CN115579373A - Image sensor pixel structure and preparation method thereof - Google Patents
Image sensor pixel structure and preparation method thereof Download PDFInfo
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- CN115579373A CN115579373A CN202211394999.3A CN202211394999A CN115579373A CN 115579373 A CN115579373 A CN 115579373A CN 202211394999 A CN202211394999 A CN 202211394999A CN 115579373 A CN115579373 A CN 115579373A
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- 238000002360 preparation method Methods 0.000 title abstract description 6
- 239000000758 substrate Substances 0.000 claims abstract description 108
- 230000005684 electric field Effects 0.000 claims abstract description 38
- 238000002955 isolation Methods 0.000 claims abstract description 19
- 238000000034 method Methods 0.000 claims description 37
- 238000005468 ion implantation Methods 0.000 claims description 24
- 229920002120 photoresistant polymer Polymers 0.000 claims description 24
- 230000008569 process Effects 0.000 claims description 19
- 239000002019 doping agent Substances 0.000 claims description 5
- 229910052796 boron Inorganic materials 0.000 claims description 4
- -1 boron ions Chemical class 0.000 claims description 4
- 150000002500 ions Chemical class 0.000 claims description 4
- 238000005530 etching Methods 0.000 claims description 3
- 238000004519 manufacturing process Methods 0.000 description 16
- 238000009792 diffusion process Methods 0.000 description 5
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
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- GYHNNYVSQQEPJS-UHFFFAOYSA-N Gallium Chemical compound [Ga] GYHNNYVSQQEPJS-UHFFFAOYSA-N 0.000 description 2
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 229910052799 carbon Inorganic materials 0.000 description 2
- 230000002349 favourable effect Effects 0.000 description 2
- 229910052733 gallium Inorganic materials 0.000 description 2
- 229910052732 germanium Inorganic materials 0.000 description 2
- GNPVGFCGXDBREM-UHFFFAOYSA-N germanium atom Chemical compound [Ge] GNPVGFCGXDBREM-UHFFFAOYSA-N 0.000 description 2
- 238000003384 imaging method Methods 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 229910052757 nitrogen Inorganic materials 0.000 description 2
- 229910052710 silicon Inorganic materials 0.000 description 2
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- 230000009471 action Effects 0.000 description 1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
- H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
- H01L27/144—Devices controlled by radiation
- H01L27/146—Imager structures
- H01L27/14601—Structural or functional details thereof
- H01L27/1464—Back illuminated imager structures
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
- H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
- H01L27/144—Devices controlled by radiation
- H01L27/146—Imager structures
- H01L27/14601—Structural or functional details thereof
- H01L27/14603—Special geometry or disposition of pixel-elements, address-lines or gate-electrodes
- H01L27/14605—Structural or functional details relating to the position of the pixel elements, e.g. smaller pixel elements in the center of the imager compared to pixel elements at the periphery
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
- H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
- H01L27/144—Devices controlled by radiation
- H01L27/146—Imager structures
- H01L27/14601—Structural or functional details thereof
- H01L27/1463—Pixel isolation structures
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
- H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
- H01L27/144—Devices controlled by radiation
- H01L27/146—Imager structures
- H01L27/14683—Processes or apparatus peculiar to the manufacture or treatment of these devices or parts thereof
Abstract
The invention provides an image sensor pixel structure and a preparation method thereof, wherein the image sensor pixel structure comprises the following steps: a substrate; the photodiode is positioned in the substrate, and a groove isolation structure is formed between adjacent photodiodes; the U-shaped doping area is positioned in the substrate and wraps the bottom surface and the side surface of the photodiode, the U-shaped doping area comprises a first doping area, a second doping area and a third doping area, the first doping area and the second doping area are arranged from top to bottom along the thickness direction of the substrate to wrap the side surface of the photodiode, the third doping area wraps the bottom surface of the photodiode and is connected with the second doping area, the doping concentrations of the first doping area and the third doping area are all larger than that of the second doping area, and the doping concentrations of the first doping area, the second doping area and the third doping area are all larger than that of the substrate to form a U-shaped electric field; the invention can improve the signal-to-noise ratio of the pixel to improve the pixel quality.
Description
Technical Field
The invention relates to the technical field of semiconductors, in particular to an image sensor pixel structure and a preparation method thereof.
Background
The back-illuminated image sensor becomes one of the mainstream of the current image sensor market due to the characteristics of low power consumption, high running speed and the like, but along with the continuous reduction of the pixel size, the electrical crosstalk between adjacent photodiodes in the imaging process becomes one of the important factors influencing the imaging quality. When light irradiates the pixel region, the diffusion of photo-generated electrons in the non-electric field region can cause the adjacent photodiodes to generate crosstalk interference, and the electric signal is not output by the corresponding pixel point signal, so that the electric signal can become noise in the pixel and the quality of the pixel is reduced.
Disclosure of Invention
The present invention is directed to an image sensor pixel structure and a method for fabricating the same, which can prevent electrical crosstalk between neighboring photodiodes and improve the signal-to-noise ratio of the pixel, thereby improving the pixel quality.
In order to achieve the above object, the present invention provides an image sensor pixel structure, comprising:
a substrate;
the photodiode is positioned in the substrate, and a groove isolation structure is formed between the adjacent photodiodes;
the U-shaped doping area is positioned in the substrate and wraps the bottom surface and the side surface of the photodiode, the U-shaped doping area comprises a first doping area, a second doping area and a third doping area, the first doping area and the second doping area are arranged from top to bottom along the thickness direction of the substrate to wrap the side surface of the photodiode, the third doping area wraps the bottom surface of the photodiode and is connected with the second doping area, the doping concentrations of the first doping area and the third doping area are all larger than the doping concentration of the second doping area, and the doping concentrations of the first doping area, the second doping area and the third doping area are all larger than the doping concentration of the substrate to form a U-shaped electric field.
Optionally, the dopant ions of the first doped region, the second doped region, and the third doped region all include boron ions.
Optionally, the doping type of the substrate is P-type.
Optionally, the thicknesses of the first doped region and the second doped region in the thickness direction of the substrate are the same.
Optionally, a bottom surface of the second doped region is aligned with a bottom surface of the third doped region.
Optionally, the photodiode includes a P-type clamping layer and an N-type photosensitive region arranged from top to bottom, the first doped region and the second doped region wrap the side surfaces of the P-type clamping layer and the N-type photosensitive region, and the third doped region wraps the bottom surface of the N-type photosensitive region.
Optionally, at least one of every two adjacent photodiodes is wrapped by the U-shaped doped region.
The invention also provides a preparation method of the pixel structure of the image sensor, which comprises the following steps:
providing a substrate;
forming photodiodes in the substrate, wherein a groove isolation structure is formed between every two adjacent photodiodes; and the number of the first and second groups,
forming a U-shaped doped region which is positioned in the substrate and wraps the bottom surface and the side surface of the photodiode;
the U-shaped doped region comprises a first doped region, a second doped region and a third doped region, the first doped region and the second doped region are arranged from top to bottom along the thickness direction of the substrate to wrap the side face of the photodiode, the third doped region wraps the bottom face of the photodiode and is connected with the second doped region, the doping concentration of the first doped region and the doping concentration of the third doped region are all larger than that of the second doped region, and the doping concentration of the first doped region, the doping concentration of the second doped region and the doping concentration of the third doped region are all larger than that of the substrate to form a U-shaped electric field.
Optionally, the step of forming the photodiode and the trench isolation structure includes:
etching the substrate to form a groove in the substrate, and filling an isolation layer in the groove to form the groove isolation structure; and (c) a second step of,
and carrying out ion implantation on the substrate to form a P-type clamping layer and an N-type photosensitive area which are arranged from top to bottom in the substrate, wherein the P-type clamping layer and the N-type photosensitive area form the photodiode.
Optionally, the step of forming the U-shaped doped region includes:
forming a first patterned photoresist layer on the substrate and the photodiode, wherein the first patterned photoresist layer is provided with a plurality of first openings, and part of the surface of the substrate is exposed by the first openings;
performing a first ion implantation process to form the first doped region in the substrate, and performing a second ion implantation process to form the second doped region in the substrate;
removing the first patterned photoresist layer;
forming a second patterned photoresist layer on the substrate and the photodiode, wherein the second patterned photoresist layer is provided with a plurality of second openings, and at least the surfaces of the photodiode are exposed by the second openings;
performing a third ion implantation process to form the third doped region in the substrate; and (c) a second step of,
and removing the second patterned photoresist layer.
In the pixel structure of the image sensor and the preparation method thereof provided by the invention, the photodiodes are positioned in the substrate, and a groove isolation structure is formed between the adjacent photodiodes; the U-shaped doping area is located in the substrate and wraps the bottom face and the side face of the photodiode, the U-shaped doping area comprises a first doping area, a second doping area and a third doping area, the first doping area and the second doping area are arranged from top to bottom along the thickness direction of the substrate to wrap the side face of the photodiode, the third doping area wraps the bottom face of the photodiode and is connected with the second doping area, the doping concentration of the first doping area and the doping concentration of the third doping area are all larger than that of the second doping area, and the doping concentration of the first doping area, the doping concentration of the second doping area and the doping concentration of the third doping area are all larger than that of the substrate to form a U-shaped electric field. In the invention, because the doping concentration of the first doping region is greater than that of the second doping region, an electric field pointing to the first doping region from the second doping region can be formed; the doping concentration of the third doping area is greater than that of the second doping area, so that an electric field pointing to the third doping area from the second doping area is formed; the doping concentration of the third doping area is greater than that of the substrate, and an electric field pointing to the third doping area from the substrate can be formed to form a U-shaped electric field; the U-shaped electric field pulls the noise electrons between the adjacent photodiodes away from the photodiodes, so as to prevent the noise electrons between the adjacent photodiodes from generating electrical crosstalk, improve the signal-to-noise ratio of the pixel and improve the pixel quality.
Drawings
Fig. 1 is a flowchart of a method for manufacturing a pixel structure of an image sensor according to an embodiment of the present invention.
Fig. 2 is a schematic cross-sectional view illustrating a photodiode formed in a method for manufacturing a pixel structure of an image sensor according to an embodiment of the invention.
Fig. 3 is a schematic cross-sectional view illustrating a first doped region formed in a method for manufacturing a pixel structure of an image sensor according to an embodiment of the invention.
Fig. 4 is a schematic cross-sectional view illustrating a second doped region formed in a method for manufacturing a pixel structure of an image sensor according to an embodiment of the invention.
Fig. 5 is a schematic cross-sectional view illustrating a first patterned photoresist layer is removed in a manufacturing method of a pixel structure of an image sensor according to an embodiment of the invention.
Fig. 6 is a schematic cross-sectional view illustrating a third doped region formed in a method for manufacturing a pixel structure of an image sensor according to an embodiment of the invention.
Fig. 7 is a schematic cross-sectional view of a pixel structure of an image sensor according to an embodiment of the invention.
Wherein the reference numbers are:
10-a substrate; 20-a photodiode; a 21-P type clamp layer; a 22-N type photosensitive region; 30-a trench isolation structure; 41-a first patterned photoresist layer; 42-a second patterned photoresist layer; 51-a first doped region; 52-a second doped region; 53-third doped region.
Detailed Description
The following describes in more detail embodiments of the present invention with reference to the schematic drawings. The advantages and features of the present invention will become more apparent from the following description. It is to be noted that the drawings are in a very simplified form and are not to precise scale, which is merely for the purpose of facilitating and distinctly claiming the embodiments of the present invention.
Fig. 7 is a schematic cross-sectional view of a pixel structure of an image sensor provided in this embodiment. Referring to fig. 7, the present embodiment provides an image sensor pixel structure, including: a substrate 10, a photodiode 20, a trench isolation structure 30 and a U-shaped doped region, wherein the material of the substrate 10 includes one or more of silicon, germanium, gallium, nitrogen or carbon, the doping type of the substrate 10 is P-type, and the substrate 10 includes a pixel region (not shown).
The photodiode 20 is located in a pixel region of the substrate 10, the photodiode 20 includes a P-type clamping layer 21 and an N-type photosensitive region 22 arranged from top to bottom, and a trench isolation structure 30 is formed between adjacent photodiodes 20. When light irradiates the photodiode 20 (pixel) in the pixel region, some dissociated noise electrons (photo-generated electrons) are generated in the substrate 10 around the photodiode 20 (especially in the substrate 10 below the photodiode 20), and the noise electrons diffuse to the adjacent photodiode 20, thereby affecting the output of the adjacent photodiode 20, forming noise in the pixel region, and reducing the pixel quality.
The U-shaped doped region is located in the substrate 10 and wraps the bottom surface and the side surface of the photodiode 20, the U-shaped doped region includes a first doped region 51, a second doped region 52 and a third doped region 53, wherein the first doped region 51 and the second doped region 52 are arranged from top to bottom along the thickness direction of the substrate 10 to wrap the side surface of the photodiode 20 (wrapping the side surfaces of the P-type clamping layer 21 and the N-type photosensitive region 22), and the third doped region 53 wraps the bottom surface of the photodiode 20 (wrapping the bottom surface of the N-type photosensitive region 22) and is connected with the second doped region 52 to form the U-shaped doped region to wrap the bottom surface and the side surface of the photodiode 20. In the present embodiment, the second doping region 52 extends downward along the thickness direction of the substrate 10 to contact the side surface of the third doping region 53, and the bottom surface of the second doping region 52 can be aligned with the bottom surface of the third doping region 53, which is favorable for forming a uniform electric field. In this embodiment, the thicknesses of the first doped region 51 and the second doped region 52 in the thickness direction of the substrate 10 are preferably the same, but are not limited thereto, and the thicknesses of the first doped region 51 and the second doped region 52 in the thickness direction of the substrate 10 are different; it is preferable that the first doping region 51 and the second doping region 52 have the same width in the horizontal direction of the substrate 10 and the side of the first doping region 51 and the side of the second doping region 52 are aligned to facilitate the formation of a uniform electric field. In the present embodiment, at least one of each two adjacent photodiodes 20 is wrapped by the U-shaped doped region, specifically, each photodiode 20 may be wrapped by the U-shaped doped region (as shown in fig. 7), or one of each two adjacent photodiodes 20 is wrapped by the U-shaped doped region, that is, only one photodiode 20 may be wrapped by the U-shaped doped region in fig. 7.
In the present embodiment, the doping concentrations of the first doping region 51 and the third doping region 53 are all greater than the doping concentration of the second doping region 52, and the doping concentrations of the first doping region 51, the second doping region 52 and the third doping region 53 are all greater than the doping concentration of the substrate 10. In the present embodiment, the dopant ions of the first, second and third doped regions 51, 52 and 53 each include boron ions.
Since the doping concentration of the first doping region 51 is greater than the doping concentration of the second doping region 52, an electric field pointing from the second doping region 52 to the first doping region 51 is formed, and the direction of the noise electrons is that the first doping region 51 points to the second doping region 52 (i.e. downward in fig. 7); the doping concentration of the third doping region 53 is greater than the doping concentration of the second doping region 52, so that an electric field pointing from the second doping region 52 to the third doping region 53 is formed, and the direction of noise electrons is the direction (i.e., the left-right direction in fig. 7) of the third doping region 53 pointing to the second doping region 52; the doping concentration of the third doped region 53 is greater than the doping concentration of the substrate 10, an electric field is formed from the substrate 10 to the third doped region 53, and the direction of the noise electrons is such that the third doped region 53 points to the substrate 10 (i.e., downward in fig. 7), thereby forming a U-shaped electric field. Under the action of the U-shaped electric field, when noise electrons (shown in fig. 7) diffuse around the U-shaped electric field, the U-shaped electric field pulls the noise electrons between adjacent photodiodes 20 away from the photodiodes 20, i.e., the diffusion direction of the noise electrons in fig. 7 is downward (the curved dotted line in fig. 7 is the diffusion path of the noise electrons), so as to prevent the noise electrons between adjacent photodiodes 20 from generating electrical crosstalk, and improve the signal-to-noise ratio of the pixel, thereby improving the pixel quality.
Fig. 1 is a flowchart of a method for manufacturing a pixel structure of an image sensor according to this embodiment. Referring to fig. 1, the present invention further provides a method for manufacturing a pixel structure of an image sensor, which is used for manufacturing the pixel structure of the image sensor, and the method includes:
step S1: providing a substrate;
step S2: forming photodiodes in the substrate, and forming a trench isolation structure between adjacent photodiodes;
and step S3: forming a U-shaped doped region which is positioned in the substrate and wraps the bottom surface and the side surface of the photodiode;
the U-shaped doping area comprises a first doping area, a second doping area and a third doping area, the first doping area and the second doping area are arranged from top to bottom along the thickness direction of the substrate to wrap the side face of the photodiode, the third doping area wraps the bottom face of the photodiode and is connected with the second doping area, the doping concentration of the first doping area and the doping concentration of the third doping area are all larger than that of the second doping area, and the doping concentration of the first doping area, the doping concentration of the second doping area and the doping concentration of the third doping area are all larger than that of the substrate to form a U-shaped electric field.
Fig. 2 is a schematic cross-sectional view illustrating a photodiode formed in the method for manufacturing a pixel structure of an image sensor according to this embodiment; fig. 3 is a schematic cross-sectional view illustrating a first doped region formed in the method for manufacturing a pixel structure of an image sensor according to the embodiment; fig. 4 is a schematic cross-sectional view illustrating a second doped region formed in the method for manufacturing a pixel structure of an image sensor according to the embodiment; fig. 5 is a schematic cross-sectional view illustrating the first patterned photoresist layer is removed in the method for manufacturing a pixel structure of an image sensor according to the embodiment; fig. 6 is a schematic cross-sectional view illustrating a third doped region formed in the method for manufacturing a pixel structure of an image sensor according to the present embodiment; fig. 7 is a schematic cross-sectional view of a pixel structure of an image sensor provided in this embodiment, where fig. 7 is a schematic cross-sectional view of the pixel structure of the image sensor provided in this embodiment after the second patterned photoresist layer is removed. The following describes in detail a method for manufacturing a pixel structure of an image sensor according to this embodiment with reference to fig. 2 to 7.
Referring to fig. 2, step S1 is executed: a substrate 10 is provided, the material of the substrate 10 including one or more of silicon, germanium, gallium, nitrogen or carbon. The doping type of the substrate 10 is P-type, and the substrate 10 includes a pixel region (not shown).
With continued reference to fig. 2, step S2 is performed: etching the substrate 10 to form a trench in the substrate 10, and filling an isolation layer in the trench to form a trench isolation structure 30; and, ion implantation is performed on the substrate 10 to form a P-type clamping layer 21 and an N-type photosensitive region 22 arranged from top to bottom in the substrate 10, and the P-type clamping layer 21 and the N-type photosensitive region 22 constitute the photodiode 20.
Executing the step S3: the step of forming the U-shaped doped region comprises the following steps:
referring to fig. 3, a first patterned photoresist layer 41 is formed on the substrate 10 and the photodiode 20, the first patterned photoresist layer 41 has a plurality of first openings, and the first openings expose a portion of the surface of the substrate 10; further, a first ion implantation process is performed to form a first doped region 51 in the substrate 10 (the direction of the arrow in fig. 3 is the ion implantation direction), and the first doped region 51 wraps the upper side of the photodiode 20.
Referring to fig. 4, a second ion implantation process is performed to form a second doped region 52 in the substrate 10 (the direction of the arrow in fig. 4 is the ion implantation direction) by using the first patterned photoresist layer 41 as a mask, wherein the second doped region 52 is located right below the first doped region 51 and wraps the lower portion of the photodiode 20, and the second doped region 52 further extends a partial depth downward along the thickness direction of the substrate 10. In this embodiment, the thicknesses of the first doped region 51 and the second doped region 52 in the thickness direction of the substrate 10 are preferably the same, but the thicknesses of the first doped region 51 and the second doped region 52 in the thickness direction of the substrate 10 may not be limited thereto; it is preferable that the first and second doped regions 51 and 52 have the same width in the horizontal direction of the substrate 10, and the side of the first doped region 51 and the side of the second doped region 52 are aligned, which facilitates the formation of a uniform electric field. In the present embodiment, fig. 3 and fig. 4 show that the first doping region 51 is formed first, and then the second doping region 52 is formed; in practice, the second doping region 52 may be formed first, and then the first doping region 51 may be formed.
Referring to fig. 5, the first patterned photoresist layer is removed, and the first doped region 51 and the second doped region 52 are arranged from top to bottom along the thickness direction of the substrate 10 to wrap the side surface of the photodiode 20.
Referring to fig. 6, a second patterned photoresist layer 42 is formed on the substrate 10 and the photodiode 20, the second patterned photoresist layer 42 has a plurality of second openings, and the second openings at least expose the surface of the photodiode 20; furthermore, a third ion implantation process is performed to form a third doped region 53 in the substrate 10 (the direction of the arrow in fig. 6 is the ion implantation direction), and the third doped region 53 wraps the bottom surface of the photodiode 20 and is connected to the second doped region 52. In the present embodiment, the second doping region 52 extends downward along the thickness direction of the substrate 10 to contact the side surface of the third doping region 53, and the bottom surface of the second doping region 52 can be aligned with the bottom surface of the third doping region 53, which is favorable for forming a uniform electric field. In this embodiment, the doping concentrations of the first ion implantation process and the third ion implantation process are both greater than the doping concentration of the second ion implantation process, and the doping concentrations of the first ion implantation process, the third ion implantation process and the second ion implantation process are all greater than the doping concentration of the substrate, so as to form a U-shaped electric field. In this embodiment, the dopant ions of the first ion implantation process, the third ion implantation process, and the second ion implantation process each include boron ions.
Referring to fig. 7, the second patterned photoresist layer is removed. Since the doping concentration of the first doping region 51 is greater than the doping concentration of the second doping region 52, an electric field pointing from the second doping region 52 to the first doping region 51 is formed, and the direction of the noise electrons is that the first doping region 51 points to the second doping region 52 (i.e. downward in fig. 7); the doping concentration of the third doping region 53 is greater than the doping concentration of the second doping region 52, so that an electric field pointing from the second doping region 52 to the third doping region 53 is formed, and the direction of noise electrons is the direction (i.e., the left-right direction in fig. 7) of the third doping region 53 pointing to the second doping region 52; the doping concentration of the third doped region 53 is greater than the doping concentration of the substrate 10, which results in an electric field directed from the substrate 10 to the third doped region 53, while the noise electrons are directed in a direction such that the third doped region 53 is directed toward the substrate 10 (i.e., downward in fig. 7) to form a U-shaped electric field. Under the effect of the U-shaped electric field, when noise electrons (shown in fig. 7) diffuse around the U-shaped electric field, the U-shaped electric field pulls the noise electrons between adjacent photodiodes 20 away from the photodiodes 20, i.e. the diffusion direction of the noise electrons in fig. 7 is downward (the curved dotted line in fig. 7 is the diffusion path of the noise electrons), so as to prevent the noise electrons between adjacent photodiodes 20 from generating electrical crosstalk, improve the signal-to-noise ratio of the pixel, and improve the pixel quality.
In summary, in the pixel structure of the image sensor and the manufacturing method thereof provided by the present invention, the photodiodes are located in the substrate, and a trench isolation structure is formed between adjacent photodiodes; the U-shaped doping area is located in the substrate and wraps the bottom surface and the side surface of the photodiode, the U-shaped doping area comprises a first doping area, a second doping area and a third doping area, the first doping area and the second doping area are arranged from top to bottom along the thickness direction of the substrate to wrap the side surface of the photodiode, the third doping area wraps the bottom surface of the photodiode and is connected with the second doping area, the doping concentrations of the first doping area and the third doping area are all larger than that of the second doping area, and the doping concentrations of the first doping area, the second doping area and the third doping area are all larger than that of the substrate to form a U-shaped electric field. In the invention, because the doping concentration of the first doping region is greater than that of the second doping region, an electric field pointing to the first doping region from the second doping region can be formed; the doping concentration of the third doping area is greater than that of the second doping area, so that an electric field pointing to the third doping area from the second doping area can be formed; the doping concentration of the third doping area is greater than that of the substrate, and an electric field pointing to the third doping area from the substrate can be formed to form a U-shaped electric field; the U-shaped electric field pulls the noise electrons between the adjacent photodiodes away from the photodiodes, so as to prevent the noise electrons between the adjacent photodiodes from generating electrical crosstalk, improve the signal-to-noise ratio of the pixel and improve the pixel quality.
The above description is only a preferred embodiment of the present invention, and does not limit the present invention in any way. It will be understood by those skilled in the art that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (10)
1. An image sensor pixel structure, comprising:
a substrate;
the photodiode is positioned in the substrate, and a groove isolation structure is formed between every two adjacent photodiodes;
the U-shaped doping area is positioned in the substrate and wraps the bottom surface and the side surface of the photodiode, the U-shaped doping area comprises a first doping area, a second doping area and a third doping area, the first doping area and the second doping area are arranged from top to bottom along the thickness direction of the substrate to wrap the side surface of the photodiode, the third doping area wraps the bottom surface of the photodiode and is connected with the second doping area, the doping concentrations of the first doping area and the third doping area are all larger than the doping concentration of the second doping area, and the doping concentrations of the first doping area, the second doping area and the third doping area are all larger than the doping concentration of the substrate to form a U-shaped electric field.
2. The image sensor pixel structure of claim 1, wherein the dopant ions of the first, second, and third dopant regions each comprise boron ions.
3. The image sensor pixel structure of claim 2, wherein the substrate is doped P-type.
4. The image sensor pixel structure of claim 1, wherein the first doped region and the second doped region have the same thickness along a thickness direction of the substrate.
5. The image sensor pixel structure of claim 1 or 4, wherein a bottom surface of the second doped region and a bottom surface of the third doped region are aligned.
6. The image sensor pixel structure of claim 1, wherein the photodiode comprises a P-type clamping layer and an N-type photosensitive region arranged from top to bottom, the first doped region and the second doped region wrap around sides of the P-type clamping layer and the N-type photosensitive region, and the third doped region wraps around a bottom surface of the N-type photosensitive region.
7. The image sensor pixel structure of claim 1, wherein at least one of each adjacent two of the photodiodes is encapsulated by the U-shaped doped region.
8. A method for preparing a pixel structure of an image sensor is characterized by comprising the following steps:
providing a substrate;
forming photodiodes in the substrate, wherein a groove isolation structure is formed between every two adjacent photodiodes; and (c) a second step of,
forming a U-shaped doped region which is positioned in the substrate and wraps the bottom surface and the side surface of the photodiode;
the U-shaped doped region comprises a first doped region, a second doped region and a third doped region, the first doped region and the second doped region are arranged from top to bottom along the thickness direction of the substrate to wrap the side face of the photodiode, the third doped region wraps the bottom face of the photodiode and is connected with the second doped region, the doping concentration of the first doped region and the doping concentration of the third doped region are all larger than that of the second doped region, and the doping concentration of the first doped region, the doping concentration of the second doped region and the doping concentration of the third doped region are all larger than that of the substrate to form a U-shaped electric field.
9. The method of claim 8, wherein forming the photodiode and the trench isolation structure comprises:
etching the substrate to form a groove in the substrate, and filling an isolation layer in the groove to form the groove isolation structure; and the number of the first and second groups,
and carrying out ion implantation on the substrate to form a P-type clamping layer and an N-type photosensitive region which are arranged from top to bottom in the substrate, wherein the P-type clamping layer and the N-type photosensitive region form the photodiode.
10. The method of claim 8, wherein forming the U-shaped doped region comprises:
forming a first patterned photoresist layer on the substrate and the photodiode, wherein the first patterned photoresist layer is provided with a plurality of first openings, and part of the surface of the substrate is exposed by the first openings;
performing a first ion implantation process to form the first doped region in the substrate, performing a second ion implantation process to form the second doped region in the substrate;
removing the first patterned photoresist layer;
forming a second patterned photoresist layer on the substrate and the photodiode, wherein the second patterned photoresist layer has a plurality of second openings, and the second openings at least expose the surface of the photodiode;
performing a third ion implantation process to form the third doped region in the substrate; and the number of the first and second groups,
and removing the second patterned photoresist layer.
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