阅读说明：本技术 图像传感器及其制作方法 (image sensor and manufacturing method thereof ) 是由 胡杏 刘天建 贺吉伟 于 2019-09-02 设计创作，主要内容包括：本发明提供的图像传感器及其制作方法,包括：提供一衬底,在所述衬底中位于转移区的两侧分别设置有感光区和读取区；刻蚀去除部分厚度的所述转移区,使剩余的所述转移区在所述厚度方向上低于浅沟道隔离区；去除所述介质层；形成多晶硅层,所述多晶硅层填充于相邻的所述浅沟道隔离区之间。在传统的闪存工艺的基础上,刻蚀去除部分厚度的所述转移区,打通所述感光区到读取区的通道,不再被传统的闪存工艺浅沟道隔离断开,通过多晶硅层实现图像传感器中感光区的电荷向读取区的转移,从而正确识别光信号强度。本发明提供的图像传感器,通过多晶硅层实现图像传感器中感光区的电荷向读取区的转移,提高了图像传感器的性能。(the invention provides an image sensor and a manufacturing method thereof, comprising the following steps: providing a substrate, wherein a photosensitive area and a reading area are respectively arranged on two sides of a transfer area in the substrate; etching to remove part of the transfer region with the thickness, so that the rest of the transfer region is lower than the shallow trench isolation region in the thickness direction; removing the dielectric layer; and forming a polysilicon layer which is filled between the adjacent shallow trench isolation regions. On the basis of the traditional flash memory process, the transfer area with partial thickness is removed by etching, a channel from the photosensitive area to the reading area is opened, the channel is not isolated and disconnected by a shallow channel in the traditional flash memory process, and the charge of the photosensitive area in the image sensor is transferred to the reading area through a polycrystalline silicon layer, so that the intensity of an optical signal is correctly identified. According to the image sensor provided by the invention, the charge of the sensing area in the image sensor is transferred to the reading area through the polycrystalline silicon layer, so that the performance of the image sensor is improved.)

1. a method of fabricating an image sensor, comprising:

providing a substrate, wherein a dielectric layer is arranged on the substrate, shallow trench isolation regions and transfer regions which are arranged at intervals are periodically distributed in the substrate and the dielectric layer, the shallow trench isolation regions and the transfer regions both extend from the substrate to the dielectric layer along the thickness direction, and photosensitive regions and reading regions are respectively arranged on two sides of the transfer region in the substrate;

Etching to remove part of the transfer region with the thickness, so that the rest of the transfer region is lower than the shallow trench isolation region in the thickness direction;

removing the dielectric layer;

And forming a polysilicon layer which is filled between the adjacent shallow trench isolation regions.

2. The method of claim 1, wherein the polysilicon layer includes a transfer gate region covering the transfer region, a portion of the photosensitive region, and a portion of the read region, the transfer gate region controlling transfer of charge generated in the photosensitive region to the read region.

3. The method for manufacturing an image sensor as claimed in claim 1, wherein the etching to remove a portion of the thickness of the transfer region specifically comprises:

Forming a patterned photoresist layer, wherein the patterned photoresist layer covers the dielectric layer and the shallow trench isolation region and is provided with a photoresist window positioned above the transfer region; etching and removing the transfer region with partial thickness by taking the patterned photoresist layer as a mask; on a cross section perpendicular to the substrate, a cross sectional width of the photoresist window is greater than or equal to a cross sectional width of the transfer region.

4. The method of claim 1, wherein the shallow trench isolation region and the transfer region are made of silicon oxide.

5. an image sensor, comprising:

A substrate;

a polysilicon layer overlying the substrate;

Shallow trench isolation regions which are arranged at intervals, wherein each shallow trench isolation region penetrates through the polycrystalline silicon layer and the substrate with partial depth along the thickness direction;

In the substrate, a photosensitive area, a transfer area and a reading area are sequentially distributed between adjacent shallow trench isolation areas, the transfer area is lower than the shallow trench isolation areas in the thickness direction, and the polycrystalline silicon layer covers the photosensitive area, the transfer area and the reading area.

6. the image sensor of claim 5, wherein the polysilicon layer includes a transfer gate region overlying the transfer region, a portion of the photosensitive region, and a portion of the read region, the transfer gate region controlling transfer of charge generated in the photosensitive region to the read region.

7. the image sensor as in claim 6, wherein the photosensitive area is distributed with photosensitive elements.

8. The image sensor as claimed in claim 7, wherein in the photosensitive region, a first photodiode and a second photodiode are stacked and distributed along a thickness direction of the substrate, and the first photodiode is located above the second photodiode.

9. the image sensor of claim 8, wherein in the photosensitive region, a side of the first photodiode and the second photodiode in a stacked distribution near the shallow trench isolation region has a vertical charge transfer region distributed therein.

10. The image sensor of any of claims 5 to 9, wherein the read region is connected to a pixel circuit for sensing charge-induced voltage changes in the read region.

Technical Field

The invention belongs to the field of image sensors, and particularly relates to an image sensor and a manufacturing method thereof.

background

The vertical charge transfer image sensor (VPS) is a three-dimensional image sensor based on a standard flash memory process or a semiconductor image sensor based on a floating gate structure array, has the characteristics of high Pixel density, small Pixel size and the like, and has the working principle that charges generated by photo-generated carriers in a photosensitive area are coupled to a reading area to change the reading current of the reading area so as to realize the light intensity identification. The conventional flash memory and the vertical charge transfer image sensor have partially similar structures, the photosensitive region and the upper part of the reading region in the same working unit of the vertical charge transfer image sensor need to be communicated through a polycrystalline silicon layer, and the floating gate (usually made of polycrystalline silicon) above the photosensitive region and the reading region corresponding to the conventional flash memory process is isolated and disconnected by a shallow trench, so that the charge of the photosensitive region in the image sensor cannot be transferred to the reading region by the conventional flash memory process.

disclosure of Invention

The invention aims to provide an image sensor and a manufacturing method thereof, which realize the transfer of charges in a sensing area of the image sensor to a reading area and improve the performance of the image sensor.

The invention provides a manufacturing method of an image sensor, which comprises the following steps:

providing a substrate, wherein a dielectric layer is arranged on the substrate, shallow trench isolation regions and transfer regions which are arranged at intervals are periodically distributed in the substrate and the dielectric layer, the shallow trench isolation regions and the transfer regions both extend from the substrate to the dielectric layer along the thickness direction, and photosensitive regions and reading regions are respectively arranged on two sides of the transfer region in the substrate;

Etching to remove part of the transfer region with the thickness, so that the rest of the transfer region is lower than the shallow trench isolation region in the thickness direction;

Removing the dielectric layer;

and forming a polysilicon layer which is filled between the adjacent shallow trench isolation regions.

Further, the polysilicon layer includes a transfer gate region covering the transfer region, a portion of the photosensitive region, and a portion of the read region, the transfer gate region controlling transfer of charges generated in the photosensitive region to the read region.

Further, the etching to remove the transfer region with a partial thickness specifically includes:

Forming a patterned photoresist layer, wherein the patterned photoresist layer covers the dielectric layer and the shallow trench isolation region and is provided with a photoresist window positioned above the transfer region; etching and removing the transfer region with partial thickness by taking the patterned photoresist layer as a mask; on a cross section perpendicular to the substrate, a cross sectional width of the photoresist window is greater than or equal to a cross sectional width of the transfer region.

furthermore, the shallow trench isolation region and the transfer region are made of silicon oxide.

The present invention also provides an image sensor comprising:

A substrate;

A polysilicon layer overlying the substrate;

Shallow trench isolation regions which are arranged at intervals, wherein each shallow trench isolation region penetrates through the polycrystalline silicon layer and the substrate with partial depth along the thickness direction;

in the substrate, a photosensitive area, a transfer area and a reading area are sequentially distributed between adjacent shallow trench isolation areas, the transfer area is lower than the shallow trench isolation areas in the thickness direction, and the polycrystalline silicon layer covers the photosensitive area, the transfer area and the reading area.

further, the polysilicon layer includes a transfer gate region covering the transfer region, a portion of the photosensitive region, and a portion of the read region, the transfer gate region controlling transfer of charges generated in the photosensitive region to the read region.

Furthermore, photosensitive elements are distributed in the photosensitive area.

Further, in the photosensitive area, a first photodiode and a second photodiode are stacked and distributed along the thickness direction of the substrate, and the first photodiode is located above the second photodiode.

further, in the photosensitive region, vertical charge transfer regions are distributed on one sides, close to the shallow channel isolation region, of the first photodiodes and the second photodiodes which are distributed in a stacked manner.

further, the reading area is connected with a pixel circuit for sensing a voltage change caused by the charge in the reading area.

Compared with the prior art, the invention has the following beneficial effects:

The invention provides a method for manufacturing an image sensor, which comprises the steps of providing a substrate, wherein a photosensitive area and a reading area are respectively arranged on two sides of a transfer area in the substrate; etching to remove part of the thickness of the transfer region; making the remaining transfer region lower than the shallow trench isolation region in the thickness direction; and forming a polysilicon layer which is filled between the adjacent shallow trench isolation regions. On the basis of the traditional flash memory process, the transfer area with partial thickness is removed by etching, a channel from the photosensitive area to the reading area is opened, the channel is not isolated and disconnected by a shallow channel in the traditional flash memory process, and the charge of the photosensitive area in the image sensor is transferred to the reading area through a polycrystalline silicon layer, so that the intensity of an optical signal is correctly identified. The manufacture of the three-dimensional image sensor is realized by combining the traditional flash memory process, the application range of the flash memory process is expanded, and the three-dimensional imaging can be quickly realized.

according to the image sensor provided by the invention, the transfer region is lower than the shallow trench isolation region in the thickness direction, the polycrystalline silicon layer covers the photosensitive region, the transfer region and the reading region, and the charge of the photosensitive region in the image sensor is transferred to the reading region through the polycrystalline silicon layer on the basis of the traditional flash memory process.

Further, in the photosensitive region, the first photodiode and the second photodiode are stacked and distributed along the thickness direction of the substrate, and the charge of the deep potential well with higher potential can be allowed to be transferred from the lower potential well to the vertical direction with lower potential. Sensing light in this manner allows for longer storage of charge, a compact pixel structure with high performance, high charge storage well capacity. The image sensor may exhibit higher pixel density, higher image resolution and higher sensitivity.

drawings

FIG. 1 is a schematic flow chart illustrating a method for fabricating an image sensor according to an embodiment of the present invention;

FIG. 2 is a schematic view of a substrate structure provided in an embodiment of the invention;

FIG. 3 is a schematic diagram illustrating a structure after a patterned photoresist layer is formed according to an embodiment of the present invention;

FIG. 4 is a schematic structural diagram of a transfer region with a partial thickness removed by etching according to an embodiment of the present invention;

FIG. 5 is a schematic structural diagram of the patterned photoresist layer after being removed according to the embodiment of the present invention;

FIG. 6 is a schematic structural diagram of the semiconductor device after the dielectric layer is removed according to the embodiment of the invention;

FIG. 7 is a schematic diagram illustrating a structure after forming a polysilicon layer according to an embodiment of the present invention;

FIG. 8 is a schematic diagram illustrating another structure after forming a polysilicon layer according to another embodiment of the present invention;

FIG. 9 is a schematic diagram of a region including a transmission gate according to an embodiment of the present invention;

Wherein the reference numbers are as follows:

10-a substrate; 20-a dielectric layer; 31-shallow trench isolation region; 32-a transfer zone; 41-photosensitive area; 42-a reading zone; 43-transfer gate area; 50-a photoresist layer; 60-polysilicon layer.

Detailed Description

The embodiment of the invention provides an image sensor and a manufacturing method thereof. The invention is described in further detail below with reference to the figures and specific examples. The advantages and features of the present invention will become more apparent from the following description. It is to be noted, however, that the drawings are designed in a simplified form and are not to scale, but rather are to be construed in an illustrative and descriptive sense only and not for purposes of limitation.

An embodiment of the present invention provides a method for manufacturing an image sensor, as shown in fig. 1, including:

providing a substrate, wherein a dielectric layer is arranged on the substrate, shallow trench isolation regions and transfer regions which are arranged at intervals are periodically distributed in the substrate and the dielectric layer, the shallow trench isolation regions and the transfer regions both extend from the substrate to the dielectric layer along the thickness direction, and photosensitive regions and reading regions are respectively arranged on two sides of the transfer region in the substrate;

Etching to remove part of the transfer region with the thickness, so that the rest of the transfer region is lower than the shallow trench isolation region in the thickness direction; removing the dielectric layer;

And forming a polysilicon layer which is filled between the adjacent shallow trench isolation regions.

The image sensor and the method for fabricating the same according to the embodiments of the present invention are described in detail below with reference to fig. 2 to 8.

As shown in fig. 2, a substrate 10 is provided, a dielectric layer 20 is disposed on the substrate 10, shallow trench isolation regions 31 and transfer regions 32 are periodically disposed in the substrate 10 and the dielectric layer 20, the shallow trench isolation regions 31 and the transfer regions 32 both extend from the substrate 10 to the dielectric layer 20 along a thickness direction, photosensitive regions 41 and read regions 42 are disposed on two sides of the transfer regions 32 in the substrate 10, specifically, the dielectric layer 20 is deposited on the substrate 10, the dielectric layer 20 is, for example, a silicon nitride layer, trenches are etched at intervals at a certain depth, the trenches penetrate through the dielectric layer 20 and the substrate 10 at a partial depth, an oxide layer (for example, SiO ₂) can be deposited in the trenches by Chemical Vapor Deposition (CVD) to form the shallow trench isolation regions 31 and the transfer regions 32, i.e., the shallow trench isolation regions 31 and the transfer regions 32 are formed in the same process and are, for example, both silicon oxide layers are planarized by Chemical Mechanical Polishing (CMP).

In one embodiment, the photosensitive region 41 includes a photosensitive element (e.g., a photodiode PD), and the photosensitive element of the photosensitive region 41 generates photo-generated carriers under the action of light. In another embodiment, in the photosensitive region 41, a first photodiode and a second photodiode are stacked and distributed along a thickness direction of the substrate, and the first photodiode is located above the second photodiode. In the photosensitive region 41, vertical charge transfer regions are distributed on one sides of the first photodiode and the second photodiode which are distributed in a stacked manner and close to the shallow trench isolation region. The reading area is connected to a pixel circuit for sensing a voltage change caused by the charge in the reading area.

As shown in fig. 3, a patterned photoresist layer 50 is formed, wherein the patterned photoresist layer 50 covers the dielectric layer 20 and the shallow trench isolation region 31 and has a photoresist window located above the transfer region 32. Specifically, in a cross section perpendicular to the substrate 10, the cross sectional width of the photoresist window is greater than or equal to the cross sectional width of the transfer region 32, so that while the transfer region 32 is etched and removed along the thickness direction for a part of the thickness, the transfer region 32 in the entire width direction (parallel to the substrate direction) is etched away within the thickness range of the removed transfer region, instead of etching away a part of the width, so as to open a channel from the light sensing region 41 to the reading region 42 in the direction parallel to the substrate.

As shown in fig. 4, the patterned photoresist layer 50 is used as a mask to etch and remove a part of the thickness of the transfer region 32, and the remaining transfer region 32 is lower than the shallow trench isolation region 31 in the thickness direction by using dry etching or wet etching with a high selectivity ratio, or by combining the dry etching and the wet etching; the photosensitive region 41 and the read region 42 are facilitated to communicate by a subsequently formed polysilicon layer.

As shown in fig. 4 to 6, the patterned photoresist layer 50 and the dielectric layer 20 are sequentially removed.

As shown in fig. 7 and 8, a polysilicon layer 60 is formed, and a Chemical Vapor Deposition (CVD) process is used to grow the polysilicon layer 60, wherein the polysilicon layer 60 is filled between adjacent shallow trench isolation regions 31. A Chemical Mechanical Polishing (CMP) process is then performed to planarize the upper surfaces of the polysilicon layer 60 and the shallow trench isolation regions 31. The polysilicon layer 60 is disconnected by the shallow trench isolation regions 31, and the adjacent shallow trench isolation regions 31, i.e. the photosensitive region 41 and the read region 42 in the same operating unit, are connected together by the polysilicon layer 60. The photosensitive elements of the photosensitive region 41 generate photo-generated carriers under the influence of light, and the charge generated by the photo-generated carriers is transferred or coupled to the read region 42 through the polysilicon layer 60, thereby changing the device state of the read region 42. Specifically, the polysilicon layer includes a transfer gate region 43, the transfer gate region 43 covers the transfer region 32, a portion of the photosensitive region 41, and a portion of the readout region 42, and the transfer gate region 43 controls the transfer of the charges generated in the photosensitive elements in the photosensitive region 41 to the readout region 42.

in the method for manufacturing the image sensor provided by the embodiment of the invention, a substrate is provided, and a photosensitive area and a reading area are respectively arranged on two sides of a transfer area in the substrate; etching to remove part of the thickness of the transfer region; and forming a polysilicon layer which is filled between the adjacent shallow trench isolation regions. On the basis of the traditional flash memory process, the transfer area with partial thickness is removed by etching, a channel from the photosensitive area to the reading area is opened, the channel is not isolated and disconnected by a shallow channel in the traditional flash memory process, and the charge of the photosensitive area in the image sensor is transferred to the reading area through a polycrystalline silicon layer, so that the intensity of an optical signal is correctly identified. The manufacture of the three-dimensional image sensor is realized by combining the traditional flash memory process, the application range of the flash memory process is expanded, and the three-dimensional imaging can be quickly realized. The image sensor manufactured by the method of the embodiment can store charges for a longer time, and has a compact pixel structure with high performance and high charge storage well capacity. The image sensor may exhibit higher pixel density, higher image resolution and higher sensitivity.

An embodiment of the present invention further provides an image sensor, as shown in fig. 7 and 8, including:

A substrate 10;

A polysilicon layer 60, the polysilicon layer 60 covering the substrate 10;

Shallow trench isolation regions 31, the shallow trench isolation regions 31 being arranged at intervals, the shallow trench isolation regions 31 penetrating the polysilicon layer 60 and the substrate 10 with a partial depth;

in the substrate 10, a photosensitive region 41, a transfer region 32 and a reading region 42 are sequentially distributed between adjacent shallow trench isolation regions 31, the transfer region 32 is lower than the shallow trench isolation regions 31 in the thickness direction, and the polysilicon layer 60 covers the photosensitive region 41, the transfer region 32 and the reading region 42. As shown in fig. 7, the transfer region 32 may be lower than or equal to the upper surface of the substrate 10 in the thickness direction; as shown in fig. 8, the transfer region 32' may also be higher than the upper surface of the substrate 10 in the thickness direction.

illustratively, the material of the shallow trench isolation region 31 and the transfer region 32 is, for example, silicon oxide.

as shown in fig. 9, the polysilicon layer 60 includes a transfer gate region 43, the transfer gate region 43 covers the transfer region 32, a portion of the photosensitive region 41, and a portion of the read region 42, and the transfer gate region 43 controls the transfer of the charges generated in the photosensitive region 41 to the read region 42.

an image sensor fabricated in accordance with embodiments of the present invention includes an array of image sensor pixels. A pixel in an image sensor may include a photosensitive element such as a photodiode that converts incident light into electrons. The image sensor may have any number of pixels (e.g., hundreds or thousands or more). A typical image sensor may, for example, have millions of pixels (e.g., mega pixels). In high-end devices, the image sensor may have tens of millions of pixels. Among them, a pixel (working unit) of the image sensor includes a photosensitive region, a transfer region, a reading region, and a polysilicon layer.

In one embodiment, the photosensitive region 41 includes a photosensitive element (e.g., a photodiode PD), and the photosensitive element of the photosensitive region 41 generates photo-generated carriers under the action of light. The charge generated by the incident photons is collected in the n-type doped region of the photodiode. Charge may be transferred from the photosensitive region 41 to a read region 42 through a transfer gate region 43 located in the polysilicon layer 60, the read region 42 being, for example, an n + doped region, the read region 42 being connectable to a pixel circuit for sensing a voltage change caused by charge stored in the read region 42. The pixel circuit includes, for example, a reset transistor, a sense transistor, an address transistor, and the like. With the pixel circuit, on the one hand, a reset data value is written to the image sensor pixel to reset the read-out area, and on the other hand, data is read out from the image sensor pixel by the pixel circuit, the data corresponding to a part of the captured image.

In another embodiment, the image sensor has the ability to separate charges according to the wavelength of incident photons, including stacked photodiodes. When a photon strikes the image sensor photosensitive region, the photon penetrates the substrate according to its corresponding wavelength and generates an electron. Specifically, the photosensitive region 41 includes a first photodiode and a second photodiode stacked and distributed in the thickness direction of the substrate 10, the first photodiode is located above the second photodiode, the first photodiode includes a first n-type doped region, the first n-type doped region is a shallow injection region, and the shallow injection region can be used for storing a shallow potential well of charges generated at a shallow depth; the second photodiode includes a second n-type doped region that is a deep implanted region that can be used to store a deep potential well of charge generated at a greater depth. The shallow and deep implanted regions may be separated by a P + doped barrier region.

In the photosensitive region 41, vertical charge transfer regions are distributed on one side of the first photodiode and the second photodiode which are distributed in a stacked manner and close to the shallow trench isolation region 31.

The image sensor has the ability to detect and store charges generated at different depths according to the wavelength of incident light. For example, blue light is less able to penetrate the substrate 10 than green light and less able to penetrate red light, the blue light being substantially absorbed by the first n-type doped region (light), and the green and red light being absorbed by the second n-type doped region (deep). The image sensor has different depths of potential well regions capable of separating the charge generated by blue light, the charge generated by green and red light.

Charges (electrons) generated by the irradiation of photons in the shallower region are collected and stored in the first n-type doped region (shallow), and charges (electrons) generated by the irradiation of photons in the deeper region are collected and stored in the second n-type doped region (deep).

In the first phase, the charges (electrons) stored in the first n-type doped region (shallow) are activated through the transfer gate region 43 located in the polysilicon layer 60 and transferred to the read region 42.

In the second stage, a voltage is applied across the polysilicon layer 60 and the substrate, forming an electric field along the thickness of the substrate 10, transferring the charge in the second n-doped region (deep) to a temporary storage region on top of the vertical charge transfer region, the charge (electrons) effecting a transfer in a direction perpendicular to the substrate.

in the third stage, the charges (electrons) in the temporary storage region on top of the vertical charge transfer region are activated through the first n-type doped region (shallow), and then transferred to the read region 42 through the transfer gate region 43 located in the polysilicon layer 60. This process may be repeated a number of times until the charge in all of the second n-type doped regions (deep) is transferred to the read region 42. For example, the transfer gate region 43 may be opened multiple times using several pulse signals to ensure that the charge in all of the second n-doped regions (deep) is read out. Read region 42 may be coupled to a storage capacitor to temporarily store image charge. The read region 42 may be connected to a pixel circuit for sensing a voltage change caused by the charge stored in the read region 42. With the pixel circuit, on the one hand, a reset data value is written to the image sensor pixel to reset the read-out area, and on the other hand, data is read out from the image sensor pixel by the pixel circuit, the data corresponding to a part of the captured image.

According to the image sensor in the embodiment of the invention, on the basis of the traditional flash memory process, the charge of a sensing area in the image sensor is transferred to a reading area through a polycrystalline silicon layer; the charge of the deep potential well having a higher potential can be allowed to transfer from the lower potential well to the vertical direction having a lower potential. Sensing light in this manner allows for longer storage of charge, a compact pixel structure with high performance, high charge storage well capacity. The image sensor may exhibit higher pixel density, higher image resolution and higher sensitivity.

The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. For the method disclosed by the embodiment, the description is relatively simple because the method corresponds to the device disclosed by the embodiment, and the relevant points can be referred to the description of the method part.

The above description is only for the purpose of describing the preferred embodiments of the present invention, and is not intended to limit the scope of the present invention, and any variations and modifications made by those skilled in the art based on the above disclosure are within the scope of the appended claims.