Back-illuminated image sensor and method for manufacturing the same

Abstract

The present disclosure relates to a back-illuminated image sensor and a manufacturing method thereof, and relates to the field of integrated circuit technologies. The manufacturing method includes: providing a substrate, the substrate including opposite first and second surfaces, a first isolation structure being formed in the substrate, the first isolation structure extending from the first surface to the second surface; forming a second isolation structure and a metal grid, the second isolation structure being disposed corresponding to the first isolation structure on the first surface, the second isolation structures being spaced apart on the first surface, the second isolation structure and the metal grid being arranged in sequence along a direction away from the first surface; forming a photodiode between the second isolation structures, the photodiode and the second isolation structures being alternately disposed on the first surface; forming a filter element on a side of the photodiode away from the substrate, the filter element being located between adjacent metal grids; the present disclosure reduces the crosstalk problem of the back-illuminated image sensor.

Description

Technical Field

[0001] The present disclosure relates to the field of integrated circuit technologies, and particularly to a back-illuminated image sensor and a manufacturing method thereof. Background Art

[0002] A back-illuminated (BSI) image sensor is a type of image sensor. Under low light conditions, the BSI image sensor has better performance compared to a front-illuminated image sensor.

[0003] However, the crosstalk effect of the back-illuminated image sensor is relatively serious, which limits the application of the back-illuminated image sensor. Summary of the Invention

[0004] Based on this, it is necessary to provide a back-illuminated image sensor and a manufacturing method thereof for the problem of serious crosstalk in the existing back-illuminated image sensor.

[0005] In a first aspect, the present disclosure provides a manufacturing method of a back-illuminated image sensor, including:

[0006] Providing a substrate, the substrate includes opposite first and second surfaces, and a first isolation structure is formed in the substrate, and the first isolation structure extends from the first surface to the second surface;

[0007] Forming a second isolation structure and a metal grid, the second isolation structure is disposed corresponding to the first isolation structure on the first surface, the second isolation structures are spaced apart on the first surface, and the second isolation structure and the metal grid are arranged in sequence along a direction away from the first surface;

[0008] Forming a photodiode between the second isolation structures, and the photodiode and the second isolation structure are alternately disposed on the first surface;

[0009] Forming a filter element on a side of the photodiode away from the substrate, and the filter element is located between adjacent metal grids.

[0010] Optionally, forming the second isolation structure and the metal grid includes:

[0011] Forming a metal stack on the first surface, the metal stack includes multiple stacked metal layers;

[0012] Patterning the metal stack, the top metal layer of the metal stack forms the metal grid, and the metal layer below the metal grid forms the second isolation structure.

[0013] Optionally, during the process of patterning the metal stack, a dry process is used to etch the metal stack. As the etching depth increases, the etching process parameters are adjusted to gradually increase the etching rate in the horizontal direction, so that in the direction away from the first surface, the horizontal dimension of the second isolation structure gradually increases and the horizontal dimension of the metal grid gradually increases.

[0014] Optionally, a photodiode is formed between the second isolation structures, including: epitaxially forming a first functional layer, a second functional layer, and a third functional layer in sequence on the first surface exposed by the second isolation structures, and the top surface of the third functional layer is on the same horizontal plane as the top surface of the second isolation structures.

[0015] Optionally, in the direction from the filter element to the first surface, the horizontal dimension of the photodiode gradually increases.

[0016] In a second aspect, the present disclosure provides a back-illuminated image sensor, including:

[0017] A substrate, the substrate includes opposite first and second surfaces, and a first isolation structure is formed in the substrate, and the first isolation structure extends from the first surface to the second surface;

[0018] A second isolation structure, the second isolation structure is disposed corresponding to the first isolation structure on the first surface, and the second isolation structures are spaced apart on the first surface;

[0019] A metal grid, disposed on a side of the second isolation structure away from the first surface, and the second isolation structure and the metal grid are integrally formed;

[0020] A photodiode, disposed between the second isolation structures, and the photodiode and the second isolation structures are alternately disposed on the first surface;

[0021] A filter element, disposed on a side of the photodiode away from the first surface, and the filter element is located between adjacent metal grids.

[0022] Optionally, in the direction away from the first surface, the horizontal dimension of the second isolation structure gradually increases and the horizontal dimension of the metal grid gradually increases;

[0023] In the direction from the filter element to the first surface, the horizontal dimension of the photodiode gradually increases.

[0024] Optionally, the photodiode includes a first functional layer, a second functional layer, and a third functional layer stacked in sequence in the direction away from the first surface.

[0025] Optionally, the top surface of the third functional layer and the top surface of the second isolation structure are located on the same horizontal plane.

[0026] Optionally, the second isolation structure includes multiple metal layers stacked in sequence in a direction away from the first surface.

[0027] The unexpected technical effect of the present disclosure is that after forming the second isolation structure and the metal grid by optimizing the process, a photodiode is formed between the second isolation structures. The photodiode can be formed without etching, which can avoid etching damage to the photodiode, ensure the structural integrity of the photodiode, and at the same time avoid residual photosensitive materials after etching, and prevent electrons from moving between the photodiodes through the residual photosensitive materials, thereby improving the crosstalk problem of the back-illuminated image sensor. Description of the Drawings

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure or in the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present disclosure. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0029] Figure 1 It is a process flow chart of a manufacturing method of a back-illuminated image sensor provided in an embodiment;

[0030] Figure 2 It is a cross-sectional schematic diagram of a substrate provided in an embodiment;

[0031] Figure 3 It is a cross-sectional schematic diagram after forming a metal stack on the first surface provided in an embodiment;

[0032] Figure 4 It is a cross-sectional schematic diagram after forming the second isolation structure and the metal grid provided in an embodiment;

[0033] Figure 5 It is a cross-sectional schematic diagram after forming the first functional layer provided in an embodiment;

[0034] Figure 6 It is a cross-sectional schematic diagram after forming the second functional layer provided in an embodiment;

[0035] Figure 7 It is a cross-sectional schematic diagram after forming a photodiode between the second isolation structures provided in an embodiment;

[0036] Figure 8 It is a cross-sectional schematic diagram of a back-illuminated image sensor provided in an embodiment.

[0037] Description of reference numerals:

[0038] 10. Substrate; 10a. First surface; 10b. Second surface; 11. First isolation structure; 12. Isolation layer; 13. Logic circuit layer; 20. Second isolation structure; 30. Metal grid; 40. Photodiode; 41. First functional layer; 42. Second functional layer; 43. Third functional layer; 50. Filter element; 51. Filter; 52. Filter; 60. Metal stack; 61. First metal layer; 62. Second metal layer; 63. Third metal layer; 64. Fourth metal layer; 65. Fifth metal layer. DETAILED DESCRIPTION

[0039] In order to facilitate understanding of the present disclosure, the present disclosure will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present disclosure are shown in the drawings. However, the present disclosure can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present disclosure more thorough and comprehensive.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present disclosure belongs. The terms used herein in the specification of the present disclosure are only for the purpose of describing specific embodiments and are not intended to limit the present disclosure.

[0041] Research has found that when the front end of line (FEOL) of a back-illuminated image sensor is formed into a photodiode (PD), a photosensitive stack is usually formed on the substrate, and then the photosensitive stack is etched to form a photodiode, and a deep trench isolation structure is formed between the photodiodes to isolate the photodiodes. However, the etching process may damage the photodiode, and the photosensitive material may be etched away. Electrons move between the photodiodes through the residual photosensitive material, causing crosstalk problems in back-illuminated image sensors.

[0042] In addition, the use of high-energy ion implantation in the process of forming photodiodes can cause damage to the substrate. Electrons may move between photodiodes or to other structures through the damaged area of ​​the substrate, affecting the performance and stability of the photodiode and causing crosstalk problems in the back-illuminated image sensor.

[0043] In view of this, the present disclosure provides a back-illuminated image sensor and a manufacturing method thereof. After forming a second isolation structure and a metal grid by optimizing the process, a photodiode is formed between the second isolation structures without etching, which can avoid etching damage to the photodiode, ensure the structural integrity of the photodiode, and at the same time avoid residual photosensitive materials after etching, and prevent electrons from moving between photodiodes through the residual photosensitive materials, thereby improving the crosstalk problem of the back-illuminated image sensor.

[0044] According to an exemplary embodiment, the present disclosure provides a manufacturing method of a back-illuminated image sensor. As Figure 1 shown, the manufacturing method of the back-illuminated image sensor includes the following steps:

[0045] Step S10: Provide a substrate. The substrate includes opposite first and second surfaces, and a first isolation structure is formed in the substrate, and the first isolation structure extends from the first surface to the second surface.

[0046] Step S20: Form a second isolation structure and a metal grid. The second isolation structure is disposed corresponding to the first isolation structure on the first surface, the second isolation structures are spaced apart on the first surface, and the second isolation structure and the metal grid are arranged in sequence along a direction away from the first surface.

[0047] Step S30: Form a photodiode between the second isolation structures. The photodiode and the second isolation structure are alternately arranged on the first surface.

[0048] Step S40: Form a filter element on a side of the photodiode away from the substrate. The filter element is located between adjacent metal grids.

[0049] Figures 2 - 8 shows a schematic diagram of each stage of the manufacturing method of a semiconductor structure in some embodiments of this example. The following will refer to Figures 2 - 8 to introduce the manufacturing method of a semiconductor structure in some embodiments of this example.

[0050] In step S10, the substrate 10 may be a semiconductor substrate. The material of the semiconductor substrate may include silicon (Si), silicon germanium (SiGe), silicon germanium carbide (SiGeC), silicon carbide (SiC), gallium arsenide (GaAs), indium arsenide (InAs), indium phosphide (InP), or other III / V semiconductor materials or II / VI semiconductor materials. Or, for another example, the semiconductor substrate may be a layered substrate including, such as Si / SiGe, Si / SiC, silicon on insulator (SOI), or silicon germanium on insulator. In this embodiment, the substrate 10 is a silicon substrate.

[0051] Please refer to Figure 1As shown, the substrate 10 includes a first surface 10a and a second surface 10b which are oppositely arranged. A first isolation structure 11 (shallow trench isolation structure) is formed in the substrate 10. The first isolation structure 11 extends from the first surface 10a to the second surface 10b. That is, the first surface 10a includes the surface of the semiconductor substrate and the surface of the first isolation structure 11.

[0052] It should be noted that the first surface 10a and the second surface 10b are used to distinguish the two surfaces of the substrate 10. Among them, the first surface 10a is the side of the back-illuminated image sensor for receiving incident light, and the second surface 10b is arranged relative to the first surface 10a.

[0053] Exemplarily, the substrate 10 can be fabricated by the following implementation: providing a semiconductor substrate, forming a photoresist layer on the second surface 10b of the semiconductor substrate, and patterning the semiconductor substrate according to the photoresist layer to form shallow trenches. After forming the shallow trenches, an isolation medium is deposited in the shallow trenches, and the isolation medium is, for example, an insulating substance such as silicon oxide. The first isolation structure 11 is formed in the shallow trenches. Then, the back surface of the semiconductor substrate is polished by a chemical mechanical polish (CMP) process until the surface of the first isolation structure 11 is exposed to obtain the substrate 10, and the first surface 10a opposite to the second surface 10b is formed.

[0054] In some embodiments, please refer to Figure 2 As shown, an isolation layer 12 and a logic circuit layer 13 are further formed on the second surface 10b of the substrate 10 in sequence. A plurality of logic control devices are formed in the logic circuit layer 13. The plurality of logic control devices can control the photodiode 40 to perform photoelectric conversion to form an electrical signal, quantify the electrical signal through analog-to-digital conversion, and read out the converted digital signal.

[0055] In step S20, forming the second isolation structure 20 and the metal grid 30 includes the following steps:

[0056] Step S21: Forming a metal stack 60 on the first surface 10a. The metal stack 60 includes multiple stacked metal layers.

[0057] Please refer to Figure 3 As shown, multiple metal layers can be deposited on the first surface 10a by atomic layer deposition (ALD) or physical vapor deposition (PVD) to form the metal stack 60. The metal stack 60 can include two, three, four, five or more metal layers.

[0058] In some embodiments, the metal stack 60 includes a first metal layer 61, a second metal layer 62, a third metal layer 63, a fourth metal layer 64, and a fifth metal layer 65 that are sequentially stacked on the first surface 10a. Among them, the material of the first metal layer 61 includes hafnium oxide (HfO), the material of the second metal layer 62 includes titanium nitride (TiN), the material of the third metal layer 63 includes tantalum nitride (TaN), the material of the fourth metal layer 64 includes titanium aluminide (TiAl), and the material of the fifth metal layer 65 includes aluminum (Al).

[0059] Step S22: Pattern the metal stack 60. The top metal layer of the metal stack 60 forms a metal grid 30, and the metal layers below the metal grid 30 form a second isolation structure 20.

[0060] Please refer to Figure 3 、 Figure 4 As shown, a photoresist layer (not shown in the figure) is formed on the side of the metal stack 60 away from the first surface 10a. The photoresist layer is exposed and developed to define the pattern of the metal grid 30 in the photoresist layer. Then, the metal stack 60 is etched according to the photoresist layer to the first surface 10a, and at the same time, the second isolation structure 20 and the metal grid 30 are formed. The top metal layer of the metal stack 60 is etched to form the metal grid 30, and the multi-layer metal layers covered below the metal grid 30 form the second isolation structure 20. In this embodiment, the fifth metal layer 65 forms the metal grid 30, and the second isolation structure 20 includes the first metal layer 61, the second metal layer 62, the third metal layer 63, and the fourth metal layer 64 that are sequentially stacked on the first surface 10a.

[0061] In this way, the second isolation structure 20 and the metal grid 30 are integrally formed in the same patterning process, streamlining the process steps, which is beneficial to improving the process efficiency. At the same time, the second isolation structure 20 and the metal grid 30 are integrally formed, avoiding the problem of alignment deviation between the metal grid 30 and the second isolation structure 20, improving the connection firmness between the metal grid 30 and the second isolation structure 20, and improving the structural stability and product yield of the back-illuminated image sensor.

[0062] Moreover, the second isolation structure 20 of this embodiment includes multi-layer metal layers. The second isolation structure 20 and the metal grid 30 form a composite metal grid 30 (Composite Metal Grid, CMG), which can further enhance the isolation effect of the second isolation structure 20, avoid the electron overflow of the photodiode 40, and the composite metal grid 30 helps to further improve the anti-crosstalk ability of the back-illuminated image sensor and improve the image quality of the back-illuminated image sensor.

[0063] In this embodiment, the second isolation structure 20 is arranged corresponding to the first isolation structure 11, the second isolation structures 20 are arranged at intervals on the first surface 10a, and the second isolation structures 20 expose the surface of the substrate 10 on the first surface 10a except for the first isolation structure 11.

[0064] In some embodiments, the horizontal dimension of the side of the second isolation structure 20 away from the first surface 10a is greater than the horizontal dimension of the side of the second isolation structure 20 close to the first surface 10a; the horizontal dimension of the side of the metal grid 30 away from the second isolation structure 20 is greater than the horizontal dimension of the side of the second isolation structure 20 close to the first surface 10a. Thus, the space between the second isolation structures 20 is increased, the size of the subsequent formed photodiode 40 can be increased, the area of the photosensitive region of the back-illuminated image sensor can be increased, the light flux can be increased, which is beneficial to improving the sensitivity of the back-illuminated image sensor to light and improving the display effect of the back-illuminated image sensor.

[0065] In some embodiments, please refer to Figure 3 As shown, during the patterning of the patterned metal stack 60, a dry process is used to etch the metal stack 60. As the etching depth increases, the etching process parameters are adjusted, and the etching rate in the horizontal direction is gradually increased, so that in the direction away from the first surface 10a, the horizontal dimension of the second isolation structure 20 gradually increases and the horizontal dimension of the metal grid 30 gradually increases.

[0066] The multi-layer metal layers of the metal stack 60 are made of different materials, and the reaction rates of the multi-layer metal layers in the dry etching process may be different. By adjusting the etching gas and process conditions, the etching rate of the metal layer can be made larger closer to the first surface 10a, so that after etching is completed, in the direction away from the first surface 10a, the horizontal dimension of the second isolation structure 20 gradually increases and the horizontal dimension of the metal grid 30 gradually increases.

[0067] Alternatively, during the etching process, the etching process parameters can also be gradually adjusted, such as increasing the flow rate of the etching gas, increasing the plasma density, changing the type of the etching gas, or increasing the bias power applied to the plasma, so as to gradually increase the etching rate in the horizontal direction as the etching depth increases, so that after etching is completed, in the direction away from the first surface 10a, the horizontal dimension of the second isolation structure 20 gradually increases and the horizontal dimension of the metal grid 30 gradually increases.

[0068] Wherein, the "horizontal dimension" in the present disclosure refers to the dimension of the structure in the direction parallel to the first surface 10a of the substrate 10.

[0069] In step S30, refer to Figure 5 、 Figure 6 、 Figure 7As shown, a photodiode 40 is formed on the first surface 10a exposed by the second isolation structure 20 using an epitaxial process.

[0070] In some embodiments, forming a photodiode 40 between the second isolation structures 20 includes: epitaxially forming a first functional layer 41, a second functional layer 42, and a third functional layer 43 in sequence on the first surface 10a exposed by the second isolation structure 20, and the top surface of the third functional layer 43 is in the same horizontal plane as the top surface of the second isolation structure 20. It can be understood that in other embodiments, four, five, or more functional layers can be epitaxially formed on the first surface 10a exposed by the second isolation structure 20, and the present disclosure does not limit this.

[0071] Among them, the materials of the functional layers of the photodiode 40 include compounds of Group VA elements and silicon. Group VA elements include nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi), and moscovium (Mc), etc. By way of example, the material of each functional layer can include silicon phosphide, silicon arsenide, or silicon antimonide, etc.

[0072] In some embodiments, by controlling the concentration of Group VA elements in each functional layer, the closer the photodiode 40 is to the first surface 10a, the greater the concentration of Group VA elements in the functional layer. In this way, the performance of the photodiode 40 can be optimized, which is beneficial to improving the sensitivity of the back-illuminated image sensor and reducing noise, etc.

[0073] In some embodiments, referring to Figure 7 As shown, the first functional layer 41 is a silicon phosphide layer, the second functional layer 42 is a silicon arsenide layer, and the third functional layer 43 is also a silicon arsenide layer. During the epitaxial formation of the photodiode 40, controlling the process parameters so that the concentration of arsenic element in the second functional layer 42 is greater than the concentration of arsenic element in the third functional layer 43 can optimize the concentration distribution of Group VA elements in the photodiode 40, which helps to improve the overall quality of the back-illuminated image sensor.

[0074] By way of example, the following implementation manner can be adopted to form the photodiode 40: Referring to Figure 5 As shown, the structure forming the second isolation structure 20 and the metal grid 30 is placed in a reaction chamber, and a silicon source gas (such as silane SiH 4 ) and a phosphorus source gas (such as phosphine PH 3 ) are introduced into the heated reaction chamber, and hydrogen is used as a carrier gas. The silicon source gas and the phosphorus source gas react at high temperature to grow silicon phosphide on the first surface 10a exposed by the second isolation structure 20 as the first functional layer 41.

[0075] Then, referring to Figure 6As shown, stop introducing the phosphorus source gas into the reaction chamber, and instead introduce the silicon source gas and the arsenic source gas (such as arsine AsH 3 ), and the silicon source gas and the arsenic source gas react at high temperature to grow silicon arsenide on the first functional layer 41 as the second functional layer 42.

[0076] Next, refer to Figure 7 As shown, reduce the flow rate of the arsenic source gas introduced into the reaction chamber, and grow silicon arsenide on the second functional layer 42 as the third functional layer 43. The concentration of arsenic elements in the second functional layer 42 is greater than the concentration of arsenic elements in the third functional layer 43.

[0077] During the epitaxial formation of the third functional layer 43, by controlling the thickness of the third functional layer 43, the top surface of the third functional layer 43 and the top surface of the second isolation structure 20 are located on the same horizontal plane, so as to reserve sufficient space above the photodiode 40 to form the light filtering element 50.

[0078] In some embodiments, along the direction away from the first surface 10a, the horizontal dimension of the second isolation structure 20 gradually increases, and the horizontal dimension of the metal grid 30 gradually increases. The first functional layer 41, the second functional layer 42, and the third functional layer 43 grow in the region between the second isolation structures 20. From the light filtering element 50 to the direction of the first surface 10a, the horizontal dimension of the photodiode 40 gradually increases.

[0079] In this embodiment, the second isolation structure 20 and the metal grid 30 are first formed, and the region for forming the photodiode 40 is defined by the second isolation structure 20. The functional layers of the photodiode 40 are formed by epitaxial growth between the second isolation structures 20. On the one hand, there is no need to perform etching on the functional layers, avoiding etching damage to the photodiode 40 and also avoiding crosstalk caused by the residue of the photosensitive material. On the other hand, the formation of the functional layers does not require high-energy ion implantation, avoiding the formation of damaged regions on the substrate 10 and preventing electrons from moving between the photodiodes 40 or moving to other structures through the damaged regions, further improving the crosstalk problem of the back-illuminated image sensor.

[0080] In step S40, refer to Figure 8 As shown, a light filtering element 50 is formed on the side of each photodiode 40 away from the first surface 10a. The light filtering element 50 allows light of a specific wavelength to pass through, so that the photodiode 40 can sense light of a specific color. For example, one photodiode 40 may only receive red light, while another photodiode 40 may only receive green light.

[0081] Exemplarily, forming the filter element 50 includes: coating a layer of photosensitive glue, which is used to screen monochromatic light of different spectra, such as red light, orange light, yellow light, green light, blue light, and purple light, and forming a filter 51 corresponding to the photodiode 40 through exposure, development, and baking. Repeat the above process to form filters 51 for screening monochromatic light of different spectra on multiple photodiodes 40.

[0082] Then, attach the filter lens 52 to the filter 51 with glue, and perform ultraviolet curing or thermal curing after attachment to form the filter element 50. That is, each filter element 50 includes a filter 51 and a filter lens 52 formed in sequence on the photodiode 40. In this embodiment, the filter lens 52 is a convex lens protruding in a direction away from the photodiode 40.

[0083] According to an exemplary embodiment, the present disclosure provides a back-illuminated image sensor. Refer to Figure 8 as shown, and in combination with reference to Figures 2 - 7 , the back-illuminated image sensor includes a substrate 10, a second isolation structure 20, a metal grid 30, and a photodiode 40; the substrate 10 includes opposite first and second surfaces 10a and 10b, and a first isolation structure 11 is formed in the substrate 10, and the first isolation structure 11 extends from the first surface 10a to the second surface 10b; the second isolation structure 20 is disposed corresponding to the first isolation structure 11 on the first surface 10a, and the second isolation structure 20 is spaced apart on the first surface 10a; the metal grid 30 is disposed on a side of the second isolation structure 20 away from the first surface 10a, and the second isolation structure 20 and the metal grid 30 are integrally formed; the photodiode 40 is disposed between the second isolation structures 20, and the photodiode 40 and the second isolation structure 20 are alternately arranged on the first surface 10a; the filter element 50 is disposed on a side of the photodiode 40 away from the first surface 10a, and the filter element 50 is located between adjacent metal grids 30.

[0084] Among them, the photodiode 40 is disposed on the first surface 10a of the substrate 10, and the photodiode 40 is used to convert the received optical signal energy into an electrical signal.

[0085] The filter element 50 is disposed on the photodiode 40, and the filter element 50 is used to allow light of a specific wavelength to pass through, so that the photodiode 40 can sense light of a specific color. In this embodiment, the filter element 50 includes a filter 51 and a filter lens 52 disposed in sequence in a direction away from the photodiode 40.

[0086] The second isolation structure 20 is disposed on the first surface 10a of the substrate 10. The second isolation structure 20 is configured to define the region of the photodiode 40 on the first surface 10a and isolate adjacent photodiodes 40, preventing crosstalk of optical signals and electrical signals between different photodiodes 40 and ensuring that each photodiode 40 can operate independently.

[0087] The metal grid 30 is disposed on the top surface of the second isolation structure 20. The light filtering element 50 is disposed between adjacent metal grids 30. The metal grid 30 is configured to further control the incident direction and angle of light, so as to reduce the influence of stray light and reflected light on the photodiode 40. The metal grid 30 can also serve as a light guiding structure to ensure that light can be accurately projected onto the photodiode 40.

[0088] In this embodiment, the second isolation structure 20 and the metal grid 30 are integrally formed. The second isolation structure 20 and the metal grid 30 are etched in the same manufacturing process. In this way, the problem of alignment deviation between the metal grid 30 and the second isolation structure 20 is avoided, the connection firmness between the metal grid 30 and the second isolation structure 20 is improved, and the structural stability and product yield of the back-illuminated image sensor are improved.

[0089] In some embodiments, referring to Figure 8 shown, and with reference to Figures 2 - 7 , the second surface 10b of the substrate 10 has a sequentially stacked isolation layer 12 and a logic circuit layer 13. A plurality of logic control devices are formed in the logic circuit layer 13. The plurality of logic control devices can control the photodiode 40 to perform photoelectric conversion to form an electrical signal, quantize the electrical signal through analog-to-digital conversion, and read out the converted digital signal.

[0090] In some embodiments, referring to Figure 8 shown, and with reference to Figures 2 - 7 , along the direction away from the first surface 10a, the horizontal dimension of the second isolation structure 20 gradually increases, and the horizontal dimension of the metal grid 30 gradually increases; in the direction from the light filtering element 50 to the first surface 10a, the horizontal dimension of the photodiode 40 gradually increases.

[0091] In this way, the space between the second isolation structures 20 is increased, the size of the photodiode 40 is increased, the area of the photosensitive region of the back-illuminated image sensor is increased, the light flux can be increased, which is beneficial to improving the sensitivity of the back-illuminated image sensor to light and improving the display effect of the back-illuminated image sensor.

[0092] In some embodiments, referring to Figure 8 shown, and with reference to Figures 2 - 7, the photodiode 40 includes a first functional layer 41, a second functional layer 42, and a third functional layer 43 stacked in sequence away from the first surface 10a. It can be understood that in other embodiments, four, five, or more functional layers can be epitaxially formed on the first surface 10a exposed by the second isolation structure 20, and the present disclosure places no limitation thereon.

[0093] Among them, the materials of the functional layers of the photodiode 40 include compounds of Group VA elements and silicon. The Group VA elements include nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi), moscovium (Mc), etc. By way of example, the material of each functional layer can include silicon phosphide, silicon arsenide, or silicon antimonide, etc.

[0094] In some embodiments, with reference to Figure 8 shown, in combination with reference to Figures 2 - 7 , by controlling the concentration of Group VA elements in each functional layer, the concentration of Group VA elements in the functional layer increases as the photodiode 40 is closer to the first surface 10a. In this way, the performance of the photodiode 40 can be optimized, which is beneficial to improving the sensitivity of the back-illuminated image sensor, reducing noise, etc.

[0095] By way of example, the first functional layer 41 is a silicon phosphide layer, the second functional layer 42 is a silicon arsenide layer, and the third functional layer 43 is also a silicon arsenide layer. The concentration of arsenic element in the second functional layer 42 is greater than the concentration of arsenic element in the third functional layer 43.

[0096] In some embodiments, with reference to Figure 8 shown, in combination with reference to Figures 2 - 7 , the top surface of the third functional layer 43 and the top surface of the second isolation structure 20 are located on the same horizontal plane, so as to reserve sufficient space above the photodiode 40 to arrange the filter element 50, ensure the filtering effect of the filter element 50, and prevent other color lights from entering the photodiode 40.

[0097] In some embodiments, with reference to Figure 8 shown, in combination with reference to Figures 2 - 7 , the second isolation structure 20 includes multiple metal layers stacked in sequence away from the first surface 10a. In this way, the second isolation structure 20 and the metal grid 30 form a composite metal grid 30 (Composite Metal Grid, CMG), which can further enhance the isolation effect of the second isolation structure 20, prevent the electrons of the photodiode 40 from overflowing, thereby maintaining its normal working state, provide better electrical shielding for the photodiode 40, prevent it from being subject to unnecessary interference or damage, and the composite metal grid 30 helps to further improve the anti-crosstalk ability of the back-illuminated image sensor and improve the image quality of the back-illuminated image sensor.

[0098] Exemplarily, the second isolation structure 20 includes a first metal layer 61, a second metal layer 62, a third metal layer 63, and a fourth metal layer 64 that are sequentially stacked on the first surface 10a. Among them, the material of the first metal layer 61 includes hafnium oxide (HfO), the material of the second metal layer 62 includes titanium nitride (TiN), the material of the third metal layer 63 includes tantalum nitride (TaN), and the material of the fourth metal layer 64 includes titanium aluminide (TiAl).

[0099] In this embodiment, the metal grid 30 is formed by patterning a fifth metal layer 65, and the fifth metal layer 65 is an aluminum (Al) layer.

[0100] According to an exemplary embodiment, the present disclosure provides an electronic device including the back-illuminated image sensor of the above embodiment.

[0101] The unexpected technical effect of the present disclosure is that after forming the second isolation structure and the metal grid by optimizing the process, a photodiode is formed between the second isolation structures. The photodiode can be formed without etching, which can avoid etching damage to the photodiode, ensure the structural integrity of the photodiode, and at the same time avoid residual photosensitive materials after etching, and prevent electrons from moving between the photodiodes through the residual photosensitive materials, thereby improving the crosstalk problem of the back-illuminated image sensor.

[0102] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features of the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0103] The above-described embodiments merely represent several implementation manners of the present disclosure, and the description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present disclosure, several modifications and improvements can be made, and these all belong to the protection scope of the present disclosure. Therefore, the protection scope of the patent of the present disclosure should be subject to the appended claims.

Claims

1. A method for manufacturing a back-illuminated image sensor, characterized in that: include: Providing a substrate, the substrate comprising a first surface and a second surface opposite to each other, a first isolation structure formed in the substrate, and the first isolation structure extending from the first surface to the second surface; forming a second isolation structure and a metal grid, wherein the second isolation structure is arranged on the first surface corresponding to the first isolation structure, the second isolation structure is arranged at intervals on the first surface, and the second isolation structure and the metal grid are arranged in sequence in a direction away from the first surface; forming photodiodes between the second isolation structures, wherein the photodiodes and the second isolation structures are alternately arranged on the first surface; forming a filter element on a side of the photodiode away from the substrate, wherein the filter element is located between adjacent metal grids; Forming a second isolation structure and a metal grid, comprising: forming a metal stack on the first surface, the metal stack comprising a plurality of stacked metal layers; The metal stack is patterned, the top metal layer of the metal stack forms the metal grid, and the metal layer below the metal grid forms the second isolation structure.

2. The method for manufacturing a back-illuminated image sensor according to claim 1, characterized in that: During the process of patterning the metal stack, the metal stack is etched using a dry process. As the etching depth increases, the etching process parameters are adjusted to gradually increase the etching rate along the horizontal direction so that the horizontal size of the second isolation structure gradually increases in the direction away from the first surface and the horizontal size of the metal grid gradually increases.

3. The method for manufacturing a back-illuminated image sensor according to claim 1 or 2, characterized in that: A photodiode is formed between the second isolation structures, including: epitaxially forming a first functional layer, a second functional layer and a third functional layer in sequence on the first surface exposed by the second isolation structure, wherein the top surface of the third functional layer is located at the same horizontal plane as the top surface of the second isolation structure.

4. The method for manufacturing a back-illuminated image sensor according to claim 3, characterized in that: The horizontal size of the photodiode gradually increases from the filter element toward the first surface.

5. A back-illuminated image sensor, characterized in that: The back-illuminated image sensor is manufactured by the manufacturing method of any one of claims 1 to 4, wherein the back-illuminated image sensor comprises: A substrate, the substrate comprising a first surface and a second surface opposite to each other, a first isolation structure formed in the substrate, and the first isolation structure extending from the first surface to the second surface; a second isolation structure, the second isolation structure being arranged on the first surface corresponding to the first isolation structure, and the second isolation structure being arranged at intervals on the first surface; a metal grid, disposed on a side of the second isolation structure away from the first surface, wherein the second isolation structure and the metal grid are integrally formed; A photodiode is arranged between the second isolation structures, and the photodiode and the second isolation structure are alternately arranged on the first surface; The filter element is arranged on a side of the photodiode away from the first surface, and the filter element is located between adjacent metal grids.

6. The back-illuminated image sensor according to claim 5, characterized in that: Along the direction away from the first surface, the horizontal size of the second isolation structure gradually increases, and the horizontal size of the metal grid gradually increases; The horizontal size of the photodiode gradually increases from the filter element toward the first surface.

7. The back-illuminated image sensor according to claim 5, characterized in that: The photodiode includes a first functional layer, a second functional layer, and a third functional layer sequentially stacked away from the first surface.

8. The back-illuminated image sensor according to claim 7, wherein: A top surface of the third functional layer and a top surface of the second isolation structure are located at the same horizontal plane.

9. The back-illuminated image sensor according to claim 5, wherein: The second isolation structure includes a plurality of metal layers stacked in sequence in a direction away from the first surface.

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