CN110634901A - an image sensor - Google Patents

Abstract

An embodiment of the present invention provides an image sensor, including a substrate, the substrate has an opposite first surface and a second surface; the substrate has a photosensitive area on a side close to the second surface, the The photosensitive region is used to receive incident light irradiation and generate photogenerated carrier pairs with the first charge and the second charge; the substrate has a a corresponding transmission channel, the transmission channel is used to transport the photo-generated carriers with the first electrical property to a specific position and lead out the substrate from the specific position; The two surfaces have a first groove extending toward the first surface, the first groove is located at the edge of the photosensitive area, and a conductor material for loading a first electrical voltage is arranged in the first groove .

Description

an image sensor

technical field

The present invention relates to the technical field of image sensing, in particular to an image sensor.

Background technique

An image sensor is a device used to convert an optical image into an electrical signal. It utilizes the photoelectric conversion function of the photosensitive area to generate photogenerated carriers (positive and negative charges, or electron-air) when the photosensitive area receives incident light. Hole pair), so as to convert the light image into an electrical signal proportional to the light image; and then realize the image sensing function by deriving the electrical signal for reading.

However, existing image sensors often have the problem that the charge far away from the transfer transistor cannot be exported to the substrate, resulting in charge residue; especially for back-illuminated image sensors, this charge residue problem is more obvious due to the thicker substrate , resulting in image smear defects. In order to solve the problem of charge residue, it is proposed in the related art to adjust the ion implantation gradient of the N-type well region in the substrate, so that the photogenerated carriers can be drawn to the floating diffusion region to the greatest extent; however, when the ion implantation depth is too deep or the ion implantation When the implantation process is unstable, it is difficult to guarantee the ion implantation gradient in the N-type well region, and the problem of charge residue still cannot be well solved.

Contents of the invention

In view of this, the main purpose of the present invention is to provide an image sensor.

In order to achieve the above object, technical solution of the present invention is achieved in that way:

An embodiment of the present invention provides an image sensor, including:

a substrate having opposing first and second surfaces;

The substrate has a photosensitive area on a side close to the second surface, and the photosensitive area is used to receive incident light and generate photogenerated carrier pairs with the first electrical property and the second electrical property;

The substrate has a transport channel corresponding to the photosensitive region on a side close to the first surface, and the transport channel is used to transport the photogenerated carriers with the first electrical property to a specific position and deriving the substrate from the specific location;

There is a first groove extending toward the first surface on the second surface of the substrate, the first groove is located at the edge of the photosensitive region, and the first groove is provided in the first groove for A conductive material loaded with a first electrical voltage.

In the solution above, the first electrical property is negative, and the voltage of the first electrical property loaded on the conductor material ranges from -0.5V to -3V.

In the above solution, the sidewall of the first groove is inclined toward the direction of the photosensitive region.

In the above solution, the angle between the sidewall of the first groove and the first surface is greater than or equal to 60° and less than 90°.

In the above solution, the first opening width of the first trench at the second surface is in the range of 0.1-0.8 μm, and the second opening width of the first trench bottom in the substrate is in the range of 0.1-0.8 μm. is 0.1-0.2 μm, and the depth range of the first groove in the substrate is 0.1-2 μm.

In the solution above, the width of the first opening of the first groove at the second surface is smaller than the width of the photosensitive region.

In the solution above, the conductor material includes at least one of the following: TiN-Ti-W laminated layers, TiN-Ti-Cu laminated layers, and TiN-Ti-Al laminated layers.

In the above solution, the width of the conductive material at the second surface is in the range of 0.05-0.4 μm, the width of the bottom of the conductive material in the substrate is in the range of 0.05-0.4 μm, and the conductive material is in the range of 0.05-0.4 μm. The depth range in the substrate is 0.09-1.8 μm.

In the above solution, an insulating layer is further provided in the first trench, and the insulating layer is used to electrically isolate the conductor material from the substrate.

In the above solution, the material of the insulating layer includes silicon oxide.

In the above solution, the first surface of the substrate further has a second groove extending toward the second surface, and the position of the second groove corresponds to the position of the first groove; The second trench is a shallow isolation trench STI, and the first trench is a deep isolation trench DTI.

In the above solution, the bottom of the first trench and the bottom of the second trench are connected in the substrate.

The image sensor provided by the embodiment of the present invention includes a substrate, the substrate has an opposite first surface and a second surface; the substrate has a photosensitive area on a side close to the second surface, and the photosensitive area is The region is used to receive incident light irradiation and generate photogenerated carrier pairs with the first charge and the second charge; the side of the substrate close to the first surface has a a transport channel for transporting photo-generated carriers with a first electrical property to a specific position and leading out the substrate from the specific position; in the second of the substrate The surface has a first groove extending toward the first surface, the first groove is located at the edge of the photosensitive area, and a conductor material for loading a first electrical voltage is arranged in the first groove. In this way, by setting the first trench structure, the conductor material in the first trench structure is loaded with the first electrical voltage, thereby generating an electric field force repelling the photo-generated carriers with the first electrical nature, Under the action of the electric field force, the photo-generated carriers with the first electrical property are pushed to the transmission channel, and then exported to the substrate, so as to solve the charge residue problem of the image sensor and improve the image smear defect.

Description of drawings

FIG. 1 is a schematic structural diagram of an image sensor provided by an embodiment of the present invention;

FIG. 2 is a schematic flowchart of a method for preparing an image sensor provided by an embodiment of the present invention;

3 to 9 are schematic cross-sectional views of the device structure during the manufacturing process of the image sensor provided by the embodiment of the present invention.

Detailed ways

Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present invention are shown in the drawings, it should be understood that the invention may be embodied in various forms and should not be limited to the specific embodiments set forth herein. On the contrary, these embodiments are provided for a more thorough understanding of the present invention and to fully convey the scope of the disclosure of the present invention to those skilled in the art.

In the following description, numerous specific details are given in order to provide a more thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without one or more of these details. In other examples, in order to avoid confusion with the present invention, some technical features known in the art are not described; that is, all features of the actual embodiment are not described here, and well-known functions and structures are not described in detail.

In the drawings, the size of layers, regions, elements and their relative sizes may be exaggerated for clarity. Like reference numerals refer to like elements throughout.

It will be understood that when an element or layer is referred to as being "on," "adjacent to," "connected to" or "coupled to" another element or layer, it can be directly on the other element or layer. , adjacent to, connected to, or coupled to other elements or layers, or intervening elements or layers may be present. In contrast, when an element is referred to as being "directly on," "directly adjacent to," "directly connected to" or "directly coupled to" another element or layer, there are no intervening elements or layers present. It will be understood that, although the terms first, second, third etc. may be used to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present invention. Whereas a second element, component, region, layer or section is discussed, it does not necessarily mean that the present invention must be present with a first element, component, region, layer or section.

Spatial terms such as "below...", "below...", "below", "below...", "on...", "above" and so on, can be used here for convenience are used in description to describe the relationship of one element or feature to other elements or features shown in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use and operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements or features described as "below" or "beneath" or "beneath" other elements or features would then be oriented "above" the other elements or features. Thus, the exemplary terms "below" and "beneath" can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatial descriptors used herein interpreted accordingly.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms "a", "an" and "the/the" are intended to include the plural forms as well, unless the context clearly dictates otherwise. It should also be understood that the terms "consists of" and/or "comprising", when used in this specification, identify the presence of stated features, integers, steps, operations, elements and/or parts, but do not exclude one or more other Presence or addition of features, integers, steps, operations, elements, parts and/or groups. As used herein, the term "and/or" includes any and all combinations of the associated listed items.

In order to thoroughly understand the present invention, detailed steps and detailed structures will be provided in the following description, so as to illustrate the technical solution of the present invention. Preferred embodiments of the present invention are described in detail below, however, the present invention may have other embodiments besides these detailed descriptions.

FIG. 1 is a schematic structural diagram of an image sensor provided by an embodiment of the present invention. As shown in the figure, the image sensor of the embodiment of the present invention includes a substrate 100, and the substrate 100 has an opposite first surface 101 and a second surface 102; the substrate 100 is close to the second surface 102 One side has a photosensitive area, and the photosensitive area is used to receive incident light irradiation and generate photogenerated carrier pairs with the first charge and the second charge; the substrate 100 is close to the first surface One side of 101 has a transmission channel corresponding to the photosensitive region, and the transmission channel is used to transport the photo-generated carriers with the first electrical property to a specific position and lead out the substrate from the specific position 100; the second surface 102 of the substrate 100 has a first trench T1 extending toward the first surface 101, the first trench T1 is located at the edge of the photosensitive region, and on the second surface A conductive material 112 for loading a first electrical voltage is disposed in a trench T1 .

Here, for ease of understanding, taking a 4T pixel image sensor as an example, the pixel area consists of four transmission gates Tx (only two transmission gates Tx1 and Tx2 are schematically shown in Figure 1), source follower devices, and row selection devices. , reset device, and photosensitive area. The incident light filtered by the filter generates and accumulates charges in the corresponding photosensitive area (equivalent to photogenerated carriers with the first electrical property), and after the transfer gate Tx is turned on, the charges are transferred into the floating diffusion area (Floating Diffusion, FD), through the source follower device to convert the charge into a voltage that can be processed later, and then through the row selection device, the voltage signal is output through the common output column. Reset The device performs a reset function after performing an operation.

When the image sensor is working, the first electrical voltage is applied to the conductor material 112 in the first trench structure T1, thereby generating an electric field force that repels the photo-generated carriers with the first electrical nature. Under the action of force, the photo-generated carriers with the first electrical property are pushed to the transmission channel, and then lead out to the substrate 100, which solves the charge residue problem of the image sensor and improves the image smear defect.

The substrate 100 is, for example, a silicon substrate; in other embodiments, it may also include a germanium substrate, a silicon carbide substrate, or a silicon germanium substrate.

A transmission gate Tx is formed on the first surface 101 of the substrate 100, and the transmission channel is formed in the substrate 100 corresponding to the transmission gate Tx. When the transfer gate Tx is turned on, the transfer channel has the effect of transferring charges, thereby transferring the photo-generated carriers to a specific position; understandably, the specific position here is, for example, the floating diffusion region FD, where the photo-generated carriers Substrates are then led out of the substrate 100 from the floating diffusion area.

In one embodiment, the first charge is negative, that is, the photo-generated carriers with the first charge are photoelectrons; at this time, the first charge loaded on the conductor material 112 The range of the voltage is -0.5～-3V, so that the photoelectrons are pushed to the transmission channel through the repulsion effect of the negative voltage.

Please continue to refer to Figure 1. As a specific implementation manner, the sidewall of the first trench T1 is inclined toward the direction of the photosensitive region. In this way, the electric field force generated during operation can better push the photoelectrons; in this embodiment, it is recommended that the angle range between the sidewall of the first trench T1 and the first surface 101 be greater than or equal to 60° and If the angle is less than 90°, at this time, not only the pushing ability of the generated electric field force is good, but also the encroachment of the substrate 100 by the first trench T1 is minimized.

Further, the first opening width of the first trench T1 at the second surface 102 should be smaller than the width of the photosensitive region, so as to avoid adverse effects on the photosensitive performance of the image sensor.

As a specific implementation manner, the first opening width of the first trench T1 at the second surface 102 ranges from 0.1 to 0.8 μm, and the bottom of the first trench T1 is in the substrate 100 The width of the second opening is in a range of 0.1-0.2 μm, and the depth of the first trench T1 in the substrate 100 is in a range of 0.1-2 μm. Here, the first trench T1 is a deep trench isolation (Deep trench isolation, DTI); its size can be adjusted according to the actual performance and process capability of the device; the first trench T1 is, for example, etched by dry method craft formation.

After forming the first trench T1, an insulating layer 111 may be filled in the first trench T1; the insulating layer 111 is used to electrically isolate the subsequently formed conductor material 112 from the substrate 100, To prevent external electrons from flowing into the substrate 100 after a voltage is applied to the conductor material 112 , causing noise.

In an embodiment, the material of the insulating layer 111 includes silicon oxide, such as SiO ₂ . At this time, the incident light can penetrate the silicon oxide filled in the first trench T1, thereby minimizing the impact of the setting of the first trench T1 on the photosensitivity of the photosensitive region.

Next, in order to form the conductive material 112 in the first trench T1, the insulating layer 111 may be etched to form a trench T2, so that the conductive material 112 is filled in the trench T2. The trench T2 can also be formed by a dry etching process.

The conductor material 112 includes at least one of the following: TiN-Ti-W stack, TiN-Ti-Cu stack, TiN-Ti-Al stack. Specifically, the outermost layer of the conductor material 112 is a TiN layer, the middle layer is a Ti layer, and the innermost layer is a W, Cu or Al layer.

The width of the conductive material 112 at the second surface 102 is in the range of 0.05-0.4 μm, the width of the bottom of the conductive material 112 in the substrate 100 is in the range of 0.05-0.4 μm, and the conductive material 112 is in the The depth range of the substrate 100 is 0.09-1.8 μm. The size of the conductive material 112 is the size of the trench T2 formed by etching.

In one embodiment, the first surface 101 of the substrate 100 further has a second groove extending toward the second surface 102, the position of the second groove is the same as that of the first groove corresponding to the positions; the second trench is a shallow isolation trench (Shallow trench isolation, STI), and the first trench is a deep isolation trench DTI.

Understandably, the second trench STI separates each pixel of the image sensor. The position of the first trench T1 corresponds to the position of the second trench STI, that is, the first trench T1 is arranged at the position where each pixel is separated on the edge of the photosensitive area. In a specific embodiment, the bottom of the first trench T1 is contiguous with the bottom of the second trench STI in the substrate 100 .

In addition, the image sensor may further include a dielectric layer 110, and the dielectric layer 110 covers the transmission gate Tx. The dielectric layer 110 also has a wiring layer 111 and the like.

The image sensor provided in the embodiment of the present invention may be a back-illuminated image sensor; in another embodiment, the image sensor may also be a stacked image sensor.

In addition, the embodiment of the present invention also provides a method for manufacturing an image sensor. Please refer to attached drawing 2 for details. As shown, the method includes the following steps:

Step 201, providing a substrate, the substrate has an opposite first surface and a second surface; the substrate has a photosensitive area on a side close to the second surface, and the photosensitive area is used to receive incident light irradiation and generate photogenerated carrier pairs with the first electrical property and the second electrical property; the substrate has a transmission channel corresponding to the photosensitive region on the side close to the first surface, and the The transport channel is used to transport the photogenerated carriers with the first electrical type to a specific position and lead out the substrate from the specific position;

Step 202, forming a first groove extending toward the first surface on the second surface of the substrate, the first groove is located at the edge of the photosensitive region, and in the first groove A conductor material for loading a first electrical voltage is formed inside.

In the following, the image sensor provided by the embodiment of the present invention and the manufacturing method thereof will be further described in detail with reference to the device structure cross-sectional schematic diagrams in the manufacturing process of the image sensor shown in FIG. 3 to FIG. 9 .

First, please refer to Figure 3. A substrate 100 that has completed the front-end process is provided.

At this time, the substrate 100 has a first surface 101 and a second surface 102 opposite to each other. The substrate 100 has a photosensitive area on a side close to the second surface 102, and the photosensitive area is used to receive incident light and generate photogenerated carriers with the first electrical property and the second electrical property. Yes; in other words, after the image sensor is formed, the side of the second surface 102 is used as the side of the image sensor facing the incident light. There is a second trench (Shallow Isolation Trench STI) at the edge of the photosensitive area. The second trench STI separates each pixel of the image sensor. The substrate 100 has a transport channel corresponding to the photosensitive region on a side close to the first surface 101, and the transport channel is used to transport the photogenerated carriers with the first electrical property to a specific position and derive the substrate 100 from the specific position.

Here, a transfer gate Tx is formed on the first surface 101 of the substrate 100, and the transfer channel is formed in the substrate 100 below the transfer gate Tx. The specific position may specifically refer to the position where the floating diffusion region FD is located; through the function of the transmission channel, the photogenerated carriers with the first electrical property are transported to the FD, and then led out from the FD to the substrate 100 .

A dielectric layer 110 is further stacked on the first surface 101 of the substrate 100, and the dielectric layer 110 covers the transmission gate Tx. A wiring layer 111 and the like are provided in the dielectric layer 110 .

Next, please refer to Figure 4. A carrier substrate 120 is bonded on the first surface 101 side of the substrate 100 ; specifically, the carrier substrate 120 may be bonded on the exposed surface of the dielectric layer 110 . The substrate 100 is turned over so that the second surface 102 faces upwards and faces the process direction.

Next, please refer to Figure 5. The substrate 100 is thinned from the second surface 102 of the substrate 100 . The specific process can be mechanical grinding, acid etching, chemical mechanical grinding and the like.

Next, please refer to Figure 6. A dry etching process is performed on the second surface 102 of the substrate 100 to form the first trench T1. The first trench T1 is located at the edge of the photosensitive area; in a specific embodiment, the formation position of the first trench T1 corresponds to the position of the second trench STI. The bottom of the first trench T1 may be contiguous with the bottom of the second trench STI in the substrate 100 .

As a specific implementation manner, the first opening width of the first trench T1 at the second surface 102 ranges from 0.1 to 0.8 μm, and the bottom of the first trench T1 is in the substrate 100 The width of the second opening is in a range of 0.1-0.2 μm, and the depth of the first trench T1 in the substrate 100 is in a range of 0.1-2 μm. Here, the first trench T1 is a deep isolation trench DTI; its size can be adjusted according to the actual performance and process capability of the device; the deepest is connected to the bottom of the second trench STI, thereby forming a The trench structure of the substrate 100.

The first trench T1 can be formed by etching in a direction perpendicular to the thickness of the substrate; however, as a better implementation manner, the sidewall of the first trench T1 faces the direction of the photosensitive region The inclination, like this, makes the electric field force generated during work have a better ability to push the photoelectrons. In this embodiment, it is recommended that the angle range between the sidewall of the first trench T1 and the first surface 101 is greater than or equal to 60° and less than 90°. At this time, not only the pushing ability of the generated electric field force is good, but also Moreover, the occupation of the substrate 100 by the first trench T1 is minimized. The specific inclination angle of the sidewall of the first trench T1 can be adjusted according to actual design requirements and device performance.

Next, please refer to Figure 7. An insulating layer 111 is filled in the first trench T1; the insulating layer 111 is used to electrically isolate the subsequently formed conductor material 112 from the substrate 100, preventing external electrons from flowing in after the conductor material 112 is loaded with a voltage substrate 100, causing noise.

In an embodiment, the material of the insulating layer 111 includes silicon oxide, such as SiO ₂ . At this time, the incident light can penetrate the silicon oxide filled in the first trench T1, thereby minimizing the impact of the setting of the first trench T1 on the photosensitivity of the photosensitive region.

Next, please refer to Figure 8. In order to form the conductive material 112 in the first trench T1, the insulating layer 111 is etched to form a trench T2. The trench T2 can also be formed by a dry etching process.

In this etching process, a certain thickness of the insulating layer 111 is reserved on the bottom and side walls of the first trench T1, for example, a thickness range of 0.01-0.2um is left on the bottom of the first trench T1 In this way, it is ensured that the subsequently formed conductor material 112 is covered by the insulating layer 111 and does not have a portion directly contacting the substrate 100 .

The width of the trench T2 at the second surface 102 is in the range of 0.05-0.4 μm, the width of the bottom of the trench T2 in the substrate 100 is in the range of 0.05-0.4 μm, and the trench T2 is in the The depth range of the substrate 100 is 0.09-1.8 μm. The size of the trench T2 is the size of the conductor material 112 formed later.

Next, please refer to Figure 9. The conductive material 112 is filled in the trench T2.

The conductor material 112 can be formed by filling a metal connection hole in the art. The conductor material 112 includes at least one of the following: TiN-Ti-W stack, TiN-Ti-Cu stack, TiN-Ti-Al stack. Specifically, the outermost layer of the conductor material 112 is a TiN layer, the middle layer is a Ti layer, and the innermost layer is a W, Cu or Al layer.

Finally, the method may also include growing an oxide medium, forming deep TSVs, depositing metals, depositing optical filters, forming microlenses, etc. (not shown in the figure).

After the image sensor is prepared, an additional metal connection is used to connect the conductor material 112 in the first trench T1 to a negative voltage input terminal, so that the image sensor can be loaded with a negative voltage during operation, for example- 0.5～-3V. Of course, the specific voltage range needs to be adjusted according to the actual performance of the device.

It should be noted that the embodiment of the image sensor provided by the present invention and the embodiment of the preparation method of the image sensor belong to the same idea; the technical features in the technical solutions recorded in each embodiment can be combined arbitrarily if there is no conflict .

The above description is only a preferred embodiment of the present invention, and is not used to limit the protection scope of the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention shall be included in the within the protection scope of the present invention.

Claims (12)

1. An image sensor, comprising:

a substrate having opposing first and second surfaces;

the substrate is provided with a photosensitive area on one side close to the second surface, and the photosensitive area is used for receiving incident light irradiation and generating photo-generated carrier pairs with a first electric property and a second electric property;

the substrate is provided with a transmission channel corresponding to the photosensitive area on one side close to the first surface, and the transmission channel is used for transmitting the photon-generated carriers with the first electrical property to a specific position and guiding the photon-generated carriers out of the substrate from the specific position;

the second surface of the substrate is provided with a first groove extending towards the first surface, the first groove is located at the edge of the photosensitive area, and a conductor material used for loading a first electric voltage is arranged in the first groove.

2. The image sensor as in claim 1, wherein the first electrical property is negative, and the voltage of the first electrical property applied to the conductive material is in a range of-0.5V to-3V.

3. The image sensor of claim 1, wherein sidewalls of the first trench are sloped toward a direction of the photosensitive region.

4. The image sensor of claim 3, wherein the sidewall of the first trench forms an angle with the first surface in a range of 60 ° or more and less than 90 °.

5. The image sensor of claim 1, wherein a first opening width of the first trench at the second surface is in a range of 0.1-0.8 μm, a second opening width of the first trench bottom in the substrate is in a range of 0.1-0.2 μm, and a depth of the first trench in the substrate is in a range of 0.1-2 μm.

6. The image sensor of claim 1, wherein a first opening width of the first trench at the second surface is less than a width of the photosensitive region.

7. The image sensor of claim 1, wherein the conductor material comprises at least one of: TiN-Ti-W stack, TiN-Ti-Cu stack, TiN-Ti-Al stack.

8. The image sensor of claim 1, wherein the width of the conductive material at the second surface is in a range of 0.05-0.4 μm, the width of the bottom of the conductive material within the substrate is in a range of 0.05-0.4 μm, and the depth of the conductive material within the substrate is in a range of 0.09-1.8 μm.

9. The image sensor of claim 1, wherein an insulating layer is further disposed within the first trench, the insulating layer for electrically isolating the conductor material from the substrate.

10. The image sensor of claim 9, wherein the material of the insulating layer comprises silicon oxide.

11. The image sensor of claim 1, further comprising a second trench on the first surface of the substrate extending toward the second surface, the second trench corresponding in position to the first trench; the second trench is a shallow isolation trench STI, and the first trench is a deep isolation trench DTI.

12. The image sensor of claim 11, wherein a bottom of the first trench is contiguous with a bottom of the second trench within the substrate.

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