Image sensor and preparation method thereof

Abstract

The invention provides an image sensor and a preparation method thereof, and the method comprises the steps: forming a plurality of groups of first deep grooves and second deep grooves which are periodically arranged at intervals in one side of a substrate, each second deep groove comprises a first groove and a second groove which are communicated with each other, the second groove is located at the bottom of the first groove, and the first deep grooves and the second deep grooves are communicated with each other; the width of the first groove is larger than that of the second groove. Compared with the prior art that the pitch value of the upper half part of the deep trench isolation structure is consistent with that of the lower half part of the deep trench isolation structure, the width of the first groove is larger than that of the second groove. The sum of the groove width of the first groove, the groove width of the first deep groove and the distance between the first groove and the first deep groove is larger than the sum of the groove width of the second groove, the groove width of the first deep groove and the distance between the second groove and the first deep groove. Therefore, each photodiode can obtain two pixel values at the upper half part and the lower half part between the adjacent deep grooves.

Description

Technical Field

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

[0002] The back-illuminated image sensor (BSI) places the photosensitive layer components (such as microlenses and photodiodes) on the back side of the substrate and allows light to enter directly from the back of the substrate, avoiding the light being affected by the circuits and transistors between the microlenses and photodiodes in the front-illuminated image sensor structure, thereby significantly improving the efficiency of light and greatly improving the photosensitivity of the image sensor under low light conditions. Figure 1 As shown, in the current advanced manufacturing process of the back-illuminated image sensor, since the pitch value a of the deep trench isolation structure is fixed in depth, the photodiode (PD) between adjacent deep trench isolation structures has only one pixel value. Summary of the invention

[0003] The object of the present invention is to provide an image sensor and a method for manufacturing the same, which can solve the problem that the photodiodes between adjacent deep trench isolation structures have only one pixel value to choose from.

[0004] In order to solve the above problems, the present invention provides a method for preparing an image sensor, comprising the following steps: A plurality of groups of first deep grooves and second deep grooves are formed on one side of the substrate and are periodically spaced apart, wherein the second deep grooves include a first groove and a second groove that are connected to each other, the second groove is located at the bottom of the first groove, and the groove width of the first groove is greater than the groove width of the second groove; Insulating materials are filled in the first deep trench and the second deep trench to form a first deep trench structure and a second deep trench structure, and a photodiode is formed between the first deep trench structure and the second deep trench structure, thereby forming an image sensor.

[0005] Optionally, a specific method for forming the first deep trench is: Providing a substrate, wherein the substrate has a back side, a second core mold material layer is formed on the back side, a plurality of first core mold structures are arranged at intervals on the second core mold material layer, and first sidewall structures are arranged on both sides of each of the first core mold structures; Removing the first core mold structure, and etching the second core mold material layer using the first sidewall structure as a mask to obtain a plurality of second core mold structures arranged at intervals, removing the first sidewall structure, and forming second sidewall structures on both sides of each of the second core mold structures; The second core mold structure is removed by a dry etching process to form an opening, wherein the opening exposes the back surface, and a first groove is formed in the substrate between adjacent openings.

[0006] Furthermore, the specific method of forming the second deep trench is: Using the second sidewall structure as a mask, etching the substrate by a dry etching process to form a first deep trench at the opening and a second groove below the first groove; The second side wall is removed.

[0007] Furthermore, an etching speed of the etching gas used when forming the first groove is greater than an etching speed of the etching gas used when forming the second groove.

[0008] Furthermore, the etching gas used when forming the first groove is CF4, and the etching gas used when forming the second groove is CF3H or CF2H2.

[0009] Furthermore, the specific method of forming the image sensor is: Filling the first deep trench and the second deep trench with insulating material to form a first deep trench structure and a second deep trench structure; forming a grid structure, wherein the grid structure is located above the first deep trench structure and the second deep trench structure; forming a photodiode in the substrate between the first deep trench structure and the second deep trench structure; Color filters are formed on the substrate between the grid structures.

[0010] Optionally, the sum of the groove width of the first groove, the groove width of the first deep groove and the spacing between the first groove and the first deep groove is a first size, the sum of the groove width of the second groove, the groove width of the first deep groove and the spacing between the second groove and the first deep groove is a second size, and the first size is greater than the second size.

[0011] Optionally, the ratio of the depth of the first groove to the depth of the second groove is 1:2.

[0012] On the other hand, the present invention also provides an image sensor, which is prepared by the above-mentioned method for preparing the image sensor, and includes a plurality of groups of first deep grooves and second deep grooves periodically arranged on one side of a substrate, the second deep grooves include a first groove and a second groove connected to each other, the second groove is located at the bottom of the first groove, a first deep groove structure and a second deep groove structure are formed in the first deep groove and the second deep groove, and a photodiode is formed in the substrate between the first deep groove structure and the second deep groove structure, wherein the groove width of the first groove is greater than the groove width of the second groove.

[0013] Optionally, a grid structure is further formed on the first deep trench structure and the second deep trench structure, and a color filter is formed on the substrate between adjacent grid structures.

[0014] Compared with the prior art, the present invention has the following unexpected technical effects: The present invention provides an image sensor and a method for preparing the same. The method for preparing the image sensor comprises the following steps: forming a plurality of groups of first deep grooves and second deep grooves periodically spaced on one side of a substrate, wherein the second deep grooves include a first groove and a second groove connected to each other, the second groove is located at the bottom of the first groove, and the groove width of the first groove is greater than the groove width of the second groove; filling the first deep groove and the second deep groove with insulating material to form a first deep groove structure and a second deep groove structure, and forming a photodiode between the first deep groove structure and the second deep groove structure, thereby forming an image sensor. In the present invention, the groove width of the first groove is greater than the groove width of the second groove, and compared with the pitch value of the upper half and the pitch value of the lower half of the deep trench isolation structure in the prior art being consistent, the groove width of the first groove, the groove width of the first deep groove, and the sum of the spacing between the first groove and the first deep groove in this embodiment are greater than the groove width of the second groove, the groove width of the first deep groove, and the sum of the spacing between the second groove and the first deep groove, so that each photodiode can obtain two pixel values ​​in the upper half and the lower half between adjacent deep grooves. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic structural diagram of a deep trench isolation structure formed in the prior art.

[0016] Figure 2 A schematic structural diagram of a substrate provided in one embodiment of the present invention.

[0017] Figure 3 A schematic diagram of the structure after forming the first core mold structure provided by one embodiment of the present invention.

[0018] Figure 4A schematic diagram of a structure after forming a first sidewall structure according to an embodiment of the present invention.

[0019] Figure 5 A schematic diagram of the structure after removing the first core mold structure provided in one embodiment of the present invention.

[0020] Figure 6 A schematic diagram of the structure after forming the second core mold structure provided by one embodiment of the present invention.

[0021] Figure 7 A schematic diagram of the structure after forming the second sidewall structure provided by one embodiment of the present invention.

[0022] Figure 8 A schematic diagram of the structure after removing the second core mold structure provided in one embodiment of the present invention.

[0023] Fig. 9 A schematic diagram of a structure after forming a first deep trench and a second deep trench according to an embodiment of the present invention.

[0024] Fig.10 A schematic diagram of a structure after forming a first deep trench structure and a second deep trench structure according to an embodiment of the present invention.

[0025] Fig.11 A schematic diagram of a structure after a grid structure is formed according to an embodiment of the present invention.

[0026] Description of reference numerals: Figure 1 Middle: 1-deep trench isolation structure; Figure 2-Figure 11 In: 100-substrate; 101-oxide layer; 102-metal interconnection structure; 103-second core mold material layer; 103'-second core mold structure; 104-first core mold material layer; 104'-first core mold structure; 105-first groove; 106-second groove; 107-first deep trench; 111-first sidewall structure; 112-second sidewall structure; 200-mask layer; 310-first deep trench structure; 320-second deep trench structure; 330-grid structure. DETAILED DESCRIPTION

[0027] The following will further describe in detail an image sensor and a method for manufacturing the same of the present invention. The present invention will be described in more detail with reference to the accompanying drawings, in which preferred embodiments of the present invention are shown. It should be understood that those skilled in the art can modify the present invention described herein and still achieve the beneficial effects of the present invention. Therefore, the following description should be understood as being widely known to those skilled in the art and not as a limitation of the present invention.

[0028] For the sake of clarity, not all features of the actual embodiments are described. In the following description, well-known functions and structures are not described in detail because they would clutter the invention with unnecessary detail. It should be recognized that in the development of any actual embodiment, a large number of implementation details must be made to achieve the developer's specific goals, such as changing from one embodiment to another according to the limitations of the relevant system or the relevant business. In addition, it should be recognized that such development work may be complex and time-consuming, but it is just a routine task for those skilled in the art.

[0029] In order to make the purpose and features of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are further described below in conjunction with the accompanying drawings. It should be noted that the accompanying drawings are all in a very simplified form and use inaccurate ratios, which are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention.

[0030] This embodiment provides a method for preparing an image sensor, comprising the following steps: Step S1: forming a plurality of groups of first deep grooves and second deep grooves periodically spaced apart on one side of the substrate, wherein the second deep grooves include first grooves and second grooves connected to each other, the second grooves are located at the bottom of the first grooves, and the groove width of the first grooves is greater than the groove width of the second grooves; Step S2: filling the first deep trench and the second deep trench with insulating material to form a first deep trench structure and a second deep trench structure, and forming a photodiode between the first deep trench structure and the second deep trench structure, thereby forming an image sensor.

[0031] In this embodiment, the groove width of the first groove is larger than the groove width of the second groove. Compared with the pitch value of the upper half and the pitch value of the lower half of the deep trench isolation structure in the prior art being consistent, the groove width of the first groove, the groove width of the first deep groove and the sum of the spacing between the first groove and the first deep groove in this embodiment is larger than the groove width of the second groove, the groove width of the first deep groove and the sum of the spacing between the second groove and the first deep groove, so that each photodiode can obtain two pixel values ​​in the upper half and the lower half between adjacent deep trenches.

[0032] The following combination Figure 2-Figure 11 A method for preparing an image sensor provided in this embodiment is described in detail.

[0033] Please refer to Figure 2-Figure 9First, step S1 is performed to form a plurality of groups of first deep grooves 107 and second deep grooves periodically spaced apart on one side of the substrate 100, wherein the second deep grooves include a first groove 105 and a second groove 106 connected to each other, wherein the second groove 106 is located at the bottom of the first groove 105, and the groove width of the first groove 105 is greater than the groove width of the second groove 106.

[0034] This step specifically includes the following steps: Please refer to Figure 2-Figure 4 In step S11, a substrate 100 is provided, wherein the substrate 100 has a back side, a second core mold material layer 103 is formed on the back side, a plurality of first core mold structures 104' spaced apart are arranged on the second core mold material layer 103, and first sidewall structures 111 are arranged on both sides of each of the first core mold structures 104'.

[0035] Detailed, such as Figure 2 As shown, a substrate 100 is first provided. The substrate 100 has a front side and a back side that are arranged opposite to each other. A metal interconnection structure 102 is formed on the front side. The metal interconnection structure 102 is used to realize interconnection and conduction of devices in the substrate 100 .

[0036] The substrate 100 may be a silicon substrate, but is not limited thereto. The substrate 100 may be a germanium substrate, a silicon germanium substrate, a silicon on insulator (SOI) or a germanium on insulator (GOI), etc. Certain doping particles may be implanted into the substrate 100 according to design requirements to change electrical parameters.

[0037] Please continue reading Figure 2 , and then sequentially form an oxide layer 101, a second core mold material layer 103, a first core mold material layer 104 and a patterned mask layer 200 on the back side of the substrate 100. The material of the mask layer 200 may be photoresist; the oxide layer 101 may be a silicon oxide layer, and may be formed by a thermal oxidation process or a chemical vapor deposition process, but is not limited thereto. The materials of the second core mold material layer 103 and the first core mold material layer 104 may include but are not limited to silicon, amorphous silicon or amorphous carbon, and may be formed by an epitaxial process, spin coating or spray coating.

[0038] like Figure 3 As shown, the patterned mask layer 200 is used as a mask to etch the first core mold material layer 104 to form a plurality of first core mold structures 104 ′ arranged at intervals.

[0039] Next, the mask layer 200 is removed.

[0040] like Figure 4 As shown, first sidewall structures 111 are formed on both sides of each of the first core mold structures 104 ′.

[0041] See also Figure 5-Figure 7 In step S12, the first core mold structure 104' is removed, and the second core mold material layer 103 is etched using the first sidewall structure 111 as a mask to obtain a plurality of second core mold structures 103', the first sidewall structure is removed, and second sidewall structures 112 are formed on both sides of each of the second core mold structures 103'.

[0042] Detailed, such as Figure 5 As shown, first, the first core mold structure 104' is removed to expose the second core mold material layer 103. At this time, a plurality of first spacer structures 111 with a relatively narrow width are disposed on the second core mold material layer 103.

[0043] like Figure 6 As shown, the second core mold material layer 103 is then etched using the first sidewall structure 111 as a mask to expose the oxide layer 101, thereby obtaining a plurality of second core mold structures 103' spaced apart from each other. At this time, the width of the second core mold structure 103' is smaller than that of the first core mold structure 104', and a photodiode can be formed in the substrate 100 below the second core mold structure 103'.

[0044] Next, the first sidewall structure 111 is removed.

[0045] like Figure 7 As shown, then, second sidewall structures 112 are formed on both sides of each of the second core mold structures 103 ′.

[0046] like Figure 8 As shown, in step S13, the second core mold structure 103' is removed by a dry etching process to form an opening, wherein the opening exposes the back surface, and a first groove 105 is formed in the substrate 100 between adjacent openings.

[0047] Specifically, the second core mold structure 103' is removed by a dry etching process to form an opening, and the substrate 100 exposed between adjacent second core mold structures 103' is etched to form a first groove 105, wherein the opening size of the first groove 105 is larger than the opening size of the opening.

[0048] like Fig. 9As shown, step S14, using the second sidewall structure 112 as a mask, the substrate 100 is etched by a dry etching process to form a first deep groove 107 at the opening, and a second groove 106 is formed below the first groove 105. The first groove 105 and the second groove 106 constitute a second deep groove, and the groove width of the first groove 105 is greater than the groove width of the second groove 106, and the ratio of the depth of the first groove 105 to the depth of the second groove 106 is 1:2; at the same time, the sum of the groove width of the first groove 105, the groove width of the first deep groove 107, and the spacing between the first groove 105 and the first deep groove is a first size p1, and the sum of the groove width of the second groove 106, the groove width of the first deep groove 107, and the spacing between the second groove 106 and the first deep groove is a second size p2, and the first size p1 is different from the second size p2. Further, the first size p1 is greater than the second size p2.

[0049] The etching speed of the etching gas used when forming the first groove is greater than the etching speed of the etching gas used when forming the second groove. Further, the etching gas used when forming the first groove is CF4, and this step uses etching gases such as CF3H and CF2H2 for dry etching process. Since the etching speed of CF3H and CF2H2 is slower than that of CF4, the width of the second groove 106 formed is smaller than that of the first groove 105, so that the width of the second groove 106 can be adjusted by selecting etching gas and other etching parameters (such as time, etc.), and the width of the photodiode between the second groove 106 and the first deep groove 107 is adjusted by the width of the second groove 106, that is, the pixel value of the photodiode between them, and as the width of the second groove 106 gradually decreases, the pixel value of the photodiode between the second groove 106 and the first deep groove 107 gradually increases, and vice versa, as the width of the second groove 106 gradually increases, the pixel value of the photodiode between the second groove 106 and the first deep groove 107 gradually decreases. Compared with the prior art, the spacing between the first deep groove 107 and the second deep groove formed in this step is extremely small, which is conducive to improving the process accuracy of the image sensor.

[0050] Finally, the second sidewall spacer is removed by a dry etching process to expose the oxide layer 101 .

[0051] See also Figure 10-11 Then, step S2 is performed to fill the first deep trench 107 and the second deep trench with insulating material to form a first deep trench 107 structure and a second deep trench structure 320, and a photodiode is formed between the first deep trench 107 structure and the second deep trench structure 320, thereby forming an image sensor.

[0052] Detailed, such as Fig.10 As shown, first, insulating material is filled in the first deep trench 107 and the second deep trench to form a first deep trench structure 310 and a second deep trench structure 320, and the surfaces of the first deep trench structure 310 and the second deep trench structure 320 are flush with the surface of the oxide layer 101. The insulating material may be silicon dioxide.

[0053] like Fig.11 As shown, next, a grid structure 330 is formed, and the grid structure 330 is located above the first deep trench structure 310 and the second deep trench structure 320. The grid structure 330 may be a composite grid including a metal layer and an insulating layer covering the sidewall and top surface of the metal layer, which helps to improve the isolation effect of the grid structure.

[0054] Next, a sacrificial layer having doping elements is formed on the oxide layer 101 , and rapid thermal processing is performed to diffuse the doping elements into the substrate 100 , so as to form a photodiode in the substrate 100 between the first deep trench structure 310 and the second deep trench structure 320 .

[0055] In this embodiment, the solid phase diffusion (SPD) method is used to form the photodiode region. The solid phase diffusion increases the temperature by performing heat treatment, so that the doping elements in the sacrificial layer with doping elements diffuse into the substrate 100. In detail, a sacrificial layer with doping elements is first formed on the exposed substrate 100, and the sacrificial layer covers the exposed substrate 100 and covers the sidewalls and top of the grid structure 330. Exemplarily, the sacrificial layer can be formed by chemical vapor deposition. Rapid heat treatment is then performed to diffuse the doping elements in the sacrificial layer into the substrate 100 to form a photodiode region in the substrate 100 between the first deep trench structure 310 and the second deep trench structure 320. Finally, the remaining sacrificial layer is removed. Compared with the photodiode region defined by the deep trench isolation structure formed by using the patterned mask layer 200 as a mask in the prior art, or compared, this step forms a photodiode of smaller size.

[0056] Next, the oxide layer 101 is removed.

[0057] Next, a color filter is formed on the substrate 100 between the grid structures 330 .

[0058] This embodiment provides an image sensor, including a plurality of groups of first deep grooves 107 and second deep grooves periodically spaced apart on one side of a substrate 100, wherein the second deep grooves include a first groove 105 and a second groove 106 connected to each other, wherein the second groove 106 is located at the bottom of the first groove 105, and a first deep groove 107 structure and a second deep groove structure 320 are formed in the first deep groove 107 and the second deep groove, and a photodiode is formed in the substrate between the first deep groove 107 structure and the second deep groove structure 320.

[0059] The width of the first groove 105 is greater than the width of the second groove 106 .

[0060] A grid structure 330 is further formed on the first deep trench structure 310 and the second deep trench structure 320 , and a color filter is formed on the substrate 100 between adjacent grid structures 330 .

[0061] In summary, the present invention provides an image sensor and a method for preparing the same, the method for preparing the image sensor comprising the following steps: forming a plurality of groups of first deep grooves and second deep grooves periodically spaced on one side of a substrate, the second deep grooves comprising a first groove and a second groove connected to each other, the second groove being located at the bottom of the first groove, the groove width of the first groove being greater than the groove width of the second groove; filling the first deep groove and the second deep groove with insulating material to form a first deep groove structure and a second deep groove structure, forming a photodiode between the first deep groove structure and the second deep groove structure, thereby forming an image sensor. In the present invention, the groove width of the first groove is greater than the groove width of the second groove, and compared with the pitch value of the upper half and the pitch value of the lower half of the deep trench isolation structure in the prior art being consistent, the groove width of the first groove, the groove width of the first deep groove, and the sum of the spacing between the first groove and the first deep groove in this embodiment are greater than the groove width of the second groove, the groove width of the first deep groove, and the sum of the spacing between the second groove and the first deep groove, so that each photodiode can obtain two pixel values ​​in the upper half and the lower half between adjacent deep grooves.

[0062] In addition, it should be noted that, unless otherwise specified or indicated, the terms "first" and "second" in the specification are only used to distinguish the various components, elements, steps, etc. in the specification, and are not used to indicate the logical relationship or sequential relationship between the various components, elements, steps, etc.

[0063] It is to be understood 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 person skilled in 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 embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing an image sensor, characterized in that: The following steps are involved: A plurality of groups of first deep grooves and second deep grooves are formed on one side of the substrate and are periodically spaced apart, wherein the second deep grooves include a first groove and a second groove that are connected to each other, the second groove is located at the bottom of the first groove, and the groove width of the first groove is greater than the groove width of the second groove; Insulating materials are filled in the first deep trench and the second deep trench to form a first deep trench structure and a second deep trench structure, and a photodiode is formed between the first deep trench structure and the second deep trench structure, thereby forming an image sensor.

2. The method for preparing an image sensor according to claim 1, wherein: The specific method of forming the first deep trench is: Providing a substrate, wherein the substrate has a back side, a second core mold material layer is formed on the back side, a plurality of first core mold structures are arranged at intervals on the second core mold material layer, and first sidewall structures are arranged on both sides of each of the first core mold structures; Removing the first core mold structure, and etching the second core mold material layer using the first sidewall structure as a mask to obtain a plurality of second core mold structures arranged at intervals, removing the first sidewall structure, and forming second sidewall structures on both sides of each of the second core mold structures; The second core mold structure is removed by a dry etching process to form an opening, wherein the opening exposes the back surface, and a first groove is formed in the substrate between adjacent openings.

3. The method for preparing an image sensor according to claim 2, wherein: The specific method of forming the second deep trench is: Using the second sidewall structure as a mask, etching the substrate by a dry etching process to form a first deep trench at the opening and a second groove below the first groove; The second side wall is removed.

4. The method for preparing an image sensor according to claim 3, wherein: The etching speed of the etching gas used when forming the first groove is greater than the etching speed of the etching gas used when forming the second groove.

5. The method for preparing an image sensor according to claim 4, wherein: The etching gas used when forming the first groove is CF4, and the etching gas used when forming the second groove is CF3H or CF2H2.

6. The method for preparing an image sensor according to claim 3, wherein: The specific method of forming the image sensor is: Filling the first deep trench and the second deep trench with insulating material to form a first deep trench structure and a second deep trench structure; forming a grid structure, wherein the grid structure is located above the first deep trench structure and the second deep trench structure; forming a photodiode in the substrate between the first deep trench structure and the second deep trench structure; Color filters are formed on the substrate between the grid structures.

7. The method for preparing an image sensor according to claim 1, wherein: The sum of the groove width of the first groove, the groove width of the first deep groove and the spacing between the first groove and the first deep groove is a first size, and the sum of the groove width of the second groove, the groove width of the first deep groove and the spacing between the second groove and the first deep groove is a second size, and the first size is greater than the second size.

8. The method for preparing an image sensor according to claim 1, wherein: The ratio of the depth of the first groove to the depth of the second groove is 1:

2.

9. An image sensor, prepared by the method for preparing an image sensor according to any one of claims 1 to 8, characterized in that: The invention comprises a plurality of groups of first deep grooves and second deep grooves which are periodically spaced and located on one side of a substrate, wherein the second deep grooves comprise first grooves and second grooves which are interconnected, the second grooves are located at the bottom of the first grooves, a first deep groove structure and a second deep groove structure are formed in the first deep grooves and the second deep grooves, a photodiode is formed in the substrate between the first deep groove structure and the second deep groove structure, wherein the groove width of the first groove is greater than the groove width of the second groove.

10. The image sensor according to claim 9, wherein: A grid structure is further formed on the first deep trench structure and the second deep trench structure, and a color filter is formed on the substrate between adjacent grid structures.

Images