JPH09321271A - Integrated circuit with built-in photodiode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To use polyimide resin and prevent entry of light due to multipath reflection by placing a dummy island adjacent to a photodiode and disposing a vent of polyimide resin above the dummy island. SOLUTION: A dummy island 26 is placed adjacent to a photodiode 24a. A semiconductor chip is covered with a shielding film 23 made of an aluminum wiring layer. An opening 35 for incident optical signals is formed in the shielding film 23 above the photodiode 24a, and a vent 27 of polyimide resin is formed above the dummy island 26. The dummy island 26 is reverse-biased to form a dummy photodiode. This construction absorbs light entering through the opening 25 and the vent 27, and prevents it from reaching the internal circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct and multi-reflection type integrated circuit having a photodiode for receiving an optical signal and a circuit element for signal processing and using a polyimide resin as an interlayer insulating film. Preventing malfunction due to incident light.

[0002]

2. Description of the Related Art On the receiving side of an optical signal transmitting means by infrared rays or the like, or an optical signal reading device of an optical pickup device, a semiconductor device in which a photodiode for receiving light is integrated with its peripheral circuits has come to be used. . I
The C-ized device has the advantages that cost reduction can be expected and the device is more resistant to noise due to an external electromagnetic field, as compared with a device hybridized with individual parts.

In the above-described semiconductor device with a built-in photodiode, since the photodiode and the NPN transistor coexist, it is necessary to block the region other than the photodiode portion from the incident light so that an extra photocurrent due to the incident light on the peripheral circuit does not occur. is there. As such a light shielding means, the method of covering the peripheral circuit portion with the uppermost aluminum wiring by using a multilayer wiring technology of a semiconductor integrated circuit is the simplest (for example, Japanese Patent Application No. 4-287584).

FIG. 5 shows an example of the integrated circuit. In FIG. 5, 1 is a semiconductor chip, 2 is a light shielding film, 3 is an electrode pad, 4 is a photodiode, and 5 is a circuit element. The upper portion of the circuit element 5 is covered with the light shielding film 2, and the photodiode 4
Is opened for light incidence. Electrode pads for external connection are arranged in the electrode pads 3 so as to alternately overlap with each other so as not to short-circuit with the light shielding film 3.

FIG. 6 shows a partial sectional view. In FIG.
6 is a P-type semiconductor substrate, 7 is an N-type island region formed by separating an epitaxial layer with a P + isolation region 8, 9 is an NPN transistor formed in one of the island regions 7 as a circuit element, and 10 is an insulating It is a film. Photodiode 4 is island area 7
Is a cathode, the substrate 6 and the isolation region 8 are anodes, and an N + type cathode contact region 11 is provided on the surface of the island region 7. This integrated circuit employs a two-layer multilayer wiring structure as a whole, and the light-shielding film 2 is composed of a second aluminum wiring layer. The wiring for electrical connection of each element of the circuit element 5 is formed. The NPN transistor 9 has a P-type base region 13 and an N-type on the surface of the island region 7 serving as a collector.
The + type emitter region 14 is formed. Reference numeral 15 is an N + type collector contact region, and 16 is an N + buried layer.

[0006]

However, light incident from the outside enters the substrate not only vertically but also obliquely. In addition, light not only passes through the silicon surface but also reflects at portions having different reflectivities (such as an interface between silicon and a silicon oxide film).
Therefore, as shown in FIG. 7, the obliquely incident light 17 is reflected by the back surface side of the light-shielding film 2 and the silicon surface, and this is repeated a plurality of times (referred to as multiple reflection) to enter the area other than the photodiode. is there. If the penetrating light reaches the inside of the silicon, an undesired photocurrent is generated, which has a disadvantage that the circuit element 5 malfunctions.

There is also a demand for using an inexpensive polyimide resin as an interlayer insulating film of a multilayer wiring. However, when the surface of the polyimide resin is covered with an aluminum electrode having a certain area or more, there is a phenomenon that the aluminum electrode swells due to the gas generated from the resin. Therefore, when the aluminum electrode is covered with a large area, it is necessary to arrange a gas vent hole for each constant area, and light leaks from this hole, so that it cannot be used as an interlayer insulating film.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and a dummy island is disposed adjacent to a photodiode, and a light-shielding film covers the upper portion of the dummy island to achieve the multiple reflection. The incident light from is captured by the dummy island. Another object of the present invention is to propose a structure in which a polyimide resin can be used as an interlayer insulating film without increasing the occupied area by arranging the gas vent holes of the polyimide insulating film on the dummy islands.

Further, by providing an electrode on the dummy island and extending the electrode while interlayer-connecting it with the light-shielding film, there is provided a structure that eliminates a gap through which multiple reflected light can pass and does not reach an internal circuit. Is.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a sectional view showing an integrated circuit of the present invention. Referring to FIG. 1, 21 is a semiconductor chip, 22 is a bonding pad for external connection, 23 is a light-shielding film that covers almost the entire surface of the semiconductor chip 21, 24
a, 24b and 24c are photodiodes, 25 is an opening of the light shielding film 23 formed on each of the photodiodes 24a, 24b and 24c, and 26 is the photodiodes 24a and 2c.
Dummy islands surrounding 4b and 24c, 27
Is a gas vent hole formed in the light shielding film 23 above the dummy island 26. Although not shown, the circuit elements are arranged around the dummy island 26.

FIG. 2 is a sectional view taken along the line AA of FIG. Reference numeral 31 is a P-type semiconductor substrate, and 32 is a P + -type isolation region for separating an N-type epitaxial layer formed on the substrate by an epitaxial growth method to form a plurality of island regions 33. The photodiode 24a includes the island region 33 as a cathode, the substrate 31
The isolation region 32 is configured as an anode. An N + type cathode contact region 34 is formed on the surface of the island region 33.
The cathode electrode 35a is formed on the surface of the cathode contact region 34a, and the cathode electrode 34a is connected to the signal input terminal of the internal circuit. An anode electrode 36a is arranged on the surface of the isolation region 32 that divides the island region 33 to apply a ground potential (GND) to the anode.

An island region 33 different from the photodiode 24a
Passive elements and active elements are formed as circuit elements. The NPN transistor 37 is shown as an example. NP
The N-transistor 37 uses the island region 33 as a collector, and has a P-type base region 38 formed on the surface of the island region 33, an N + type emitter region 39 formed on the surface of the base region 38, and a collector contact region formed on the surface of the island region 33. Four
Consists of Reference numeral 41 is an N + type buried layer.

Circuit elements such as NPN transistor 37,
A dummy island 26 is provided between the photodiode 24a and the photodiode 24a.
Place. The dummy island 26 is a region in which the epitaxial layer is separated by the separation region 32 like the island region 33 for element formation. Then, a cathode region 34b is formed on the surface of the dummy island 26, and the cathode region 34b is formed.
Applying a reverse bias power supply potential (VCC) such as + 5V to the cathode electrode 35b of the dummy island 2
A dummy photodiode having 6 as a cathode and the substrate 31 and the isolation region 32 as an anode is formed.

The surface of the epitaxial layer is a silicon oxide film 4.
2 is covered with aluminum electrode 43
Extend to electrically connect each circuit element to form an integrated circuit network. In this example, a two-layer wiring structure is employed. In the two-layer wiring structure, the upper (second) electrode layer covers almost the entire surface of the oxide film to form the light shielding film 23. First
The electrode wiring of the second layer and the electrode wiring of the second layer (light-shielding film 23) are interlayer-insulated by an interlayer insulating film 44 made of a polyimide resin. In the light shielding film 23, the upper portion of the photodiode 24a is opened to have a size similar to the size of the island region forming the photodiode 24a for the incidence of an optical signal. Further, in the light-shielding film 23, on the dummy island 26, a hole 27 for degassing the polyimide resin used as the interlayer insulating film is formed with a size of about 4 μ × 4 μ.

FIG. 3 is an enlarged sectional view of the photodiode 24a portion. In the figure, the solid line indicates the diffusion region, the alternate long and short dash line indicates the first layer electrode, and the dotted line indicates the second layer electrode.
The isolation region 32 for partitioning the photodiode 24a and the dummy island 26 is designed to have a line width of about 50 μ, which is larger than the line width for partitioning other elements. This is for the purpose of separating the opening 25 of the photodiode 24a and the internal circuit element as far as possible. Further separation area 3
The anode electrode 36a formed on the surface of No. 2 is extended while contacting almost the entire surface of the isolation region 32, except for the portions where the cathode electrodes 35a of the photodiodes 24a and 24b extend. When the cathode electrode 35b is bent on the separation region 32, it becomes a structure in which the light penetrating the gap between the cathode electrode 35a and the anode electrode 36a does not easily propagate deep inside.

The light-shielding film 23 is made up of photodiodes 24a, 24.
The upper part b is removed to form the light incident opening 25, and the dummy island 26 is partially removed to form the gas vent hole 27. The cathode contact region 34b of the dummy island 26 is arranged adjacent to the gas vent hole 27, and the cathode electrode 35b is formed. The cathode electrode 35b and the cathode contact region 34b extend in a direction in which light does not enter the gas vent hole 27, that is, in the internal circuit side. The cathode electrode 35b is connected to the light shielding film 23 through a hole formed in the polyimide-based interlayer insulating film 44. That is, the light source film has a power supply potential V
Apply a fixed potential like CC. The through hole is formed over almost the entire length of the cathode electrode 35b.

FIG. 4 is an enlarged sectional view showing the vicinity of the dummy island 26. In the figure, the same parts are denoted by the same reference numerals and the description thereof will be omitted. Opening 25 above photodiode 24a
The light 50 that is obliquely incident from the light source and is repeatedly reflected on the back surface of the light shielding film 23 and is incident on the dummy island 26 is captured as a photocurrent of a dummy photodiode formed by the dummy island 26 when incident on the dummy island 26. , The photocurrent is generated between the anode electrode 36a and the cathode electrode 35b, so that it does not flow out to the internal circuit. Further, the light 50 is partially incident on the silicon surface at the silicon surface,
Since the rest is reflected, it is gradually attenuated by repeating multiple reflections. Therefore, if the line width of the separation region 32 is formed to a certain size, most of it will reach before reaching the internal circuit elements. The light 50 can be captured by the dummy photodiode.

An anode electrode 36 is formed on the isolation region 32.
By providing a, the thickness of the interlayer insulating film 44 between the anode electrode 36a and the light shielding film 23 becomes a gap through which the light 50 can enter, so that the gap can be narrowed. At the same time, the light 51 incident on the separation region 32 can be reduced by expanding the anode electrode 36a to the full width of the separation region 32 to such an extent as to cover the island region. Since the photocurrent generated in the isolation region 32 becomes a diffusion current that reaches the depletion layer by diffusion, the reaction speed is slow and the speedup of the photodiode 24a is hindered. However, by expanding the anode electrode 36a in this manner, The diffusion current can be reduced.

Further, the cathode electrode 34b of the dummy island 26 is interlayer-connected to the light-shielding film 23 through the through hole, so that the gap between the multilayer wirings, that is, the gap where the light 52 enters can be closed. Therefore, if the through hole is extended longer, the effect of blocking the invasion of the light 52 becomes higher, but this is in balance with the degassing effect described later.

The light 53 entering from the gas vent hole 27 formed on the dummy island 26 is also absorbed as a photocurrent by the dummy photodiode 26 formed by the dummy island. In addition, the shielding effect due to the interlayer connection between the cathode electrode 35b and the light shielding film 23 can be similarly obtained. Therefore, the shielding effect is highest when the cathode electrode 35b and the through hole are formed so as to surround the gas vent hole 27. However, the degassing effect disappears. Here, since the gas generated from the polyimide resin does not have straightness like light, it suffices that it be continuous with the surrounding polyimide resin even at one place. Therefore, for example, it is effective to form the through hole in a U shape and direct the open portion toward the photodiode 24a.

It is necessary to provide one gas vent hole 27 every time a certain amount or more of polyimide resin is covered with aluminum. Therefore, when the gas vent hole 27 formed on the dummy island 26 around the photodiode 24a is insufficient,
A structure equivalent to the dummy island 26 may be appropriately arranged and a gas vent hole may be arranged thereover.

[0022]

As described above, according to the present invention, since the light 50 due to the multiple reflection is absorbed by the dummy island 26, the malfunction of the internal circuit element due to the light 50 can be prevented. Furthermore, by connecting the cathode electrode 35b to the interlayer, it is possible to close the gap into which the multiple reflected light enters, which has an advantage that the invasion into the inside can be more effectively prevented.

By arranging the polyimide resin gas vent hole 27 on the dummy island 26, the dummy island 26 plays a role of absorbing the light 51, 51 from the opening 25 and the light 52 from the gas vent hole 27. Since it plays a dual role of absorbing the gas, the number of dummy islands can be reduced and the chip area can be reduced as compared with, for example, a design in which one dummy island is arranged for each gas vent hole. You can

Further, since such a design allows the use of an inexpensive polyimide resin, it can contribute to the cost reduction of the product.

[Brief description of drawings]

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

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

FIG. 3 is an enlarged plan view for explaining the present invention.

FIG. 4 is an enlarged sectional view for explaining the present invention.

FIG. 5 is a plan view for explaining a conventional example.

FIG. 6 is a cross-sectional view for explaining a conventional example.

FIG. 7 is an enlarged cross-sectional view for explaining a conventional example.

Claims (4)

[Claims] 1. A photodiode formed on a part of a semiconductor chip, a circuit element formed on another part of the semiconductor chip, and a dummy island formed adjacent to the photodiode and between the circuit element and the photodiode. An electrode wiring layer for connecting elements of the circuit element, a polyimide-based interlayer insulating film covering the electrode wiring layer, and a surface covering the surface of the interlayer insulating film on the circuit element upper part and the dummy island upper part. A light-shielding film, an opening formed in the light-shielding film for light incidence formed on the photodiode, and a gas vent hole for the light-shielding film formed on the dummy island. . 2. The integrated circuit with a built-in photodiode according to claim 1, wherein the dummy island surrounds the photodiode. 3. The integrated circuit with a built-in photodiode according to claim 1, wherein the dummy island is reversely biased to form a dummy photodiode. 4. An electrode is formed on the surface of the dummy island, the electrode is interlayer-connected to the light shielding film through a through hole, and the light shielding film is arranged near the gas vent hole on the side where light incidence is not desired. The integrated circuit with a built-in photodiode according to claim 1, wherein: