JPH0516668B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The present invention relates to a photodetector with a built-in circuit, in which a photodiode and a signal processing circuit for amplifying and shaping the waveform thereof are formed on the same substrate.

<Prior Art> This type of conventional light-receiving element with a built-in circuit generally has a structure as shown in FIGS. 8 and 9. First, in the light-receiving element of FIG. 8, as shown in the figure, an N-type epitaxial layer 2 formed on a P-type substrate 1 is separated from a signal processing circuit 4 by a separation diffusion layer 3. A photodiode is formed between the P-type substrate 1 and the N-type epitaxial layer 2 and the isolation diffusion layer 3, and metal electrodes 6 and 7 are provided on the isolation diffusion layer 3 of the N-type diffusion layer 5. It's summery. Since a reverse bias is applied to the PN junction of the photodiode by setting the electrode 6 as positive and the electrode 7 as negative, the photodiode is used in a state in which a current I is drawn from the signal processing circuit 4, as shown in FIG.

On the other hand, in the light-receiving element of FIG. 9, as shown in FIG. A photodiode is separated from the signal processing circuit 4 by an isolation diffusion layer 3, and a photodiode is formed between the N-type epitaxial layer 2 and a P-type diffusion layer 9 formed on the surface of the N-type epitaxial layer 2. Diffusion layer 9
The structure is such that metal electrodes 6 and 7 are provided on the sides. Since the electrode 6 is made positive and the electrode 7 is made negative to apply a reverse bias to the PN junction of the photodiode, the photodiode is used in a state in which a current I flows into the signal processing circuit 4, as shown in FIG.

<Problems to be Solved by the Invention> By the way, the light-receiving element shown in FIG.
Therefore, it can only be set to ground potential.

On the other hand, the photodetector shown in FIG. 9 has a photodiode formed between an N-type epitaxial layer 2 and a P-type diffusion layer 9, and is used with current flowing into the circuit 4, in which case the cathode side The N-type epitaxial layer 2 is normally set to a constant potential Vs or a power supply voltage Vcc, and has the advantage that both the anode and cathode can be set to any potential. On the other hand, when the photodiode D1 is used in a state where the current is drawn from the circuit 4 to the photodiode D1 as shown by the solid line in Fig. c of the same figure, the N-type epitaxial layer 2 and P A parasitic photodiode D2 is formed between the type substrate 1 and the N-type epitaxial layer 2 and the isolation diffusion layer 3.
Since there is a problem that a photocurrent flows through the sensor and this photocurrent is also processed as a signal current by the signal processing circuit 4, it can only be used in a state where a current flows.

That is, the light-receiving element shown in FIG. 8 is limited to use in a state in which current is extracted from the circuit 4, and the potentials of the anode and the sword cannot be arbitrarily set.On the other hand, the light-receiving element shown in FIG. Although the anode and cathode potentials can be set arbitrarily,
When used in a state in which current is drawn from the circuit 4, it is affected by a parasitic photodiode, so use is limited to a state in which current flows into the circuit 4. Therefore, there has been no light-receiving element that can be used while drawing current from the circuit 4 without being affected by the parasitic photodiode and that can arbitrarily set the potentials of the anode and cathode. Therefore, there is a problem in that the design of the circuit 4 is naturally restricted and cannot be designed freely.

The present invention has been made in view of the above-mentioned conventional problems, and allows use in a state in which current is drawn from the circuit to the photodiode without being affected by parasitic photodiodes, and the potentials of the anode and cathode can be arbitrarily set. The object of the present invention is to provide a light-receiving element with a built-in circuit.

<Means for Solving the Problems> In order to achieve the above object, the present invention provides a light receiving element with a built-in circuit in which a photodiode and its signal processing circuit are formed on the same substrate. a first N-type epitaxial layer formed and separated from the signal processing circuit by a P-type isolation diffusion layer; and a second N-type epitaxial layer isolated from the first N-type epitaxial layer by a P-type diffusion layer. type epitaxial layer, the first N-type epitaxial layer and the P-type diffusion layer are electrically short-circuited, and between the first N-type epitaxial layer and the P-type isolation diffusion layer and the aluminum wiring that shields parasitic diodes formed between the first N-type epitaxial layer and the P-type substrate, and between the second N-type epitaxial layer and the P-type diffusion layer; forming a photodiode, and connecting an electrode provided in the P-type diffusion layer on the anode side of the photodiode to a constant potential;
The gist of the present invention is that an electrode provided in electrical connection with the second N-type epitaxial layer on the cathode side is connected to the signal processing circuit.

<Function> P on the anode side of the photodiode formed between the second N-type epitaxial layer and the P-type diffusion layer
Since the type diffusion layer is connected to a constant potential and the second N-type epitaxial layer on the cathode side is connected to the signal processing circuit, the anode and cathode can be set to an arbitrary potential to draw current from the signal processing circuit. In addition to being able to be used in the same state, the influence of parasitic photodiodes can be completely excluded. In other words, the photocurrent flowing in the parasitic photodiode formed between the first N-type epitaxial layer and the P-type diffusion layer flows in a closed circuit connecting the anode and cathode due to the short circuit caused by the aluminum wiring. The parasitics are independent of the signal current and are formed between the first N-type epitaxial layer and the P-type isolation diffusion layer and between the first N-type epitaxial layer and the P-type substrate. The photodiode does not function as a photodiode because it is shielded from light by aluminum wiring.

<Example> Examples of the present invention will be described in detail below.

In FIG. 1 showing an embodiment of the present invention, P
A first N-type epitaxial layer 10 formed on a type substrate 1 is separated from the signal processing circuit 4 by P-type isolation diffusion layers 11 and 12, and a P-type diffusion layer is separated from this first N-type epitaxial layer 10. A photodiode is formed between the second N-type epitaxial layer 15 isolated by 13 and 14 and the P-type diffusion layers 13 and 14 used for the above-mentioned isolation. Electrodes 6 and 7 are provided on the N-type diffusion layer 5 and the P-type diffusion layer 13 formed in the hollow layer 15. Further, the P-type diffusion layer 14 is isolated from the P-type substrate 1 by a buried diffusion layer 16, and furthermore, the P-type diffusion layer 13 and the first N-type epitaxial layer 15 are electrically short-circuited by an aluminum wiring 17. and the first N
type epitaxial layer 10 and P type isolation diffusion layer 11,
The upper part of 12 is covered with aluminum wiring 17 via SiO ₂ insulating film 18 .

As shown in FIG. 2, in the light receiving element with a built-in circuit having the above structure, a photodiode D1 is formed between the second N-type epitaxial layer 15 and the P-type diffusion layers 13 and 14. The anode and cathode can be set to arbitrary potentials with the P-type diffusion layers 13 and 14 at a constant potential Vs, and are used in a state where current is drawn from the circuit 4. Moreover, the first N-type epitaxial layer 10 and the P-type diffusion layer 11,1
A parasitic photodiode D2 formed between
Since the photocurrent that is not used for the signal current flowing in circuit 4 is short-circuited by the aluminum wiring 17, it flows in a closed circuit connecting the anode and cathode as shown by the arrow in FIG. 2, and the signal current in circuit 4 is It's irrelevant. Furthermore, a first N-type epitaxial layer 10
The parasitic photodiodes D3 formed between the first N-type epitaxial layer 10 and the P-type isolation diffusion layer 11 and between the first N-type epitaxial layer 10 and the P-type substrate 1 are shown in FIG.
As shown by the dotted line, aluminum wiring 17
Because it is coated with a light shield and is shielded from light, it does not function as a photodiode.

The manufacturing process of the light receiving element of the above embodiment will be explained based on FIGS. 3 and 4. First, as shown in FIG. 3, a buried diffusion layer 16 is formed in a P-type substrate 1, and then a P-type impurity ( P-type diffusion layer 14 and P-type isolation diffusion layer 12 are formed by depositing boron (boron) into the photodiode forming area and isolation diffusion area by a method such as ion implantation, followed by epitaxial growth. Move on to the process. However, the isolation diffusion layer 11 may be formed shallower than usual.

Further, in FIG. 5 showing another embodiment of the present invention, the same or equivalent parts as in FIG. 1 are given the same reference numerals. As is clear from both Figures 1 and 5, they are almost identical in structure, but due to differences in the manufacturing process, the slight drawbacks of the light-receiving element in Figure 1 have been eliminated. . That is, in the light receiving element of FIG. 1, the resistance value of the P-type diffusion layer 14 for forming the photodiode D1 becomes high due to impurity compensation with the buried diffusion layer 16, and as a result, the series resistance of the photodiode D1 becomes high. hand,
This affects the response speed of photodiode D1.

Therefore, first, as shown in FIG. 6, a buried diffusion layer 16 is formed in the P-type substrate 1, and then N-type epitaxial layers 15 and 10 with a thickness of about 2 to 5 μm are formed, and then, as shown in FIG. As shown, a P-type diffusion layer 12 and a P-type diffusion layer 14 are formed by performing P-type diffusion in the photodiode formation region and isolation diffusion region, respectively, and then epitaxial growth is performed and the process is carried out in a normal process. Move. Through this process, impurity compensation between the P-type diffusion layer 14 of the photodiode D1 and the buried diffusion layer 16 is reduced, and the series resistance value of the photodiode D1 is reduced. Other manufacturing steps are the same as those in FIG.

<Effects of the Invention> As described above, according to the circuit built-in light receiving element of the present invention, the first N-type epitaxial layer in which a parasitic photodiode is formed between the P-type substrate and the P-type isolation diffusion layer, respectively. The second isolated from
A photodiode is formed between the N-type epitaxial layer and the P-type diffusion layer used for the above-mentioned isolate, and the P on the anode side of this photodiode is
Since the type diffusion layer is connected to a constant potential, and the second N-type epitaxial layer on the cathode side is connected to the signal processing circuit, the anode and cathode can be set to any potential, and current can be drawn from the signal processing circuit. It can be used in a state where it is pulled out. Moreover, even when used in this state, the photocurrent flowing through the parasitic photodiode formed between the first N-type epitaxial layer and the P-type diffusion layer is short-circuited by the aluminum wiring, so that the photocurrent flows through the anode. The signal current flows in a closed circuit connecting the cathode and the first N-type epitaxial layer, and is independent of the signal current.
The parasitic photodiodes formed between the type isolation diffusion layer and between the first N-type epitaxial layer and the P-type substrate do not act as photodiodes because they are shielded from light by the aluminum wiring, so the parasitic photodiodes do not function as photodiodes. Completely eliminates photodiode effects. Therefore, the degree of freedom in circuit design is greatly improved.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the configuration of an embodiment of a light receiving element with a built-in circuit according to the present invention, FIG. 2 is a block diagram showing the circuit configuration of FIG. 1, and FIGS. 3 and 4 are respectively similar to those in FIG. FIG. 3 is a vertical cross-sectional view showing the manufacturing process. Fifth
The figure is a longitudinal sectional view showing the configuration of another embodiment of the present invention.
6 and 7 are longitudinal sectional views showing the manufacturing process of FIG. 5, respectively. Figures 8a and 8b are a vertical cross-sectional view and a block diagram showing the circuit configuration of a conventional light-receiving element with a built-in circuit, respectively; Figures 9a and b are a vertical cross-sectional view and a block diagram of another conventional example;
The figure is a block diagram when the light-receiving element shown in figure a is used in a form that draws current from the circuit. 1...P-type board, 4...signal processing circuit, 10...
...First N-type epitaxial layer, 11, 12...
P-type separation diffusion layer, 13, 14...P-type diffusion layer, 1
5... Second N-type epitaxial layer, 17... Aluminum wiring, D1... Photodiode,
D2, D3...parasitic photodiode, 6,7...
electrode.

Claims (1)

[Claims] 1 In a light receiving element with a built-in circuit in which a photodiode and its signal processing circuit are formed on the same substrate, a first photodiode formed on a P-type substrate and separated from the signal processing circuit by a P-type separation diffusion layer is used. an N-type epitaxial layer, a second N-type epitaxial layer isolated from the first N-type epitaxial layer by a P-type diffusion layer, and the first N-type epitaxial layer;
type epitaxial layer and the P type diffusion layer, and between the first N type epitaxial layer and the P type isolation diffusion layer and between the first N type epitaxial layer and the P type diffusion layer. aluminum wiring for shielding parasitic photodiodes formed between the second N-type epitaxial layer and the P-type diffusion layer, and forming a photodiode between the second N-type epitaxial layer and the P-type diffusion layer. An electrode provided on the P-type diffusion layer on the anode side of the diode is connected to a constant potential, and an electrode provided in electrical connection with the second N-type epitaxial layer on the cathode side is connected to the signal processing circuit. A light receiving element with a built-in circuit.