Image sensor and method for manufacturing the same

Abstract

The present invention provides an image sensor and a method for preparing the same. The method comprises: providing a substrate, the substrate comprising a pixel region and a logic region; forming a gate material layer, the gate material layer covering the surface of the pixel region and the logic region; forming a patterned photoresist layer, the patterned photoresist layer shielding the logic region and exposing the gate material layer located in the pixel region; performing an ion implantation process to dope an adsorption material in the exposed gate material layer. It can be seen that the present invention dopes the gate material layer in the pixel region with an adsorption material to utilize the adsorption property of the adsorption material to adsorb metal ions in the pixel region, thereby alleviating the white pixel problem caused by the diffusion of metal ions and improving pixel performance and imaging quality. At the same time, the ion implantation process has no effect on the circuit structure of the logic region, and no additional mask is required, and the process operation is simple.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to an image sensor and a preparation method thereof. Background Art

[0002] Image sensors are semiconductor devices that convert optical signals into electrical signals. Depending on the principles used, they can be divided into charge-coupled device (CCD) image sensors and complementary metal oxide semiconductor (CMOS) image sensors. Among them, according to the different light incidence methods, CMOS image sensors can be divided into front side illumination (FSI) image sensors and back side illumination (BSI) image sensors.

[0003] In a back-illuminated image sensor, light is directly irradiated from the back of the substrate to the photodiode without passing through the logic circuit, which improves the efficiency of light reception and greatly improves the imaging effect. However, due to various factors such as changes in raw materials, process fluctuations, and impurity ion contamination, back-illuminated image sensors are prone to white pixel (WP) problems. Under normal circumstances, no light is incident on the pixel unit, and the dark current generated by the pixel unit is very small. However, when there is metal impurity contamination and other conditions, the pixel unit itself will generate an electric charge, and the dark current will increase, resulting in bright spots in the pixel unit in a completely dark field, that is, white pixels, which has a serious impact on the imaging effect.

[0004] Therefore, a new method for preparing an image sensor is urgently needed to improve the white pixel problem and enhance pixel performance. Summary of the invention

[0005] The object of the present invention is to provide an image sensor and a method for manufacturing the same, so as to solve the problem of how to improve white pixels.

[0006] In order to solve the above technical problems, the present invention provides a method for preparing an image sensor, comprising:

[0007] Providing a substrate, the substrate comprising a pixel area and a logic area;

[0008] forming a gate material layer, wherein the gate material layer covers surfaces of the pixel area and the logic area;

[0009] forming a patterned photoresist layer, wherein the patterned photoresist layer shields the logic area and exposes the gate material layer located in the pixel area;

[0010] An ion implantation process is performed to dope the exposed gate material layer with an adsorption material.

[0011] Optionally, in the method for preparing the image sensor, during the ion implantation process, the implanted ion types include carbon ions.

[0012] Optionally, in the method for preparing the image sensor, before forming the gate material layer, a shallow trench isolation structure is formed in the substrate, and the shallow trench isolation structure is distributed in the pixel area and the logic area.

[0013] Optionally, in the method for preparing the image sensor, after the shallow trench isolation structure is formed, a plurality of photodiodes are formed in the pixel area, and a P-well area and an N-well area are formed in the logic area; wherein the shallow trench isolation structure is arranged between adjacent photodiodes, and the shallow trench isolation structure is also arranged between adjacent P-well areas and N-well areas.

[0014] Optionally, in the method for preparing the image sensor, after forming the photodiode, the P-well region and the N-well region, an oxide layer is formed on the substrate to cover surfaces of the logic region and the pixel region.

[0015] Optionally, in the method for preparing the image sensor, the gate material layer is formed on the oxide layer.

[0016] Optionally, in the method for preparing the image sensor, after performing ion implantation, the patterned photoresist layer is removed, and the gate material layer is etched to form a first gate structure in the pixel area and a second gate structure in the logic area.

[0017] Based on the same inventive concept, the present invention also provides an image sensor, comprising:

[0018] A substrate, the substrate comprising a pixel area and a logic area;

[0019] an oxide layer, wherein the oxide layer covers surfaces of the pixel area and the logic area;

[0020] A first gate structure and a second gate structure, wherein the first gate structure and the second gate structure are formed on the oxide layer, and the first gate structure is located in the pixel area, and the second gate structure is located in the logic area; wherein the first gate structure is doped with an adsorption material.

[0021] Optionally, in the image sensor, the adsorption material includes carbon ions.

[0022] Optionally, in the image sensor, a plurality of photodiodes are formed in the pixel area, a P-well area and an N-well area are formed in the logic area, and a shallow trench isolation structure is arranged between adjacent photodiodes, and the shallow trench isolation structure is also arranged between adjacent P-well areas and N-well areas.

[0023] In summary, the present invention provides an image sensor and a method for preparing the same. The method includes: providing a substrate, the substrate including a pixel area and a logic area; forming a gate material layer, the gate material layer covering the surface of the pixel area and the logic area; forming a patterned photoresist layer, the patterned photoresist layer shielding the logic area and exposing the gate material layer located in the pixel area; performing an ion implantation process to dope an adsorption material in the exposed gate material layer. It can be seen that the present invention dopes the gate material layer in the pixel area with an adsorption material to utilize the adsorption property of the adsorption material to adsorb metal ions in the pixel area, thereby alleviating the white pixel problem caused by the diffusion of metal ions and improving pixel performance and imaging quality. At the same time, the ion implantation process has no effect on the circuit structure of the logic area, and no additional mask is required, and the process operation is simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 4 is a flow chart of a method for preparing an image sensor in an embodiment of the present invention.

[0025] Figure 2 4 is a top view of a back-illuminated image sensor according to an embodiment of the present invention.

[0026] Figure 3-6 Schematic diagram of a semiconductor structure during a method for preparing an image sensor in an embodiment of the present invention.

[0027] Figure 7 It is a line graph comparing white pixels of the first gate structure doped with carbon ions and undoped with carbon ions in an embodiment of the present invention.

[0028] The reference numerals in the accompanying drawings of the specification are:

[0029] 100-substrate; 101-shallow trench isolation structure; 102-oxide layer; 103-gate material layer; 103a-first gate structure; 103b-second gate structure; 104-patterned photoresist layer;

[0030] 11- logic area; 111- P well area; 112- N well area;

[0031] 12-pixel area; 121-photodiode. DETAILED DESCRIPTION

[0032] In order to make the purpose, advantages and features of the present invention clearer, the present invention is further described in detail 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, and are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention. In addition, the structure shown in the drawings is often a part of the actual structure. In particular, the emphasis of each drawing is different, and sometimes different proportions are used. It should also be understood that, unless otherwise specified or indicated, the terms "first", "second", "third", etc. in the specification are only used to distinguish between the various components, elements, steps, etc. in the specification, and are not used to represent the logical relationship or sequential relationship between the various components, elements, steps, etc.

[0033] See also Figure 1 This embodiment provides a method for preparing an image sensor, comprising:

[0034] Step 1 S10: providing a substrate, wherein the substrate includes a pixel area and a logic area;

[0035] Step 2 S20: forming a gate material layer, wherein the gate material layer covers the surfaces of the pixel area and the logic area;

[0036] Step three S30: forming a patterned photoresist layer, wherein the patterned photoresist layer shields the logic area and exposes the gate material layer located in the pixel area;

[0037] Step 4 S40: performing an ion implantation process to dope the exposed gate material layer with an adsorption material.

[0038] It can be seen that the method for preparing the image sensor provided in this embodiment dopes the gate material layer of the pixel area with an adsorption material to utilize the adsorption property of the adsorption material to adsorb the metal ions in the pixel area, thereby alleviating the white pixel problem caused by the diffusion of metal ions and improving the pixel performance and imaging quality. At the same time, the ion implantation process has no effect on the circuit structure of the logic area, and no additional mask is required, and the process operation is simple.

[0039] The following is combined with Figure 2-6 The method for preparing the image sensor provided in this embodiment is specifically described.

[0040] Step 1 S10: Please refer to Figure 2-3 , a substrate 100 is provided, wherein the substrate 100 includes a logic area 11 and a pixel area 12.

[0041] in, Figure 2is a top view of the image sensor, wherein the logic area 11 is located in the peripheral area of ​​the pixel area 12. A logic circuit is disposed in the logic area 11, and a plurality of pixel units are disposed in the pixel area 12 to realize the conversion between optical signals and electrical signals. Figure 3 It is a cross-sectional view of a part of the image sensor, that is, on the same substrate 100, part of the area is the logic area 11, and part of the area is the pixel area 12. The device structure shown in this embodiment is only an illustrative example, and does not limit the specific location of each device.

[0042] See also Figure 3 The substrate 100 can provide an operating platform for subsequent processes. It can be any substrate for carrying semiconductor integrated circuit components known to those skilled in the art, and can be a bare chip or a wafer processed by an epitaxial growth process. Further, the substrate 100 can be selected as a silicon-on-insulator (SOI) substrate, a bulk silicon substrate, a germanium substrate, a germanium silicon substrate, an indium phosphide (InP) substrate, a gallium arsenide (GaAs) substrate, or a germanium-on-insulator substrate. Further, the substrate 100 is at least divided into a logic area 11 and a pixel area 12. The pixel area 12 is used to form a plurality of pixel units, including a plurality of photodiodes, a transmission gate, a floating drain, etc. The logic area 11 is used to form a logic circuit, including an NMOS device, a PMOS device, and various metal interconnect structures.

[0043] Furthermore, a shallow trench isolation structure 101 is formed on the substrate 100 to define an active area and provide electrical isolation for subsequently formed devices. Preferably, the shallow trench isolation structure 101 is made of silicon dioxide or polysilicon. After the shallow trench isolation structure 101 is formed, ion implantation processes are performed on the logic area 11 and the pixel area 12, respectively, to form a plurality of well areas in the logic area 11, and to form a photodiode 121 in the pixel area 12. Among them, the well area formed in the logic area 11 includes a P-well area 111 and an N-well area 112. The formed P-well area 111 is used to subsequently form an NMOS device, and the formed N-well area 112 is used to subsequently form a PMOS device. Furthermore, the P-well area 111 is doped with P-type ions, such as boron ions or gallium ions. The N-well area 112 is doped with N-type ions, such as phosphorus ions or arsenic ions. It should be noted that, Figure 3 The locations of the N-well region 112 and the P-well region 111 are merely exemplary illustrations, and this embodiment does not limit the specific locations of the NMOS device and the PMOS device to be formed subsequently.

[0044] Furthermore, the shallow trench isolation structure 101 is distributed in the logic area 11 and the pixel area 12. In addition, the shallow trench isolation structure 101 is disposed between adjacent photodiodes 121, and the shallow trench isolation structure 101 is also disposed between adjacent P-well areas 111 and N-well areas 112, thereby avoiding interference between the photodiodes 121 and interference between subsequently formed NMOS devices and PMOS devices.

[0045] Please continue reading Figure 3 After forming the P-well region 111, the N-well region 112 and the photodiode 121, an oxide layer 102 is formed on the substrate 100 to cover the surface of the logic region 11 and the pixel region 12. The oxide layer 102 is used to protect the surface of the substrate 100, and its material includes but is not limited to silicon dioxide. Optionally, the oxide layer 102 is formed on the surface of the substrate 100 by a thermal oxidation process.

[0046] Step 2 S20: Please refer to Figure 4 , forming a gate material layer 103 , wherein the gate material layer 103 covers surfaces of the pixel area 12 and the logic area 11 .

[0047] Optionally, a chemical vapor deposition process is used to form the gate material layer 103 on the oxide layer 102. The gate material layer 103 is used to form the gate structure of the NMOS device and the PMOS device in the logic area 11, and to form the transmission gate in the pixel area 12. Furthermore, the gate material layer 103 is made of polysilicon.

[0048] Step 3 S30: Please refer to Figure 5 , forming a patterned photoresist layer 104 , wherein the patterned photoresist layer 104 shields the logic area 11 and exposes the gate material layer 103 located in the pixel area 12 .

[0049] Specifically, a photoresist layer is coated on the surface of the gate material layer 103, and then the patterned photoresist layer 104 is formed through an existing photomask, that is, a photomask used for ion implantation in the pixel region 12. The patterned photoresist layer 104 is used as a barrier layer for subsequent ion implantation processes, and the patterned photoresist layer 104 shields the logic region 11 to avoid affecting the logic region 11, while exposing the gate material layer 103 in the pixel region 12.

[0050] Step 4 S40: Please refer to Figure 5-6 , performing an ion implantation process to dope the exposed gate material layer 103 with an adsorption material.

[0051] Under the blocking of the patterned photoresist layer 104, the ion implantation process only performs ion doping on the gate material layer 103 in the pixel area 12, and has no effect on the logic area 11. Furthermore, the types of ions implanted include carbon ions. Carbon ions have strong adsorption properties and can adsorb metal impurities in the pixel area 12, thereby avoiding the serious white pixel problem caused by the contamination of metal impurities in the pixel area 12, thereby improving the performance of the pixel and the imaging quality of the image sensor. Furthermore, this embodiment does not limit the doping concentration of the carbon ions, which can be set according to the specific needs of the device.

[0052] After the ion implantation process is performed, the patterned photoresist layer 104 is cleaned and removed, and a patterned mask layer (not shown) is formed on the gate material layer 103. Then, the patterned mask layer is used as an etching barrier layer, and the gate material layer 103 is etched by a dry etching process to form a first gate structure 103a in the pixel region 12 and a second gate structure 103b in the logic region 11. Figure 6 As shown, each of the photodiodes 121 is provided with a corresponding first gate structure 103a. And the first gate structure 103a blocks part of the photodiode 121 to serve as a transmission gate of the photodiode 121. Further, the second gate structure 103b is provided on the P-well region 111 and the N-well region 112 to serve as the gate of NMOS and PMOS respectively. It should be noted that the second gate structure 103b on the P-well region 111 and the second gate structure 103b on the N-well region 112 can be connected or separately provided, and the specific structural setting can be determined according to the needs of the logic circuit design.

[0053] In subsequent processes, the source and drain structures of NMOS and PMOS in the logic area 11, metal connecting lines and other circuit structures, and the pixel structure in the pixel area 12 will be further completed, which will not be described in detail in this embodiment.

[0054] Based on the same inventive concept, this embodiment also provides an image sensor. Figure 6 , the image sensor comprises:

[0055] A substrate 100, wherein the substrate 100 includes a pixel area 12 and a logic area 11;

[0056] An oxide layer 102, wherein the oxide layer 102 covers the surface of the pixel area 12 and the logic area 11, and is used to protect the pixel area 12 and the logic area 11;

[0057] A first gate structure 103a and a second gate structure 103b are formed on the oxide layer 102, and the first gate structure 103a is located in the pixel area 12, and the second gate structure 103b is located in the logic area 11; wherein the first gate structure 103a is doped with an adsorption material.

[0058] Furthermore, the adsorption material includes carbon ions, which have strong adsorption properties and are used to adsorb metal impurities in the pixel area 12 to alleviate the problem of white pixels in the pixel area 12 caused by the contamination of metal impurities, and improve pixel performance and imaging quality. Among them, a plurality of photodiodes 121 are formed in the pixel area 12 for realizing photoelectric conversion. The logic area 11 is formed with a P-well area 111 and an N-well area 112 for subsequent formation of NMOS devices and PMOS devices. Further, in order to ensure electrical isolation, a shallow trench isolation structure 101 is provided between adjacent photodiodes 121, and a shallow trench isolation structure 101 is also provided between adjacent P-well areas 111 and N-well areas 112. Among them, each of the photodiodes 121 is correspondingly provided with a first gate structure 103a. And the first gate structure 103a blocks part of the photodiode 121 to serve as a transmission gate of the photodiode 121. Furthermore, the second gate structure 103 b is disposed on both the P-well region 111 and the N-well region 112 to serve as the gates of the NMOS and PMOS, respectively.

[0059] In order to verify the effect of the image sensor and its preparation method provided in this embodiment on improving the white pixel problem, the applicant conducted a comparative test on an image sensor not doped with carbon ions and an image sensor doped with carbon ions. Figure 7 , curve a is a white pixel change curve without carbon ion doping, and curve b is a white pixel change curve with carbon ion doping. Obviously, under the same pixel value, the white pixel of curve a is significantly higher than the white pixel of curve b. Therefore, it can be understood that doping carbon ions in the first gate structure 103a can better alleviate the white pixel problem of the image sensor and improve the imaging quality.

[0060] In summary, the present embodiment provides an image sensor and a method for preparing the same. The method includes: providing a substrate 100, the substrate 100 including a pixel area 12 and a logic area 11; forming a gate material layer 103, the gate material layer 103 covering the surface of the pixel area 12 and the logic area 11; forming a patterned photoresist layer 104, the patterned photoresist layer 104 shielding the logic area 11 and exposing the gate material layer 103 located in the pixel area 12; performing an ion implantation process to dope an adsorption material in the exposed gate material layer 103. It can be seen that the present embodiment dopes the gate material layer 103 of the pixel area 12 with an adsorption material to utilize the adsorption property of the adsorption material to adsorb metal ions in the pixel area 12, thereby alleviating the white pixel problem caused by the diffusion of metal ions and improving pixel performance and imaging quality. At the same time, the ion implantation process has no effect on the circuit structure of the logic area 11, and no additional mask is required, and the process operation is simple.

[0061] In addition, it should be recognized that although the present invention has been disclosed as a preferred embodiment, the above embodiment is not intended to limit the present invention. For any technician familiar with the art, without departing from the scope of the technical solution of the present invention, the technical content disclosed above can be used to make many possible changes and modifications to the technical solution of the present invention, or modified into equivalent embodiments of equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still belongs to the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing an image sensor, characterized in that: include: Providing a substrate, the substrate comprising a pixel area and a logic area; forming a gate material layer, wherein the gate material layer covers surfaces of the pixel area and the logic area; forming a patterned photoresist layer, wherein the patterned photoresist layer shields the logic area and exposes the gate material layer located in the pixel area; Performing an ion implantation process to dope the exposed gate material layer with an adsorption material; wherein, during the ion implantation process, the implanted ion species include carbon ions; The patterned photoresist layer is removed, and the gate material layer is etched to form a first gate structure in the pixel area and a second gate structure in the logic area.

2. The method for preparing an image sensor according to claim 1, characterized in that: Before forming the gate material layer, a shallow trench isolation structure is formed in the substrate, and the shallow trench isolation structure is distributed in the pixel area and the logic area.

3. The method for preparing an image sensor according to claim 2, characterized in that: After forming the shallow trench isolation structure, a plurality of photodiodes are formed in the pixel area, and a P-well area and an N-well area are formed in the logic area; wherein the shallow trench isolation structure is arranged between adjacent photodiodes, and the shallow trench isolation structure is also arranged between adjacent P-well areas and N-well areas.

4. The method for preparing an image sensor according to claim 3, characterized in that: After forming the photodiode, the P-well region and the N-well region, an oxide layer is formed on the substrate to cover surfaces of the logic region and the pixel region.

5. The method for preparing an image sensor according to claim 4, characterized in that: The gate material layer is formed on the oxide layer.

6. An image sensor, characterized in that: The image sensor is manufactured by the method for manufacturing an image sensor according to any one of claims 1 to 5, wherein the image sensor comprises: A substrate, the substrate comprising a pixel area and a logic area; an oxide layer, wherein the oxide layer covers surfaces of the pixel area and the logic area; A first gate structure and a second gate structure, wherein the first gate structure and the second gate structure are formed on the oxide layer, and the first gate structure is located in the pixel area, and the second gate structure is located in the logic area; wherein the first gate structure is doped with an adsorption material, and the adsorption material includes carbon ions.

7. The image sensor according to claim 6, characterized in that: A plurality of photodiodes are formed in the pixel area, a P-well area and an N-well area are formed in the logic area, and a shallow trench isolation structure is arranged between adjacent photodiodes, and the shallow trench isolation structure is also arranged between adjacent P-well areas and N-well areas.

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