Light detection element and distance sensor

Abstract

The present disclosure relates to a light detection element and a distance sensor with which it is possible to further improve pixel characteristics. This light detection element is configured by laminating a light-receiving substrate provided with an avalanche multiplication region for multiplying electrons generated by one incident photon, and a multilayer wiring layer in which a plurality of wiring including output wiring for outputting the electrons generated in the avalanche multiplication region are provided in multiple layers within an insulation film. The multilayer wiring layer is provided with: a resistor for improving high-light-intensity resistance, the resistor being connected to the output wiring; and one or more charge-injection-blocking films that are disposed closer to the light-receiving substrate than the resistor and block injection of charges into the light-receiving substrate. The present technology can be applied, for example, to a distance sensor in which a SPAD element is used.

Description

Light-detecting elements and distance sensors

[0001] The present disclosure relates to a light detection element and a distance sensor, and more particularly to a light detection element and a distance sensor that are capable of further improving pixel characteristics.

[0002] In recent years, development has been progressing on distance sensors that measure the distance to a target object using the d-tof (direct - time of flight) method, using a SPAD (Single Photon Avalanche Diode) element, a photodetector element that utilizes avalanche multiplication, which amplifies electrons from a single photon like an avalanche.

[0003] For example, Patent Document 1 discloses a technology for reducing potential changes on the surface of a semiconductor layer caused by hot carriers being trapped in a protective film by thickening the oxide film so that the thickness of the oxide film relative to the protective film satisfies certain conditions in a photoelectric conversion device using a SPAD element.

[0004] JP 2023-45837 A

[0005] However, there is a demand for improving the pixel characteristics of SPAD elements by improving their resistance to high-intensity laser light and suppressing deterioration of the DCR (Dark Count Rate) and degradation over time.

[0006] The present disclosure has been made in view of such circumstances, and aims to make it possible to further improve pixel characteristics.

[0007] A photodetector element according to one aspect of the present disclosure is configured by stacking a light-receiving substrate provided with an avalanche multiplication region that multiplies electrons generated by one incident photon, and a multilayer wiring layer in which a plurality of wirings including an output wiring for outputting electrons generated in the avalanche multiplication region are provided in an insulating film in multiple layers, and the multilayer wiring layer is provided with a resistor connected to the output wiring for improving resistance to high light levels, and one or more layers of charge injection blocking film that are arranged closer to the light-receiving substrate than the resistor and block the injection of charge into the light-receiving substrate.

[0008] A distance sensor according to one aspect of the present disclosure is configured by stacking a light-receiving substrate having an avalanche multiplication region that multiplies electrons generated by one incident photon, and a multilayer wiring layer in which a plurality of wirings including an output wiring for outputting electrons generated in the avalanche multiplication region are arranged in multiple layers within an insulating film, and the multilayer wiring layer is provided with a photodetector element having a resistor connected to the output wiring for improving resistance to high light levels, and one or more layers of charge injection blocking film that is arranged on the light-receiving substrate side of the resistor and prevents injection of charge into the light-receiving substrate.

[0009] In one aspect of the present disclosure, the light-receiving substrate is provided with an avalanche multiplication region that multiplies electrons generated by one incident photon, and the wiring layer is provided with multiple wirings in an insulating film, including output wiring for outputting the electrons generated in the avalanche multiplication region, and the light-receiving substrate and the multilayer wiring layer are stacked together. The multilayer wiring layer is provided with resistors connected to the output wirings and for improving resistance to high light levels, and is provided with one or more charge injection blocking films arranged on the light-receiving substrate side of the resistors and for blocking injection of charges into the light-receiving substrate.

[0010] It is a block diagram showing an example of the configuration of an embodiment of a distance sensor to which the present technology is applied. It is a circuit diagram showing an example of the configuration of a SPAD pixel. It is a cross-sectional view of a SPAD element provided in an optical sensor. It is a cross-sectional view showing a modified example of the SPAD element. It is a diagram explaining a manufacturing process of a SPAD element.

[0011] Hereinafter, specific embodiments to which the present technology is applied will be described in detail with reference to the drawings.

[0012] <Configuration Example of Distance Sensor> FIG. 1 is a block diagram showing a configuration example of a distance sensor to which the present technology is applied.

[0013] As shown in Figure 1, the distance sensor 11 is configured to include an illumination unit 12 that emits laser light toward an object to be measured, a light receiving unit 13 that receives the reflected laser light reflected by the object to be measured, and a control unit 14 that controls the illumination unit 12 and the light receiving unit 13.

[0014] The illumination unit 12 has a laser driving unit 21, a laser light source 22, and a diffusing lens 23. The laser driving unit 21 drives the laser light source 22 under the control of the control unit 14, causing the laser light source 22 to emit pulsed irradiation laser light, which is then diffused by the diffusing lens 23 and directed toward the object to be measured.

[0015] The light receiving unit 13 has a condenser lens 31, an optical sensor 32, and a signal processing unit 33. Pulse-shaped reflected laser light reflected by the object to be measured is collected by the condenser lens 31 onto the light receiving surface of the optical sensor 32. A plurality of SPAD pixels (SPAD pixels 41 shown in FIG. 2 , which will be described later) are arranged in an array on the light receiving surface of the optical sensor 32. Light receiving signals are output from the SPAD pixels that receive the pulse-shaped reflected laser light, and the light receiving signals that have been subjected to signal processing in the signal processing unit 33 are supplied to the control unit 14.

[0016] The control unit 14 controls the timing at which the pulsed irradiated laser light is emitted by controlling the laser driving unit 21. The control unit 14 then measures the time (time of flight of light) from the timing at which the pulsed irradiated laser light is emitted to the timing at which the pulsed reflected laser light is detected by the optical sensor 32, based on the light reception signal supplied from the signal processing unit 33. This allows the control unit 14 to measure the distance to the object being measured.

[0017] In this way, the distance sensor 11 can measure the distance to the object to be measured using the d-tof method for each SPAD pixel arranged in an array, and acquire a distance image in which these distances are arranged in an array.

[0018] FIG. 2 is a circuit diagram showing an example of the configuration of the SPAD pixel 41.

[0019] The SPAD pixel 41 includes a SPAD element 42 , a p-type MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) 43 , and a CMOS inverter 44 .

[0020] The SPAD element 42 applies a large negative voltage V ＢＤBy applying a negative voltage V ＢＤ When the voltage reaches , the electrons multiplied by the SPAD element 42 are released, and recharge is performed to return the voltage to the initial voltage. The CMOS inverter 44 shapes the voltage generated by the electrons multiplied by the SPAD element 42, and outputs a photodetection signal (APD OUT) in which a pulse waveform is generated starting from the arrival time of one photon.

[0021] An example of the cross-sectional configuration of the SPAD element 42 provided in the optical sensor 32 will be described with reference to FIG.

[0022] As shown in FIG. 3, the optical sensor 32 is configured such that a multilayer wiring layer 52 is stacked on the surface of a light-receiving substrate 51, and an on-chip lens 53 that focuses light for each SPAD element 42 is provided on the light-receiving surface side (upper side in FIG. 3), which is the back side of the light-receiving substrate 51.

[0023] The light-receiving substrate 51 is made of, for example, a semiconductor substrate thinly sliced ​​from single-crystal silicon, and the concentration of p-type or n-type impurities in the semiconductor substrate is controlled. The light-receiving surface is provided with a moth-eye structure in which multiple concave and convex shapes are formed. In addition, in the light-receiving substrate 51, adjacent SPAD elements 42 are separated from each other by an insulating film 54 and a metal film 55 provided between them.

[0024] In the SPAD element 42, an avalanche multiplication region 61 is provided at the interface 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 interface between the P-type diffusion layer and the N-type diffusion layer by a large negative voltage applied to the N-type diffusion layer, and multiplies electrons generated by one photon incident on the SPAD element 42.

[0025] The multilayer wiring layer 52 is configured by providing a plurality of wirings 71 and a plurality of through electrodes 72 within an insulating film 73. The multilayer wiring layer 52 is provided with a plurality of wirings 71 in multiple layers, including a wiring 71-2 for outputting electrons generated in the avalanche multiplication region 61, and these wirings 71 are connected by through electrodes 72. For example, the wiring 71-1 and the through electrode 72-1 are used to apply a negative voltage to the SPAD element 42, and the wiring 71-2 and the through electrode 72-2 are used to output electrons generated in the SPAD element 42. Note that the multilayer wiring layer 52 is configured by providing a plurality of wirings 71 (not shown) in multiple layers in addition to the wirings 71-1 and 71-2, and the wirings 71-1 and 71-2 are arranged in the layer of the wirings 71 provided in the multilayer wiring layer 52 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 tolerance 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. Furthermore, the distance D between the insulating film 73 provided closer to the light-receiving substrate 51 than the polysilicon resistor 74 is set to have a sufficient thickness, for example, 150 nm or more. In this way, by providing the insulating film 73 with a sufficient thickness, it is possible to prevent the adverse effects of the electric field caused by providing the polysilicon resistor 74 in the multilayer wiring layer 52 from affecting the light-receiving substrate 51.

[0027] The SPAD element 42 is configured by providing two layers of silicon nitride films 75-1 and 75-2 between the light-receiving substrate 51 and wiring 71-1 and wiring 71-2, which are arranged in the layer closest to the light-receiving substrate 51 among the multiple wirings provided in the multilayer wiring layer 52.

[0028] The silicon nitride film 75-1 functions as an etching protection film during the process of processing the through electrode 72-3 connected to the polysilicon resistor 74.

[0029] The silicon nitride film 75-2 functions as a charge injection blocking film for preventing charges generated by defects in the insulating film 73 of the multilayer wiring layer 52 from being injected into the avalanche multiplication region 61 of the light-receiving substrate 51. Furthermore, the silicon nitride film 75-2 functions as an etching protection film during the process of processing the through electrodes 72-1 and 72-2 connected to the light-receiving substrate 51.

[0030] For example, the silicon nitride film 75-2 is provided closer to the light-receiving substrate 51 than the polysilicon resistor 74, and is preferably provided on the bonding surface between the light-receiving substrate 51 and the insulating film 73, as shown in the figure. The silicon nitride film 75-2 is also provided so as to cover the entire surface of the light-receiving substrate 51 except for the portions where the through electrodes 72 penetrate.

[0031] The SPAD element 42 configured in this manner can improve its high light tolerance by providing the polysilicon resistor 74. Furthermore, by providing the polysilicon resistor 74 in the SPAD element 42, electric field concentration occurs at the interface closer to the light-receiving substrate 51 than the polysilicon resistor 74, modulating the pixel potential in the light-receiving substrate 51 and increasing the electric field near the avalanche multiplication region 61, which can adversely affect pixel characteristics such as DCR. This can be suppressed by providing the insulating film 73 with a sufficient thickness as described above.

[0032] However, there is a concern that an increase in defects in the film due to thickening of the insulating film 73 provided on the light-receiving substrate 51 side relative to the polysilicon resistor 74 will cause charge injection into the avalanche multiplication region 61 due to charge trapping / detrapping, resulting in a deterioration of the DCR and deterioration over time. Therefore, by providing the silicon nitride film 75-2 in the SPAD element 42, it is possible to prevent electrons generated in the insulating film 73 from being injected into the avalanche multiplication region 61, thereby suppressing the deterioration of the DCR and deterioration over time. The silicon nitride film 75-2 can also be used as an etching protection film.

[0033] In this way, the SPAD element 42 can improve the high light intensity resistance and can suppress the deterioration of DCR and degradation over time, thereby further improving the pixel characteristics.

[0034] The SPAD element 42 may have a configuration in which three or more layers of silicon nitride films 75 are provided between the light-receiving substrate 51 and the wirings 71 - 1 and 71 - 2 of the multilayer wiring layer 52 .

[0035] 4, the SPAD element 42 can be configured such that a silicon nitride film 75-3 is provided in addition to silicon nitride films 75-1 and 75-2 between the light-receiving substrate 51 and the wiring 71-1 and wiring 71-2 of the multilayer wiring layer 52. This allows the SPAD element 42 to reliably prevent electrons generated in the insulating film 73 from being injected into the avalanche multiplication region 61, thereby further improving pixel characteristics.

[0036] 5, in the manufacturing process for manufacturing the SPAD element 42, a manufacturing process can be employed in which a light-receiving substrate 51 in which the avalanche multiplication region 61 is provided and a multilayer wiring layer 52 in which the polysilicon resistor 74, the silicon nitride film 75, etc. are provided are separately produced, and then these are bonded together to form the SPAD element 42. In such a manufacturing process, the silicon nitride film 75-2 provided on the surface of the multilayer wiring layer 52 can function as a protective film in the planarization process.

[0037] In addition, instead of the silicon nitride film 75, the SPAD element 42 can use a material that can prevent electrons generated in the insulating film 73 from being injected into the avalanche multiplication region 61, such as 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.

[0038] Furthermore, in the SPAD element 42, a metal resistor, a germanium resistor, a carbon resistor, or the like may be used in addition to the polysilicon resistor 74 as a resistor element for improving the high light resistance of the SPAD element 42.

[0039] Furthermore, the material used for the light-receiving substrate 51 is not limited to silicon, but may be, for example, a germanium semiconductor or an indium gallium arsenide (InGaAs) semiconductor.

[0040] The distance sensor 11 equipped with the SPAD element 42 configured as described above can be installed in devices used for traffic purposes, such as in-vehicle sensors that photograph the front, rear, surroundings, and interior of a vehicle for safe driving such as automatic stopping, or for recognizing the driver's condition, surveillance cameras that monitor moving vehicles and roads, and distance measuring sensors that measure distances between vehicles, etc.

[0041] <Examples of Combinations of Configurations> The present technology can also be configured as follows. (1) A photodetector configured by stacking a photodetector substrate provided with an avalanche multiplication region that multiplies electrons generated by one incident photon, and a multilayer wiring layer in which a plurality of wirings including an output wiring for outputting electrons generated in the avalanche multiplication region are provided in an insulating film, wherein the multilayer wiring layer is provided with: a resistor connected to the output wiring for improving tolerance to high light; and one or more charge injection blocking films arranged on the photodetector substrate side of the resistor for blocking injection of charges into the photodetector substrate. (2) The photodetector according to (1) above, wherein two layers of silicon nitride films are provided between the photodetector substrate and the output wiring that is arranged closest to the photodetector substrate among the multiple wirings provided in the multilayer wiring layer. (3) The photodetector according to (2) above, wherein of the two silicon nitride films, the silicon nitride film provided between the resistor and the output wiring functions as an etching protection film during a process for processing a through electrode connected to the resistor, and the silicon nitride film provided between the resistor and the light-receiving substrate functions as the charge injection blocking film and as an etching protection film during a process for processing a through electrode connected to the light-receiving substrate. (4) The photodetector according to any of (1) to (3) above, wherein the insulating film located closer to the light-receiving substrate than the resistor has a thickness of 150 nm or more. (5) The photodetector according to any of (1) to (4) above, wherein the charge injection blocking film is provided at least on a bonding surface between the light-receiving substrate and the insulating film of the multilayer wiring layer. (6) The photodetector according to any of (1) to (5) above, 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 photodetector element according to any one of (1) to (6) above, wherein the resistor is a polysilicon resistor, a metal resistor, a germanium resistor, or a carbon resistor.(8) A photodetector according to any one of (1) to (7) above, which is configured by forming the photodetector substrate and the multilayer wiring layer separately and then bonding the photodetector substrate and the multilayer wiring layer together. (9) A distance sensor including a photodetector configured by laminating a photodetector substrate provided with an avalanche multiplication region that multiplies electrons generated by one incident photon, and a multilayer wiring layer in which a plurality of wirings including an output wiring for outputting electrons generated in the avalanche multiplication region are provided in an insulating film, and the multilayer wiring layer is provided with: a resistor connected to the output wiring and for improving resistance to high light; and one or more layers of charge injection blocking film arranged on the photodetector substrate side of the resistor and for blocking injection of charge into the photodetector substrate.

[0042] It should be noted that the present embodiment is not limited to the above-described embodiment, and various modifications are possible within the scope of the gist of the present disclosure. Furthermore, the effects described in this specification are merely examples and are not intended to be limiting, and other effects may also be obtained.

[0043] REFERENCE SIGNS LIST 11 Distance sensor, 12 Illumination unit, 13 Light receiving unit, 14 Control unit, 21 Laser driving unit, 22 Laser light source, 23 Diffusion lens, 31 Condenser lens, 32 Light sensor, 33 Signal processing unit, 41 SPAD pixel, 42 SPAD element, 43 p-type MOSFET, 44 CMOS inverter, 51 Light receiving substrate, 52 Multilayer wiring layer, 53 On-chip lens, 54 Insulating film, 55 Metal film, 61 Avalanche multiplication region, 71 Wiring, 72 Through electrode, 73 Insulating film, 74 Polysilicon resistor, 75 Silicon nitride film

Claims

1. A photodetector element comprising: a photodetector substrate provided with an avalanche multiplication region that multiplies electrons generated by a single incident photon; and a multilayer wiring layer in which multiple wirings, including output wiring for outputting electrons generated in the avalanche multiplication region, are provided within an insulating film; the multilayer wiring layer is provided with: a resistor connected to the output wiring to improve resistance to high light; and one or more layers of charge injection blocking film that are located closer to the photodetector substrate than the resistor and that block the injection of charge into the photodetector substrate.

2. The photodetector element according to claim 1, wherein two layers of silicon nitride film are provided between the output wiring, which is arranged closest to the light-receiving substrate among the multiple wirings provided in the multilayer wiring layer, and the light-receiving substrate.

3. The photodetector element according to claim 2, wherein of the two silicon nitride film layers, the silicon nitride film provided between the resistor and the output wiring functions as an etching protection film during the process of processing a through electrode connected to the resistor, and the silicon nitride film provided between the resistor and the light-receiving substrate functions as the charge injection blocking film and also as an etching protection film during the process of processing a through electrode connected to the light-receiving substrate.

4. The photodetector element according to claim 1, wherein the insulating film disposed closer to the light-receiving substrate than the resistor has a thickness of 150 nm or more.

5. The photodetector according to claim 1, wherein the charge injection blocking film is provided at least on the junction surface between the light-receiving substrate and the insulating film of the multilayer wiring layer.

6. The photodetector 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 photodetector element according to claim 1, wherein the resistor is a polysilicon resistor, a metal resistor, a germanium resistor, or a carbon resistor.

8. The photodetector according to claim 1, wherein the photodetector is constructed by forming the photoreceptor substrate and the multilayer wiring layer separately and then bonding the photoreceptor substrate and the multilayer wiring layer together.

9. A distance sensor comprising a photodetector element configured by laminating a photodetector substrate provided with an avalanche multiplication region that multiplies electrons generated by one incident photon, and a multilayer wiring layer in which multiple wirings including output wiring for outputting electrons generated in the avalanche multiplication region are provided in an insulating film, wherein the multilayer wiring layer is provided with: a resistor connected to the output wiring for improving resistance to high light; and one or more layers of charge injection blocking film arranged on the photodetector substrate side of the resistor for blocking injection of charge into the photodetector substrate.

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