Pixel cell for backside illumination image sensor and method of making the same

Abstract

This application relates to a pixel unit for a back-illuminated image sensor and a method for fabricating the same. The pixel unit includes: providing a substrate, the top surface of which includes a sacrificial layer and a first trench arranged alternately along a first direction; forming an isolation structure on the side of the first trench near the sacrificial layer, and then removing the sacrificial layer to form a second trench; the isolation structure includes a first dielectric layer; forming a first photosensitive layer in the second trench and the remaining first trench; utilizing the deposition process morphology inheritance effect, forming a second photosensitive layer in the second trench and the remaining first trench, and a groove extending into the second photosensitive layer along a direction toward the substrate; the angle between the sidewall and the bottom surface of the groove is greater than 90 degrees; the second photosensitive layer, the first photosensitive layer, and the substrate are used to constitute a pixel structure; forming a second dielectric layer on the pixel structure and the isolation structure; the second dielectric layer is in contact with the first dielectric layer for grounding. This method can improve the quality of deep trench isolation structures and BM structures.

Description

Technical Field

[0001] This application relates to the field of integrated circuit technology, and in particular to a pixel unit for a back-illuminated image sensor and a method for fabricating the same. Background Technology

[0002] Back-illuminated (BSI) CMOS image sensors significantly improve imaging performance by optimizing the photosensitive layout. To address the photon crosstalk problem at small pixel sizes, deep trench isolation (DTI) technology has emerged. It achieves pixel isolation by filling deep trenches with insulating material. However, the deep and narrow structure is prone to defects such as premature sealing and incomplete filling, affecting the isolation effect and yield.

[0003] The increasing demand for near-infrared imaging in high-end applications such as automotive night vision has led to the introduction of light-shielding layer (BM) structures, which can increase the near-infrared optical path and concentrate photons. However, during the fabrication of BM structures, the yellow light in the pixel area and the etching process can easily cause pattern displacement and damage to the silicon substrate, resulting in decreased imaging quality and reduced device reliability. Summary of the Invention

[0004] Based on this, it is necessary to provide a semiconductor structure and its fabrication method, as well as a semiconductor device, to address the technical problems in the existing technology, which can at least improve the quality of deep trench isolation structures and BM structures.

[0005] In a first aspect, this application provides a method for fabricating a pixel unit for a back-illuminated image sensor, comprising: providing a substrate, the top surface of which includes a sacrificial layer and a first trench alternately arranged along a first direction;

[0006] After forming an isolation structure on the side of the first trench near the sacrificial layer, the sacrificial layer is removed to form a second trench; the isolation structure includes a first dielectric layer;

[0007] A first photosensitive layer is formed in the second trench and the remaining first trench;

[0008] Utilizing the morphology inheritance effect of the deposition process, a second photosensitive layer is formed in the second trench and the remaining first trench, and a groove extends into the second photosensitive layer along the direction toward the substrate; the angle between the sidewall and the bottom surface of the groove is greater than 90 degrees; the second photosensitive layer, the first photosensitive layer and the substrate are used to form a pixel structure;

[0009] A second dielectric layer is formed on the pixel structure and the isolation structure; the second dielectric layer is in contact with the first dielectric layer and is used for current conduction and grounding.

[0010] In the pixel unit fabrication method described above, a sacrificial layer is used as a temporary template to laterally construct the isolation structure. Compared with the traditional deposition-filled isolation structure, this avoids the filling hole defects caused by the high aspect ratio in the traditional process, and further ensures the uniformity and density of the dielectric layer, thereby significantly improving the electrical and optical isolation performance between pixels and laying the foundation for high-quality image output of the sensor. Furthermore, by utilizing the step height difference between the formed isolation structure and the silicon substrate, as well as the morphology inheritance characteristics inherent in the deposition process, the light-shielding layer (BM) and its specific tilt angle groove structure are formed in a self-aligned manner without additional photolithography, thereby reducing the photolithography error introduced by the original photolithography process and avoiding the damage to the substrate material caused by etching.

[0011] In some embodiments, forming the isolation structure includes:

[0012] After forming a first oxide material layer and a first dielectric material layer that are stacked sequentially on the inner surface of the first trench and the top surface of the sacrificial layer, with an L-shaped longitudinal section, a second oxide material layer is formed that is attached to the sidewall of the first dielectric material layer and the L-shaped corner.

[0013] A second dielectric material layer is formed in the first trench, which is attached to the sidewall of the second oxide material layer and to a portion of the upper surface of the first dielectric material layer; the first dielectric material layer and the second dielectric material layer are used to constitute the first dielectric layer;

[0014] A third oxide material layer is formed in contact with the sidewall of the first dielectric layer and the first oxide material layer; the longitudinal section of the third oxide material layer is I-shaped.

[0015] In some embodiments, the second dielectric material layer and the third oxide material layer are formed using a diffusion process.

[0016] In some embodiments, the first photosensitive layer is formed using an epitaxial growth process;

[0017] The longitudinal section of the first photosensitive layer is rectangular.

[0018] In some embodiments, the first photosensitive layer is formed using a deposition process;

[0019] The longitudinal section of the first photosensitive layer is concave.

[0020] Secondly, this application also provides a pixel unit for a back-illuminated image sensor, comprising: a substrate, wherein the top surface of the substrate includes an isolation structure and a pixel structure alternately arranged along a first direction;

[0021] The isolation structure includes a first dielectric layer;

[0022] The pixel structure includes a first photosensitive layer and a second photosensitive layer arranged sequentially along a direction away from the substrate;

[0023] The second photosensitive layer is fabricated using the morphology inheritance effect of the deposition process, and includes a groove extending from the top surface of the second photosensitive layer into the second photosensitive layer; the angle between the sidewall and the bottom surface of the groove is greater than 90 degrees; the second photosensitive layer, the first photosensitive layer and the substrate are used to form a pixel structure;

[0024] The second dielectric layer is located on the top surface of the isolation structure and the pixel structure, and is in contact with the first dielectric layer for grounding.

[0025] In the aforementioned pixel unit, the second photosensitive layer, as a light-shielding layer of the pixel structure, can concentrate light and effectively improve photoelectric conversion efficiency by optimizing the optical path of incident light. The second dielectric layer, covering the entire pixel structure and the isolation structure, is in close contact with the first dielectric layer embedded in the isolation structure, forming a continuous conductive path extending to the device ground. This allows dark currents that may accumulate in the pixel structure to be promptly conducted away, thereby stabilizing the electrical environment of the pixel and suppressing the noise generated therefrom. From a structural perspective, this systematically enhances the imaging quality and reliability of the back-illuminated image sensor.

[0026] In some embodiments, the isolation structure includes:

[0027] A first oxide layer is located between adjacent pixel structures;

[0028] The first dielectric layer extends into the first oxide layer via the top surface of the isolation structure, and its width is smaller than that of the first oxide layer;

[0029] The second oxide layer extends into the first dielectric layer via the top surface of the isolation structure, and its width is smaller than that of the first dielectric layer.

[0030] In some embodiments, the angle between the sidewall and bottom surface of the groove is negatively correlated with the thickness of the first photosensitive layer.

[0031] Thirdly, this application also provides a back-illuminated image sensor, such as the pixel unit described in any of the above embodiments; or a pixel unit prepared by the preparation method described in any of the above embodiments.

[0032] In some embodiments, the back-illuminated image sensor includes a plurality of pixel units; the plurality of pixel units are arranged sequentially along a first direction.

[0033] In the back-illuminated image sensor with the aforementioned pixel configuration or fabrication method, the sensor effectively suppresses optical and electrical crosstalk between pixels through a high-quality, hole-free deep trench isolation structure, ensuring image purity and color fidelity at high resolution. Simultaneously, its self-aligned light-shielding layer structure optimizes the near-infrared spectral response, enhancing photosensitivity and signal-to-noise ratio under low-light conditions. Furthermore, the conductive path design of the first and second dielectric layers effectively manages and conducts dark current, significantly reducing image noise and improving electrical stability. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 This is a flowchart of a pixel unit fabrication method provided in one embodiment;

[0036] Figure 2 This is a schematic cross-sectional view of the structure obtained after forming the first trench in step S102 of the preparation method provided in one embodiment;

[0037] Figure 3 This is a cross-sectional schematic diagram of the structure obtained after forming the first oxide material layer, the first dielectric material layer, and the second oxide layer in step S1042 of the preparation method provided in one embodiment;

[0038] Figure 4 for Figure 3 A cross-sectional schematic diagram of the structure obtained after removing part of the second oxide material layer from the middle pixel unit;

[0039] Figure 5 This is a schematic cross-sectional view of the structure obtained after forming the second dielectric material layer in step S1044 of the preparation method provided in one embodiment;

[0040] Figure 6 for Figure 5 A cross-sectional schematic diagram of the structure obtained after removing part of the second dielectric material layer from the middle pixel unit;

[0041] Figure 7 This is a schematic cross-sectional view of the structure obtained after forming the third oxide material layer in step S1046 of the preparation method provided in one embodiment;

[0042] Figure 8 for Figure 7 A schematic diagram of the cross-section of the structure after the isolation structure and the second trench are formed;

[0043] Figure 9 This is a cross-sectional schematic diagram of the structure obtained after forming the first photosensitive layer in step S106 of the preparation method provided in one embodiment;

[0044] Figure 10 This is a schematic cross-sectional view of the structure obtained after forming the second photosensitive layer in step S108 of the preparation method provided in one embodiment;

[0045] Figure 11 for Figure 10 A cross-sectional schematic diagram of the structure obtained after removing excess film layers from the middle pixel unit;

[0046] Figure 12 This is a schematic cross-sectional view of the structure obtained after forming the second dielectric layer in step S110 of the preparation method provided in one embodiment;

[0047] Figure 13 for Figure 12 A cross-sectional schematic diagram of the structure obtained after the middle pixel unit forms the dielectric layer;

[0048] Figure 14 This is a cross-sectional schematic diagram of a pixel unit structure provided in one embodiment;

[0049] Figure 15 This is a schematic diagram comparing the structure of the pixel unit with that provided in this application, based on related technologies.

[0050] Explanation of reference numerals in the attached figures:

[0051] 10. Substrate; 11. Sacrificial layer; 12. First trench; 13. Second trench; 14. Groove; 20. Isolation structure; 201. First oxide layer; 202. Second oxide layer; 203. Third oxide layer; 301. First dielectric layer; 302. Second dielectric layer; 21. First oxide layer; 22. Second oxide layer; 31. First dielectric layer; 32. Second dielectric layer; 41. First photosensitive layer; 42. Second photosensitive layer; 40. Pixel structure; 51. Dielectric layer. Detailed Implementation

[0052] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings, which illustrate preferred embodiments of the application. However, this application may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of this application will be thorough and complete.

[0053] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0054] It should be understood that when an element or layer is referred to as "on," "adjacent to," "connected to," or "coupled to" other elements or layers, it may be directly on, adjacent to, connected to, or coupled to other elements or layers, or there may be intervening elements or layers. Conversely, when an element is referred to as "directly on," "directly adjacent to," "directly connected to," or "directly coupled to" other elements or layers, there are no intervening elements or layers. It should be understood that although the terms first, second, third, etc., may be used to describe various elements, parts, regions, layers, doping types, and / or portions, these elements, parts, regions, layers, doping types, and / or portions should not be limited by these terms. These terms are only used to distinguish one element, part, region, layer, doping type, or portion from another element, part, region, layer, doping type, or portion. Therefore, without departing from the teachings of this application, the first element, component, region, layer, doping type, or portion discussed below may be represented as a second element, component, region, layer, or portion; for example, the first doping type may be referred to as the second doping type, and similarly, the second doping type may be referred to as the first doping type; the first doping type and the second doping type are different doping types, for example, the first doping type may be P-type and the second doping type may be N-type, or the first doping type may be N-type and the second doping type may be P-type.

[0055] Spatial relation terms such as “below,” “under,” “below,” “under,” “above,” “above,” etc., are used herein to describe the relationship between one element or feature shown in the figure and other elements or features. It should be understood that, in addition to the orientation shown in the figure, spatial relation terms also include different orientations of the device in use and operation. For example, if the device in the figure is flipped, the element or feature described as “below,” “under,” or “below” will be oriented “above” the other element or feature. Therefore, the exemplary terms “below” and “under” can include both above and below orientations. Furthermore, the device may also include other orientations (e.g., rotated 90 degrees or other orientations), and the spatial descriptive terms used herein will be interpreted accordingly.

[0056] When used herein, the singular forms of “a,” “an,” and “the” may also include the plural forms unless the context clearly indicates otherwise. It should also be understood that when the terms “comprise” and / or “comprising” are used in this specification, the presence of the stated feature, integer, step, operation, element, and / or part is established, but the presence or addition of one or more other features, integers, steps, operations, elements, parts, and / or groups is not excluded. Meanwhile, when used herein, the term “and / or” includes any and all combinations of the associated listed items.

[0057] Embodiments of the invention are described herein with reference to cross-sectional views illustrating ideal embodiments (and intermediate structures) of this application, thus allowing for variations in the illustrated shapes due to, for example, manufacturing techniques and / or tolerances. Therefore, embodiments of this application should not be limited to the specific shapes of the regions shown herein, but rather include shape deviations due to, for example, manufacturing techniques. For instance, implantation regions shown as rectangular typically have rounded or curved features at their edges and / or implantation concentration gradients, rather than a binary change from implantation regions to non-implantation regions. Similarly, the buried regions formed by implantation can result in some implantation in the region between the buried region and the surface traversed during implantation. Therefore, the regions shown in the figures are substantially schematic, and their shapes do not represent the actual shapes of regions of the device and do not limit the scope of this application.

[0058] Please see Figures 1-13 This application provides a method for preparing a pixel unit, including: steps S102-S110.

[0059] Step S102: Provide a substrate 10, the top surface of which includes sacrificial layers 11 and first trenches 12 arranged alternately along the OY direction.

[0060] Step S104: After forming an isolation structure 20 on the side of the first trench 12 near the sacrificial layer 11, the sacrificial layer 11 is removed to form a second trench 13; the isolation structure 20 includes a first dielectric layer 31.

[0061] Step S106: Form a first photosensitive layer 41 in the second trench 13 and the remaining first trench 12.

[0062] Step S108: Utilizing the morphology inheritance effect of the deposition process, a second photosensitive layer 42 is formed in the second trench 13 and the remaining first trench 12, and a groove 14 extends along the ZO direction into the second photosensitive layer 42; the angle between the sidewall and the bottom surface of the groove 14 is greater than 90 degrees; the second photosensitive layer 42, the first photosensitive layer 41 and the substrate 10 are used to form a pixel structure 40.

[0063] Step S110: Form a second dielectric layer 32 on the pixel structure 40 and the isolation structure 20; the second dielectric layer 32 is in contact with the first dielectric layer 31 and is used for grounding.

[0064] The pixel units obtained after steps S102-S110 can be found in [reference]. Figure 13 For ease of understanding this application, Figure 13 The example given is a pixel unit prepared using the preparation method of this application. Other suitable examples of pixel units prepared using this application are also possible, and this application does not limit them.

[0065] The following is combined Figures 2 to 13 This document details the steps of the pixel unit formation method in this embodiment. For ease of understanding, in this embodiment, the substrate may include a first surface on the front side and a back surface, i.e., a second surface, opposite the front side. Ignoring the flatness of the first and second surfaces, a first direction parallel to the first surface is defined, and the direction toward the substrate includes a second direction perpendicular to the first surface of the substrate. Intersecting (e.g., perpendicular) first and third directions are defined on the top and bottom surfaces of the substrate (i.e., the plane containing the substrate). For example, the arrangement direction of the isolation structure is the first direction, and the plane containing the substrate can be determined based on the first and third directions. The first, second, and third directions can be mutually perpendicular. In this embodiment, the first direction is defined as the Y-axis direction, and the second direction is defined as the Z-axis direction.

[0066] Please see Figure 2 In the extended step of step S102, after providing the substrate 10, a sacrificial layer 11 is formed using any deposition process. Then, a photoresist layer is uniformly coated on the top surface of the sacrificial layer 11. An isolation region is defined by a series of processes such as exposure and development. The sacrificial layer 11 outside the isolation region is then removed by a dry etching process to obtain the first trench 12. The sacrificial layer 11 corresponding to the isolation region is retained for subsequent processes.

[0067] For example, in this embodiment, carbon is used as the sacrificial layer, and the carbon layer needs to be oxidized before the photoresist layer is coated to optimize its surface adhesion and photolithographic compatibility, and ensure the accuracy of the subsequent photolithographic pattern.

[0068] For example, in this embodiment, the substrate 10 is made of silicon (Si), specifically P-type conductivity. Of course, other substrate materials suitable for semiconductor manufacturing processes can also be selected.

[0069] Please see Figures 3-8 In some embodiments, step S104, which involves forming the isolation structure 20 and the second trench 13, is specifically as follows:

[0070] Step S1042: After forming a first oxide material layer 201 and a first dielectric material layer 301 with an L-shaped longitudinal section, which are stacked sequentially on the inner surface of the first trench 12 and the top surface of the sacrificial layer 11, a second oxide material layer 202 is formed that is attached to the sidewall and L-shaped corner of the first dielectric material layer 301.

[0071] Specifically, after removing the photoresist layer, a first oxide layer 201, a first dielectric layer 301, and a second oxide layer 202 are sequentially deposited, as shown in the specific structure. Figure 3 As shown; subsequently, dry etching is used to remove part of the second oxide material layer 202, with the first dielectric material layer 301 as the etching stop layer. Finally, the remaining second oxide material layer 202 only covers the sidewall of the first dielectric material layer 301 and is attached to the L-shaped corner, with an I-shaped longitudinal section. The specific structure is as follows. Figure 4 As shown.

[0072] Step S1044: A second dielectric material layer 302 is formed in the first trench 12, which is attached to the sidewall of the second oxide material layer 202 and part of the upper surface of the first dielectric material layer 301; the first dielectric material layer 301 and the second dielectric material layer 302 are used to form the first dielectric layer 31.

[0073] Specifically, based on the structure obtained in step S1042, a second dielectric material layer 302 is formed using a diffusion process. This layer uniformly covers the surfaces of the first dielectric material layer 301 and the second oxide material layer 202, as shown in the specific structure below. Figure 5 As shown; then, a portion of the second dielectric material layer 302 and the first dielectric material layer 301 are removed by dry etching, as shown in the specific structure. Figure 6 As shown, the remaining first dielectric material layer 301 and the second dielectric material layer 302 together constitute the first dielectric layer 31.

[0074] Step S1046: Form a third oxide material layer 203 that is in contact with the sidewall of the first dielectric layer 31 and the first oxide material layer 201; the longitudinal section of the third oxide material layer 203 is I-shaped.

[0075] Specifically, a diffusion process is used to first prepare a third oxide material layer 203 covering the structure obtained in step S1044, with the specific structure as follows: Figure 7 As shown in the figure. Next, etching and chemical mechanical polishing processes were used to remove the excess film layer, resulting in the structure shown in the figure. Figure 8 As shown.

[0076] For example, the materials of the first oxide layer 201, the second oxide layer 202, and the third oxide layer 203 may be the same or different. In this embodiment, all three are made of silicon oxide (SiO2).

[0077] For example, the first dielectric material layer 301 and the second dielectric material layer 302 may be made of the same or different materials, and may be formed by materials with a high k dielectric constant. For example, aluminum oxide (Al2O3), hafnium oxide (HfO2), hafnium oxynitride (HfON), zirconium oxide (ZrO2), tantalum oxide (Ta2O5), titanium oxide (TiO2), or strontium titanium oxide (SrTiO3).

[0078] Please see Figure 9 In the extension step of step S106, the first photosensitive layer 41 can be formed using a deposition process or an epitaxial growth process; specifically, when the deposition process is used, the cross-sectional schematic diagram of the resulting structure is shown below. Figure 9 As shown in (a) above; when prepared using epitaxial growth, the cross-sectional schematic diagram of the obtained structure is shown below. Figure 9 As shown in (b), the two processes can be flexibly selected according to the process flow adaptation requirements.

[0079] For example, the first photosensitive layer 41 can be either N-type or P-type. If you want to "form a P-type first photosensitive layer on an N-type epitaxial layer and / or a silicon substrate", you can follow the method described above and simply interchange the "P" and "N" in each step of the above method.

[0080] Please see Figures 10-11 In the extended step of step S108, a second photosensitive layer 42 is formed in the first trench 12 and the remaining second trench 13 using a deposition process. Because deposition processes (such as CVD and ALD) have a morphology inheritance effect (i.e., the deposited film roughly replicates the surface morphology of the underlying layer), a groove 14 is naturally formed at the step between the isolation structure 20 (higher) and the first photosensitive layer 41 (lower). Subsequently, a chemical mechanical polishing process is used to remove the excess film layer of the second photosensitive layer 42 that is higher than the isolation structure 20, resulting in a structure as shown... Figure 11 As shown.

[0081] Specifically, Figure 10 (a) in the text corresponds to the scenario described earlier where the first photosensitive layer 41 is formed using a deposition process. Figure 10 (b) in the above context corresponds to the scenario in which the first photosensitive layer 41 is formed by epitaxial growth process, and the structure is adapted to the process described above. Figure 11 (a) and Figure 11 (b) Naming rules and Figure 10 The same applies, so it will not be repeated here. The pattern of the second photosensitive layer 42 (BM layer) is naturally defined by the physical structure (steps), rather than by photolithography, which eliminates the potential damage to the photosensitive material caused by photolithographic alignment errors and etching.

[0082] For example, the conductivity type of the second photosensitive layer 42 may be the same as or different from that of the first photosensitive layer 41. In this embodiment, the conductivity type of the second photosensitive layer 42 is also N-type, and together with the N-type first photosensitive layer 41 and the P-type substrate 10, it constitutes the pixel structure 40.

[0083] For example, the materials of the first photosensitive layer 41 and the second photosensitive layer 42 can be silicon (Si) to form a homogeneous PN junction with the P-type substrate 10. Alternatively, other suitable semiconductor materials can be selected to form a heterojunction according to the photosensitive performance requirements of the device. Since this is not the focus of this application, it will not be elaborated on here.

[0084] Please see Figure 12 In the extended step of step S110, a second dielectric layer 32 with a high k dielectric constant is formed by a deposition process, covering the pixel structure 40 and the isolation structure 20. The second dielectric layer 32 is in contact with the first dielectric layer 31 in the isolation structure 20, forming a conductive path to ground to discharge the dark current in the pixel structure 40. It should be noted that when silicon (Si) is used as the material for the first photosensitive layer 41 and the second photosensitive layer 42, the top surface of the pixel structure 40 will naturally oxidize to form an oxide layer. This oxide layer is relatively thin and has no significant impact on the overall device performance, requiring no additional processing.

[0085] Please see Figure 13 After step S110, a dielectric layer 51 can also be formed on the top surface of the second dielectric layer 32.

[0086] This application embodiment also provides a pixel unit, referenced... Figure 14 It includes: a substrate 10, on the top surface of which an isolation structure 20 and a pixel structure 40 are alternately arranged along a first direction; and a second dielectric layer 32 located on the top surface of the isolation structure 20 and the pixel structure 40.

[0087] Specifically, the pixel structure 40 includes a first photosensitive layer 41 and a second photosensitive layer 42 arranged sequentially along the OZ direction; the second photosensitive layer 42 is fabricated using the morphology inheritance effect of the deposition process, and includes a groove 14 extending from the top surface of the second photosensitive layer 42 into the second photosensitive layer 42; the angle between the sidewall and the bottom surface of the groove 14 is greater than 90 degrees; the second photosensitive layer 42, the first photosensitive layer 41 and the substrate 10 are used to form the pixel structure 40;

[0088] Please continue reading. Figure 14 In some embodiments, the isolation structure 20 includes a first oxide layer 21 located between adjacent pixel structures 40;

[0089] The first dielectric layer 31 extends into the first oxide layer 21 via the top surface of the isolation structure 20, and its width (i.e., the dimension along the OY direction) is smaller than that of the first oxide layer 21.

[0090] The second oxide layer 22 extends into the first dielectric layer 31 via the top surface of the isolation structure 20, and its width is smaller than that of the first dielectric layer 31.

[0091] like Figure 14 As shown, the second dielectric layer 32 is located on the top surface of the isolation structure 20 and the pixel structure 40, and is connected to the first dielectric layer 31 in the isolation structure 20. Due to its high dielectric constant, it can form an efficient charge transfer path.

[0092] In addition, in some embodiments, the angle between the sidewall and the bottom surface of the groove 14 is negatively correlated with the thickness of the first photosensitive layer 41. In actual manufacturing, the angle can be precisely controlled by adjusting the thickness of the first photosensitive layer 41 to meet the requirements of subsequent processes.

[0093] Figure 15 The present application provides a structural comparison diagram of the back-illuminated image sensor in this application and related technologies. Figure 15 (a) in the text corresponds to the structure in the related technology. Figure 15 (b) corresponds to the structure provided in this application. The second photosensitive layer, as a light-shielding layer, has a sidewall tilt angle of its internal groove that can more effectively guide large-angle refracted light, reduce photon collisions at the isolation structure, reduce photon loss, and thus significantly improve photon absorption probability and quantum efficiency.

[0094] In some embodiments, this application also provides a back-illuminated image sensor, including the pixel units described in any of the above embodiments; or pixel units fabricated by the fabrication method described in any of the above embodiments. Multiple pixel units are arranged sequentially along the OY direction.

[0095] Since the back-illuminated image sensor in the above embodiments is based on the same inventive concept as the pixel unit and its preparation method provided in this application, the back-illuminated image sensor using this pixel unit has all the advantages of the pixel unit and its preparation method provided in this application, which will not be elaborated here.

[0096] In the above embodiments, the unexpected technical effect of this application is:

[0097] Compared to traditional deep trench isolation structure filling methods, the isolation structure in this application is formed using a sidewall process, effectively improving the filling quality and isolation effect of the isolation structure, laying the foundation for enhancing the imaging stability of the sensor. The first and second photosensitive layers, located between adjacent isolation structures, are formed using deposition or epitaxial technology, replacing traditional photolithography and etching processes. This fundamentally avoids damage to the photosensitive material caused by bias voltage during dry etching, while also reducing the amount of photomask used and lowering process costs. Furthermore, the second photosensitive layer, as a BM structure, can reduce photon loss, improve photoelectric conversion efficiency, increase the photosensitive area of ​​the pixel region, and further enhance sensor sensitivity.

[0098] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features of the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0099] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method of fabricating a pixel cell for a backside illuminated image sensor, the method comprising: ​ A substrate is provided, the top surface of which includes sacrificial layers and a first trench arranged alternately along a first direction; After forming an isolation structure on the side of the first trench near the sacrificial layer, the sacrificial layer is removed to form a second trench; the isolation structure includes a first dielectric layer. A first photosensitive layer is formed in the second trench and the remaining first trench; Utilizing the morphology inheritance effect of the deposition process, a second photosensitive layer is formed in the second trench and the remaining first trench, and a groove extends into the second photosensitive layer along the direction toward the substrate; the angle between the sidewall and the bottom surface of the groove is greater than 90 degrees; the second photosensitive layer, the first photosensitive layer and the substrate are used to form a pixel structure; A second dielectric layer is formed on the pixel structure and the isolation structure; the second dielectric layer is in contact with the first dielectric layer; the materials of the first dielectric layer and the second dielectric layer include materials with a high k dielectric constant.

2. The production method according to claim 1, characterized by, Forming the isolation structure includes: After forming a first oxide material layer and a first dielectric material layer with an L-shaped longitudinal section, which are sequentially stacked on the inner surface of the first trench and the top surface of the sacrificial layer, a second oxide material layer is formed that is attached to the sidewall of the first dielectric material layer and the L-shaped corner. A second dielectric material layer is formed within the first trench, which is attached to the sidewall of the second oxide material layer and the upper surface of a portion of the first dielectric material layer; the first dielectric layer and the second dielectric layer are used to constitute the first dielectric layer; A third oxide material layer is formed in contact with the sidewall of the first dielectric layer and the first oxide material layer; the longitudinal section of the third oxide material layer is I-shaped.

3. The method of claim 2, wherein, The second dielectric material layer and the third oxide material layer are formed using a diffusion process.

4. The production method according to claim 3, characterized by, The first photosensitive layer is formed using an epitaxial growth process; The longitudinal section of the first photosensitive layer is rectangular.

5. The preparation method according to claim 3, characterized in that, The first photosensitive layer is formed using a deposition process; The longitudinal section of the first photosensitive layer is concave.

6. A pixel unit, characterized in that, A back-illuminated image sensor includes: a substrate, wherein the top surface of the substrate includes an isolation structure and a pixel structure alternately arranged along a first direction; The isolation structure includes a first dielectric layer; The pixel structure includes a first photosensitive layer and a second photosensitive layer arranged sequentially along a direction away from the substrate; The second photosensitive layer is fabricated using the morphology inheritance effect of the deposition process, and includes a groove extending from the top surface of the second photosensitive layer into the second photosensitive layer; the angle between the sidewall and the bottom surface of the groove is greater than 90 degrees; the second photosensitive layer, the first photosensitive layer and the substrate are used to form a pixel structure; The second dielectric layer is located on the top surface of the isolation structure and the pixel structure, and is in contact with the first dielectric layer; the materials of the first dielectric layer and the second dielectric layer include materials with a high k dielectric constant.

7. The pixel cell of claim 6, wherein, The isolation structure includes: A first oxide layer is located between adjacent pixel structures; The first dielectric layer extends into the first oxide layer via the top surface of the isolation structure, and its width is smaller than that of the first oxide layer; The second oxide layer extends into the first dielectric layer via the top surface of the isolation structure, and its width is smaller than that of the first dielectric layer.

8. The pixel cell of claim 6, wherein, The angle between the sidewall and bottom surface of the groove is negatively correlated with the thickness of the first photosensitive layer.

9. A backside illuminated image sensor, characterized by include: The pixel unit is prepared by the preparation method according to any one of claims 1-5; or The pixel unit described in any one of claims 6-8 is used.

10. The backside illumination image sensor of claim 9, wherein, Includes multiple pixel units; The plurality of pixel units are arranged sequentially along the first direction.

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