Solid-state imaging device and imaging system

Abstract

A solid-state imaging device includes a first semiconductor and a second semiconductor having a different composition from the first semiconductor and electrically connected to the first semiconductor. The first semiconductor has a photodiode that photoelectrically converts incident light, a plurality of first charge accumulation portions that accumulate electric charges generated by the photoelectric conversion, and a transfer gate that moves the electric charges generated by the photoelectric conversion to a certain one of the plurality of first charge accumulation portions. The second semiconductor has a second charge accumulation portion that can accumulate electric charges, and a potential detection node that detects a potential of the second charge accumulation portion. The solid-state imaging device further includes a reset transistor that resets a potential of the first charge accumulation portion to a prescribed potential.

Description

Technical Field

[0001] This invention relates to solid-state imaging elements and imaging systems.

[0002] This application is based on and claims priority to Japan Patent Application No. 2020-054149 filed on March 25, 2020, the contents of which are incorporated herein by reference. Background Technology

[0003] Camera elements are used in various fields. One of them is the camera system capable of ranging.

[0004] Such a camera system typically includes a light source that generates light to illuminate the subject, and an imaging element. The imaging element functions as a camera sensor that captures images of the reflected light from the subject.

[0005] As a problem related to the aforementioned camera element, there is noise caused by external light. One countermeasure to reduce this noise is the use of light in the near-infrared to short-wavelength infrared band (preferably in the 1350nm to 1400nm range, which is almost entirely absent in sunlight). This would reduce the influence of more external light, including sunlight, to almost zero.

[0006] To construct a distance-measuring camera system using light in this wavelength band, a camera element capable of efficiently converting the light in this band into photoelectric components is required. Germanium (Ge) and similar materials with high absorption coefficients can be considered for this purpose.

[0007] Patent document 1 discloses a device in which a photodiode is formed on a layer containing Ge and silicon (Si).

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: U.S. Patent Application Publication No. 2017 / 0040362 Summary of the Invention

[0011] The problem that the invention aims to solve

[0012] The device described in Patent Document 1 has a first semiconductor in which a photodiode is formed, and a second semiconductor in which a silicon substrate is formed. Charge generated by photoelectric conversion in the first semiconductor moves to the second semiconductor to perform charge-voltage conversion, but the specific method of charge transfer is not described; only a known interconnect using conductive wiring and a diffusion layer is shown as an example.

[0013] In imaging elements, the charge generated in a photodiode is sometimes distributed and driven to multiple charge accumulation regions. Patent Document 1 also describes a TOF (time of flight) optical sensor in which the charge transferred to a second semiconductor is distributed and driven to two charge accumulation regions.

[0014] However, in the device described in Patent Document 1, when the first semiconductor and the second semiconductor are joined in the manner illustrated above, there is a diffusion layer between the photodiode and the gate for dispensing, so the dispensing drive may not actually be able to be performed well.

[0015] In view of the above, the object of the present invention is to provide a solid-state imaging element that can efficiently utilize light in the near-infrared to short-wavelength infrared band and can perform good distribution driving.

[0016] Methods for solving problems

[0017] The solid-state imaging element of the first aspect of the present invention includes a first semiconductor and a second semiconductor having a different composition from the first semiconductor and being electrically connected to the first semiconductor.

[0018] The first semiconductor includes a photodiode that performs photoelectric conversion using incident light, a plurality of first charge storage units that store the charge generated by the photoelectric conversion, and a transfer controller that moves the charge generated by the photoelectric conversion to one of the first charge storage units.

[0019] The second semiconductor has a second charge storage section capable of storing charge and a potential detector for detecting the potential of the second charge storage section.

[0020] The solid-state imaging element further includes a resetter that resets the potential of the first charge accumulation section to a predetermined potential.

[0021] The imaging system of the second aspect of the present invention includes a light source unit that emits emitted light having a predetermined wavelength distribution, and a solid-state imaging element of the first aspect.

[0022] The effects of the invention

[0023] According to the above-described method of the present invention, light in the near-infrared to short-wavelength infrared band can be utilized efficiently, and the distribution drive can be well performed. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of a solid-state imaging element according to one embodiment of the present invention.

[0025] Figure 2 This is a schematic diagram of a modified example of the solid-state imaging element.

[0026] Figure 3 This is a diagram illustrating an example of a camera element that uses multiple of the same solid-state camera element.

[0027] Figure 4 This is a diagram illustrating an example of a camera system that uses this solid-state imaging element.

[0028] Figure 5 This is a partial schematic diagram of a solid-state imaging element according to a modified example of the present invention.

[0029] Figure 6 This is a partial schematic diagram of a solid-state imaging element according to a modified example of the present invention.

[0030] Figure 7 This is a partial schematic diagram of a solid-state imaging element according to a modified example of the present invention.

[0031] Figure 8 This is a partial schematic diagram of a solid-state imaging element according to a modified example of the present invention.

[0032] Figure 9 This is a partial schematic diagram of a solid-state imaging element according to a modified example of the present invention.

[0033] Figure 10 This is a schematic diagram of a solid-state imaging element according to a modified example of the present invention.

[0034] Figure 11 This is a schematic diagram of a solid-state imaging element according to a modified example of the present invention. Detailed Implementation

[0035] Reference Figures 1 to 4 One embodiment of the present invention will be described.

[0036] Figure 1 This is a schematic diagram illustrating the configuration of the solid-state imaging element 1 according to this embodiment. The solid-state imaging element 1 is configured by electrically connecting a first semiconductor 10 and a second semiconductor 30. The first semiconductor 10 and the second semiconductor 30 have different constituent elements and different lattice constants.

[0037] The first semiconductor 10 is configured to have a known photodiode (PD) 11, which performs photoelectric conversion on incident light and can store signal charge. Depending on the impurity concentration of the first semiconductor 10, the photodiode 11 can also be omitted. In this case, the geometric region occupied by the photodiode 11 in the first semiconductor 10 has the function of photoelectric conversion.

[0038] The first semiconductor 10 is configured such that, at least in a portion of the photodiode 11, it contains a large number of elements or compounds that have excellent absorption characteristics for light in the near-infrared to short-wavelength infrared band, particularly in the 1350 nm to 1400 nm range. Typical examples of such materials are Ge, and other examples include germanium compounds such as GeSi (germanium silicon) and GaSb (gallium antimonide). Hereinafter, these materials will be collectively referred to as "Ge, etc."

[0039] The physical structure of the first semiconductor 10 is not particularly limited. It can be a uniform composition formed entirely of Ge monomers or mixed crystals such as Ge, or it can have a structure in which Ge and other materials such as silicon are alternately stacked.

[0040] The following explanation assumes that the first semiconductor 10 is a P-type semiconductor, but the same explanation can be given if the first semiconductor 10 is an N-type semiconductor. Furthermore, when the semiconductor is a P-type semiconductor, "p" is sometimes added to the diagram. Similarly, when it is an N-type semiconductor, "n" is sometimes added; when it is a p+ type semiconductor region, "p+" is sometimes added; and when it is an n+ type semiconductor region, "n+" is sometimes added.

[0041] The first semiconductor 10 has a plurality of first charge storage sections 12. In this embodiment, the first charge storage section 12 is, for example, an n+ type semiconductor region. Two first charge storage sections 12, including a first charge storage section 12A and a first charge storage section 12B, are provided in the first semiconductor 10. A transfer gate (transfer controller) 13 is provided between the photodiode 11 and each of the first charge storage sections 12. The transfer gate (transfer controller) 13 causes the charge generated by photoelectric conversion through the photodiode to move to one of the plurality of first charge storage sections 12. The construction of the transfer gate 13 is known, for example, a MOS (Metal Oxide Semiconductor) construction.

[0042] The second semiconductor 30 is a semiconductor that primarily performs signal processing, and is formed, for example, from silicon. The second semiconductor 30 is electrically connected to the first semiconductor 10 via interconnects through a diffusion layer.

[0043] The second semiconductor 30 includes a second charge storage section 33, a drain 32 of a reset transistor (resetter) 35, a potential detection node 31 (potential detector), and a reset gate 34 of the reset transistor (resetter) 35. Each second charge storage section 33 is connected to a readout circuit (not shown). The potential detection node 31 (potential detector) detects the potential of the second charge storage section 33. The reset gate 34 of the reset transistor (resetter) 35 controls the charge movement between the second charge storage section 33 and the drain 32.

[0044] The reset transistor (resetter) 35 resets the potential of the first charge storage section 12 to a predetermined potential. The reset transistor 35 may also be, for example, a FET (Field Effect Transistor).

[0045] The second charge storage section 33, drain 32, potential detection node 31, and reset gate 34 are provided corresponding to each of the first charge storage sections 12A and 12B. The potential detection node 31 is configured to detect the potential of the corresponding second charge storage section 33.

[0046] In the solid-state imaging element 1 of this embodiment, configured as described above, by applying a voltage as a control signal to each transmission gate 13, the charge generated in the photodiode 11 is transferred to either of the first charge storage units 12A and 12B. The destination of the charge transfer changes over time according to the control signal, thereby driving the charge distribution.

[0047] In the solid-state imaging element 1, the charge generated in the photodiode 11 is distributed and driven within the first semiconductor 10, and then transferred to an electrostatic capacitor consisting of a first charge storage section 12 (12A, 12B) as a diffusion layer, a corresponding second charge storage section 33, a connecting line (not shown) connecting the first charge storage section 12 and the second charge storage section 33, and a gate electrode within the second semiconductor 30. Therefore, the charge entering the electrostatic capacitor is not subsequently distributed.

[0048] Generally, charge distribution using large-capacitance capacitors can easily lead to performance issues. In particular, during high-speed distribution, the charge transfer time from the capacitor becomes problematic, sometimes making it difficult to achieve satisfactory distribution characteristics.

[0049] In the solid-state imaging element 1 of this embodiment, the distribution drive is performed within the first semiconductor 10. Therefore, problems such as charge movement from a large electrostatic capacitance are avoided. As a result, the distribution drive can be performed efficiently.

[0050] As described above, the solid-state imaging element 1 of this embodiment includes a first semiconductor 10, which has a transmission gate 13 serving as a transmission controller and a first charge storage section 12 serving as a transmission destination. Therefore, good distribution drive can be achieved in the configuration of heterojunction bonding of heterogeneous semiconductors, namely the first semiconductor 10 and the second semiconductor 30.

[0051] In the solid-state imaging element 1, a photodiode 11 is constructed using Ge or similar materials as the primary semiconductor material. This results in a structure that can operate well as a multi-grating type TOF sensor that uses light in the near-infrared to short-wavelength infrared band, particularly in the 1350nm to 1400nm range.

[0052] In this embodiment, the number of first charge storage units can be appropriately set. That is, in the example above, an example with two first charge storage units was described, but it is also possible to provide three or more charge storage units.

[0053] Figure 2 This is a schematic diagram of a modified solid-state imaging element 1A according to this embodiment. In the solid-state imaging element 1A, a p+ type semiconductor region 15 is disposed between the photodiode 11 and the first charge storage unit 12 instead of the transmission gate 13. A voltage signal generation unit 16 is connected to each p+ type semiconductor region 15, and based on the signal from the voltage signal generation unit 16, the charge generated in the photodiode 11 is transferred to either of the first charge storage units 12A and 12B.

[0054] That is, the transmission controller 17 of the solid-state imaging element 1A has a p+ type semiconductor region 15 and a voltage signal generation unit 16, and performs distribution drive by a known current assisted method.

[0055] In the solid-state imaging element of this embodiment, the transmission controller is not limited to the gate electrode, and the above-mentioned effects can be achieved in this configuration.

[0056] exist Figure 2 In the process, the p+ type semiconductor region 15 is disposed between the photodiode 11 and the first charge storage section 12, but the p+ type semiconductor region 15 only needs to be located near the first charge storage section 12, and there is also a degree of freedom in the configuration.

[0057] In addition, Figure 2 In the first semiconductor 10, a photodiode 11 is formed on the side not opposite to the second semiconductor, illustrating a surface-illuminated (FSI) solid-state imaging element. All solid-state imaging elements described in this specification can be configured as either surface-illuminated or back-illuminated (BSI), and the appropriate configuration can be selected based on the application, relationship with other configurations, etc.

[0058] The solid-state imaging element of this embodiment can be used alone, but multiple elements can also be arranged in a two-dimensional matrix to form an imaging element with multiple pixels.

[0059] exist Figure 3 An example of such an imaging element is shown as a block diagram. The imaging element 40 has a light-receiving area 41 in which a plurality of solid imaging elements 1 are arranged in two dimensions. The imaging element 40 includes a control circuit 50, a vertical drive circuit 60, a horizontal drive circuit 70, an AD conversion circuit 80, and an output circuit 90, but this is only an example, and various known configurations can be appropriately combined considering specifications, etc.

[0060] In the imaging element 40, the number and arrangement of the solid-state imaging elements disposed in the light-receiving area 41 can also be appropriately set. Multiple solid-state imaging elements can be arranged in a two-dimensional manner without gaps. At this time, multiple solid-state imaging elements arranged in a two-dimensional manner can also be formed on a single semiconductor wafer.

[0061] Figure 4 An example of a camera system that uses the solid-state imaging element of this embodiment is shown schematically. Figure 4 The camera system 100 shown includes a light source unit 110 with a light source 101 and a light receiving unit 120 with a camera sensor 121.

[0062] The light source unit 110 includes a light source 101 and a filter that adjusts the wavelength of the light emitted from the light source 101 as needed, and emits emitted light L1 with a predetermined wavelength and band (wavelength distribution) toward the subject O. The emitted light L1 can be light in the wavelength region from near-infrared to short-wavelength infrared (e.g., a band around 1350nm to 1400nm). The reflected light L2 generated by the reflection of the emitted light L1 by the subject O is incident on the image sensor 121 of the light receiving unit 120. One or more solid-state imaging elements of this embodiment can be used as the image sensor 121.

[0063] In the camera system 100, by setting the wavelength distribution of the emitted light L1 to a band of 1350nm to 1400nm, it is possible to perform distance measurement and other functions based on the TOF method appropriately even when used outdoors, with almost no influence from external light.

[0064] The above description, with reference to the accompanying drawings, details one embodiment of the present invention. However, the specific configuration is not limited to this embodiment and may include changes and combinations of configurations that do not depart from the spirit of the present invention.

[0065] For example, it can also be like Figure 5As shown in the modified example, the drain 32 and reset gate 34 of the reset transistor 35 are disposed in the first semiconductor 10. In this case, it is capacitively coupled to the second semiconductor 30 only through the high-resistance gate electrode, so the distributed charge moves only within the first semiconductor 10. As a result, the degree of freedom in setting the reset voltage, etc., is increased, and noise is not introduced through the second charge accumulation section 33, which serves as a diffusion layer, thus improving the performance.

[0066] The configuration of the reset transistor is not limited to... Figure 5 The example shown.

[0067] Figure 6 The modified reset transistor (resetter) 35A shown does not have a reset gate 34, but has a voltage signal generation section 36. When the applied voltage to the drain 32 rises according to the signal from the voltage signal generation section 36, the depletion layer around the drain 32 connects to the depletion layer of the first charge accumulation section 12A, and the potential of the first charge accumulation section 12A can be set to a voltage with characteristics determined by the potential distribution of the coupled depletion layer. That is, the first charge accumulation section 12A can be reset. Thus, the potential of the first charge accumulation section can be reset without using a FET gate such as a reset gate 34. In addition, in order to perform the reset operation with good controllability, the impurity concentration of each first charge accumulation section and the drain 32 can be made different. In addition, an appropriate impurity region can be formed between each first charge accumulation section and the drain 32 for the same purpose.

[0068] Figure 7 The diagram shows a solid-state imaging element 1A with a reset transistor 35A. In this case, the same effect as described above can be obtained. The solid-state imaging element 1A has a transmission controller 17 and is driven by an externally applied voltage. Therefore, by providing the reset transistor 35A, the first semiconductor 10 is configured without a FET gate. As a result, the manufacturing process can be greatly simplified, and manufacturing costs can be significantly reduced.

[0069] Figure 8 This is an example of a drain configuration 38 attached to the first semiconductor 10 to release signal charge (electrons if the first semiconductor 10 is P-type). The drain configuration 38 has a voltage signal generation section 39. When a voltage that reverse-biases the first semiconductor 10 is applied to the drain configuration 38 from the voltage signal generation section 39, unwanted charge from the first charge accumulation section 12A is discharged to the drain configuration 38. As a result, unwanted charge can be removed in advance, thereby improving the signal-to-noise ratio of the distributed signal.

[0070] Figure 9This is a diagram showing a solid-state imaging element 1A with an added drain configuration 38. In this case, it is not necessary to form a FET gate in the first semiconductor 10.

[0071] exist Figure 8 as well as Figure 9 In either case, the drain configuration 38 is combined with the reset transistor 35A. In this case, the drain configuration 38 and the reset transistor 35A may also share a portion of their configuration.

[0072] Alternatively, it can be like Figure 10 As shown in the modified solid-state imaging element 1B, a charge discharge section 18 connected to a photodiode 11 via a gate is provided in the first semiconductor 10. In this case, during periods when no charge distribution drive is performed in the first semiconductor 10, the charge generated in the photodiode 11 due to incident light and the charge generated due to dark current can be appropriately discharged. Furthermore, in Figure 10 Since it is difficult to represent them on the same surface, the first charge accumulation part 12B and the corresponding parts of the second semiconductor 30 are omitted.

[0073] Figure 11 This example replaces the transmission gate 13 of the solid-state imaging element 1B with a transmission controller 17 having a p+ type semiconductor region 15 and a voltage signal generation unit 16, and replaces the gate of the charge discharge unit 18 with a p+ type semiconductor region 18a and a voltage signal generation unit 18b. In this case, the above-mentioned advantages can also be obtained by making the first semiconductor 10 have no FET gate.

[0074] The charge discharge section 18 can also be combined with a reset transistor and a drain structure.

[0075] Explanation of reference numerals in the attached figures

[0076] 1, 1A, 1B Solid-state imaging elements

[0077] 10 First Semiconductor

[0078] 11. Photodiode

[0079] 12, 12A, 12B First charge accumulation section

[0080] 13. Transfer gate (transfer controller)

[0081] 17. Conveyor Controller

[0082] 30 Second Semiconductor

[0083] 31 Potential Detection Node (Potential Detector)

[0084] 33 Second charge accumulation section

[0085] 35, 35A Reset Transistor (Resetter)

[0086] 40 camera elements

[0087] 100 camera system

[0088] 110 Light Source Department

[0089] L1 emitted light

Claims

1. A solid-state imaging element, comprising: First Semiconductor; and The second semiconductor has a different composition from the first semiconductor and is electrically connected to the first semiconductor. The first semiconductor described above has: A photodiode converts incident light into photoelectric value. Multiple first charge storage units store the charge generated by the aforementioned photoelectric conversion; and The transmission controller causes the charge generated by the photoelectric conversion to move to one of the first charge accumulation units. The second semiconductor described above has: The second charge storage section is capable of storing charge; and A potential detector detects the potential of the second charge accumulation section. The aforementioned solid-state imaging element includes a resetter that resets the potential of the first charge accumulation section to a predetermined potential. The drain and reset gate of the aforementioned reset device are disposed on the aforementioned first semiconductor, and the aforementioned first semiconductor is capacitively coupled to the aforementioned second semiconductor.

2. The solid-state imaging element as claimed in claim 1, wherein, The aforementioned resetter is disposed on the aforementioned first semiconductor.

3. The solid-state imaging element as claimed in claim 1, wherein, The elements that make up the aforementioned photodiode include germanium.

4. A camera system, comprising: The light source emits light with a prescribed wavelength distribution; and The solid-state imaging element according to any one of claims 1 to 3.

5. The camera system as described in claim 4, wherein, The aforementioned light source emits light in the wavelength range from near-infrared to short-wavelength infrared as the emitted light.

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