JPH06275861A - Photodetector with built-in circuit - Google Patents

Abstract

PURPOSE:To enhance the optical sensitivity of a photodetector, with a built-in circuit, which is provided with a divided photodiode by a method wherein an anode is formed of a P-type buried diffused layer buried in an N-type epitaxial layer and of a P-type diffused layer diffused from the surface. CONSTITUTION:A P-type anode diffused layer for photodiode A is constituted of a P-type diffused layer 14b buried in an N-type high-resistivity semiconductor substrate 1 and of a P-type diffused layer 7b diffused from the surface. In addition, an interelement isolated and diffused layer for an NPN transistor B is formed simultaneously with an anode diffused layer for the photodiode A, the P-type anode diffused layer 7b diffused from the surface out of the anode diffused layer is formed simultaneously with a P-type base diffused layer 7 for the NPN transistor. Thereby, since the diffusion in the transverse direction of the anode diffused layer can be reduced to about 1/2 of that of conventional structures, the division width of a divided photodiode can be reduced, and the high reception sensitivity of the title photodetector can be increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light receiving element with a built-in circuit having a built-in signal processing circuit, and particularly to a light receiving element with a built-in circuit having a split photodiode used for an optical pickup or the like, which has improved photosensitivity It is related to the structure for making.

[0002]

2. Description of the Related Art A light receiving element with a built-in circuit has been conventionally used for signal detection of an optical pickup. When using a light receiving element with a built-in circuit for an optical pickup, it is important to improve the following two characteristics.

The first is to improve the photosensitivity in order to improve the S / N ratio, and the second is to improve the operating speed so that a high frequency signal such as a video signal can be handled.

As a structure for improving these two characteristics, a structure as shown in the schematic sectional views of FIGS. 6 and 7 can be considered. In each case, the surface silicon oxide film, the antireflection film, etc. are omitted.

In FIG. 6, a two-division type photodiode A is composed of an N-type epitaxial layer 4 grown on an N-type high resistivity semiconductor substrate 1 and an N-type epitaxial layer 4 in a predetermined region. The P-type anode diffusion layers 5 and 5 formed on the N-type high resistivity semiconductor substrate 1 through the epitaxial layer 4 and the N-type high resistivity at a predetermined distance from the P-type anode diffusion layers 5 and 5. N-type buried diffusion layers 3 and 3 formed to be embedded in the semiconductor substrate 1, and N-type cathode compensation diffusion layers 6 and 6 formed in the N-type epitaxial layer 4 on the N-type buried diffusion layers 3 and 3. Is formed by.

The NPN transistor B has a P-type buried diffusion layer 2 formed so as to be buried in the N-type high specific resistance semiconductor substrate 1, and an N-type buried diffusion layer 3a formed on the surface of the P-type buried diffusion layer 2. And an N type epitaxial layer 4 formed on the P type buried diffusion layer 2 and the N type buried diffusion layer 3a.
A P-type base diffusion layer 7 formed in a predetermined region on the surface of the N-type epitaxial layer 4, an N-type emitter diffusion layer 8 formed in a predetermined region on the surface of the P-type base diffusion layer 7,
N-type collector compensation diffusion layer 6a formed on N-type buried diffusion layer 3a separated from P-type base diffusion layer 7 by a predetermined distance.
It is formed by.

The photodiode A and the NPN transistor B are separated by a P-type separation diffusion layer 5a. Further, the anode diffusion layer 5 of the photodiode A is divided for focus error detection. The number of divisions depends on the detection method.

In the structure of FIG. 6, the photodiode A
Since the depletion layer that spreads over the substrate spreads in the N-type high resistivity semiconductor substrate 1, the width of the depletion layer can be widened and the photosensitivity and the operating speed can be improved.

The structure of FIG. 7 differs from the structure of FIG. 6 in that instead of the N-type high specific resistance semiconductor substrate 1, an N-type low specific resistance substrate 9 is used.
The difference is that a layered N-type high resistivity epitaxial layer 10 is used on top of this. By adopting the structure of FIG. 7, the photocarriers generated in the N-type low resistivity substrate 9 of the photodiode A have a short lifetime and hardly contribute to the photocurrent, so that the current component due to the diffusion of the photocarriers is generated. It can be reduced and the operation speed is increased. The internal series resistance of the photodiode A is shown in FIG.
The structure is reduced compared to the structure of (1), and the operation speed is also increased by reducing the CR time constant of the photodiode A.

[0010]

In order to realize a light receiving element with a built-in circuit used for an optical pickup with the structure shown in FIGS. 6 and 7, there are the following problems.

When used for an optical pickup, it is necessary to divide the anode of the photodiode A. This is to detect the focus error.

FIG. 8 shows the state of the spot 11 of the light beam in the astigmatism method, which is one of the methods for detecting the focus error with the four-division photodiode consisting of the photodiodes a, b, c and d. FIG. When (a) is in focus, (b) and (c) correspond to when the disc is too close and too far. Normal,
The focus error is detected by taking the sum of the optical signals of the photodiodes at the diagonal positions and observing the difference between the sum signals. That is, S = {(optical signal of a) + (optical signal of d)}-{(optical signal of b) + (optical signal of c)} is calculated, and S = 0 in the example of FIG. If it is, then the focus is on, if S> 0, if the disc is too close, then S <0
Then, if the disk is too far, it is detected.

Here, it can be seen from FIG. 8 that the light beam is radiated to the divided portion of the photodiode to a large extent.

FIG. 9 shows an enlarged sectional view of this divided portion.
In the figure, X is a pattern width by opening a window when the P-type anode diffusion layer 5 is formed, Y is a pattern width for directly attaching the light reflection preventing film 13 made of a silicon nitride film on the P-type anode diffusion layer, and Z is It is the effective distance between the P-type anode diffusion layers 5 and 5.

In the light receiving element with a built-in circuit having such a divided photodiode, in order to improve the signal receiving sensitivity, it is necessary to reduce the width of X and Y (hereinafter, simply referred to as division width). This will be explained below.

As is apparent from FIG. 9, a light reflection preventing film 13 made of a silicon nitride film is formed on the P type anode diffusion layer 5. However, there is a PN junction in the divided part,
Since the leak current increases when the light reflection preventing film 13 is attached, the SiO ₂ film 12 is left. For this reason, the light reflectance in the divided portion becomes large, and the signal strength becomes lower as the divided width becomes larger.

In the structure of FIGS. 6 and 7, the P-type anode diffusion layer 5 needs to penetrate the epitaxial layer 4. This is because the P-type anode diffusion layer 5 reaches the N-type high specific resistance semiconductor substrate 1 so that the depletion layer spreads in the N-type high specific resistance semiconductor substrate 1. For this reason, the P-type anode diffusion layer 5 needs to diffuse considerably deeply. At this time, the anode diffusion layer also spreads in the lateral direction. There is a problem that the sensitivity cannot be increased.

Further, if the division width is large, there is a problem that signal interference (crosstalk) between adjacent photodiodes becomes large.

[0019]

According to the present invention, an anode diffusion layer which is a second conductivity type semiconductor layer forming a photodiode is embedded in an N type high resistivity semiconductor layer which is a first conductivity type. The P-type diffusion layer and the P-type diffusion layer diffused from the surface of the N-type epitaxial layer.

[0020]

With the above structure, the lateral spread of the P-type anode diffusion layer is reduced, and the photodiode division width can be reduced, so that the light receiving sensitivity can be increased. it can. It also becomes possible to reduce crosstalk between adjacent photodiodes.

[0021]

1 is a schematic cross-sectional view when the present invention is applied to the structure of FIG. 6, and FIG. 2 is a schematic cross-sectional view when the present invention is applied to the structure of FIG. In FIG. 1, the P-type anode diffusion layer of the photodiode A is shown as an N-type high resistivity semiconductor substrate 1.
And a P-type diffusion layer 7b diffused from the surface. In FIG. 2, the P type diffusion layer 1 embedded in the N type high resistivity epitaxial layer 10 is shown.
4b and the P-type diffusion layer 7b diffused from the surface form a P-type anode diffusion layer.

In this embodiment, the element isolation diffusion of the NPN transistor B is formed simultaneously with the anode diffusion of the photodiode A. Further, of the anode diffusion, the P-type anode diffusion layer 7b that diffuses from the surface is formed simultaneously with the P-type base diffusion layer 7 of the NPN transistor.

The manufacturing process of the embodiment shown in FIG. 1 will be described below with reference to FIGS.
A schematic cross-sectional view of each step in FIG. 5 will be described. Note that FIG.
1 is used in place of the N-type high resistivity semiconductor substrate 1 except that an N-type low resistivity semiconductor substrate 9 on which an N-type high resistivity epitaxial layer 10 is grown is used.
Since it is exactly the same as the embodiment of FIG.

First, as shown in FIG. 3, a P type buried diffusion layer 2 is formed in a signal processing circuit element forming region on an N type high resistivity semiconductor substrate 1. An N type buried diffusion layer 3a is formed in a predetermined region on the surface of the P type buried diffusion layer 2. At the same time, the N-type buried diffusion layer 3 is formed on the N-type high specific resistance semiconductor substrate 1 in the photodiode formation region at a predetermined interval. The N-type buried diffusion layer 3 becomes a cathode electrode extraction region.

Further, in the anode forming region of the photodiode and the isolation diffusion forming region of the NPN transistor,
P-type diffusion layers 14b and 14a are formed, respectively.

Next, as shown in FIG. 4, several Ωc over the entire surface
The N-type epitaxial layer 4 of about m is grown. At this time, the P-type buried diffusion layers 2, 14a and 14b and the N-type buried diffusion layers 3, 3a respectively diffuse upward.

Next, as shown in FIG. 5, an N type cathode compensation diffusion layer 6 is formed in a predetermined region on the N type epitaxial layer 4.
A P-type anode diffusion layer 7b forming a photodiode,
And the P-type isolation diffusion layer 7a is formed by diffusion. In this embodiment, the P-type base diffusion layer 7 of the NPN transistor is formed at the same time. These P-type diffusion layers may be formed separately.

After that, the N-type emitter diffusion layer 8 of the NPN transistor is formed to obtain the structure of FIG. The surface is covered with a SiO ₂ film, the light receiving element portion is provided with a light reflection preventing film, and electrodes are formed at necessary portions.

The application of the present invention is not limited to the light receiving element with a built-in circuit having the structure shown in FIGS. 6 and 7, and the active layer of the photodiode is formed of a plurality of semiconductor layers of the same conductivity type. However, it is applicable to a structure in which an anode or cathode diffusion layer of the opposite conductivity type is formed penetrating one of the layers.

[0030]

According to the present invention, since the lateral diffusion of the anode diffusion layer can be reduced to about 1/2 of that of the conventional structure, the division width of the divided photodiode can be reduced and the light receiving sensitivity can be increased. can do. Also, crosstalk between adjacent photodiodes is reduced. Furthermore, the area of the light receiving element with a built-in circuit can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of another embodiment of the present invention.

FIG. 3 is a schematic cross-sectional view of a step for obtaining the structure of FIG.

4 is a schematic cross-sectional view of a step for obtaining the structure of FIG.

5 is a schematic cross-sectional view of a step for obtaining the structure of FIG.

FIG. 6 is a schematic cross-sectional view of a conventional example.

FIG. 7 is a schematic cross-sectional view of another example of the related art.

FIGS. 8A to 8C are explanatory views showing states of spots of a light beam in the astigmatism method.

FIG. 9 is an enlarged cross-sectional view of a divided portion of a photodiode.

[Explanation of symbols]

1 N-type high resistivity semiconductor substrate 2 P-type buried diffusion layer 3 N-type buried diffusion layer 4 N-type epitaxial layer 5 P-type anode diffusion layer 6 N-type cathode compensation diffusion layer 7 P-type base diffusion layer 8 N-type emitter diffusion layer 9 N-type low-resistivity substrate 10 N-type high-resistivity epitaxial layer 12 SiO ₂ film 13 Optical antireflection film 14a, 14b P-type buried diffusion layer

Claims (1)

[Claims] 1. A light receiving element and a signal processing circuit formed on a surface of a first conductivity type semiconductor substrate, wherein the light receiving element includes an epitaxial layer on a surface of the first conductivity type semiconductor substrate. And a plurality of second-conductivity-type semiconductor layers that reach the first-conductivity-type semiconductor substrate from the surface thereof. A semiconductor layer embedded in a first conductivity type semiconductor layer;
2. A light receiving element with a built-in circuit, comprising a semiconductor layer diffused from the surface of a conductive type semiconductor layer.