JP2584360B2 - Optical semiconductor device - Google Patents

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 and a bipolar IC are integrated.

[0002]

2. Description of the Related Art An optical semiconductor device in which a light receiving element and a peripheral circuit are integrated and formed in a monolithic manner is different from a hybrid IC in which a light receiving element and a circuit element are separately manufactured, and cost reduction can be expected. It has the advantage of being strong against noise due to external electromagnetic fields.

The conventional structure of such an optical semiconductor device is
For example, Japanese Patent Application Laid-Open No.
Those are known. This is shown in FIG. Smell
(1) is a P-type semiconductor substrate, and (2) is a P-type epitaxial substrate.
Axial layer, (3) N-type epitaxial layer, (4)
Is P⁺Mold separation area, (5) is N⁺Type diffusion region, (6) is N
⁺Mold buried layer, (7) is P-type base region, (8) is N⁺
Type emitter region. Photodiode (9) Is P-type
The epitaxial layer (2) and the N-type epitaxial layer (3)
Formed at the PN junction of N⁺Type diffusion region (5) as cathode
The extraction and separation area (4) is the anode extraction
is there. NPN transistor (10) Is a P-type epitaxy
Buried in the boundary between the silicon layer (2) and the N-type epitaxial layer (3).
An embedded layer (6) is provided, and an N-type epitaxial layer (3) is formed.
It was a collector. And from the substrate (1)
An acceleration electric field is formed by the auto-doping layer (11),
Easy migration of carriers generated in the region deeper than the scarce layer
It was done.

[0004] Such a device is molded with a resin through which light having the wavelength of the optical signal can pass because of the necessity of receiving the optical signal. In addition, even in a region such as the NPN transistor ( 10 ), light-generated carriers are generated by light incidence, and these carriers cause a parasitic effect or a malfunction. Therefore, it is necessary to provide the IC chip with a means for irradiating light only to the photodiode ( 9 ).

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

[0006]

However, if an Al film is deposited over the entire surface of the polyimide resin, there is a difference in the coefficient of thermal expansion between the polyimide resin and the Al film. ), The polyimide-based resin expands, causing a so-called blister defect in which the Al film swells.

[0007] Some polyimide resins alleviate the stress with the Al film, but these have the drawback that wet etching is difficult and that the cost cannot be reduced.

[0008]

SUMMARY OF THE INVENTION The present invention addresses the above disadvantages.
The electrode wiring (38) for connecting the elements,
Polyimide-based interlayer insulating film (3
9) and a photodiode (39) on the interlayer insulating film (39).2
1A light-shielding film (40) covering except for the portion ()) and a light-shielding film (40)
And a lower portion of the through hole (42).
Second light-shielding film (43) formed using the electrode wiring
To prevent blister defect of the Al film.
At the same time as the photodiode (21Light input to parts other than)
An object of the present invention is to provide an optical semiconductor device capable of preventing radiation.

[0009]

According to the present invention, since a large number of through holes (42) are formed in the light shielding film (40), the through holes (42) absorb the stress caused by the difference in thermal expansion coefficient between the polyimide resin and the Al film. it can. In addition, since the light passing through the through-hole (42) can be blocked by disposing the second light-shielding film (43) below the through-hole (42), the photodiode ( 21 )
It is possible to prevent the generation of photo-generated carriers in portions other than the portion.

[0010]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
This will be described in detail. Figure 1 shows a photodiode (21) And N
PN transistor (22Sectional view of an IC incorporating
It is. In the figure, (23) indicates a P-type single crystal silicon.
Semiconductor substrate, (24) is a vapor deposition method on the substrate (23).
15-20 μm thick first non-doped layer
Epitaxial layer, (25) is first epitaxial layer
(24) Stacked with phosphorus (P) dope by vapor phase epitaxy
A second epitaxial layer having a thickness of 4 to 6 μm. Base
The plate (23) is more impurity than that of a general bipolar IC
Use the one with low specific resistance of 40-60Ωcm,
The first epitaxial layer (24) is stacked without doping.
In this way, the diffusion area
200 after completion of the heat treatment for forming the region.
It has a specific resistance of １1500 Ω · cm. The second epitaki
The char layer (25) is formed by adding phosphorus (P) to 10 ^Fifteen-10¹⁶cm
^-3By doping about 0.5 to 3.0 Ω · cm
Has specific resistance.

First and second epitaxial layers (24)
(25) is a P that completely penetrates both ⁺Type separation area (2
6) By the photodiode (21) Forming part and NPN
Transistor (22) Formed part and electrically separated
You. This separation area (26) Is from the surface of the substrate (23)
A first separation region (27) diffused downward;
2 from the boundary between the epitaxial layers (24) and (25)
A second isolation region (28) diffused in the direction;
Third isolation region formed from the surface of the axial layer (25)
(29) and the first and second
The epitaxial layers (24) and (25) are separated into islands.

On the surface of the second epitaxial layer (25) in the photodiode ( 21 ) portion, the photodiode ( 21 )
To form an N ⁺ -type diffusion region (30) for taking out the cathode. When the N ⁺ -type diffusion region (30) is expanded to substantially the entire surface of the first island region, the take-out 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) is formed so as to cover the opening and directly contact the silicon surface. The anti-reflection film (31) is made of a silicon nitride film (SiN) having a thickness of 800 to 1000 °. 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 part. 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 ),
An N ⁺ type buried layer (34) is buried. Second epitaxial layer (25) above buried layer (34)
On the surface, 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 each diffusion region, an electrode wiring (3
8) makes ohmic contact via the contact hole.
The anode electrode (32) and the cathode electrode (33)
Is based on the first wiring layer. Electrode wiring (38)
Extends over the insulating film to electrically connect the elements, and a photodiode ( 21 ) connects the optical signal input section to the NPN
The transistor ( 22 ) forms a signal processing circuit together with other elements.

PIX (Hitachi Chemical:
Film thickness of 1.0 to 2.
0 μm interlayer insulating film (39) covers the interlayer insulating film (39)
A light shielding film (40) of an Al film is formed thereon. The light-shielding film (40) is again covered with a jacket coat (41) made of a polyimide resin. The light-shielding film (40) covers most of the area other than the photodiode ( 21 ), and is provided with slit-like through holes (42) at approximately constant intervals. The through-holes (42) have a size of about 10 μ × 10 μ, and are provided at a large number of places so that the light-shielding film (40) is not continuous with an area of 300 μ × 300 μ or more.

As shown in FIG. 2, a second light-shielding film (43) is formed below the through-hole (42) of the light-shielding film (40) to cover the through-hole (42) by the first-layer electrode wiring. I do.
The second light-shielding film (43) is formed to have a size larger than the size of the through hole (42) and about 40 μ × 40 μ. Even if it is a part of the electrode wiring (38) for connection between the elements, Dummy wirings that do not participate in the connection between them may be used.

The interlayer insulating film (39) and the light-shielding film (40) on the photodiode ( 21 ), and the
The coat (41) is removed for light incidence, and the entire chip is molded with an epoxy resin having a light refractive index equivalent to that of a silicon oxide film and transmitting light having a wavelength of an optical signal. According to the configuration of the present invention described above, since the area other than the photodiode ( 21 ) is covered with the light shielding film (40), it is possible to prevent light from entering the area other than the photodiode ( 21 ). Therefore, generation of photogenerated carriers in unnecessary portions can be prevented, and noise and malfunction can be prevented.

Further, by forming the through hole (42) in the light shielding film (40), the strain caused by the difference between the thermal expansion coefficient of the polyimide resin and the aluminum can be absorbed by the through hole (42). The blister defect of the light shielding film (40) can be prevented.
Further, a second light shielding film (43) is provided below the through hole (42).
Since the light passing through the through-hole (42) can be shielded by the second light-shielding film (43), unnecessary generation of photo-generated carriers can be prevented.

Next, the operation of the photodiode ( 21 ) will be described. The photodiode ( 21 ) is connected to the cathode electrode (3).
The such V _CC potential of the 2) + 5V, the anode electrode (33)
Are operated in a reverse bias state in which a GND potential is applied to the circuit.
When such a reverse bias is applied, the photodiode ( 2
1 ) First and second epitaxial layers (24) and (25)
The depletion layer spreads from the boundary of, and because the first epitaxial layer (24) is a high resistivity layer, it particularly greatly expands in the first epitaxial layer (24). The depletion layer spreads easily until it reaches the substrate (23) and has a thickness of 20-25.
An extremely thick depletion layer of μ can be obtained. for that reason,
The junction capacitance of the photodiode ( 21 ) is reduced to enable a high-speed response.

It should be noted that also in the present invention, the impurity (boron) in the substrate (23) is diffused into the first epitaxial layer (24) by the heat treatment of each diffusion region to form a P-type auto-doped layer. However, since the impurity concentration is not so high because it is superimposed on the non-doped layer, the effect is doubled when a substrate (23) having a relatively low impurity concentration of 40 to 60 Ω · cm is used. for that reason,
The auto-doped layer by thermal diffusion does not inhibit the expansion of the depletion layer, and a thick depletion layer can be obtained also in this regard.

Further, a first epitaxial layer (24)
When non-doped is deposited, during the epitaxial growth process, the epitaxial layer is likely to have boron (B) scattered from the substrate (23) or the first isolation region (27) recombined with silicon atoms and deposited, or to be expected from the outside. A non-impurity (mainly boron) intrusion can result in a P-type layer very close to the intrinsic layer. However, since N-type inversion is unlikely, it is possible to easily form a PIN junction or a PN junction suitable for forming a depletion layer by forming the N-type second epitaxial layer (25).

Further, since a thick depletion layer having a thickness equal to or greater than the thickness of the first epitaxial layer (24) is obtained, absorption efficiency of incident light is high, and the carrier generated in the deep portion of the photodiode ( 21 ) by that amount (outside the depletion layer). The ratio of generated carriers is also reduced, and the speed of the photodiode ( 21 ) can be increased. In addition, carriers generated by the light incidence enter the anode electrode (3) through the low-resistance separation region ( 26 ) on the anode side.
Since 3) is reached, the series resistance of the photodiode ( 21 ) can be reduced. Since the cathode side is recovered by the N ⁺ type diffusion region (30) formed so as to cover the entire surface, the series resistance can be reduced.

The structure shown in FIG. 1 can be achieved by the following manufacturing method. First, the surface of the P-type substrate (23) is thermally oxidized to form an oxide film, and the oxide film is photo-etched to form a selection mask. Then, boron (B) forming the first isolation region (27) of the isolation region ( 26 ) is diffused on the surface of the substrate (23) (FIG. 3). Next, after all the oxide film used as the selection mask is removed, the substrate (23) is placed on a susceptor of the epitaxial growth apparatus, a high temperature of about 1140 ° C. is applied to the substrate (23) by lamp heating, and SiH ₂ Cl is introduced into the reaction tube. By introducing the ₂ gas and the H ₂ gas, the non-doped first epitaxial layer (2
4) grow 15-20μ. In this way, when the growth is performed undoped, 200 to 15 at the time of completion when all processes are completed.
It can be formed on a high resistivity layer of 00 Ω · cm (FIG. 4).

Next, the surface of the first epitaxial layer (24) is thermally oxidized to form a selection mask, and antimony forming the N ⁺ type buried layer (34) of the NPN transistor ( 22 ) is diffused (FIG. 5). This heat treatment also slightly diffuses the first isolation region (27). Next, the selection mask is changed, and boron (B) forming the second isolation region (28) of the isolation region ( 26 ) is diffused. Then, a heat treatment is applied to the entire substrate (23) while applying an oxide film, and the first and second separation regions (27) and (28) are connected by diffusion. In this step, the first separation region (27) is 8 to 10
μ, the second separation region (28) is diffused by 6 to 8 μ (FIG. 6). Thereafter, the oxide film is removed to form a phosphorus-doped second epitaxial layer (25) having a thickness of 4 to 6 μ on the first epitaxial layer (24).

Next, the surface of the second epitaxial layer (25) is thermally oxidized to form a selective mask, and the isolation region ( 26 ) is formed.
The boron (B) forming the third isolation region (29) is diffused, and heat treatment is applied to the second and third isolation regions (28).
(29) is connected. In this step, the second separation region (2
8) is 4-5 μ upward, and the third separation region (29) is 1 μm.
３3μ is diffused (FIG. 7).

[0025] then under base diffusion to form a base region (35) of the NPN transistor (22), further emitter region (36) and the collector contact region of the NPN transistor (22) by performing the emitter diffusion (37),
And N ⁺ -type diffusion region (3 photodiode (21)
0) is formed (FIG. 8). Incidentally, the third separation region (29)
Can be formed by the base diffusion described above.

Next, the oxide film on the N ⁺ type diffusion region (30) is removed, a silicon nitride film (SixNy) having a thickness of about 900 ° is deposited by a CVD method, and the deposited silicon nitride film is reflected by photoetching. The prevention film (31) is formed (FIG. 9). Next, a contact hole is formed by photo-etching the oxide film, and a first wiring layer is formed by Al deposition and photo-etching. The first wiring layer forms an electrode wiring (38) in ohmic contact with each region, and also forms a second light shielding film (43) (FIG. 10).

Thereafter, the polyimide resin is spin-on
And baking to form an interlayer insulating film (39). Must
If necessary, remove the external connection electrode pad
Open by ching. And Al deposition and photo etching
A light shielding film (40) is formed by
And a photodiode (41) is formed.2
1) Jacket coat (41) and interlayer insulating film (3)
9) is removed to obtain the structure of FIG.

The structure of the photodiode ( 21 ) of the present invention is not limited to the above embodiment. For example, an N-type single-layer epitaxial layer structure, and an N ⁺ -type diffusion region (30)
Instead, a P-type region formed by base diffusion may be used. Further, the wiring structure is not limited to the above-described embodiment. For example, the inter-element connection is performed in a two-layer structure, and the light-shielding film (40) can be formed in the third layer. In this case, 1
The second light-shielding film (43) is formed as either the second layer or the second layer.

[0029]

As described above, according to the present invention,
Providing a large number of through-holes (42) in the light-shielding film (40) has an advantage that blistering failure of the light-shielding film (40) due to a difference in thermal expansion coefficient can be prevented. Further, a second light-shielding film (4) utilizing a lower layer wiring is formed below the through hole (42).
Since 3) is arranged, light passing through the through hole (42) can be shielded. Therefore, there is an advantage that generation of unnecessary light-generated carriers other than the photodiode ( 21 ) can be prevented, thereby preventing occurrence of a parasitic effect, noise, and malfunction.

Further, since the second light-shielding film (43) is formed using the lower wiring layer, there is an advantage that the number of steps is not increased. Further, since a polyimide-based resin capable of wet etching can be used, there is an advantage that the process can be simplified and the manufacturing can be performed at low cost.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an optical semiconductor device of the present invention.

FIG. 2 is a plan view for explaining the optical semiconductor device of the present invention.

FIG. 3 is a first drawing illustrating the manufacturing method of FIG. 1;

FIG. 4 is a second drawing illustrating the manufacturing method of FIG. 1;

FIG. 5 is a third drawing explaining the manufacturing method of FIG. 1;

FIG. 6 is a fourth drawing illustrating the manufacturing method of FIG. 1;

FIG. 7 is a fifth drawing for explaining the manufacturing method of FIG. 1;

FIG. 8 is a sixth drawing illustrating the manufacturing method of FIG. 1;

FIG. 9 is a seventh drawing illustrating the manufacturing method of FIG. 1;

FIG. 10 is an eighth drawing explaining the manufacturing method of FIG. 1;

FIG. 11 is a sectional view showing a conventional example.

Claims (3)

(57) [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 excluding the region of the photodiode is covered with a light shielding film, and a circuit layer is formed by a wiring layer below the light shielding film. In connection with the connection between the elements, in an optical semiconductor device in which the light-shielding film and the wiring layer are interlayer-insulated with a polyimide-based insulating film, a large number of through holes are provided in the light-shielding film, An optical semiconductor device, wherein the lower wiring layer is disposed below a through hole to form a second light-shielding film. 2. The light-shielding film according to claim 1, wherein the second light-shielding film is used to connect between circuit elements.
2. The method according to claim 1, wherein the electrode wiring is a part of the electrode wiring.
Optical semiconductor device. 3. The second light-shielding film is a dummy electrode wiring.
2. The optical semiconductor device according to claim 1, wherein: