Image sensor and method for manufacturing the same

Abstract

This disclosure relates to an image sensor and a method for fabricating the same. The image sensor includes at least one pixel unit, each pixel unit of the at least one pixel unit including a photodetector and a pseudo-random array diffractive optical element (PRADOE) which includes an array of unit structures located on the front of the light-receiving surface of the photodetector and oriented at a pseudo-random angle. The PRADOE is configured to cause multiple-order diffraction of light received by the photodetector.

Description

Technical Field

[0001] This application is based on Chinese Patent Application No. 202410891090.1 filed on July 4, 2024, the entire disclosure of which is incorporated herein by reference, and claims the priority thereof.

[0002] The present disclosure generally relates to the field of image sensors, and more particularly to image sensors and methods for fabricating image sensors.

Background Art

[0003] Complementary metal oxide semiconductor (CMOS) image sensors, such as silicon (Si)-based CMOS image sensors, have made significant progress in terms of process cost and performance, especially in the visible spectrum.

Summary of the Invention

[0004] According to one aspect of the present disclosure, an image sensor including at least one pixel unit is provided. Each pixel unit of the at least one pixel unit includes a light detection element and a pseudo-random array diffractive optical element (PRADOE) including an array of unit structures located on the surface of the light receiving surface of the light detection element and oriented at pseudo-random angles, the PRADOE being configured to cause multiple diffractions of light received by the light detection element.

[0005] According to another aspect of the present disclosure, a method for fabricating an image sensor is provided. The method includes providing a light detection element on a substrate and forming a pseudo-random array diffractive optical element (PRADOE) including an array of unit structures oriented at pseudo-random angles on the surface of the light receiving surface of the light detection element, the PRADOE being configured to cause multiple diffractions of light received by the light detection element.

[0006] Other features and advantages of this disclosure will become more apparent from the following detailed description of exemplary embodiments of this disclosure, with reference to the accompanying drawings.

[0007] The accompanying drawings, which constitute part of this specification, illustrate embodiments of the present disclosure and, together with this specification, help to illustrate the principles of the present disclosure.

[0008] This disclosure can be better understood from the following detailed description with reference to the attached drawings. [Brief explanation of the drawing]

[0009] [Figure 1] These are schematic cross-sectional side views and top views of image sensors according to some embodiments of the present disclosure. [Figure 2] Figure 1 shows a schematic top view and perspective view of the PRADOE included in the image sensor, as well as a top view of a single unit structure of the PRADOE. [Figure 3] This figure exemplifies the multiple-order diffraction of light caused by PRADOE formed beneath the light-receiving surface. [Figure 4] This figure exemplifies the multiple-order diffraction of light caused by PRADOE formed on a light-receiving surface. [Figure 5A] This is a schematic diagram showing several examples of PRADOE according to some embodiments of the present disclosure, where the spacing between the centers of adjacent unit structures of PRADOE is varied. [Figure 5B] This is a schematic diagram showing several examples of PRADOE according to some embodiments of the present disclosure, where the spacing between the centers of adjacent unit structures of PRADOE is varied. [Figure 6] This is a schematic diagram showing several examples of PRADOE according to some embodiments of the present disclosure, where the orientation angle of the unit structure of PRADOE is changed. [Figure 7] This is a schematic diagram showing several examples of PRADOE according to some embodiments of the present disclosure, where the lateral dimensions of the unit structure of PRADOE are changed. [Figure 8] These are schematic cross-sectional side views and top views of image sensors according to some embodiments of the present disclosure. [Figure 9] These are schematic cross-sectional side views and top views of image sensors according to some embodiments of the present disclosure. [Figure 10] These are schematic cross-sectional side views and top views of image sensors according to some embodiments of the present disclosure. [Figure 11] This is a schematic diagram showing some examples of PRADOE according to some embodiments of the present disclosure, in which the perimeter of the PRADOE is reduced relative to the perimeter of the pixel unit. [Figure 12] This is a schematic diagram illustrating some examples of image sensors according to some embodiments of the present disclosure. [Figure 13] This is a schematic diagram illustrating some examples of image sensors according to some embodiments of the present disclosure. [Figure 14] This is a schematic diagram illustrating some examples of image sensors according to some embodiments of the present disclosure. [Figure 15] This is a schematic diagram illustrating some examples of image sensors according to some embodiments of the present disclosure. [Figure 16] This is a schematic diagram showing one example of PRADOE applied to a 2x2 array pixel unit according to some embodiments of the present disclosure. [Figure 17] This is a schematic diagram showing another example of PRADOE applied to a 2x2 array pixel unit according to some embodiments of the present disclosure. [Figure 18] This is a flowchart illustrating a method for fabricating an image sensor according to some embodiments of the present disclosure. [Figure 19A] These are schematic cross-sectional side views of the device obtained from each step of the process for fabricating the image sensor shown in Figure 14, to which the method shown in Figure 2 is applied. [Figure 19B] These are schematic cross-sectional side views of the device obtained from each step of the process for fabricating the image sensor shown in Figure 14, to which the method shown in Figure 2 is applied. [Figure 19C] Schematic cross-sectional side views of devices obtained from respective steps of a process for fabricating an image sensor of FIG. 14 to which the method of FIG. 2 is applied. [Figure 19D] Schematic cross-sectional side views of devices obtained from respective steps of a process for fabricating an image sensor of FIG. 14 to which the method of FIG. 2 is applied. [Figure 19E] Schematic cross-sectional side views of devices obtained from respective steps of a process for fabricating an image sensor of FIG. 14 to which the method of FIG. 2 is applied. [Figure 19F] Schematic cross-sectional side views of devices obtained from respective steps of a process for fabricating an image sensor of FIG. 14 to which the method of FIG. 2 is applied. [Figure 19G] Schematic cross-sectional side views of devices obtained from respective steps of a process for fabricating an image sensor of FIG. 14 to which the method of FIG. 2 is applied. [Figure 19H] Schematic cross-sectional side views of devices obtained from respective steps of a process for fabricating an image sensor of FIG. 14 to which the method of FIG. 2 is applied. [Figure 19I] Schematic cross-sectional side views of devices obtained from respective steps of a process for fabricating an image sensor of FIG. 14 to which the method of FIG. 2 is applied. [Figure 19J] Schematic cross-sectional side views of devices obtained from respective steps of a process for fabricating an image sensor of FIG. 14 to which the method of FIG. 2 is applied. [Figure 19K] Schematic cross-sectional side views of devices obtained from respective steps of a process for fabricating an image sensor of FIG. 14 to which the method of FIG. 2 is applied. [Figure 19L] Schematic cross-sectional side views of devices obtained from respective steps of a process for fabricating an image sensor of FIG. 14 to which the method of FIG. 2 is applied.

BEST MODE FOR CARRYING OUT THE INVENTION

[0010] Note that in the following embodiments, the same reference numerals may be shared between different drawings to indicate the same part or part having the same function, and repeated explanations will be omitted. In this specification, the same reference numerals and letters are used to indicate the same item; therefore, if a particular item is defined in one drawing, further explanation of that item is unnecessary in subsequent drawings.

[0011] For ease of understanding, the location, dimensions, and extent of structures shown in drawings and other materials do not necessarily represent their actual location, dimensions, and extent. Therefore, the disclosed invention is not limited to the location, dimensions, and extent disclosed in the drawings and other materials. Furthermore, drawings are not necessarily drawn to scale, and some features may be enlarged to show details of specific components.

[0012] Herein, various embodiments of this disclosure will be described in detail with reference to the accompanying drawings. It should be noted that the relative arrangement, numerical representations, and numerical values ​​of the components and steps described in these embodiments are not intended to limit the scope of this disclosure unless otherwise specified.

[0013] The following description of at least one embodiment is illustrative and not intended to limit the disclosure or its application or use. Those skilled in the art will understand that these are merely examples of exemplary methods in which the disclosure may be carried out, and not exhaustive.

[0014] Techniques, methods, and devices known to those skilled in the art in the relevant field may not be described in detail, but should be considered part of this specification as such.

[0015] Si-based CMOS image sensors exhibit very low quantum efficiency (QE) in wavelengths longer than the visible spectrum, such as the near-infrared (NIR) spectrum, because the absorption coefficient of Si for NIR wavelengths is low.

[0016] To improve the quality enhancement (QE) of image sensors, techniques are needed that allow for increased light absorption in the photodetector element. One method is to increase the vertical dimension of the photodetector element. However, in the case of the most commonly used Si-based image sensors, there are limitations to increasing the thickness of Si due to factors such as the difficulty of forming deep photodiodes (PDs), ensuring sufficient separation between pixels, and constraints on pixel design and process technology. Therefore, further methods are desired to enhance light absorption in the photodetector element of image sensors.

[0017] This disclosure provides an image sensor with improved QE, which is equipped with a pseudo-random array diffractive optical element (PRADOE) to induce multiple-order diffraction in light irradiated onto (or received by) the image sensor. As a result, light that would normally be incident perpendicularly to the photodetector of the image sensor (i.e., with an incident angle of 0°) has an increased incident angle and therefore travels a longer path before being absorbed within the photodetector. In this way, more light absorption occurs in the photodetector, thereby improving the QE of the image sensor.

[0018] Various embodiments of the image sensor of this disclosure are described in detail below with reference to the accompanying drawings. While actual image sensors may include other components, please understand that these other components are not described herein and are not shown in the accompanying drawings, so as not to confuse the essence of this application.

[0019] Figure 1 shows an image sensor 100 according to several embodiments of the present disclosure. The image sensor 100 includes at least one pixel unit, one of which is illustrated as an example in Figure 1. Each pixel unit of the image sensor 100 includes a photodetector 112. The photodetector 112 may be, for example, a photodiode, or any other suitable photoelectric element capable of converting received light into an electrical signal. In some embodiments, the photodetector is formed in a substrate. In some other embodiments, the photodetector is formed in an epitaxial layer formed on the substrate. Thus, the portion indicated by 110 in Figure 1 may be a substrate or an epitaxial layer.

[0020] The substrate includes, but is not limited to, a semiconductor substrate. In some embodiments, the substrate may include any semiconductor material suitable for forming an image sensor, such as, for example, a single semiconductor material (e.g., Si, germanium (Ge), etc.), a compound semiconductor material (e.g., silicon carbide (SiC), silicon germanium (SiGe), gallium arsenide (GaAs), gallium phosphide (GaP), indium phosphide (InP), indium arsenide (InAs), and / or indium antimonide (InSb), etc.), or a combination thereof. In some embodiments, part or all of the substrate may be doped with an impurity element at a certain concentration, for example, N-type or P-type impurities. Those skilled in the art will understand that the substrate is not particularly limited herein and may be specifically selected according to the actual application.

[0021] The epitaxial growth process uses the principle of two-dimensional structural similarity nucleation at the crystal interface to grow single-crystal layers on a single-crystal substrate, maintaining the original crystal lattice, and potentially incorporating impurity doping and varying thicknesses along the original crystal orientation. The single-crystal layers obtained by epitaxial growth are called epitaxial layers, and they can have the same or different conductivity types as the original single-crystal substrate. Epitaxy includes homoepitaxial and heteroepitaxial growth. Epitaxial layers obtained by homoepitaxial growth can be made of the same material as the substrate (e.g., epitaxial Si on a Si substrate), while epitaxial layers obtained by heteroepitaxial growth can be made of a different material (e.g., epitaxial GaAs on a Si substrate). Epitaxial growth processes can include gas-phase epitaxy, liquid-phase epitaxy, and molecular beam epitaxy.

[0022] As shown in Figure 1, each pixel unit of at least one pixel unit of the image sensor 100 further includes a pseudo-random array diffractive optical element (PRADOE) 120 located on the front of the light-receiving surface of the photodetector element 112. Note that in this specification, the term “on the front of” is used with respect to the optical path, and for example, “A” being on the front of “B” means that light reaches “A” before reaching “B”. It is known in the art that in the case of a front-side illumination (FIS) image sensor, the light-receiving surface of the image sensor is its front surface, and in the case of a back-side illumination (BIS) image sensor, the light-receiving surface of the image sensor is its back surface.

[0023] PRADOE120 includes an array of unit structures oriented at pseudo-random angles. "Oriented at pseudo-random angles" includes spatially modulating the diffraction angles by rotating each unit structure in the array at a different angle. Thus, although the angles at which each unit structure is rotated appear to be substantially different, this is not a true random distribution. In this specification, such an angular distribution is referred to as "pseudo-random angles," an array of unit structures having such an angular distribution is referred to as a "pseudo-random array," and a diffractive optical element provided by such an array is referred to as a "pseudo-random array diffractive optical element."

[0024] In some embodiments, the array of unit structures is a periodic array of unit structures. For example, referring to Figure 2, the period of the periodic array of unit structures is indicated by P, which refers to the distance between the centers of adjacent unit structures in PRADOE120. In the case of a periodic array of unit structures, the distance between the centers of each of two adjacent unit structures in PRADOE120 is substantially equal to the period P. The term “substantially” as used herein means to include any small variations caused by design or manufacturing defects, tolerances of the device or components, environmental influences, and / or other factors. Each unit structure in PRADOE120 has a length L, a width W, and a thickness D. The coordinates (x) in the two-dimensional xy-plane (parallel to the horizontal cross-section of the image sensor 100) i ,y i In the case of a unit structure located at ), its orientation angle is θ i The unit structure of PRADOE may be, for example, a rectangular parallelepiped, but may also be, but is not limited to, other suitable shapes that can have directionality in the xy-plane such that orientation makes sense, such as prisms and cylinders.

[0025] PRADOE120 is configured to induce multiple-order diffraction of light received by the photodetector 112, as shown, for example, in Figure 3. The central diffraction angle is determined by the period P. In some embodiments, the period P is determined based on the wavelength of the light configured to be detected by the pixel unit. This is because, even with the same diffraction angle, short wavelengths may be too small to sufficiently increase the angle of incident light and therefore not substantially increase light absorption, while long wavelengths may be too large, causing light to travel to adjacent pixel units and thus increasing crosstalk to an undesirable degree. In practice, an acceptable diffraction angle may first be determined based on the target wavelength, primarily considering absorption and crosstalk, and then the period P may be determined by simulation based on the determined diffraction angle.

[0026] Periodic arrays offer superior simulation solveability and can suppress crosstalk. However, it should be noted that the array of unit structures does not necessarily have to be periodic; it can be partially or entirely aperiodic. That is, the spacing between the centers of adjacent unit structures in PRADOE120 may vary across the entire array of unit structures. Thus, the array of unit structures may have multiple different spacings, and these spacings may be determined by simulation based on the determined diffraction angles. For example, Figure 5A shows an example of a PRADOE with a single pixel unit having two different spacings, where the first and fourth rows of unit structures have narrower spacings than the second and third rows of unit structures. Figure 5A shows a partially aperiodic array where some unit structures have the same spacing as others. In contrast, in an entirely aperiodic array, the spacing between the centers of any two adjacent unit structures may be different.

[0027] While this disclosure primarily uses periodic arrays of unit structures as examples for illustrative purposes rather than limitation, it should be understood that the “periodic P” as used herein refers to the “distance between the centers of adjacent unit structures” in a non-periodic array, and that this distance may not be the same.

[0028] In some embodiments, the size of the pixel unit is a multiple of the period P. For example, Figure 5B shows several examples of PRADOE for a single pixel unit with different periods P, where the period P of the left PRADOE is one-third of the pixel unit size, the period P of the middle PRADOE is one-quarter of the pixel unit size, and the period P of the right PRADOE is one-fifth of the pixel unit size. This is advantageous for giving periodic continuity to the PRADOE between pixel units.

[0029] In many applications, image sensors may be required to detect multiple wavelengths or wavelength ranges. Therefore, even if an image sensor is optimized for a single wavelength, it may not be possible to apply the image sensor to a wide wavelength range simultaneously, because light of different wavelengths will have different diffraction angles after passing through the same diffractive optical element. In other words, for example, if a single diffraction angle is set by optimization for a central wavelength from a wavelength range within the NIR range, light in a wavelength range longer than the central wavelength (e.g., near the upper limit of the wavelength range) may cause more crosstalk than light of the central wavelength if both are diffracted at a single diffraction angle, while light in a wavelength range shorter than the central wavelength (e.g., near the lower limit of the wavelength range) may show a smaller increase in absorption than light of the central wavelength if both are diffracted at a single diffraction angle, thereby degrading the imaging quality of the image sensor. For this purpose, in some embodiments, the pseudo-random angles of the unit structure of PRADOE120 may be configured such that different orders of multi-order diffraction have different diffraction angles. In other words, the central diffraction angle is determined by the period P, but the pseudo-random angle of the unit structure of PRADOE120 can still cause variations in the diffraction angle at each order. Therefore, a wide range of diffraction angles can be achieved rather than a single diffraction angle for each wavelength, thereby increasing the design freedom for optimizing the image sensor over a wide range of light sources or multiple wavelengths. In practice, an acceptable diffraction angle range may first be determined based on a target range of wavelengths, primarily considering absorption and crosstalk; then, the period P may be determined by simulation based on the central diffraction angle of the determined diffraction angle range; and further, the pseudo-random angle of the unit structure may be determined by simulation based on the variation in the diffraction angle within the determined diffraction angle range. For example, Figure 6 shows several examples of PRADOE for single pixel units with different distributions of pseudo-random angles.

[0030] Once the period P and pseudo-random angle are determined, simulations of the PRADOE can be performed by varying other design parameters, including length L, width W, thickness D, and / or refractive index n of the PRADOE material, while keeping the period P and pseudo-random angle constant at their determined values. Ultimately, the design parameters for the PRADOE with the highest QE are selected. Typically, the material selection for the PRADOE is limited by the CMOS process, and therefore, in practice, the refractive index n may not be so freely adjustable. Thus, the refractive index n is usually determined in advance, and simulations of the PRADOE can be performed by varying the length L, width W, and thickness D while keeping the refractive index n, period P, and pseudo-random angle constant at their determined values.

[0031] In some embodiments, as shown in the left portion of Figure 7, the unit structures of PRADOE120 may have the same length and width as one another. This may help reduce the computational load of the simulation. In some embodiments, as shown in the right portion of Figure 7, at least some of the unit structures of PRADOE120 may have different lengths or widths as one another. If it is possible for each unit structure to have individually modified dimensions, this may help the simulation yield optimal results. Also, considering the difficulty of the process, the unit structures of PRADOE120 may have the same thickness as one another. However, it is still possible to have at least some of the PRADOE120 unit structures have different thicknesses, for example, by multiple etching.

[0032] Various methods exist for fabricating PRADOE120. In some embodiments, as shown in Figures 1 and 3, for example, PRADOE120 is formed beneath the light-receiving surface of a substrate or epitaxial layer 110. For example, the substrate or epitaxial layer 110 may be etched from its light-receiving surface to form an array of trenches corresponding to an array of unit structures, and the array of trenches may then be filled with PRADOE material. The PRADOE material may be any suitable material having a refractive index different from that of the substrate or epitaxial layer 110.

[0033] In some other embodiments, as shown in Figure 4, for example, the PRADOE 120 is formed on the light-receiving surface of the substrate or epitaxial layer 110. For example, a layer of material other than the PRADOE material (used, for example, as a sacrificial layer) may be formed on the light-receiving surface of the substrate or epitaxial layer and etched to form an array of trenches corresponding to an array of unit structures, which may then be filled with the PRADOE material. The PRADOE material may be any suitable material having a refractive index different from that of the sacrificial layer. In another example, a layer of the PRADOE material may be formed on the light-receiving surface of the substrate or epitaxial layer and then etched to form an array of unit structures.

[0034] PRADOE may comprise one or more materials. In some embodiments, PRADOE comprises a single or multilayer anti-reflection (AR) material. For example, the AR material may include, but is not limited to, silicon oxide (e.g., SiO2), silicon nitride (e.g., Si3N4), silicon oxynitride (e.g., Si3N4O), or a combination thereof. In some embodiments, PRADOE comprises a first layer of passivation material and a second layer of AR material on top of the first layer. The passivation material can contribute to passivating defects (such as dangling bonds) resulting from etching to form the PRADOE, otherwise the defects could become dark sources and introduce significant noise to the image sensor. For example, the passivation material may be a negatively charged material such as hafnium oxide (e.g., HfO2) or aluminum oxide (e.g., Al2O3). These negatively charged materials induce positive charges in the defect regions covered by them, thereby trapping electrons generated within those defect regions and preventing dark sources from entering the photodetector.

[0035] There are other instances in PRADOE where two or more materials are used. For example, sometimes, depending on the depth and / or width of the etched area, it may be difficult to fill the etched area with a single material. In particular, when filling the etched area using techniques such as atomic layer deposition (ALD), the deposition rate can be very slow, resulting in a long processing time. In such cases, it is possible to partially fill the etched area with one material using ALD, and then fill the remaining part with another material using a deposition process with a faster deposition rate.

[0036] Figure 8 shows an image sensor 200 according to some embodiments of the present disclosure, the image sensor 200 comprising a substrate or epitaxial layer 210 having a photodetector element 212 and a PRADOE 220. The image sensor 200 differs from the image sensor 100 only in that the PRADOE 220 comprises two layers of material. Specifically, the PRADOE 220 comprises a first layer 222 and a second layer 224 on top of the first layer 222. As described above, the first layer 222 may be composed of a passivation material, the second layer 224 may be composed of an AR material, or alternatively, the first layer 222 may be formed of one material using a first deposition process, and the second layer 224 may be formed of another material using a second deposition process with a higher deposition rate than the first deposition process. Furthermore, it can be understood that the PRADOE of this disclosure is not limited to a single-layer or double-layer structure, but may have even more layers.

[0037] To avoid crosstalk between pixel units, in some embodiments, the pixel unit further includes an isolation structure that at least partially surrounds the photodetector. The isolation structure extends along part or all of the depth of the photodetector and can suppress crosstalk and blooming. The PRADOE may contain the same or different materials as the isolation structure, and the same or different etching and filling processes may be used for the PRADOE and the isolation structure. For example, the isolation structure may be formed using conventional techniques used for shallow trench isolation (STI) or deep trench isolation (DTI), and therefore conventional materials for STI or DTI, such as silicon oxide (e.g., SiO2), silicon nitride (e.g., Si3N4), silicon oxynitride (e.g., Si3N4O), or combinations thereof, may be used. In some embodiments, a layer of passivation material as described above may also be formed between the isolation trench and the isolation structure to prevent the generation of dark sources due to defects in the etched portion.

[0038] In some embodiments, the distance between the center of the separation structure and the center of the PRADOE unit structure closest to the separation structure may be the same as the period P. This can improve the periodicity of the diffraction pattern to some extent. Lower periodicity leads to a wider range of light diffraction angles. If the range of light diffraction angles is too wide, crosstalk between adjacent pixel units may increase.

[0039] Figure 9 shows an image sensor 300 according to several embodiments of the present disclosure, the image sensor 300 comprising a substrate or epitaxial layer 310 having a photodetector 312 and a PRADOE 320. The image sensor 300 differs from the image sensor 100 only in that the pixel units of the image sensor 300 further include a separation structure 330 that surrounds the photodetector 312 and extends along a portion of the depth of the photodetector 312. Specifically, the separation structure 330 may be formed by etching the substrate or epitaxial layer 310 to form a separation trench surrounding the photodetector 312, and then filling the separation trench with a separation material. For example, the etching may be performed from the light-receiving surface, for example, the etching may be back-side etching of the BSI image sensor. In some cases, both etching of the separation structure 330 and etching of the PRADOE 320 may be performed from the light-receiving surface. Furthermore, the separation trenches of separation structure 330 and the trench array of PRADOE320 may be filled with the same material in the same deposition process.

[0040] Figure 10 shows an image sensor 300' according to several embodiments of the present disclosure, the image sensor 300' comprising a substrate or epitaxial layer 310 having a photodetector 312, a PRADOE 320, and a separation structure 330' surrounding the photodetector 312. The image sensor 300' differs from the image sensor 300 only in that the separation structure 330' extends along the entire depth of the photodetector 312. Specifically, the separation structure 330' may be formed by etching the substrate or epitaxial layer 310 to form a separation trench surrounding the photodetector 312, and then filling the separation trench with a separation material. For example, the etching may be performed from the side facing the light-receiving surface, for example, the etching may be surface etching of a BSI image sensor. Alternatively, the etching may be performed partially from the light-receiving surface and partially from the opposite side.

[0041] In some of the above examples where the PRADOE is formed on the light-receiving surface of a substrate or epitaxial layer, it can be understood that etching of the isolation structure may include etching a sacrificial layer so that the upper surface of the isolation structure is aligned with the upper surface of the PRADOE.

[0042] In some embodiments, the periphery of the PRADOE is reduced relative to the periphery of the pixel unit. For example, as shown in Figure 11, which illustrates both pixel units with and without a separation structure, the area of ​​the PRADOE is applied in a reduced form rather than filling the entire area of ​​the pixel unit. This may be a process consideration, as it may be desirable to keep the PRADOE away from the separation structure for ease of manufacturing. Typically, it is desirable that the PRADOE be aligned laterally with the photodetector. For example, the center of the PRADOE may be aligned laterally with the center of the photodetector. In some cases, it may be desirable that the area of ​​the PRADOE be substantially the same as or larger than the area of ​​the photodetector. However, this is not always necessary, as the pixel unit typically includes microlenses that can focus light so that the beam size of the light can be reduced within the area of ​​the PRADOE.

[0043] Figures 12–15 schematically illustrate several examples of image sensors according to some embodiments of the present disclosure. While these figures illustrate BIS image sensors as examples, this does not imply any limitation to the present disclosure. It is understood that the teachings of the present disclosure are also applicable to FIS image sensors. For example, the PRADOE may be located on the front of the light-receiving surface of the photodetector element of the FIS image sensor, but typically it may be located behind the metal wiring layer of the FIS image sensor.

[0044] Figure 12 shows an image sensor 400 according to several embodiments of the present disclosure, the top view showing a 2x2 array pixel unit and the cross-sectional side view showing two adjacent pixel units in the 2x2 array. As shown in Figure 12, the pixel unit of the image sensor 400 includes a microlens 401, a color filter 402, a light shield 403 (e.g., in the form of a metal grid), an AR layer 404 (e.g., in the form of a composite layer having multiple sublayers), a PRADOE 405, a photodetector 406 in a substrate 407, an active element 408 (e.g., a transistor), and a metal interconnect structure 409. Note that the lowest sublayer of the AR layer 404 may be formed of the same material as the PRADOE 405 in the same deposition process as the PRADOE 405.

[0045] Figure 13 shows an image sensor 500 according to several embodiments of the present disclosure, the top view showing a 2x2 array of pixel units and the cross-sectional side view showing two adjacent pixel units in the 2x2 array. As shown in Figure 13, the pixel units of the image sensor 500 include a microlens 501, a color filter 502, a light shield 503 (e.g., in the form of a metal grid), an AR layer 504 (e.g., in the form of a composite layer having multiple sublayers), a PRADOE 505, a photodetector 506 in a substrate 507, an active element 508 (e.g., a transistor), and a metal interconnect structure 509. The image sensor 500 further includes a separation structure 510 that separates the pixel units from each other. The separation structure 510 extends along a portion of the depth of the photodetector 506. It should be noted that the lowest sublayer of the AR layer 504 may be formed using the same deposition process as PRADOE 505 and the separation structure 510, and using the same materials as PRADOE 505 and the separation structure 510.

[0046] Figure 14 shows an image sensor 600 according to several embodiments of the present disclosure, the top view showing a 2x2 array pixel unit and the cross-sectional side view showing two adjacent pixel units in the 2x2 array. As shown in Figure 14, the pixel unit of the image sensor 600 includes a microlens 601, a color filter 602, a light shield 603 (e.g., in the form of a metal grid), an AR layer 604 (e.g., in the form of a composite layer having multiple sublayers), a PRADOE 605, a photodetector 606 in a substrate 607, an active element 608 (e.g., a transistor), a metal interconnect structure 609, and a separation structure 610. The separation structure 610 extends along a portion of the depth of the photodetector 606. Specifically, the PRADOE 605 and the separation structure 610 include a first layer of passivation material and a second layer of AR material on top thereof. It should be noted that the lowest sublayer of AR layer 604 may be formed using the same deposition process as PRADOE 605 and separation structure 610, and with the same materials as PRADOE 605 and separation structure 610.

[0047] Figure 15 shows an image sensor 700 according to several embodiments of the present disclosure, the top view showing a 2x2 array pixel unit and the cross-sectional side view showing two adjacent pixel units in the 2x2 array. As shown in Figure 15, the pixel unit of the image sensor 700 includes a microlens 701, a color filter 702, a light shield 703 (e.g., in the form of a metal grid), an AR layer 704 (e.g., in the form of a composite layer having multiple sublayers), a PRADOE 705, a photodetector 706 in a substrate 707, an active element 708 (e.g., a transistor), a metal interconnect structure 709, and a separation structure 710. The separation structure 710 extends along the entire depth of the photodetector 706. Specifically, the PRADOE 705 and the separation structure 710 include a first layer of passivation material and a second layer of AR material on top thereof. It should be noted that the lowest sublayer of the AR layer 704 may be formed using the same deposition process as PRADOE 705 and the separation structure 710, and with the same material as PRADOE 705 and the separation structure 710. More specifically, the formation of PRADOE 705 includes back surface etching, and the formation of the separation structure 710 includes front surface etching.

[0048] In this disclosure, the image sensor may be a near-infrared (NIR) image sensor. For example, the image sensor may be an NIR BIS image sensor, such as a Si-based NIR BIS image sensor. As described above, conventional Si-based image sensors have insufficient performance in the NIR spectrum. In contrast, the NIR image sensor according to this disclosure has a significantly improved QE due to the increased light absorption brought about by PRADOE.

[0049] Furthermore, the image sensor may be a visible image sensor. For example, the image sensor may be a visible BIS image sensor, such as a Si-based visible BIS image sensor. While conventional Si-based image sensors already have good performance in the visible spectrum, the visible image sensor according to this disclosure has further improved QE due to the increased light absorption provided by PRADOE.

[0050] The figures above mainly show a single pixel unit or a 2x2 array of pixel units, but an image sensor can have two, three, four, five, or more pixel units. In some embodiments, the image sensor includes a first pixel unit configured to detect light of a first wavelength and comprising a first PRADOE, and a second pixel unit configured to detect light of a second wavelength different from the first wavelength and comprising a second PRADOE. The first and second PRADOEs may differ from each other in at least one of the following: the length of the unit structure, the width of the unit structure, the orientation angle of the unit structure, and the distance between the centers of adjacent unit structures (e.g., period P). The first and second PRADOEs may have different thicknesses or refractive indices, but changing these two parameters may make the process more complex. As described above, the parameters of the PRADOE for the pixel unit may be optimized to match the target wavelength of the pixel unit.

[0051] For example, Figure 16 schematically shows one example of a PRADOE applied to a 2x2 array pixel unit (two green pixel units G, one red pixel unit R, and one blue pixel unit B) similar to a Bayer array, according to some embodiments of the present disclosure. The PRADOEs of the green pixel unit G, blue pixel unit B, and red pixel unit R have different periods (P), different lateral dimensions (L, W), and different pseudo-random angle distributions. For various types of arrays of pixel units, optimization of the PRADOE for each pixel unit can be performed. Specifically, pixel units designed for different wavelengths or wavelength ranges will have different levels of absorption and crosstalk without PRADOE. When PRADOE is applied, this increases absorption and thus improves the signal-to-noise ratio, while the increase in crosstalk is kept within acceptable limits, and therefore the image contrast and color accuracy are not substantially reduced. Thus, different types of PRADOE can be applied to each pixel unit to suit the specific characteristics of each pixel unit.

[0052] In some embodiments, the image sensor includes a first pixel unit configured to detect light of a first wavelength and a second pixel unit configured to detect light of a second wavelength different from the first wavelength, wherein the first pixel unit includes a PRADOE, but the second pixel unit does not. In some examples, the absorption of light of the first wavelength by the first pixel unit is less than the absorption of light of the second wavelength by the second pixel unit. In some examples, when both lights have the same angle of incidence, the crosstalk caused by light of the second wavelength between the second pixel unit and adjacent pixel units of the second pixel unit is greater than the crosstalk caused by light of the first wavelength between the first pixel unit and adjacent pixel units of the first pixel unit.

[0053] For example, Figure 17 schematically shows another example of PRADOE applied to a 2x2 array pixel unit (two green pixel units G, one red pixel unit R, and one blue pixel unit B) similar to a Bayer array, according to some embodiments of the present disclosure. PRADOE is provided only on the green pixel unit G and the red pixel unit R. For example, Si already has a high absorption coefficient for blue light, and therefore there is no need to further increase the absorption of blue light, so PRADOE is not provided on the blue pixel unit B. In practice, if the absorption of blue light is too dominant over the absorption of other colors of light, it can cause color cast and degrade image quality. In practice, PRADOE can be selectively applied to certain types of pixel units, for example, when an improvement in QE is needed. Typically, PRADOE can be applied when the improvement in QE is significant while the increase in crosstalk is small enough to be acceptable.

[0054] In some cases, PRADOE may be selectively excluded from certain types of pixel units, such as when crosstalk reduction is required. Reducing crosstalk can favorably improve image contrast. In some examples, PRADOE may be provided only to the green pixel unit G, while it is not provided to the red pixel unit R and the blue pixel unit B.

[0055] Therefore, the present disclosure also provides a method for fabricating an image sensor. As shown in Figure 18, the method 800 for fabricating an image sensor includes, in step S802, providing a photodetector on a substrate, and in step S804, forming a pseudo-random array diffractive optical element (PRADOE) on the light-receiving surface of the photodetector, which includes an array of unit structures oriented at pseudo-random angles. The PRADOE is configured to cause multiple-order diffraction of light received by the photodetector. In some embodiments, the array of unit structures may be a periodic array of unit structures. In some other embodiments, the array of unit structures may be a (partially or entirely) aperiodic array of unit structures.

[0056] In some embodiments, the photodetector is formed in a substrate, and the step of forming the PRADOE includes etching the substrate from the light-receiving surface of the substrate to form an array of trenches corresponding to an array of unit structures and filling the array of trenches with a first material, or forming a layer of a second material on the light-receiving surface of the substrate, etching the layer of the second material to form an array of trenches corresponding to an array of unit structures and filling the array of trenches with a first material, or forming a layer of a first material on the light-receiving surface of the substrate and etching the layer of the first material to form an array of unit structures.

[0057] In some embodiments, the photodetector is formed within an epitaxial layer formed on a substrate, and the step of forming the PRADOE includes one of the following: etching the epitaxial layer from the light-receiving surface of the epitaxial layer to form an array of trenches corresponding to an array of unit structures and filling the array of trenches with a first material; forming a layer of a second material on the light-receiving surface of the epitaxial layer, etching the layer of the second material to form an array of trenches corresponding to an array of unit structures and filling the array of trenches with a first material; or forming a layer of a first material on the light-receiving surface of the epitaxial layer and etching the layer of the first material to form an array of unit structures.

[0058] For example, the first material may be any of the above-mentioned materials for PRADOE, and the second material may be any suitable material having a different refractive index than PRADOE. In some examples, the layer of the second material may be formed by epitaxial growth or deposition.

[0059] In some embodiments, filling an array of trenches with a first material includes first filling the array of trenches with a passivation material and then with an anti-reflective material. For example, the passivation material is a negatively charged material.

[0060] In some embodiments, filling an array of trenches with a first material includes filling an array of trenches with multiple materials at different deposition rates.

[0061] In some embodiments, Method 800 further includes the steps of etching a substrate or epitaxial layer to form isolation trenches that at least partially surround a photodetector, and filling the isolation trenches with a third material to form an isolation structure. For example, the isolation structure extends along part or all of the depth of the photodetector. The third material may be any suitable material capable of achieving isolation between pixel units, such as those used for STI or DTI. The third material may be the same as or different from the first material.

[0062] In some embodiments, both the etching of the isolation trenches and the etching of the trench array are performed from the light-receiving surface. For example, the isolation trenches and the trench array are filled with the same material in the same deposition process. In some embodiments, the etching of the isolation trenches is performed from the side opposite the light-receiving surface.

[0063] In some embodiments, the distance between the center of a separation structure and the center of the nearest PRADOE unit structure is the same as the distance between the centers of adjacent PRADOE unit structures.

[0064] In some embodiments, method 800 further includes the step of forming an anti-reflective layer on top of the PRADOE, wherein the anti-reflective layer or the lowest sublayer of the anti-reflective layer is formed of the same material as the PRADOE in the same deposition process.

[0065] In some embodiments, the unit structure of the PRADOE is a rectangular parallelepiped. In some embodiments, at least some of the unit structures of the PRADOE differ from one another in at least one of their length and width. In some embodiments, the unit structures of the PRADOE have the same length and width. In some embodiments, the spacing between the centers of adjacent unit structures of the PRADOE is determined based on the wavelength of light that the pixel unit is configured to detect.

[0066] In some embodiments, the photodetector includes a first photodetector configured to detect light of a first wavelength and a second photodetector configured to detect light of a second wavelength different from the first wavelength, and the PRADOE includes a first PRADOE for the first photodetector and a second PRADOE for the second photodetector, wherein the first PRADOE and the second PRADOE differ from each other in at least one of the length of the unit structure, the width of the unit structure, the orientation angle of the unit structure, and the distance between the centers of adjacent unit structures.

[0067] In some embodiments, the photodetector includes a first photodetector configured to detect light of a first wavelength and a second photodetector configured to detect light of a second wavelength different from the first wavelength, wherein a PRADOE is present on the table of the first photodetector but not on the table of the second photodetector.

[0068] In some embodiments, the image sensor is a near-infrared back-illuminated image sensor.

[0069] The embodiments of Method 800 are similar to the embodiments of the image sensor described above, and various embodiments of the image sensor of the present disclosure can be referenced; therefore, repeated descriptions are omitted here.

[0070] Figures 19A to 19L schematically show cross-sectional side views of devices obtained from each step of the process for fabricating the image sensor in Figure 14, to which the method in Figure 2 is applied, for non-limiting illustrative purposes. Two adjacent pixel units are shown illustratively.

[0071] As shown in Figure 19A, a substrate 901 is provided. As shown in Figure 19B, a photodetector 902 such as a photodetector PD is formed on the substrate 901. As shown in Figure 19C, peripheral circuits 903 such as transistors and metal wiring are formed on the photodetector 902. As shown in Figure 19D, the substrate 901 on which the photodetector 902 and peripheral circuits 903 are formed is turned over and then subjected to a thinning process. As shown in Figure 19E, the back side of the substrate 901 (shown here as facing upwards) is etched to form a periodic array of trenches 904 corresponding to a periodic array of PRADOE unit structures designed for two pixel units. As shown in Figure 19F, the back side of the substrate 901 is further etched to form isolation trenches 905 surrounding each pixel unit. As shown in Figure 19G, a passivation layer 906 is partially filled into the trenches. As shown in Figure 19H, an AR layer 907 fills the remaining part of the trenches. The portion of the AR layer 907 within the periodic array of trenches forms a PRADOE, the portion of the AR layer 907 within the isolation trenches forms an isolation structure, and the remaining portion of the AR layer 907 forms the bottom layer of the two-layer AR structure. As shown in Figure 19I, an additional AR layer 908 is deposited as the top layer of the two-layer AR structure. As shown in Figure 19J, a metal grid 909 is formed on top of the two-layer AR structure, functioning as a light shield to avoid crosstalk. As shown in Figure 19K, each pixel unit is fitted with a color filter 910 that allows light of wavelengths within the design wavelength range of the respective pixel unit to pass through and blocks light of wavelengths outside the design wavelength range. As shown in Figure 19L, each pixel unit is fitted with a microlens 911 that plays a role in focusing the received light to avoid crosstalk.

[0072] Where terms such as “left,” “right,” “front,” “back,” “top,” “bottom,” “up,” “down,” “high,” and “low” appear in this specification and the claims, they are for illustrative purposes only and do not necessarily describe permanent relative positions. It should be understood that these terms are interchangeable where appropriate so that the embodiments of this disclosure described herein may operate in orientations different from those shown herein or otherwise described. For example, if a device in a drawing is inverted, a feature initially described as “above” another feature may now be described as “below” another feature. The device may also be oriented in other ways (rotated 90 degrees or in other orientations), in which case the relative spatial relationships will be interpreted accordingly.

[0073] In this specification and the claims, when an element is described as "on top of," "attached to," "connected to," "bonded to," or "in contact with" another element, the element may be directly on top of, directly attached to, directly connected to, directly bonded to, or directly in contact with the other element, or there may be one or more intermediate elements. In contrast, when an element is described as "on top of," "directly attached to," "directly connected to," "directly bonded to," or "in direct contact with" another element, there are no intermediate elements. In this specification and the claims, when a feature is described as being "adjacent" to another feature, it may mean that the feature has a portion that overlaps with the adjacent feature, or a portion that is above or below the adjacent feature.

[0074] As used herein, terms such as “exemplary” mean “to serve as an example, case, or illustration,” and do not mean “model” to be exactly reproduced. Implementations described exemplary herein should not necessarily be construed as being preferable or advantageous to other implementations. Furthermore, this disclosure is not limited by the technical field, background art, summary of the invention, or any explicit or implicit theory presented in the forms for carrying out the invention. As used herein, the term “substantially” means to include any minor variations caused by design or manufacturing defects, tolerances of the device or component, environmental influences, and / or other factors. “Substantially” also takes into account any differences from the complete or ideal situation caused by parasitic components, noise, and other practical considerations that may be present in a practical implementation.

[0075] In addition, similar terms such as “first,” “second,” etc., used herein may be used for reference purposes only and are therefore not intended to be limiting. For example, unless explicitly indicated by the context, terms such as “first,” “second,” etc., and other numerical terms including structures or elements, do not imply order or sequence. Furthermore, the term “comes with / includes” as used herein is to identify the presence of a described feature, complete, step, operation, unit, and / or component, and not to exclude the presence or addition of one or more other features, complete, step, operation, unit, component, and / or combination thereof. In this disclosure, the term “provide” is used in a broad sense to encompass all methods of obtaining the Subject Matter, and therefore “provide the Subject Matter” includes, but is not limited to, “purchasing,” “preparing / manufacturing,” “positioning / setting up,” “installing / assembling,” and / or “ordering” the Subject Matter.

[0076] As used herein, the terms “and / or” include any combination of one or more of the related enumerated items. The terms used herein are for illustrative purposes only and are not intended to limit this disclosure. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural form unless otherwise explicitly indicated by the context.

[0077] Those skilled in the art will understand that the boundaries between the operations described above are merely illustrative. Multiple operations can be combined into a single operation, a single operation can be distributed among additional operations, and the execution of operations can overlap at least partially in time. Furthermore, alternative embodiments may include multiple instances of a particular operation, and the order of operations can be changed in various other embodiments. However, other modifications, variations, and substitutions are also possible. All embodiments and elements disclosed above can be combined in any way and / or with embodiments or elements of other embodiments to provide a number of additional embodiments. Accordingly, this specification and the accompanying drawings should be considered illustrative and not limiting.

[0078] In addition, the words “here,” “above,” “below,” “in this specification,” “below,” “above,” and similar terms used in this disclosure refer to the entire disclosure and not to any particular part of this disclosure. Furthermore, unless expressly stated otherwise or interpreted differently in the context in which they are used, conditional language used herein, such as “may,” “may,” “for example,” and “such as,” is generally intended to indicate that certain embodiments include certain features, elements, and / or conditions, while other embodiments do not. Accordingly, such conditional language is generally not intended to imply that one or more embodiments require any features, elements, and / or conditions, or that such features, elements, and / or conditions are included or performed in any particular embodiment.

[0079] While several specific embodiments of this disclosure have been described in detail through examples, it will be understood by those skilled in the art that these examples are for illustrative purposes only and do not limit the scope of this disclosure. The embodiments disclosed herein can be combined in any way without departing from the spirit and scope of this disclosure. Those skilled in the art will also understand that various modifications can be made to the embodiments without departing from the scope and spirit of this disclosure. The scope of this disclosure is defined by the appended claims.

Claims

1. An image sensor comprising at least one pixel unit, wherein each pixel unit of the at least one pixel unit is A light-sensing element, A pseudo-random array diffractive optical element (PRADOE) comprising an array of unit structures located on the surface of the light-receiving surface of the aforementioned photodetector and oriented at a pseudo-random angle, wherein the PRADOE is configured to cause multiple-order diffraction of light received by the photodetector, and An image sensor equipped with [a specific feature].

2. The image sensor according to claim 1, wherein the pseudo-random angle is configured such that different orders of the multi-order diffraction have different diffraction angles.

3. The photodetector element is formed within the substrate, and the PRADOE is formed on the light-receiving surface of the substrate, or The image sensor according to claim 1, wherein the light sensing element is formed in an epitaxial layer formed on a substrate, and the PRADOE is formed on the light-receiving surface of the epitaxial layer.

4. The photodetector element is formed within the substrate, and the PRADOE is formed beneath the light-receiving surface of the substrate, or The image sensor according to claim 1, wherein the light sensing element is formed in an epitaxial layer formed on a substrate, and the PRADOE is formed below the light-receiving surface of the epitaxial layer.

5. The image sensor according to claim 1, wherein the unit structure of the PRADOE is a rectangular parallelepiped.

6. The image sensor according to claim 1, wherein at least some of the unit structures of the PRADOE differ from each other in at least one of length and width.

7. The image sensor according to claim 1, wherein the unit structures of the PRADOE have the same length and width as each other.

8. The image sensor according to claim 1, wherein the spacing between the centers of adjacent unit structures of the PRADOE is determined based on the wavelength of light configured to be detected by the pixel unit.

9. The image sensor according to claim 1, wherein the PRADOE comprises a first layer of passivation material and a second layer of anti-reflective material on the first layer.

10. The image sensor according to claim 9, wherein the passivation material is a material having a negative charge.

11. The image sensor according to claim 1, wherein the array of unit structures is a periodic array of unit structures.

12. The image sensor according to claim 11, wherein the size of the pixel unit is a multiple of the distance between the centers of adjacent unit structures of the PRADOE.

13. The image sensor according to claim 1, wherein the outer circumference of the PRADOE is reduced in size relative to the outer circumference of the pixel unit.

14. The image sensor according to any one of claims 1 to 13, wherein the pixel unit further comprises a separation structure that at least partially surrounds the light sensing element.

15. The image sensor according to claim 14, wherein the separation structure extends along part or all of the depth of the photodetector.

16. The image sensor according to claim 14, wherein the PRADOE is made of the same material as the separation structure.

17. The image sensor according to claim 14, wherein the array of unit structures is a periodic array of unit structures, and the distance between the center of the separation structure and the center of the PRADOE unit structure closest to the separation structure is the same as the distance between the centers of adjacent PRADOE unit structures.

18. The aforementioned at least one pixel unit, A first pixel unit configured to detect light of a first wavelength and comprising a first PRADOE, A second pixel unit configured to detect light of a second wavelength different from the first wavelength and comprising a second PRADOE The image sensor according to claim 1, comprising, wherein the first PRADOE and the second PRADOE differ from each other in at least one of the length of the unit structure, the width of the unit structure, the orientation angle of the unit structure, and the distance between the centers of adjacent unit structures.

19. The image sensor according to claim 1, wherein the image sensor further comprises a first pixel unit configured to detect light of a first wavelength, the first pixel unit configured to detect light of a second wavelength different from the first wavelength, the first pixel unit includes a PRADOE, but the second pixel unit does not.

20. The image sensor according to claim 19, wherein the absorption of light of the first wavelength by the first pixel unit is less than the absorption of light of the second wavelength by the second pixel unit.

21. The image sensor according to claim 19, wherein, when both lights have the same angle of incidence, the crosstalk caused by light of a second wavelength between the second pixel unit and adjacent pixel units of the second pixel unit is greater than the crosstalk caused by light of a first wavelength between the first pixel unit and adjacent pixel units of the first pixel unit.

22. The image sensor according to claim 1, wherein the image sensor is a near-infrared back-illuminated image sensor.

23. A method for fabricating an image sensor, The steps include: providing a photodetector on the substrate, The steps include forming a pseudo-random array diffractive optical element (PRADOE) on the light-receiving surface of the aforementioned photodetector, which comprises an array of unit structures oriented at pseudo-random angles. A method comprising the PRADOE being configured to cause multiple-order diffraction of light received by the photodetector.

24. The photodetector is formed in the substrate, and the step of forming the PRADOE is, Etching the substrate from the light-receiving surface to form an array of trenches corresponding to the array of unit structures, and filling the array of trenches with the first material, or Forming a layer of a second material on the light-receiving surface of the substrate, etching the layer of the second material to form an array of trenches corresponding to the array of unit structures, and filling the array of trenches with the first material, or Forming a layer of the first material on the light-receiving surface of the substrate, and etching the layer of the first material to form an array of the unit structure. The method according to claim 23, including the method described in claim 23.

25. The photodetector is formed in an epitaxial layer formed on the substrate, and the step of forming the PRADOE is, Etching the epitaxial layer from the light-receiving surface of the epitaxial layer to form an array of trenches corresponding to the array of unit structures, and filling the array of trenches with the first material, or Forming a layer of a second material on the light-receiving surface of the epitaxial layer, etching the layer of the second material to form an array of trenches corresponding to the array of unit structures, and filling the array of trenches with the first material, or Forming a layer of the first material on the light-receiving surface of the epitaxial layer, and etching the layer of the first material to form an array of the unit structure. The method according to claim 23, including the method described in claim 23.

26. The method according to claim 24 or 25, wherein filling the array of trenches with the first material includes first filling the array of trenches with a passivation material and then filling it with an anti-reflective material.

27. The method according to claim 26, wherein the passivation material is a material having a negative charge.

28. The method according to claim 24 or 25, wherein filling the array of trenches with the first material includes filling the array of trenches with a plurality of materials at different deposition rates.

29. The steps include etching the substrate to form a separation trench that at least partially surrounds the photodetector element, The steps include filling the separation trench with a third material to form a separation structure, and The method according to claim 24, further comprising:

30. The steps include etching the epitaxial layer to form a separation trench that at least partially surrounds the photodetector element, The steps include filling the separation trench with a third material to form a separation structure, and The method according to claim 25, further comprising:

31. The method according to claim 29 or 30, wherein both the etching of the isolation trench and the etching of the trench array are performed from the light-receiving surface.

32. The method according to claim 31, wherein the separation trench and the array of trenches are filled with the same material in the same deposition process.

33. The method according to claim 29 or 30, wherein the etching of the separation trench is performed from the side facing the light-receiving surface.

34. The method according to claim 29 or 30, wherein the separation structure extends along part or all of the depth of the photodetector.

35. The method according to claim 29 or 30, wherein the array of unit structures is a periodic array of unit structures, and the distance between the center of the separation structure and the center of the PRADOE unit structure closest to the separation structure is the same as the distance between the centers of adjacent PRADOE unit structures.

36. The method according to claim 23, further comprising the step of forming an anti-reflective layer on the PRADOE, wherein the anti-reflective layer or the lowest sublayer of the anti-reflective layer is formed of the same material as the PRADOE in the same deposition process.

37. The method according to claim 23, wherein the unit structure of the PRADOE is a rectangular parallelepiped.

38. The method according to claim 23, wherein at least some of the unit structures of the PRADOE differ from each other in at least one of length and width.

39. The method according to claim 23, wherein the unit structures of the PRADOE have the same length and width.

40. The method according to claim 23, wherein the spacing between the centers of adjacent unit structures of the PRADOE is determined based on the wavelength of light configured to be detected by the pixel unit.

41. The method according to claim 23, wherein the photodetector includes a first photodetector configured to detect light of a first wavelength and a second photodetector configured to detect light of a second wavelength different from the first wavelength, and the PRADOE includes a first PRADOE for the first photodetector and a second PRADOE for the second photodetector, and the first PRADOE and the second PRADOE differ from each other in at least one of the length of the unit structure, the width of the unit structure, the orientation angle of the unit structure, and the distance between the centers of adjacent unit structures.

42. The method according to claim 23, wherein the photodetector includes a first photodetector configured to detect light of a first wavelength and a second photodetector configured to detect light of a second wavelength different from the first wavelength, and a PRADOOE is present on the surface of the first photodetector but not on the surface of the second photodetector.

43. The method according to claim 23, wherein the image sensor is a near-infrared back-illuminated image sensor.

44. The method according to claim 23, wherein the array of unit structures is a periodic array of unit structures.

Images