Image sensor, preparation method thereof and electronic equipment

Abstract

The invention provides an image sensor and a preparation method thereof, and electronic equipment, and the preparation method comprises the steps: providing a semiconductor substrate which comprises an ion doping region of a first doping type; forming a device function layer; performing heat treatment on the semiconductor substrate to enable the doped ions in the ion doped region to be diffused into the material layer above the semiconductor substrate so as to form a light absorption driving layer; and preparing a semiconductor device to obtain the image sensor. The structure of the image sensor comprises the light absorption driving layer, the light absorption driving layer is formed based on a mode of carrying out heat treatment on the semiconductor substrate in preparation, the quantum efficiency of the image sensor can be improved based on the existence of the light absorption driving layer, especially the quantum efficiency of near-infrared light is improved, and the application flexibility of a device is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of image acquisition, and particularly relates to an image sensor, a preparation method thereof, and an electronic device. Background Art

[0002] An image sensor is an important component of a digital camera. According to different components, it can be divided into two categories: CCD (Charge Coupled Device) and CMOS (Complementary Metal - Oxide Semiconductor). With the continuous development of CMOS integrated circuit manufacturing technology, especially the design and manufacturing technology of CMOS image sensors, CMOS image sensors have gradually replaced CCD image sensors and become the mainstream. CMOS image sensors have advantages such as low voltage, low power consumption, low cost, and high integration, and have important application values in fields such as machine vision, consumer electronics, high - definition monitoring, and medical imaging.

[0003] In addition, near - infrared (NIR) imaging is a very valuable technology, which can be used in a variety of applications, including agriculture, food detection, medical diagnosis, and environmental monitoring. Near - infrared cameras using CMOS technology can capture images in the infrared wavelength range below visible light, revealing information hidden under the ordinary spectrum for us. Near - infrared imaging is in the infrared band between visible light and thermal infrared imaging. This band includes light that cannot be perceived by the human eye and can be used to measure the chemical composition, moisture content, and temperature of objects, so it has a wide range of applications in agriculture, medicine, and the food industry. However, the main problem faced by near - infrared band response is the small QE (Quantum Efficiency) value. For example, in some CMOS image sensors, the QE at 550nm is nearly 70%, while the QE at 900nm is only about 10%. In addition, due to the very low QE value, in order to be able to image in the near - infrared band, it is necessary to increase the power of the supplementary light source, which will cause a sharp rise in system heat loss, increasing both energy consumption and reducing the reliability of the system.

[0004] Therefore, it is necessary to provide an image sensor, a preparation method thereof, and an electronic device to solve problems such as quantum efficiency, large system heat loss, and high power consumption in the prior art.

[0005] It should be noted that the above introduction to the technical background is only for the convenience of clearly and completely explaining the technical solutions of the present application and facilitating the understanding of those skilled in the art. It cannot be considered that the above - mentioned technical solutions are well - known to those skilled in the art just because these solutions are described in the background art section. Summary of the Invention

[0006] In view of the above-mentioned disadvantages of the prior art, the object of the present invention is to provide an image sensor, a method for manufacturing the same, and an electronic device, which are used to solve the problems such as low quantum efficiency of the image sensor, large system heat loss and high power consumption in the prior art.

[0007] To achieve the above object and other related objects, the present invention provides a method for manufacturing an image sensor, and the manufacturing method includes:

[0008] Providing a semiconductor substrate, the semiconductor substrate includes an ion doping region of a first doping type;

[0009] Forming a device functional layer on the semiconductor substrate;

[0010] Performing heat treatment on the semiconductor substrate to diffuse the doping ions in the ion doping region into a material layer located above the semiconductor substrate to form a light absorption driving layer; and

[0011] Fabricating a semiconductor device in the device functional layer, the semiconductor device includes a photoelectric conversion element of a second doping type different from the first doping type, so as to obtain the image sensor.

[0012] Optionally, the photoelectric conversion element has an extension extending into the light absorption driving layer, wherein the depth of the extension does not exceed 20% of the depth of the photoelectric conversion element.

[0013] Optionally, before forming the device functional layer, the manufacturing method further includes:

[0014] Forming an absorption assisting layer on the semiconductor substrate, wherein during the heat treatment, the doping ions in the ion doping region at least diffuse into the absorption assisting layer.

[0015] Optionally, a prefabricated ion doping layer of the first doping type is formed in the absorption assisting layer.

[0016] Optionally, the prefabricated ion doping layer includes N sub-ion doping layers, and the concentrations of the N sub-ion doping layers show a decreasing trend in the direction from the semiconductor substrate towards the device functional layer.

[0017] Optionally, the prefabricated ion doping layer is a single-layer material layer with a concentration showing a decreasing trend in the direction from the semiconductor substrate towards the device functional layer.

[0018] Optionally, during the heat treatment, the doping ions in the prefabricated ion doping layer diffuse into a material layer located above the semiconductor substrate to form a light absorption driving assisting layer.

[0019] Optionally, when the prefabricated ion-doped layer includes N sub-ion-doped layers, the thickness of the top sub-ion-doped layer is greater than or equal to 3 μm.

[0020] Optionally, the processing temperature of the heat treatment process is greater than or equal to 950 °C and less than or equal to 1150 °C.

[0021] Optionally, when an absorption auxiliary layer is formed on the semiconductor substrate, the thickness of the absorption auxiliary layer is between 1 - 6 μm.

[0022] Optionally, the doping concentration of the ion-doped layer of the first doping type in the semiconductor substrate is greater than the doping concentration in the prefabricated ion-doped layer and greater than the doping concentration of the ion-doping of the first doping type in the device functional layer.

[0023] Optionally, the doping concentration of the ion-doped region in the semiconductor substrate is greater than 2E18 atom / CM3, the device functional layer has doping of the first doping type with a concentration less than 2E15 atom / CM3, and when the image sensor includes a prefabricated ion-doped layer with the first doping type, the doping concentration is between 5E15 - 1E17 atom / CM3.

[0024] Optionally, the first doping type is P-type and the second doping type is N-type.

[0025] The present invention also provides an image sensor. The image sensor can be prepared by the preparation method described above. Of course, it can also be prepared by other methods. The image sensor includes:

[0026] A semiconductor substrate, which includes an ion-doped layer of the first doping type;

[0027] A device functional layer, located on the semiconductor substrate;

[0028] A semiconductor device, located in the device functional layer, and the semiconductor device includes a photoelectric conversion element having a second doping type different from the first doping type;

[0029] Wherein, a light absorption driving layer is formed in the interface region between the semiconductor substrate and the device functional layer.

[0030] Optionally, the light absorption driving layer extends from the bottom of the device functional layer towards the inside and has ion doping of the first doping type.

[0031] Optionally, the image sensor further includes an absorption auxiliary layer. The absorption auxiliary layer is located between the semiconductor substrate and the device functional layer, and the light absorption driving layer extends from the bottom of the absorption auxiliary layer towards the inside.

[0032] Optionally, the absorption assisting layer includes a prefabricated ion-doped layer having ion doping of the first doping type, and the photoabsorption driving layer is at least formed in the prefabricated ion-doped layer.

[0033] Optionally, the prefabricated ion-doped layer includes N sub-ion-doped layers, and the concentrations of the N sub-ion-doped layers show a decreasing trend in the direction from the semiconductor substrate towards the device functional layer; alternatively, the prefabricated ion-doped layer is a single-layer material layer with a concentration showing a decreasing trend in the direction from the semiconductor substrate towards the device functional layer.

[0034] Optionally, the image sensor further includes a photoabsorption driving assisting layer which extends from the bottom of the device functional layer towards the inside and has ion doping of the first doping type.

[0035] Optionally, the image sensor further includes a plurality of pixel units arranged in an array, there is an isolation structure between adjacent pixel units, each pixel unit shares the photoabsorption driving layer, and when there is an absorption assisting layer, each pixel unit shares the absorption assisting layer.

[0036] Optionally, the image sensor is a front-illuminated image sensor.

[0037] The present invention also provides an electronic device, and the electronic device includes the image sensor according to any one of the above solutions.

[0038] As described above, the image sensor, its manufacturing method, and the electronic device of the present invention have the following beneficial effects: The image sensor structure of the present invention includes a photoabsorption driving layer. In addition, in the preparation of the image sensor of the present invention, the photoabsorption driving layer is formed by heat-treating the semiconductor substrate. Based on the design of the photoabsorption driving layer, the quantum efficiency of the image sensor for optical signals can be improved due to the presence of the photoabsorption driving layer, especially the quantum efficiency for near-infrared light, and the application flexibility of the device can be improved. Description of the Drawings

[0039] Figure 1 Shown is a basic structural block diagram of an image sensor system.

[0040] Figure 2 Shown is a schematic diagram of a pixel circuit of an image sensor.

[0041] Figure 3 Shown is a flowchart of the preparation of the image sensor in the embodiment of the present application.

[0042] Figure 4 Shown is a schematic diagram of providing a semiconductor substrate in the preparation of the image sensor in the embodiment of the present application.

[0043] Figure 5 It shows a schematic diagram of forming a device functional layer in the fabrication of the image sensor according to an embodiment of the present application.

[0044] Figure 6 It shows a schematic diagram of forming a light absorption driving layer in the fabrication of the image sensor according to an embodiment of the present application.

[0045] Figure 7 It shows a schematic diagram of forming a semiconductor device in the fabrication of the image sensor according to an embodiment of the present application.

[0046] Figure 8 It shows a schematic diagram of forming an absorption assisting layer in the fabrication of the image sensor according to an embodiment of the present application.

[0047] Figure 9 It shows in Figure 8 A schematic diagram of forming a light absorption driving layer in the example of the shown structure.

[0048] Figure 10 It shows in Figure 8 A schematic diagram of forming a semiconductor device in the example of the shown structure.

[0049] Figure 11 It shows in Figure 8 A schematic diagram of forming a light absorption driving assisting layer in the example of the shown structure.

[0050] Figure 12 It shows the influence of different heat treatment times on the diffusion of B ion doping in this embodiment.

[0051] Figure 13 It shows the influence of heat treatment being carried out or not on the near-infrared light sensitivity in this embodiment.

[0052] Figure 14 It shows the influence of whether the absorption assisting layer is prepared and heat treated or not on the dark current performance of the image sensor compared with the reference example in this embodiment.

[0053] Description of component labels

[0054] 101 Semiconductor substrate

[0055] 201 Device functional layer

[0056] 300 Light absorption driving layer

[0057] 401 First isolation structure

[0058] 402 Second isolation structure

[0059] 501 Pixel circuit

[0060] 502 Photoelectric conversion element

[0061] 503 Transistor

[0062] 600 Absorption auxiliary layer

[0063] 700 Light absorption driving auxiliary layer Detailed implementation manners

[0064] The following describes the implementation manners of the present invention through specific examples. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0065] It should be emphasized that the term "including / containing" when used herein refers to the presence of features, whole parts, steps or components, but does not exclude the presence or addition of one or more other features, whole parts, steps or components.

[0066] Features described and / or shown for one implementation manner can be used in the same or similar manner in one or more other implementation manners, combined with features in other implementation manners, or replace features in other implementation manners.

[0067] When detailing the embodiments of the present invention, for ease of explanation, the cross-sectional views showing the device structure will be enlarged locally out of the general proportion, and the schematic diagrams are only examples and should not limit the scope of protection of the present invention herein. In addition, in actual production, three-dimensional spatial dimensions of length, width and depth should be included.

[0068] For convenience of description, spatial relationship terms such as "under", "below", "lower than", "beneath", "above", "on" etc. may be used herein to describe the relationship between one element or feature shown in the drawings and other elements or features. It will be understood that these spatial relationship terms are intended to encompass other directions of the device in use or operation in addition to the directions depicted in the drawings. Further, when a layer is referred to as being "between" two layers, it can be the only layer between the two layers, or there can be one or more intervening layers.

[0069] In the context of the present application, the structure in which the first feature is "above" the second feature described may include embodiments where the first and second features are formed in direct contact, and may also include embodiments where additional features are formed between the first and second features, such that the first and second features may not be in direct contact.

[0070] It should be noted that the illustrations provided in this embodiment only schematically illustrate the basic concept of the present invention. Therefore, only the components related to the present invention are shown in the illustrations, rather than being drawn according to the number, shape, and size of the components in actual implementation. The type, quantity, and proportion of each component in actual implementation can be arbitrarily changed, and the component layout type may also be more complex.

[0071] The following will give a detailed description of the content proposed by the present invention in conjunction with each attached drawing of the present invention.

[0072] Figure 1 It is shown as a basic structural block diagram of an image sensor system. The image sensor includes a readout circuit and a control circuit connected to a pixel array. In addition, a functional logic unit is connected to the readout circuit, and the readout circuit and the control circuit are connected to a status register to implement the control of the pixel array. The pixel array includes a plurality of pixels (P1, P2, P3) arranged in rows (R1, R2, R3... Ry) and columns (C1, C2, C3... Cx). The pixel signals output by the pixel array are output to the readout circuit via column lines. In some applications, after the pixels acquire image data, they are read out in the readout mode specified by the status register and then transmitted to the functional logic unit. In a specific implementation, the readout circuit may include an analog-to-digital conversion (ADC) circuit and other circuits.

[0073] In some applications, the status register may include a programmed selection system to determine whether the readout system reads out through a rolling shutter mode or a global shutter mode. The functional logic unit can store the original image data or the image data after image processing. In some implementations, the readout circuit may read out one row of image data along the readout column line at a time. Of course, other methods can also be used to read out the image data. The operation of the control circuit can be determined by the current settings of the status register. For example, the control circuit generates a shutter signal for controlling image acquisition. In some applications, this shutter signal can be a global exposure signal, enabling all pixels of the pixel array to acquire their image data simultaneously through a single acquisition window. In other applications, this shutter signal can also be a rolling exposure signal, enabling the pixels of each pixel row of the pixel array to continuously perform exposure reading operations through the acquisition window.

[0074] Figure 2 It is shown as a schematic diagram of a pixel unit in an image sensor. As Figure 2As shown, each pixel unit includes a photoelectric conversion element (e.g., a photodiode) and a pixel circuit (shown as transistors within the dashed box in the figure). The photodiode can be a buried photodiode (PPD) applied in the current image sensor. In an application example, the pixel circuit includes a reset transistor (RST), a source follower transistor (SF), and a pixel selection transistor (RS), which are connected to a transfer transistor (TX) and a photodiode as shown in Figure 2 . In an application example of a stacked structure, the pixel circuit includes a reset transistor, a source follower transistor, and a pixel selection transistor disposed on a first circuit chip, and further includes a transfer transistor disposed on a second circuit chip. The photodiode in the second circuit chip is connected to other transistors in the first circuit chip based on the transfer transistor. In a further application example, the pixel circuit may further include a gain control transistor (DCG) connected between a floating diffusion region (FD) and the reset transistor. During operation, the photoelectric conversion element generates photo charges in response to incident light during the exposure process. The transfer transistor connects and transmits a signal, which controls the transfer transistor to transfer the charges accumulated in the photoelectric conversion element to the floating diffusion region. The reset transistor is connected between the power supply voltage and the floating diffusion region, and responds to the reset signal to reset the sensor pixel circuit (e.g., discharge or charge the floating diffusion region and the photodiode to the current voltage). The floating diffusion region is connected to the gate of the source follower transistor. The source follower transistor is connected between the power supply voltage and the pixel selection transistor, responds to the potential of the floating diffusion region and outputs it. The pixel selection transistor connects the source follower transistor and the bit line, and responds to the pixel selection control signal to achieve pixel selection readout and output it to the readout column.

[0075] However, in existing image sensors, the main problem faced by the near-infrared band response is the small QE value. The silicon substrate has weak absorption in the near-infrared band of 750 nm - 1100 nm. In addition, due to the very low QE value, in order to be able to image in the near-infrared band, it is necessary to increase the power of the supplementary light source, which will cause a sharp rise in the system heat loss, increasing both the energy consumption and reducing the reliability of the system. The present invention can effectively improve the above problems through the setting of the light absorption driving layer and the design of the process. This will be described in detail below in conjunction with the embodiments.

[0076] Embodiment 1:

[0077] Please refer to Figure 3 shown. This embodiment provides a method for manufacturing an image sensor, Figure 3 which is shown as a flowchart of this manufacturing method. Among them, this manufacturing method includes the following steps:

[0078] S1: Provide a semiconductor substrate, and the semiconductor substrate includes an ion doping region of a first doping type;

[0079] S2: Form a device functional layer on the semiconductor substrate;

[0080] S3: Heat-treat the semiconductor substrate to diffuse the doping ions in the ion doping region into the material layer located above the semiconductor substrate to form a light absorption driving layer; and

[0081] S4: Fabricate a semiconductor device in the device functional layer, the semiconductor device including a photoelectric conversion element of a second doping type different from the first doping type, to obtain the image sensor.

[0082] In this embodiment, a light absorption driving layer is formed in the image sensor based on the semiconductor substrate, so that the photoelectric conversion and signal transmission can be further compensated based on the light absorption driving layer, which is beneficial to the improvement of the quantum efficiency of various optical signals, especially beneficial to the improvement of the infrared light quantum efficiency, thereby improving the application flexibility of the image sensor, broadening its application fields, and improving the image quality. It should be noted that the preparation sequence of the above steps can be changed according to the actual process, as long as the light absorption driving layer of the present application can be realized.

[0083] Next, the preparation of the image sensor of the present application will be described in detail with specific embodiments.

[0084] First, as Figure 4 shown, perform step S1: Provide a semiconductor substrate 101, the semiconductor substrate 101 including an ion doping region of a first doping type, and in this embodiment, the first doping type is described as P-type.

[0085] In one example, the entire semiconductor substrate 101 may be doped with ions of the first doping type, so that the entire semiconductor substrate is considered as the ion doping region. Of course, in other examples, the ion doping region may also be obtained by doping ions of the first doping type in the required regions.

[0086] Specifically, in this example, the semiconductor substrate 101 has opposite first surface 101a (upper surface) and second surface 101b (lower surface). The semiconductor substrate 101 can be a structure composed of a single-layer material layer, including but not limited to a silicon substrate, and its material can be single-crystalline silicon, single-crystalline germanium, polycrystalline silicon, amorphous silicon, or a silicon-germanium compound, etc. Of course, the semiconductor substrate 101 can also be silicon-on-insulator (SOI), etc. In addition, the semiconductor substrate 101 can also have N-type doped or P-type doped regions to meet actual requirements. Among them, the semiconductor substrate 101 can be used as the substrate of an image sensor, and an epitaxial layer is prepared thereon to realize the preparation of the devices of the image sensor. In addition, in other embodiments, the semiconductor substrate 101 can be any structure in the field of image sensors used to prepare the functional regions of the image sensor, and the photosensitive elements, various transistors, and interconnection wirings, etc. of the CMOS image sensor can be prepared based on the semiconductor substrate 101.

[0087] Next, as Figure 5 shown, step S2 is performed: a device functional layer 201 is formed on the semiconductor substrate 101.

[0088] Specifically, when forming the device functional layer 201 on the semiconductor substrate 101, each functional region in the image sensor can be fabricated therein. Of course, in other cases where needed, the structures required for the image sensor can also be fabricated in the semiconductor substrate 101 or other material layers. In this example, the device functional layer 201 has opposite first surface 201a (upper surface) and second surface 201b (lower surface). Among them, the second surface 201b of the device functional layer 201 is fabricated on the first surface 101a of the semiconductor substrate 101.

[0089] In a specific example, the device functional layer 201 can be an epitaxial layer (EPI) formed on the semiconductor substrate 101 (such as a silicon substrate), and the device functional layer 201 can be directly formed by an epitaxial process. For example, the epitaxial layer can be a P-type silicon epitaxial layer, and the photoelectric conversion elements and transistor components (such as including charge transport elements) are fabricated in this epitaxial layer. Of course, the device functional layer 201 can also be formed by other methods of existing processes. Further, a front-illuminated image sensor can be fabricated based on this semiconductor substrate and the device functional layer.

[0090] Next, as Figure 6As shown, step S3 is performed: the semiconductor substrate 101 is heat-treated to diffuse the doped ions in the ion-doped region into the material layer located above the semiconductor substrate 101 to form a light absorption driving layer 300; in this embodiment, the doped ions in the ion-doped region diffuse into the device functional layer 201 located above the semiconductor substrate 101, that is, the light absorption driving layer 300 extends upward from the first surface 101a of the semiconductor substrate 101 and extends inward from the second surface 201b of the device functional layer 201. Among them, the light absorption driving layer 300 formed based on ion diffusion has ion doping of the first doping type, which can facilitate the photoelectric conversion in the interval at the bottom of the device functional layer 201 and the transfer of the generated electrons to the collection region, thereby facilitating the improvement of the quantum efficiency of the optical signal, especially the near-infrared light with a longer wavelength.

[0091] As an example, the processing temperature of the heat treatment process is greater than or equal to 950 °C and less than or equal to 1150 °C. For example, it can be selected as 980 °C, 1000 °C, 1080 °C, etc., which can improve the formation efficiency and performance of the light absorption driving layer 300 while meeting the performance requirements of the device of the present application. In addition, in this example, this heat treatment process is carried out before the device functional layer 201 and the semiconductor device are formed, which can prevent the influence of high temperature on other devices.

[0092] See Figure 12 and Figure 13 As shown, through the SIMS test results of different front-end annealing process conditions, it is found that as the thermal budget increases, the upward diffusion degree of the substrate P-type doping becomes larger and larger, among which, Figure 12 shows the SIMS diagram of B element under different heat treatment conditions (thermal, taking time h as an example). In addition, see Figure 13 As shown, by comparing the near-infrared light sensitivity under different heat treatment conditions (the comparison between heat treatment and non-heat treatment is shown in the figure), it is found that heat treatment can effectively improve the near-infrared light sensitivity. It can be seen that heat treatment increases the concentration gradient width from the substrate to the epitaxial layer, which can improve the near-infrared performance.

[0093] Finally, as Figure 7 shown, step S4 is performed: a semiconductor device is fabricated in the device functional layer 201, and the semiconductor device includes a photoelectric conversion element 502 of a second doping type different from the first doping type to obtain an image sensor. Further, other transistors in the image sensor can also be fabricated. The transfer transistor 503 is shown in the figure. Of course, there are other transistors, and pixel units 501 are formed corresponding to the photoelectric conversion elements.

[0094] Continue to see Figure 7As shown, in one example, the optoelectronic conversion element 502 has an extension extending into the light absorption driving layer 300, where the depth of the extension does not exceed 20% of the depth of the optoelectronic conversion element.

[0095] In this example, the optoelectronic conversion element 502 prepared after forming the light absorption driving layer 300 extends into the light absorption driving layer 300, which can simultaneously improve the dark current problem generated during the operation of the device, prevent electrons from transferring to adjacent pixel units, and affect the image quality. In addition, in a further example, the set depth of the extension is less than 20% of the depth of the optoelectronic conversion element itself. As Figure 7 shown, the distance D2 is less than 20% of the distance D1. For example, 2%, 8%, 10%, 12%, 15%, etc. can be selected to optimize the full well while improving the dark current.

[0096] Please refer to Figures 8 - 10 As shown, in one example, before forming the device functional layer 201, the method for manufacturing an image sensor further includes: forming an absorption auxiliary layer 600 on the semiconductor substrate 101. The absorption auxiliary layer 600 can be prepared by an epitaxial process on the semiconductor substrate 101.

[0097] During the heat treatment process, the doping ions in the ion-doped region of the semiconductor substrate 101 diffuse at least into the absorption auxiliary layer 600, so that the width of the light absorption driving layer 300 can be further enlarged, and the quantum efficiency of the image sensor can be improved. In addition, in this example, forming the absorption auxiliary layer 600 before the heat treatment process can improve the defects generated during the preparation of the absorption auxiliary layer 600 while forming the light absorption driving layer 300 based on the heat treatment annealing process. The material of the absorption auxiliary layer 600 can be the same as the material of the semiconductor substrate 101, and the materials include but are not limited to silicon. Further, doping ions can also be configured in the absorption auxiliary layer 600 to further assist the absorption and driving of light signals based on heat treatment.

[0098] In addition, the design of the absorption auxiliary layer 600 can improve the problem that the increase in ion diffusion due to annealing during heat treatment has a limit. In the structure, the width of the concentration gradient between the epitaxial layer and the substrate can be greatly increased, and higher near-infrared sensitivity can be obtained. In addition, due to the limitations of the epitaxial layer process, as the thickness of the epitaxial layer (absorption auxiliary layer 600) increases, lattice defects and the like of the epitaxial layer may increase, thereby deteriorating the high-temperature performance of the chip itself. Based on the design of the process method of the present application, these adverse effects can be alleviated. On the basis of the structure of the absorption auxiliary layer 600, the process conditions for improving the front-end annealing budget are combined. Through reasonable annealing budget, the lattice defects of the epitaxial layer can be reduced. It can be seen Figure 14As shown, the reference example is an example without heat treatment and for preparing the absorption auxiliary layer. At the same time, comparative examples of only preparing the auxiliary absorption layer and simultaneously preparing the auxiliary absorption layer and heat treatment are given in the figure, with other conditions being the same. It can be seen that thermal annealing can improve the high-temperature performance (dark current performance) to the level of the original structure, so that while obtaining an improvement in near-infrared sensitivity, there is no need to worry about the side effects of high-temperature performance, thereby improving the comprehensive performance.

[0099] Furthermore, the doping ions in the ion-doped region of the semiconductor substrate 101 further diffuse upward from the absorption auxiliary layer 600 into the device functional layer 201. The absorption auxiliary layer 600 has a second surface 600b (lower surface) formed on the first surface 101a of the semiconductor substrate 101 and a first surface 600a (upper surface) of the absorption auxiliary layer 600 opposite thereto. Refer to Figure 9 As shown, the doping ions in the ion-doped region of the semiconductor substrate 101 diffuse upward from the first surface 101a of the semiconductor substrate 201, and diffuse through the absorption auxiliary layer 600 into the device functional layer 201 to form the photoabsorption driving layer 300.

[0100] In a further example, a prefabricated ion-doped layer of the first doping type is formed in the absorption auxiliary layer 600. Among them, the prefabricated ion-doped layer can be formed throughout the absorption auxiliary layer 600, that is, the entire absorption auxiliary layer 600 can be regarded as the prefabricated ion-doped layer. Of course, in other examples, it can also be that a part of the absorption auxiliary layer 600 is doped to form the prefabricated ion-doped layer. Among them, the prefabricated ion-doped layer with doping of the first doping type can be directly formed in the epitaxial process. Of course, it can also be ion implantation after forming the base material layer of the absorption auxiliary layer. For example, P-type ion implantation is performed in a silicon material to form it.

[0101] Please refer to Figure 10 As shown, it is a schematic structural diagram of forming a semiconductor device after heat treatment to form the photoabsorption driving layer 300 when the absorption auxiliary layer 600 is formed. Other structures are similar to the foregoing. The depth relationship between the photoelectric conversion element 502 and the extended photoabsorption driving layer 300 can refer to the foregoing description of 20%.

[0102] Please refer to Figure 11 As shown, during the heat treatment process, the doping ions of the prefabricated ion-doped layer diffuse into the material layer above the semiconductor substrate 101 to form the photoabsorption driving auxiliary layer 700.

[0103] Specifically, in this example, the doped ions in the prefabricated ion-doped layer diffuse into the material layer located above it and diffuse into the device functional layer 201, thereby forming a light absorption driving auxiliary layer 700. In addition, the doped ions in the ion-doped layer in the semiconductor substrate 101 also diffuse into the material layer above to form a light absorption driving layer 300. Among them, the light absorption driving layer 300 and the light absorption driving auxiliary layer 700 are in contact with each other or further extend from the contact surface to form an overlap, which can further improve the signal conversion driving efficiency based on the combination of the two and facilitate the formation of an electron transport gradient from the surface of the semiconductor substrate upward. It should be noted that the diffusion during the heat treatment process also includes its own diffusion, and is not strictly limited to the diffusion into the material layer above described in this application. This is understandable to those skilled in the art, and the above description facilitates the understanding of the invention.

[0104] Continue to refer to Figure 8 As shown, in one example, the doping concentration of the ion-doped layer of the first doping type in the semiconductor substrate is greater than the doping concentration in the prefabricated ion-doped layer of the absorption auxiliary layer, which is greater than the doping concentration of the first doping type in the device functional layer. This is beneficial to form a concentration gradient from bottom to top during the heat treatment process, and then an electric field from bottom to top can be formed to drive charge transport. Among them, when the prefabricated ion-doped layer includes N sub-ion-doped layers or the prefabricated ion-doped layer has a varying doping concentration, the doping concentration of the ion-doped layer of the first doping type in the semiconductor substrate is greater than the maximum doping concentration in the prefabricated ion-doped layer of the absorption auxiliary layer, and the minimum doping concentration in the prefabricated ion-doped layer is greater than the doping concentration of the first doping type in the device functional layer.

[0105] As an example, the doping concentration of the ion-doped region in the semiconductor substrate 101 is greater than 2E18 atom / CM3, the device functional layer 201 has a doping of the first doping type with a concentration less than 2E15 atom / CM3, and when the image sensor includes a prefabricated ion-doped layer of the first doping type, the doping concentration is between 5E15 - 1E17 atom / CM3. In a specific example, the ion doping concentration in the semiconductor substrate 101 can be 3E18 atom / CM3, 3E18 atom / CM3, etc., the ion concentration of the device functional layer 201 can be 2E14 atom / CM3, 1E15 atom / CM3, etc., and the ion doping concentration of the prefabricated ion-doped layer can be 6E15 atom / CM3, 6E15 atom / CM3 or have a gradient doping. In other examples, the concentrations of each doped layer can be designed according to the actual situation.

[0106] In an alternative example, the prefabricated ion-doped layer is a single-layer material layer with a concentration decreasing from the semiconductor substrate 101 towards the device functional layer 201, or the prefabricated ion-doped layer includes N sub-ion-doped layers (the stacked structure is not specifically shown in the figure), and the concentration of the N sub-ion-doped layers decreases from the semiconductor substrate 101 towards the device functional layer 201. Herein, the decreasing trend means that the numerical value of the concentration gradually decreases. Of course, there are also cases where at least two adjacent concentration values are equal.

[0107] In this example, by setting a decreasing concentration gradient, a gradient factor can be further introduced into the light absorption driving layer 300 of the present application, which is further beneficial to the formation of an electric field for electron transport, that is, an electric field that transmits upward from the bottom side below the photoelectric conversion element, and improves the transmission power of the photoelectric conversion signal.

[0108] As an example, the thickness of the absorption auxiliary layer 600 is between 1 - 6 μm. For example, it can be set to 2 μm, 3 μm, 4 μm, 5 μm, so that the quantum efficiency of the optical signal, especially the quantum efficiency of infrared light, can be improved in combination with the heat treatment process of the present application. At the same time, on the basis of the heat treatment process, it is beneficial to increase the thickness of the absorption auxiliary layer 600, so as to form a light absorption driving efficiency based on this material layer. In addition, the design within the above range is beneficial to alleviating problems such as lattice defects caused by the overly thick absorption auxiliary layer 600.

[0109] In an alternative example, the prefabricated ion-doped layer includes N sub-ion-doped layers, and the thickness of the multi-layer sub-ion-doped layers can be set according to actual requirements and the total thickness of the absorption auxiliary layer 600 required for practice. Optionally, the thickness of each sub-ion-doped layer is the same. In a further example, the thickness of the top sub-ion-doped layer is greater than or equal to 3 μm. For example, it can be selected as 3.5 μm, 4 μm. The design within the above thickness range can be beneficial to reducing defects and improving the performance of the device functional layer 201 located above it.

[0110] Continue to refer to Figure 7 and Figure 11As shown, the image sensor further includes a plurality of pixel units arranged in an array, and there is an isolation structure between adjacent pixel units. For example, it is composed of the first isolation structure 401 and the second isolation structure 402 in the figure. Each pixel unit shares the light absorption driving layer 300, and when there is an absorption auxiliary layer 600, each pixel unit shares the light absorption driving layer 600, and a shared light absorption driving auxiliary layer 700 can be further formed. In one example, the first isolation structure 401 is a P-type doped isolation, and the second isolation structure 402 is a shallow trench isolation structure STI. In addition, in this embodiment, the first doping type is P-type and the second doping type is N-type. Of course, they can be interchanged when forming other types of image sensors. In addition, the image sensor of this embodiment can be a front-illuminated image sensor, so as to further solve the problem of long-wavelength, especially infrared light quantum efficiency caused by the limited depth of the photoelectric conversion element of the front-illuminated image sensor.

[0111] Embodiment 2:

[0112] Please refer to Figure 7 、 Figure 10 and Figure 11 As shown, the present application also provides an image sensor. Among them, the image sensor in this embodiment is prepared by using the preparation method of the image sensor in Embodiment 1. The related structures and corresponding features can be referred to the description in the preparation method and will not be elaborated here. Of course, in other embodiments, it can also be obtained based on other preparation methods. Among them, the image sensor includes: a semiconductor substrate, a device functional layer, a semiconductor device, and a light absorption driving layer. Specifically:

[0113] The semiconductor substrate 101 includes an ion doping layer of the first doping type;

[0114] The device functional layer 201 is located on the semiconductor substrate;

[0115] The semiconductor device is located in the device functional layer. The semiconductor device includes a photoelectric conversion element 502 having a second doping type different from the first doping type;

[0116] Among them, a light absorption driving layer 300 is formed in the interface region between the semiconductor substrate 101 and the device functional layer 201. The interface region can be understood as the relatively surface region where the two are closest or in contact, including the material layer extending upward from the corresponding surface of the semiconductor substrate or further extending into the material layer in the device functional layer. The above-mentioned light absorption driving layer 300 can be formed by diffusion from the semiconductor substrate according to the description in the preparation method. Of course, in other embodiments, it can also be formed by other methods to be formed in the image sensor, so as to facilitate photoelectric conversion and the driving and transmission of electrical signals, and improve the quantum efficiency.

[0117] In one example, the light absorption driving layer 300 extends inwardly from the bottom of the device functional layer 201 and has ion doping of the first doping type, which can be formed by diffusion as described in the method description.

[0118] In one example, the image sensor further includes an absorption assisting layer 600. The absorption assisting layer is located between the semiconductor substrate 101 and the device functional layer 201. The light absorption driving layer 300 extends inwardly from the bottom of the absorption assisting layer 600. It can be only located in the absorption assisting layer 600 or further extend into the device functional layer 201. In this example, the light absorption driving layer extends from the absorption assisting layer into the device functional layer.

[0119] In one example, the absorption assisting layer 600 includes a prefabricated ion doping layer, which has ion doping of the first doping type. The light absorption driving layer 300 is at least formed in the prefabricated ion doping layer. In this example, the light absorption driving layer 300 extends from the prefabricated ion doping layer into the device functional layer 201.

[0120] As an example, the image sensor further includes a light absorption driving assisting layer 700. The light absorption driving assisting layer 700 extends inwardly from the bottom of the device functional layer 201 and has ion doping of the first doping type. It can be formed by diffusion through the prefabricated ion doping layer of the assisting absorption layer 600 as described in the method description.

[0121] In one example, the prefabricated ion doping layer includes N sub-ion doping layers, and the concentrations of the N sub-ion doping layers show a decreasing trend in the direction from the semiconductor substrate towards the device functional layer; or, the prefabricated ion doping layer is a single-layer material layer with a concentration showing a decreasing trend in the direction from the semiconductor substrate towards the device functional layer.

[0122] Embodiment 3:

[0123] The present invention also provides an electronic device, including the image sensor described in any one of the above solutions. The electronic device can be a security monitoring device, a vehicle-mounted electronic device, a mobile phone camera, a machine vision device, etc. Based on the image sensor of the present invention, high-quality image information can be obtained, especially for infrared utilization devices.

[0124] In summary, the image sensor structure of the present invention includes a light absorption driving layer. In addition, in the preparation of the image sensor of the present invention, the light absorption driving layer is formed by heat-treating the semiconductor substrate. Based on the design of the light absorption driving layer, the quantum efficiency of the image sensor for light signals can be improved due to the presence of the light absorption driving layer, especially the quantum efficiency of near-infrared light, and the application flexibility of the device can be improved. Therefore, the present invention effectively overcomes various disadvantages in the prior art and has high industrial utilization value.

[0125] The above embodiments are only illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. All equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A method for manufacturing an image sensor, characterized in that, The preparation method includes: providing a semiconductor substrate, the semiconductor substrate including an ion doping region of a first doping type; forming a device functional layer on the semiconductor substrate; performing a heat treatment on the semiconductor substrate to cause doping ions in the ion doping region to diffuse into a material layer located above the semiconductor substrate to form a light absorption driving layer; and fabricating a semiconductor device in the device functional layer, the semiconductor device including a photoelectric conversion element of a second doping type different from the first doping type to obtain the image sensor.

2. The method for manufacturing an image sensor according to claim 1, wherein The photoelectric conversion element has an extension extending into the light absorption driving layer, wherein the depth of the extension does not exceed 20% of the depth of the photoelectric conversion element.

3. The method for manufacturing an image sensor according to claim 1, wherein, Before forming the device functional layer, the preparation method further includes: forming an absorption assisting layer on the semiconductor substrate, wherein during the heat treatment, doping ions in the ion doping region diffuse at least into the absorption assisting layer.

4. The method for manufacturing an image sensor according to claim 3, wherein, A prefabricated ion doping layer of the first doping type is formed in the absorption assisting layer.

5. The manufacturing method of the image sensor according to claim 4, characterized in that, The prefabricated ion doping layer includes N sub-ion doping layers, and the concentrations of the N sub-ion doping layers show a decreasing trend in the direction from the semiconductor substrate towards the device functional layer; or, the prefabricated ion doping layer is a single-layer material layer with a concentration showing a decreasing trend in the direction from the semiconductor substrate towards the device functional layer; and / or, during the heat treatment, doping ions in the prefabricated ion doping layer diffuse into a material layer located above the semiconductor substrate to form a light absorption driving assisting layer.

6. The manufacturing method of the image sensor according to claim 5, characterized in that, When the prefabricated ion doping layer includes N sub-ion doping layers, the thickness of the top sub-ion doping layer is greater than or equal to 3 μm.

7. The manufacturing method of the image sensor according to claim 1, characterized in that, The treatment temperature of the heat treatment process is greater than or equal to 950 °C and less than or equal to 1150 °C; and / or when an absorption auxiliary layer is formed on the semiconductor substrate, the thickness of the absorption auxiliary layer is between 1 and 6 μm 。 8. The method for manufacturing an image sensor according to any one of claims 1-7, characterized in that, The doping concentration of the ion doping layer of the first doping type in the semiconductor substrate is greater than the doping concentration in the prefabricated ion doping layer and greater than the doping concentration of the ion doping of the first doping type in the device functional layer; and / or, the first doping type is P type and the second doping type is N type.

9. The method for manufacturing an image sensor according to claim 8, characterized in that, The doping concentration of the ion doping region in the semiconductor substrate is greater than 2E18 atom / CM3, the device functional layer has a doping of the first doping type with a concentration less than 2E15 atom / CM3, and when the image sensor includes a prefabricated ion doping layer of the first doping type, the doping concentration is between 5E15 - 1E17 atom / CM3.

10. An image sensor, characterized in that, The image sensor includes: a semiconductor substrate, the semiconductor substrate including an ion doping layer of a first doping type; a device functional layer located on the semiconductor substrate; a semiconductor device located in the device functional layer, the semiconductor device including a photoelectric conversion element of a second doping type different from the first doping type; wherein a light absorption driving layer is formed in the interface region between the semiconductor substrate and the device functional layer.

11. The image sensor according to claim 10, characterized in that, The light absorption driving layer extends from the bottom of the device functional layer towards the inside and has ion doping of the first doping type; and / or, the image sensor further includes an absorption auxiliary layer located between the semiconductor substrate and the device functional layer, and the light absorption driving layer extends from the bottom of the absorption auxiliary layer towards the inside.

12. The image sensor according to claim 11, wherein The absorption auxiliary layer includes a prefabricated ion doping layer having ion doping of the first doping type, and the light absorption driving layer is at least formed in the prefabricated ion doping layer.

13. The image sensor according to claim 12, wherein, The prefabricated ion doping layer includes N sub-ion doping layers, and the concentrations of the N sub-ion doping layers show a decreasing trend in the direction from the semiconductor substrate towards the device functional layer; or, the prefabricated ion doping layer is a single-layer material layer with a concentration decreasing in the direction from the semiconductor substrate towards the device functional layer.

14. The image sensor according to claim 9, characterized in that, The image sensor further includes a plurality of pixel units arranged in an array, there is an isolation structure between adjacent pixel units, each pixel unit shares the light absorption driving layer, and when there is an absorption auxiliary layer, each pixel unit shares the absorption auxiliary layer; and / or, the image sensor is a front-illuminated image sensor.

15. The image sensor according to any one of claims 9-14, characterized in that, The image sensor further includes a light absorption driving auxiliary layer that extends from the bottom of the device functional layer towards the inside and has ion doping of the first doping type.

16. An electronic device, characterized in that, The electronic device includes the image sensor according to any one of claims 9-15.

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