Patent Publication Number: US-2022231074-A1

Title: Image sensor

Description:
BACKGROUND 
     Technical Field 
     The present disclosure relates in general to an image sensor, and in particular, it relates to an image sensor providing high dynamic range (HDR). 
     Description of the Related Art 
     Image sensors, such as complementary metal oxide semiconductor (CMOS) image sensors (also known as CIS), are widely used in various image-capturing apparatus such as digital still-image cameras, digital video cameras, and the like. The light-sensing portion of the image sensor may detect ambient color change, and signal electric charges may he generated depending on the amount of light received in the light-sensing portion. In addition, the signal electric charges generated in the light-sensing portion may be transmitted and amplified, to obtain an image signal. 
     Image sensors should be able to capture images quickly, and the accuracy, spatial resolution, and dynamic range must be as high as possible. However, conventional imaging sensors face the problem of missing scene detail or blurring or severe distortion due to the limited dynamic range. Therefore, image sensors capable of achieving high dynamic range (HDR) imaging are called for. 
     SUMMARY 
     In accordance with some embodiments of the disclosure, an image sensor is provided. The image sensor includes a substrate, first photodiodes, second photodiodes, an interlayer, a light-guiding structure, and a micro-lens layer. The first photodiodes and the second photodiodes are alternately disposed in the substrate. The area of each of the first photodiodes is less than the area of each of the second photodiodes from a top view. The interlayer is disposed on the substrate. The light-guiding structure is disposed in the interlayer and over at least one of the first photodiodes or the second photodiodes. The refractive index of the light-guiding structure is greater than the refractive index of the interlayer. The micro-lens layer is disposed on the interlayer. 
     In accordance with some other embodiments of the disclosure, another image sensor is also provided. The image sensor includes a substrate, first photodiodes, second photodiodes, an interlayer, a light-guiding structure, a color filter array, and a micro-lens layer. The first photodiodes and the second photodiodes are alternately disposed in the substrate. The area of each of the first photodiodes is less than the area of each of the second photodiodes from a top view. The interlayer is disposed on the substrate. The light-guiding structure is disposed in the interlayer and over at least one of the first photodiodes or the second photodiodes. The color filter array has a plurality of color filters disposed on the interlayer. The micro-lens layer is disposed on the color filter array, and includes a plurality of micro-lenses. Each of the color filters overlaps two adjacent macro-lenses. 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure may be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIGS. 1A-1F  are cross-sectional diagrams of an image sensor in accordance h various embodiments of the disclosure. 
         FIG. 2A  is a top view diagram of an image sensor in accordance with some embodiments of the disclosure. 
         FIG. 2B  is an enlarged top view diagram of an image sensor in accordance with some embodiments of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The image sensor of the present disclosure are described in detail in the following description. In the following detailed description, for purposes of explanation, numerous specific details and embodiments are set forth in order to provide a thorough understanding of the present disclosure. The specific elements and configurations described in the following detailed description are set forth in order to dearly describe the present disclosure. It will be apparent, however, that the exemplary embodiments set forth herein are used merely for the purpose of illustration, and the concept of the present disclosure may be embodied in various forms without being limited to those exemplary embodiments. 
     In addition, the drawings of different embodiments may use like and/or corresponding numerals to denote like and/or corresponding elements in order to clearly describe the present disclosure. However, the use of like and/or corresponding numerals in the drawings of different embodiments does not suggest any correlation between different embodiments. It should be understood that this description of the exemplary embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description. The drawings are not drawn to scale. In addition, structures and devices are shown schematically in order to simplify the drawing. 
     In addition, the expressions “a layer overlying another layer”, “a layer is disposed above another layer”, “a layer is disposed on another layer” and “a layer is disposed over another layer” may indicate that the layer is in direct contact with the other layer, or that the layer is not in direct contact with the other layer, there being one or more intermediate layers disposed between the layer and the other layer. 
     In addition, in this specification, relative expressions are used. For example, “lower”, “bottom”, “upper” or “top” are used to describe the position of one element relative to another. It should be appreciated that if a device is flipped upside down, an element that is “lower” will become an element that is “upper”. 
     It should be understood that, although the terms first, second, third etc. may be used herein to describe various elements, components, regions, layers, portions and/or sections, these elements, components, regions, layers, portions and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer, portion or section from another element, component, region, layer or section. Thus, a first element, component, region, layer, portion or section discussed below could be termed a second element, component, region, layer, portion or section without departing from the teachings of the present disclosure. 
     The terms “about” and “substantially” typically mean +/−10% of the stated value, more typically mean +/−5% of the stated value, more typically +/−3% of the stated value, more typically +/−2% of the stated value, more typically +/−1% of the stated value and even more typically +/−0.5% of the stated value. The stated value of the present disclosure is an approximate value. When there is no specific description, the stated value includes the meaning of “about” or “substantially”. 
     Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It should be appreciated that, in each case, the term, which is defined in a commonly used dictionary, should be interpreted as having a meaning that conforms to the relative skills of the present disclosure and the background or the context of the present disclosure, and should not be interpreted in an idealized or overly formal manner unless so defined. 
     In accordance with some embodiments of the disclosure, high dynamic range (HDR) may be achieved by disposing a light-guiding structure in the interlayer of the image sensor. Specifically, the light-guiding structure with high light transmission may be disposed and above large photodiodes to increase the sensitivity of the large photodiodes, while the light guiding structure with high light attenuation may be disposed and above small photodiodes to decrease the sensitivity of the small photodiodes. Accordingly, a greater sensitivity ratio of the large photodiodes to the small photodiodes may be achieved, thereby realizing better HDR imaging. 
     Referring to  FIG. 1A ,  FIG. 1A  is a cross-sectional diagram of an image sensor  10  in accordance with some embodiments of the disclosure. The image sensor  10  includes a substrate  100 , first photodiodes  102 A, second photodiodes  102 B, an interlayer  104 , a light-guiding structure  106 A, and a micro-lens layer  108 . In some embodiments, the substrate  102  may be, for example, a wafer or a chip, but the present disclosure is not limited thereto. In some embodiments, the substrate  102  may be a semiconductor substrate, for example, silicon substrate. Furthermore, in some embodiments, the semiconductor substrate may also be an elemental semiconductor including germanium, a compound semiconductor including gallium nitride (GaN), silicon carbide (SiC), gallium arsenide (GaAs), gallium phosphide (GaP), indium phosphide (InP), indium arsenide (InAs), and/or indium antimonide (InSb), an alloy semiconductor including silicon germanium (SiGe) alloy, gallium arsenide phosphide (GaAsP) alloy, aluminum indium arsenide (AlInAs) alloy, aluminum gallium arsenide (AlGaAs) alloy, gallium indium arsenide (GaInAs) alloy, gallium indium phosphide (GaInP) alloy, and/or gallium indium arsenide phosphide (GaInAsP) alloy, or a combination thereof. 
     The first photodiodes  102 A and the second photodiodes  102 B are alternately disposed in the substrate  100 . The area of the cross-section of the first photodiodes  102 A is smaller than the area of the cross-section of the second photodiodes  102 B. Furthermore, from a top view of the image sensor  10  (not shown), the area of each of the first photodiodes  102 A is also smaller than the area of each of the second photodiodes  102 B. 
     The interlayer  104  is disposed on the substrate  100 . In some embodiments, the interlayer  104  may include an organic transparent material, a dielectric material, a semiconductor material such as silicon, any other suitable transparent material, or a combination thereof More specifically, the material of the interlayer  104  may have a light transmittance to light with a wavelength in a range from 200 nm to 1100 nm greater than 90%, or preferably greater than 95%. In some embodiments, the dielectric material includes silicon oxide, silicon nitride, silicon oxynitride, any other suitable dielectric material, or a combination thereof The interlayer  104  may be formed using suitable deposition techniques, such as a spin-on coating process, chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), other suitable deposition methods, or a combination thereof. 
     In some embodiments, the extinction coefficient of the interlayer  104  may be between about 0.001 and about 0.01, such as about 0.005. In some embodiments, the refractive index of the interlayer  104  may be between about 1.2 and about 1.8, such as about 1.6. 
     The light-guiding structure is disposed in the interlayer  104  and over at least one of the first photodiodes  102 A or the second photodiodes  102 B. In particular, in some embodiments, the light-guiding structure may be disposed over at least one of the first photodiodes  102 A only, or may be disposed over at least one of the second photodiodes  102 B only. In other embodiments, the light-guiding structure may also be disposed over at least one of the first photodiodes  102 A and at least one of second photodiodes  102 B. That is, the light-guiding structure may be disposed over one or more of the first photodiodes  102 A and one or more of the second photodiodes  102 B simultaneously. 
     According to some embodiments of the disclosure, as shown in  FIG. 1A , the light-guiding structure  106 A may be disposed in the interlayer  104  and over part of the first photodiodes  102 A, but the present disclosure is not limited thereto. It should be noted that other aspects with respect to the arrangement of the light-guiding structure will be described and shown in the following context and figures. 
     In some embodiments, the light-guiding structure  106 A may include an organic material, such as an acrylate polymer. For example, the acrylate polymer may be formed of methyl methacrylate, ethyl methacrylate, N-butyl methacrylate, sec-butyl methacrylate, tern-butyl methacrylate, methyl acrylate, isopropyl acrylate, cyclohexyl methacrylate, 2-methyl cyclohexyl methacrylate, dicyclopentenyl acrylate, dicyclopentanyl acrylate, dicyclopentenyl methacrylate, dicyclopentanyl methacrylate, dicyclopentanyloxyethyl methacrylate, isobornyl methacrylate, cyclohexyl acrylate, 2-methylcyclohexyl acrylate, dicyclopentanyloxyethyl acrylate, isobomyl acrylate, phenyl methacrylate, phenyl acrylate, benzyl acrylate, 2-hydroxyethyl methacrylate, or a combination thereof. Furthermore, the light-guiding structure  106 A may further include additional organic materials to adjust the extinction coefficient and the refractive index of the light-guiding structure  106 A within the desired range. In some embodiments, the additional organic materials may include propylene glycol alkyl ether acetates, methoxy-containing organic esters, or a combination thereof For example, the propylene glycol alkyl ether acetates may include propylene glycol methyl ether acetate, propylene glycol ethyl ether acetate, propylene glycol propyl ether acetate and propylene glycol butyl ether acetate, or a combination thereof. For example, the methoxy-containing organic esters may include methyl methoxy acetate, ethyl methoxy acetate, propyl methoxy acetate, butyl methoxy acetate, methyl 2-methoxypropionate, ethyl 2-methoxypropionate, propyl 2-methoxypropionate, butyl 2-methoxypropionate, methyl 3-methoxypropionate, ethyl 3-methoxypropionate, propyl 3-methoxypropionate, butyl 3-methoxypropionate, or a combination thereof. 
     In some embodiments, the light-guiding structure  106 A may be formed by forming openings (not shown) for the light-guiding structure  106 A in the interlayer  104  followed by depositing the material of the light-guiding structure  106 A using any suitable process, such as a photolithography processes. For example, the photolithography process may include coating, exposure, developing, other suitable processes, or a combination thereof Then, excess material of the light-guiding structure  106 A may be removed using any suitable planarization process, such as chemical mechanical polishing (CMP), such that the top surfaces of the interlayer  104  and the light-guiding structure  106 A are level. 
     It is beneficial to use organic materials for the light-guiding structure  106 A since the refractive index or the extinction coefficient of the light guiding structure  106 A may be adjusted by altering the amounts of the respective organic materials depending on the design demand. Furthermore, compared with the conventional processes for materials other than organic materials by physical vapor deposition, the complexity of the forming process of the light-guiding structure  106 A using the organic materials may be reduced as 
     In addition, in some embodiments, the light-guiding structure  106 A may have a rectangular or a trapezoidal shape in the cross-sectional view. Moreover, in some embodiments, an angle θ 1  between the sidewall and the top surface of the light-guiding structure  106 A may be between about 65°and about 90°, such as about 75° or about 80°. Given the light-guiding structure  106 A with the fixed top surface area, the volume of the light-guiding structure  106 A may be tuned by altering the angle θ 1  of the light-guiding structure  106 A, thereby adjusting the light attenuation efficiency of the light-guiding structure  106 A to achieve desired effect according to the design demand. 
     In some embodiments, the extinction coefficient of the light-guiding structure  106 A may be between about 0.1 and about 0.3. such as about 0.2. The refractive index of the light-guiding structure  106 A is greater than the interlayer  104 . In some embodiments, the refractive index of the light-guiding structure  106 A may be between about 1.4 and about 2.0, such as about 1.7. The light-guiding structure  106 A with higher refractive index may enable the incident light to enter the light-guiding structure  106 A rather than the interlayer  104  in the proximity of the light-guiding structure  106 A. In addition, the light-guiding structure  106 A having the extinction coefficient within the above range may decrease the sensitivity of the first photodiodes  102 A that is disposed below the light-guiding structure  106 A, thereby increasing the sensitivity ratio of the second photodiodes  102 B to the first photodiodes  102 A and achieving a high dynamic range. 
     The micro-lens layer  108  is disposed on the interlayer  104 . In some embodiments, the micro-lens layer  108  may include a plurality of micro-lenses  108 M, and each of the micro-lenses  108 M may be disposed over one of the first photodiodes  102 A and one of the second photodiodes  102 B. In some embodiments, the material of micro-lens layer  108  may a transparent material. More specifically, the material of the micro-lens layer  108  may have a light transmittance to light with a wavelength in a ramie from 200 nm to 1100 nm greater than 90%, or preferably greater than 95%. For example, the material may include epoxy resin, silicone resin, polyurethane, any other applicable material, or a combination thereof. The micro-lens layer  108  may be formed by depositing the material of the micro-lens layer  108  followed by patterning the material of the micro-lens layer  108 . The micro-lenses  108 M of the micro-lens layer  108  may be formed to have a desired shape, such as a dome shape as shown in  FIG. 1A . 
     Still referring to  FIG. 1A , in some embodiments, the image sensor  10  may further include a color filter array  110  disposed between the interlayer  104  and the micro-lens layer  108 . The color filter array  110  may have a plurality of color filters  110 A,  110 B and  110 C. As shown in  FIG. 1A , in some embodiments, each of the color filters  110 A,  110 B and  110 C may overlap two adjacent micro-lenses  108 M in the micro-lens layer  108 . Furthermore, in some embodiments, each of the color filters  110 A,  110 B and  110 C may correspond to one of the first photodiodes  102 A below one of the micro-lenses  108 M and one of the second photodiodes  102 B below another one of the micro-lenses  108 M that is adjacent to the former one of the micro-lenses  108 M. That is, in these embodiments, the arrangement of color filters  110 A,  110 B and  110 C is offset from the arrangement of the micro-lenses  108 M such that each of the color filters  110 A,  110 B and  110 C does not correspond to one of the first photodiodes  102 A and one of the second photodiodes  102 B below the same micro-lens  108 M. In the embodiments shown in  FIG. 1A , the bottom surface of the light-guiding structure  106 A may contact the first photodiodes  102 A, and the top surface of the light-guiding  106 A may the color filter array  110  as well. 
     In sonic embodiments, the color filters  110 A,  110 B and  110 C may have different colors from one another. For example, the color of the color filters  110 A,  110 B and  110 C may be red, green, blue, or white. The color filter a  110  may be formed in sequence by a coating, exposure, and development process at different steps. Alternatively, the color filter array  110  may be formed by ink-jet printing. 
     Still referring to  FIG. 1A , the image sensor  10  may further include a passivation layer  112 . The passivation layer  112  may be deposited conformally on the micro-lens layer  108  to cover the entire surface of the respective micro-lens  108 M. The material of the passivation layer  112  may be similar to or the same as that of the micro-lens layer  108 , which is not repeated herein. However, in some embodiments, the refractive index of the passivation layer  112  may be less than the refractive index of the micro-lens layer  108  so that the incident light may enter the image sensor  10  in a gradual manner. The passivation layer  112  may also protect the micro-lens layer  108 . 
     Still referring to  FIG. 1A , the image sensor  10  may further include a wiring layer  114  disposed in the interlayer  104 . The wiring layer  114  may be metal wiring lines that interconnect the first photodiodes  102 A, the second photodiodes  102 B, and the transistors (not shown) with the peripheral circuits and the outside of the device, respectively. In some embodiments, the material of the wiring layer  114  may include silver (Ag), aluminum (Al), gold (Au), copper (Cu), niobium (Nb), nickel (Ni), titanium (Ti), tungsten (W), silver alloy, aluminum alloy, gold alloy, copper alloy, niobium alloy, nickel alloy, titanium alloy, tungsten alloy, or a combination thereof. 
     As described above, according to the embodiments of the disclosure, the image sensor  10  may include the light-guiding structure  106 A disposed in the interlayer  104  and over at least one of the first photodiodes  102 A (i.e., small photodiodes). The refractive index of the light-guiding structure  106 A is greater than the refractive index of the interlayer  104 , and the light-guiding structure  106 A may have high light attenuation efficiency. Therefore, the sensitivity of part of the first photodiodes  102 A (i.e., small photodiodes) may be reduced, and the sensitivity ratio of the second photodiodes  102 B (i.e., large photodiodes) to the first photodiodes  102 A may be increased. High dynamic range imaging may be realized using the image sensor  10  provided by the embodiments of the disclosure. 
     Next, referring to  FIG. 1B ,  FIG. 1B  is a cross-sectional diagram of an image sensor  20  in accordance with other embodiments of the disclosure. The image sensor  20  in  FIG. 1B  is similar to the image sensor  10  in  FIG. 1A , except that the light-guiding structure  106 A is disposed over all of the first photodiodes  102 A. In this way, the sensitivity ratio of the second photodiodes  102 B to the first photodiodes  102 A may be further increased to achieve better high dynamic range. 
     Next, referring to  FIG. 1C ,  FIG. 1C  is a cross-sectional diagram of an image sensor  30  in accordance with other embodiments of the disclosure. The image sensor  30  in  FIG. 1C  is similar to the image sensor  10  in  FIG. 1A , except that the image sensor  30  includes the light-guiding structure  106 B instead of the light-guiding structure  106 A. According to some embodiments of the disclosure, as shown in  FIG. 1C , the light-guiding structure  106 B may be disposed in the interlayer  104  and over part of the second photodiodes  102 B (i.e., large photodiodes). In addition, in some embodiments, the extinction coefficient of the light-guiding structure  106 B may be less than the extinction coefficient of the light-guiding structure  106 A, and thus the light-guiding structure  106 B may have better light transmission efficiency. 
     In some embodiments, the light-guiding structure  106 B may include an organic material, such as a resin polymer. For example, the resin polymer may include an epoxy resin; an acrylic resin such as polymethyl methacrylate (PMMA); various resins such as polydimethylsiloxane (PDMS), polycarbonate (PC), polyester, polyketone, polyurethane, polyimide, polyvinyl alcohol, fluororesin, and polyolefin; or a combination thereof in some specific embodiments, the light-guiding structure  106 B may be formed of polydimethylsiloxane (PDMS), polymethyl methacrylate (PMMA), polycarbonate (PC), or a combination thereof The forming method of the light-guiding structure  106 B may be similar to or the same as the forming method of the light-guiding structure  106 A, which is not repeated herein. 
     It is beneficial to use organic materials for the light-guiding structure  106 B since the refractive index or the extinction coefficient of the light guiding structure  106 B may be adjusted by altering the composition of the organic material depending on the design demand. Furthermore, as described above, compared with the conventional processes for materials other than organic materials by physical vapor deposition, the complexity of the forming process of the light-guiding structure  106 B using the organic materials may be reduced as well. 
     In addition, in some embodiments, the light-guiding structure  106 B may have a rectangular or a trapezoidal shape in the cross-sectional view. Moreover, in some embodiments, an angle θ 2  between the sidewall and the top surface of the light-guiding structure  106 B may be between about 65° and about 90°, such as about 75° or about 80°. Given the light-guiding structure  106 B with the fixed top surface area, the volume of the light-guiding structure  106 B may be tuned by altering the angle θ 2  of the light-guiding structure  106 B, thereby adjusting the light transmission efficiency of the light-guiding structure  106 B to achieve desired effect according to the design demand. 
     In some embodiments, the extinction coefficient of the light-guiding structure  106 B may be between about 0.001 and about 0.01, such as about 0.005. The refractive index of the light-guiding structure  106 B is greater than the interlayer  104 . In some embodiments, the refractive index of the light-guiding structure  106 B may be between about 1.4 and about 2.0, such as about 1.7. The light-guiding structure  106 B with higher refractive index may enable the incident light to enter the light-guiding structure  106 B rather than the interlayer  104  in the proximity of the light-guiding structure  106 B. In addition, the light-guiding structure  106 B haying the extinction coefficient within the above range may increase the sensitivity of the second photodiodes  102 B that is disposed below the light-guiding structure  106 B, thereby increasing the sensitivity ratio of the second photodiodes  102 B to the first photodiodes  102 A and achieving desired high dynamic range. 
     Next, referring to  FIG. 1D ,  FIG. 1D  is a cross-sectional diagram of an image sensor  40  in accordance with other embodiments of the disclosure. The image sensor  40  in  FIG. 1D  is similar to the image sensor  30  in  FIG. 1C , except that the light-guiding structure  106 B is disposed over all of the second photodiodes  102 B. In this way, the sensitivity ratio of the second photodiodes  102 B to the first photodiodes  102 A may be further increased to achieve better high dynamic range. 
     Next, referring to  FIG. 1E ,  FIG. 1E  is a cross-sectional diagram of an image sensor  50  in accordance with other embodiments of the disclosure. The image sensor  50  in  FIG. 1E  is similar to the image sensor  10  in  FIG. 1A , except that the image sensor  50  further includes the light-guiding structure  106 B. The light-guiding structure  106 B may be disposed in the interlayer  104  and over part of the second photodiodes  102 B. It should be noted that, in the embodiments shown in  FIG. 1E , the light-guiding structures  106 A and  106 B may be respectively disposed over part of the first photodiodes  102 A and part of the second photodiodes  102 B below the same color filters. That is, the light-guiding structures  106 A and  106 B may be disposed below part of the color filters instead of all of the color filters. For example, as shown in  FIG. 1E , the light-guiding structures  106 A and  106 B may be disposed over the first photodiode  102 A and the second photodiode  102 B below the color filter  110 A and/or  110 C, whereas the light-guiding structures  106 A and  106 B may not be disposed over the first photodiode  102 A and the second photodiode  102 B below the color filter  110 B. 
     By disposing the light-guiding structures  106 A and  106 B over part of the first photodiodes  102 A and part of the second photodiodes  102 B simultaneously, the sensitivity of the first photodiodes  102 A may be reduced, and the sensitivity of the second photodiodes  102 B may be increased. Therefore, the sensitivity ratio of the second photodiodes  102 B to the first photodiodes  102 A may be increased to achieve better high dynamic range. 
     Next, referring to  FIG. 1F ,  FIG. 1F  is a cross-sectional diagram of an image sensor  60  in accordance with other embodiments of the disclosure. The image sensor  60  in  FIG. 1F  is similar to the image sensor  50  in  FIG. 1E , except that the light-guiding structures  106 A and  106 B are disposed over all of the first photodiodes  102 A and second photodiodes  102 B. Meanwhile, the light-guiding structures  106 A and  106 B may be disposed below all of the color filters  110 A,  110 B, and  1100 . By this way, the sensitivity ration of the second photodiodes  102 B to the first photodiodes  102 A may be further increased, thereby providing better high dynamic range. 
     Referring to  FIG. 2A and 2B ,  FIG. 2A  is a top view diagram of an image sensor  10  in accordance with some embodiments of the disclosure, and  FIG. 2B  is an enlarged top view diagram of an image sensor in accordance with some embodiments of the disclosure. It should be noted that the cross-sectional diagrams of  FIGS. 1A  is taken along the line A-A′ in  FIG. 2A . In addition, in  FIGS. 2A and 2B , the passivation layer  112  is omitted merely for brevity. 
     In some embodiments, as shower in  FIG. 2A , the image sensor  10  may be formed of a minim um repeating unit  116 . The minimum repeating unit  116  may be a sensor array defined by four acro-lenses  108 M that are arranged in 2×2. The enlarged diagram of the minimum repeating unit  116  is shown in  FIG. 2B . In some embodiment, the color filters  110 A,  110 B, and  110 C may have a rectangular shape, a square shape, or a combination thereof. As shown in  FIG. 2B , in the minimum repeating unit  116 , the color filter  110 A has a square shape, the color filter  110 B has a rectangular shape or a square shape, and the color filter  110 C has a rectangular shape, but the present disclosure is not limited thereto. In other embodiments where the minimum repeating unit  116  is defined by other micro-lenses  108 M arranged in 2×2, the color filter  110 A may also have a rectangular shape, and the color filter  110 C may also have a square shape. 
     As described previously, in  FIG. 2B , each of the color filters  110 A,  110 B, and  110 C may overlap two adjacent micro-lenses  108 M. In addition, any two adjacent color filters  110 A,  110 B, and  110 C may have different colors. 
     In summary, according to some embodiments of the disclosure, the image sensor may include light-guiding structure disposed over at least one of the first photodiodes (i.e., small photodiodes) or second photodiodes (i.e., large photodiodes). More specifically, the light-guiding structure with high light transmission may be disposed in the interlayer and above large photodiodes to increase the sensitivity of the large photodiodes, and the light guiding structure with high light attenuation may be disposed in the interlayer and above small photodiodes to decrease the sensitivity of the small photodiodes. Accordingly, greater sensitivity ratio of the large photodiodes to the small photodiodes may be achieved, and image sensors with higher sensitivity ratio may realize HDR imaging. 
     Although some embodiments of the present disclosure and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the disclosure as defined by the appended claims. For example, it will be readily understood by one of ordinary skill in the art that many of the features, functions, processes, and materials described herein may be varied while remaining within the scope of the present disclosure. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the present disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present disclosure. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.