JP2003188404A - Photodiode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photodiode suitable for a photodetector of an optical disk device reproducing and recording/reproducing CD and DVD while having nearly the same sensitivity between a wavelength of 650 nm and a wavelength of 780 nm. <P>SOLUTION: In the photodiode detecting the light by a pn-injection that a p-type layer 36 is formed in a n-type layer 34, nearly the same sensitivity is achieved between the wavelength of 650 nm and the wavelength of 780 nm by variably setting the depth from the surface, on which light is made incident, to the pn-injection. At the same time, the same output is achieved between CD and DVD when applying the photodiode to the photodetector of the optical disk device reproducing and recording/reproducing CD and DVD. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photodiode, and more particularly to a photodiode having a desired spectral sensitivity characteristic.

[0002]

2. Description of the Related Art FIG. 1 is a sectional view of a conventional general photodiode, and FIG. 2 is a spectral sensitivity characteristic diagram of a conventional general photodiode. In FIG. 1, an n ⁺ type embedded diffusion layer 12 for reducing parasitic resistance is formed on a p type semiconductor substrate 10, and an n type for forming a pn junction on the surface side of the n ⁺ type embedded diffusion layer 12 is formed. The epitaxial layer 14 is formed, and the p ⁺ -type diffusion layer 16 is formed in the n-type epitaxial layer 14. n-type epitaxial layer 1
An electrode 18 for applying a reverse bias is connected to 4 and p ⁺
An electrode 20 for signal extraction is connected to the mold diffusion layer 16. An insulating film 22 is formed on the surfaces of the n-type epitaxial layer 14 and the p ⁺ -type diffusion layer 16.

As shown in FIG. 2, a conventional photodiode has a spectral sensitivity characteristic in which the sensitivity peaks at a wavelength of 650 nm and decreases in a mountainous manner. The spectral sensitivity characteristic of the photodiode is affected by the depth of the pn junction forming the element from the element surface. That is, light having a shorter wavelength is absorbed at a shallower position on the element surface, and light having a longer wavelength reaches a deeper position from the element surface.

[0004]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
Disk) and DVD (Digital Versa)
In an optical disc device for reproducing and recording / reproducing a title disk, a CD uses a laser beam having a wavelength of 780 nm, whereas a DVD uses a laser beam having a wavelength of 650 nm, and a circuit for amplifying a reproduction signal has a CD and a DVD. It is required to be commonly used in and.

For this reason, as shown in FIG.
When using a general photodiode having a spectral sensitivity characteristic of peaking at 50 nm and reducing the peaks as a light receiving element of the optical pickup of the optical disk device, the output signal level of the light receiving element differs between a CD and a DVD. was there.

The present invention has been made in view of the above points, and provides a photodiode suitable for a light receiving element of an optical disk device for reproducing and recording / reproducing CD and DVD with wavelengths of 650 nm and 780 nm having substantially the same sensitivity. The purpose is to provide.

[0007]

The invention according to claim 1 is a pn in which a p-type layer (36) is formed in an n-type layer (34).
In a photodiode that performs photodetection at a junction, the depth from the surface on which light is incident to the pn junction is variably set, so that the wavelengths of 650 nm and 780 nm can be made to have substantially the same sensitivity. When applied to a light receiving element of an optical disk device for reproducing or recording / reproducing, the same output can be obtained for a CD and a DVD.

According to a second aspect of the present invention, in the photodiode according to the first aspect, the depth from the surface to the pn junction is a plurality of n-type layers (38) within the p-type layer (36). It is formed deeper by forming, and the depth from the surface to the pn junction can be easily variably set.

The invention according to claim 3 provides the n-type layer (54).
In a photodiode for detecting light at a pn junction in which a p-type layer (56) is formed, a polysilicon film (64) is provided to cover an upper portion of the pn junction where light is incident. By appropriately selecting the film thickness of (1), the wavelengths of 650 nm and 780 nm can be made to have substantially the same sensitivity, which is suitable for a light receiving element of an optical disk device for reproducing and recording / reproducing CD and DVD.

According to a fourth aspect of the present invention, in the photodiode according to the third aspect, the pn junction has a wavelength of 65.
With the spectral sensitivity characteristic of decreasing to a peak at 0 nm, by providing the polysilicon film (64), the wavelengths of 650 nm and 780 nm have almost the same sensitivity. When applied to a light receiving element of an optical disc device, the same output can be obtained for a CD and a DVD.

It should be noted that the reference numerals in the above parentheses are given for easy understanding and are merely examples, and the present invention is not limited to the illustrated modes.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 3 is a sectional structural view of a first embodiment of a photodiode of the present invention. In the figure, an n ⁺ type buried diffusion layer 32 for reducing parasitic resistance is formed on the p type semiconductor substrate 30, and an n type for forming a pn junction on the surface side of the n ⁺ type buried diffusion layer 32. The epitaxial layer 34 is formed, and the p ⁺ -type diffusion layer 36 is formed in the n-type epitaxial layer 34.

Further, a plurality of n type diffusion layers 38 are formed in the p ⁺ type diffusion layer 36. As shown in the plan view of FIG. 4A, the plurality of n-type diffusion layers 38 are rectangular and are uniformly arranged in an array. In addition to this, as shown in FIG. 4B, a plurality of n-type diffusion layers 38 may be formed in a strip shape and arranged in a comb tooth shape.

When diffusing and forming the plurality of n-type diffusion layers 38 in the p ⁺ -type diffusion layer 36, a portion of the p ⁺ -type diffusion layer 36 which is in contact with the n-type epitaxial layer 34 is extruded to thereby form an n-type epitaxial layer. It is pushed out to the 34 side. As a result, from the surface of the p ⁺ type diffusion layer 36 to the p ⁺ type diffusion layer 3
The depth to the pn junction formed by the n-type epitaxial layer 34 and the n-type epitaxial layer 34 changes depending on whether or not the position where the n-type diffusion layer 38 is formed on the surface, and in the cross section shown in FIG.
The joint becomes wavy.

A reverse bias is applied to the n-type epitaxial layer 34.
Is connected to the electrode 39 for applying ⁺In the mold diffusion layer 36
An electrode 40 for signal extraction is connected. Also, n
Type epitaxial layers 34 and p⁺On the surface of the mold diffusion layer 36
Is SiO_TwoThe insulating film 42 is formed.

As a characteristic of the light described above, the shorter the wavelength of light is, the more the light is absorbed on the surface of the semiconductor chip constituting the photodiode, and the longer the wavelength of light is, the deeper it reaches from the surface of the semiconductor chip. When the depth becomes a waveform and the depth changes, it becomes possible to widen the light absorption region with respect to the wavelength. Therefore, the spectral sensitivity characteristic of the photodiode of the present invention, which changes depending on whether or not the depth of the pn junction is at the formation position of the n-type diffusion layer 38, has a wavelength of 650 nm and a wavelength of 780 n as shown by the solid line in FIG.
With m, the sensitivity is almost the same.

The broken line in FIG. 5 shows the spectral sensitivity characteristic when the n-type diffusion layer 38 is not provided. That is, by forming the n-type diffusion layer 38, the light absorption region on the long wavelength side becomes large, the sensitivity on the short wavelength side in the spectral sensitivity characteristic of the broken line decreases, the sensitivity on the long wavelength side increases, and the solid line indicates Spectral sensitivity characteristics can be obtained.

As described above, in the photodiode of the present invention, a laser beam having a wavelength of 780 nm used in a CD and a DVD are used.
Since it has the same sensitivity to the laser light having a wavelength of 650 nm used in the above, when it is applied to a light receiving element of an optical disk device for reproducing and recording / reproducing CD and DVD, the same output can be obtained for CD and DVD.

FIG. 6 shows a second photodiode of the present invention.
The sectional structure figure of an example is shown. In the figure, a p-type semiconductor substrate 5
0, an n ⁺ type buried diffusion layer 52 for reducing parasitic resistance is formed, and an n type epitaxial layer 54 for forming a pn junction on the surface side of the n ⁺ type buried diffusion layer 52.
And ap ⁺ type diffusion layer 56 is formed in the n type epitaxial layer 54. An electrode 58 for applying a reverse bias is connected to the n-type epitaxial layer 54, and an electrode 60 for signal extraction is connected to the p ⁺ -type diffusion layer 56.
In addition, the n-type epitaxial layer 54 and the p ⁺ -type diffusion layer 56
An SiO ₂ insulating film 62 is formed on the surface of the.

From the n-type epitaxial layer 54 to SiO
The structure up to the _second insulating film 62 is the same as the conventional structure shown in FIG. Further, according to the present invention, a light-shielding polysilicon film 64 having a predetermined thickness is formed on a portion of the SiO ₂ insulating film 62 corresponding to the p ⁺ type diffusion layer 56 to cover the upper portion of the pn junction. A light shielding film 66 is formed around the polysilicon film 64.

Light having a shorter wavelength is absorbed on the surface of the semiconductor chip forming the photodiode, and light having a longer wavelength reaches a deeper position from the surface of the semiconductor chip. Then, a large amount of light on the short wavelength side is absorbed. Therefore, by properly selecting the film thickness of the polysilicon film 64, the spectral sensitivity characteristics of the photodiode of the present invention have substantially the same sensitivity at the wavelength of 650 nm and the wavelength of 780 nm as shown by the solid line in FIG. The broken line in FIG. 7 shows the spectral sensitivity characteristic when the polysilicon film 64 is not provided.

As described above, in the photodiode of the present invention, the laser beam having a wavelength of 780 nm used for CD and DVD are used.
Since it has the same sensitivity to the laser light having a wavelength of 650 nm used in the above, when it is applied to a light receiving element of an optical disk device for reproducing and recording / reproducing CD and DVD, the same output can be obtained for CD and DVD.

The photodiode of the present invention is not limited to the light receiving element for CDs and DVDs, but can be applied to other devices or illuminance sensors.

[0024]

As described above, the invention according to claim 1 is
By variably setting the depth from the surface on which light is incident to the pn junction, the same sensitivity can be obtained at a wavelength of 650 nm and a wavelength of 780 nm, and a light receiving element of an optical disk device for reproducing and recording / reproducing CD and DVD When applied to, the same output can be obtained for a CD and a DVD.

Further, in the invention described in claim 2, the depth from the surface to the pn junction is formed deeper by forming a plurality of n-type layers in the p-type layer, and the depth from the surface to the pn junction is formed. The depth can be easily variably set.

Further, in the invention described in claim 3, since the polysilicon film covering the upper portion of the pn junction on which light is incident is provided, the wavelength of 650 nm and the wavelength of 780 nm can be obtained by appropriately selecting the film thickness of the polysilicon film. It is possible to obtain almost the same sensitivity by and, which is suitable for a light receiving element of an optical disk device for reproducing and recording / reproducing CD and DVD.

Further, in the invention according to claim 4, the pn junction has a spectral sensitivity characteristic that peaks at a wavelength of 650 nm and reduces to a peak, and by providing a polysilicon film, the wavelengths of 650 nm and 780 nm are substantially the same. Due to the sensitivity, the same output can be obtained for the CD and the DVD when applied to the light receiving element of the optical disc device for performing the reproduction and the recording / reproduction of the CD and the DVD.

[Brief description of drawings]

FIG. 1 is a cross-sectional structure diagram of a conventional general photodiode.

FIG. 2 is a spectral sensitivity characteristic diagram of a conventional general photodiode.

FIG. 3 is a sectional structural view of a first embodiment of a photodiode of the present invention.

FIG. 4 is a plan view of a photodiode of the present invention.

FIG. 5 is a spectral sensitivity characteristic diagram of the photodiode of the present invention.

FIG. 6 is a sectional structural view of a second embodiment of the photodiode of the present invention.

FIG. 7 is a spectral sensitivity characteristic diagram of the photodiode of the present invention.

[Explanation of symbols]

30, 50 p type semiconductor substrate 32, 52 n ⁺ type buried diffusion layer 34, 54 n type epitaxial layer 36, 56 p ⁺ type diffusion layer 38 n type diffusion layer 39, 40, 58, 60 electrode 42, 62 SiO ₂ insulation Film 64 Polysilicon film

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Sadahisa Watanabe             1601 Sakai, Atsugi, Kanagawa Mitsumi Electric Co., Ltd.             Company Atsugi Office (72) Inventor Hidenori Gonda             1601 Sakai, Atsugi, Kanagawa Mitsumi Electric Co., Ltd.             Company Atsugi Office F-term (reference) 5F049 MA02 NA10 NB08 PA09 QA03                       QA15 SZ12 SZ13 WA01 WA03

Claims (4)

[Claims] 1. A photodiode for performing photodetection at a pn junction in which a p-type layer is formed in an n-type layer, wherein a depth from a surface on which light is incident to the pn junction is variably set. diode. 2. The photodiode according to claim 1, wherein the depth from the surface to the pn junction is variably set by forming a plurality of n-type layers in the p-type layer. Photodiode. 3. A photodiode for detecting light at a pn junction in which a p-type layer is formed in an n-type layer, wherein a polysilicon film is provided to cover an upper portion of the pn junction where light is incident. diode. 4. The photodiode according to claim 3, wherein the pn junction has a spectral sensitivity characteristic that peaks at a wavelength of 650 nm and reduces to peaks, and by providing the polysilicon film, a wavelength of 650 nm and a wavelength of 780 nm are obtained. A photodiode characterized by having almost the same sensitivity.