JP2004320065A - Photodiode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photodiode having a structure insusceptible to electromagnetic noise and requiring no shield case. <P>SOLUTION: An n-type layer is formed on a p-type substrate becoming a first p-type layer, the n-type layer is isolated from the edge by providing a p-type isolation belt around the n-type layer, a second p-type layer is formed in contact with the p-type isolation belt while leaving a part thereof on the n-type layer, and covered with a protective film layer. First and second electrodes are provided on the protective film layer, the first electrode is connected with the n-type layer through an opening formed in the protective film layer, and the second electrode is connected with the p-type isolation belt. The second electrode is connected with the ground potential, the first and second p-type layers are brought to the ground potential, and charges generated through photoelectric conversion are outputted from the first electrode. Since the second p-type layer is connected with the ground potential and has a low impedance, it exhibits shield effect and electromagnetic noise from the surface is shielded. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to photodiodes, and more particularly, to photodiodes that are less susceptible to electromagnetic noise.

2. Description of the Related Art Photodiodes that receive light and convert it into electric signals are frequently used as receiving elements in remote control and optical communication devices.
As shown in FIG. 5, a conventional photodiode is formed by forming an n-type layer 52 on a p-type substrate 51, and a lower surface of the p-type substrate 51 is connected to a ground potential by a silver paste 53 or the like. 54 is die-bonded. Therefore, the anode 56 is on the frame side, and the cathode 55 is on the chip surface side that receives light.

The light incident from the chip surface is photoelectrically converted at the bonding surface between the n-type layer 52 and the p-type substrate 51, and the generated charges are extracted from the cathode 55 as a signal indicating the amount of received light.
As shown in FIG. 6, the cathode 55 is connected to the signal processing circuit 9, and a weak signal output from the cathode is amplified and then subjected to processing according to the device.

  However, in the photodiode having the above configuration, the cathode on the chip surface has high impedance, so that it receives electromagnetic noise from other parts of the device in which the photodiode is incorporated, such as a cathode ray tube or a computer, and easily outputs a false signal. Has become. The false signal causes a malfunction of the signal processing circuit, and causes serious problems such as a malfunction of the remote control and a change in information by optical communication.

For this reason, conventionally, electromagnetic noise is cut off by covering the photodiode with a metallic shield case, thereby preventing the photodiode from outputting a false signal.
However, covering with a shield case increases the size of the photodiode, increases the number of parts, increases the cost, and increases the number of manufacturing steps. Although the shield case is an effective method for blocking electromagnetic noise, it does not essentially solve the weak point of the photodiode, which is easily affected by electromagnetic noise.

  An object of the present invention is to provide a photodiode that has a structure that is not easily affected by electromagnetic noise and does not require a shield case.

  The invention according to claim 1 has a first p-type layer and an n-type layer formed on the first p-type layer, and receives light from the n-type layer side and performs photoelectric conversion to generate the light. A second p-type layer provided on the n-type layer; a first electrode for outputting charge from the n-type layer; a second electrode for connecting the p-type layer and the second p-type layer to a predetermined potential that makes them low impedance, wherein the second p-type layer includes the first electrode and the n-type layer. A photodiode formed so as to surround a connection portion with a mold layer.

  Light enters from the second p-type layer, and photoelectric conversion is performed at the junction surface between the second p-type layer and the n-type layer and between the n-type layer and the first p-type layer. The charge generated by the photoelectric conversion is output from the n-type layer, and a second p-type layer is provided above the n-type layer. Since the second p-type layer is connected to a predetermined potential such as a ground potential and has a low impedance, it has a shielding effect and can block external electromagnetic noise. Therefore, no electromagnetic noise reaches the n-type layer, and no charge generated by the noise is output from the n-type layer.

Therefore, according to the photodiode of the present invention, since the external electromagnetic noise is cut off by the second p-type layer, no signal due to the noise is output. Therefore, it is not necessary to cover the photodiode with the shield case, and the cost can be reduced and the number of manufacturing steps can be reduced.
The invention according to claim 2 is characterized in that the second p-type layer covers the entire area of the n-type layer except for a connection portion between the first electrode and the n-type layer. A photodiode according to claim 1.

The invention according to claim 3 further includes a p-type band formed around the n-type layer and connected to the first p-type layer, wherein the second p-type layer is connected to the p-type band. The photodiode according to claim 1, wherein:
The invention according to claim 4 is the photodiode according to any one of claims 1 to 3, wherein the first electrode is ohmic-connected to the n-type layer.

  The invention according to claim 5 is characterized in that, in the n-type layer, a high-concentration layer containing an n-type impurity at a higher concentration than the surroundings is arranged at an ohmic connection with the first electrode. A photodiode according to claim 4.

Embodiment of the Invention

Hereinafter, the photodiode of the present invention will be described with reference to the drawings.
FIG. 1 shows a cross-sectional view of a chip of a photodiode 1 according to a reference example, and FIG. 2 shows a plan view thereof. The photodiode 1 includes a first p-type layer 11, an n-type layer 12, a second p-type layer 13, a protective film layer 14, and two electrodes 15 and 16.
The n-type layer 12 is formed by epitaxial growth on a p-type Si substrate, which is the first p-type layer 11, and is separated from the chip edge by a p-type band 11a formed around by diffusion of p-type impurities. Have been. The second p-type layer 13 is formed by implanting ions into the n-type layer 12, and is provided above a region excluding a peripheral portion of the n-type layer 12.

The protective film layer 14 is made of SiO ₂ or SiN and is provided so as to cover the entire upper surface of the chip. The protective film layer 14 has an opening 14a for exposing the n-type layer 12, an opening 14b for exposing the second p-type layer 13, and an opening 14c for exposing the p-type band 11a. Is formed.
The first electrode 15 is provided on the opening 14 a and is connected to the n-type layer 12. The second electrode 16 is provided on the opening 14b and the opening 14c, is connected to the second p-type layer 13, and is connected to the first p-type layer 11 via the p-type band 11a. . The electrode 15 is ohmic-connected to the n-type layer 12. In the ohmic connection, a high-concentration layer containing an n-type impurity at a higher concentration than the surroundings is provided at the ohmic connection with the electrode 15 in the n-type layer 12. It is arranged and formed. Similarly, the electrode 16 is ohmically connected to the second p-type layer 13 and the p-type band 11a.

The electrode 16 is connected to the ground potential. As a result, both the first p-type layer 11 and the second p-type layer 13 have the ground potential.
The photodiode 1 receives light from the chip surface side on which the protective film layer 14 is provided. The light passes through the protective film layer 14, and photoelectric conversion is performed at the bonding surface between the second p-type layer 13 and the n-type layer 12 and between the n-type layer 12 and the first p-type layer 11. The charge generated by the photoelectric conversion is output from the n-type layer 12 to the electrode 15.

In the above configuration, the electrode 15 functions as a cathode and the electrode 16 functions as an anode. The electrode 15 is connected to a signal processing circuit (not shown) at the time of mounting, and an output signal from the electrode 15 representing the amount of light received by the photodiode 1 is amplified by the signal processing circuit and then processed according to a device incorporating the photodiode 1. Receive.
Even if other parts of the device generate electromagnetic noise and enter the photodiode 1 from the chip surface, the second p-type layer 13 is connected to the ground potential and has a low impedance. Is blocked by the second p-type layer 13. Therefore, the electromagnetic noise does not reach the n-type layer 12, and no charge due to external electromagnetic noise appears on the electrode 15. Therefore, the signal processing circuit always operates correctly, and the reliability of the device incorporating the photodiode 1 is extremely high.

The second p-type layer 13 performs the same function as a conventional shield case. That is, the photodiode 1 has a structure for shielding electromagnetic noise inside, and operates stably without being covered by the shield case. Therefore, the photodiode 1 can be used alone.
Here, the opening 14b of the protective film layer 14 is formed along one side of the second p-type layer 13, and the second p-type layer 13 and the electrode 16 are connected linearly. The opening 14 b may be formed along four sides of the second p-type layer 13, and the second p-type layer 13 may be surrounded by the electrode 16. The entire range of the second p-type layer 13 is uniformly at the ground potential, and the function of blocking electromagnetic noise is further enhanced.

  FIG. 3 shows a cross section of the photodiode according to the first embodiment of the present invention. In the photodiode 2, the second p-type layer 13 and the p-type band 11a are internally connected, and the second p-type layer 13 is formed on the protective film layer 14 of the photodiode 1 of the above-described reference example. An opening 14b for connecting the layer 13 and the electrode 16 is not formed. The second p-type layer 13 is connected to the electrode 16 via the p-type band 11a, similarly to the first p-type layer 11.

  In the photodiode 2, a second p-type layer 13 is formed over the entire n-type layer 12 except for an edge required for connection with the electrode 15. In this way, the second p-type layer 13 is connected to the p-type band 11a at three edges, so that the entire second p-type layer 13 is uniformly at the ground potential, and the electromagnetic noise is reduced. The effect of blocking increases. In addition, since the entire range of the n-type layer 12 is covered with the second p-type layer 13 or the electrode 15, electromagnetic noise can be reliably shut off.

  More specifically, as shown by hatching in FIG. 3A, the second p-type layer 13 covers the entire area of the n-type layer 12 except for the connection between the electrode 15 and the n-type layer 12. ing. More specifically, as shown in an enlarged manner in FIG. 3B, since the connection between the electrode 15 and the n-type layer 12 is disposed inside the edge of the n-type layer, a region other than the connection is used. In this case, the first p-type layer 13 covering the entire range of the n-type layer 12 is also formed at the edge of the n-type layer 12 on the electrode 15 side. As a result, the second p-type layer 13 surrounds the connection between the electrode 15 and the n-type layer 12 over the entire circumference.

Further, since the second p-type layer 13 is connected to the p-type band 11a surrounding the n-type layer 12, the p-type portion composed of the second n-type layer and the p-type band 11a is The connection between the electrode 15 and the n-type layer 12 is surrounded over the entire circumference.
Other configurations are the same as those of the photodiode 1, and the description is omitted.
FIG. 4 shows a cross section of the photodiode according to the second embodiment. In the photodiode 3, the second p-type layer 13 and the p-type band 11a are internally connected, and the first p-type layer 11 is connected to the ground potential from an electrode 16a provided on the lower surface thereof. You. The second p-type layer 13 is connected to the ground potential via the p-type band 11a and the first p-type layer 11.

In the photodiode 1 of the reference example, the two openings 14 b and 14 c of the protective film layer 14 and the electrode 16 are not formed in the photodiode 3. The photodiode 3 is die-bonded to a frame by using silver paste or the like.
Other configurations are the same as those of the photodiode 2, and the description is omitted.

FIG. 4 is a cross-sectional view schematically illustrating a structure of a photodiode according to a reference example. FIG. 2 is a plan view schematically showing the structure of the photodiode in FIG. 1. FIG. 2 is a cross-sectional view schematically illustrating the structure of the photodiode according to the first embodiment. FIG. 4 is a plan view schematically showing the structure of the photodiode in FIG. 3. FIG. 4 is an enlarged sectional view of a part of the photodiode of FIG. 3. FIG. 4 is a cross-sectional view schematically illustrating a structure of a photodiode according to a second embodiment. FIG. 9 is a diagram schematically illustrating a structure of a conventional photodiode. FIG. 7 is a diagram showing connection between a conventional photodiode and a circuit for processing an output signal of the photodiode.

Explanation of reference numerals

Reference Signs List 1 photodiode 2 photodiode 3 photodiode 11 first p-type layer 11a p-type band 12 n-type layer 13 second p-type layer 14 protective film layer 14a opening 14b opening 14c opening 15 electrode (cathode)
16 electrodes (anode)

Claims (5)

It has a first p-type layer and an n-type layer formed on the first p-type layer, receives light from the n-type layer side, performs photoelectric conversion, and outputs generated charges from the n-type layer. In a photodiode,
A second p-type layer provided on the n-type layer;
A first electrode for outputting a charge from the n-type layer;
A second electrode for connecting the first p-type layer and the second p-type layer to a predetermined potential that makes them low impedance,
The photodiode, wherein the second p-type layer is formed to surround a connection between the first electrode and the n-type layer.   2. The photodiode according to claim 1, wherein the second p-type layer covers an entire area of the n-type layer except for a connection portion between the first electrode and the n-type layer. 3. A p-type band formed around the n-type layer and connected to the first p-type layer;
The photodiode according to claim 1, wherein the second p-type layer is connected to the p-type band.   4. The photodiode according to claim 1, wherein the first electrode is ohmically connected to the n-type layer.   5. The photodiode according to claim 4, wherein in the n-type layer, a high-concentration layer containing an n-type impurity at a higher concentration than the surroundings is arranged at an ohmic connection with the first electrode.

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