CN113838881A - Image sensor and method for manufacturing the same - Google Patents
Image sensor and method for manufacturing the same Download PDFInfo
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- H01L27/144—Devices controlled by radiation
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Abstract
The invention provides an image sensor and a manufacturing method thereof. Wherein, the image sensor includes: the protective layer, the third oxide layer and the barrier layer are deposited on the substrate in sequence. And the third oxide layer is formed by back etching the second oxide layer covering the surface of the first oxide layer, so that the top surface of the third oxide layer is a curved surface, and the barrier layer formed on the third oxide layer is correspondingly curved, so that more light rays can be collected into the photosensitive element, the photon quantity is increased, and the sensitivity of the image sensor is improved. In addition, the third oxidation layer is arranged between the protective layer and the barrier layer, so that the film stress of the barrier layer is weakened to a certain extent, and the dislocation of a floating diffusion region caused by directly depositing the barrier layer is avoided. Therefore, the invention can improve the sensitivity of the image sensor, has simple process and low cost, can reduce the film stress generated by the barrier layer, avoids the dislocation of the floating diffusion region and improves the performance of the device.
Description
Technical Field
The invention relates to the technical field of semiconductor device manufacturing, in particular to an image sensor and a preparation method thereof.
Background
An image sensor is a device that converts an optical image into an electronic signal, and is widely used in digital cameras, mobile phones, and other electronic optical devices. Among them, CMOS Image Sensors (CIS) devices have a wide audience due to their advantages of low power consumption and high signal-to-noise ratio. However, as the integration of the device is higher and higher, the process platform is gradually reduced, the pixel density of the image sensor is higher and higher, and the size of the pixel unit is smaller and smaller. The reduction in the size of the pixel unit may reduce the photosensitive area of the photodiode, lowering the photosensitive sensitivity of the photodiode, thereby causing deterioration in image quality at low illumination. In contrast, the conventional process employs a Back-side Illumination (BSI CIS) process to alleviate this problem. The BSI is a follow-up process that a logic device and a pixel device are formed in a semiconductor substrate, a metal interconnection structure is formed on the surface of the semiconductor substrate, then a bearing wafer is adopted to be bonded with the front side of the semiconductor substrate, the back side of the semiconductor substrate is thinned, and the CIS is formed on the back side of the semiconductor substrate. It can be seen that BSI CIS is much more complex in process than CIS and is expensive to manufacture.
In addition, in the CIS manufacturing process, as shown in fig. 1, after depositing a Salicide Area Block (SAB) 30, a Contact Etch Stop Layer (CESL) 40 is directly deposited, and the thickness of the CESL40 is much greater than that of the SAB30, so that the CESL40 generates a large film stress, which causes a dislocation d (displacement) in a Floating Diffusion (FD) region, thereby seriously affecting the performance of the device.
Therefore, a new image sensor and a method for manufacturing the same are needed to solve the problem of low photosensitivity and the problem of misalignment of the floating diffusion region.
Disclosure of Invention
The invention aims to provide an image sensor and a preparation method thereof, which are used for solving the problem of at least one of improving the photosensitive sensitivity of a photodiode and avoiding the dislocation of a suspended diffusion region.
In order to solve the above technical problem, the present invention provides a method for manufacturing an image sensor, including:
providing a substrate, wherein the substrate comprises a photosensitive element area and a floating diffusion area, the photosensitive element area comprises a plurality of photosensitive elements, a grid electrode and a first oxidation layer covering the grid electrode and the surface of the substrate are formed on the substrate;
forming a protective layer, wherein the protective layer covers the surface of the first oxide layer;
forming a second oxide layer, wherein the second oxide layer covers the surface of the protective layer;
performing back etching on the second oxide layer, and removing part of the second oxide layer to form a third oxide layer, wherein the top surface of the third oxide layer is a curved surface;
and forming a barrier layer, wherein the barrier layer covers the top surface of the third oxidation layer, and the top surface of the barrier layer is a curved surface.
Optionally, in the method for manufacturing an image sensor, after the etching back is performed, the top surface of the third oxide layer includes a plurality of convex curved surfaces, and a projection of the convex curved surfaces toward the substrate covers the photosensitive element and/or the gate.
Optionally, in the method for manufacturing an image sensor, the projection of the convex curved surface toward the substrate covers a photosensitive surface of the photosensitive element; and the convex curved surface is convex towards the direction of the incident light so as to converge the incident light to the photosensitive surface.
Optionally, in the method for manufacturing an image sensor, the barrier layer is grown along a top surface of the third oxide layer, so that the top surface of the barrier layer formed includes a plurality of convex curved surfaces.
Optionally, in the method for manufacturing an image sensor, the outer contour shapes of the convex curved surfaces of the third oxide layer and the barrier layer include a parabolic shape.
Optionally, in the method for manufacturing an image sensor, after the forming the blocking layer, the method for manufacturing an image sensor further includes:
forming a dielectric layer, wherein the dielectric layer covers the surface of the barrier layer;
forming a plurality of through holes, wherein the through holes sequentially penetrate through the dielectric layer, the barrier layer, the third oxide layer, the protective layer and the first oxide layer, part of the through holes extend into the grid electrode, and part of the through holes extend into the substrate of the floating diffusion region;
and filling a metal material into the through holes to form a plurality of metal lines.
Optionally, in the method for manufacturing an image sensor, the photosensitive element and the floating diffusion region are arranged at an interval along an extension direction of the substrate surface, and the gate is located on the substrate between the photosensitive element and the floating diffusion region.
Optionally, in the method for manufacturing an image sensor, the photosensitive element includes a photodiode.
Based on the same inventive concept, the present invention also provides an image sensor, comprising:
the substrate comprises a photosensitive element area and a floating diffusion area, the photosensitive element area comprises a plurality of photosensitive elements, and the photosensitive elements and the floating diffusion area are arranged at intervals along the extension direction of the surface of the substrate;
a gate located on the substrate between the photosensitive element and the floating diffusion region;
the first oxidation layer covers the grid and the surface of the substrate;
the protective layer covers the surface of the first oxide layer;
the third oxidation layer covers the surface of the protection layer, and the top surface of the third oxidation layer is a curved surface;
the barrier layer covers the top surface of the third oxide layer, and the top surface of the barrier layer is a curved surface;
and the metal wires sequentially penetrate through the barrier layer, the third oxidation layer, the protective layer and the first oxidation layer, part of the metal wires extend into the grid electrode, and part of the metal wires extend into the substrate of the floating diffusion region.
Optionally, in the image sensor, the image sensor further includes a dielectric layer, the dielectric layer covers the surface of the blocking layer, and the plurality of metal lines penetrate through the dielectric layer.
In summary, the present invention provides an image sensor and a method for manufacturing the same. During the process of preparing the image sensor, a back-etching process is adopted to remove part of the second oxide layer so as to form a third oxide layer, wherein the top surface of the third oxide layer is a curved surface; accordingly, the barrier layer formed on the third oxide layer also has a curved shape accordingly. Compared with a plane shape, the shape of the curved surface can collect more light rays so as to enable the light rays to enter the photosensitive element, and therefore the problem that the sensitivity of the image sensor is low due to the fact that the photoelectric reaction is influenced because the quantity of received photons is small because of large pixel density and small photosensitive area is avoided.
In addition, the third oxide layer is additionally arranged between the protective layer and the barrier layer, so that the film stress of the barrier layer can be weakened to a certain extent, and the dislocation of the floating diffusion region caused by directly depositing the barrier layer is avoided. Therefore, the invention can improve the sensitivity of the image sensor, has simple process and low cost, can reduce the film stress generated by the barrier layer, avoids the dislocation of the floating diffusion region and improves the performance of the device.
Drawings
FIG. 1 is a schematic diagram of a semiconductor structure of an image sensor in the prior art;
FIG. 2 is a flow chart of a method of manufacturing an image sensor in an embodiment of the invention;
FIGS. 3-8 are schematic views of semiconductor structures at various steps in a method of fabricating an image sensor in accordance with an embodiment of the present invention;
wherein the reference numerals are:
10-a substrate; 20-an oxide layer; 30-SAB layer; 40-CESL layer; a PD-photodiode; an FD-suspended diffusion region; a TX-transmission gate; d-dislocation;
100-a substrate; 101-a photosensitive element; 102-a floating diffusion region; 103-a gate; 104-a first oxide layer; 105-a protective layer; 106-a second oxide layer; 107-a third oxide layer; 108-a barrier layer; 109-a dielectric layer; 110-metal lines.
Detailed Description
To further clarify the objects, advantages and features of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. It is to be noted that the drawings are in greatly simplified form and are not to scale, but are merely intended to facilitate and clarify the explanation of the embodiments of the present invention. Further, the structures illustrated in the drawings are often part of actual structures. In particular, the drawings may have different emphasis points and may sometimes be scaled differently. It should be further understood that the terms "first," "second," "third," and the like in the description are used for distinguishing between various components, elements, steps, and the like, and are not intended to imply a logical or sequential relationship between various components, elements, steps, or the like, unless otherwise indicated or indicated.
To solve the above technical problem, the present embodiment provides a method for manufacturing an image sensor, as shown in fig. 2 and 8, including:
step one S10: providing a substrate 100, wherein the substrate 100 comprises a photosensitive element region and a floating diffusion region 102, the photosensitive element region comprises a plurality of photosensitive elements 101, a gate 103 is further formed on the substrate 100, and a first oxide layer 104 covers the gate 103 and the surface of the substrate 100;
step two S20: forming a protective layer 105, wherein the protective layer 105 covers the surface of the first oxide layer 104;
step three S30: forming a second oxide layer 106, wherein the second oxide layer 106 covers the surface of the protective layer 105;
step four S40: performing back etching on the second oxide layer 106, and removing a part of the second oxide layer 106 to form a third oxide layer 107, wherein the top surface of the third oxide layer 107 is a curved surface;
step five S50: forming a barrier layer 108, wherein the barrier layer 108 covers the top surface of the third oxide layer 107, and the top surface of the barrier layer 108 is a curved surface.
The method for manufacturing the image sensor is described in detail below with reference to fig. 3 to 8.
Step one S10: referring to fig. 3, a substrate 100 is provided, the substrate 100 includes a photosensitive device region and a floating diffusion region 102, the photosensitive device region includes a plurality of photosensitive devices 101, a gate 103 is further formed on the substrate 100, and a first oxide layer 104 covers the gate 103 and the surface of the substrate 100.
The substrate 100 may be any substrate known to those skilled in the art for supporting semiconductor integrated circuit components, such as a die, a wafer processed by an epitaxial growth process, or a circuit layer formed with devices. Optionally, the substrate 100 includes a silicon-on-insulator (SOI) substrate, a bulk silicon (bulk silicon) substrate, a germanium substrate, a silicon-germanium substrate, an indium phosphide (InP) substrate, a gallium arsenide (GaAs) substrate, or a germanium-on-insulator substrate.
Further, along the extending direction of the surface of the substrate 100, the photosensitive elements 101 and the floating diffusion regions 102 are disposed at intervals, and each gate 103 is located on the substrate 100 between one photosensitive element 101 and one floating diffusion region 102, that is, one photosensitive element 101 and one floating diffusion region 102 are respectively located in the substrate 100 on both sides of one gate 103. The photosensitive element 101 is configured to receive light and realize photoelectric conversion, and is optionally a photodiode. The gate 103 is used for connecting a transmission control signal, and the floating diffusion region 102 may also be referred to as a floating diffusion region.
And, as shown in fig. 3, a first oxide layer 104 covers around the gate 103 and the top surface of the substrate 100 to protect and isolate the substrate 100 and the gate 103. The process of forming the first oxide layer 104 may be a thermal oxidation process. Firstly, forming an oxide layer on the surface of the substrate, then forming the gate 103 on the oxide layer, and continuously forming the oxide layer with a certain thickness to cover the gate 103, so as to isolate the gate 103 from the substrate 100, where the oxide layers formed twice are the first oxide layer 104. Optionally, the material of the first oxide layer 104 includes silicon dioxide.
Step two S20: referring to fig. 4, a protection layer 105 is formed, wherein the protection layer 105 covers the surface of the first oxide layer 104. The protection layer 105 may be referred to as a salicide block (SAB) for protecting the device structure, and the material of the protection layer includes silicon nitride.
Step three S30: referring to fig. 5-7, a second oxide layer 106 is formed, wherein the second oxide layer 106 covers the surface of the protection layer 105.
In the conventional process, as shown in fig. 1, after the salicide region block film 30 is formed, a contact etch stop layer 40 is formed directly on the protection layer 105, and the thickness of the salicide region block film 30 is small, generally about 100 angstroms. The thickness of the contact etch stop layer 40 is relatively large, typically about 400 angstroms, so that the film stress generated by the contact etch stop layer 40 is relatively large. The suspension diffusion region FD cannot counter the extrusion effect of large film stress, and a certain dislocation occurs, deviating from the original position, thereby affecting the performance of the device. In the image sensor provided in this embodiment, before depositing the barrier layer 108, a second oxide layer 106 is deposited on the protective layer 105. The second oxide layer 106 generates a film stress opposite to the barrier layer 108 to resist a larger film stress generated by the barrier layer 108 deposited subsequently, so as to avoid the dislocation of the floating diffusion region 102 caused by the larger stress generated by the barrier layer 108. Therefore, the top surface of the floating diffusion region 102 and the top surface of the photosensitive element 101 in the image sensor provided by the present example can be flush with the top surface of the substrate 100, and there is no problem of misalignment, thereby improving the performance of the device.
Further, the material of the second oxide layer 106 includes silicon dioxide. Wherein, the thickness of the second oxide layer 106 is determined by the thickness of the barrier layer 108, so as to offset the film stress generated by the barrier layer 108.
Step four S40: referring to fig. 6, a back etching process is performed on the second oxide layer 106 to remove a portion of the second oxide layer 106, so as to form a third oxide layer 107, wherein a top surface of the third oxide layer 107 is a curved surface.
The back etching process is not limited in this embodiment, and a wet etching process or a dry etching process may be selected as the back etching process.
The top surface of the third oxide layer 107 includes a plurality of convex curved surfaces, which may be continuous or continuous with a flat surface. And, the projection of the convex curved surface toward the substrate 100 covers the photosensitive element 101 and/or the gate 103. In other words, in the direction perpendicular to the substrate 100, the gate 103 and the corresponding third oxide layer 107 on the photosensitive element 101 are convex curved surfaces. Further, as shown in fig. 6, the photosensitive surface of the photosensitive element 101 is close to the top surface of the substrate 100. Wherein, the projection of the convex curved surface towards the substrate 100 covers the photosensitive surface of the photosensitive element 101; and the convex curved surface is convex towards the direction of the incident light so as to converge the incident light to the photosensitive element. In other words, the top surface of the portion of the third oxide layer 107 opposite to the photosensitive surface of the photosensitive element 101 is convex toward the direction of the incident light, so as to form the convex curved surface, thereby increasing the incident light. Compared with a flat surface, the convex curved surface has stronger light convergence capacity, so that more photons enter the photosensitive element 101, the photoelectric conversion efficiency is improved, and the sensitivity of the device is further improved. Optionally, the shape of the convex curved surface is the same as that of the surface of the macro lens, and is similar to that of the convex surface of the convex lens.
Step five S50: referring to fig. 7, a blocking layer 108 is formed, wherein the blocking layer 108 covers the top surface of the third oxide layer 107, and the top surface of the blocking layer 108 is a curved surface.
Wherein the barrier layer 108 may be referred to as a contact etch barrier layer 108. Optionally, the material of the barrier layer 108 includes silicon nitride. Since the blocking layer 108 is deposited along the top surface of the third oxide layer 107, the shape of the formed blocking layer 108 is similar to that of the third oxide layer 107, and has a plurality of convex curved surfaces. At a position opposite to the photosensitive surface of the photosensitive element 101, the blocking layer 108 protrudes toward the incident light ray, forming the convex curved surface. Moreover, the outer contour shapes of the convex curved surfaces of the third oxide layer 107 and the barrier layer 108 include, but are not limited to, a parabolic shape, and may also be similar to a meniscus shape.
Therefore, in the image sensor provided by this embodiment, the blocking layer 108 having a convex curved surface can avoid the problem that the area of the photosensitive element 101 is reduced to reduce the amount of received photons when the pixels are densely arranged. Under the action of the curved surface, light rays can be converged, the quantity of photons entering the photosensitive surface is increased, the photoelectric conversion efficiency is improved, and the sensitivity is enhanced. Moreover, the third oxide layer 107 is additionally arranged between the protective layer 105 and the barrier layer 108, so that the film stress of the barrier layer 108 is weakened to a certain extent, the dislocation of the floating diffusion region 102 caused by directly depositing the barrier layer 108 is avoided, and the performance of the device is further improved.
After forming the barrier layer 108, as shown in fig. 8, the method for manufacturing the image sensor further includes:
forming a dielectric layer 109, wherein the dielectric layer 109 covers the surface of the barrier layer 108;
forming a plurality of through holes, wherein the through holes sequentially penetrate through the dielectric layer 109, the barrier layer 108, the third oxide layer 107, the protective layer 105 and the first oxide layer 104, and a part of the through holes extend into the gate 103 and a part of the through holes extend into the substrate of the floating diffusion region 102;
a metal material is filled into the plurality of via holes to form a plurality of metal lines 110.
The dielectric layer 109 is made of an insulating material to ensure that no leakage crosstalk exists between the film layers. The metal material may be tungsten, so as to form a plurality of metal lines 110. A portion of the metal line 110 is in communication with the gate 103, and a portion of the metal line 110 is in communication with the floating diffusion region 102, so as to be able to tap out the gate 103 and the floating diffusion region 102 to a logic region.
Based on the same inventive concept, the present embodiment further provides an image sensor, please refer to fig. 8, which includes:
the substrate 100, the substrate 100 includes a photosensitive element region and a floating diffusion region 102, the photosensitive element region includes a plurality of photosensitive elements 101 and is along the extending direction of the substrate 100 surface, the photosensitive elements 101 and the floating diffusion region 102 are arranged at intervals;
a gate 103, the gate 103 being located on the substrate 100 between the photosensitive element 101 and the floating diffusion region 102;
a first oxide layer 104 covering the gate 103 and the surface of the substrate 100;
a protective layer 105 covering the surface of the first oxide layer 104;
a third oxide layer 107 covering the surface of the protective layer 105, wherein the top surface of the third oxide layer 107 is a curved surface;
a barrier layer 108 covering the top surface of the third oxide layer 107, wherein the top surface of the barrier layer 108 is a curved surface;
a dielectric layer 109 covering the surface of the barrier layer 108;
a plurality of metal lines 110, wherein the metal lines 110 sequentially penetrate through the dielectric layer 109, the barrier layer 108, the third oxide layer 107, the protective layer 105, and the first oxide layer 104, a portion of the metal lines 110 extends into the gate 103, and a portion of the metal lines 110 extends into the substrate of the floating diffusion region 102, so as to connect the gate 103 and the floating diffusion region 102 to a logic region.
In summary, the present embodiment provides an image sensor and a method for manufacturing the same. The third oxide layer 107 in the image sensor is formed by performing push-back etching on the second oxide layer 106 covering the surface of the protective layer 105, so that the top surface of the third oxide layer 107 is a curved surface, and the barrier layer 108 formed on the third oxide layer 107 also has a curved surface shape accordingly. Compared with a planar form, the curved form can collect more light rays to enable the light rays to enter the photosensitive element 101, so that the problems that the photoelectric reaction is influenced due to the fact that the quantity of received photons is small because of large pixel density and small photosensitive area, the sensitivity of the image sensor is low, and the image quality is deteriorated under low illumination are avoided.
In addition, in this embodiment, the third oxide layer 107 is disposed between the protective layer 105 and the barrier layer 108 to weaken the film stress of the barrier layer 108 to some extent, so as to avoid the dislocation of the floating diffusion region 102 caused by directly depositing the barrier layer 108. Therefore, the image sensor provided by the embodiment can not only enhance the light convergence capability and improve the sensitivity of the image sensor, but also reduce the film stress generated by the barrier layer 108, avoid the dislocation of the floating diffusion region 102 and improve the device performance, and the process is simple and low in cost.
It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. It will be apparent to those skilled in the art from this disclosure that many changes and modifications can be made, or equivalents modified, in the embodiments of the invention without departing from the scope of the invention. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention are still within the protection scope of the technical solution of the present invention, unless the content of the technical solution of the present invention is departed from.
Claims (10)
1. A method of manufacturing an image sensor, comprising:
providing a substrate, wherein the substrate comprises a photosensitive element area and a floating diffusion area, the photosensitive element area comprises a plurality of photosensitive elements, a grid electrode and a first oxidation layer covering the grid electrode and the surface of the substrate are formed on the substrate;
forming a protective layer, wherein the protective layer covers the first oxide layer;
forming a second oxide layer covering the protective layer;
performing back etching on the second oxide layer, and removing part of the second oxide layer to form a third oxide layer, wherein the top surface of the third oxide layer is a curved surface;
and forming a barrier layer, wherein the barrier layer covers the third oxidation layer, and the top surface of the barrier layer is a curved surface.
2. The method according to claim 1, wherein after the etching back is performed, a top surface of the third oxide layer includes a plurality of convex curved surfaces, and a projection of the convex curved surfaces toward the substrate covers the photosensitive element and/or the gate.
3. The method of claim 2, wherein the projection of the convex curved surface toward the substrate covers a photosensitive surface of the photosensitive element; and the convex curved surface is convex towards the direction of the incident light so as to converge the incident light to the photosensitive surface.
4. The method of claim 2, wherein the barrier layer is grown along a top surface of the third oxide layer such that the top surface of the barrier layer is formed to include a plurality of convex curved surfaces.
5. The method according to claim 4, wherein the outer contour shapes of the convex curved surfaces of the third oxide layer and the barrier layer each include a parabolic shape.
6. The method of manufacturing an image sensor according to claim 1, further comprising, after forming the barrier layer:
forming a dielectric layer, wherein the dielectric layer covers the surface of the barrier layer;
forming a plurality of through holes, wherein the through holes sequentially penetrate through the dielectric layer, the barrier layer, the third oxide layer, the protective layer and the first oxide layer, part of the through holes extend into the grid electrode, and part of the through holes extend into the substrate of the floating diffusion region;
and filling a metal material into the through holes to form a plurality of metal lines.
7. The method of claim 1, wherein the photosensitive element and the floating diffusion are spaced apart along a direction of extension of the surface of the substrate, and the gate is located on the substrate between the photosensitive element and the floating diffusion.
8. The method for manufacturing an image sensor according to claim 1, wherein the photosensitive element includes a photodiode.
9. An image sensor, comprising:
the substrate comprises a photosensitive element area and a floating diffusion area, the photosensitive element area comprises a plurality of photosensitive elements, and the photosensitive elements and the floating diffusion area are arranged at intervals along the extension direction of the surface of the substrate;
a gate located on the substrate between the photosensitive element and the floating diffusion region;
the first oxidation layer covers the grid and the surface of the substrate;
the protective layer covers the surface of the first oxide layer;
the third oxidation layer covers the surface of the protection layer, and the top surface of the third oxidation layer is a curved surface;
the barrier layer covers the top surface of the third oxide layer, and the top surface of the barrier layer is a curved surface;
and the metal wires sequentially penetrate through the barrier layer, the third oxidation layer, the protective layer and the first oxidation layer, part of the metal wires extend into the grid electrode, and part of the metal wires extend into the substrate of the floating diffusion region.
10. The image sensor of claim 9, further comprising a dielectric layer covering a surface of the barrier layer, wherein the plurality of metal lines extend through the dielectric layer.
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| CN114664876A (en) * | 2022-05-25 | 2022-06-24 | 合肥晶合集成电路股份有限公司 | Image sensor and manufacturing method thereof |
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