WO2020103131A1 - 图像传感器及其制造方法 - Google Patents

图像传感器及其制造方法

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Publication number
WO2020103131A1
WO2020103131A1 PCT/CN2018/117194 CN2018117194W WO2020103131A1 WO 2020103131 A1 WO2020103131 A1 WO 2020103131A1 CN 2018117194 W CN2018117194 W CN 2018117194W WO 2020103131 A1 WO2020103131 A1 WO 2020103131A1
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Prior art keywords
dielectric layer
substrate
image sensor
layer
conformal dielectric
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PCT/CN2018/117194
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English (en)
French (fr)
Inventor
姚国峰
沈健
李运宁
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深圳市汇顶科技股份有限公司
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Application filed by 深圳市汇顶科技股份有限公司 filed Critical 深圳市汇顶科技股份有限公司
Priority to EP18918406.2A priority Critical patent/EP3686931B1/en
Priority to CN201880002253.9A priority patent/CN111480235B/zh
Priority to JP2019564061A priority patent/JP6934277B2/ja
Priority to PCT/CN2018/117194 priority patent/WO2020103131A1/zh
Priority to KR1020197034475A priority patent/KR102343456B1/ko
Priority to US16/687,689 priority patent/US11315975B2/en
Publication of WO2020103131A1 publication Critical patent/WO2020103131A1/zh

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    • H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
    • H01L27/144—Devices controlled by radiation
    • H01L27/146—Imager structures
    • H01L27/14601—Structural or functional details thereof
    • H01L27/1464—Back illuminated imager structures
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    • H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
    • H01L27/144—Devices controlled by radiation
    • H01L27/146—Imager structures
    • H01L27/14601—Structural or functional details thereof
    • H01L27/14603—Special geometry or disposition of pixel-elements, address-lines or gate-electrodes
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    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
    • H01L27/144—Devices controlled by radiation
    • H01L27/146—Imager structures
    • H01L27/14601—Structural or functional details thereof
    • H01L27/14609—Pixel-elements with integrated switching, control, storage or amplification elements
    • H01L27/1461—Pixel-elements with integrated switching, control, storage or amplification elements characterised by the photosensitive area
    • H—ELECTRICITY
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    • H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
    • H01L27/144—Devices controlled by radiation
    • H01L27/146—Imager structures
    • H01L27/14601—Structural or functional details thereof
    • H01L27/14625—Optical elements or arrangements associated with the device
    • H—ELECTRICITY
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    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
    • H01L27/144—Devices controlled by radiation
    • H01L27/146—Imager structures
    • H01L27/14601—Structural or functional details thereof
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    • H01L27/14627—Microlenses
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    • H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
    • H01L27/144—Devices controlled by radiation
    • H01L27/146—Imager structures
    • H01L27/14601—Structural or functional details thereof
    • H01L27/14625—Optical elements or arrangements associated with the device
    • H01L27/14629—Reflectors
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    • H01L27/144—Devices controlled by radiation
    • H01L27/146—Imager structures
    • H01L27/14643—Photodiode arrays; MOS imagers
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    • H01L27/144—Devices controlled by radiation
    • H01L27/146—Imager structures
    • H01L27/14683—Processes or apparatus peculiar to the manufacture or treatment of these devices or parts thereof
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    • H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
    • H01L27/144—Devices controlled by radiation
    • H01L27/146—Imager structures
    • H01L27/14683—Processes or apparatus peculiar to the manufacture or treatment of these devices or parts thereof
    • H01L27/14685—Process for coatings or optical elements
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    • H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
    • H01L27/144—Devices controlled by radiation
    • H01L27/146—Imager structures
    • H01L27/14601—Structural or functional details thereof
    • H01L27/14609—Pixel-elements with integrated switching, control, storage or amplification elements
    • H01L27/14612—Pixel-elements with integrated switching, control, storage or amplification elements involving a transistor
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    • H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
    • H01L27/144—Devices controlled by radiation
    • H01L27/146—Imager structures
    • H01L27/14601—Structural or functional details thereof
    • H01L27/1463—Pixel isolation structures

Definitions

  • the present application relates to the technical field of image sensors, and in particular, to an image sensor and a manufacturing method thereof.
  • CMOS image sensors are widely used in mobile phones, digital cameras, driving recorders and security monitoring equipment. Its working principle is based on the photoelectric conversion effect. When light illuminates the pixel array in the image sensor, each pixel unit generates a corresponding amount of charge according to the light intensity at its corresponding position, and converts it into a digital signal. Finally, all pixels The signal of the unit is processed and output as an image.
  • the CMOS image sensor can be divided into a front-illuminated image sensor and a back-illuminated image sensor. Because the incident light directly illuminates the photosensitive area from the back, the response of the back-illuminated image sensor is higher than that of the front-illuminated The image sensor is higher.
  • a circuit diagram of a pixel unit of a back-illuminated image sensor common in the prior art, as shown in FIG. 1, includes a photodiode 11 and four transistors 12, 14, 16, and 18, wherein the transfer transistor 12 controls the photodiode 11. The transfer of the generated charge to the floating diffusion node.
  • the dotted frame area represents the schematic structure of the pixel unit structure 10.
  • a photodiode 101 that is, the photodiode 11 in FIG. 1, and a floating diffusion node 102, which are shown on the silicon substrate 100, are included.
  • 13 in 1 the gate structure 105 of the transfer transistor provided on the silicon substrate 100, the incident light 140 illuminates the photodiode 101 from the back of the silicon substrate 100 and generates electric charges.
  • new technologies such as AR / VR and 3D face recognition have emerged, because these technologies mostly use near-infrared light that is invisible to the human eye as a light source (for example, 940 nm VCSEL is used as the light source of Apple iphoneX dot matrix projection module), so the demand for image sensors with high responsiveness in near infrared light is increasing.
  • near-infrared light has a low absorption rate in the photodiode due to its long wavelength; when the thickness of silicon is small, part of the near-infrared light will penetrate through the silicon, as shown in FIG. 2 at 141 That is light that cannot be absorbed and penetrates. Therefore, the conventional back-illuminated image sensor has a problem that the absorption ratio of incident light is low, resulting in poor signal quality of the image.
  • An object of some embodiments of the present application is to provide an image sensor and a manufacturing method thereof, so that the absorption ratio of incident light by the image sensor can be increased, and the signal quality of the image can be improved.
  • An embodiment of the present application provides an image sensor, including: a substrate and at least one pixel unit; the pixel unit includes a photodetector disposed in the substrate, and the photosensitive surface of the photodetector faces the back of the substrate, It is used to generate electric charge when receiving incident light from the back of the substrate; spherical crown-shaped structure, which is arranged on the substrate and located on the opposite side of the photosensitive surface; conformal dielectric layer, which is arranged on the spherical-crown structure The upper part is used to generate the reflected light of the dielectric layer when the incident light reaches the conformal medium layer; the reflective layer is provided above the conformal medium layer to generate the reflected light of the reflective layer when the incident light reaches the reflective layer.
  • An embodiment of the present application also provides a method for manufacturing an image sensor, including: providing a substrate, forming a photodetector in the substrate, and a photosensitive surface of the photodetector facing the back of the substrate; A spherical crown structure is formed on the opposite surface of the photosensitive surface of the photodetector; a conformal dielectric layer is formed on the spherical crown structure; and a reflective layer is formed above the conformal dielectric layer.
  • the pixel unit of the image sensor is provided with a spherical crown structure on the opposite surface of the photosensitive surface of the photodetector, and a conformal dielectric layer is provided above the spherical crown structure for When the incident light reaches the conformal dielectric layer, the reflected light of the dielectric layer is generated.
  • the spherical crown structure and the conformal dielectric layer make the incident light incident at any angle, the optical path from entering the photodetector to passing through the substrate to the conformal dielectric layer is the same, the medium generated by the incident light when reaching the conformal dielectric layer
  • the layer-reflected light can give the incident light that has passed through the substrate a chance to return to the photodetector again, thereby increasing the absorption of incident light at different incident angles.
  • the reflective layer disposed above the conformal dielectric layer is used to generate the reflected light of the reflective layer, so that the incident light reaching the reflective layer has a chance to return to the photodetector again, so that the photodetector can be fully
  • the incident light that is incident at different incident angles is used, thereby increasing the absorption ratio of the incident light and improving the signal quality of the image.
  • the conformal dielectric layer is specifically: a multi-layer conformal dielectric layer; wherein, the adjacent two conformal dielectric layers have different refractive indexes. That is to say, the conformal dielectric layer can adopt a structure in which dielectric materials with different refractive indexes are alternately stacked, which is beneficial to further increase the light absorption ratio.
  • the multi-layer conformal dielectric layer is specifically: three conformal dielectric layers; wherein the three conformal dielectric layers are: the first silica dielectric layer on the spherical crown structure; A titanium dioxide dielectric layer on a silicon dioxide dielectric layer; and, a second silicon dioxide dielectric layer on the titanium dioxide dielectric layer.
  • the conformal dielectric layer has a preset thickness that satisfies the optical resonance conditions of incident light. By controlling the thickness of the conformal dielectric layer to meet the optical resonance conditions of the incident light, the incident light at different angles can be optically resonated in the same structure, which is beneficial to the maximum use of the incident light.
  • phase ⁇ of the reflected light of the dielectric layer and the phase of the reflected light of the reflective layer Specifically calculated by the following formula:
  • d is the preset thickness of the conformal dielectric layer
  • n d is the refractive index of the conformal dielectric layer
  • ⁇ is the wavelength of incident light
  • n r is the refractive index of the reflective layer
  • k r is the extinction coefficient of the reflective layer
  • the spherical crown-shaped structure specifically a spherical crown-shaped silicon structure, provides a material type of the spherical crown-shaped structure.
  • the incident light is specifically near-infrared monochromatic light.
  • the absorption ratio of near-infrared monochromatic light is optimized, which helps Improve the responsivity of the image sensor in the near infrared band.
  • FIG. 1 is a circuit diagram of a pixel unit of a back-illuminated image sensor according to the background technology of the present application;
  • FIG. 2 is a schematic structural diagram of a pixel unit of a back-illuminated image sensor according to the background technology of the present application;
  • FIG. 3 is a schematic diagram of a silicon layer-single conformal dielectric layer-reflection layer used in the image sensor according to the first embodiment of the present application;
  • FIG. 4 is a schematic diagram of the pixel unit structure of the image sensor according to the first embodiment of the present application.
  • FIG. 5 is a graph showing the variation of the absorption ratio of the photodetector for incident light with a wavelength of 940 nm according to the thickness of the silicon dioxide dielectric layer according to the second embodiment of the present application;
  • FIG. 6 is a schematic diagram of a pixel unit structure of an image sensor according to a third embodiment of the present application.
  • FIG. 7 is a graph showing a change curve of the light absorption ratio of the photodetector according to the wavelength of incident light according to the third embodiment of the present application.
  • FIG. 8 is a flowchart of a method of manufacturing an image sensor according to a fourth embodiment of the present application.
  • 9a to 9f are schematic structural diagrams of each process flow in the fourth embodiment of the present application.
  • FIG. 10 is a flowchart of a method of manufacturing an image sensor according to a fifth embodiment of the present application.
  • the first embodiment of the present application relates to an image sensor, including: a substrate, and at least one pixel unit; a photodetector, disposed in the substrate, and a photosensitive surface of the photodetector facing the back of the substrate, When the incident light is received on the back of the bottom, a charge is generated; a spherical crown structure is provided on the substrate and is located on the opposite side of the photosensitive surface; the spherical crown structure is the same material as the substrate; the conformal dielectric layer, It is arranged above the spherical crown structure and is used to generate the reflected light of the dielectric layer when the incident light reaches the conformal dielectric layer; The reflected light makes it possible to increase the proportion of incident light absorption and improve the signal quality of the image.
  • the implementation details of the pixel unit structure of the image sensor of this embodiment are described below in detail. The following content is only for the implementation details provided for easy understanding, and is not necessary for implementing this solution.
  • the conformal dielectric layer in the image sensor is exemplified by a single conformal dielectric layer, but it is not limited to this in practical applications.
  • FIG. 3 is for the convenience of explaining the difference between the incident light and the spherical crown structure 300, the single conformal dielectric layer 320, and the reflective layer 330.
  • the reflected light does not reflect the shape structure of the spherical crown structure 300, the single-layer conformal dielectric layer 320, and the reflective layer 330.
  • the spherical crown structure in this embodiment uses a silicon layer as an example.
  • the single-layer conformal dielectric layer may be a silicon dioxide dielectric layer or a titanium dioxide dielectric layer.
  • the reflective layer is generally aluminum, silver, or other metals.
  • a beam of incident light 340 with a single wavelength that is perpendicularly incident produces reflected light 341 when it reaches the interface 301 between the air 350 and the silicon layer; when the incident light reaches the silicon layer and the single layer conformal
  • the reflected light 342 is generated at the interface 310 of the dielectric layer 320; the reflected light 343 is generated when the incident light reaches the interface 325 of the single conformal dielectric layer 320 and the reflective layer 330.
  • the image sensor in this embodiment includes a substrate 400 and a pixel unit structure as shown in FIG. 4, including: a photodetector 401, a floating diffusion node 402, a shallow trench isolation 403, and a gate dielectric layer 404 2.
  • the substrate 400 may be a silicon substrate.
  • the silicon substrate has a front surface and a back surface. As shown in FIG. 4, the direction of the upward arrow is the rear surface, and the direction of the downward arrow is the front surface.
  • the photodetector 401 is disposed in the substrate 400, and the photosensitive surface of the photodetector 401 faces the back surface of the substrate 400, and is used to generate electric charges and incident light when incident light is received from the back surface of the substrate 400. It can be incident at any angle of incidence, such as normal incident light 440 and non-normal incident light 450 in FIG. 4, where the photodetector 401 in this embodiment may be a photodiode.
  • the incident light is near-infrared monochromatic light with a wavelength of 780 to 1100 nm, it will help to improve the image sensor in the near-infrared band in the application scenario of using a laser with good monochromaticity as a near-infrared light source Responsiveness.
  • the floating diffusion node 402 is provided in the substrate 400 and is used to store the received charge and convert the stored charge into a voltage signal.
  • the shallow trench isolation 403 is provided on both sides of the substrate 400 to isolate the interference of the adjacent pixel unit structure.
  • the gate structure 405 of the transfer transistor is disposed on the gate dielectric layer 404, and the gate dielectric layer 404 is disposed on the substrate 400.
  • the transfer transistor is used to control the charge generated by the photodetector 401 to the floating diffusion node 402 transfer, the gate structure 405 can be used as a switch to control the transfer of charge, to control the start of charge transfer or stop transfer of charge.
  • the gate structure of the transfer transistor 12 in FIG. 1 is the gate structure 405 of the transfer transistor in FIG. 4.
  • the spherical crown structure 406 may be a spherical crown structure with a radius of curvature R.
  • the spherical crown structure 406 and the substrate 400 use the same material.
  • the material used may be a common semiconductor material.
  • the substrate is a silicon substrate, and the spherical crown structure is a spherical crown silicon structure, but in practical applications, it is not limited to this.
  • the spherical crown-shaped silicon structure is disposed on the substrate 400 and is located on the opposite side of the photosensitive surface of the photodetector 401.
  • the single-layer conformal dielectric layer 420 is disposed above the spherical crown-shaped structure 406 and is used to generate reflected light from the dielectric layer when the incident light reaches the single-layer conformal dielectric layer 420.
  • the single-layer conformal dielectric layer 420 may Has a certain thickness.
  • the reflective layer 430 is disposed above the single-layer conformal dielectric layer 420, and is used to generate reflected light from the reflective layer when the incident light reaches the reflective layer 430.
  • the optical path to the reflective layer 430 is the same for both the normally incident light 440 and the non-normally incident light 450.
  • a spherical crown-shaped silicon structure with a specific radius of curvature is formed in the area above the image opposite to the photosensitive surface of the photodetector, and then a single layer with a specific thickness is formed on the spherical crown-shaped silicon structure
  • the conformal dielectric layer and the reflective layer, through the pixel unit structure in this embodiment can allow incident light penetrating through the silicon layer to return to the photodetector again, thereby increasing light absorption.
  • it can also ensure that the incident light incident at different angles has the same optical path, thereby optimizing the absorption ratio of incident light incident at different angles in the photodetector.
  • the second embodiment of the present application relates to an image sensor.
  • the conformal dielectric layer has a preset thickness, and the preset thickness satisfies the optical resonance condition.
  • the optical resonance effect is used to maximize the reflectivity, which further increases the incidence Light absorption ratio.
  • the optical resonance condition is that the phase difference between the reflected light 342 and the reflected light 343 in FIG. 3 is zero or an integral multiple of 2 ⁇ , that is, a standing wave is formed.
  • the source of the above phase difference has two parts: First, the phase change ⁇ caused by the thickness d of the single conformal dielectric layer 320 is as follows: (1):
  • phase change ⁇ due to the light absorption of the reflective layer 330 is as follows (2):
  • n d is the refractive index of the single-layer conformal dielectric layer 320
  • n r and k r are the refractive index and extinction coefficient of the reflective layer 330, respectively
  • ⁇ is the wavelength of incident light.
  • the wavelength of 940 nm, the curve of the absorption ratio of the incident light in silicon with the thickness of the silicon dioxide dielectric layer is shown in Figure 5.
  • the single-layer conformal dielectric layer 420 provided in this embodiment is beneficial to increase the absorption ratio of incident light.
  • the single-layer conformal dielectric layer in this embodiment only uses the conformal silica dielectric layer as an example, and is not limited to this in practical applications.
  • conformal described herein refers to maintaining the same shape as a certain structure, for example, the conformal dielectric layer maintains the same shape as the spherical crown-shaped silicon structure.
  • the conformal dielectric layer has a preset thickness, and the preset thickness satisfies the optical resonance condition of the incident light, so that the incident light at different angles passes through the spherical crown silicon structure and the conformal medium
  • Both the layer and the reflective layer can form an optical resonance, optimizing the absorption ratio of incident light, and conducive to the maximum use of incident light.
  • the same structure can be used to make the incident light at different angles satisfy the conditions of optical resonance.
  • the calculation formula is conducive to accurately passing ⁇ and The relationship between them yields the preset thickness of the conformal dielectric layer.
  • the third embodiment of the present application relates to an image sensor.
  • This embodiment is substantially the same as the second embodiment, except that the conformal dielectric layer in the second embodiment is a single-layer conformal dielectric layer, while this embodiment Among them, the conformal dielectric layer is specifically a multi-layer conformal dielectric layer, which provides an implementation of the conformal dielectric layer.
  • the conformal dielectric layer in the pixel unit structure of the image sensor in this embodiment, two adjacent conformal dielectric layers have different refractive indexes. That is to say, the conformal dielectric layer can adopt a structure in which dielectric materials with different refractive indexes are alternately stacked.
  • the following uses three conformal dielectric layers as an example for description, but in practical applications, it is not limited to three layers and has three layers.
  • the pixel unit structure of the image sensor of the conformal dielectric layer may be as shown in FIG. 6.
  • the three conformal dielectric layers may be: a first silicon dioxide dielectric layer 620 on the spherical crown structure; a titanium dioxide dielectric layer 621 on the first silicon dioxide dielectric layer 620; and, a titanium dioxide dielectric layer The second silicon dioxide dielectric layer 622 on the dielectric layer 621.
  • the refractive index of silicon dioxide is 1.45, which is a low refractive index material
  • the refractive index of titanium dioxide is 2.25, which is a high refractive index material.
  • the structure of this high and low refractive index materials stacked alternately is beneficial to further increase the proportion of light absorption .
  • different dielectric materials are only exemplified by silica and titania, but in practical applications, it is not limited to this.
  • each layer of dielectric material satisfies the optical resonance condition of monochromatic light of a specific wavelength.
  • the light resonance conditions it can be calculated that when the thickness of the first silicon dioxide dielectric layer 620 is 485.8 nanometers, the thickness of the titanium dioxide dielectric layer is 104.5 nanometers, and the thickness of the second silicon dioxide dielectric layer is 144.9 nanometers, it can be satisfied Optical resonance conditions for monochromatic light with a wavelength of 940 nanometers. As shown in the variation curve of the light absorption ratio of the photodetector with the incident light wavelength in FIG. 7, at this time, the light absorption ratio reaches a maximum value, which is 40.5%.
  • the conformal dielectric layer is specifically: a multi-layer conformal dielectric layer; wherein, the adjacent two conformal dielectric layers have different refractive indexes. That is to say, the conformal dielectric layer can adopt a structure in which dielectric materials with different refractive indexes are alternately stacked, which is beneficial to further increase the light absorption ratio.
  • the fourth embodiment of the present application relates to a method for manufacturing a pixel unit structure of an image sensor, comprising: providing a substrate, forming a photodetector in the substrate, the photosensitive surface of the photodetector facing the back of the substrate; A spherical crown structure is formed on the bottom and on the opposite surface of the photosensitive surface of the photodetector; wherein, the spherical crown structure is the same material as the substrate; a conformal dielectric layer is formed on the spherical crown structure; and the conformal dielectric layer
  • the reflection layer is formed above so that the pixel unit structure of the image sensor as in the first embodiment can be manufactured.
  • the implementation details of the manufacturing method of the pixel unit structure of the image sensor of the present embodiment are described below in detail. The following content is merely an implementation detail provided for easy understanding, and is not necessary for implementing the solution.
  • the prepared conformal dielectric layer of the pixel unit structure is a single conformal dielectric layer, that is, the prepared pixels of the image sensor in the first embodiment or the second embodiment Unit structure.
  • Figure 8 The specific flow chart of the manufacturing method is shown in Figure 8, which specifically includes:
  • Step 801 Provide a substrate and form shallow trench insulation on the substrate.
  • shallow trench insulation 901 is formed on both sides of the substrate 900 to isolate interference from adjacent pixels.
  • Step 802 Form a spherical crown structure on the substrate and on the surface opposite to the photosensitive surface of the photodetector.
  • the spherical crown-shaped silicon structure is a kind of spherical crown-shaped structure, and the material of the spherical crown-shaped structure and the substrate are the same.
  • the substrate in this embodiment uses a silicon substrate as an example, and the spherical crown-shaped structure uses a spherical crown Shaped silicon structure is used as an example, but in practical applications, it is not limited to this.
  • a spherical crown-shaped photoresist can be formed by photoresist reflow or gray-scale mask exposure process, and then the shape of the spherical crown-shaped photoresist can be transferred to the substrate 900 by reactive ion etching As shown in FIG.
  • a spherical crown-shaped silicon structure 904 is formed above the photodetector 903 region.
  • the photodetector 903 in this embodiment may be a photodiode, and the photodiode is disposed in the substrate 900.
  • Step 803 Form an ion-doped region, a gate, and a first interlayer dielectric layer on the substrate.
  • the ion-doped region formed in the substrate may include: a photodetector 903, a floating diffusion node 906, etc., a gate dielectric layer 907, a gate structure 908, and a first Interlayer dielectric layer 910 and other structures.
  • Step 804 Remove the first interlayer dielectric layer on the opposite side of the photosensitive surface of the photodetector to expose the spherical crown silicon structure.
  • the first interlayer dielectric layer 910 above the area of the photodetector 903 is removed to expose the spherical crown-shaped silicon structure 904.
  • Step 805 Form a conformal dielectric layer on the spherical crown-shaped silicon structure and form a reflective layer above the conformal dielectric layer.
  • a conformal dielectric layer 920 and a reflective layer 930 with a specific thickness are formed on the spherical crown-shaped silicon structure 904, and then a second interlayer dielectric layer 940 is deposited and planarized.
  • the conformal dielectric layer 920 may have a preset thickness, and the preset thickness may satisfy the optical resonance condition.
  • the content of the optical resonance condition has been described in detail in the second embodiment, and reference may be made to the description in the second embodiment In order to avoid repetition, this embodiment will not be repeated here.
  • the remaining processes can be completed according to the process flow of the standard image sensor.
  • FIG. 9f which includes conductive vias 911, metal interconnections 912, and intermetallic
  • the fifth embodiment of the present application relates to an image sensor manufacturing method.
  • This embodiment is substantially the same as the fourth embodiment, except that the conformal dielectric layer in the pixel unit structure of the image sensor prepared in the fourth embodiment It is a single layer, and the conformal dielectric layer in the pixel unit structure of the image sensor prepared in this embodiment is multiple layers, that is, this embodiment provides a method for preparing the pixel unit structure of the image sensor in the third embodiment .
  • FIG. 10 The specific flowchart of the method for manufacturing the image sensor in this embodiment is shown in FIG. 10, and specifically includes:
  • Step 1001 Provide a substrate, and form a shallow trench insulation on the substrate.
  • Step 1002 Form a spherical crown structure on the substrate and on the surface opposite to the photosensitive surface of the photodetector.
  • Step 1003 forming an ion-doped region, a gate, a first interlayer dielectric layer and the like on the substrate.
  • Step 1004 Remove the first interlayer dielectric layer on the opposite side of the photosensitive surface of the photodetector to expose the spherical crown silicon structure.
  • Steps 1001 to 1004 are substantially the same as steps 901 to 904 in the fourth embodiment, and will not be repeated here to avoid repetition.
  • Step 1005 Form two or more layers of a conformal dielectric layer with a specific thickness on the spherical crown-shaped silicon structure and form a reflective layer above the conformal dielectric layer.
  • two or more conformal dielectric layers are alternately stacked structures of high and low refractive index materials.
  • the following uses three conformal dielectric layers as an example for description.
  • the thicknesses of the conformal dielectric layers of three different dielectric materials can be obtained according to the light resonance conditions.
  • a first silicon dioxide dielectric layer can be formed on the spherical crown silicon structure; then a titanium dioxide dielectric layer is formed on the first silicon dioxide dielectric layer; then, in A second silicon dioxide dielectric layer is formed on the titanium dioxide dielectric layer, so that a 3-layer conformal dielectric layer stack structure is finally formed.
  • a reflective layer is formed on the second silicon dioxide dielectric layer.
  • different dielectric materials are only exemplified by silica and titania, but in practical applications, it is not limited to this.
  • step 1005 reference may be made to the steps after step 905 in the fourth embodiment to complete the remaining processes according to the process flow of the standard image sensor. In order to avoid repetition, details are not repeated here.

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Abstract

本申请部分实施例提供了一种图像传感器及其制造方法。图像传感器包括衬底(400)和至少一个像素单元，像素单元包括光电探测器(401)，设置于衬底内，光电探测器的感光面朝向衬底的背面，用于在从衬底的背面接收到入射光时，产生电荷；球冠形结构(406)，设置于衬底上且位于感光面的相对面；保形介质层(420)，设置于球冠形结构上方，用于在入射光达到保形介质层时，产生介质层反射光；反射层(430)，设置于保形介质层上方，用于在入射光达到反射层时，产生反射层反射光，使得可以增加入射光的吸收比例，提高图像的信号质量。

Description

图像传感器及其制造方法 技术领域
本申请涉及图像传感器技术领域，特别涉及一种图像传感器及其制造方法。
背景技术
CMOS图像传感器广泛应用于手机、数码相机、行车记录仪以及安防监控等设备中。其工作原理是基于光电转换效应，当光照射图像传感器中的像素阵列(pixel array)时，每个像素单元根据其对应位置的光强产生相应数量的电荷，并转化成数字信号，最终所有像素单元的信号经过处理后输出为图像。按照结构分类，CMOS图像传感器可分为前照式图像传感器和背照式图像传感器，背照式图像传感器由于入射光直接从背面照射在感光区域，因此背照式图像传感器的响应度比前照式图像传感器更高。
现有技术中常见的背照式图像传感器的像素单元的电路图，如图1所示，包括一个光电二极管11和四个晶体管12，14，16及18，其中，传输晶体管12控制着光电二极管11所产生的电荷向浮置扩散节点的传输。虚线框区域所表示的即为像素单元结构10的示意性结构可参考图2，在硅衬底100上包括了一个光电二极管101即图1中的光电二极管11和一个浮置扩散节点102即图1中的13，硅衬底100上设置的传输晶体管的栅极结构105，入射光140从硅衬底100 的背面照射光电二极管101并产生电荷。
发明人发现现有技术至少存在以下问题：近年来，AR/VR、3D人脸识别等新技术不断涌现，由于这些技术中多采用了人眼不可见的近红外光作为光源(例如采用940纳米VCSEL作为光源的Apple iphoneX点阵投射模组)，因此对于在近红外光具有高响应度的图像传感器的需求日益增强。相比于可见光波段，近红外光由于波长较长，在光电二极管中的吸收率本来就低；当硅的厚度较小时，一部分近红外光会从硅中穿透出去，如图2中的141即为无法被吸收而穿透的光。因此传统的背照式图像传感器存在对于入射光的吸收比例较低，从而导致图像的信号质量较差的问题。
发明内容
本申请部分实施例的目的在于提供一种图像传感器及其制造方法，使得可以增加图像传感器对入射光的吸收比例，提高图像的信号质量。
本申请实施例提供了一种图像传感器，包括：衬底和至少一个像素单元；所述像素单元包括光电探测器，设置于衬底内，光电探测器的感光面朝向所述衬底的背面，用于在从衬底的背面接收到入射光时，产生电荷；球冠形结构，设置于所述衬底上且位于所述感光面的相对面；保形介质层，设置于球冠形结构上方，用于在入射光达到保形介质层时，产生介质层反射光；反射层，设置于保形介质层上方，用于在入射光达到反射层时，产生反射层反射光。
本申请实施例还提供了一种图像传感器的制造方法，包括：提供一衬底，在衬底内形成光电探测器，光电探测器的感光面朝向所述衬底的背面；在所述衬底上且在光电探测器的感光面的相对面上形成球冠形结构；在球冠形结构上 形成保形介质层；在保形介质层上方形成反射层。
本申请实施例相对于现有技术而言，图像传感器的像素单元在光电探测器的感光面的相对面设置有球冠形结构，以及球冠形结构上方设置有保形介质层，用于在入射光达到保形介质层时，产生介质层反射光。球冠形结构和保形介质层使得入射光以任意角度入射时，从进入光电探测器到穿过衬底到达保形介质层的光程相同，入射光在到达保形介质层时产生的介质层反射光可以让穿透衬底的入射光有机会再次回到光电探测器内，从而可以增加对于不同入射角度的入射光的吸收。对于穿透保形介质层的入射光利用设置于保形介质层上方的反射层产生反射层反射光，使得到达反射层的入射光有机会再次回到光电探测器内，使得光电探测器可以充分利用到以不同入射角度入射的入射光，从而增加入射光的吸收比例，提高图像的信号质量。
例如，保形介质层具体为：多层保形介质层；其中，相邻两个保形介质层的折射率不同。也就是说保形介质层可以采用具有不同折射率的介质材料交替堆叠的结构，有利于进一步增加光的吸收比例。
在一些实施例中，多层保形介质层具体为：3层保形介质层；其中，3层保形介质层分别为：位于球冠形结构上的第一二氧化硅介质层；位于第一二氧化硅介质层上的二氧化钛介质层；以及，位于二氧化钛介质层上的第二二氧化硅介质层。
在一些实施例中，保形介质层具有预设厚度，预设厚度满足入射光的光学谐振条件。通过控制保形介质层的厚度满足入射光的光学谐振条件，可以使不同角度入射的入射光在同一个结构里均可实现光学谐振，有利于最大程度的利用入射光。
在一些实施例中，介质层反射光的相位θ和反射层反射光的相位
Figure PCTCN2018117194-appb-000001
具体通过以下公式计算：
Figure PCTCN2018117194-appb-000002
Figure PCTCN2018117194-appb-000003
其中，d为保形介质层的预设厚度，n d为保形介质层的折射率，λ为入射光的波长；n r为反射层的折射率，k r为反射层的消光系数，提供了一种θ和
Figure PCTCN2018117194-appb-000004
的计算公式，有利于准确的通过θ和
Figure PCTCN2018117194-appb-000005
之间的关系得到保形介质层的预设厚度。
在一些实施例中，球冠形结构，具体为：球冠形硅结构，提供了一种球冠形结构的材料类型。
在一些实施例中，入射光具体为：近红外单色光，在采用人眼不可见的近红外单色光作为光源的场景中，优化了对近红外单色光的吸收比例，有助于提高图像传感器在近红外波段的响应度。
附图说明
一个或多个实施例通过与之对应的附图中的图片进行示例性说明，这些示例性说明并不构成对实施例的限定，附图中具有相同参考数字标号的元件表示为类似的元件，除非有特别申明，附图中的图不构成比例限制。
图1是根据本申请背景技术中的背照式图像传感器的像素单元的电路图；
图2是根据本申请背景技术中背照式图像传感器的像素单元的结构示意图；
图3是根据本申请第一实施例中的图像传感器所采用的硅层-单层保形介质层-反射层的示意图；
图4是根据本申请第一实施例中的图像传感器的像素单元结构的示意图；
图5是根据本申请第二实施例中的光电探测器对于波长为940nm的入射光的吸收比例随二氧化硅介质层厚度的变化曲线；
图6是根据本申请第三实施例中的图像传感器的像素单元结构的示意图；
图7是根据本申请第三实施例中的光电探测器的光吸收比例随入射光的波长的变化曲线；
图8是根据本申请第四实施例中的图像传感器的制造方法的流程图；
图9a到图9f是根据本申请第四实施例中的每一步工艺流程的结构示意图；
图10是根据本申请第五实施例中的图像传感器的制造方法的流程图。
具体实施方式
为了使本申请的目的、技术方案及优点更加清楚明白，以下结合附图及实施例，对本申请部分实施例进行进一步详细说明。应当理解，此处所描述的具体实施例仅仅用以解释本申请，并不用于限定本申请。以下各个实施例的划分是为了描述方便，不应对本发明的具体实现方式构成任何限定，各个实施例在不矛盾的前提下可以相互结合相互引用。
本申请第一实施例涉及一种图像传感器，包括：衬底，和至少一个像素单元；光电探测器，设置于衬底内，光电探测器的感光面朝向衬底的背面，用于在从衬底的背面接收到入射光时，产生电荷；球冠形结构，设置于所述衬底上且位于所述感光面的相对面；球冠形结构与衬底的材质相同；保形介质层，设置于球冠形结构上方，用于在入射光达到保形介质层时，产生介质层反射光； 反射层，设置于保形介质层上方，用于在入射光达到反射层时，产生反射层反射光，使得可以增加入射光的吸收比例，提高图像的信号质量。下面对本实施方式的图像传感器的像素单元结构的实现细节进行具体的说明，以下内容仅为方便理解提供的实现细节，并非实施本方案的必须。
本实施例中图像传感器中保形介质层以单层保形介质层为例，但在实际应用中并不以此为限。为方便理解本实施例，先根据图3进行具体说明，需要说明的是图3是为了方便说明入射光在球冠形结构300、单层保形介质层320和反射层330之间产生的不同反射光，并不体现球冠形结构300、单层保形介质层320和反射层330的形状结构。其中，本实施例中的球冠形结构以硅层为例，单层保形介质层可以为二氧化硅介质层、二氧化钛介质层等，反射层一般是铝、银等金属。
具体的说，如图3所示，一束垂直入射的单一波长的入射光340，在达到空气350与硅层的界面301时、产生反射光341；入射光在达到硅层与单层保形介质层320的界面310时产生反射光342；入射光在达到单层保形介质层320与反射层330的界面325时产生反射光343。
进一步的，本实施例中的图像传感器包括衬底400、和如图4所示的像素单元结构，包括：光电探测器401、浮置扩散节点402、浅沟槽隔离403、栅极介质层404、传输晶体管的栅极结构405、球冠形结构406、层间介质层410、单层保形介质层420和反射层430。
具体的说，衬底400，可以为硅衬底，硅衬底具有正面和背面，如图4中向上的箭头的方向为背面，向下的箭头的方向为正面。
具体的说，光电探测器401，设置于衬底400内，光电探测器401的感 光面朝向衬底400的背面，用于在从衬底400的背面接收到入射光时，产生电荷，入射光可以以任意入射角度入射，如图4中的垂直入射的入射光440和非垂直入射的入射光450，其中，本实施例中的光电探测器401可以为光电二极管。
进一步的，随着AR/VR、3D人脸识别等新技术不断涌现，由于这些技术中多采用了人眼不可见的近红外光作为光源，因此对于在近红外光具有高响应度的图像传感器的需求日益增强，相比于可见光波段，近红外光由于波长较长，在光电探测器中的吸收率本来就低；当硅的厚度较薄时，一部分近红外光会从硅中穿透出去，不利于对光的利用。而本实施例中的图像传感器的像素单元结构使得可以让穿透硅层的以不同角度入射的近红外光有机会再次回到光电探测器内，从而增加光的吸收。也就是说，如果入射光为波长为780～1100nm的近红外单色光，则在采用单色性较好的激光作为近红外光光源的应用场景中，有助于提高图像传感器在近红外波段的响应度。
具体的说，浮置扩散节点402，设置于衬底400内，用于存储接收到的电荷，并将存储的电荷转化为电压信号。
具体的说，浅沟槽隔离403，设置于衬底400的两侧，用于隔绝相邻像素单元结构的干扰。
具体的说，传输晶体管的栅极结构405，设置于栅极介质层404上，栅极介质层404设置于衬底400上，传输晶体管用于控制光电探测器401产生的电荷向浮置扩散节点402传输，栅极结构405可作为控制电荷传输的开关，控制开始传输电荷或是停止传输电荷。其中，图1中的传输晶体管12的栅极结构即为图4中的传输晶体管的栅极结构405。
具体的说，球冠形结构406，可以为曲率半径为R的球冠形结构，球冠形结构406与衬底400所使用的材质相同，比如所使用的材质可以为常见的半导体材料，较佳的，本实施例中衬底为硅衬底，球冠形结构为球冠形硅结构，但在实际应用中，并不以此为限。球冠形硅结构设置于所述衬底400上且位于光电探测器401的感光面的相对面。
具体的说，单层保形介质层420，设置于球冠形结构406上方，用于在入射光达到单层保形介质层420时，产生介质层反射光，单层保形介质层420可具有一定的厚度。
具体的说，反射层430，设置于单层保形介质层420上方，用于在入射光达到反射层430时，产生反射层反射光。
通过上述的像素单元结构可以看出，无论是垂直入射的入射光440还是非垂直入射的入射光450，到达反射层430的光程相同。
本实施例相对于现有技术而言，在光电探测器的感光面的像对面上方区域形成一个特定曲率半径的球冠形硅结构，然后在该球冠形硅结构上面形成特定厚度的单层保形介质层和反射层，通过本实施例中的像素单元结构可以让穿透硅层的入射光有机会再次回到光电探测器内，从而增加光的吸收。而且，还可以保证不同角度入射的入射光，其光程都相同，从而优化了以不同角度入射的入射光在光电探测器中的吸收比例。
本申请第二实施例涉及一种图像传感器，本实施例中：保形介质层具有预设厚度，预设厚度满足光学谐振条件，利用光学谐振效应来使得反射率最大化，进一步增加了对于入射光的吸收比例。
具体的说，光学谐振条件为图3中反射光342和反射光343的相位差为 零或是2π的整数倍，即形成驻波。上述相位差的来源有两部分：一是单层保形介质层320的厚度d导致的相位改变θ，如下公式(1)：
Figure PCTCN2018117194-appb-000006
二是在反射层330的界面325时，由于反射层330的吸光而引起的相位改变φ，如下公式(2)：
Figure PCTCN2018117194-appb-000007
其中，n d为单层保形介质层320的折射率，n r和k r分别为反射层330的折射率和消光系数，λ为入射光的波长。形成驻波的条件，也就是反射光342和反射光343的相位差满足如下公式(3)，其中N为自然数：
Figure PCTCN2018117194-appb-000008
进一步的，由上述公式(1)～(3)可知，对于以不同角度入射的入射光，只需要单层保形介质层320的厚度d满足特定的条件，就可以满足光的谐振条件，从而极大的增加光的吸收比例。
在一个例子中，如图4所示，单层保形介质层420具体可以为保形的二氧化硅介质层，厚度为d SiO2，球冠形结构406的曲率半径R＝2215纳米，入射光的波长为940纳米，该入射光在硅中的吸收比例随二氧化硅介质层厚度变化的曲线如图5所示。根据公式(3)可以计算出，当d SiO2＝144.9纳米、468.8纳米或792.6纳米时，均可满足光学谐振条件，此时对应吸收比例的极大值，为38.5％。另外，由图5可以看到若没有二氧化硅介质层，吸收比例只有5％，也即本实施例中的设置的单层保形介质层420有利于提高对于入射光的吸收比例。需要说明的是，本实施例中的单层保形介质层只是以保形的二氧化硅介质层为例，在实际应用中并不以此为限。应当注意，本文所述“保形”是指保持 与某种结构形状相同，例如，保形介质层保持与球冠形硅结构相同的形状。
本实施例相对于现有技术而言，保形介质层具有预设厚度，预设厚度满足入射光的光学谐振条件，可使得不同角度入射的入射光在经过球冠形硅结构、保形介质层和反射层后均能够形成光学谐振，优化了对于入射光的吸收比例，有利于最大程度的利用入射光。而且利用本实施例中的像素结构单元，可通过同一种结构来使得不同角度入射的入射光均满足光学谐振的条件。同时根据所提供了得θ和
Figure PCTCN2018117194-appb-000009
的计算公式，有利于准确的通过θ和
Figure PCTCN2018117194-appb-000010
之间的关系得到保形介质层的预设厚度。
本申请第三实施例涉及一种图像传感器，本实施例与第二实施例大致相同，不同之处在于，第二实施例中保形介质层具体为单层保形介质层，而本实施例中，保形介质层具体为多层保形介质层，提供了一种保形介质层的实现方式。
本实施例中的图像传感器的像素单元结构中的多层保形介质层中，相邻两个保形介质层的折射率不同。也就是说保形介质层可以采用具有不同折射率的介质材料交替堆叠的结构，下面以3层保形介质层为例进行说明，但在实际应用中并不以3层为限，具有3层保形介质层的图像传感器的像素单元结构可以如图6所示。
具体的说，3层保形介质层可以分别为：位于球冠形结构上的第一二氧化硅介质层620；位于第一二氧化硅介质层620上的二氧化钛介质层621；以及，位于二氧化钛介质层621上的第二二氧化硅介质层622。其中，二氧化硅的折射率为1.45，为低折射率材料；二氧化钛的折射率为2.25，为高折射率材料，采用这种高低折射率材料交替堆叠的结构，有利于进一步增加光的吸收比例。 需要说明的是，本实施例中，不同的介质材料只是以二氧化硅和二氧化钛为例，但在实际应用中并不以此为限。
进一步的，各层介质材料的厚度满足特定波长单色光的光学谐振条件。根据光的谐振条件可以计算出：当第一二氧化硅介质层620的厚度为485.8纳米，二氧化钛层介质层的厚度为104.5纳米，第二二氧化硅介质层的厚度为144.9纳米时，可满足波长为940纳米的单色光的光学谐振条件。如图7中光电探测器的光吸收比例随入射光波长的变化曲线所示，此时，光的吸收比例达到极大值，为40.5％。
本实施例相对于现有技术而言，保形介质层具体为：多层保形介质层；其中，相邻两个保形介质层的折射率不同。也就是说保形介质层可以采用具有不同折射率的介质材料交替堆叠的结构，有利于进一步增加光的吸收比例。
本申请第四实施例涉及一种图像传感器的像素单元结构的制造方法，包括：提供一衬底，在衬底内形成光电探测器，光电探测器的感光面朝向所述衬底的背面；衬底上且在光电探测器的感光面的相对面上形成球冠形结构；其中，球冠形结构与衬底的材质相同；在球冠形结构上形成保形介质层；在保形介质层上方形成反射层，使得可以制造出如第一实施例中的图像传感器的像素单元结构。下面对本实施方式的图像传感器的像素单元结构的制造方法的实现细节进行具体的说明，以下内容仅为方便理解提供的实现细节，并非实施本方案的必须。
本实施例中的图像传感器的制造方法中，所制备的像素单元结构的保形介质层为单层保形介质层，即制备的为第一实施例或第二实施例中的图像传感器的像素单元结构。制造方法的具体流程图如图8所示，具体包括：
步骤801：提供一衬底，在衬底上形成浅沟槽绝缘。
具体的说，可以参照图9a，在衬底900的两侧形成浅沟槽绝缘901，用以隔绝相邻像素的干扰。
步骤802：在衬底上且在光电探测器的感光面的相对面上形成球冠形结构。
具体的说，球冠形硅结构为球冠形结构的一种，球冠形结构与衬底的材质相同，本实施例中的衬底以硅衬底为例，球冠形结构以球冠形硅结构为例，但在实际应用中，并不以此为限。具体的，可通过光刻胶回流或是灰度掩模曝光工艺，先形成球冠形的光刻胶，再通过反应离子刻蚀将球冠形光刻胶的形貌转移到衬底900上，可参照图9b，其中在光电探测器903区域的上方制作形成的即为球冠形硅结构904。本实施例中的光电探测器903可以为光电二极管，将光电二极管设置于衬底900内。
步骤803：在衬底上形成离子掺杂区、栅极、第一层间介质层等结构。
具体的说，可参照图9c，在衬底内形成的离子掺杂区可以包括：光电探测器903，浮置扩散节点906等，还可以形成栅极介质层907、栅极结构908和第一层间介质层910等结构。
步骤804：去除光电探测器的感光面的相对面上的第一层间介质层，露出球冠形硅结构。
具体的说，可以参照图9d，去除光电探测器903区域上方的第一层间介质层910，露出球冠形硅结构904。
步骤805：在球冠形硅结构上形成保形介质层并在保形介质层上方形成反射层。
具体的说，可以参照图9e，在球冠形硅结构904上形成一层特定厚度的保形介质层920以及反射层930，然后沉积第二层间介质层940并平坦化。较佳的，保形介质层920可以具有预设厚度，预设厚度可以满足光学谐振条件，光学谐振条件的内容在第二实施例中已做了详细介绍，可参考第二实施例中的描述，为避免重复本实施例在此不再重复。
需要说明的是，在沉积第二层间介质层940并平坦化后，可以按照标准图像传感器的工艺流程完成剩余的工艺，可参照图9f，包括导电通孔911、金属互联线912以及金属间介质层915的制作，与载片晶圆950的键合，衬底900的背面减薄，抗反射层960以及微透镜970的制作等。由于这些均为图像传感器的标准工艺，在此不再一一赘述。
本申请第五实施例涉及一种图像传感器的制造方法，本实施例与第四实施例大致相同，不同之处在于，第四实施例中制备的图像传感器的像素单元结构中的保形介质层为单层，而本实施例中制备的图像传感器的像素单元结构中的保形介质层为多层，即本实施例提供了一种制备第三实施例中的图像传感器的像素单元结构的方法。
本实施例中的图像传感器的制造方法的具体流程图如图10所示，具体包括：
步骤1001：提供一衬底，在衬底上形成浅沟槽绝缘。
步骤1002：在衬底上且在光电探测器的感光面的相对面上形成球冠形结构。
步骤1003：在衬底上形成离子掺杂区、栅极、第一层间介质层等结构。
步骤1004：去除光电探测器的感光面的相对面上的第一层间介质层，露 出球冠形硅结构。
步骤1001至步骤1004与第四实施例中步骤中901至步骤904大致相同，为避免重复此处不再一一赘述。
步骤1005：在球冠形硅结构上形两层或两层以上特定厚度的保形介质层并在保形介质层上方形成反射层。
具体的说，两层或两层以上的保形介质层为高低折射率材料的交替堆叠结构。下面以3层保形介质层为例进行说明，首先可以根据光的谐振条件分别求得3种不同介质材料的保形介质层的厚度。在形成3层具有特定厚度的保形介质层时，可以先在球冠形硅结构上形成第一二氧化硅介质层；接着在第一二氧化硅介质层上形成二氧化钛介质层；然后，在二氧化钛介质层上形成第二二氧化硅介质层，使得最终形成3层保形介质层堆叠结构。最后在第二二氧化硅介质层上形成反射层。需要说明的是，本实施例中，不同的介质材料只是以二氧化硅和二氧化钛为例，但在实际应用中并不以此为限。
需要说明的是，在步骤1005之后可参照第四实施例中步骤905之后的步骤按照标准图像传感器的工艺流程完成剩余的工艺，为避免重复，此处不再一一赘述。
应当理解，上述方法中以单个像素结构为描述对象，对应的图9a-9f中所显示的衬底900的边界并非衬底的真实边界。
上面各种方法的步骤划分，只是为了描述清楚，实现时可以合并为一个步骤或者对某些步骤进行拆分，分解为多个步骤，只要包括相同的逻辑关系，都在本专利的保护范围内；对算法中或者流程中添加无关紧要的修改或者引入无关紧要的设计，但不改变其算法和流程的核心设计都在该专利的保护范围内。
本领域的普通技术人员可以理解，上述各实施例是实现本申请的具体实施例，而在实际应用中，可以在形式上和细节上对其作各种改变，而不偏离本申请的精神和范围。

Claims (23)

  1. 一种图像传感器，包括衬底和至少一个像素单元，其特征在于，所述像素单元包括：
    光电探测器，设置于所述衬底内，所述光电探测器的感光面朝向所述衬底的背面，用于在从所述衬底的背面接收到入射光时产生电荷；
    球冠形结构，设置于所述衬底上且位于所述感光面的相对面；
    保形介质层，设置于所述球冠形结构上方，用于在所述入射光达到所述保形介质层时，产生介质层反射光；以及
    反射层，设置于所述保形介质层上方，用于在所述入射光达到所述反射层时，产生反射层反射光。
  2. 根据权利要求1所述的图像传感器，其特征在于，所述保形介质层是多层保形介质层；其中，相邻两个保形介质层的折射率不同。
  3. 根据权利要求2所述的图像传感器，其特征在于，所述多层保形介质层是3层保形介质层；其中，所述3层保形介质层分别为：
    位于所述球冠形结构上的第一二氧化硅介质层；
    位于所述第一二氧化硅介质层上的二氧化钛介质层；以及，
    位于所述二氧化钛介质层上的第二二氧化硅介质层。
  4. 根据权利要求1所述的图像传感器，其特征在于，所述保形介质层具有预设厚度，所述预设厚度满足所述入射光的光学谐振条件。
  5. 根据权利要求4所述的图像传感器，其特征在于，所述光学谐振条件为：所述介质层反射光的相位θ和所述反射层反射光的相位
    Figure PCTCN2018117194-appb-100001
    满足如下公式：
    Figure PCTCN2018117194-appb-100002
    其中，所述N为自然数。
  6. 根据权利要求5所述的图像传感器，其特征在于，所述介质层反射光的相位θ和所述反射层反射光的相位
    Figure PCTCN2018117194-appb-100003
    具体通过以下公式计算：
    Figure PCTCN2018117194-appb-100004
    Figure PCTCN2018117194-appb-100005
    其中，所述d为所述保形介质层的预设厚度，所述n d为所述保形介质层的折射率，所述λ为所述入射光的波长；所述n r为所述反射层的折射率，所述k r为所述反射层的消光系数。
  7. 根据权利要求1所述的图像传感器，其特征在于，所述球冠形结构是球冠形硅结构。
  8. 根据权利要求1所述的图像传感器，其特征在于，还包括：
    传输晶体管的栅极结构，设置于栅极介质层上，所述栅极介质层设置于所述衬底上，所述传输晶体管用于控制所述光电探测器产生的电荷向浮置扩散节点传输，所述栅极结构为控制电荷传输的开关；
    所述浮置扩散节点，设置于所述衬底内，用于存储接收到的电荷，并将存储的电荷转化为电压信号。
  9. 根据权利要求1所述的图像传感器，其特征在于，还包括：
    浅沟槽隔离，设置于所述衬底的两侧，用于隔绝相邻像素单元结构的干扰。
  10. 根据权利要求1所述的图像传感器，其特征在于，所述入射光为近红外单色光。
  11. 根据权利要求1-10任意一项所述的图像传感器，其中，所述球冠形结构与所述衬底的材质相同。
  12. 根据权利要求1-11任意一项所述的图像传感器，其中，所述光电探测器为光电二极管。
  13. 一种图像传感器的制造方法，其特征在于，包括：
    提供一衬底，在所述衬底内形成光电探测器，所述光电探测器的感光面朝向所述衬底的背面；
    在所述衬底上且在所述光电探测器的感光面的相对面上形成球冠形结构；其中，所述球冠形结构与衬底的材质相同；
    在所述球冠形结构上形成保形介质层；
    在所述保形介质层上方形成反射层。
  14. 根据权利要求13所述的图像传感器的制造方法，其特征在于，所述在所述衬底上且在所述光电探测器的感光面的相对面上形成球冠形结构，具体包括：
    通过光刻胶回流或灰度掩模曝光工艺，形成球冠形的光刻胶；
    通过反应离子刻蚀将所述球冠形的光刻胶转移到所述衬底内；
    在所述衬底上形成第一层间介质层；
    去除位于所述光电探测器的感光面的相对面的上方区域的第一层间介质层，露出所述球冠形结构。
  15. 根据权利要求14所述的图像传感器的制造方法，其特征在于，在所述保形介质层上方形成反射层之后，还包括：
    在所述反射层上沉积第二层间介质层并平坦化。
  16. 根据权利要求13所述的图像传感器的制造方法，其特征在于，在所述衬底内形成光电探测器之后，还包括：
    在所述衬底内形成浮置扩散节点，并在所述衬底上形成传输晶体管的栅极结构。
  17. 根据权利要求13所述的图像传感器的制造方法，其特征在于，在所述衬底内形成光电探测器之前，还包括：
    在所述衬底的两侧形成浅沟槽隔离。
  18. 根据权利要求13所述的图像传感器的制造方法，其特征在于，所述保形介质层是多层保形介质层；其中，相邻两个保形介质层的折射率不同。
  19. 根据权利要求18所述的图像传感器，其特征在于，所述多层保形介质层为3层保形介质层；其中，所述3层保形介质层分别为：
    位于所述球冠形结构上的第一二氧化硅介质层；
    位于所述第一二氧化硅介质层上的二氧化钛介质层；以及，
    位于所述二氧化钛介质层上的第二二氧化硅介质层。
  20. 根据权利要求13所述的图像传感器的制造方法，其特征在于，所述保形介质层具有预设厚度，所述预设厚度满足预设单色光的光学谐振条件。
  21. 根据权利要求20所述的图像传感器的制造方法，其特征在于，所述光学谐振条件为：介质层反射光的相位θ和反射层反射光的相位
    Figure PCTCN2018117194-appb-100006
    满足如下公式：
    Figure PCTCN2018117194-appb-100007
    其中，所述介质层反射光为所述保形介质层对所述预设单色光的反射光，所述反射层反射光为所述反射层对所述预设单色光的反射光，所述N为自然数。
  22. 根据权利要求21所述的图像传感器的制造方法，其特征在于，所述介 质层反射光的相位θ和所述反射层反射光的相位
    Figure PCTCN2018117194-appb-100008
    具体通过以下公式计算：
    Figure PCTCN2018117194-appb-100009
    Figure PCTCN2018117194-appb-100010
    其中，所述n d为所述介质层的折射率，所述λ为所述入射光的波长；所述n r为所述反射层的折射率，所述k r为所述反射层的消光系数。
  23. 根据权利要求13所述的图像传感器的制造方法，其特征在于，所述球冠形结构为球冠形硅结构。
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