Image sensor and preparation method thereof

Abstract

The present invention discloses an image sensor and a preparation method thereof, belonging to the field of semiconductor technology. The image sensor comprises: a substrate, comprising a first surface and a second surface arranged opposite to each other; a well region, extending from the first surface into the substrate; a photoelectric sensing region, arranged in the well region, and a preset distance between the photoelectric sensing region and the first surface; a floating diffusion region, arranged at intervals on one side of the photoelectric sensing region; a transmission gate, arranged on the first surface between the floating diffusion region and the photoelectric sensing region; a deep well region, arranged in the well region; a pinning layer, extending from the first surface to the photoelectric sensing region, the pinning layer comprises a first pinning layer and a second pinning layer, the first pinning layer is arranged between the second pinning layer and the photoelectric sensing region; and a plurality of doping regions, arranged at intervals in the second pinning layer on the first pinning layer. The image sensor and the preparation method thereof provided by the present invention can improve the white spot phenomenon and improve the imaging quality of the image sensor.

Description

Technical Field

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

[0002] Complementary Metal Oxide Semiconductor (CMOS) image sensors have the advantages of small size, low cost, low power consumption and good process compatibility. They are widely used in smart phones, digital cameras, automotive optical imaging systems and surveillance cameras.

[0003] In CMOS image sensors, the white spot phenomenon is a common defect that seriously affects the image quality. The causes of the white spot phenomenon include dark current and image overflow. The dark current mainly comes from the dark current generated inside the depletion region, the lattice defects / dangling bonds generated by the lattice mismatch at the Si-SiO2 interface, and the diffused dark current in the neutral region. Therefore, it is urgent to solve the problems of dark current and image overflow, and then improve the white spot phenomenon. Summary of the invention

[0004] In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide an image sensor and a method for preparing the same, which can reduce dark current, avoid image overflow, and further improve the white spot phenomenon and the imaging quality of the image sensor.

[0005] To solve the above technical problems, the present invention is implemented through the following technical solutions.

[0006] The present invention provides an image sensor, comprising at least:

[0007] A substrate comprising a first surface and a second surface disposed opposite to each other;

[0008] a well region extending from the first surface into the substrate;

[0009] A photoelectric sensing region is disposed in the well region, and a preset distance exists between the photoelectric sensing region and the first surface;

[0010] A floating diffusion region is spaced apart and arranged on one side of the photoelectric sensing region;

[0011] a transmission gate disposed on the first surface between the floating diffusion region and the photoelectric sensing region;

[0012] A deep well region is arranged in the well region, the deep well region is arranged at least on one side of the photoelectric sensing region, and the deep well region is opened at least on one side of the photoelectric sensing region adjacent to the transmission gate;

[0013] a pinning layer extending from the first surface to the photoelectric sensing region, the pinning layer comprising a first pinning layer and a second pinning layer, the first pinning layer being disposed between the second pinning layer and the photoelectric sensing region; and

[0014] A plurality of doped regions are spaced apart and arranged in the second pinning layer on the first pinning layer.

[0015] In one embodiment of the present invention, the first pinning layer extends from a side of the deep well region close to the photoelectric sensing region to the photoelectric sensing region.

[0016] In one embodiment of the present invention, the second pinning layer extends from the deep well region at least to a side of the photoelectric sensing region close to the floating diffusion region.

[0017] In an embodiment of the present invention, the doped region extends from the first surface into the second pinned layer.

[0018] In one embodiment of the present invention, the well region, the deep well region, the first pinned layer and the second pinned layer are P-type doped regions, and the doped region is an N-type doped region.

[0019] In one embodiment of the present invention, the doping concentration of the first pinned layer is greater than the doping concentration of the second pinned layer, the doping concentration of the second pinned layer is greater than the doping concentration of the deep well region, and the doping concentration of the deep well region is greater than the doping concentration of the well region.

[0020] In one embodiment of the present invention, the doping concentration of the second pinning layer is less than the doping concentration of the doping region.

[0021] In one embodiment of the present invention, the first pinned layer and the second pinned layer are connected to a low potential, and the doped region is connected to a high potential.

[0022] The present invention also provides a method for preparing an image sensor, which comprises at least the following steps:

[0023] Providing a substrate, the substrate comprising a first surface and a second surface arranged opposite to each other;

[0024] forming a well region in the substrate, wherein the well region extends from the first surface into the substrate;

[0025] forming a photoelectric sensing region in the well region, wherein a preset distance exists between the photoelectric sensing region and the first surface;

[0026] A floating diffusion region is formed at one side of the photoelectric sensing region;

[0027] forming a transfer gate on the first surface between the floating diffusion region and the photoelectric sensing region;

[0028] A deep well region is formed in the well region at least on one side of the photoelectric sensing region, and the deep well region is opened at least on one side of the photoelectric sensing region adjacent to the transmission gate;

[0029] forming a pinning layer between the first surface and the photoelectric sensing region, the pinning layer comprising a first pinning layer and a second pinning layer, the first pinning layer being disposed between the second pinning layer and the photoelectric sensing region; and

[0030] A plurality of doping regions are formed in the second pinning layer on the first pinning layer at intervals.

[0031] In one embodiment of the present invention, after the doping region is formed, an oxide layer is formed on the transmission gate and the first surface, and the oxide layer is generated by an in-situ water vapor method.

[0032] In summary, the present invention provides an image sensor and a method for preparing the same. By improving the structure of the image sensor, the unexpected technical effect of the present application is that the dark current can be reduced, white spots can be avoided in the imaging of the image sensor, and the imaging quality can be improved. Moreover, the image sensor and the method for preparing the same provided by the present invention can prevent the photogenerated electrons in the photoelectric sensing area from overflowing into adjacent pixel units, improve the white spot phenomenon caused by image overflow, and further improve the imaging quality.

[0033] Of course, any method of implementing the present invention does not necessarily need to achieve all of the advantages mentioned above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0035] Figure 1 FIG. 4 is a top view of an image sensor according to an embodiment of the present invention.

[0036] Figure 2 A schematic diagram of forming a well region.

[0037] Figure 3 A schematic diagram of forming a photoelectric sensing area.

[0038] Figure 4 Schematic diagram of forming a deep well region.

[0039] Figure 5 A schematic diagram of forming a first photoresist layer and a first window.

[0040] Figure 6 Schematic diagram of forming the first pinning layer.

[0041] Figure 7 Schematic diagram of forming a second pinning layer.

[0042] Figure 8 It is a schematic diagram of forming a gate oxide layer, a gate material layer and a second photoresist layer.

[0043] Fig. 9 A schematic diagram of forming a transmission gate.

[0044] Fig.10 A schematic diagram of forming a side wall.

[0045] Fig.11 A schematic diagram of forming a floating diffusion region.

[0046] Fig.12 is a schematic diagram of forming a third photoresist layer.

[0047] Fig.13 A schematic diagram of forming a doped region.

[0048] Fig.14 Schematic diagram of the formation of an oxide layer.

[0049] Fig.15 Schematic diagram of forming a barrier layer.

[0050] Fig.16 for Fig.15 Schematic diagram of the transistor at A in the middle.

[0051] Fig.17 for Fig.15 Schematic diagram of the diode at B in the figure.

[0052] Description of labels:

[0053] 11. substrate; 111. first surface; 112. second surface; 12. well region; 13. photoelectric sensing region; 14. deep well region; 15. first pinning layer; 151. first photoresist layer; 152. first window; 153. second window; 16. second pinning layer; 17. gate oxide layer; 18. transfer gate; 181. gate material layer; 182. second photoresist layer; 19. side wall; 20. floating diffusion region; 21. third photoresist layer; 211. first opening; 212. second opening; 213. third opening; 214. fourth opening; 22. doping region; 23. oxide layer; 24. blocking layer. DETAILED DESCRIPTION

[0054] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0055] It should be understood that the present invention can be implemented in different forms and should not be interpreted as limited to the embodiments set forth herein. On the contrary, these embodiments are provided to make the disclosure thorough and complete and to fully convey the scope of the present invention to those skilled in the art.

[0056] The technical solution of the present invention is further described in detail below in conjunction with the embodiments and drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0057] See also Figure 1 and Fig.15As shown, the present invention provides an image sensor, which includes, for example, a substrate 11, a well region 12, a photoelectric sensing region 13, a floating diffusion region 20, a transmission gate 18, a deep well region 14, a pinning layer and a doping region 22. The substrate 11 includes a first surface 111 and a second surface 112 that are oppositely arranged. The well region 12 extends from the first surface 111 into the substrate 11. The photoelectric sensing region 13 is arranged in the well region 12, and a preset distance exists between the photoelectric sensing region 13 and the first surface 111. The floating diffusion region 20 is arranged on one side of the photoelectric sensing region 13. The transmission gate 18 is arranged on the first surface 111 between the floating diffusion region 20 and the photoelectric sensing region 13. The deep well region 14 is arranged in the well region 12. The deep well region 14 is at least arranged on one side of the photoelectric sensing region 13, and the deep well region 14 is at least opened on one side of the photoelectric sensing region 13 adjacent to the transmission gate 18. The pinning layer extends from the first surface 111 to the photoelectric sensing region 13. The pinning layer includes a first pinning layer 15 and a second pinning layer 16. The first pinning layer 15 is arranged between the second pinning layer 16 and the photoelectric sensing region 13. The doping region 22 is arranged in the second pinning layer 16 on the first pinning layer 15. In the image sensor provided by the present invention, the doping region 22-pinning layer-photoelectric sensing region 13 constitutes a parasitic NPN transistor, wherein the pinning layer-photoelectric sensing region 13 serves as the emitter junction of the parasitic NPN transistor, and the doping region 22-pinning layer serves as the collector junction of the parasitic NPN transistor. When the emitter junction is forward biased and the collector junction is reverse biased, the transistor enters the on state, and the photogenerated electrons overflowing from the photoelectric sensing region 13 pass through the pinning layer and are attracted by the reverse bias electric field of the doping region 22, and then flow out from the doping region 22, thereby avoiding the photogenerated electrons from overflowing into adjacent pixel units, improving the image overflow problem, and further avoiding the white spot phenomenon in the imaging of the image sensor. Moreover, the image sensor provided by the present invention, by providing the doping region 22 and the second pinning layer 16, constitutes a parasitic NP diode, and uses the reverse bias state of the parasitic NP diode to place the first surface 111 in the depletion region, shielding the electron / hole pairs generated by the interface defects of the first surface 111, reducing the dark current, and further avoiding the white spot phenomenon in the imaging of the image sensor. The present invention also provides a method for preparing an image sensor. The method for preparing the image sensor is, for example, Figure 1 The sectional view of section AA in FIG. 2 is used as an example to illustrate this.

[0058] See also Figure 2 As shown, in one embodiment of the present invention, the substrate 11 includes a first surface 111 and a second surface 112 arranged opposite to each other, and first ions are injected into the substrate 11 from the first surface 111 to form a well region 12. The well region 12 extends from the first surface 111 into the substrate 11, and the type and concentration of the first ions can be selected according to actual conditions. In this embodiment, the first ions are, for example, P-type ions such as boron (B) or indium (In).

[0059] See also Figures 2 to 3 As shown, in one embodiment of the present invention, after the well region 12 is formed, the second ions are injected into the well region 12 from the first surface 111 to form the photoelectric sensing region 13. Among them, a preset distance is maintained between the top of the photoelectric sensing region 13 and the first surface 111, and the distance between the bottom of the photoelectric sensing region 13 and the second surface 112 is, for example, smaller than the distance between the bottom of the well region 12 and the second surface 112. In this embodiment, the type of the second ion is different from the type of the first ion, and the second ion is, for example, an N-type ion such as phosphorus (P) or arsenic (As). By setting the photoelectric sensing region 13, the optical signal received by the image sensor can be converted into an electrical signal.

[0060] See also Figure 3 to Figure 4 As shown, in one embodiment of the present invention, after the photoelectric sensing region 13 is formed, the third ion is injected into the well region 12 from the first surface 111 to form a deep well region 14. The deep well region 14 is at least arranged on one side of the photoelectric sensing region 13, and at most on three sides of the photoelectric sensing region 13, that is, the deep well region 14 is opened at least on one side of the photoelectric sensing region 13. In this embodiment, the deep well region 14 is arranged on three sides of the photoelectric sensing region 13. In the thickness direction of the substrate 11, the deep well region 14 extends from the first surface 111 to the well region 12, the deep well region 14 and the photoelectric sensing region 13 are arranged at intervals, and the distance between the bottom of the deep well region 14 and the second surface 112 is, for example, greater than the distance between the bottom of the photoelectric sensing region 13 and the second surface 112, for example, less than the distance between the bottom of the well region 12 and the second surface 112, the third ion is, for example, a P-type ion such as B or In, and the doping concentration of the deep well region 14 is, for example, greater than the doping concentration of the well region 12. Specifically, the ratio of the doping concentration of the deep well region 14 to the doping concentration of the well region 12 is, for example, (1.05-1.4):1, or, for example, 1.3:1, 1.2:1, or 1.1:1.

[0061] See also Figures 4 to 5 As shown, in one embodiment of the present invention, after the deep well region 14 is formed, a first photoresist layer 151 is formed on the first surface 111, and a first window 152 is formed in the first photoresist layer 151. One side of the first window 152 is aligned with the side of the deep well region 14 close to the photoelectric sensing region 13, and the other side is located on the first surface 111 on the photoelectric sensing region 13. The thickness of the first photoresist layer 151 is, for example, 1 μm-3 μm.

[0062] See also Figures 5 and 6As shown, in one embodiment of the present invention, the first photoresist layer 151 is used as a mask to inject fourth ions into the well region 12 exposed by the first window 152 to form a first pinned layer 15. The first pinned layer 15 extends from the side of the deep well region 14 close to the photoelectric sensing region 13 to the well region 12 on the photoelectric sensing region 13, and part of the first pinned layer 15 is in contact with the photoelectric sensing region 13. In this embodiment, the fourth ion is, for example, a P-type ion such as B or In, and the doping concentration of the first pinned layer 15 is, for example, greater than the doping concentration of the deep well region 14. Specifically, the ratio of the doping concentration of the first pinned layer 15 to the doping concentration of the deep well region 14 is, for example, (1.5-1.8):1, and for example, 1.5:1, 1.6:1 or 1.7:1, etc.

[0063] See also Figure 6 to Figure 7 As shown, in one embodiment of the present invention, after forming the first pinning layer 15, the first photoresist layer 151 is modified and etched, and a portion of the first photoresist layer 151 on both sides of the first window 152 is removed, and the width of the first window 152 is enlarged to form a second window 153. Wherein, relative to the width of the first window 152, the width of the second window 153 is enlarged by, for example, 0.2-0.5 μm, and one side of the second window 153 is located on the first surface 111 on the deep well region 14, and the other side at least extends to the side of the photoelectric sensing region 13 away from the deep well region 14. In this embodiment, the other side of the second window 153 is aligned with the side of the photoelectric sensing region 13 away from the deep well region 14.

[0064] See also Figure 7As shown, in one embodiment of the present invention, the first photoresist layer 151 after etching and modification is used as a mask, and the fifth ion is injected into the well region 12 and the deep well region 14 exposed by the second window 153 to form the second pinning layer 16, and the second pinning layer 16 and the first pinning layer 15 are defined as the pinning layer, and then the first photoresist layer 151 is removed. The second pinning layer 16 is arranged in the well region 12 and the deep well region 14 between the first pinning layer 15 and the first surface 111, and the second pinning layer 16 extends from the deep well region 14 to the direction where the well region 12 on the photoelectric sensing region 13 is located, and at least extends to the side of the photoelectric sensing region 13 away from the deep well region 14, and the thickness of the second pinning layer 16 is, for example, greater than the thickness of the first pinning layer 15. In this embodiment, the second pinned layer 16 extends from the deep well region 14 to the side of the photoelectric sensing region 13 away from the deep well region 14, the fifth ion is, for example, a P-type ion such as B or In, and the doping concentration of the second pinned layer 16 is, for example, less than the doping concentration of the first pinned layer 15, so as to effectively prevent the photoelectric sensing region 13 and the subsequently arranged doping region 22 from penetrating, and the doping concentration of the second pinned layer 16 is, for example, greater than the doping concentration of the deep well region 14. Specifically, the ratio of the doping concentration of the first pinned layer 15 to the doping concentration of the second pinned layer 16 is, for example, (1.2-1.6):1, and for example, 1.4:1 or 1.5:1, and the ratio of the doping concentration of the second pinned layer 16 to the doping concentration of the deep well region 14 is, for example, (1.1-1.3):1, and for example, 1.2:1 or 1.3:1, and for example. In this embodiment, the first photoresist layer 151 is used as a mask in the process of forming the first pinning layer 15 and the second pinning layer 16 , which can simplify the preparation process and save preparation costs.

[0065] See also Figures 7 and 8 As shown, in one embodiment of the present invention, after forming the second pinning layer 16, a gate oxide layer 17 is formed on the first surface 111. The gate oxide layer 17 is formed, for example, by a thermal oxidation method, an in-situ water vapor growth method, or a chemical vapor deposition method, and the material of the gate oxide layer 17 is, for example, silicon oxide, and the silicon oxide is, for example, silicon dioxide or silicon oxynitride, and the thickness of the gate oxide layer 17 can be set according to actual conditions. In this embodiment, the thickness of the gate oxide layer 17 is, for example, 70Å-100Å.

[0066] See also Figure 8 As shown, in one embodiment of the present invention, after the gate oxide layer 17 is formed, a gate material layer 181 is formed on the gate oxide layer 17. The gate material layer 181 is formed by, for example, chemical vapor deposition, physical vapor deposition, electroplating or atomic layer deposition, etc. The thickness of the gate material layer 181 can be set according to actual conditions, and the material of the gate material layer 181 includes, for example, polysilicon, etc. In this embodiment, the thickness of the gate material layer 181 is, for example, 200nm-250nm.

[0067] See also Figures 8 to 9 As shown, in one embodiment of the present invention, after forming the gate material layer 181, a second photoresist layer 182 is formed on the gate material layer 181, and the second photoresist layer 182 covers a portion of the gate material layer 181 on the side of the photoelectric sensing region 13 away from the deep well region 14, and then the second photoresist layer 182 is used as a mask to etch the exposed gate material layer 181 and the gate oxide layer 17, and then the second photoresist layer 182 is removed, and the retained gate material layer 181 is defined as a transmission gate 18. The transmission gate 18 is located on the first surface 111 on the side of the photoelectric sensing region 13 away from the deep well region 14, and partially overlaps with the photoelectric sensing region 13.

[0068] See also Figures 9 and 10 As shown, in one embodiment of the present invention, after the transmission gate 18 is formed, a sidewall dielectric layer (not shown in the figure) is formed on the first surface 111 and the transmission gate 18, and the material of the sidewall dielectric layer is, for example, silicon oxide, silicon nitride, or a stack of silicon oxide and silicon nitride. After the sidewall dielectric layer is formed, for example, an etching process such as dry etching or wet etching can be used to remove the sidewall dielectric layer on the transmission gate 18 and part of the first surface 111, and the sidewall dielectric layer on both sides of the transmission gate 18 is retained to form a sidewall 19. Among them, the sum of the thickness of the transmission gate 18 and the gate oxide layer 17 is consistent with the height of the sidewall 19, and the shape of the sidewall 19 is, for example, an arc shape, a triangle shape, or an L shape. In this embodiment, the shape of the sidewall 19 is, for example, an arc shape. By providing an insulating sidewall 19, leakage of the image sensor is prevented.

[0069] See also Figure 10 to Figure 11 As shown, in one embodiment of the present invention, after forming the sidewall 19, the sixth ion is injected into the well region 12 on the side of the transmission gate 18 away from the photoelectric sensing region 13 through the source / drain injection process to form a floating diffusion region 20, that is, the transmission gate 18 is located on the first surface 111 between the floating diffusion region 20 and the photoelectric sensing region 13. Among them, the floating diffusion region 20 extends from the first surface 111 to the well region 12, and the width and depth of the floating diffusion region 20, as well as the type and concentration of the sixth ion and other parameters can be selected according to actual conditions. In this embodiment, the type of the sixth ion is different from the type of the first ion, and the sixth ion is, for example, an N-type ion such as P or As.

[0070] See also Figure 11 to Figure 12As shown, in one embodiment of the present invention, after forming the floating diffusion region 20, a third photoresist layer 21 is formed on the first surface 111, the transmission gate 18 and the sidewall 19, and a plurality of openings are formed in the third photoresist layer 21. The plurality of openings are arranged at intervals on a portion of the second pinning layer 16 on the first pinning layer 15, and the widths of the plurality of openings may be equal or unequal. In this embodiment, there are four openings, for example, and the four openings include a first opening 211, a second opening 212, a third opening 213 and a fourth opening 214. The first opening 211, the second opening 212, the third opening 213 and the fourth opening 214 are arranged, for example, equidistantly on a portion of the second pinning layer 16 on the first pinning layer 15, and the widths of the four openings are equal.

[0071] See also Figure 12 to Figure 13 As shown, in one embodiment of the present invention, after forming the third photoresist layer 21, the third photoresist layer 21 is used as a mask to implant the seventh ion into the second pinned layer 16 exposed by the opening to form the doping region 22, and then the third photoresist layer 21 is removed. There are multiple doping regions 22, and the multiple doping regions 22 are arranged at intervals in the second pinned layer 16 on the first pinned layer 15, and extend from the first surface 111 to the second pinned layer 16. The interface of the doping region 22 in the substrate 11 is located in the second pinned layer 16, and the orthographic projections of the multiple doping regions 22 in the thickness direction of the substrate 11 all fall within the region of the first pinned layer 15 to avoid the photoelectric sensing region 13 and the doping region 22 from penetrating. In this embodiment, there are, for example, four doping regions 22, and the four doping regions 22 are equidistantly arranged in the second pinned layer 16 on the first pinned layer 15. The seventh ion is, for example, an N-type ion such as P or As, and the doping concentration of the doping region 22 is, for example, greater than the doping concentration of the second pinned layer 16. Specifically, the ratio of the doping concentration of the doping region 22 to the doping concentration of the second pinned layer 16 is at least 2:1.

[0072] See also Figure 13 to Figure 14 As shown, in one embodiment of the present invention, after the doping region 22 is formed, an oxide layer 23 is formed on the first surface 111, the transmission gate 18 and the sidewall 19. The oxide layer 23 is formed, for example, by an in-situ water vapor method or the like, and the material of the oxide layer 23 includes, for example, silicon oxide, etc. The present invention does not limit the thickness of the oxide layer 23, and the thickness can be selected according to actual needs. In this embodiment, the thickness of the oxide layer 23 is, for example, 80Å-150Å, and for example, 100Å or 120Å, etc. Through the in-situ water vapor method, an oxide layer 23 with a dense structure and few interface defects can be formed, thereby avoiding damage to the substrate 11 caused by plasma when the barrier layer 24 is subsequently formed, improving the interface state of the barrier layer 24, reducing the interface defects of the barrier layer 24, and thereby reducing the generation of electron / hole pairs at the interface of the barrier layer 24, thereby reducing the dark current of the entire image sensor.

[0073] See also Figure 14 to Figure 15As shown, in one embodiment of the present invention, after the oxide layer 23 is formed, a barrier layer 24 is formed on the oxide layer 23. The barrier layer 24 is formed, for example, by a method such as plasma enhanced chemical vapor deposition (PECVD), and the material of the barrier layer 24 includes, for example, silicon oxide, etc. The present invention does not limit the thickness of the barrier layer 24, which can be selected according to actual needs. In this embodiment, the thickness of the barrier layer 24 is, for example, 200Å-300Å, and for example, 220Å, 250Å, or 270Å.

[0074] See also Fig.15 As shown, in one embodiment of the present invention, after the barrier layer 24 is formed, subsequent processes such as interlayer dielectric, contact hole and metal interconnect layer can be performed, which will not be elaborated here.

[0075] See also Figure 15 to Figure 16 As shown, in one embodiment of the present invention, the doped region 22 on the photoelectric sensing region 13, the pinning layer (the first pinning layer 15 and the second pinning layer 16) on the photoelectric sensing region 13, and the photoelectric sensing region 13 form a parasitic NPN transistor structure. Among them, the pinning layer-photoelectric sensing region 13 serves as the emitter junction of the parasitic NPN transistor, the doped region 22-pinning layer serves as the collector junction of the parasitic NPN transistor, and the second pinning layer 16 and the first pinning layer 15 are connected to a low potential, and the doped region 22 is connected to a high potential. The potential of the photoelectric sensing region 13 is determined by the working state. Specifically, the second pinning layer 16 and the first pinning layer 15 are connected to a negative power supply voltage (V ss ), the doped region 22 is connected to a positive power supply voltage (V dd ). When the emitter junction is forward biased and the collector junction is reverse biased, the transistor enters the on state, and the photogenerated electrons overflowing from the photoelectric sensing region 13 pass through the first pinning layer 15 and the second pinning layer 16 and are attracted by the reverse bias electric field of the doping region 22, and then flow out from the doping region 22, thereby preventing the photogenerated electrons from overflowing into adjacent pixel units, improving the image overflow problem, and further avoiding the white spot phenomenon in the imaging of the image sensor.

[0076] See also Fig.15 and Fig.17 As shown, in one embodiment of the present invention, the doped region 22 and the second pinned layer 16 between the deep well region 14 and the photoelectric sensing region 13 form a parasitic NP diode. The doped region 22 is connected to a high potential, and the second pinned layer 16 is connected to a low potential. Specifically, the doped region 22 is connected to V dd The second pinning layer 16 is connected to V ssWhen the second pinned layer 16 is connected to a low potential and the doped region 22 is connected to a high potential, the parasitic NP diode is in a reverse bias state, the doped region 22 is in a fully depleted state, and the spaced doped regions 22 are in contact with each other to form a continuous depletion region. A strong electric field exists in the entire depletion region. When the interface defects between the first surface 111 and the subsequently arranged oxide layer 23 cause electron / hole pairs to be generated, the electrons will be drawn away by the external electric field and will not move to the photoelectric sensing region 13, thereby effectively shielding the electrons / holes generated by the interface defects of the first surface 111, reducing the dark current, and further avoiding the white spot phenomenon in the imaging of the image sensor.

[0077] In summary, the present invention provides an image sensor and a method for preparing the same. By forming a doped region and a pinning layer, the unexpected technical effect of the present application is that it can reduce dark current, avoid white spots in the imaging of the image sensor, and improve the imaging quality of the image sensor. Moreover, the image sensor and the method for preparing the same provided by the present invention, by setting a doped region, a pinning layer and a photoelectric sensing region to form a parasitic triode, can avoid the photogenerated electrons in the photoelectric sensing region from overflowing into adjacent pixel units, improve the white spot phenomenon caused by image overflow, and further improve the imaging quality to improve.

[0078] The embodiments of the present invention disclosed above are only used to help illustrate the present invention. The embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments described. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. An image sensor, characterized in that: At least: A substrate comprising a first surface and a second surface disposed opposite to each other; a well region extending from the first surface into the substrate; A photoelectric sensing region is disposed in the well region, and a preset distance exists between the photoelectric sensing region and the first surface; A floating diffusion region is spaced apart and arranged on one side of the photoelectric sensing region; a transmission gate disposed on the first surface between the floating diffusion region and the photoelectric sensing region; A deep well region is arranged in the well region, the deep well region is arranged at least on one side of the photoelectric sensing region, and the deep well region is opened at least on one side of the photoelectric sensing region adjacent to the transmission gate, and the deep well region is not arranged at all on at least one side of the photoelectric sensing region adjacent to the transmission gate; A pinning layer extending from the first surface to the photoelectric sensing region, the pinning layer comprising a first pinning layer and a second pinning layer, the first pinning layer being arranged between the second pinning layer and the photoelectric sensing region; as well as a plurality of doped regions, spaced apart and disposed in the second pinning layer on the first pinning layer; Wherein, the conductivity type of the photoelectric sensing region and the doping region is opposite to that of the pinning layer.

2. The image sensor according to claim 1, characterized in that The first pinning layer extends from a side of the deep well region close to the photoelectric sensing region to the photoelectric sensing region.

3. The image sensor according to claim 1, characterized in that The second pinning layer extends from the deep well region at least to a side of the photoelectric sensing region close to the floating diffusion region.

4. The image sensor according to claim 1, characterized in that The doped region extends from the first surface into the second pinned layer.

5. The image sensor according to claim 1, characterized in that The well region, the deep well region, the first pinning layer and the second pinning layer are P-type doping regions, and the doping region is an N-type doping region.

6. The image sensor according to claim 5, characterized in that The doping concentration of the first pinned layer is greater than the doping concentration of the second pinned layer, the doping concentration of the second pinned layer is greater than the doping concentration of the deep well region, and the doping concentration of the deep well region is greater than the doping concentration of the well region.

7. The image sensor according to claim 6, characterized in that: The doping concentration of the second pinning layer is lower than the doping concentration of the doping region.

8. The image sensor according to claim 1, characterized in that The first pinning layer and the second pinning layer are connected to a low potential, and the doping region is connected to a high potential.

9. A method for preparing an image sensor, characterized in that: At least the following steps are included: Providing a substrate, the substrate comprising a first surface and a second surface arranged opposite to each other; forming a well region in the substrate, wherein the well region extends from the first surface into the substrate; forming a photoelectric sensing region in the well region, wherein a preset distance exists between the photoelectric sensing region and the first surface; A floating diffusion region is formed at one side of the photoelectric sensing region; forming a transfer gate on the first surface between the floating diffusion region and the photoelectric sensing region; A deep well region is formed in the well region at least on one side of the photoelectric sensing region, and the deep well region is opened at least on one side of the photoelectric sensing region adjacent to the transmission gate, and the deep well region is not completely disposed at least on one side of the photoelectric sensing region adjacent to the transmission gate; forming a pinning layer between the first surface and the photoelectric sensing region, wherein the pinning layer comprises a first pinning layer and a second pinning layer, and the first pinning layer is disposed between the second pinning layer and the photoelectric sensing region; as well as A plurality of doping regions are formed in the second pinning layer on the first pinning layer at intervals, and the photoelectric sensing region and the doping region are both of opposite conductivity type to that of the pinning layer.

10. The method for preparing an image sensor according to claim 9, characterized in that: After forming the doped region, an oxide layer is formed on the transmission gate and the first surface, and the oxide layer is generated by an in-situ water vapor method.

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