Image sensor and method for manufacturing the same

Abstract

This application provides an image sensor and a method for manufacturing the same. The image sensor may include a first substrate, a plurality of light absorption regions located in the first substrate, a device layer located on one side of the first substrate, and a contact structure. A photodiode and a floating diffusion region are disposed in the light absorption region. A shallow trench isolation structure is disposed between adjacent light absorption regions. The contact structure connects the floating diffusion region and penetrates through the device layer and extends into the first substrate. One end of the contact structure embedded in the first substrate surrounds the top of a portion of the shallow trench isolation structure. In this way, the same contact structure can connect different floating diffusion regions through its end, so that the floating diffusion regions of multiple light absorption regions can share the contact structure, thereby reducing the number of contact structures, reducing parasitic capacitance, and improving device performance.

Description

Technical Field

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

[0002] Image sensors are devices that convert light signals into electrical signals. According to the different photoelectric conversion methods, image sensors can be divided into two categories: charge coupled device (CCD) image sensors and complementary metal-oxide-semiconductor (CMOS) image sensors (CIS). Specifically, image sensors can receive light signals, which excite electrons inside the image sensor and are collected. That is, image sensors can generate corresponding electrical signals based on light signals, thus realizing the conversion from light signals to electrical signals.

[0003] Image sensors may include photodiodes, which are used to generate photogenerated carriers (electron-hole pairs) under the action of light signals using the photoelectric effect, thereby generating electrical signals. A photodiode can be considered as a pixel. As the demand for resolution increases, the size of a single pixel continues to shrink, and the requirements for the design of the connection structure in the image sensor are also increasing.

[0004] Image sensors may also include transfer transistors, floating diffusions, and other transistors, such as amplifier transistors, reset transistors, and selection transistors. Transfer transistors, floating diffusions, and other transistors and photodiodes may be arranged on the same layer. However, as the size of a single pixel continues to shrink, the size of other transistors is affected by the short channel effect and does not match the pixel size. Therefore, other transistors and photodiodes may be arranged on different layers to form a double-layer device. Different layers are connected through contact holes, which can effectively reduce the device size and pixel size.

[0005] However, there is currently a problem of too many contact holes in double-layer devices. Too many contact holes produce higher parasitic capacitance, which easily leads to problems such as random noise. Summary of the invention

[0006] In view of this, the purpose of the present application is to provide an image sensor and a manufacturing method thereof, wherein floating diffusion regions of multiple light absorption regions can share a contact structure, thereby reducing the number of contact structures and improving device performance.

[0007] The present application provides an image sensor, including:

[0008] A first substrate, and a plurality of light absorption regions located in the first substrate, wherein a photodiode and a floating diffusion region are disposed in the light absorption region, and a shallow trench isolation structure is disposed between adjacent light absorption regions;

[0009] A device layer, located on one side of the first substrate;

[0010] A contact structure is provided, wherein the contact structure is connected to the floating diffusion region, the contact structure penetrates the device layer and extends into the first substrate, and one end of the contact structure embedded in the first substrate surrounds a portion of the top of the shallow trench isolation structure.

[0011] Optionally, one end of the contact structure embedded in the first substrate includes a plurality of connection structures, the plurality of connection structures are separated by the shallow trench isolation structure, and each connection structure is respectively connected to a floating diffusion region located on a different side of the shallow trench isolation structure.

[0012] Optionally, one end of the contact structure embedded in the first substrate includes a connection structure, and the connection structure is a continuous ring structure, and the connection structure is respectively connected to floating diffusion regions located on different sides of the shallow trench isolation structure.

[0013] Optionally, the multiple light absorption regions are arranged in an array, and the multiple light absorption regions include a first light absorption region, a second light absorption region, a third light absorption region and a fourth light absorption region, and the adjacently arranged first light absorption region, the second light absorption region, the third light absorption region and the fourth light absorption region share one contact structure.

[0014] Optionally, the image sensor further includes: a back deep trench isolation structure, wherein the back deep trench isolation structure is connected to the shallow trench isolation structure to form a full isolation structure, and the full isolation structure is used to isolate adjacent light absorption regions.

[0015] Optionally, an isolation doping region is further provided in the first substrate, the isolation doping region at least covers the sidewalls of the shallow trench isolation structure, and the contact structure is embedded in the isolation doping region.

[0016] Optionally, the image sensor further includes: a first dielectric layer, the first dielectric layer is located on the surface of the first substrate, a transfer transistor is arranged in the first dielectric layer, and the transfer transistor controls the charge transfer between the photodiode and the floating diffusion region.

[0017] Optionally, the graphic sensor further includes: a lead-out structure penetrating the device layer, the lead-out structure being used to connect to a control terminal of the transfer transistor.

[0018] Optionally, the device layer includes a second substrate and a second dielectric layer, pixel transistors are arranged in the second substrate, the pixel transistors include an amplifying transistor, a selecting transistor and a reset transistor, and the second dielectric layer is in contact with and connected to the first dielectric layer.

[0019] The present application provides a method for manufacturing an image sensor, comprising:

[0020] Providing a first substrate, forming a plurality of light absorption regions in the first substrate, and a shallow trench isolation structure for isolating adjacent light absorption regions; forming a photodiode and a floating diffusion region in each of the light absorption regions;

[0021] forming a device layer on one side of the first substrate;

[0022] A contact structure is formed that penetrates the device layer, the contact structure is connected to the floating diffusion region, the contact structure extends into the first substrate, and one end of the contact structure embedded in the first substrate surrounds a portion of the top of the shallow trench isolation structure.

[0023] Optionally, a contact structure is formed that penetrates the device layer, including: forming a first contact hole, the first contact hole penetrates the device layer, the bottom of the first contact hole exposes the floating diffusion area and the shallow trench isolation structure, etching the exposed portion of the floating diffusion area to form a second contact hole located between the floating diffusion area and the shallow trench isolation structure, and filling the second contact hole and the first contact hole with conductive material to form the contact structure.

[0024] Optionally, a contact structure penetrating the device layer is formed, including: forming a first contact hole, the first contact hole penetrating the device layer, the bottom of the first contact hole exposing the floating diffusion area and the shallow trench isolation structure, etching the exposed portion of the floating diffusion area and the exposed portion of the shallow trench isolation structure to form an annular third contact hole, and filling the third contact hole and the first contact hole with conductive material to form the contact structure.

[0025] Optionally, the multiple light absorption regions are arranged in an array, and the multiple light absorption regions include a first light absorption region, a second light absorption region, a third light absorption region and a fourth light absorption region, and the adjacently arranged first light absorption region, the second light absorption region, the third light absorption region and the fourth light absorption region share one contact structure.

[0026] Optionally, the method further includes:

[0027] A back deep trench isolation structure is formed, and the back deep trench isolation structure is connected with the shallow trench isolation structure to form a full isolation structure, and the full isolation structure is used to isolate the adjacent light absorption areas.

[0028] Optionally, the method further includes:

[0029] An isolation doping region is provided in the first substrate, the isolation doping region at least covers the sidewall of the shallow trench isolation structure, and the contact structure is embedded in the isolation doping region.

[0030] Optionally, the method further includes:

[0031] A first dielectric layer and a transfer transistor in the first dielectric layer are formed on the surface of the first substrate, and the transfer transistor controls the charge transfer between the photodiode and the floating diffusion region.

[0032] Optionally, the method further includes:

[0033] A lead-out structure is formed that penetrates the device layer, and the lead-out structure is used to connect the control terminal of the transfer transistor.

[0034] Optionally, the device layer includes a second substrate and a second dielectric layer, pixel transistors are arranged in the second substrate, the pixel transistors include an amplifying transistor, a selecting transistor and a reset transistor, and the second dielectric layer is in contact with and connected to the first dielectric layer.

[0035] The present application provides an image sensor and a manufacturing method thereof. The image sensor may include a first substrate, multiple light absorption regions located in the first substrate, a device layer located on one side of the first substrate, and a contact structure. A photodiode and a floating diffusion region are arranged in the light absorption region, a shallow trench isolation structure is arranged between adjacent light absorption regions, and the contact structure connects the floating diffusion region. The contact structure passes through the device layer and extends toward the inside of the first substrate. One end embedded in the inside of the first substrate surrounds the top of a portion of the shallow trench isolation structure, so that the same contact structure can be connected to different floating diffusion regions through the end, so that the floating diffusion regions of multiple light absorption regions can share the contact structure, thereby reducing the number of contact structures, reducing parasitic capacitance, and improving device performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0037] Figure 1A cross-sectional schematic diagram of an image sensor provided by an embodiment of the present application is shown;

[0038] Figure 2A and 2B A top view of the image sensor provided by an embodiment of the present application on the surface of the first substrate;

[0039] Figure 3 A schematic diagram of a three-dimensional structure of an image sensor provided in an embodiment of the present application;

[0040] Figure 4 A circuit diagram of a double-layer pixel structure provided in an embodiment of the present application;

[0041] Figure 5 A flowchart of a method for manufacturing an image sensor provided in an embodiment of the present application;

[0042] Figure 6-10 Schematic diagram of the structure of the image sensor during the manufacturing process in the embodiment of the present application. DETAILED DESCRIPTION

[0043] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0044] In the following description, many specific details are set forth to facilitate a full understanding of the present application, but the present application may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present application. Therefore, the present application is not limited to the specific embodiments disclosed below.

[0045] This application is described in detail with reference to schematic diagrams. When describing the embodiments of this application in detail, for the sake of convenience, the cross-sectional diagrams showing the device structure will not be partially enlarged according to the general scale, and the schematic diagrams are only examples, which should not limit the scope of protection of this application. In addition, in actual production, the three-dimensional dimensions of length, width and depth should be included.

[0046] In order to better understand the technical solution and technical effects of the present application, specific embodiments will be described in detail below with reference to the accompanying drawings.

[0047] See also Figure 1 , which is a cross-sectional schematic diagram of an image sensor provided in an embodiment of the present application, with reference to Figure 2A , 2BFIG. 1 is a top view of the image sensor provided in the embodiment of the present application on the surface of the first substrate, with reference to FIG. Figure 3 FIG. 1 is a schematic diagram of a three-dimensional structure of an image sensor provided in an embodiment of the present application. Figure 3 The left side is a schematic diagram of the three-dimensional structure of a traditional image sensor, and the right side is a schematic diagram of the three-dimensional structure of the image sensor in an embodiment of the present application. The image sensor may include: a first substrate 100, a plurality of light absorption regions (for example, including 1001 and 1002) located in the first substrate 100, and a device layer 20 located on one side of the first substrate, and a contact structure 10A that passes through the device layer.

[0048] In the embodiment of the present application, the first substrate 100 is used to form a light absorption region of the image sensor, and its material may be a semiconductor material, such as silicon, germanium, etc. The first substrate 100 may be doped, for example, may be doped with a P-type element, and the P-type element is a Group III element.

[0049] The light absorption region is formed in the first substrate 100, which can be arranged toward the first side (e.g., the upper side) of the first substrate 100, and one light absorption region serves as a pixel. A photodiode (PD) is provided in the light absorption region for receiving light signals, and electron-hole pairs are excited by the light signals. The electron-hole pairs are separated and transmitted in opposite directions and collected to form electrical signals. The photodiode may include a light absorption doping region 110 and a substrate region outside the light absorption doping region 110. The light absorption doping region 110 is of opposite type to the first substrate, forming a PN junction, and the light absorption doping region 110 can absorb photons, and the photogenerated carriers are transmitted to the peripheral substrate region. The light absorption doping region 110 may be N-type doped, and the doping element is a Group V element.

[0050] A floating diffusion region (FD) 150 may also be provided in the light absorption region, one end of which is connected to the photodiode for collecting carriers generated by the photodiode, and the other end is connected to the contact structure 10A for conducting the carriers outward. The setting of the contact structure 10A refers to the subsequent description. The floating diffusion region 150 may include a first doping region and a second doping region in the light absorption region, and the first doping region and the second doping region have opposite doping types (one of which is P-type doping and the other is N-type doping), forming a PN junction. The end connected to the photodiode may be one of the first doping region and the second doping region, and the end connected to the contact structure may be the other of the first doping region and the second doping region. The floating diffusion region 150 is provided in the first substrate 100, so the end connected to the photodiode is equivalent to contacting the substrate region outside the light absorption doping region 110, and the end connected to the contact structure 10A is in contact with the contact structure 10A.

[0051] A shallow trench isolation (STI) 120 may be provided between adjacent light absorption regions. The shallow trench isolation structure 120 is located in the first substrate 100 and may be provided toward the first side (e.g., the upper side) of the first substrate to isolate adjacent light absorption regions. The shallow trench isolation structure 120 is an insulating structure, and the material of the insulating structure is, for example, silicon oxide. A surface on one side of the shallow trench isolation structure 120 is flush with a surface on the first side of the first substrate 100. When a plurality of light absorption regions are arranged in an array, the shallow trench isolation structure 120 is composed of a plurality of substructures, and the plurality of substructures may be distributed in a cross shape or a tic-tac-toe shape. The plurality of substructures may be connected into an unbounded shallow trench isolation mesh structure, and there is no actual boundary between the plurality of substructures. The plurality of substructures are distinguished by their setting positions.

[0052] The device layer 20 is located on the first side (e.g., the upper side) of the first substrate. The device layer 20 is formed outside the first substrate 100, and a pixel transistor (Pixel MOSFET) is arranged therein. In this way, the pixel transistor and the photodiode can be arranged on different layers, which is conducive to reducing the size of the pixel transistor and improving the resolution. The pixel transistor may include an amplifying transistor (DX), a selecting transistor (SX), and a reset transistor (RX).

[0053] The image sensor may further include a first dielectric layer 140, the first dielectric layer 140 is located on the surface of the first substrate 100, a transfer transistor (TX) is arranged in the first dielectric layer 140, the transfer transistor is used to control the charge transfer between the photodiode and the floating diffusion region, a channel region of the transfer transistor may also be arranged in the light absorption region, the channel region is connected between the photodiode and the floating diffusion region, a gate structure 130 for controlling the conductive state of the channel region may be formed in the first dielectric layer 140, the channel region may be a part of the substrate region outside the light absorption doping region, so that the photodiode includes another part of the substrate region outside the light absorption doping region, refer to Figure 1 As shown, the gate structure 130 can control the conductive state of the channel region between the photodiode and the floating diffusion region below. The channel region in the light absorption region 1001 is located at the lower right of the gate structure 130, and the channel region in the light absorption region 1002 is located at the lower left of the gate structure 130.

[0054] refer to Figure 1 As shown, the gate structure 130 may be located on the first side of the first substrate 100, and its material may be polysilicon. The gate structure 130 may be located in the first dielectric layer 140 on the first side of the first substrate 100, and the first dielectric layer 140 has a flat surface after being planarized. The first substrate and its internal structure, as well as the dielectric layer and its internal structure, serve as the first layer 10.

[0055] The device layer 20 as the second layer 20 may include a second substrate 200 and a second dielectric layer 220. A pixel transistor is formed in the second dielectric layer 220. A gate 230 and a channel region of the pixel transistor may be formed in the second dielectric layer. The second substrate 200 may be formed on the first substrate 100 by bonding. A bonding layer 210 may be formed between the second substrate 200 and the first substrate 100. Figure 1 Specifically, the second dielectric layer 220 can be bonded to the first dielectric layer 140 forming the gate structure through the bonding layer 210 to form a bonding interface 1A, and the second dielectric layer 220 can also be contacted and connected to the first dielectric layer to form a bonding interface (not shown).

[0056] The device layer 20 and the photoelectric absorption region are arranged in different layers, forming a double-layer pixel structure. Figure 4 As shown, it is a circuit diagram of a double-layer pixel structure provided by an embodiment of the present application, wherein a first substrate 100 and its attached film layer of a photodiode and a transfer transistor are provided as the first layer (1st layer), and a device layer 200 of a pixel transistor is provided as the second layer (2nd layer). In the first layer, the photodiode includes photodiodes L1 to L4 (PDL1 to PDL4), and photodiodes R1 to R4 (PDR1 to PDR4), a total of 8, and the transfer transistor includes transfer transistors L1 to L4 (TGL1 to TGL4), and transfer transistors R1 to R4 (TGR1 to TGR4), a total of 8; in the second layer, it includes a selection transistor SEL, an amplifier transistor AMP, and a reset transistor RST.

[0057] In the embodiment of the present application, the image sensor may further include a contact structure 10A that penetrates the device layer. The contact structure 10A may be connected to the floating diffusion region 150 in the first substrate 100, and may also be connected to the pixel transistor in the device layer 20. Since the contact structure 10A penetrates the device layer 20, the signal of the floating diffusion region 150 may be led out of the device layer 20. Since the first substrate 100 and the device layer 20 constitute a double-layer pixel structure, the contact structure 10A serves as a deep contact structure (Deep CONT). The material of the contact structure 10A may be a metal material, such as tungsten, copper, molybdenum, etc.

[0058] The contact structure 10A can extend into the interior of the first substrate 100. One end of the contact structure 10A embedded in the interior of the first substrate 100 surrounds the top of a portion of the shallow trench isolation structure. In this way, the same contact structure can be connected to different floating diffusion regions through the end portions, so that the floating diffusion regions of multiple light absorption regions can share the contact structure, thereby reducing the number of contact structures, reducing parasitic capacitance, and improving device performance.

[0059] One end of the contact structure 10A embedded in the first substrate 100 may include a plurality of connection structures, and the plurality of connection structures are separated by shallow trench structures. Figure 2A As shown, that is, the contact structure 10A includes a sub-contact structure outside the first substrate 100 and a plurality of connection structures embedded in the first substrate 100, the sub-contact structure and each connection structure are connected respectively, the contact structure 10A is an integral structure, the sub-contact structure and the connection structure are named for the convenience of explanation, and there is actually no obvious boundary between the two. Each connection structure is respectively connected to the floating diffusion area 150 located on different sides of the shallow trench isolation structure 120, so that the same contact structure 10A can be connected to different floating diffusion areas through the connection structure at the end, so that the floating diffusion areas of multiple light absorption areas can share the contact structure 10A, reducing the number of contact structures 10A, reducing parasitic capacitance, and improving device performance.

[0060] One end of the contact structure 10A embedded in the first substrate 100 may include a connection structure, which is a continuous ring structure. Figure 2B As shown, the connection structures are respectively connected to the floating diffusion regions located at different sides of the shallow trench isolation structure. That is, the connection structures are not separated by the shallow trench structure, but as a whole, connected to the sub-contact structure outside the first substrate 100 to form the overall structure of the contact structure 10A.

[0061] As a possible implementation, the contact structure 10A can be disposed between two light absorption regions, and the two light absorption regions share one contact structure 10A, so that the number of contact structures 10A is reduced to 1 / 2 of the original. Specifically, the multiple light absorption regions include a first light absorption region and a second light absorption region, and the shallow trench isolation structure between the first light absorption region and the second light absorption region is recorded as a first isolation structure. The contact structure 10A can be an integral structure, and one side surface of the integral contact structure 10A is connected to the floating diffusion region of the first light absorption region, and the other side surface is connected to the floating diffusion region of the second light absorption region.

[0062] Alternatively, the contact structure 10A may include a first connection structure covering the side wall of the first isolation structure facing the first light absorption region, and a second connection structure covering the side wall of the first isolation structure facing the second light absorption region, wherein the first connection structure and the second connection structure are separated by the first isolation structure, the first connection structure connects the floating diffusion region of the first light absorption region, and the second connection structure connects the floating diffusion region of the second light absorption region. The first connection structure and the second connection structure may be semicircular in a plane parallel to the surface of the first substrate.

[0063] As a possible implementation, the contact structure 10A may be disposed between the four light absorption regions, and the four light absorption regions share one contact structure 10A, so that the number of contact structures 10A is reduced to 1 / 4 of the original. Figure 3 As shown, multiple light absorption regions are arranged in an array, and the multiple light absorption regions include a first light absorption region 1001, a second light absorption region 1002, a third light absorption region 1003 and a fourth light absorption region 1004, and the adjacent first light absorption region, second light absorption region, third light absorption region and fourth light absorption region share the contact structure.

[0064] The shallow trench isolation structure between the first light absorption region 1001 and the second light absorption region 1002 is recorded as the first isolation structure 121, the shallow trench isolation structure between the second light absorption region 1002 and the third light absorption region 1003 is recorded as the second isolation structure 122, the shallow trench isolation structure between the fourth light absorption region 1004 and the third light absorption region 1003 is recorded as the third isolation structure 123, and the shallow trench isolation structure between the first light absorption region 1001 and the fourth light absorption region 1004 is recorded as the fourth isolation structure 124. The first isolation structure 121, the second isolation structure 122, the third isolation structure 123 and the fourth isolation structure 124 intersect with the contact structure 10A in the same area. The first isolation structure 121, the second isolation structure 122, the third isolation structure 123 and the fourth isolation structure 124 form a cross on the surface of the first substrate, and the contact structure 10A is perpendicular to the surface of the first substrate 100 and embedded in the area where the center of the cross is located.

[0065] The contact structure 10A can be an integral structure, through which the first side surface of the integral contact structure 10A is connected to the floating diffusion region of the first light absorption region 1001, the second side surface is connected to the floating diffusion region of the second light absorption region 1002, the third side surface is connected to the floating diffusion region of the third light absorption region 1003, and the fourth side surface is connected to the floating diffusion region of the fourth light absorption region 1004.

[0066] Alternatively, the contact structure 10A includes a first connection structure 10A1 covering the side walls of the first isolation structure 121 and the fourth isolation structure 124 facing the first light absorption region 1001, a second connection structure 10A2 covering the side walls of the first isolation structure 121 and the second isolation structure 122 facing the second light absorption region 1002, a third connection structure 10A3 covering the side walls of the second isolation structure 122 and the third isolation structure 123 facing the third light absorption region 1003, and a fourth connection structure 10A4 covering the side walls of the first isolation structure 121 and the fourth isolation structure 124 facing the fourth light absorption region 1004, and the first connection structure 10A1, the second connection structure 10A2, the third connection structure 10A3 and the fourth connection structure 10A4 are isolated by a cross-shaped shallow trench isolation structure 120. The first connection structure 10A1 connects the floating diffusion area 150 of the first light absorption area 1001, the second connection structure 10A2 connects the floating diffusion area 150 of the second light absorption area 1002, the third connection structure 10A3 connects the floating diffusion area 150 of the third light absorption area 1003, and the fourth connection structure 10A4 connects the floating diffusion area 150 of the fourth light absorption area 1004. The first connection structure 10A1, the second connection structure 10A2, the third connection structure 10A3 and the fourth connection structure 10A4 can form a discontinuous ring, and the four can be presented as a 1 / 4 circle in a plane parallel to the surface of the first substrate 100, and the overall structure of the floating diffusion area 150 is also a ring.

[0067] In an embodiment of the present application, the image sensor may further include a backside deep trench isolation structure (BDTI), which may be located in the first substrate 100 toward the second side (e.g., the lower side) for isolating adjacent light absorption regions, the second side and the first side being opposite sides, the first side being the side facing the first surface of the first substrate, the second side being the side facing the second surface of the first substrate, and the first surface and the second surface being opposite surfaces. The backside deep trench isolation structure may be flush with the second side surface of the first substrate. It may run through the entire first substrate 100, or it may run through to one end of the shallow trench isolation structure 120 in the first substrate, in which case the backside deep trench isolation structure may be connected to the shallow trench isolation structure, and the two constitute a full isolation structure, which runs through the entire first substrate for isolating adjacent light absorption regions. The full isolation structure may also be referred to as a full backside deep trench isolation structure (FBDTI).

[0068] The back deep trench isolation structure may include an insulating structure 10C and a high-k dielectric layer 10B around the insulating structure 10C. Figure 1As shown, the material of the insulating structure 10C is silicon oxide, etc., and the high-k dielectric layer 10B has a larger dielectric constant and better insulation, and its material is aluminum oxide, halogen oxide, zirconium oxide, etc. This can achieve physical isolation between different light absorption regions and reduce crosstalk and dark current.

[0069] In the embodiment of the present application, an isolation doping region may also be provided in the first substrate, the isolation doping region at least covers the sidewall of the shallow trench isolation structure, and the contact structure is embedded in the isolation doping region. Specifically, a part of the sidewall of the shallow trench isolation structure 120 in the full isolation structure is covered by the contact structure 10A, and an isolation doping region 160 is provided around the sidewall of the full isolation structure not covered by the contact structure 10A, for isolating adjacent light absorption regions, and the doping type of the isolation doping region 160 may be the same as the doping type of the first substrate 100, for example, P-type doping, and its doping concentration is greater than the doping concentration of the first substrate.

[0070] In addition, the image sensor may further include a lead-out structure 10D that penetrates the device layer, and the lead-out structure 10D is used to connect the control terminal of the transfer transistor. For example, the lead-out structure 10D may be connected to the gate structure 130 on one side of the first substrate 100, and is used to transmit a gate signal to the gate structure 130. Since the first substrate 100 and the device layer 20 form a double-layer pixel structure, the lead-out structure 10D serves as a deep contact structure (Deep CONT). The material of the lead-out structure 10D may be a metal material, such as tungsten, copper, molybdenum, etc.

[0071] A back-end process structure may be provided on a side of the device layer 20 facing away from the first substrate 100 for connecting various devices.

[0072] The present application provides an image sensor, comprising a first substrate, a plurality of light absorption regions in the first substrate, a device layer on one side of the first substrate, and a contact structure, wherein a photodiode and a floating diffusion region are arranged in the light absorption region, a shallow trench isolation structure is arranged between adjacent light absorption regions, the contact structure connects the floating diffusion region, the contact structure passes through the device layer, and extends toward the inside of the first substrate, and one end embedded in the inside of the first substrate surrounds the top of a portion of the shallow trench isolation structure, so that the same contact structure can be connected to different floating diffusion regions through the end, so that the floating diffusion regions of the plurality of light absorption regions can share the contact structure, thereby reducing the number of contact structures, reducing parasitic capacitance, and improving device performance.

[0073] Based on the image sensor provided in the above embodiments, the present application also provides a method for manufacturing an image sensor, referring to Figure 5 FIG. 1 is a flowchart of a method for manufacturing an image sensor provided in an embodiment of the present application, with reference to FIG. Figure 6-10FIG. 1 is a schematic diagram of the structure of an image sensor in a manufacturing process according to an embodiment of the present application. The manufacturing method may include:

[0074] S101, providing a first substrate, forming a plurality of light absorption regions in the first substrate, and a shallow trench isolation structure for isolating adjacent light absorption regions, forming a photodiode and a floating diffusion region in each light absorption region, referring to Figure 6 , Figure 7 and Figure 8 shown.

[0075] In the embodiment of the present application, the first substrate 100 is used to form a light absorption region of the image sensor, and its material may be a semiconductor material, such as silicon, germanium, etc. The first substrate 100 may be doped, for example, may be doped with a P-type element, and the P-type element is a Group III element.

[0076] A shallow trench isolation structure may be formed in the first substrate to define a plurality of light absorption regions. Figure 6 Specifically, an isolation shallow trench can be obtained by etching the first side surface of the first substrate, and an isolation structure can be formed in the isolation shallow trench.

[0077] The shallow trench isolation structure 120 is located in the first substrate 100, and it can be arranged toward the first side (e.g., the upper side) of the first substrate to isolate adjacent light absorption regions. The shallow trench isolation structure 120 is an insulating structure, and the material of the insulating structure is, for example, silicon oxide. One side surface of the shallow trench isolation structure 120 is flush with the first side surface of the first substrate 100. When multiple light absorption regions are arranged in an array, the shallow trench isolation structure 120 is composed of multiple substructures, and the multiple substructures can be distributed in a cross shape or a tic-tac-toe shape. The multiple substructures can be connected into an unbounded shallow trench isolation mesh structure, and there are no actual boundaries between the multiple substructures. The multiple substructures are distinguished by their setting positions.

[0078] After forming the shallow trench isolation structure, a photodiode and a floating diffusion region can be formed in each light absorption region, referring to Figure 7 Specifically, doping can be performed in the relevant regions of the light absorption region to obtain a photodiode and a floating diffusion region, and the doping method can be ion implantation.

[0079] The light absorption region is formed in the first substrate 100, which can be arranged toward the first side (e.g., the upper side) of the first substrate 100, and one light absorption region serves as a pixel. A photodiode (PD) is provided in the light absorption region for receiving light signals, and electron-hole pairs are excited by the light signals. The electron-hole pairs are separated and transmitted in opposite directions and collected to form electrical signals. The photodiode may include a light absorption doping region 110 and a substrate region outside the light absorption doping region 110. The light absorption doping region 110 is of opposite type to the first substrate, forming a PN junction, and the light absorption doping region 110 can absorb photons, and the photogenerated carriers are transmitted to the peripheral substrate region. The light absorption doping region 110 may be N-type doped, and the doping element is a Group V element.

[0080] One end of the floating diffusion region (FD) 150 is connected to the photodiode for collecting the carriers generated by the photodiode, and the other end is connected to the contact structure 10A for conducting the carriers outward. The setting of the contact structure 10A refers to the subsequent description. The floating diffusion region 150 may include a first doping region and a second doping region in the light absorption region. The first doping region and the second doping region have opposite doping types (one of which is P-type doping and the other is N-type doping), forming a PN junction. The end connected to the photodiode may be one of the first doping region and the second doping region, and the end connected to the contact structure may be the other of the first doping region and the second doping region. The floating diffusion region 150 is disposed in the first substrate 100, so the end connected to the photodiode is equivalent to contacting the substrate region outside the light absorption doping region 110, and the end connected to the contact structure 10A is in contact with the contact structure 10A.

[0081] In addition, a first dielectric layer 140 may be formed on the surface of the first substrate, and a transfer transistor may be formed in the first dielectric layer. The transfer transistor is used to control the charge transfer between the photodiode and the floating diffusion region. Specifically, a gate structure 130 in the transfer transistor located on the first layer of the first substrate and a first dielectric layer 140 covering the gate structure 130 may be formed. The first dielectric layer 140 may be planarized to make the plane of the first dielectric layer 140 flat. Figure 8 The material of the first dielectric layer 140 may be silicon oxide, and the planarization method may be mechanical grinding.

[0082] The transfer transistor is connected between the photodiode and the floating diffusion region. The transfer transistor includes a channel region connected between the photodiode and the floating diffusion region, and a gate structure 130 for controlling the conductive state of the channel region. The channel region may be a portion of the substrate region outside the light absorption doping region. Thus, the photodiode includes another portion of the substrate region outside the light absorption doping region. Figure 1As shown, the gate structure 130 can control the conductive state of the channel region between the photodiode and the floating diffusion region below, the channel region in the light absorption region 1001 is located at the lower right of the gate structure 130, and the channel region in the light absorption region 1002 is located at the lower left of the gate structure 130. The gate structure 130 can be made of polysilicon.

[0083] In addition, an isolation doping region may be formed in the first substrate, the isolation doping region at least covering the sidewall of the shallow trench isolation structure, and the contact structure is embedded in the isolation doping region. The isolation doping region is formed around the shallow trench isolation structure and in the area facing the second side, and is used to isolate adjacent light absorption regions. The doping type of the isolation doping region 160 may be the same as the doping type of the first substrate 100, for example, P-type doping, and its doping concentration is greater than the doping concentration of the first substrate. The isolation doping region may be formed by ion implantation.

[0084] S102, forming a device layer on one side of the first substrate, referring to Fig. 9 shown.

[0085] The device layer 20 is located on the surface of the first substrate, which can be located on the first side (e.g., the upper side) of the first substrate. The device layer 20 is formed outside the first substrate 100, and a pixel transistor (Pixel MOSFET) is arranged therein. The device layer 20 and the photoelectric absorption region are arranged in different layers to form a double-layer pixel structure. In this way, the pixel transistor and the photodiode can be arranged in different layers, which is conducive to reducing the size of the pixel transistor and improving the resolution. The pixel transistor may include an amplification transistor (DX), a selection transistor (SX), and a reset transistor (RX).

[0086] The device layer 20 may include a second substrate 200 and a second dielectric layer 220. A pixel transistor is formed in the second dielectric layer 220. A gate 230 and a channel region of the pixel transistor may be formed in the second dielectric layer. The second substrate 200 may be formed on the first substrate 100 by bonding. A bonding layer 210 may be formed between the second substrate 200 and the first substrate 100. Figure 1 Specifically, the second dielectric layer 220 can be bonded to the first dielectric layer 140 forming the gate structure through the bonding layer 210 to form a bonding interface 1A, and the second dielectric layer 220 can also be contacted and connected to the first dielectric layer to form a bonding interface (not shown).

[0087] Specifically, an empty substrate can be bonded to the first substrate 100, the empty substrate can be thinned to obtain a second substrate 200, the second substrate 200 can be processed to obtain a pixel transistor, the pixel transistor includes a gate 230, and then a dielectric layer 220 covering the gate 230 is formed on the second substrate 200, and the dielectric layer 220 is planarized, and the planarization method can be mechanical grinding.

[0088] S103, forming a contact structure that penetrates the device layer, referring to Fig.10 shown.

[0089] In the embodiment of the present application, the image sensor may further include a contact structure 10A that penetrates the device layer. The contact structure 10A may be connected to the floating diffusion region 150 in the first substrate 100, and may also be connected to the pixel transistor in the device layer 20. Since the contact structure 10A penetrates the device layer 20, the signal of the floating diffusion region 150 may be led out of the device layer 20. Since the first substrate 100 and the device layer 20 constitute a double-layer pixel structure, the contact structure 10A serves as a deep contact structure (Deep CONT). The material of the contact structure 10A may be a metal material, such as tungsten, copper, molybdenum, etc.

[0090] The contact structure 10A can extend into the interior of the first substrate 100. One end of the contact structure 10A embedded in the interior of the first substrate 100 surrounds the top of a portion of the shallow trench isolation structure. In this way, the same contact structure can be connected to different floating diffusion regions through the end portions, so that the floating diffusion regions of multiple light absorption regions can share the contact structure, thereby reducing the number of contact structures, reducing parasitic capacitance, and improving device performance.

[0091] One end of the contact structure 10A embedded in the first substrate 100 may include multiple connection structures, and the multiple connection structures are separated by a shallow trench structure. That is to say, the contact structure 10A includes a sub-contact structure outside the first substrate 100 and multiple connection structures embedded in the first substrate 100. The sub-contact structure and each connection structure are connected respectively. The contact structure 10A is an integral structure. The sub-contact structure and the connection structure are named for the convenience of explanation. There is actually no obvious boundary between the two. Each connection structure is respectively connected to the floating diffusion area 150 located on different sides of the shallow trench isolation structure 120. In this way, the same contact structure 10A can be connected to different floating diffusion areas through the connection structure at the end, so that the floating diffusion areas of multiple light absorption areas can share the contact structure 10A, reducing the number of contact structures 10A, reducing parasitic capacitance, and improving device performance.

[0092] One end of the contact structure 10A embedded in the first substrate 100 may include a connection structure, which is a continuous ring structure, and the connection structure is respectively connected to the floating diffusion regions located on different sides of the shallow trench isolation structure. In other words, the connection structure is not separated by the shallow trench structure, but as a whole, is connected to the sub-contact structure outside the first substrate 100 to form the overall structure of the contact structure 10A.

[0093] As a possible implementation, the contact structure 10A can be disposed between two light absorption regions, and the two light absorption regions share one contact structure 10A, so that the number of contact structures 10A is reduced to 1 / 2 of the original. Specifically, the multiple light absorption regions include a first light absorption region and a second light absorption region, and the shallow trench isolation structure between the first light absorption region and the second light absorption region is recorded as a first isolation structure. The contact structure 10A can be an integral structure, and one side surface of the integral contact structure 10A is connected to the floating diffusion region of the first light absorption region, and the other side surface is connected to the floating diffusion region of the second light absorption region.

[0094] Alternatively, the contact structure 10A may include a first connection structure covering the side wall of the first isolation structure facing the first light absorption region, and a second connection structure covering the side wall of the first isolation structure facing the second light absorption region, wherein the first connection structure and the second connection structure are separated by the first isolation structure, the first connection structure connects the floating diffusion region of the first light absorption region, and the second connection structure connects the floating diffusion region of the second light absorption region. The first connection structure and the second connection structure may be semicircular in a plane parallel to the surface of the first substrate.

[0095] As a possible implementation, the contact structure 10A may be disposed between the four light absorption regions, and the four light absorption regions share one contact structure 10A, so that the number of contact structures 10A is reduced to 1 / 4 of the original. Figure 3 As shown, multiple light absorption regions are arranged in an array, and the multiple light absorption regions include a first light absorption region 1001, a second light absorption region 1002, a third light absorption region 1003 and a fourth light absorption region 1004, and the adjacent first light absorption region, second light absorption region, third light absorption region and fourth light absorption region share the contact structure.

[0096] The shallow trench isolation structure between the first light absorption region 1001 and the second light absorption region 1002 is recorded as the first isolation structure 121, the shallow trench isolation structure between the second light absorption region 1002 and the third light absorption region 1003 is recorded as the second isolation structure 122, the shallow trench isolation structure between the fourth light absorption region 1004 and the third light absorption region 1003 is recorded as the third isolation structure 123, and the shallow trench isolation structure between the first light absorption region 1001 and the fourth light absorption region 1004 is recorded as the fourth isolation structure 124. The first isolation structure 121, the second isolation structure 122, the third isolation structure 123 and the fourth isolation structure 124 intersect with the contact structure 10A in the same area. The first isolation structure 121, the second isolation structure 122, the third isolation structure 123 and the fourth isolation structure 124 form a cross on the surface of the first substrate, and the contact structure 10A is perpendicular to the surface of the first substrate 100 and embedded in the area where the center of the cross is located.

[0097] The contact structure 10A can be an integral structure, through which the first side surface of the integral contact structure 10A is connected to the floating diffusion region of the first light absorption region 1001, the second side surface is connected to the floating diffusion region of the second light absorption region 1002, the third side surface is connected to the floating diffusion region of the third light absorption region 1003, and the fourth side surface is connected to the floating diffusion region of the fourth light absorption region 1004.

[0098] Alternatively, the contact structure 10A includes a first connection structure 10A1 covering the side walls of the first isolation structure 121 and the fourth isolation structure 124 facing the first light absorption region 1001, a second connection structure 10A2 covering the side walls of the first isolation structure 121 and the second isolation structure 122 facing the second light absorption region 1002, a third connection structure 10A3 covering the side walls of the second isolation structure 122 and the third isolation structure 123 facing the third light absorption region 1003, and a fourth connection structure 10A4 covering the side walls of the first isolation structure 121 and the fourth isolation structure 124 facing the fourth light absorption region 1004, and the first connection structure 10A1, the second connection structure 10A2, the third connection structure 10A3 and the fourth connection structure 10A4 are isolated by a cross-shaped shallow trench isolation structure 120. The first connection structure 10A1 connects the floating diffusion area 150 of the first light absorption area 1001, the second connection structure 10A2 connects the floating diffusion area 150 of the second light absorption area 1002, the third connection structure 10A3 connects the floating diffusion area 150 of the third light absorption area 1003, and the fourth connection structure 10A4 connects the floating diffusion area 150 of the fourth light absorption area 1004. The first connection structure 10A1, the second connection structure 10A2, the third connection structure 10A3 and the fourth connection structure 10A4 can form a discontinuous ring, and the four can be presented as a 1 / 4 circle in a plane parallel to the surface of the first substrate 100, and the overall structure of the floating diffusion area 150 is also a ring.

[0099] Specifically, a first contact hole may be formed, the first contact hole penetrates the device layer, the bottom of the first contact hole exposes the floating diffusion region and the shallow trench isolation structure, the exposed floating diffusion region is etched to form a second contact hole located between the floating diffusion region and the shallow trench isolation structure, and a conductive material is filled in the second contact hole and the first contact hole to form a contact structure including a plurality of connection structures, with reference to Fig.10 As shown. The first contact hole and the second contact hole can be obtained by dry etching. Since the shallow trench isolation structure and the first substrate are made of different materials, the shallow trench isolation structure can be retained when etching the first substrate, so that the upper surface of the shallow trench isolation structure is higher than the bottom of the contact hole. The position of the first contact hole can be defined by a photomask.

[0100] Specifically, a first contact hole can also be formed, the first contact hole penetrates the device layer, the bottom of the first contact hole exposes the floating diffusion area and the shallow trench isolation structure, the exposed part of the floating diffusion area and the exposed shallow trench isolation structure are etched to form a ring-shaped third contact hole, and conductive material is filled in the third contact hole and the first contact hole to form a contact structure including a connecting structure.

[0101] In the embodiment of the present application, a lead-out structure penetrating the device layer may also be formed, and the lead-out structure is used to connect the control terminal of the transfer transistor. For example, the lead-out structure 10D may be connected to the gate structure 130 on one side of the first substrate 100, and is used to transmit a gate signal to the gate structure 130. Since the first substrate 100 and the device layer 20 constitute a double-layer pixel structure, the lead-out structure 10D serves as a deep contact structure (Deep CONT). The material of the lead-out structure 10D may be a metal material, such as tungsten, copper, molybdenum, etc.

[0102] A back-end process structure may be provided on the side of the device layer 20 away from the first substrate 100 for connecting various devices. Afterwards, the wafer may be flipped over to perform related processes on the back, such as forming a back deep trench isolation structure.

[0103] In an embodiment of the present application, the image sensor may further include a back deep trench isolation structure, which may be located in the first substrate 100 toward the second side (e.g., the lower side) to isolate adjacent light absorption regions. The back deep trench isolation structure may be flush with the second side surface of the first substrate. It may run through the entire first substrate 100, or it may run through to one end of the shallow trench isolation structure 120 in the first substrate, in which case the back deep trench isolation structure may be connected to the shallow trench isolation structure, and the two constitute a full isolation structure, which runs through the entire first substrate to isolate adjacent light absorption regions. The full isolation structure may also be referred to as a full back deep trench isolation structure (FBDTI).

[0104] The back deep trench isolation structure may include an insulating structure 10C and a high-k dielectric layer 10B around the insulating structure 10C. Figure 1 As shown, the material of the insulating structure 10C is silicon oxide, etc., and the high-k dielectric layer 10B has a larger dielectric constant and better insulation, and its material is aluminum oxide, halogen oxide, zirconium oxide, etc. This can achieve physical isolation between different light absorption regions and reduce crosstalk and dark current.

[0105] Specifically, an isolation deep trench can be etched on the second side of the first substrate, and the isolation deep trench can be aligned with the shallow trench isolation structure, so that the etching of the isolation deep trench stays on the shallow trench isolation structure, so that after the isolation deep trench is filled to obtain the back deep trench isolation structure, the back deep trench isolation structure is connected to the shallow trench isolation structure, and the two constitute a full isolation structure, and the full isolation structure runs through the entire first substrate. The filling of the isolation deep trench can be specifically formed by forming a high-k dielectric layer on the inner wall of the isolation deep trench, and then filling the isolation deep trench with an insulating material to obtain an insulating structure.

[0106] In the embodiment of the present application, if an isolation doping region has been formed, part of the sidewall of the shallow trench isolation structure 120 in the full isolation structure is covered by the contact structure 10A, and an isolation doping region 160 is also provided around the sidewall of the full isolation structure not covered by the contact structure 10A.

[0107] An embodiment of the present application provides a method for manufacturing an image sensor, providing a first substrate, forming multiple light absorption regions in the first substrate, and a shallow trench isolation structure for isolating adjacent light absorption regions, forming a photodiode and a floating diffusion region in each of the light absorption regions, forming a device layer on one side of the first substrate, forming a contact structure that penetrates the device layer, and extending toward the interior of the first substrate. The contact structure is embedded in the interior of the first substrate at one end and surrounds the top of a portion of the shallow trench isolation structure, so that the same contact structure can be connected to different floating diffusion regions through the end, so that the floating diffusion regions of multiple light absorption regions can share the contact structure, thereby reducing the number of contact structures, reducing parasitic capacitance, and improving device performance.

[0108] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the method embodiment, since it is basically similar to the device embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the device embodiment.

[0109] The above is only a preferred implementation of the present application. Although the present application has been disclosed as a preferred embodiment, it is not intended to limit the present application. Any technician familiar with the art can use the above disclosed methods and technical contents to make many possible changes and modifications to the technical solution of the present application without departing from the scope of the technical solution of the present application, or modify it into an equivalent embodiment of equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present application without departing from the content of the technical solution of the present application still falls within the scope of protection of the technical solution of the present application.

Claims

1. An image sensor, characterized in that: include: A first substrate, and a plurality of light absorption regions located in the first substrate, wherein a photodiode and a floating diffusion region are disposed in the light absorption region, and a shallow trench isolation structure is disposed between adjacent light absorption regions; A device layer, located on one side of the first substrate; A contact structure, wherein the contact structure is connected to the floating diffusion region, the contact structure passes through the device layer and extends into the first substrate, one end of the contact structure embedded in the first substrate surrounds a portion of the top of the shallow trench isolation structure, and one end of the contact structure embedded in the first substrate is respectively connected to the floating diffusion regions located on different sides of the shallow trench isolation structure.

2. The image sensor according to claim 1, characterized in that One end of the contact structure embedded in the first substrate includes a plurality of connection structures, the plurality of connection structures are separated by the shallow trench isolation structure, and each connection structure is respectively connected to a floating diffusion region located on a different side of the shallow trench isolation structure.

3. The image sensor according to claim 1, characterized in that One end of the contact structure embedded in the first substrate includes a connection structure, and the connection structure is a continuous ring structure, and the connection structure is respectively connected to the floating diffusion regions located on different sides of the shallow trench isolation structure.

4. The image sensor according to claim 1, characterized in that The multiple light absorption regions are arranged in an array, and the multiple light absorption regions include a first light absorption region, a second light absorption region, a third light absorption region and a fourth light absorption region. The adjacently arranged first light absorption region, the second light absorption region, the third light absorption region and the fourth light absorption region share a contact structure.

5. The image sensor according to claim 1, characterized in that Also includes: A back deep trench isolation structure is connected with the shallow trench isolation structure to form a full isolation structure, and the full isolation structure is used to isolate the adjacent light absorption areas.

6. The image sensor according to claim 5, characterized in that An isolation doping region is also provided in the first substrate. The isolation doping region at least covers the sidewalls of the shallow trench isolation structure. The contact structure is embedded in the isolation doping region.

7. The image sensor according to any one of claims 1 to 6, characterized in that: Also includes: A first dielectric layer, wherein the first dielectric layer is located on the surface of the first substrate, a transfer transistor is arranged in the first dielectric layer, and the transfer transistor controls the charge transfer between the photodiode and the floating diffusion region.

8. The image sensor according to claim 7, characterized in that: Also includes: A lead-out structure runs through the device layer, and the lead-out structure is used to connect the control terminal of the transfer transistor.

9. The image sensor according to claim 7, characterized in that: The device layer includes a second substrate and a second dielectric layer. The second substrate is provided with pixel transistors. The pixel transistors include an amplifying transistor, a selecting transistor and a resetting transistor. The second dielectric layer is in contact with and connected to the first dielectric layer.

10. A method for manufacturing an image sensor, characterized in that: include: Providing a first substrate, forming a plurality of light absorption regions in the first substrate, and a shallow trench isolation structure for isolating adjacent light absorption regions; forming a photodiode and a floating diffusion region in each of the light absorbing regions; forming a device layer on one side of the first substrate; A contact structure is formed that penetrates the device layer, the contact structure is connected to the floating diffusion region, the contact structure extends into the first substrate, one end of the contact structure embedded in the first substrate surrounds a portion of the top of the shallow trench isolation structure, and one end of the contact structure embedded in the first substrate is respectively connected to the floating diffusion regions located on different sides of the shallow trench isolation structure.

11. The method according to claim 10, characterized in that A contact structure is formed that penetrates the device layer, including: forming a first contact hole, the first contact hole penetrates the device layer, the bottom of the first contact hole exposes the floating diffusion area and the shallow trench isolation structure, etching the exposed part of the floating diffusion area to form a second contact hole located between the floating diffusion area and the shallow trench isolation structure, and filling the second contact hole and the first contact hole with conductive material to form the contact structure.

12. The method according to claim 10, characterized in that A contact structure is formed that penetrates the device layer, including: forming a first contact hole, the first contact hole penetrates the device layer, the bottom of the first contact hole exposes the floating diffusion area and the shallow trench isolation structure, etching the exposed part of the floating diffusion area and the exposed part of the shallow trench isolation structure to form a ring-shaped third contact hole, and filling the third contact hole and the first contact hole with conductive material to form the contact structure.

Images