of the axial layer (25)
It consists of (29), and by connecting the three parties, the first and second
The epitaxial layers (24) and (25) are separated into islands.

On the surface of the second epitaxial layer (25) of the photodiode ( 21 ) portion, the photodiode ( 21 ) is formed.
An N ⁺ type diffusion region (30) is formed, which serves as a cathode extraction region. When the N ⁺ type diffusion region (30) is expanded over substantially the entire area of the first island region, the extraction series resistance of the cathode can be reduced. The oxide film on the N ⁺ type diffusion region (30) is partially opened, and an antireflection film (31) that directly contacts the silicon surface is formed so as to cover the opening. The antireflection film (31) is composed of a silicon nitride film (SiN) having a film thickness of 400 to 1000Å and a silicon oxide film (SiO ₂ ) having a film thickness of 4000 to 7000Å. A part of the antireflection film (31) is removed, and the cathode electrode (32) makes ohmic contact with the N ⁺ type diffusion region (30) through the contact hole in the removed portion. Further, the isolation region ( 26 ) is used as the anode-side low resistance extraction region of the photodiode ( 21 ), and the anode electrode (33) contacts the surface of the isolation region ( 26 ).

At the boundary between the first and second epitaxial layers (24) and (25) of the NPN transistor ( 22 ) part,
An N ⁺ type buried layer (34) is buried. Second epitaxial layer (25) above the buried layer (34)
A P-type base region (35), an N ⁺ -type emitter region (36), and an N ⁺ -type collector contact region (37) of the NPN transistor ( 22 ) are formed on the surface.
The electrode wiring (3
8) makes ohmic contact through the contact hole.
The anode electrode (32) and the cathode electrode (33)
Is due to the first wiring layer. PIX on it
An interlayer insulating film (39) made of the like and the second layer electrode wiring (4
0) is provided. The electrode wirings (38) and (39) extend over the insulating film to electrically connect the respective elements, and the photodiode ( 21 ) forms an optical signal input section and the NPN transistor ( 22 ) forms a signal processing circuit together with other elements. Constitute.

The PIX (Hitachi Chemical:
A film thickness of a polyimide resin such as (trade name) 1.0-2.
The 0 μ interlayer insulating film (41) covers and the interlayer insulating film (41)
A light-shielding film (42) made of a third-layer Al film is formed thereon. The light-shielding film (42) is again covered with a jacket coat made of polyimide resin. The light-shielding film (42) covers most of the region other than the photodiode ( 21 ) part, and slit-shaped through holes (43) are provided at regular intervals. The through-hole (43) has a size of about 10 μ × 10 μ, and is provided at a large number of places so that the light-shielding film (42) does not continue in an area of 300 μ × 300 μ or more.

Below the through hole (43) of the light shielding film (42), the through hole (43) is formed by the electrode wiring (40) of the second layer.
Forming a second light-shielding film (44). The second light shielding film (44) is larger than the size of the through hole (43) by 60.
It is formed to have a size of about μ × 70 μ, and it may be a part of the electrode wiring (40) for connecting the elements or a dummy wiring not involved in the connection between the elements.

Then, the interlayer insulating films (39) (41) and the light-shielding film (42) on the photodiode ( 21 ) and the jacket coat are removed for light incidence, and the entire chip is equivalent to the silicon oxide film. It is molded with an epoxy resin that has a light refractive index and allows light of the wavelength of the optical signal to pass through. The photodiode ( 21 ) applies a V _CC potential such as + 5V to the cathode electrode (32) and the anode electrode (3).
It is operated in the reverse bias state in which the GND potential is applied to 3). When such a reverse bias is applied, the first and second epitaxial layers (24) (2) of the photodiode ( 21 ) are
The depletion layer spreads from the boundary of 5), and since the first epitaxial layer (24) is a high resistivity layer, the depletion layer particularly spreads greatly in the first epitaxial layer (24). The depletion layer spreads easily until it reaches the substrate (23) and has a thickness of 20-2.
An extremely thick depletion layer of 5μ can be obtained. Therefore, the junction capacitance of the photodiode ( 21 ) is reduced and high-speed response is enabled.

Subsequently, the through hole (43) which is a feature of the present invention
The details of the section will be described. 1 is a plan view showing the through hole (43) portion, and FIG. 2 is a sectional view taken along the line AA of FIG. Through hole (4
A second light-shielding film (44) formed by the electrode wiring (40) of the second layer is arranged under the layer 3) so as to close the through hole (43), and a through hole is formed in the surrounding interlayer insulating film (41). Set up. The light-shielding film (42) and the second light-shielding film (44) are in contact with each other through the through hole to make a connection portion (45).
To form. The connection part (45) is formed so as to surround the through hole (43) (hatched part in the drawing), and a part thereof is cut. The cut portion is a polyimide-based interlayer insulating film (4
1) becomes a continuous portion, and becomes a passage (46) through which the gas generated in the interlayer insulating film (41) can pass through the path shown by the arrow. In the middle of the passage (46), the connecting portion (4
5) is protruding, and the passage (4
6) is meandered and bent to have a pattern shape so that the entrance of the passage (46) and the through hole (43) cannot be connected in a straight line.

According to such a pattern shape, the gas generated in the interlayer insulating film (41) can escape from the through hole (43) through the passage (45), so that the blistering phenomenon of Al can be prevented. On the other hand, since light has a straight-line property unlike gas, light passing through the through hole (43) passes through the passage (46).
Bending prevents the person from getting out of the passageway (46). Furthermore, since the second light-shielding film (44) exists below, it does not reach the silicon substrate (23). As described above, the present application focuses on the properties of gas and light, and can simultaneously perform degassing and light shielding.

The pattern of the connecting portion (45) is not limited to that shown in FIG. The point is that a passage through which gas can pass can be secured, and at the same time, the passage must be bent to prevent light from leaking outside. This variation is shown in Figure 3 ~
It is shown in FIG. All are patterns in which the effects of the present application can be obtained.

[0019]

As described above, according to the present invention, in an optical semiconductor device in which interlayer connection is made of a polyimide resin and a region other than the photodiode portion is covered with a light shielding film (42), degassing and excess light are prevented. This is useful because it can simultaneously shield the light.

[Brief description of drawings]

FIG. 1 is a plan view for explaining the present invention.

FIG. 2 is a cross-sectional view taken along the line AA of FIG.

FIG. 3 is a plan view showing another embodiment.

FIG. 4 is a plan view showing another embodiment.

FIG. 5 is a plan view showing another embodiment.

FIG. 6 is a plan view showing another embodiment.

FIG. 7 is a plan view showing another embodiment.

FIG. 8 is a cross-sectional view for explaining the present invention.

FIG. 9 is a cross-sectional view for explaining a conventional example.

Claims (4)

[Claims] 1. A photodiode for inputting an optical signal and a transistor for a signal processing circuit are formed on the same substrate, a region except the region of the photodiode is covered with a light shielding film, and a wiring layer lower than the light shielding film is used. In an optical semiconductor device in which a transistor is connected and interlayer insulation is performed between the light-shielding film and the wiring layer with a polyimide-based insulating film, a large number of through holes are provided in the light-shielding film, and a lower layer is formed below the through-holes. A second light-shielding film is formed of a wiring layer, a through-hole is provided in an interlayer insulating film around the through hole, and the periphery of the through-hole is surrounded by a connecting portion between the light-shielding film and the second light-shielding film, An optical semiconductor device, wherein a part of the connecting portion is cut to form a passage for degassing, and the passage is bent. 2. The optical semiconductor device according to claim 1, wherein the light shielding film and the underlying wiring layer are made of Al or Al—Si. 3. The optical semiconductor device according to claim 1, wherein the second light shielding film is an electrode wiring for connecting the circuit elements. 4. The optical semiconductor device according to claim 1, wherein the second light shielding film is a dummy electrode wiring.