Light detecting element and distance sensor

Abstract

The present application relates to a light detecting element and a distance sensor capable of further improving pixel characteristics. The light detecting element is configured by laminating a light-receiving substrate and a multilayer wiring layer. An avalanche multiplication region for multiplying electrons generated by one incident photon is provided in the light-receiving substrate. In the multilayer wiring layer, a plurality of wirings including an output wiring for outputting electrons generated in the avalanche multiplication region are provided in a multilayer form within an insulating film. A resistor and one or more charge injection prevention films are also provided in the multilayer wiring layer. The resistor is connected to the output wiring and is configured to improve high light amount resistance. The charge injection prevention film is arranged closer to the light-receiving substrate than the resistor and functions to prevent charge injection into the light-receiving substrate. For example, the present technology can be applied to a distance sensor using a SPAD element.

Description

Technical Field

[0001] This invention relates to light detection elements and distance sensors, and more particularly to light detection elements and distance sensors capable of further improving pixel characteristics. Background Technology

[0002] In recent years, the development of distance sensors that use SPAD (single photon avalanche diode) elements and the d-tof (direct-time of flight) method to measure the distance to a target object has been underway. The SPAD element is a photodetector that utilizes the avalanche multiplication effect, which allows electrons caused by a single photon to multiply like an avalanche.

[0003] For example, Patent Document 1 discloses a technique in which, in a photoelectric conversion device using SPAD elements, the oxide film is thickened in such a way that the thickness of the oxide film relative to the protective film meets specific conditions, thereby reducing the potential change at the surface of the semiconductor layer due to the hot carriers trapped in the protective film. Citation List Patent documents

[0004] Patent Document 1: Japanese Patent Application JP2023-45837A Summary of the Invention The technical problem to be solved by the present invention

[0005] Incidentally, it is also expected that the pixel characteristics of SPAD elements can be improved by increasing resistance to high-intensity lasers and by suppressing the degradation of DCR (dark count rate) and its deterioration over time.

[0006] The present invention was made in view of the above-described situation, and the object of the present invention is to further improve pixel characteristics. Technical solutions to solve technical problems

[0007] According to one aspect of the present invention, a photodetector element includes a photoreceiving substrate and a multilayer wiring layer. An avalanche multiplication region for multiplying electrons generated by an incident photon is provided in the photoreceiving substrate. In the multilayer wiring layer, multiple wirings are provided in a multilayer configuration within an insulating film, including output wirings for outputting electrons generated in the avalanche multiplication region. The multilayer wiring layer is stacked on the photoreceiving substrate. Here, the multilayer wiring layer includes: a resistor connected to the output wirings and configured to improve high light intensity tolerance; and one or more charge injection blocking films disposed closer to the photoreceiving substrate than the resistors and used to prevent charge injection into the photoreceiving substrate.

[0008] A distance sensor according to one aspect of the present invention includes a light detection element comprising a light receiving substrate and a multilayer wiring layer. An avalanche multiplication region for multiplying electrons generated by an incident photon is provided in the light receiving substrate. In the multilayer wiring layer, multiple wirings are arranged in a multilayer configuration within an insulating film, including output wirings for outputting electrons generated in the avalanche multiplication region. The multilayer wiring layer is stacked on the light receiving substrate. Here, the multilayer wiring layer includes: a resistor connected to the output wirings and configured to improve high light intensity tolerance; and one or more charge injection blocking films disposed closer to the light receiving substrate than the resistors and used to prevent charge injection into the light receiving substrate.

[0009] In one aspect of the invention, an avalanche multiplication region for multiplying electrons generated by an incident photon is provided in the light-receiving substrate; a plurality of wirings are provided in a multilayer configuration within an insulating film, including output wirings for outputting electrons generated in the avalanche multiplication region; and the light-receiving substrate and the multilayer wiring layer are stacked together. A resistor and one or more charge injection blocking films are also provided in the multilayer wiring layer. The resistor is connected to the output wirings and configured to improve high-light-quantity resistance, and the one or more charge injection blocking films are arranged closer to the light-receiving substrate than the resistors to prevent charge injection into the light-receiving substrate. Attached Figure Description

[0010] Figure 1 This is a block diagram illustrating a construction example of a distance sensor using this technology. Figure 2 This is a circuit diagram showing an example of the construction of a SPAD pixel. Figure 3 This is a cross-sectional view of the SPAD element installed in the light sensor. Figure 4 This is a cross-sectional view showing a variant example of a SPAD element. Figure 5 This is a diagram illustrating the manufacturing process of SPAD components. Detailed Implementation

[0011] The specific embodiments of this technology will be described in detail below with reference to the accompanying drawings.

[0012] <Example of Distance Sensor Construction> Figure 1 This is a block diagram illustrating an example of the construction of a distance sensor using this technology.

[0013] like Figure 1 As shown, the distance sensor 11 includes: an illumination unit 12 that emits an illumination laser toward the ranging target object; a light receiving unit 13 that receives the reflected laser light reflected back from the ranging target object; and a control unit 14 that controls the illumination unit 12 and the light receiving unit 13.

[0014] The illumination unit 12 includes a laser drive unit 21, a laser source 22, and a diffusion lens 23. The laser drive unit 21 drives the laser source 22 under the control of the control unit 14, causing the laser source 22 to emit pulsed illumination laser light, which is diffused by the diffusion lens 23 and then illuminates the ranging target object.

[0015] The light receiving unit 13 includes a condenser lens 31, a light sensor 32, and a signal processing unit 33. Pulsed reflected laser light from the ranging target object is focused by the condenser lens 31 onto the light receiving surface of the light sensor 32. Multiple SPAD pixels (described later) are arranged in an array on the light receiving surface of the light sensor 32. Figure 2 The SPAD pixel 41 shown outputs a light receiving signal from the SPAD pixel that has received a pulsed reflected laser, and the light receiving signal is provided to the control unit 14 after being processed in the signal processing unit 33.

[0016] The control unit 14 controls the laser drive unit 21, thereby controlling the timing of the pulsed irradiation laser emission. Then, based on the light receiving signal provided by the signal processing unit 33, the control unit 14 measures the time period (time of flight of light) from the timing of the pulsed irradiation laser emission until the timing of the pulsed reflected laser being detected by the light sensor 32. As a result, the control unit 14 is able to measure the distance to the ranging target object.

[0017] In this way, the distance sensor 11 can measure the distance to the target object by means of the d-tof method for each of the SPAD pixels arranged in an array, and can acquire a distance image of these distances arranged in an array.

[0018] Figure 2 This is a circuit diagram showing an example of the construction of SPAD pixel 41.

[0019] SPAD pixel 41 includes SPAD element 42, p-type MOSFET (metal-oxide-semiconductor field-effect transistor) 43 and CMOS (complementary metal-oxide-semiconductor) inverter 44.

[0020] By applying a large negative voltage V to the cathode of SPAD element 42 BD The SPAD element 42 can form an avalanche multiplication region and can avalanche multiply electrons generated by the incident photon. When the voltage generated by the avalanche multiplied electrons in the SPAD element 42 reaches a negative voltage V... BD At this time, the p-type MOSFET 43 releases the electrons multiplied in the SPAD element 42 and performs a recharge to restore the voltage to the initial voltage. The CMOS inverter 44 shapes the voltage generated by the electrons multiplied in the SPAD element 42 and outputs an optical receiving signal (APD OUT) in which a pulse waveform is generated starting from the arrival time of a photon.

[0021] The following will refer to Figure 3 To illustrate an example of the cross-sectional structure of the SPAD element 42 disposed in the light sensor 32.

[0022] like Figure 3 As shown, the light sensor 32 has the following structure: a multilayer wiring layer 52 is stacked on the surface of the light receiving substrate 51, and an on-chip lens 53 for converging light for the corresponding SPAD element 42 is disposed on the light receiving surface side, which is the back side of the light receiving substrate 51. Figure 3 (The upper side of the middle).

[0023] For example, the light-receiving substrate 51 is made of a semiconductor substrate obtained by thinly slicing single-crystal silicon. The concentration of p-type or n-type impurities in the semiconductor substrate is controlled, and a moth-eye structure is provided on the light-receiving surface, in which a plurality of concave and convex shapes are formed. Furthermore, in the light-receiving substrate 51, the SPAD elements 42 are spaced apart from each other by an insulating film 54 and a metal film 55 disposed between adjacent SPAD elements 42.

[0024] In the SPAD element 42, an avalanche multiplication region 61 is provided at the boundary surface where the P-type diffusion layer and the N-type diffusion layer are connected. The avalanche multiplication region 61 is a high electric field region formed at the boundary surface between the P-type diffusion layer and the N-type diffusion layer by using a large negative voltage applied to the N-type diffusion layer, and the avalanche multiplication region 61 multiplies the electrons generated by an incident photon in the SPAD element 42.

[0025] The multilayer wiring layer 52 includes multiple wirings 71 disposed in the insulating film 73 and multiple through electrodes 72. In the multilayer wiring layer 52, multiple wirings 71 are disposed in a multilayer configuration, including wirings 71-2 for outputting electrons generated in the avalanche multiplication region 61, and these wirings 71 are connected by through electrodes 72. For example, wirings 71-1 and through electrodes 72-1 are used to apply a negative voltage to the SPAD element 42, while wirings 71-2 and through electrodes 72-2 are used to output electrons generated in the SPAD element 42. It should be noted that in addition to wirings 71-1 and 71-2, the multilayer wiring layer 52 also includes multiple wirings 71 (not shown) disposed in a multilayer configuration, and wirings 71-1 and 71-2 are arranged in the layer of the multilayer wirings 71 closest to the light-receiving substrate 51.

[0026] Furthermore, a polysilicon resistor 74 is provided in the multilayer wiring layer 52 to improve the high light intensity resistance of the SPAD element 42. The polysilicon resistor 74 is connected to the wiring 71-2 via a through electrode 72-3 and is arranged closer to the light-receiving substrate 51 than the wiring 71-2. Moreover, the section D of the insulating film 73 that is positioned closer to the light-receiving substrate 51 than the polysilicon resistor 74 is designed to have a sufficient thickness, for example, of 150 nm or more. In this way, by providing an insulating film 73 with sufficient thickness, the adverse effects of the electric field caused by the polysilicon resistor 74 in the multilayer wiring layer 52 on the light-receiving substrate 51 can be suppressed.

[0027] Furthermore, in the SPAD element 42, two silicon nitride films 75-1 and 75-2 are provided between the wiring 71-1 and 71-2 arranged in the layer closest to the light receiving substrate 51 and the multilayer wiring provided in the multilayer wiring layer 52.

[0028] During the fabrication of the through electrode 72-3 connected to the polysilicon resistor 74, the silicon nitride film 75-1 functions as an etching protection film.

[0029] The silicon nitride film 75-2 functions as a charge injection barrier to prevent charge injection caused by defects in the insulating film 73 of the multilayer wiring layer 52 into the avalanche multiplication region 61 of the light-receiving substrate 51. Furthermore, during the fabrication of the through-electrode 72-1 and through-electrode 72-2 connected to the light-receiving substrate 51, the silicon nitride film 75-2 also functions as an etching protection film.

[0030] For example, the silicon nitride film 75-2 is positioned closer to the light-receiving substrate 51 than the polysilicon resistor 74, and preferably as follows: Figure 3 The silicon nitride film 75-2 is provided at the bonding surface between the light receiving substrate 51 and the insulating film 73. In addition, the silicon nitride film 75-2 is provided to cover the entire surface of the light receiving substrate 51 except for the portion through which the through electrode 72 passes.

[0031] The SPAD element 42 constructed in this way can improve high light intensity resistance due to the presence of a polysilicon resistor 74. Furthermore, in the SPAD element 42, the presence of the polysilicon resistor 74 causes electric field concentration at the interface of the polysilicon resistor 74 on the light-receiving substrate 51 side, thereby modulating the pixel potential in the light-receiving substrate 51 and increasing the electric field near the avalanche multiplication region 61. This adversely affects pixel characteristics such as DCR, but as mentioned above, these adverse effects can be suppressed by providing an insulating film 73 of sufficient thickness.

[0032] Incidentally, increasing the thickness of the insulating film 73, which is positioned closer to the light-receiving substrate 51 than the polysilicon resistor 74, would lead to an increase in intrafilm defects. Therefore, there are concerns that charge injection into the avalanche multiplication region 61 due to trapping / detrapping might occur; DCR (Discharge Reduction) might deteriorate; and degradation over time might occur. Therefore, by providing a silicon nitride film 75-2, the SPAD element 42 can prevent electrons generated in the insulating film 73 from being injected into the avalanche multiplication region 61, and can suppress DCR deterioration and degradation over time. Furthermore, the silicon nitride film 75-2 can also be used as an etching protection film.

[0033] As mentioned above, the SPAD element 42 can improve high light intensity tolerance, suppress DCR degradation and degradation over time, and further improve pixel characteristics.

[0034] It should be noted that the SPAD element 42 may also have the following structure: three or more layers of silicon nitride film 75 are disposed between the light receiving substrate 51 and the wiring 71-1 and 71-2 of the multilayer wiring layer 52.

[0035] For example, such as Figure 4 As shown, the SPAD element 42 can have the following structure: In addition to silicon nitride films 75-1 and 75-2, a silicon nitride film 75-3 is also disposed between the wirings 71-1 and 71-2 of the light-receiving substrate 51 and the multilayer wiring layer 52. As a result, the SPAD element 42 can reliably prevent electrons generated in the insulating film 73 from being injected into the avalanche multiplication region 61, and can further improve pixel characteristics.

[0036] In addition, such as Figure 5 As shown, the manufacturing process of the SPAD element 42 can be carried out as follows: a light-receiving substrate 51 having an avalanche multiplication region 61 is prepared, and a multilayer wiring layer 52 having a polysilicon resistor 74 and a silicon nitride film 75 is prepared, etc., are then bonded together to form the SPAD element 42. In this manufacturing process, the silicon nitride film 75-2 disposed on the surface of the multilayer wiring layer 52 can serve as a protective film during the planarization process.

[0037] It should be noted that instead of silicon nitride film 75, SPAD element 42 can use materials such as silicon oxynitride film, silicon carbide film, silicon carbonitride film, beryllium oxide film, silicon dioxide film and magnesium oxide film, which can prevent electrons generated in insulating film 73 from being injected into avalanche multiplication region 61.

[0038] In addition, as a resistive element for improving the high light resistance of SPAD element 42, besides polysilicon resistor 74, SPAD element 42 can also use metal resistor, germanium resistor or carbon resistor, etc.

[0039] Furthermore, the material used in the light receiving substrate 51 is not limited to silicon, but may also include, for example, germanium semiconductors or indium gallium arsenide (InGaAs) semiconductors.

[0040] The distance sensor 11, which includes the SPAD element 42 constructed as described above, can be installed in devices used for transportation purposes, such as vehicle-mounted sensors that capture images of the area in front of, behind, around, or inside a vehicle for safe driving such as automatic parking and for identifying the driver's state; surveillance cameras for monitoring moving vehicles or roads; and distance measuring sensors for measuring the distance between vehicles.

[0041] <Example of constructing a combination> It should be noted that this technology can also be constructed in the following ways. (1) A photodetector element, including: A light-receiving substrate, wherein an avalanche multiplication region is provided for multiplying electrons generated by an incident photon; and A multilayer wiring layer, wherein multiple wirings are arranged in a multilayer form within an insulating film, including output wirings for outputting electrons generated in the avalanche multiplication region. The multilayer wiring layer is stacked on the optical receiving substrate. The multilayer wiring layer includes: A resistor, connected to the output wiring, is configured to improve high light intensity resistance; and One or more charge injection blocking films are arranged closer to the light receiving substrate than the resistor and are used to prevent charge injection into the light receiving substrate. (2) The optical detection element according to (1), wherein, Two silicon nitride films are disposed between the light receiving substrate and the output wiring that is closest to the light receiving substrate among the multiple wiring layers disposed in the multilayer wiring layer. (3) The photodetector element according to (2), wherein, in the two silicon nitride films, The silicon nitride film disposed between the resistor and the output wiring functions as an etching protective film during the fabrication of the through-electrode connected to the resistor, and The silicon nitride film disposed between the resistor and the light-receiving substrate functions as a charge injection blocking film and as an etching protection film during the fabrication of the through electrode connected to the light-receiving substrate. (4) The light detection element according to any one of (1) to (3), wherein, The insulating film is arranged closer to the light-receiving substrate than the resistor, and its thickness is 150 nm or more. (5) The light detection element according to any one of (1) to (4), wherein, The charge injection blocking film is disposed at least at the interface between the light receiving substrate and the insulating film of the multilayer wiring layer. (6) The light detection element according to any one of (1) to (5), wherein, The charge injection blocking film is a silicon nitride film, a silicon oxynitride film, a silicon carbide film, a silicon carbonitride film, a beryllium oxide film, a silicon dioxide film, or a magnesium oxide film. (7) The light detection element according to any one of (1) to (6), wherein, The resistor is a polycrystalline silicon resistor, a metal resistor, a germanium resistor, or a carbon resistor. (8) The light detection element according to any one of (1) to (7), wherein, The optical detection element is constructed by the following process: preparing the optical receiving substrate and the multilayer wiring layer respectively, and then bonding the optical receiving substrate and the multilayer wiring layer together. (9) A distance sensor, comprising: a light detection element, wherein the light detection element comprises: A light-receiving substrate, wherein an avalanche multiplication region is provided for multiplying electrons generated by an incident photon; and A multilayer wiring layer, wherein multiple wirings are arranged in a multilayer form within an insulating film, including output wirings for outputting electrons generated in the avalanche multiplication region. The multilayer wiring layer is stacked on the optical receiving substrate. The multilayer wiring layer includes: A resistor, connected to the output wiring, is configured to improve high light intensity resistance; and One or more charge injection blocking films are arranged closer to the light receiving substrate than the resistor and are used to prevent charge injection into the light receiving substrate.

[0042] It should be noted that the embodiments of the present invention are not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention. Furthermore, the effects described in this specification are merely exemplary and not restrictive, and may provide other effects. Explanation of reference numerals in the attached figures

[0043] 11: Distance sensor 12: Lighting Department 13: Optical receiver 14: Control Department 21: Laser Driver Unit 22: Laser source 23: Diffuse Lens 31: Condensing lens 32: Light sensor 33: Signal Processing Department 41: SPAD pixels 42: SPAD components 43: P-type MOSFET 44: CMOS Inverter 51: Optical receiving substrate 52: Multilayer wiring 53: On-chip lens 54: Insulating film 55: Metal film 61: Avalanche Multiplication Zone 71: Wiring 72: Through electrode 73: Insulating film 74: Polycrystalline silicon resistors 75: Silicon nitride film

Claims

1. A photodetector element, including: A light-receiving substrate having an avalanche multiplication region therein for multiplying electrons generated by an incident photon; and A multilayer wiring layer, wherein multiple wirings are arranged in a multilayer form within an insulating film, including output wirings for outputting electrons generated in the avalanche multiplication region. The multilayer wiring layer is stacked on the optical receiving substrate. The multilayer wiring layer includes: A resistor, connected to the output wiring, is configured to improve high light intensity resistance; and One or more charge injection blocking films are arranged closer to the light receiving substrate than the resistor and are used to prevent charge injection into the light receiving substrate.

2. The optical detection element according to claim 1, wherein, Two silicon nitride films are disposed between the light receiving substrate and the output wiring that is closest to the light receiving substrate among the multiple wiring layers disposed in the multilayer wiring layer.

3. The optical detection element according to claim 2, wherein, Between the two silicon nitride films, The silicon nitride film disposed between the resistor and the output wiring functions as an etching protective film during the fabrication of the through-electrode connected to the resistor, and The silicon nitride film disposed between the resistor and the light-receiving substrate functions as a charge injection blocking film and as an etching protection film during the fabrication of the through electrode connected to the light-receiving substrate.

4. The optical detection element according to claim 1, wherein, The insulating film is arranged closer to the light-receiving substrate than the resistor, and its thickness is 150 nm or more.

5. The optical detection element according to claim 1, wherein, The charge injection blocking film is disposed at least at the interface between the light receiving substrate and the insulating film of the multilayer wiring layer.

6. The optical detection element according to claim 1, wherein, The charge injection blocking film is a silicon nitride film, a silicon oxynitride film, a silicon carbide film, a silicon carbonitride film, a beryllium oxide film, a silicon dioxide film, or a magnesium oxide film.

7. The optical detection element according to claim 1, wherein, The resistor is a polycrystalline silicon resistor, a metal resistor, a germanium resistor, or a carbon resistor.

8. The optical detection element according to claim 1, wherein, The optical detection element is constructed by the following process: preparing the optical receiving substrate and the multilayer wiring layer respectively, and then bonding the optical receiving substrate and the multilayer wiring layer together.

9. A distance sensor, comprising a light detection element, said light detection element comprising: A light-receiving substrate having an avalanche multiplication region therein for multiplying electrons generated by an incident photon; and A multilayer wiring layer, wherein multiple wirings are arranged in a multilayer form within an insulating film, including output wirings for outputting electrons generated in the avalanche multiplication region. The multilayer wiring layer is stacked on the optical receiving substrate. The multilayer wiring layer includes: A resistor, connected to the output wiring, is configured to improve high light intensity resistance; and One or more charge injection blocking films are arranged closer to the light receiving substrate than the resistor and are used to prevent charge injection into the light receiving substrate.

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