Image sensor and method of manufacturing the same, electronic device

Abstract

The application provides an image sensor and a preparation method thereof and an electronic device, and the image sensor comprises a semiconductor substrate, a photosensitive layer in the semiconductor substrate, and an optical structure layer on one side of the semiconductor substrate, wherein the photosensitive layer comprises a plurality of photosensitive units arranged in an array, and the optical structure layer comprises a plurality of light processing units arranged in an array, and the light processing unit comprises a first light condensing structure, a light filtering structure, and a second light condensing structure, wherein the light processing unit corresponds to the photosensitive unit, the photosensitive unit receives incident light based on the light processing unit, and at least one of the first light condensing structure and the second light condensing structure comprises a nano column. The first light condensing structure and the second light condensing structure are adopted, the first light condensing structure, the light filtering structure, and the second light condensing structure are further sequentially stacked, each light condensing structure is arranged in the mode of a nano column and a dielectric layer, the incident light is converged and filtered through twice phase adjustment, the crosstalk increase between pixel units and glare artifacts are reduced, and the imaging quality is improved.

Description

Technical Field

[0001] This invention belongs to the field of image acquisition technology, and in particular relates to an image sensor, an electronic device, and a method for manufacturing the image sensor. Background Technology

[0002] Image sensors are a crucial component of digital cameras. Based on their components, they can be broadly categorized into CCD (Charge-Coupled Device) and CMOS (Metal-Oxide-Semiconductor) sensors. With the continuous development of CMOS integrated circuit manufacturing processes, especially the design and manufacturing processes of CMOS image sensors, CMOS image sensors have gradually replaced CCD image sensors as the mainstream. Compared to CCD sensors, CMOS image sensors offer advantages such as low voltage, low power consumption, low cost, and high integration, making them valuable for applications in machine vision, consumer electronics, high-definition surveillance, and medical imaging.

[0003] With the continuous growth in demand for high-resolution, high-sensitivity image sensors in fields such as mobile imaging, security monitoring, and industrial inspection, the pixel size of CMOS image sensors has shrunk from several micrometers in the early days to the current mainstream sub-micrometer level, and the pixel structure has become increasingly complex. However, the continuous shrinking of pixel size and the increasing complexity of the structure inevitably leads to a decrease in signal-to-noise ratio, resulting in image quality degradation. The light-gathering ability of microlenses decreases due to the shrinking size, making it difficult to efficiently focus light onto the effective photosensitive area. The problem of inter-pixel crosstalk is also aggravated, resulting in a significant decrease in both sharpness and color accuracy.

[0004] It should be noted that the above background description is provided only to facilitate a clear and complete explanation of the technical solutions of this invention and to aid understanding by those skilled in the art. It should not be assumed that these solutions are known to those skilled in the art simply because they have been described in the background section. Summary of the Invention

[0005] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide an image sensor, a manufacturing method, and an electronic device to alleviate the problems in the prior art, such as the difficulty in efficiently focusing light onto the photosensitive area.

[0006] To achieve the above and other related objectives, the present invention provides an image sensor, comprising: A semiconductor substrate having opposing first and second surfaces; The photosensitive layer, located in the semiconductor substrate, includes a plurality of photosensitive units arranged in an array; An optical structure layer is located on one side of the semiconductor substrate, and the optical structure layer includes a plurality of light processing units arranged in an array, wherein: The light processing unit includes a first light-concentrating structure, a light-filtering structure, and a second light-concentrating structure. The light processing unit is configured corresponding to the photosensitive unit. The photosensitive unit receives incident light based on the light processing unit. At least one of the first light-concentrating structure and the second light-concentrating structure includes a nanopillar.

[0007] This application also provides an electronic device including an image sensor as described in any of the above embodiments.

[0008] This application also provides a method for fabricating an image sensor as described in any of the above solutions, wherein the fabrication method includes the following steps: Provide the semiconductor substrate, and prepare the photosensitive layer from the first surface of the semiconductor substrate; The optical structure layer is prepared on the second surface of the semiconductor substrate; The steps for preparing the optical structure layer include: A second light-concentrating structure layer is formed on the second surface of the semiconductor substrate; A filter structure layer is formed on the second light-concentrating structure layer; A first light-concentrating structure layer is formed on the filter structure layer, and the first light-concentrating structure layer, the filter structure layer and the second light-concentrating structure layer are stacked to form a plurality of light processing units arranged in an array.

[0009] As described above, the image sensor and its fabrication method and electronic device of the present invention adopt a configuration of a first light-gathering structure, a filter structure and a second light-gathering structure, and further stack the first light-gathering structure, the filter structure and the second light-gathering structure in sequence. Furthermore, each light-gathering structure is formed by nanopillars and a dielectric layer. The convergence and filtering of incident light are achieved based on two incident light phase adjustments. The technical solution of a novel double-layer metasurface microlens solves the technical problems of reduced sensitivity, increased crosstalk, glare artifacts and difficulties in manufacturing microlens arrays caused by the reduction of pixel size, thereby improving the imaging quality. Attached Figure Description

[0010] Figure 1 The diagram shows the basic structure of an image sensor system.

[0011] Figure 2 The diagram shows a pixel circuit of an image sensor.

[0012] Figure 3 The diagram shown illustrates the formation of pixel units during the fabrication of an image sensor according to an embodiment of this application.

[0013] Figure 4 The diagram shown is a schematic diagram of the formation of an isolation structure during the fabrication of an image sensor according to an embodiment of this application.

[0014] Figure 5 The diagram shown is a schematic diagram of the formation of a transition layer in the fabrication of an image sensor according to an embodiment of this application.

[0015] Figure 6 The diagram shown is a schematic diagram of the first light-concentrating structure layer in the fabrication of the image sensor according to an embodiment of this application.

[0016] Figure 7 The diagram shown is a schematic diagram of the filter structure layer in the fabrication of the image sensor according to an embodiment of this application.

[0017] Figure 8 The diagram shown is a schematic of the second light-concentrating structure layer in the fabrication of the image sensor according to an embodiment of this application.

[0018] Figure 9 Displayed as Figure 8 A magnified schematic diagram of the light processing unit within the dashed box.

[0019] Figure 10 Displayed as Figure 9 A three-dimensional diagram illustrating the relevant parameters of the first nanopillar.

[0020] Figure 11 The image sensor fabrication shown is a top view of the second focusing structure layer in an embodiment of this application.

[0021] Figure 12 This is one of the schematic diagrams showing the convergence of light from different color pixels in the image sensor of this application embodiment.

[0022] Figure 13 This is shown as a second schematic diagram of light convergence from different colored pixels in an image sensor according to an embodiment of this application.

[0023] Figure 14 The illustration shows an example of nanopillar configurations in different regions of the pixel array according to an embodiment of this application. Detailed Implementation

[0024] The following specific examples illustrate the implementation of the present invention. 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 embodiments, and 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.

[0025] It should be emphasized that the term "including / comprises" as used herein refers to the presence of a feature, whole, step, or component, but does not exclude the presence or addition of one or more other features, wholes, steps, or components.

[0026] Features described and / or illustrated for one embodiment may be used in the same or similar manner in one or more other embodiments, combined with features in other embodiments, or substituted for features in other embodiments. For ease of explanation in the detailed description of embodiments of the invention, cross-sectional views illustrating device structures may be partially enlarged and not to scale; these schematic diagrams are merely examples and should not limit the scope of protection of the invention. In actual fabrication, three-dimensional spatial dimensions of length, width, and depth should be included.

[0027] For ease of description, when a layer is referred to as "between" two layers, it can be the only layer between the two layers, or there may be one or more layers in between. The described structure of the first feature "above" the second feature can include embodiments where the first and second features are formed in direct contact, or 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. Additionally, "coupled" indicates that the connection can be direct or indirect.

[0028] The illustrations provided in this embodiment are merely schematic representations of the basic concept of the present invention. Therefore, the illustrations only show components relevant to the present invention and are not drawn according to the actual number, shape, and size of the components in implementation. In actual implementation, the form, quantity, and proportion of each component can be arbitrarily changed, and the component layout may be more complex. The following detailed description of the present invention is provided in conjunction with the accompanying drawings.

[0029] Figure 1 The diagram shows a basic block diagram of an image sensor system. The image sensor includes a readout circuit and a control circuit connected to a pixel array. A functional logic unit is connected to the readout circuit, and the readout circuit and control circuit are connected to a status register to control the pixel array. The pixel array includes multiple 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 using the readout mode specified by the status register and then transmitted to the functional logic unit. In specific implementations, the readout circuit may include an analog-to-digital converter (ADC) circuit and other circuits.

[0030] In some applications, the status register may contain a programmed selection system to determine whether the readout system uses rolling shutter or global shutter exposure. The functional logic unit may store raw image data or image data after image processing. In some implementations, the readout circuitry may read one or half a row of image data at a time along the readout column lines; other methods are also possible. The operation of the control circuitry can be determined by the current settings in the status register. For example, the control circuitry generates a shutter signal to control image acquisition. In some applications, this shutter signal may be a global shutter signal, allowing all pixels in the pixel array to acquire their image data simultaneously through a single acquisition window. In other applications, this shutter signal may be a rolling shutter signal, allowing pixels in each row of the pixel array to be continuously exposed and read through the acquisition window.

[0031] Figure 2 This diagram illustrates a pixel unit in an image sensor. As shown, each pixel unit includes a photoelectric conversion element (e.g., a photodiode PD) and pixel circuitry. The photodiode can be a buried photodiode used in current image sensors, with one end grounded or at a negative voltage V. In one application example, the pixel circuitry includes a reset transistor (RST), a source follower transistor (SF), and a pixel select transistor (SEL), connected to a transfer transistor (TX) and the photodiode as shown. In a stacked structure application example, the pixel circuitry includes a reset transistor, a source follower transistor, and a pixel select transistor located on a first circuit chip, and also includes a transfer transistor and a photodiode located on a second circuit chip. The photodiode is connected to other transistors in the first circuit chip via the transfer transistor. In a further application example, the pixel circuitry may also include a gain transistor (DCG) connected to a floating diffusion region (FD). During operation, the photoelectric conversion element generates photocharge in response to incident light during exposure. The transfer transistor receives a transfer control signal, which controls the transfer transistor to transfer the accumulated charge in the photoelectric conversion element to the floating diffusion region. The reset transistor is connected between the power supply voltage PIXVDD and the floating diffusion region, and resets the corresponding node of the sensor pixel circuit in response to the reset signal. The floating diffusion region is connected to the gate of the source follower transistor, which is connected between the power supply voltage and the pixel selection transistor, and responds to the potential of the floating diffusion region and outputs it. The pixel selection transistor is connected to the source follower transistor and the bit line, and responds to the pixel selection control signal to realize pixel selection readout and output it to the readout column.

[0032] However, the continuous reduction in pixel size and the increasing complexity of the structure inevitably leads to a decrease in the signal-to-noise ratio, resulting in image quality degradation. The light-gathering ability of microlenses decreases due to size reduction, making it difficult to efficiently focus light onto the effective photosensitive area. Inter-pixel crosstalk also worsens, significantly reducing sharpness and color accuracy. This invention alleviates these problems through redesigning the image sensor structure.

[0033] Example 1: Please see Figure 3-10 As shown, this embodiment provides an image sensor, wherein, Figure 3-8 The diagram shows the structure obtained during the fabrication process of the image sensor. Figure 9 Displayed as Figure 8 An enlarged schematic diagram of the structure within the dashed box. Figure 10 A 3D diagram showing different parameters of the first focusing structure.

[0034] The image sensor includes a semiconductor substrate 101, a photosensitive layer 300, and an optical structure layer 400, wherein: The semiconductor substrate 101 has a first surface 101a and a second surface 101b opposite to each other; The photosensitive layer 300 is located in the semiconductor substrate 101 and includes a plurality of photosensitive units 300a arranged in an array; The optical structure layer 400 is located on one side of the semiconductor substrate 101, wherein: The optical structure layer 400 includes a plurality of light processing units 200 arranged in an array. Each light processing unit 200 includes a first light-concentrating structure 200u, a light-filtering structure 200m, and a second light-concentrating structure 200d. The light processing units 200 are disposed corresponding to the photosensitive units 300a. The photosensitive units 300a receive incident light based on the light processing units 200. At least one of the first light-concentrating structure 200u and the second light-concentrating structure 200d includes a nanopillar.

[0035] In one implementation, the image sensor further includes an interconnect layer 500, wherein photosensitive units 300a correspond one-to-one with light processing units 200, and each photosensitive unit 300a includes one photosensitive element 104 or at least two shared photosensitive elements 104 electrically led out from the interconnect layer 500. In one example, the interconnect layer 500 is located on a first surface 101a (front side) of the semiconductor substrate 101, and the optical structure layer 400 is located on a second surface 101b (back side) of the semiconductor substrate 101, i.e., the image sensor is a back-illuminated structure.

[0036] Specifically, the semiconductor substrate 101 has a first surface 101a (front side) and a second surface 101b (back side). The semiconductor substrate 101 can be a structure composed of a single layer of material, including but not limited to a silicon substrate. The material can be monocrystalline silicon, monocrystalline germanium, polycrystalline silicon, amorphous silicon, or silicon-germanium compounds, 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 practical needs. Furthermore, the semiconductor substrate 101, as the substrate of an image sensor, can also be a multilayer structure, such as including a semiconductor substrate and an epitaxial layer formed on the surface of the semiconductor substrate. The epitaxial layer serves as the device functional layer to realize the fabrication of the image sensor device. The epitaxial layer can be a P-type silicon epitaxial layer, and each functional region (including photosensitive elements, etc.) is fabricated in the epitaxial layer. A back-illuminated image sensor can be fabricated based on this semiconductor substrate.

[0037] Additionally, the image sensor may include a pixel array comprising a plurality of periodically arranged pixel units, for example, pixel units arranged in rows and columns, wherein the pixel units are located in the photosensitive layer 300. Generally, the pixel unit 300a includes a photosensitive element 104 coupled to a floating diffusion region. The photosensitive element converts light signals into electrical signals and can accumulate photogenerated electrons based on the photoelectric effect, transferring the photogenerated electrons at least to the floating diffusion region. For example, an N-type doped region formed by ion doping from the first surface of a semiconductor substrate can be considered as the photosensitive element 104. Alternatively, a polysilicon gate 106 or similar device can be used as a transfer transistor to transfer the photoelectrons formed by the photosensitive element 104.

[0038] In one implementation, the photosensitive layer 300 is further provided with an isolation structure to separate each pixel unit 300a. The isolation structure may include at least one of a shallow trench isolation structure 103 formed on the front side, an ion-doped isolation structure 105 formed on the front side, and a deep trench isolation structure 109 formed on the back side. Furthermore, it may also include a padding layer 102 on the sidewall of the shallow trench isolation structure 103, and a first barrier layer 107 and a second barrier layer 108 on the sidewall of the deep trench isolation structure 109. It should be noted that all of the above material layers can be prepared using existing image sensor processes and materials for the isolation of pixel units 300a.

[0039] Please see Figure 8-11 As shown, at least one of the first focusing structure 200u and the second focusing structure 200d includes nanopillars. That is, in one implementation, the arrangement of the first focusing structure 200u and the second focusing structure 200d in the light processing unit 200 includes at least one of the following: The first focusing structure 200u includes a plurality of first nanopillars 119 and a first dielectric layer 118 surrounding each of the first nanopillars 119; and the second focusing structure 200d includes a plurality of second nanopillars 114 and a second dielectric layer 113 surrounding each of the second nanopillars 114. In a preferred example, the first focusing structure 200u includes first nanopillars 119 and a first dielectric layer 118, and the second focusing structure 200d includes second nanopillars 114 and a second dielectric layer 113, to process incident light based on different combinations of nanopillars in the focusing structures. Furthermore, this example employs a double-layer nanopillar design, which has significant advantages over double-layer microlenses. Double-layer microlens arrays have many problems, such as difficulty in precisely controlling the surface morphology during manufacturing, resulting in decreased focusing efficiency; enhanced diffraction and scattering effects, leading to increased crosstalk between adjacent pixels; large aberrations in edge pixels, resulting in large differences in sensitivity from the center; and strong reflection at the interface of the lower conventional lens array, leading to a decrease in the quantum efficiency (QE) of the image sensor and a tendency for glare artifacts. The novel dual-layer metasurface microlens image sensor of the present invention, through the design and manufacture of a specific metasurface flat plate lens structure, has the ability to adapt to wavelengths from visible light to near infrared, is compatible with incident light at a larger principal ray angle, increases the fill factor, reduces crosstalk between different pixels at different wavelengths, reduces glare artifacts, improves image quality, and reduces manufacturing process difficulty and shortens manufacturing time.

[0040] In one implementation, the first focusing structure 200u, the filter structure 200m, and the second focusing structure 200d in the light processing unit 200 are stacked sequentially. The first focusing structure 200u faces the incident light. The light processing unit 200 modulates the incident light to the corresponding photosensitive unit 300a based on the first focusing structure 200u, the filter structure 200m, and the second focusing structure 200d in sequence, thereby achieving the filtering and focusing of the incident light.

[0041] In an optional example, the image sensor also includes a transition layer 110 on the second side 101b of the semiconductor substrate, including but not limited to a high dielectric constant dielectric layer (High K layer, such as a dielectric constant greater than 3.9), for example, aluminum oxide, hafnium oxide, etc., as the transition layer to facilitate subsequent structure formation and light convergence.

[0042] Continue reading Figure 8-11 As shown, in one implementation, the first focusing structure 200u includes a first nanopillar 119 and a first dielectric layer 118, and the second focusing structure 200d includes a second nanopillar 114 and a second dielectric layer 113. Adjacent second focusing structures 200d are provided with anti-crosstalk grilles 112, and adjacent first focusing structures 200u are arranged adjacently based on a shared dielectric layer formed by the corresponding first dielectric layer 118.

[0043] In one implementation, the shared medium layer is correspondingly configured with the anti-crosstalk grille 112, such as... Figure 8 As indicated by the dotted arrow at point B, the center of the first focusing structure 200u corresponds to the center of the second focusing structure 200d, as shown below. Figure 8 The dashed arrow at point A indicates the location of the crosstalk grating. In this example, along the optical path, the anti-crosstalk grating 112 in the lower focusing structure corresponds to the first dielectric layer in the upper focusing structure. The two have overlapping projection areas on the semiconductor substrate surface. Furthermore, the center of the first focusing structure 200u corresponds to the center of the second focusing structure 200d; that is, their centers can project onto the semiconductor substrate surface in a coinciding manner. Alternatively, they can be offset by a certain distance, resulting in overlapping projections of the first nanopillar in the first focusing structure and the second nanopillar in the second focusing structure onto the semiconductor substrate surface. This arrangement facilitates the entry of a larger incident light signal based on the shared dielectric layer and achieves good anti-crosstalk performance based on the lower anti-crosstalk grating 112. Furthermore, the adjacent arrangement of each filter structure 116 (i.e., 200m) further facilitates the entry of a larger light signal, improving imaging quality. Additionally, the anti-crosstalk grating 112 can be made of metal or insulating dielectric material; the metal material can be tungsten, but is not limited to this.

[0044] In one implementation, at least one of the first focusing structure 200u and the second focusing structure 200d has an anti-reflection layer (not shown in the figure) on its surface, such as an anti-reflection film or surface microstructure, to further reduce interlayer reflection. The anti-reflection film can be a composite film system with anti-reflection function in the prior art, for example, it can be a film structure formed of magnesium fluoride, including but not limited to. The surface microstructure can be formed based on surface etching.

[0045] In one implementation, the first focusing structure 200u has a first phase delay, and the second focusing structure 200d has a second phase delay. The incident light is converged to the corresponding photosensitive unit 300a based on the first phase delay and the second phase delay in sequence. Furthermore, the first focusing structure, the filter structure, and the second focusing structure are stacked in sequence, and a filter structure material layer is provided between the two phase delays. In this embodiment, the light convergence and filtering are achieved based on the two phase delays, which can effectively replace the existing filter layer and microlens.

[0046] In one implementation, at least one of the cross-sectional size, shape, height, and period of the first nanopillar 119 at different positions in the first focusing structure 200u is adjusted to form a first phase delay; in addition, at least one of the cross-sectional size, shape, height, and period of the second nanopillar 114 at different positions in the second focusing structure 200d can be adjusted to form a second phase delay.

[0047] For details, see Figure 9 and Figure 10 As shown, taking the first focusing structure 200u as an example, the above parameters are explained. The cross-sectional dimension d1 of the first nanopillar 119 refers to the maximum dimension on a plane parallel to the surface of the semiconductor substrate, such as the diameter of a circle. The shape refers to the shape of the three-dimensional structure of the first nanopillar 119, such as a cylinder or a square pillar. A first phase delay can also be formed based on the height h1 of the first nanopillar 119. Furthermore, the period p1 refers to any first nanopillar 119 and a portion of the surrounding first dielectric layer 118. The division of the first dielectric layer 118 is the middle of the first dielectric layer shared by adjacent first nanopillars. In one implementation, each of the first focusing structures... The nanopillars have the same period, meaning the first focusing structure comprises several focusing structural units, each with the same size. The number of focusing structural units corresponds one-to-one with the number of first nanopillars, but the duty cycles of the first nanopillars within each focusing structural unit differ. Within the same first focusing structure 200u or second focusing structure 200d, the cross-sectional dimensions, shapes, heights, and periods of the first nanopillars 119 and 114 at different corresponding positions vary according to a preset phase distribution function, applying a spatially varying phase delay to the incident light. This forms an equivalent microlens that converges the incident light to the corresponding pixel photosensitive unit. Adjusting these parameters yields the desired phase. For example, Figure 11 The diagram shows a top view of the light-receiving surface of an image sensor. It illustrates the first focusing structure 200u in the four light processing units. In this example, the first nanopillars 119 in each first focusing structure 200u have slightly different cross-sectional areas, but the different first focusing structures 200u share the same arrangement of the first nanopillars 119. In this example, the phase delay of the first focusing structure 200u in response to the received incident light can be adjusted by adjusting the height of the first nanopillars 119. Of course, in other implementations, the phase delay of the incident light can also be adjusted based on different arrangements of the nanopillars. That is, the arrangement of the nanopillars differs between different first focusing structures; for example, different colors of incident light may have different phase delays, and the arrangement of the nanopillars can be adjusted to achieve adjustment of the incident light of different colors. Similarly, the layout design of the top view of the second focusing structure 200d can be understood by referring to this diagram, and will not be elaborated further.

[0048] In one implementation, in the first focusing structure 200u, a first phase delay is obtained based on a first phase distribution, wherein the first phase distribution is expressed as: ; Wherein, r1 is the distance from the preset position in the first focusing structure to the center of the first focusing structure, λ1 is the wavelength of the incident light incident on the first focusing structure, and f1 is the equivalent focal length for the filter structure. A first phase delay is obtained based on the first phase distribution so that the emitted light spot of the first focusing structure 200u at the preset position converges to the center of the filter structure 200m. In one example, the first nanopillar 119 is designed as a cylindrical nanopillar to achieve polarization insensitivity. Furthermore, the material of the first nanopillar is silicon nitride, and the material of the first dielectric layer is silicon dioxide. The focal length f1 is selected according to the size and depth of different filter structures (such as CFA filter structure). Furthermore, the parameters of the first nanopillar 119 are fitted according to the first phase delay required at different positions in the first focusing structure 200u, such as the diameter d, height h, and period p of the first nanopillar 119, so that the emitted light spot of the first focusing structure 200u is focused to the center of the filter structure 200m. Thus, the emitted light spot of the metasurface microlens array (first focusing structure 200u) is focused to the center of different color filter materials in the color filter material layer, realizing the first convergence modulation of the incident light.

[0049] In one implementation, in the second focusing structure 200d, a second phase delay is obtained based on a second phase distribution, wherein the second phase distribution is expressed as: ; Where r2 is the distance from the preset position in the second focusing structure to the center of the second focusing structure, λ2 is the wavelength of the incident light incident on the second focusing structure, f2 is the equivalent focal length for the photosensitive unit, the maximum wavelength of the incident light incident on the second focusing structure, and is the supplementary phase set based on λ2. The second phase delay is obtained based on the second phase distribution so that the emitted light spot of the second focusing structure 200d at the preset position converges to the center of the photosensitive unit. In one example, the second nanopillar 114 is designed as a cylindrical nanopillar to achieve polarization insensitivity. Furthermore, the material of the second nanopillar is titanium dioxide, and the material of the second dielectric layer is silicon dioxide. Here, is an additional supplementary phase, related to the incident wavelength λ2. For example, different values ​​of the additional supplementary phase can be set based on simulation results corresponding to the wavelengths of different colors (such as R, G, B). Further, the focal length f2 is selected according to the size and depth of different photosensitive elements (such as N-doped regions). Based on the required second phase delay at different positions in the second focusing structure 200d, the parameters of the second nanopillar 114 are fitted, such as the diameter d, height h, and period p of the second nanopillar 114, so that the emitted light spot of the second focusing structure 200d is converged to the center of the photosensitive unit. That is, the emitted light spot of the second metasurface microlens array (second focusing structure 200d) is converged to different corresponding pixel photosensitive areas, achieving the convergence modulation of the second incident light.

[0050] It should be noted that other methods can also be used to modulate the first and second incident light to obtain the first phase delay and the second phase delay. The aim is to modulate the incident light to the photosensitive unit by modulating the parameters of the first nanopillar 119 and the second nanopillar 114 to obtain different color signals.

[0051] In one implementation, in the light processing unit 200, the effective refractive index of the second focusing structure 200d is set to be higher than that of the first focusing structure 200u. The effective refractive index can be considered to correspond to the duty cycle of the nanopillars; that is, the duty cycle of the second nanopillars in the second focusing structure 200d is set to be higher than that of the first nanopillars in the first focusing structure 200u. Alternatively, the period of the nanopillars in the second focusing structure 200d can be set to be shorter than that in the first focusing structure 200u. Of course, both the effective refractive index and the period configuration can be configured in the above manner, so that the incident light received by the photosensitive units 300a corresponding to different color light signals converges to a consistent focal plane. Taking a 4-pixel Bayer array as the basis for the color filter layer as an example... Figure 12 and Figure 13 As shown, Figure 12 The corresponding red R pixel and the first green Gr pixel have the same focal plane, located within the elliptical dashed frame. Figure 13 The corresponding blue B pixel and the second green Gb pixel have the same focal plane, located within the elliptical dashed box. Of course, this consistency does not necessarily mean strict alignment; there can be vertical fluctuations allowed in the industry. That is, the period of the nanopillars in the second metasurface lens array (second focusing structure 200d) is smaller than that in the first metasurface lens array (first focusing structure 200u), so that light of all wavelengths, including red, green, and blue, is focused to the same focal plane, achieving wavelength adaptability, reducing reflections from the multilayer microlens array, and reducing image artifacts and glare.

[0052] Specifically, when the first focusing structure 200u includes the first nanopillar 119 and the first dielectric layer 118: In one example, the refractive index of the first nanopillar 119 is higher than that of the first dielectric layer 118; In one example, the dielectric constant ratio of the first dielectric layer 118 to the first nanopillar 119 is between 1:3.5 and 1:1.2. For example, the ratio can also be 1:3, 1:2, etc. In one example, the first nanopillar 119 comprises at least one of amorphous silicon, silicon nitride, titanium dioxide, titanium nitride, and gallium nitride, and may be selected as any one of them; the first dielectric layer 118 comprises a transparent material, which comprises at least one of silicon dioxide and polymer, and may be selected as any one of the above. In one example, the height of the first nanopillar 119 is smaller than the height of the first dielectric layer 118, which is beneficial for the structuring and modulation of incident light based on the first light-gathering structure; In one example, the shape of the first nanopillar 119 includes at least one of cylindrical, square, fin-shaped, mesh-shaped, and irregular shapes. For example, a single first nanopillar 119 can be configured as a mesh type. In one example, the arrangement of the first nanopillars 119 in the first light-concentrating structure 200u includes any one of square, triangular, or circular shapes, that is, the outer contour of each nanopillar forms any one of the above shapes; Similarly, when the second focusing structure 200d includes a second nanopillar and a second dielectric layer, the arrangement includes: In one example, the refractive index of the second nanopillar is higher than that of the second dielectric layer; In one example, the dielectric constant ratio of the second dielectric layer to the second nanopillar is between 1:3.5 and 1:1.2. For example, the ratio can also be 1:3, 1:2, etc. In one example, the second nanopillar 114 comprises at least one of amorphous silicon, silicon nitride, titanium dioxide, titanium nitride, and gallium nitride, and the second dielectric layer 113 comprises a transparent material, which comprises at least one of silicon dioxide and a polymer. In one example, the height of the second nanopillar 114 is smaller than the height of the second dielectric layer 113, which is beneficial for the structuring and modulation of incident light based on the first light-gathering structure; In one example, the shape of the second nanopillar includes at least one of cylindrical, square, fin-shaped, mesh-shaped, and irregular shapes. For example, a single second nanopillar can be set as a mesh type. In one example, the arrangement of the second nanopillars in the second light-concentrating structure 200d includes any one of square, triangular, or circular shapes, that is, the outer contour of each nanopillar forms any one of the above shapes.

[0053] In one implementation, when a corresponding nanopillar exists in each focusing structure, at least one of the cross-sectional size, shape, and period of the corresponding nanopillar is adjusted so that the corresponding focusing structure obtains a corresponding phase delay based on zero-order diffraction. For example, at least one of the cross-sectional size, shape, and period of the first nanopillar is adjusted so that the first focusing structure obtains a corresponding first phase delay based on zero-order diffraction.

[0054] In one implementation, when corresponding nanopillars are present in each focusing structure, the diameter of the nanopillars ranges from 0.1λ to λ, the height ranges from 0.5λ to 1.2λ, and the period ranges from 0.2λ to 0.8λ, where λ is the wavelength of the received incident light. For example, for the first nanopillar, λ is the incident light incident into the first focusing structure from the outside; for the second nanopillar, λ is the incident light incident into the second focusing structure after passing through the filter structure. For instance, the diameter of the first nanopillar is between 0.1λ and λ, which can be 0.2λ or 0.5λ; the height of the first nanopillar is between 0.5λ and 1.2λ, which can be 0.8λ or 1.0λ; and the period of the first nanopillar is between 0.2λ and 0.8λ, which can be 0.5λ or 0.6λ. Similarly, the arrangement of the second nanopillar is similar and will not be described further here.

[0055] Please see Figure 14 As shown, in one implementation, the duty cycle of the nanopillars in the focusing structure increases from the edge to the center of the focusing structure. Correspondingly, the effective refractive index at the center of the first focusing structure is higher than that at the edge, and the effective refractive index at the center of the second focusing structure is higher than that at the edge. This arrangement facilitates effective modulation of the optical signal based on the nanopillars at the center. It should be noted that the specific dimensions of the center and edge can be set according to actual needs, aiming to enhance modulation based on the structure at the center. In another implementation, in the optical structure layer, the effective refractive index of at least one of the first and second focusing structures increases from the edge to the center of the optical structure layer.

[0056] For example, the periods of the first and second nanopillars at the center of the pixel array are p1 and p2, respectively, while the periods of the first and second nanopillars at the edge of the pixel array are p1' and p2'. Furthermore, the size of the nanopillars can also be varied accordingly; that is, the sizes of the first and second nanopillars at the center of the pixel array are d1 and d2, and the periods of the first and second nanopillars at the edge of the pixel array are d1' and d2'. For example, in the same optical processing unit, the first nanopillar assembly in the first focusing structure moves closer to the center by a first distance, and the second nanopillar assembly in the second focusing structure moves closer to the center by a second distance. Based on the change in the duty cycle of the nanopillars according to the first and second distances, the effective refractive index moves closer to the center. In a further example, the upper focusing structure is closer to the center of the optical structure layer, with the first distance being greater than the second distance, meaning the trend of the effective refractive index of the upper structure moving towards the center is more pronounced. This adjustment method helps improve the uniformity of the optical signal of the overall pixel array.

[0057] In this embodiment, a first focusing structure and a second focusing structure are used, and the first focusing structure, the filter structure, and the second focusing structure are stacked sequentially. Furthermore, each focusing structure is composed of nanopillars, and phase adjustment is performed twice to achieve the convergence and filtering of incident light. That is, a novel double-layer metasurface microlens technology with wavelength adaptability is adopted. This technology can adjust the phase delay based on the corresponding nanopillars for different color light wavelengths, which solves the technical problems of reduced sensitivity due to reduced pixel size, increased crosstalk, glare artifacts, and difficulty in manufacturing microlens arrays. It achieves the technical effect of a high-efficiency double-layer metasurface microlens array with wavelength adaptability, thereby improving imaging quality.

[0058] Example 2: The present invention also provides an electronic device, including an image sensor as described in any one of Embodiment 1. The electronic device may be a security monitoring device, an in-vehicle electronics device, a mobile phone camera, a machine vision device, etc. The image sensor based on the present invention can acquire high-quality image information, and it may also be an infrared-based device.

[0059] Example 3: This embodiment also provides a method for fabricating an image sensor. The fabrication method provided in this embodiment is applicable to the image sensor described in any of the above solutions. The description of the relevant structure and settings is the same as that in Embodiment 1, and will not be repeated here. The fabrication method includes: Provide a semiconductor substrate 101, such as Figure 3 As shown; A photosensitive layer is prepared from the first surface 101a of the semiconductor substrate 101, such as Figure 3 As shown; An optical structure layer is fabricated on the second surface 101b of the semiconductor substrate 101, such as... Figures 4 to 8 As shown, the steps for fabricating the optical structure layer include: A second light-concentrating structure layer 111 is formed on the second surface of the semiconductor substrate 101, such as Figure 6 As shown; A filter structure layer 115 is formed on the second light-concentrating structure layer 111, such as Figure 7 As shown; A first light-concentrating structure layer 117 is formed on the light-filtering structure layer 115, such as Figure 8 As shown, the first light-concentrating structure layer, the light-filtering structure layer and the second light-concentrating structure layer are stacked to form a plurality of light processing units 200 arranged in an array, wherein the light-filtering structure layer includes a plurality of light-filtering units 116 corresponding to the photosensitive units.

[0060] In one implementation, the process of fabricating the optical structure layer 400 also includes: like Figure 4 and Figure 5 As shown, a transition layer 110 is formed on the second surface of the semiconductor substrate 101, and a second light-concentrating structure layer is formed on the surface of the transition layer 110.

[0061] In one implementation, the process of forming the second focusing structure 200d layer also includes the step of forming an anti-crosstalk grid 112, which is formed between each of the second focusing structures.

[0062] In one implementation, during the formation of the first light-concentrating structure layer, a first dielectric material layer is first formed on the filter structure layer, and each first nanopillar 119 is prepared in the first dielectric material layer to obtain each second light-concentrating structure based on the first dielectric material layer, which includes the first dielectric layer 118 and the first nanopillar.

[0063] In one implementation, the fabrication steps for preparing the optical structure layer include: In the process of forming the second light-concentrating structure layer, a second dielectric material layer is first formed on the semiconductor substrate, such as by deposition. Then, the pattern corresponding to the second nanopillar is transferred to the second dielectric material layer, such as by transferring the pattern to the photoresist layer of the second dielectric material layer using DUV technology. Then, reactive ion etching is used to transfer the pattern on the photoresist to the second dielectric material layer. Next, a second nanopillar material layer is deposited on the patterned second dielectric material layer, such as by chemical vapor deposition. Then, excess second nanopillar material layer is removed, such as by chemical mechanical polishing, to obtain a second light-concentrating structure containing the second nanopillar and the second dielectric layer. Alternatively, a second nanopillar material layer is first formed on the semiconductor substrate, such as by chemical vapor deposition. Then, the second nanopillar is etched to obtain the second nanopillar, such as by using an i-line stepper lithography machine to transfer the pattern. Then, development and etching are performed. Then, a second dielectric material layer is formed on the semiconductor substrate where the second nanopillar is formed, such as by deposition, to obtain a second light-concentrating structure containing the second nanopillar and the second dielectric layer. In one implementation, the fabrication steps for preparing the optical structure layer include: In the process of forming the first light-concentrating structure layer, a first dielectric material layer is first formed on the filter structure layer, and each first nanopillar is fabricated in the first dielectric material layer to obtain each first light-concentrating structure based on the first dielectric material layer and including the first dielectric layer and the first nanopillar. Alternatively, a first nanopillar material layer is first formed on the filter structure layer, then the first nanopillar is etched to obtain the first nanopillar, and then a first dielectric material layer is formed above the filter structure layer on which the first nanopillar is formed to obtain each first light-concentrating structure based on the first dielectric material layer and including the first dielectric layer and the first nanopillar. The relevant processes for forming the first light-concentrating structure are described in the description of the second light-concentrating structure and will not be repeated here.

[0064] It should be noted that the light-gathering structure based on double-layer nanopillars in this embodiment, compared to using a double-layer lens, faces challenges. The manufacturing process of a double-layer lens is difficult to precisely control the surface morphology, resulting in decreased focusing efficiency and enhanced diffraction and scattering effects, leading to increased crosstalk between adjacent pixels. Furthermore, edge pixels exhibit significant aberrations, resulting in large differences in sensitivity compared to the center. Additionally, the lower layer of the traditional lens array has strong interface reflection, leading to a decrease in the sensor's quantum efficiency (QE) and a higher likelihood of glare artifacts. The double-layer metasurface microstructure image sensor of this invention can be designed and manufactured with specific metasurface planar structures, exhibiting wavelength adaptability from visible to near-infrared light, compatibility with incident light at a larger principal ray angle, increased fill factor, reduced crosstalk between pixels of different wavelengths, reduced glare artifacts, improved image quality, and reduced manufacturing difficulty and time.

[0065] In summary, the image sensor, its fabrication method, and electronic device of the present invention employ a first and a second light-gathering structure, further stacking the first, a filter, and the second light-gathering structure sequentially. Furthermore, each light-gathering structure is constructed using nanopillars, undergoing two phase adjustments to achieve both focusing and filtering of incident light. This employs a novel wavelength-adaptive double-layer metasurface microlens technology, solving the technical problems of reduced sensitivity due to smaller pixel size, increased crosstalk, glare artifacts, and difficulties in manufacturing microlens arrays. It achieves the technical effect of a wavelength-adaptive, high-efficiency double-layer metasurface microlens array, improving image quality. Therefore, the present invention effectively overcomes the various shortcomings of existing technologies and possesses high industrial applicability.

[0066] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. All equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. An image sensor, characterized in that, The image sensor includes: A semiconductor substrate having a first surface and a second surface opposite to each other; The photosensitive layer, located in the semiconductor substrate, includes a plurality of photosensitive units arranged in an array; An optical structure layer is located on one side of the semiconductor substrate, and the optical structure layer includes a plurality of light processing units arranged in an array, wherein: The light processing unit includes a first light-concentrating structure, a light-filtering structure, and a second light-concentrating structure. The light processing unit is configured corresponding to the photosensitive unit. The photosensitive unit receives incident light based on the light processing unit, and at least one of the first light-concentrating structure and the second light-concentrating structure includes a nanopillar.

2. The image sensor as described in claim 1, characterized in that, The first and second focusing structures in the light processing unit are configured in at least one of the following ways: The first light-concentrating structure includes a first nanopillar and a first dielectric layer surrounding the first nanopillar; The second light-concentrating structure includes a second nanopillar and a second dielectric layer surrounding the second nanopillar.

3. The image sensor as described in claim 1 or 2, characterized in that, The first focusing structure, the filter structure, and the second focusing structure in the light processing unit are stacked in sequence. The first focusing structure faces the incident light. The light processing unit modulates the incident light onto the corresponding photosensitive unit based on the first focusing structure, the filter structure, and the second focusing structure in sequence.

4. The image sensor as described in claim 3, characterized in that, The first light-concentrating structure includes a first nanopillar and a first dielectric layer, and the second light-concentrating structure includes a second nanopillar and a second dielectric layer. Adjacent second light-concentrating structures are provided with anti-crosstalk grids, and adjacent first light-concentrating structures are arranged adjacently based on a shared dielectric layer formed by their corresponding first dielectric layers.

5. The image sensor as described in claim 4, characterized in that, The shared medium layer is correspondingly disposed to the anti-crosstalk grid, and the center of the first light-concentrating structure is correspondingly disposed to the center of the second light-concentrating structure; and / or, at least one of the first light-concentrating structure and the second light-concentrating structure has an anti-reflective layer on its surface.

6. The image sensor as described in claim 3, characterized in that, The first focusing structure has a first phase delay, and the second focusing structure has a second phase delay. The incident light is converged to the corresponding photosensitive unit based on the first phase delay and the second phase delay in sequence.

7. The image sensor as described in claim 6, characterized in that, The first focusing structure includes a first nanopillar and a first dielectric layer, and at least one of the cross-sectional size, shape, height and period of the first nanopillar at different positions in the first focusing structure is adjusted to form a first phase delay; and / or, the second focusing structure includes a second nanopillar and a second dielectric layer, and at least one of the cross-sectional size, shape, height and period of the second nanopillar at different positions in the second focusing structure is adjusted to form a second phase delay.

8. The image sensor as described in claim 6, characterized in that, In the first focusing structure, the first phase delay is obtained based on a first phase distribution, wherein the first phase distribution is: ； Where r1 is the distance from the preset position in the first light-gathering structure to the center of the first light-gathering structure, λ1 is the wavelength of the incident light incident on the first light-gathering structure, f1 is the equivalent focal length for the filter structure, and the first phase delay is obtained based on the first phase distribution so that the emitted light spot of the first light-gathering structure at the corresponding preset position converges to the center of the filter structure. And / or, in the second focusing structure, the second phase delay is obtained based on a second phase distribution, wherein the second phase distribution is expressed as: ； Where r2 is the distance from the preset position in the second light-gathering structure to the center of the second light-gathering structure, λ2 is the wavelength of the incident light incident on the second light-gathering structure, f2 is the equivalent focal length for the photosensitive unit, the maximum wavelength of the incident light incident on the second light-gathering structure, is the supplementary phase set based on λ2, and the second phase delay is obtained based on the second phase distribution so that the emitted light spot of the second light-gathering structure at the preset position converges to the center of the photosensitive unit.

9. The image sensor as described in claim 3, characterized in that, The effective refractive index of the second focusing structure in the light processing unit is higher than that of the first focusing structure, and / or the first focusing structure includes a first nanopillar and the second focusing structure includes a second nanopillar, and the period of the nanopillar in the second focusing structure is less than that of the nanopillar in the first focusing structure.

10. The image sensor as claimed in claim 2, characterized in that, When the first focusing structure includes a first nanopillar and a first dielectric layer, the arrangement includes: The refractive index of the first nanopillar is higher than that of the first dielectric layer; and / or, the dielectric constant ratio of the first dielectric layer to the first nanopillar is between 1:3.5 and 1:1.2; and / or, the material of the first nanopillar includes at least one of amorphous silicon, silicon nitride, titanium dioxide, titanium nitride, and gallium nitride, and the material of the first dielectric layer includes at least one of silicon dioxide and organic polymer; and / or, the height of the first nanopillar is less than the height of the first dielectric layer; and / or, the shape of the first nanopillar includes at least one of cylindrical, square, fin-shaped, mesh-shaped, and irregular shapes; and / or, the arrangement contour of each first nanopillar in the first light-concentrating structure includes any one of square, triangular, and annular shapes. When the second focusing structure includes a second nanopillar and a second dielectric layer, the arrangement includes: The refractive index of the second nanopillar is higher than that of the second dielectric layer; and / or, the dielectric constant ratio of the second dielectric layer to the second nanopillar is between 1:3.5 and 1:1.2; and / or, the material of the second nanopillar includes at least one of amorphous silicon, silicon nitride, titanium dioxide, titanium nitride, and gallium nitride, and the material of the second dielectric layer includes at least one of silicon dioxide and organic polymer; and / or, the height of the second nanopillar is less than the height of the second dielectric layer; and / or, the shape of the second nanopillar includes at least one of cylindrical, square, fin-shaped, mesh-shaped, and irregular shapes; and / or, the arrangement contour of each second nanopillar includes any one of square, triangular, and annular shapes.

11. The image sensor as claimed in claim 2, characterized in that, The nanopillars in the light-concentrating structure have diameters between 0.1λ and λ, heights between 0.5λ and 1.2λ, and periods between 0.2λ and 0.8λ, where λ is the corresponding incident light wavelength.

12. The image sensor as claimed in claim 2, characterized in that, In the light-concentrating structure containing nanopillars, the duty cycle of the nanopillars increases from the edge to the center of the light-concentrating structure; and / or, the effective refractive index at the center of the first light-concentrating structure is higher than that at the edge, and the effective refractive index at the center of the second light-concentrating structure is higher than that at the edge; and / or, in the optical structure layer, the effective refractive index of at least one of the first light-concentrating structure and the second light-concentrating structure increases from the edge to the center of the optical structure layer.

13. The image sensor as claimed in claim 1, characterized in that, The image sensor further includes an interconnect layer located on a first surface of the semiconductor substrate, and an optical structure layer located on a second surface. The photosensitive units correspond one-to-one with the light processing units, and each photosensitive unit includes one or at least two shared photosensitive elements electrically led out from the interconnect layer.

14. An electronic device, characterized in that, The electronic device includes an image sensor as described in any one of claims 1-13.

15. A method for fabricating an image sensor as described in any one of claims 1-13, characterized in that, The preparation method includes the following steps: Provide the semiconductor substrate, and prepare the photosensitive layer from the first surface of the semiconductor substrate; The optical structure layer is prepared on the second surface of the semiconductor substrate; The steps for preparing the optical structure layer include: A second light-concentrating structure layer is formed on the second surface of the semiconductor substrate; A filter structure layer is formed on the second light-concentrating structure layer; A first light-concentrating structure layer is formed on the filter structure layer, and the first light-concentrating structure layer, the filter structure layer and the second light-concentrating structure layer are stacked to form a plurality of light processing units arranged in an array.

16. The method for fabricating an image sensor as described in claim 15, characterized in that, During the fabrication of the optical structure layer: A transition layer is formed on the second surface of the semiconductor substrate, and a second light-concentrating structure layer is formed on the surface of the transition layer; and / or, the process of forming the second light-concentrating structure layer includes the step of forming an anti-crosstalk grid, the anti-crosstalk grid being formed between each of the second light-concentrating structures.

17. The method for fabricating an image sensor as described in claim 16, characterized in that, The fabrication process of the optical structure layer includes at least one of the following steps: In the process of forming the second light-concentrating structure layer, a second dielectric material layer is first formed above the semiconductor substrate, then the pattern corresponding to the second nanopillar is transferred to the second dielectric material layer, the second nanopillar material layer is deposited on the patterned second dielectric material layer, and the excess second nanopillar material layer is removed to obtain a second light-concentrating structure containing the second nanopillar and the second dielectric layer; or, a second nanopillar material layer is first formed above the semiconductor substrate, then the second nanopillar is etched to obtain the second nanopillar, and then a second dielectric material layer is formed above the semiconductor substrate where the second nanopillar is formed to obtain a second light-concentrating structure containing the second nanopillar and the second dielectric layer; In the process of forming the first light-concentrating structure layer, a first dielectric material layer is first formed on the filter structure layer, and each first nanopillar is prepared in the first dielectric material layer to obtain each first light-concentrating structure based on the first dielectric material layer and including the first dielectric layer and the first nanopillar. Alternatively, a first nanopillar material layer is first formed on the filter structure layer, and then the first nanopillar is etched to obtain the first nanopillar. Then, a first dielectric material layer is formed above the filter structure layer on which the first nanopillar is formed to obtain each first light-concentrating structure based on the first dielectric material layer and including the first dielectric layer and the first nanopillar.

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