Image sensor and method of forming the same

Abstract

The present invention provides an image sensor and a method for forming the same. Multiple groove groups are formed on the front surface of a substrate, each groove group comprising two sub-grooves. At least a portion of the space between the two sub-grooves is removed to connect the two sub-grooves to form a single groove, forming a photoelectric sensing reserved area. A photoelectric conversion structure is formed within the photoelectric sensing reserved area. A third etching process is performed to etch a portion of the substrate along the back surface of the substrate to expose the bottom and a portion of the sidewalls of the photoelectric conversion structure. The bottom of the photoelectric conversion structure forms a light-trapping structure, and the area between adjacent photoelectric conversion structure sidewalls forms an isolation region. The third etching process is a wet etching process. The present invention unexpectedly achieves the following: under the same pixel area, the light-trapping structure increases the area of ​​the photoelectric sensing region, thereby improving image sensor performance. The wet etching process simultaneously forms the light-trapping structure and the isolation region, saving process steps and avoiding lattice damage caused by dry etching.

Description

Technical Field

[0001] The present invention relates to the technical field of integrated circuits, and in particular to an image sensor and a method for forming the same. Background Art

[0002] The preparation process of an image sensor generally includes the following steps: first, the photoelectric sensing area and shallow trench isolation structure are formed using etching and thin film processes, then the photodiode is formed in the photoelectric sensing area using ion implantation, and then the metal interconnects and color filter structure are prepared to form the image sensor.

[0003] However, during the formation of the photodiode in the photoelectric sensing area, the ion implantation process can cause lattice damage to the silicon and the risk of metal contamination, impacting image sensor performance. Furthermore, a separate etching process is required to create the light-trapping structure of the photodiode. This etching process is difficult to manufacture and can damage the silicon lattice in the photoelectric sensing area, impacting image sensor performance. Furthermore, the shallow trench isolation structure is fabricated through an etching process, which also causes lattice damage to the silicon. Summary of the Invention

[0004] An object of the present invention is to provide a method for forming an image sensor, so as to solve the problem that the performance of the image sensor is reduced due to lattice damage during the formation of the image sensor.

[0005] To solve the above technical problems, the present invention provides a method for forming an image sensor, comprising:

[0006] Providing a substrate, the substrate comprising a front surface and a back surface disposed opposite to each other;

[0007] Performing a first etching process to form a plurality of trench groups on the front surface of the substrate, each trench group including two sub-trenches, and a spacing between adjacent trench groups being greater than a spacing between two sub-trenches within the same group;

[0008] Performing a second etching process to remove at least a portion of the space between the two sub-grooves in each of the groove groups, so that the two sub-grooves in each of the groove groups are connected to form one groove, constituting a photoelectric sensing reserved area;

[0009] forming a photoelectric conversion structure, wherein the photoelectric conversion structure is located in the photoelectric sensing reserved area;

[0010] A third etching process is performed to etch a portion of the substrate along the back side of the substrate to expose the bottom and part of the side wall of the photoelectric conversion structure, wherein the bottom of the photoelectric conversion structure constitutes a light trapping structure, and the area between the side walls of adjacent photoelectric conversion structures constitutes an isolation area, wherein the third etching process is a wet etching process.

[0011] Optionally, the step of forming the photoelectric conversion structure includes: sequentially epitaxially growing a first semiconductor material layer, a second semiconductor material layer, and a third semiconductor material layer, wherein the first semiconductor material layer and the substrate have the same doping type and the doping concentration of the first semiconductor material layer is lower than the doping concentration of the substrate.

[0012] Optionally, in the third etching process, the first semiconductor material layer serves as an etching stop layer.

[0013] Optionally, the doping type of the second semiconductor material layer is different from the doping type of the third semiconductor material layer.

[0014] Optionally, the etching solution of the third etching process is an HNA solution, and in the third etching process, the etching selectivity of the substrate is greater than the etching selectivity of the first semiconductor material layer.

[0015] Optionally, the first etching process is a dry etching process, the second etching process is a wet etching process, and the etching solution of the second etching process is an HF solution or an HNA solution.

[0016] Optionally, after the third etching process, the method further includes:

[0017] forming a first dielectric layer, wherein the first dielectric layer fills the isolation region between adjacent photoelectric conversion structures and covers the surface of the photoelectric conversion structure away from the front surface of the substrate;

[0018] A second dielectric layer and a third dielectric layer are formed in sequence, wherein the second dielectric layer covers the first dielectric layer, and the third dielectric layer covers the second dielectric layer.

[0019] Optionally, the second dielectric layer is made of a metal material, and the first dielectric layer and the third dielectric layer are made of an insulating material.

[0020] Optionally, after forming the third dielectric layer, a filter layer and a microlens are formed in sequence, and the filter layer and the microlens are located on the third dielectric layer and correspond to the photoelectric conversion structure.

[0021] Based on the same inventive concept, the present invention further provides an image sensor, which is manufactured using any of the above-mentioned methods for forming an image sensor.

[0022] In the method for forming an image sensor provided by the present invention, a first etching process is performed to form a plurality of groove groups on the front side of the substrate, each groove group including two sub-grooves, and the spacing between adjacent groove groups is greater than the spacing between the two sub-grooves in the group; then a second etching process is performed to connect the two sub-grooves in each groove group to form a groove, constituting a photoelectric sensing reserved area, and the bottom of the photoelectric sensing reserved area is formed by connecting the bottoms of the two sub-grooves; then a photoelectric conversion structure is formed in the photoelectric sensing reserved area; then a third etching process is performed to etch a portion of the substrate along the back side of the substrate to expose the bottom and part of the side wall of the photoelectric conversion structure, the bottom of the photoelectric conversion structure constituting a light trapping structure, and the area between the side walls of adjacent photoelectric conversion structures constituting an isolation area, wherein the third etching process is a wet etching process. The unexpected effect of the present invention is that, under the condition of the same pixel unit area, the light-trapping structure increases the area of ​​the photoelectric sensing area and improves the performance of the image sensor; the photoelectric conversion structure, the light-trapping structure and the isolation area are formed through the epitaxial growth process and the wet etching process, thereby avoiding the lattice damage caused by the dry etching process; and the wet etching process forms the isolation area while forming the light-trapping structure, thereby reducing the process steps and lowering the processing difficulty. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Those skilled in the art will appreciate that the drawings are provided for a better understanding of the present invention, but do not constitute any limitation on the scope of the present invention.

[0024] Figure 1 is a flow chart of a method for forming an image sensor according to an embodiment of the present invention.

[0025] Figure 2a It is a schematic structural diagram of an image sensor after a patterned photoresist layer is formed according to an embodiment of the present invention.

[0026] Figure 2b 3 is a schematic structural diagram of an image sensor after rectangular grooves are formed according to an embodiment of the present invention.

[0027] Figure 2c 3 is a schematic structural diagram of an image sensor after a groove with an inverted triangle bottom is formed according to an embodiment of the present invention.

[0028] Figure 3 4 is a schematic structural diagram of an image sensor after a photoelectric sensing reserved area is formed according to an embodiment of the present invention.

[0029] Figure 4 3 is a schematic structural diagram of an image sensor after forming a photoelectric conversion structure according to an embodiment of the present invention.

[0030] Figure 5 3 is a schematic structural diagram of an image sensor after forming a light trapping structure and an isolation region according to an embodiment of the present invention.

[0031] Figure 6 3 is a schematic structural diagram of an image sensor after forming a first dielectric layer, a second dielectric layer, and a third dielectric layer according to an embodiment of the present invention.

[0032] Figure 7 3 is a schematic structural diagram of an image sensor after forming a filter layer and a microlens according to an embodiment of the present invention.

[0033] In the accompanying drawings: 10-substrate; 10a-front side; 10b-back side; 101-hard mask layer; 102-patterned photoresist layer; 11-groove group; 11a-space between two sub-grooves; 11b-sub-grooves; 12-photoelectric conversion structure; 12a-photoelectric sensing reserved area; 12b-first semiconductor material layer; 12c-second semiconductor material layer; 12d-third semiconductor material layer; 13-first dielectric layer; 13a-isolation region; 14-second dielectric layer; 15-third dielectric layer; 16-filter layer; 17-microlens. DETAILED DESCRIPTION

[0034] To make the objects, advantages, and features of the present invention more clearly apparent, the present invention is further described below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the drawings are all in a very simplified form and are not drawn to scale. They are only used to conveniently and clearly assist in illustrating the purposes of the embodiments of the present invention. In addition, the structures shown in the drawings are often part of the actual structure. In particular, different drawings may need to illustrate different focuses and sometimes use different scales.

[0035] As used in the present invention, the singular forms "a", "an", and "the" include plural objects, the term "or" is generally used to include the meaning of "and / or", the term "several" is generally used to include the meaning of "at least one", and the term "at least two" is generally used to include the meaning of "two or more". In addition, the terms "first", "second", and "third" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features specified as "first", "second", and "third" may explicitly or implicitly include one or at least two of the features. In addition, as used in the present invention, an element is provided on another element, which generally only indicates that there is a connection, coupling, cooperation or transmission relationship between the two elements, and the connection, coupling, cooperation or transmission between the two elements can be direct or indirect through an intermediate element, and should not be understood to indicate or imply the spatial position relationship between the two elements, that is, one element can be in any orientation such as inside, outside, above, below, or to the side of another element, unless the content clearly indicates otherwise. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0036] Figure 1 FIG. 1 is a flow chart of a method for forming an image sensor according to an embodiment of the present invention. Figure 1 As shown, this embodiment provides a method for forming an image sensor, including:

[0037] Step S10, providing a substrate, wherein the substrate includes a front surface and a back surface disposed opposite to each other;

[0038] Step S20, performing a first etching process to form a plurality of trench groups on the front surface of the substrate, wherein each trench group includes two sub-trenches, and a distance between adjacent trench groups is greater than a distance between two sub-trenches in the same group;

[0039] Step S30, performing a second etching process to remove at least part of the space between the two sub-grooves in each trench group, so that the two sub-grooves in each trench group are connected to form one trench, constituting a photoelectric sensing reserved area;

[0040] Step S40, forming a photoelectric conversion structure, wherein the photoelectric conversion structure is located in the photoelectric sensing reserved area;

[0041] In step S50, a third etching process is performed to etch a portion of the substrate along the back side of the substrate to expose the bottom and part of the side wall of the photoelectric conversion structure, wherein the bottom of the photoelectric conversion structure constitutes a light trapping structure, and the area between the side walls of adjacent photoelectric conversion structures constitutes an isolation area, wherein the third etching process is a wet etching process.

[0042] Figure 2a It is a schematic structural diagram of an image sensor after a patterned photoresist layer is formed according to an embodiment of the present invention. Figure 2b 3 is a schematic structural diagram of an image sensor after rectangular grooves are formed according to an embodiment of the present invention. Figure 2c 3 is a schematic structural diagram of an image sensor after a groove with an inverted triangle bottom is formed according to an embodiment of the present invention. Figure 3 4 is a schematic structural diagram of an image sensor after a photoelectric sensing reserved area is formed according to an embodiment of the present invention. Figure 4 3 is a schematic structural diagram of an image sensor after forming a photoelectric conversion structure according to an embodiment of the present invention. Figure 5 3 is a schematic structural diagram of an image sensor after forming a light trapping structure and an isolation region according to an embodiment of the present invention. Figure 6 3 is a schematic structural diagram of an image sensor after forming a first dielectric layer, a second dielectric layer, and a third dielectric layer according to an embodiment of the present invention. Figure 7 1 is a schematic diagram of the structure of the image sensor after forming the filter layer and micro lens according to the embodiment of the present invention. Figures 2a to 7The specific embodiments of the present invention are described in detail.

[0043] like Figure 2a As shown, a substrate 10 is provided. Substrate 10 can provide an operating platform for subsequent processes. It can be any substrate known to those skilled in the art for supporting semiconductor integrated circuit components. It can be a bare die or a wafer processed by an epitaxial growth process. Specifically, substrate 10 can be, for example, a silicon-on-insulator (SOI) substrate, a bulk silicon substrate, a germanium substrate, a silicon-germanium substrate, an indium phosphide (InP) substrate, a gallium arsenide (GaAs) substrate, or a germanium-on-insulator substrate. In this embodiment, substrate 10 is a silicon substrate. Substrate 10 includes a front surface 10a and a back surface 10b disposed opposite each other.

[0044] like Figures 2a to 2c As shown, a first etching process is performed to form a plurality of groove groups 11 on the front surface 10a of the substrate. Each groove group 11 includes two sub-grooves 11b and a spacing 11a between the two sub-grooves. The spacing d2 between adjacent groove groups 11 is greater than the spacing d1 between the two sub-grooves 11b in the group. The first etching process includes a first sub-etching process and a second sub-etching process. Both the first sub-etching process and the second sub-etching process are dry etching processes. Specifically, as shown in FIG. Figure 2a As shown, a hard mask layer 101 and a photoresist layer are formed in sequence, wherein the hard mask layer 101 covers the front surface 10a of the substrate, and the photoresist layer covers the hard mask layer 101. A photolithography process is performed to form a patterned photoresist layer 102. Figure 2b As shown, a first sub-etching process is performed, using the patterned photoresist layer 102 and the hard mask layer 101 as a mask to etch the substrate 10, and form a plurality of rectangular grooves on the front side 10a of the substrate. The depth of the rectangular groove is, for example, 1um to 3um. When the depth of the rectangular groove is 1um, the first sub-etching process first uses CF4 etching gas for etching, the gas flow rate (Flow Rate) of CF4 gas is, for example, 100sccm, and the etching time (ETCH Time) is, for example, 35s, and then uses SF6 etching gas for etching, the gas flow rate (Flow Rate) of SF6 etching gas is, for example, 100sccm, and the etching time is, for example, 10min, and then uses C4F8 / O2 etching gas to etch the polymer (Polymer) remaining in the groove to remove the polymer remaining in the rectangular groove. As shown Figure 2cAs shown, a second sub-etching process is performed, using the hard mask layer 101 as a mask to etch the substrate 10, forming a plurality of inverted triangular-shaped trenches on the front surface 10a of the substrate. The depth of the inverted triangular structure is 0.5um to 2um. When the depth is 0.5um, CF4 and CH2F2 etching gases are first used for in-and-out etching, with the flow rates of the CF4 and CH2F2 etching gases being, for example, 150sccm and 30sccm, and the etching time being, for example, 35s. Then, Cl2 etching gas is used for etching, with the flow rate of the Cl2 etching gas being, for example, 60sccm and the etching time being, for example, 50s. Finally, C4F8 / O2 etching gas is used to etch the residual polymer in the trenches to remove the residual polymer in the inverted triangular-shaped trenches. The first sub-etching process and the second sub-etching process form grooves with an inverted triangle bottom, that is, multiple groove groups 11, each groove group 11 includes two sub-grooves 11b and a gap 11a between the two sub-grooves, and the spacing d2 between adjacent groove groups 11 is greater than the spacing d1 between the two sub-grooves 11b in the group.

[0045] like Figure 3 As shown, a second etching process is performed to remove at least part of the space between the two sub-trenches in each trench group 11, so that the two sub-trenches in each trench group 11 are connected to form a single trench, forming a photoelectric sensing reserved area 12a. The two sub-trenches 11b in each trench group 11 are connected to form a single trench, that is, the two small sub-trenches 11b in each trench group 11 are connected to form a large trench. The large trench formed by the second etching process constitutes the photoelectric sensing reserved area 12a, and the bottom of the photoelectric sensing reserved area 12a is w-shaped or wavy. The second etching process is a wet etching process, and the etching solution of the second etching process is HF solution or HNA solution. In this embodiment, the etching solution of the second etching process is, for example, HNA solution, which is isotropic. The second etching process etches the trench with an inverted triangular bottom into a circular bottom, and the space 11a between two adjacent sub-trenches is partially etched to connect the two sub-trenches to form a large trench, forming the photoelectric sensing reserved area 12a. The W-shape or wavy shape at the bottom of the photoelectric sensing reserved area 12 a forms a light-trapping structure in subsequent processes. Under the condition of the same pixel area, the light-trapping structure increases the photoelectric sensing area and improves the performance of the image sensor.

[0046] like Figure 4As shown, a photoelectric conversion structure 12 is formed, and the photoelectric conversion structure 12 is located in the photoelectric sensing reserved area 12a. The step of forming the photoelectric conversion structure 12 includes: performing an epitaxial growth process to sequentially epitaxially grow a first semiconductor material layer 12b, a second semiconductor material layer 12c, and a third semiconductor material layer 12d, wherein the first semiconductor material layer 12b covers the bottom wall and sidewalls of the photoelectric sensing reserved area 12a, the second semiconductor material layer 12c covers the first semiconductor material layer 12b, and the third semiconductor material layer 12d covers the second semiconductor material layer 12c and fills the photoelectric sensing reserved area 12a. Because the bottom of the photoelectric sensing reserved area 12a is w-shaped or wavy, the bottoms of the first semiconductor material layer 12b, the second semiconductor material layer 12c, and the third semiconductor material layer 12d are all w-shaped or wavy. The materials of the first semiconductor material layer 12b, the second semiconductor material layer 12c, and the third semiconductor material layer 12d are all silicon. The first semiconductor material layer 12b and the substrate 10 have the same doping type and the doping concentration of the first semiconductor material layer 12b is lower than the doping concentration of the substrate 10. The doping type of the first semiconductor material layer 12b and the substrate 10 is the first doping type. In this embodiment, the first doping type is P-type doping. Specifically, the doping type of the substrate 10 is P+, and the doping type of the first semiconductor material layer 12b is P-. The doping concentration of the substrate 10 is greater than 1E18cm ⁻3 The doping concentration of the first semiconductor material layer 12b is less than 1E17cm ⁻3 . The doping type of the second semiconductor material layer 12c is different from the doping type of the third semiconductor material layer 12d. When the doping type of the second semiconductor material layer 12c is the second doping type, the doping type of the third semiconductor material layer 12d is the first doping type. When the doping type of the second semiconductor material layer 12c is the first doping type, the doping type of the third semiconductor material layer 12d is the second doping type. That is, when the doping type of the second semiconductor material layer 12c is N-type, the doping type of the third semiconductor material layer 12d is P-type. When the doping type of the second semiconductor material layer 12c is P-type, the doping type of the third semiconductor material layer 12d is N-type. The second semiconductor material layer 12c and the third semiconductor material layer 12d form a PN junction to constitute a photodiode, and the first semiconductor material layer 12b, the second semiconductor material layer 12c and the third semiconductor material layer 12d constitute a photoelectric conversion structure 12.

[0047] like Figure 5As shown, the substrate 10 is flipped over and a third etching process is performed. A portion of the substrate 10 is etched along the back surface 10b of the substrate to expose the bottom and part of the sidewalls of the photoelectric conversion structure 12. The W-shaped bottom of the photoelectric conversion structure 12 increases the area of ​​the photoelectric sensing region. The bottom of the photoelectric conversion structure 12 forms a light trapping structure, and the area between adjacent sidewalls 12 of the photoelectric conversion structure forms an isolation region 13a. The third etching process is a wet etching process. The etching solution used in the third etching process is an HNA solution, which includes hydrofluoric acid (HF), nitric acid (HNO3), and acetic acid (CH3COOH). The concentration of hydrofluoric acid in the HNA solution can be set to, for example, 8%, the concentration of nitric acid can be set to, for example, 20%, and the concentration of acetic acid can be set to, for example, 55%. The HNA solution etches silicon (Si) isotropically, i.e., etching the silicon material uniformly and non-directionally. In the third etching process, the etching selectivity of the substrate 10 is greater than the etching selectivity of the first semiconductor material layer 12b. That is, in the third etching process, the first semiconductor material layer 12b serves as an etch stop layer, and the HNA solution etches only the back surface of the substrate 10, with little etching of the first semiconductor material layer 12b. In this embodiment, the photoelectric conversion structure 12 is formed through an epitaxial growth process, and the isolation region is simultaneously formed by exposing the light-trapping structure through a wet etching process. This avoids lattice damage caused by a dry etching process and reduces processing difficulty.

[0048] like Figure 6As shown, after the third etching process, the process also includes forming a first dielectric layer 13. The first dielectric layer 13 fills the isolation region 13a between adjacent photoelectric conversion structures 12 and covers the surface of the photoelectric conversion structure 12 facing away from the front surface of the substrate. That is, the first dielectric layer 13 covers the surface of the first semiconductor material layer 12b. The first dielectric layer 13 filled in the isolation region 13a between the photoelectric conversion structures 12 constitutes an isolation structure between the photoelectric conversion structures 12. A second dielectric layer 14 and a third dielectric layer 15 are sequentially formed. The second dielectric layer 14 covers the first dielectric layer 13, and the third dielectric layer 15 covers the second dielectric layer 14. The second dielectric layer 14 is made of a metal material and can be formed using a physical vapor deposition process. The metal material of the second dielectric layer 14 can reflect unabsorbed light back to the photoelectric conversion structure 12, thereby improving the absorption efficiency of long-wavelength light (such as red light). The first dielectric layer 13 and the third dielectric layer 15 are made of an insulating material, such as silicon oxide, and can be formed using a chemical vapor deposition process. The first dielectric layer 13 and the third dielectric layer 15 are located around the photoelectric conversion structure 12 or between metal layers, primarily providing electrical isolation to prevent short circuits between different circuit layers. They also act as passivation layers to protect the semiconductor surface, reduce interface defects and leakage current, and enhance device stability.

[0049] like Figure 7 As shown, after forming the third dielectric layer 15, a filter layer 16 and microlenses 17 are formed. These filter layers 16 and microlenses 17 are located on the third dielectric layer 15 and correspond to the photoelectric conversion structure 12. The filter layer 16 employs a structure such as a Bayer filter, ensuring that each pixel receives only specific wavelengths (red, green, and blue). The red, green, and blue filter layers 16 are arranged in a regular pattern, and a full-color image is synthesized using an interpolation algorithm. The filter layer 16 is made of a high-transmittance material, such as an organic dye or a nanostructured filter, to balance color separation accuracy and light utilization efficiency. The filter layer 16 is located below the microlenses 17, close to the photoelectric conversion structure 12, to minimize crosstalk. The microlenses at the top of each pixel unit focus incident light onto the active area of ​​the photoelectric conversion structure 12, reducing edge light loss and, in particular, improving the collection efficiency of light incident at wide angles.

[0050] Please continue to refer to Figure 7This embodiment also provides an image sensor fabricated using any of the above-described methods for forming an image sensor. The image sensor is, for example, a CMOS image sensor. The CMOS image sensor includes a substrate 10, which includes a front surface 10a and a back surface 10b. Multiple, isolated photoelectric conversion structures 12 are formed on the front surface 10a of the substrate 10. The side of the photoelectric conversion structures 12 facing away from the front surface 10a of the substrate is W-shaped or wavy, forming a light-trapping structure that increases the photoelectric sensing area. In other words, given the same pixel unit area, the light-trapping structure increases the photoelectric sensing area, improving the performance of the image sensor. A first dielectric layer 13 is formed between the photoelectric conversion structures 12 and on the side of the photoelectric conversion structures 12 facing away from the front surface 10a of the substrate. The first dielectric layer 13 between the photoelectric conversion structures 12 constitutes an isolation structure. A second dielectric layer 14 and a third dielectric layer 15 are formed on the first dielectric layer 13. A filter layer 16 and a microlens 17 are formed on the third dielectric layer. The filter layer 16 and the microlens 17 correspond to the photoelectric conversion structures 12.

[0051] In summary, it can be seen that in the method for forming an image sensor provided by an embodiment of the present invention, a first etching process is performed to form a plurality of groove groups on the front side of the substrate, each groove group includes two sub-grooves, and the spacing between adjacent groove groups is greater than the spacing between the two sub-grooves in the group; then a second etching process is performed to connect the two sub-grooves in each groove group to form a groove, constituting a photoelectric sensing reserved area, and the bottom of the photoelectric sensing reserved area is formed by connecting the bottoms of the two sub-grooves; then a photoelectric conversion structure is formed in the photoelectric sensing reserved area; then a third etching process is performed to etch a portion of the substrate along the back side of the substrate to expose the bottom and part of the side wall of the photoelectric conversion structure, the bottom of the photoelectric conversion structure constitutes a light trapping structure, and the area between the side walls of adjacent photoelectric conversion structures constitutes an isolation area, wherein the third etching process is a wet etching process. The unexpected effect of the present invention is that, under the condition of the same pixel unit area, the light-trapping structure increases the area of ​​the photoelectric sensing area and improves the performance of the image sensor; the photoelectric conversion structure, the light-trapping structure and the isolation area are formed through the epitaxial growth process and the wet etching process, thereby avoiding the lattice damage caused by the dry etching process; and the wet etching process forms the isolation area while forming the light-trapping structure, thereby reducing the process steps and lowering the processing difficulty.

[0052] Furthermore, it should be recognized that although the present invention has been disclosed above with reference to preferred embodiments, the above embodiments are not intended to limit the present invention. Any person skilled in the art can utilize the above disclosed technical content to make many possible changes and modifications to the technical solution of the present invention, or modify it into equivalent embodiments with equivalent variations, without departing from the scope of the technical solution of the present invention. Therefore, any simple modifications, equivalent variations, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the content of the technical solution of the present invention, shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for forming an image sensor, characterized in that: include: Providing a substrate, the substrate comprising a front surface and a back surface disposed opposite to each other; Performing a first etching process to form a plurality of trench groups on the front surface of the substrate, each trench group including two sub-trenches, and a spacing between adjacent trench groups being greater than a spacing between two sub-trenches within the same group; Performing a second etching process to remove at least a portion of the space between the two sub-grooves in each of the groove groups, so that the two sub-grooves in each of the groove groups are connected to form one groove, constituting a photoelectric sensing reserved area; forming a photoelectric conversion structure, wherein the photoelectric conversion structure is located in the photoelectric sensing reserved area; A third etching process is performed to etch a portion of the substrate along the back side of the substrate to expose the bottom and part of the side wall of the photoelectric conversion structure, wherein the bottom of the photoelectric conversion structure constitutes a light trapping structure, and the area between the side walls of adjacent photoelectric conversion structures constitutes an isolation area, wherein the third etching process is a wet etching process.

2. The method for forming an image sensor according to claim 1, wherein: The steps of forming the photoelectric conversion structure include: sequentially epitaxially growing a first semiconductor material layer, a second semiconductor material layer and a third semiconductor material layer, wherein the first semiconductor material layer and the substrate have the same doping type and the doping concentration of the first semiconductor material layer is lower than the doping concentration of the substrate.

3. The method for forming an image sensor according to claim 2, wherein: In the third etching process, the first semiconductor material layer serves as an etching stop layer.

4. The method for forming an image sensor according to claim 2, wherein: The doping type of the second semiconductor material layer is different from the doping type of the third semiconductor material layer.

5. The method for forming an image sensor according to claim 2, wherein: The etching solution of the third etching process is HNA solution. In the third etching process, the etching selectivity of the substrate is greater than the etching selectivity of the first semiconductor material layer.

6. The method for forming an image sensor according to claim 1, wherein: The first etching process is a dry etching process, the second etching process is a wet etching process, and the etching solution of the second etching process is an HF solution or an HNA solution.

7. The method for forming an image sensor according to claim 1, wherein: After the third etching process, the method further includes: forming a first dielectric layer, wherein the first dielectric layer fills the isolation region between adjacent photoelectric conversion structures and covers the surface of the photoelectric conversion structure away from the front surface of the substrate; A second dielectric layer and a third dielectric layer are formed in sequence, wherein the second dielectric layer covers the first dielectric layer, and the third dielectric layer covers the second dielectric layer.

8. The method for forming an image sensor according to claim 7, wherein: The second dielectric layer is made of metal, and the first dielectric layer and the third dielectric layer are made of insulating materials.

9. The method for forming an image sensor according to claim 7, wherein: After forming the third dielectric layer, a filter layer and a microlens are formed in sequence. The filter layer and the microlens are located on the third dielectric layer and correspond to the photoelectric conversion structure.

10. An image sensor, characterized in that: The image sensor is manufactured by the method for forming the image sensor according to any one of claims 1 to 9.

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