An image sensor and a method for manufacturing the same

Abstract

The present invention provides an image sensor and a method for manufacturing the same. The method for manufacturing the image sensor includes: forming a plurality of sets of first deep trenches and second deep trenches that are periodically spaced on one side of a substrate. The second deep trench includes a first groove and a second groove that communicate with 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. 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 the same, in this embodiment, the sum of the groove width of the first groove, the groove width of the first deep trench, and the spacing between the first groove and the first deep trench is greater than the sum of the groove width of the second groove, the groove width of the first deep trench, and the spacing between the second groove and the first deep trench. In this way, each photodiode can obtain two pixel values in the upper half and the lower half between adjacent deep trenches.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor manufacturing technology, and particularly relates to an image sensor and a method for manufacturing the same. Background Art

[0002] A back-illuminated image sensor (CMOS Image Sensor BSI) arranges elements of a photosensitive layer (such as microlenses and photodiodes) on the back side of a substrate, and allows light energy to directly enter from the back side of the substrate, avoiding the influence of light by circuits and transistors between the microlenses and photodiodes in the structure of a front-illuminated image sensor. Thereby, the light efficiency is significantly improved, and the photosensitive effect of the image sensor under low light conditions is greatly improved. As Figure 1 shown, in the advanced process of the current back-illuminated image sensor, due to the fixed value of the pitch a of the deep trench isolation structure in terms of depth, there is only one pixel value for the photodiodes (PDs) between adjacent deep trench isolation structures. Summary of the Invention

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

[0004] To solve the above problems, the present invention provides a method for manufacturing an image sensor, including the following steps:

[0005] Form a plurality of groups of first deep trenches and second deep trenches arranged at periodic intervals on one side of the substrate. The second deep trench includes a first groove and a second groove that communicate with 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;

[0006] Fill insulating materials in the first deep trenches and the second deep trenches to form a first deep trench structure and a second deep trench structure, and form a photodiode between the first deep trench structure and the second deep trench structure, thereby forming an image sensor.

[0007] Optionally, the specific method for forming the first deep trench is:

[0008] Provide a substrate, the substrate has a back surface, a second core mold material layer is formed on the back surface, and a plurality of spaced-apart first core mold structures are arranged on the second core mold material layer. First side wall structures are arranged on both sides of each first core mold structure;

[0009] Remove the first core mold structure, and etch 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, remove the first sidewall structure, and form second sidewall structures on both sides of each of the second core mold structures;

[0010] Remove the second core mold structure by a dry etching process to form openings that expose the back surface, and also form first grooves in the substrate between adjacent openings.

[0011] Furthermore, the specific method for forming the second deep trench is as follows:

[0012] Using the second sidewall structure as a mask, etch the substrate by a dry etching process to form a first deep trench at the opening and a second groove below the first groove;

[0013] Remove the second sidewall.

[0014] Furthermore, the etching rate of the etching gas used for forming the first groove is greater than the etching rate of the etching gas used for forming the second groove.

[0015] Furthermore, the etching gas used for forming the first groove is CF 4 , and the etching gas used for forming the second groove is CF 3 H or CF 2 H 2 .

[0016] Furthermore, the specific method for forming the image sensor is as follows:

[0017] Fill the first deep trench and the second deep trench with an insulating material to form a first deep trench structure and a second deep trench structure;

[0018] Form a grid structure, and the grid structure is located above the first deep trench structure and the second deep trench structure;

[0019] Form a photodiode in the substrate between the first deep trench structure and the second deep trench structure;

[0020] Form a color filter on the substrate between the grid structures.

[0021] Optionally, the sum of the groove width of the first groove, the groove width of the first deep trench, and the distance between the first groove and the first deep trench is a first dimension, the sum of the groove width of the second groove, the groove width of the first deep trench, and the distance between the second groove and the first deep trench is a second dimension, and the first dimension is greater than the second dimension.

[0022] Optionally, the ratio of the depth of the first groove to the depth of the second groove is 1:2.

[0023] On the other hand, the present invention also provides an image sensor, which is prepared by using the preparation method of the above-mentioned image sensor, and includes a plurality of groups of first deep trenches and second deep trenches that are periodically and spaced apart on one side of a substrate. The second deep trench includes a first groove and a second groove that communicate with each other. The second groove is located at the bottom of the first groove. A first deep trench structure and a second deep trench structure are formed in the first deep trench and the second deep trench, and a photodiode is formed in the substrate between the first deep trench structure and the second deep trench structure. Among them, the groove width of the first groove is greater than the groove width of the second groove.

[0024] Optionally, a grating 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 grating structures.

[0025] Compared with the prior art, the present invention has the following unexpected technical effects:

[0026] The present invention provides an image sensor and a preparation method thereof. The preparation method of the image sensor includes the following steps: forming a plurality of groups of first deep trenches and second deep trenches that are periodically and spaced apart on one side of a substrate. The second deep trench includes a first groove and a second groove that communicate with each other. The second groove is located at the bottom of the first groove. The groove width of the first groove is greater than the groove width of the second groove; filling an insulating material in the first deep trench and the second deep trench 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. By having the groove width of the first groove greater than the groove width of the second groove in the present invention, compared with the prior art where the pitch value of the upper half and the pitch value of the lower half of the deep trench isolation structure are the same, the sum of the groove width of the first groove, the groove width of the first deep trench, and the distance between the first groove and the first deep trench in this embodiment is greater than the sum of the groove width of the second groove, the groove width of the first deep trench, and the distance between the second groove and the first deep trench, so that each photodiode can obtain two pixel values in the upper half and the lower half between adjacent deep trenches. Description of the Drawings

[0027] Figure 1 It is a schematic structural diagram of a deep trench isolation structure formed in the prior art.

[0028] Figure 2 It is a schematic structural diagram of a substrate provided by an embodiment of the present invention.

[0029] Figure 3Schematic diagram of the structure after forming the first core mold structure provided by an embodiment of the present invention.

[0030] Figure 4 Schematic diagram of the structure after forming the first side wall structure provided by an embodiment of the present invention.

[0031] Figure 5 Schematic diagram of the structure after removing the first core mold structure provided by an embodiment of the present invention.

[0032] Figure 6 Schematic diagram of the structure after forming the second core mold structure provided by an embodiment of the present invention.

[0033] Figure 7 Schematic diagram of the structure after forming the second side wall structure provided by an embodiment of the present invention.

[0034] Figure 8 Schematic diagram of the structure after removing the second core mold structure provided by an embodiment of the present invention.

[0035] Figure 9 Schematic diagram of the structure after forming the first deep trench and the second deep trench provided by an embodiment of the present invention.

[0036] Figure 10 Schematic diagram of the structure after forming the first deep trench structure and the second deep trench structure provided by an embodiment of the present invention.

[0037] Figure 11 Schematic diagram of the structure after forming the grid structure provided by an embodiment of the present invention.

[0038] Description of reference numerals:

[0039] Figure 1 Among them: 1 - Deep trench isolation structure;

[0040] Figures 2 - 11 Among them: 100 - Substrate; 101 - Oxide layer; 102 - Metal interconnect 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 side wall structure; 112 - Second side wall structure; 200 - Mask layer; 310 - First deep trench structure; 320 - Second deep trench structure; 330 - Grid structure. Detailed description of the invention

[0041] The following will further describe an image sensor and a method for manufacturing the same according to the present invention. The present invention will be described in more detail below 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 advantageous effects of the present invention. Therefore, the following description should be understood as a broad guidance for those skilled in the art and not as a limitation on the present invention.

[0042] For clarity, not all features of actual embodiments are described. In the following description, well-known functions and structures are not described in detail because they would obscure the present invention with unnecessary details. It should be considered that in the development of any actual embodiment, numerous implementation details must be made to achieve the specific goals of the developer, such as changing from one embodiment to another according to the relevant system or business limitations. Additionally, it should be considered that such development work may be complex and time-consuming, but it is only routine work for those skilled in the art.

[0043] To make the objectives and features of the present invention more obvious and understandable, the following further describes the specific implementation manners of the present invention with reference to the accompanying drawings. It should be noted that the accompanying drawings are all in a very simplified form and use non-precise ratios, only for conveniently and clearly assisting in explaining the objectives of the embodiments of the present invention.

[0044] This embodiment provides a method for manufacturing an image sensor, including the following steps:

[0045] Step S1: Form a plurality of groups of first deep trenches and second deep trenches that are periodically spaced on one side of the substrate. The second deep trench includes a first groove and a second groove that communicate with 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;

[0046] Step S2: Fill the first deep trenches and the second deep trenches with an insulating material to form a first deep trench structure and a second deep trench structure, and form a photodiode between the first deep trench structure and the second deep trench structure, thereby forming an image sensor.

[0047] In this embodiment, since the groove width of the first groove is greater than the groove width of the second groove, compared with the prior art in which the pitch value of the upper half and the pitch value of the lower half of the deep trench isolation structure are the same, the sum of the groove width of the first groove, the groove width of the first deep trench, and the distance between the first groove and the first deep trench is greater than the sum of the groove width of the second groove, the groove width of the first deep trench, and the distance between the second groove and the first deep trench. In this way, each photodiode can obtain two pixel values in the upper half and the lower half between adjacent deep trenches.

[0048] The following will combine with Figures 2 - 11 to describe in detail a method for manufacturing an image sensor provided in this embodiment.

[0049] Please refer to Figures 2 - 9 , first, perform step S1 to form multiple groups of periodically spaced first deep trenches 107 and second deep trenches on one side of the substrate 100. The second deep trench includes a first groove 105 and a second groove 106 that communicate with each other. 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.

[0050] This step specifically includes the following steps:

[0051] Please refer to Figures 2 - 4 , step S11, provide a substrate 100. The substrate 100 has a back surface, and a second core mold material layer 103 is formed on the back surface. A plurality of spaced-apart first core mold structures 104' are provided on the second core mold material layer 103, and first sidewall structures 111 are provided on both sides of each first core mold structure 104'.

[0052] Specifically, as Figure 2 shown, first provide a substrate 100. The substrate 100 has a front surface and a back surface that are oppositely arranged. A metal interconnection structure 102 is formed on the front surface, and the metal interconnection structure 102 is used to realize the interconnection and conduction of devices in the substrate 100.

[0053] Among them, the substrate 100 can be a silicon substrate, but is not limited thereto. The substrate 100 can be a germanium substrate, a silicon-germanium substrate, silicon on insulator (SOI), or germanium on insulator (GOI), etc. Certain doping particles can also be implanted into the substrate 100 according to design requirements to change electrical parameters.

[0054] Please continue to refer to 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 surface of the substrate 100. Among them, the material of the mask layer 200 can be photoresist; the oxide layer 101 can be a silicon oxide layer and can be formed by a thermal oxidation process or a chemical vapor deposition process, etc., but is not limited thereto. The materials of the second core mold material layer 103 and the first core mold material layer 104 can include but are not limited to silicon, amorphous silicon, or amorphous carbon, and can be formed by an epitaxial process, spin coating, or spraying, etc.

[0055] As Figure 3As shown, using the patterned mask layer 200 as a mask, etch the first core mold material layer 104 to form a plurality of first core mold structures 104' spaced apart from each other.

[0056] Next, remove the mask layer 200.

[0057] As Figure 4 shown, form first sidewall structures 111 on both sides of each of the first core mold structures 104'.

[0058] Please refer to Figures 5 - 7 , in step S12, remove the first core mold structures 104', and using the first sidewall structures 111 as a mask, etch the second core mold material layer 103 to obtain a plurality of second core mold structures 103', remove the first sidewall structures, and form second sidewall structures 112 on both sides of each of the second core mold structures 103'.

[0059] Specifically, as Figure 5 shown, first, remove the first core mold structures 104' to expose the second core mold material layer 103. At this time, a plurality of first sidewall structures 111 with a relatively narrow width are provided on the second core mold material layer 103.

[0060] As Figure 6 shown, next, using the first sidewall structures 111 as a mask, etch the second core mold material layer 103 and 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 structures 103' is smaller than the width of the first core mold structures 104', and photodiodes can be formed in the substrate 100 below the second core mold structures 103'.

[0061] Next, remove the first sidewall structures 111.

[0062] As Figure 7 shown, next, form second sidewall structures 112 on both sides of each of the second core mold structures 103'.

[0063] As Figure 8 shown, in step S13, remove the second core mold structures 103' through a dry etching process to form openings, the openings expose the back surface, and first grooves 105 are also formed in the substrate 100 between adjacent openings.

[0064] Specifically, remove the second core mold structures 103' through a dry etching process to form openings, and at the same time etch the substrate 100 exposed between adjacent second core mold structures 103' to form first grooves 105, and the opening size of the first grooves 105 is larger than the opening size of the openings.

[0065] As shown Figure 9 in 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 trench 107 at the opening and a second groove 106 below the first groove 105. Among them, the first groove 105 and the second groove 106 constitute a second deep trench, 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 trench 107, and the distance between the first groove 105 and the first deep trench is a first dimension p1, and the sum of the groove width of the second groove 106, the groove width of the first deep trench 107, and the distance between the second groove 106 and the first deep trench is a second dimension p2, and the first dimension p1 is different from the second dimension p2. Further, the first dimension p1 is greater than the second dimension p2.

[0066] The etching rate of the etching gas used to form the first groove is greater than the etching rate of the etching gas used to form the second groove. Further, the etching gas used to form the first groove is CF 4 , and in this step, CF 3 H, CF 2 H 2 and other etching gases are used for the dry etching process. Since the etching rate of CF 3 H, CF 2 H 2 is slower than the etching rate of CF 4 , this results in the groove width of the formed second groove 106 being smaller than the groove width of the first groove 105, so that the groove width of the second groove 106 can be adjusted by the selection of the etching gas and the selection of other etching parameters (such as time, etc.), and the width of the photodiode located between the second groove 106 and the first deep trench can be adjusted by the groove width of the second groove 106, that is, the pixel value of the photodiode between them, and as the groove width of the second groove 106 gradually decreases, the pixel value of the photodiode between the second groove 106 and the first deep trench gradually increases, and vice versa, as the groove width of the second groove 106 gradually increases, the pixel value of the photodiode between the second groove 106 and the first deep trench gradually decreases. Compared with the prior art, the distance between the first deep trench 107 and the second deep trench formed in this step is extremely small, which is beneficial to improving the manufacturing precision of the image sensor.

[0067] Finally, the second sidewall is removed by a dry etching process to expose the oxide layer 101.

[0068] Please refer toFigures 10 - 11 , then step S2 is executed. An insulating material is filled in the first deep trench 107 and the second deep trench 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.

[0069] Specifically, as Figure 10 shown, first, an 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. Among them, the insulating material can be silicon dioxide.

[0070] As Figure 11 shown, then, 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. Among them, the grid structure 330 can be a composite grid including a metal layer and an insulating layer covering the side walls and the top surface of the metal layer, which helps to improve the isolation effect of the grid structure.

[0071] Next, a sacrificial layer with a doping element is formed on the oxide layer 101, and rapid thermal processing is performed to diffuse the doping element 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.

[0072] In this embodiment, the method of solid phase diffusion (SPD, solid phase diffusion) is used to form the photodiode region. The solid phase diffusion raises the temperature by performing heat treatment, so that the doping element in the sacrificial layer with the doping element diffuses into the substrate 100. Specifically, a sacrificial layer with a doping element is first formed on the exposed substrate 100, and the sacrificial layer covers the exposed substrate 100 and covers the side walls and the top of the grid structure 330. Exemplarily, the sacrificial layer can be formed by chemical vapor deposition. Then rapid thermal processing is performed to diffuse the doping element in the sacrificial layer into the substrate 100, so as 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 with the patterned mask layer 200 in the prior art, a smaller-sized photodiode is formed in this step.

[0073] Next, the oxide layer 101 is removed.

[0074] Next, a color filter is formed on the substrate 100 between the grating structures 330.

[0075] This embodiment provides an image sensor, including a plurality of groups of first deep trenches 107 and second deep trenches that are periodically and spaced apart on one side of a substrate 100. The second deep trenches include a first groove 105 and a second groove 106 that communicate with each other. The second groove 106 is located at the bottom of the first groove 105. A first deep trench structure and a second deep trench structure 320 are formed in the first deep trenches 107 and the second deep trenches. A photodiode is formed in the substrate between the first deep trench structure and the second deep trench structure 320.

[0076] Wherein, the groove width of the first groove 105 is greater than the groove width of the second groove 106.

[0077] A grating structure 330 is further formed on the first deep trench structure 310 and the second deep trench structure 320. A color filter is formed on the substrate 100 between adjacent grating structures 330.

[0078] In summary, the present invention provides an image sensor and a method for manufacturing the same. The method for manufacturing the image sensor includes the following steps: forming a plurality of groups of first deep trenches and second deep trenches that are periodically and spaced apart on one side of a substrate. The second deep trenches include a first groove and a second groove that communicate with each other. The second groove is located at the bottom of the first groove. The groove width of the first groove is greater than the groove width of the second groove. Filling an insulating material in the first deep trenches and the second deep trenches 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. By having the groove width of the first groove greater than the groove width of the second groove, compared with the prior art where the pitch value of the upper half and the pitch value of the lower half of the deep trench isolation structure are the same, in this embodiment, the sum of the groove width of the first groove, the groove width of the first deep trench, and the spacing between the first groove and the first deep trench is greater than the sum of the groove width of the second groove, the groove width of the first deep trench, and the spacing between the second groove and the first deep trench. This enables each photodiode to obtain two pixel values in the upper half and the lower half between adjacent deep trenches.

[0079] In addition, it should be noted that unless otherwise specified or indicated, the descriptions of the terms "first" and "second" in the specification are only used to distinguish each component, element, step, etc. in the specification, rather than to represent the logical relationship or sequential relationship between each component, element, step, etc.

[0080] It will be understood that although the present invention has been disclosed above in preferred embodiments, the above embodiments are 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, many possible variations and modifications can be made to the technical solution of the present invention by using the technical content disclosed above, or it can be modified into equivalent embodiments with 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 fall 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; Filling the first deep trench and the second deep trench with an 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; 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 spaced apart, removing the first sidewall structure, and forming second sidewall structures on both sides of each of the second core mold structures; removing the second core mold structure by a dry etching process to form an opening, wherein the opening exposes the back surface, and further forming a first groove in the substrate between adjacent openings; 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.

2. The method for preparing an image sensor according to claim 1, 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.

3. The method for preparing an image sensor according to claim 2, 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.

4. The method for preparing an image sensor according to claim 1, 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.

5. 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.

6. 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.

7. An image sensor, prepared by the method for preparing an image sensor according to any one of claims 1 to 6, 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.

8. The image sensor according to claim 7, 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