Backside illuminated image sensor and manufacturing method thereof

Abstract

The invention relates to a backside illuminated image sensor and a manufacturing method thereof, and relates to the technical field of integrated circuits. The manufacturing method comprises the steps that a substrate is provided, the substrate comprises a first surface and a second surface which are opposite, a first isolation structure is formed in the substrate, and the first isolation structure extends from the first surface to the second surface; second isolation structures and metal grids are formed, the second isolation structures correspond to the first isolation structures and are arranged on the first surface, the second isolation structures are arranged on the first surface at intervals, and the second isolation structures and the metal grids are sequentially arranged in the 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 light filtering element on one side, far away from the substrate, of the photodiode, wherein the light filtering element is located between the adjacent metal grids; according to the invention, the crosstalk problem of the backside illuminated image sensor is reduced.

Description

Technical Field

[0001] The present disclosure relates to the technical field of integrated circuits, and in particular to a back-illuminated image sensor and a manufacturing method thereof. Background Art

[0002] Back Side illumination (BSI) image sensor is a type of image sensor. In low light conditions, BSI image sensor has better performance than front-illuminated image sensor.

[0003] However, the crosstalk effect of the back-illuminated image sensor is 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 to address the serious crosstalk problem of the back-illuminated image sensor in the prior art.

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

[0006] 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;

[0007] 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;

[0008] forming photodiodes between the second isolation structures, wherein the photodiodes and the second isolation structures are alternately arranged on the first surface;

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

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

[0011] forming a metal stack on the first surface, the metal stack comprising a plurality of stacked metal layers;

[0012] 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.

[0013] Optionally, during patterning of the metal stack, the metal stack is etched using a dry process, and 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 a direction away from the first surface, and the horizontal size of the metal grid gradually increases.

[0014] Optionally, a photodiode is formed between the second isolation structures, including: sequentially epitaxially forming a first functional layer, a second functional layer and a third functional layer 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.

[0015] Optionally, the horizontal size of the photodiode gradually increases from the filter element toward the first surface.

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

[0017] 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;

[0018] 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;

[0019] 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;

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

[0021] 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.

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

[0023] The horizontal size of the photodiode gradually increases from the filter element toward the first surface.

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

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

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

[0027] The unexpected technical effect of the present invention is: by optimizing the process, after forming the second isolation structure and the metal grid, a photodiode is formed between the second isolation structures. The photodiode can be formed without etching, which can avoid etching damage to the photodiode and ensure the structural integrity of the photodiode. At the same time, it can also avoid residual photosensitive material after etching and avoid electrons moving between photodiodes through the residual photosensitive material, thereby improving the crosstalk problem of the back-illuminated image sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure or the conventional technology, the drawings required for use in the embodiments or the conventional technology descriptions will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present disclosure, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

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

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

[0031] Figure 3 is a schematic cross-sectional view after a metal stack is formed on a first surface according to an embodiment;

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

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

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

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

[0036] Figure 8 FIG. 4 is a schematic cross-sectional 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 method for manufacturing the same. By optimizing the process, a second isolation structure and a metal grid are formed, and then a photodiode is formed between the second isolation structures. The photodiode can be formed without etching, which can avoid etching damage to the photodiode and ensure the structural integrity of the photodiode. At the same time, it can also avoid residual photosensitive material after etching and avoid electrons moving between photodiodes through the residual photosensitive material, thereby improving the crosstalk problem of the back-illuminated image sensor.

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

[0045] Step S10: 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.

[0046] Step S20: 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.

[0047] Step S30: forming photodiodes between the second isolation structures, wherein the photodiodes and the second isolation structures are alternately arranged on the first surface.

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

[0049] Figure 2-Figure 8 Schematic diagrams showing various stages of a method for manufacturing a semiconductor structure of some embodiments of this example are shown below. Figure 2-Figure 8 The manufacturing methods of the semiconductor structures of some embodiments of this example are introduced.

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

[0051] See also Figure 1As shown, the substrate 10 includes a first surface 10a and a second surface 10b that are oppositely arranged, and 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 two surfaces of the substrate 10, wherein the first surface 10a is a side of the back-illuminated image sensor that receives incident light, and the second surface 10b is arranged relative to the first surface 10a.

[0053] For example, the substrate 10 can be manufactured by the following implementation: a semiconductor substrate is provided, a photoresist layer is formed on the second surface 10b of the semiconductor substrate, and a shallow groove is formed by patterning the semiconductor substrate according to the photoresist layer. After the shallow groove is formed, an isolation medium is deposited in the shallow groove, and the isolation medium is, for example, an insulating material such as silicon oxide, to form a first isolation structure 11 in the shallow groove. Then, a chemical mechanical polishing process (CMP) is used to grind the back side of the semiconductor substrate until the surface of the first isolation structure 11 is exposed to obtain the substrate 10, and a first surface 10a opposite to the second surface 10b is formed.

[0054] In some embodiments, see Figure 2 As shown, the second surface 10b of the substrate 10 is also formed with an isolation layer 12 and a logic circuit layer 13 stacked in sequence, and 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, and quantize 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 10 a , wherein the metal stack 60 includes a plurality of stacked metal layers.

[0057] See also Figure 3 As shown, multiple metal layers may be deposited on the first surface 10a by atomic layer deposition (ALD) or physical vapor deposition (PVD) to form a metal stack 60. The metal stack 60 may 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 sequentially stacked on the first surface 10a. 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 : patterning the metal stack 60 , wherein the top metal layer of the metal stack 60 forms the metal grid 30 , and the metal layer below the metal grid 30 forms the second isolation structure 20 .

[0060] See also 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, and the photoresist layer is exposed and developed to define the pattern of the metal grid 30 on the photoresist layer. Then, the metal stack 60 is etched to the first surface 10a according to the photoresist layer, and the second isolation structure 20 and the metal grid 30 are formed at the same time. The top metal layer of the metal stack 60 is etched to form the metal grid 30, and the multi-layer metal layers blocked 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 a first metal layer 61, a second metal layer 62, a third metal layer 63 and a fourth metal layer 64 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, which simplifies the process steps and is beneficial to improving the process efficiency. At the same time, the second isolation structure 20 and the metal grid 30 are integrally formed to avoid the problem of alignment deviation between the metal grid 30 and the second isolation structure 20, thereby 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] In addition, the second isolation structure 20 of the present embodiment includes multiple metal layers. The second isolation structure 20 and the metal grid 30 constitute a composite metal grid 30 (Composite Metal Grid, CMG), which can further enhance the isolation effect of the second isolation structure 20 and avoid electron overflow of the photodiode 40. The composite metal grid 30 helps to further improve the anti-crosstalk capability of the back-illuminated image sensor and improve the image quality of the back-illuminated image sensor.

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

[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. In this way, the space between the second isolation structures 20 is increased, the size of the photodiode 40 formed subsequently can be increased, the area of ​​the photosensitive area of ​​the back-illuminated image sensor can be increased, the light flux can be increased, and the sensitivity of the back-illuminated image sensor to light is improved, and the display effect of the back-illuminated image sensor is improved.

[0065] In some embodiments, see Figure 3 As shown, during the process of patterning the metal stack 60, the metal stack 60 is etched by 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 20 gradually increases and the horizontal size of the metal grid 30 gradually increases in the direction away from the first surface 10a.

[0066] The multiple metal layers of the metal stack 60 include different materials, and the reaction rates of the multiple metal layers in the dry etching process may be different. The etching gas and process conditions can be adjusted so that the closer to the first surface 10a, the greater the etching rate of the metal layer, so that after the etching is completed, the horizontal size of the second isolation structure 20 gradually increases in the direction away from the first surface 10a, and the horizontal size of the metal grid 30 gradually increases.

[0067] Alternatively, the etching process parameters can be gradually adjusted during the etching process, such as increasing the flow rate of the etching gas, increasing the plasma density, changing the type of 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 the etching is completed, the horizontal size of the second isolation structure 20 gradually increases in the direction away from the first surface 10a, and the horizontal size of the metal grid 30 gradually increases.

[0068] Here, the “horizontal dimension” in the present disclosure refers to the dimension of the structure along a direction parallel to the first surface 10 a of the substrate 10 .

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

[0070] In some embodiments, the photodiode 40 is formed between the second isolation structures 20, including: 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 located at the same horizontal plane as the top surface of the second isolation structure 20. It can be understood that in other embodiments, four functional layers, five functional layers, or more functional layers can be epitaxially formed on the first surface 10a exposed by the second isolation structure 20, and the present disclosure is not limited to this.

[0071] The material of each functional layer of the photodiode 40 includes a compound of a Group VA element and silicon. The Group VA elements include nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi), and molybdenum (Mc). For example, the material of each functional layer may include silicon phosphide, silicon arsenide, or silicon antimonide.

[0072] In some embodiments, the concentration of the VA group element in each functional layer is controlled so that the closer the photodiode 40 is to the first surface 10a, the greater the concentration of the VA group element 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.

[0073] In some embodiments, reference 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. In the process of epitaxially forming the photodiode 40, the process parameters are controlled so that the concentration of arsenic in the second functional layer 42 is greater than the concentration of arsenic in the third functional layer 43, so that the concentration distribution of the VA group elements in the photodiode 40 can be optimized, which helps to improve the overall quality of the back-illuminated image sensor.

[0074] For example, the photodiode 40 may be formed by the following implementations: 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 SiH4) and a phosphorus source gas (such as phosphine PH3) 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 a high temperature to grow silicon phosphide on the first surface 10a exposed by the second isolation structure 20 as a first functional layer 41.

[0075] Then, refer to Figure 6As shown, the introduction of phosphorus source gas into the reaction chamber is stopped, and silicon source gas and arsenic source gas (such as hydrogen arsenide AsH3) are introduced into the reaction chamber instead. 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, the flow rate of the arsenic source gas introduced into the reaction chamber is reduced, and silicon arsenide is grown on the second functional layer 42 as the third functional layer 43 . The concentration of arsenic in the second functional layer 42 is greater than that in the third functional layer 43 .

[0077] During the epitaxial formation of the third functional layer 43 , the thickness of the third functional layer 43 is controlled so that the top surface of the third functional layer 43 and the top surface of the second isolation structure 20 are located at the same horizontal plane, thereby reserving sufficient space above the photodiode 40 to form the filter element 50 .

[0078] In some embodiments, along the direction away from the first surface 10a, the horizontal size of the second isolation structure 20 gradually increases, and the horizontal size 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 structure 20, and the horizontal size of the photodiode 40 gradually increases from the filter element 50 toward the first surface 10a.

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

[0080] In step S40, referring to Figure 8 As shown, a filter element 50 is formed on a side of each photodiode 40 away from the first surface 10a, and the filter 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 only receives green light.

[0081] For example, forming the filter element 50 includes: coating a layer of photosensitive adhesive, the photosensitive adhesive is used to filter 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 filtering monochromatic light of different spectra on multiple photodiodes 40.

[0082] Then, the filter 52 is glued to the filter 51, and then cured by ultraviolet or heat to form the filter element 50. That is, each filter element 50 includes the filter 51 and the filter 52 formed on the photodiode 40 in sequence. In this embodiment, the filter 52 is a convex lens protruding in the direction away from the photodiode 40.

[0083] According to an exemplary embodiment, the present disclosure provides a back-illuminated image sensor, referring to Figure 8 As shown, combined with reference Figure 2-Figure 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 a first surface 10a and a second surface 10b opposite to each other, 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 arranged on the first surface 10a corresponding to the first isolation structure 11, and the second isolation structure 20 is arranged at intervals on the first surface 10a; the metal grid 30 is arranged 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 arranged 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 arranged 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] The photodiode 40 is disposed on the first surface 10 a 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 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 sequentially disposed 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 used to define the region of the photodiode 40 on the first surface 10a and isolate adjacent photodiodes 40 to prevent crosstalk between optical signals and electrical signals of different photodiodes 40, thereby ensuring that each photodiode 40 can work independently.

[0087] The metal grid 30 is arranged on the top surface of the second isolation structure 20, and the filter element 50 is arranged between adjacent metal grids 30. The metal grid 30 is used to further control the incident direction and angle of light 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 the light can be accurately projected onto the photodiode 40.

[0088] In this embodiment, the second isolation structure 20 is integrally formed with the metal grid 30. The second isolation structure 20 and the metal grid 30 are etched in the same 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, reference Figure 8 As shown, combined with reference Figure 2-Figure 7 The second surface 10b of the substrate 10 has an isolation layer 12 and a logic circuit layer 13 stacked in sequence, and 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, and quantize the electrical signal through analog-to-digital conversion, and read out the converted digital signal.

[0090] In some embodiments, reference Figure 8 As shown, combined with reference Figure 2-Figure 7 , along the direction away from the first surface 10a, the horizontal size of the second isolation structure 20 gradually increases, and the horizontal size of the metal grid 30 gradually increases; from the filter element 50 to the first surface 10a, the horizontal size 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, and the area of ​​the photosensitive region of the back-illuminated image sensor is increased, which can increase the luminous flux, is beneficial to improving the sensitivity of the back-illuminated image sensor to light, and improves the display effect of the back-illuminated image sensor.

[0092] In some embodiments, reference Figure 8 As shown, combined with reference Figure 2-Figure 7The 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 functional layers, five functional layers, or more functional layers can be epitaxially formed on the first surface 10a exposed by the second isolation structure 20, and the present disclosure is not limited to this.

[0093] The material of each functional layer of the photodiode 40 includes a compound of a Group VA element and silicon. The Group VA elements include nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi), and molybdenum (Mc). For example, the material of each functional layer may include silicon phosphide, silicon arsenide, or silicon antimonide.

[0094] In some embodiments, reference Figure 8 As shown, combined with reference Figure 2-Figure 7 By controlling the concentration of the VA group element in each functional layer, the closer the photodiode 40 is to the first surface 10a, the greater the concentration of the VA group element 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.

[0095] For 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 in the second functional layer 42 is greater than that in the third functional layer 43.

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

[0097] In some embodiments, reference Figure 8 As shown, combined with reference Figure 2-Figure 7 The second isolation structure 20 includes multiple metal layers stacked in sequence in a direction 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 (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, and provide better electrical shielding for the photodiode 40 to prevent it from being subjected to unnecessary interference or damage. The composite metal grid 30 helps to further improve the anti-crosstalk capability of the back-illuminated image sensor and improve the image quality of the back-illuminated image sensor.

[0098] For example, 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 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 the present embodiment, the metal grid 30 is formed by patterning the 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-mentioned embodiment.

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

[0102] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, 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, they should be considered to be within the scope of this specification.

[0103] The above-described embodiments only express several implementation methods of the present disclosure, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present disclosure, and these all belong to the protection scope of the present disclosure. Therefore, the protection scope of the patent of the present disclosure shall be subject to the attached 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; A filter element is formed on a side of the photodiode away from the substrate, and the filter element is located between adjacent metal grids.

2. The method for manufacturing a back-illuminated image sensor according to claim 1, characterized in that: 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.

3. The method for manufacturing a back-illuminated image sensor according to claim 2, wherein: 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.

4. The method for manufacturing a back-illuminated image sensor according to any one of claims 1 to 3, 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.

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

6. A back-illuminated image sensor, characterized in that: include: 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.

7. The back-illuminated image sensor according to claim 6, wherein: 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.

8. The back-illuminated image sensor according to claim 6, wherein: The photodiode includes a first functional layer, a second functional layer, and a third functional layer sequentially stacked away from the first surface.

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

10. The back-illuminated image sensor according to claim 6, 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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