CN110246856B - Image sensor forming method, image sensor and working method thereof - Google Patents

Image sensor forming method, image sensor and working method thereof Download PDF

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CN110246856B
CN110246856B CN201910516615.2A CN201910516615A CN110246856B CN 110246856 B CN110246856 B CN 110246856B CN 201910516615 A CN201910516615 A CN 201910516615A CN 110246856 B CN110246856 B CN 110246856B
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trench
forming
layer
image sensor
substrate
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CN110246856A (en
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姚公达
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ICLeague Technology Co Ltd
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ICLeague Technology Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
    • H01L27/144—Devices controlled by radiation
    • H01L27/146—Imager structures
    • H01L27/14601—Structural or functional details thereof
    • H01L27/14609—Pixel-elements with integrated switching, control, storage or amplification elements
    • H01L27/1461—Pixel-elements with integrated switching, control, storage or amplification elements characterised by the photosensitive area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
    • H01L27/144—Devices controlled by radiation
    • H01L27/146—Imager structures
    • H01L27/14601—Structural or functional details thereof
    • H01L27/1462—Coatings
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
    • H01L27/144—Devices controlled by radiation
    • H01L27/146—Imager structures
    • H01L27/14683—Processes or apparatus peculiar to the manufacture or treatment of these devices or parts thereof
    • H01L27/14685—Process for coatings or optical elements
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
    • H01L27/144—Devices controlled by radiation
    • H01L27/146—Imager structures
    • H01L27/14683—Processes or apparatus peculiar to the manufacture or treatment of these devices or parts thereof
    • H01L27/14687—Wafer level processing
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
    • H04N25/70—SSIS architectures; Circuits associated therewith
    • H04N25/76—Addressed sensors, e.g. MOS or CMOS sensors

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Abstract

The invention provides a forming method of an image sensor, the image sensor and a working method thereof, wherein the forming method comprises the following steps: providing a substrate having first and second opposing surfaces; etching from the first surface to form a first groove in the substrate; forming a first isolation layer in the first trench; forming a second trench in the first isolation layer, wherein the distance from the bottom of the second trench to the bottom of the first trench is greater than 0; filling a conducting layer in the second groove; the forming method of the invention can eliminate the problem of charge residue in the image sensor and improve the performance of the image sensor.

Description

Image sensor forming method, image sensor and working method thereof
Technical Field
The present invention relates to the field of semiconductor manufacturing technologies, and in particular, to a method for forming an image sensor, and a method for operating the image sensor.
Background
With the continuous improvement of semiconductor technology, an Image Sensor (Image Sensor) is used as a basic device for information acquisition in modern society more and more widely.
Image sensors can be classified into two major categories, i.e., CCD (Charge Coupled Device) image sensors and CMOS (Complementary Metal-Oxide Semiconductor) image sensors, according to their elements. With the development of semiconductor technology, the performance of CMOS transistors is gradually improved, and the resolution gradually surpasses that of CCD image sensors. The CMOS image sensor has the characteristics of high integration level, low power consumption, high speed, low cost and the like.
A CMOS image sensor is a typical solid-state imaging sensor. A CMOS image sensor generally consists of an image sensor cell array, a row driver, a column driver, a timing control logic, an AD converter, a data bus output interface, a control interface, and so on.
CMOS image sensors can be classified into: front-illuminated CMOS image sensors, back-illuminated CMOS image sensors, and stacked CMOS image sensors. The back-illuminated CMOS image sensor is to exchange the positions of the photodiode and the circuit transistor. The stacked CMOS image sensor is developed from a back-illuminated CMOS image sensor. The stacked CMOS image sensor places the circuit portion which is originally close to the photosensitive element below the photosensitive element, so that more space is reserved in the device. The function diversification is realized, and meanwhile, the miniaturization is realized. The back-illuminated CMOS image sensor and the stacked CMOS image sensor enable light to enter the photodiode firstly, so that the light sensing quantity is increased, the shooting effect under the low-illumination condition can be obviously improved, and the back-illuminated CMOS image sensor and the stacked CMOS image sensor are widely applied to camera structures of cameras, electronic toys, video conferences and security systems.
However, the conventional CMOS image sensor has problems such as residual charge, error of image information, distortion of image information, and the like when outputting an image, and thus the use of the CMOS image sensor is restricted.
Disclosure of Invention
The invention aims to provide a forming method of an image sensor, the image sensor and a working method thereof, which can eliminate the problem of charge residue in the image sensor and improve the performance of the image sensor.
In order to solve the above technical problem, the present invention provides a method for forming an image sensor, including: providing a substrate having first and second opposing surfaces; etching from the first surface to form a first groove in the substrate; forming a first isolation layer in the first trench; forming a second trench in the first isolation layer, wherein the distance from the bottom of the second trench to the bottom of the first trench is greater than 0; and filling a conductive layer in the second groove.
Optionally, the depth of the first trench is 0.1 to 2 micrometers.
Optionally, the width of the bottom of the first trench is 0.1 to 0.2 micrometers, and the width of the top of the first trench is 0.1 to 0.8 micrometers.
Optionally, the depth of the second groove is 0.09 to 1.8 micrometers, and the width of the second groove is 0.05 to 0.4 micrometers.
Optionally, the distance from the bottom of the second trench to the bottom of the first trench is 0.01 to 0.2 micrometers.
Optionally, an included angle between the sidewall of the first trench and the first surface is greater than 0 ° and less than or equal to 90 °.
Optionally, the substrate includes a photosensitive region and an isolation region surrounding the photosensitive region.
Optionally, the first trench is located in the isolation region.
Optionally, the method further includes: and forming a second isolation layer in the isolation region, wherein the second isolation layer is exposed out of the second surface.
Optionally, a photoelectric doped region is formed in the photosensitive region.
Optionally, before forming the first trench, forming a device layer on the second surface; the device layer includes: the transmission gate structure is located on the second surface.
Optionally, a floating diffusion region is formed in the substrate, the floating diffusion region is exposed from the second surface, and the floating diffusion region and the photosensitive region are located on two sides of the transfer gate structure.
Optionally, the material of the first isolation layer includes silicon oxide, silicon nitride, or silicon oxynitride.
Optionally, before forming the first trench, the method further includes: and thinning the first surface.
Optionally, before thinning, a carrier substrate is fixed on the surface of the device layer.
Optionally, the method further includes: forming a barrier layer in the second trench before forming the conductive layer; the conductive layer is located on the surface of the barrier layer.
Optionally, the material of the barrier layer includes one or more of titanium and titanium nitride.
Optionally, the method for forming the barrier layer and the conductive layer includes: forming a barrier film on the first surface, the surface of the first isolation layer, and the side wall and the bottom surface of the second trench; forming a conductive film filling the second trench on the surface of the barrier film; and flattening the conductive film until the first surface is exposed, and forming the barrier layer and the conductive layer.
An image sensor formed using the above method, comprising: a substrate comprising a first surface and a second surface; a first trench located within the substrate extending from the first surface to the second surface; a first isolation layer located in the first trench; the second groove is positioned in the isolation layer, and the distance from the bottom of the second groove to the bottom of the first groove is greater than 0; and the conducting layer is positioned in the second groove.
A method of using the above image sensor applies a negative bias voltage with respect to the substrate potential to the conductive layer.
Optionally, the negative bias voltage ranges from-0.5 volts to-0.3 volts.
Compared with the prior art, the technical scheme of the embodiment of the invention has the following beneficial effects:
the method comprises the steps of forming a first groove in a first surface, filling a first isolation layer in the first groove, forming a second groove in the first isolation layer, filling a conducting layer in the second groove, wherein the conducting layer, the first isolation layer and a substrate form an equivalent capacitor structure, and extra electric field force to the substrate can be generated when negative bias is applied to the conducting layer. After the photosensitive area receives the optical signal, the photodiode in the photosensitive area converts the optical signal into electric charge, and the generated electric charge is pushed to the surface of the substrate close to the transmission channel by the acceleration of the extra electric field force, so that more electric charge can pass through the transmission channel and the floating diffusion area, the electric charge is easy to pull out of the substrate, the problem of electric charge residue is solved, the smear defect of the image sensor is improved, and the performance of the formed image sensor is improved.
Drawings
FIG. 1 is a schematic diagram of an embodiment of an image sensor;
fig. 2 to 8 are schematic structural diagrams of steps of an image sensor forming method according to an embodiment of the invention.
Detailed Description
In the existing image sensor process, the problem of charge residue is serious, and the interference effect of the residual charge is large, so that the problems of image information error or image information distortion and the like are caused when the formed image sensor outputs an image, and the use of the image sensor is severely restricted, which is specifically referred to fig. 1.
Referring to fig. 1, a substrate 100, the substrate 100 comprising: first and second opposing surfaces 101 and 102; the shallow trench isolation structure 103 is located in the isolation region 130, and the second surface 102 exposes the surface of the shallow trench isolation structure 103; a photosensitive region 110 and a floating diffusion region 120 in the substrate 100, wherein a photo-electric doping region 104 is formed in the photosensitive region 110; the transfer gate structure 140 is located on the second surface 102, and the floating diffusion region 120 and the photo-electric doping region 104 are respectively located on two sides of the transfer gate structure 140; an N-well region (not shown) located in the substrate 100.
After the photosensitive region 110 receives the optical signal, the optical signal is converted into an electric charge through the photodiode, after the transfer gate structure 140 applies the turn-on voltage, the transfer channel in the substrate 100 at the bottom of the transfer gate structure 140 is opened, the electric charge generated by the photodiode is transferred to the floating diffusion region 120 through the floating diffusion region 120 and the transfer channel, and is transferred out of the substrate from the floating diffusion region 120, so that the output of the electric signal is realized.
In order to avoid charge retention in the photodiode and the floating diffusion region, one way is to facilitate charge output by forming a well region with a concentration gradient.
However, in the method for improving the charge retention problem by forming the well region with the concentration gradient, the problem that the depth of ion implantation is too deep or the implantation concentration gradient is uncontrollable is easily caused in the process of forming the well region, so that the photo-generated charges are not easily dragged to the floating diffusion region, the problem of charge retention is difficult to solve, the performance of the formed image sensor is poor, and the use of the image sensor is limited.
In order to solve the above problem, an embodiment of the present invention provides an image sensor. The first groove is formed on the first surface of the substrate, the first isolation layer is formed in the first groove, the second groove is formed in the first isolation layer, the conducting layer is formed in the second groove, an equivalent capacitor structure is formed among the conducting layer, the first isolation layer and the substrate at the moment, bias voltage is applied to the conducting layer to generate extra electric field force to the substrate, the electric field force accelerates electric charges generated by the photodiode to be pushed to the surface of the substrate close to the transmission channel, therefore, the electric charges are easy to be pulled out of the substrate, and the problem of electric charge residue is solved.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below.
Fig. 2 to 8 are schematic structural diagrams of steps of an image sensor forming method according to an embodiment of the invention.
Referring to fig. 2, a substrate 200 is provided, the substrate 200 having opposing first and second surfaces 210, 220.
In this embodiment, the substrate 200 includes a photosensitive region 201 and an isolation region 202 surrounding the photosensitive region 201.
In this embodiment, the isolation region 202 is used to isolate the adjacent photosensitive regions 201, and the isolation region 202 surrounds the photosensitive regions 201.
In this embodiment, the substrate 200 is made of silicon; in other embodiments, the material of the substrate 200 may also be germanium, silicon carbide, gallium arsenide, indium gallium arsenide, or other suitable materials applied to an image sensor, and the substrate 200 may also be a silicon substrate on the surface of an insulator or a germanium substrate on the surface of an insulator.
In this embodiment, a second isolation layer 2021 is formed in the isolation region 202, and the second surface 220 exposes a surface of the second isolation layer 2021.
In this embodiment, the step of forming the second isolation layer 2021 includes etching the substrate 200 from the second surface 220, forming a shallow trench in the substrate 200, filling the shallow trench with the material of the second isolation layer 2021, and forming the second isolation layer 2021 after chemical mechanical polishing.
In this embodiment, the material of the second isolation layer 2021 is formed by a chemical vapor deposition method; in other embodiments, the material of the second isolation layer 2021 may also be formed by physical vapor deposition.
In this embodiment, the second isolation layer 2021 is formed to have an isolation function and prevent electrical crosstalk, and the second isolation layer 2021 is made of an insulating material, so that the second isolation layer 2021 can have a good isolation effect, which is beneficial to improving the performance of the formed image sensor.
Referring to fig. 3, a device layer 230 is formed on the second surface 220 of the substrate 200.
In this embodiment, the device layer 230 includes an interconnection structure 231 and a transfer gate structure 232, the transfer gate structure 232 is located on the second surface 220, a floating diffusion region 203 is formed in the substrate 200, the floating diffusion region 203 is exposed on the second surface 220, a photo-electric doped region 2011 is formed in the photosensitive region 201, and the floating diffusion region 203 and the photo-electric doped region 2011 are respectively located on two sides of the transfer gate structure 232.
In this embodiment, the device layer 230 is used to form a logic circuit of an image sensor.
In this embodiment, the transmission gate structure 232 adopts a front gate forming process or a back gate forming process.
In this embodiment, the floating diffusion region 203 is formed before the transfer gate structure 232 is formed or after the transfer gate structure 232 is formed.
In this embodiment, the photo-doping region 2011 is formed before the transfer gate structure 232 is formed or after the transfer gate structure 232 is formed.
In this embodiment, the interconnect structure 231 includes a multi-layer conductive structure and a conductive plug.
Referring to fig. 4, a carrier substrate 240 is fixed on the surface of the device layer 230.
In this embodiment, the material of the supporting substrate 240 is silicon; in other embodiments, the material of the carrier substrate 240 may also be silicon germanium, silicon carbide, gallium arsenide, indium gallium arsenide, or the like.
In this embodiment, the carrier substrate 240 is formed to support subsequent thinning.
Referring to fig. 5, a first trench 300 is formed in the substrate 200 by etching from the first surface 210.
In this embodiment, the first trench 300 is located in the isolation region 202.
In this embodiment, before forming the first trench 300, thinning the first surface 210 is further included.
In this embodiment, the reason why the chemical mechanical polishing is used for the thinning is that the chemical mechanical polishing not only has high polishing efficiency, but also can obtain the first surface 210 with good surface quality.
In other embodiments, the thinning may also be performed by etching, etc.
In this embodiment, the first trench 300 is a deep trench structure, and the second isolation layer 2021 is a shallow trench isolation structure.
In this embodiment, the isolation structure of the second isolation layer 2021 is used for isolating adjacent photosensitive regions 201, so as to prevent electrical crosstalk between adjacent photosensitive regions 201.
In this embodiment, the first trench 300 is used to isolate optical or electrical crosstalk of the electro-optical doped region 2011.
In this embodiment, the width of the bottom of the first trench 300 is 0.1 to 0.2 microns, and when the width of the bottom of the first trench 300 is less than 0.1 micron, the bottom surface quality of the formed first trench 300 is poor due to the limitation of process conditions; when the width of the bottom of the first trench 300 is greater than 0.2 μm, at this time, because the width of the bottom of the first trench 300 is formed to be larger, and because the width of the bottom of the first trench 300 is too large, the space occupied by the corresponding first trench 300 is larger, the space occupied by the photosensitive region 201 is smaller, and the charges that can be accommodated by the photosensitive region 201 are less, which affects the performance of the formed image sensor.
In this embodiment, the width of the top of the first trench 300 is 0.1 to 0.8 microns, and when the width of the top of the first trench 300 is less than 0.1 micron, the first trench 300 with good quality cannot be formed under the existing process conditions; when the width of the top of the first trench 300 is greater than 0.8 μm, the space occupied by the first trench 300 is too large, and the capacity of the full well formed in the photosensitive region 201 is small, which reduces the performance of the formed image sensor.
In this embodiment, the depth of the first trench 300 is 0.1 to 2 microns, and when the depth of the first trench 300 is less than 0.1 micron and a first isolation layer is formed subsequently, since the depth of the first trench 300 is shallow and the isolation capability of the first isolation layer is weak, the isolation effect is poor, and the formed image sensor has poor performance; when the depth of the first trench 300 is greater than 2 μm, the depth of the first trench 300 is too deep and limited by the process conditions, so that the first trench 300 with good quality is not easily etched, and the quality of the first trench 300 is poor.
In this embodiment, an included angle between the sidewall of the first trench 300 and the first surface 210 is greater than 0 ° and less than or equal to 90 °.
Specifically, an included angle between the sidewall of the first trench 300 and the first surface 210 is 45 °.
In other embodiments, the included angle between the sidewall of the first groove 300 and the first surface 210 may also be 90 °, 30 °, 60 °, or the like.
In this embodiment, the substrate 200 is dry etched to form the first trench 300; in other embodiments, the first trench 300 may be formed by wet etching the substrate 200.
In this embodiment, the parameters of the dry etching include: the adopted etching gas comprises HBr and Ar, wherein the flow rate of HBr is 10 sccm-1000 sccm, and the flow rate of Ar is 10 sccm-1000 sccm.
Referring to fig. 6, a first isolation layer 310 is formed within the first trench 300.
In this embodiment, the material of the first isolation layer 310 is silicon oxide; in other embodiments, the material of the first isolation layer 310 may also be silicon nitride or silicon oxycarbide.
In this embodiment, the first isolation layer 310 is formed by a chemical vapor deposition process; in other embodiments, a physical vapor deposition process or an atomic layer deposition process may also be used.
Referring to fig. 7, a second trench 400 is formed in the first isolation layer 310.
In this embodiment, the distance from the bottom of the second trench 400 to the bottom of the first trench 300 is greater than 0, so that when a conductive layer is formed subsequently, an equivalent capacitance structure can be formed among the conductive layer, the first isolation structure 310 and the substrate 200, and thus an additional electric field force can be generated on the substrate when a negative bias is applied to the conductive layer, so that the additional electric field force can push charges formed by the photodiode to migrate to the surface of the substrate, thereby reducing the problem of charge residue.
In this embodiment, the distance from the bottom of the second trench 400 to the bottom of the first trench 300 is 0.01 to 0.2 microns, and when the distance from the bottom of the second trench 400 to the bottom of the first trench 300 is less than 0.01 micron, after power is turned on, because the first isolation layer 310 is too thin, an equivalent capacitance structure formed between a conductive layer and a substrate is easily broken down, and at this time, the isolation effect of the first isolation structure 310 is weakened, so that the performance of the formed image sensor is reduced; when the distance from the bottom of the second trench 400 to the top of the first trench 300 is greater than 0.2 μm, the extra electric field generated to the substrate after power-on is small due to the excessive thickness of the first isolation layer 310, so that the dragging effect of the extra electric field to the charges is reduced, and the charges are left.
In this embodiment, the first isolation layer 310 is etched, and the second trench 400 is formed in the first isolation layer 310.
In this embodiment, the material of the first isolation layer 310 is an insulating material, such as silicon dioxide; in other embodiments, the material of the first isolation layer 310 may also be silicon nitride, silicon carbide nitride, silicon boride nitride, silicon oxycarbide, or silicon oxynitride.
In this embodiment, the depth of the second trench 400 is 0.09 micrometers to 1.8 micrometers, and when the depth of the second trench 400 is less than 0.09 micrometers, the first isolation layer 310 located between the first trench 300 and the second trench 400 is too thick, so that an extra electric field force formed after power-on is small, an effect of the extra electric field on the charges at the photosensitive region 201 is weakened, a discharge rate of the charges is reduced, and the charges are left; when the depth of the second trench 400 is greater than 1.8 μm, the first isolation layer 310 between the first trench 300 and the second trench 400 is too thin, the isolation capability of the first isolation layer 310 is weak, and the equivalent capacitance formed between the conductive layer and the substrate after power-on is easily broken down, which causes electrical crosstalk.
In this embodiment, the width of the second trench 400 is 0.05 to 0.4 microns, and due to the process limitation, when the width of the second trench 400 is less than 0.05 microns, the first isolation layer 310 located between the first trench 300 and the second trench 400 is thick, and the magnitude of the formed additional electric field force is weakened, so that the acting force of the additional electric field force on the charges is reduced, the discharge of the charges is slowed down, and the charges are left; when the width of the second trench 400 is greater than 0.4 μm, the aspect ratio of the second trench 400 formed at this time is small, and is limited by the process conditions, which makes the formation difficult.
In this embodiment, the process of etching the first isolation layer 310 is an anisotropic dry etching process; in other embodiments, the process of etching the first isolation layer 310 may also be a wet etching process.
In this embodiment, the process parameters of the anisotropic dry etching include: the etching gas used includes: c4F8、CH2F2、O2And Ar, wherein C4F8The flow rate of (A) is 10 to 50 standard ml/min, CH2The flow rate of F is 30 standard ml/min-100 standard ml/min 70sccm, O2The flow rate of the high-frequency power source is 40-120 standard ml/min, the flow rate of Ar is 100-500 standard ml/min, the high-frequency power is 200-700 watts, and the high-frequency power is 1200-1800 watts.
In this embodiment, the second trench 400 having a better morphology can be formed by an anisotropic dry etching process.
Referring to fig. 8, a barrier layer 410 is formed in the second trench 400, and a conductive layer 500 is filled in the barrier layer 410.
In this embodiment, the material of the barrier layer 410 is titanium; in other embodiments, the material of the barrier layer 410 may also be titanium nitride or the like.
In this embodiment, the method for forming the barrier layer 410 and the conductive layer 500 includes: forming a barrier film on the first surface 210, the surface of the first isolation layer 310, and the sidewalls and bottom of the second trench 400, forming a conductive film filling the second trench 400 on the surface of the barrier film, planarizing the conductive film until the first surface 210 is exposed, and forming the barrier layer 410 and the conductive layer 500.
The material of the conductive layer 500 is one or more of copper, tungsten and aluminum. In this embodiment, the material of the conductive layer 500 is copper.
In this embodiment, after the first isolation layer 310 is formed, the second trench 400 is formed in the first isolation layer 310, the conductive layer 500 is filled in the second trench 400, the photosensitive region 201 receives an optical signal, and the optical signal is converted into an electric charge by a photodiode, at this time, due to the existence of the conductive layer 500, after a voltage is applied to the conductive layer 500, the conductive layer 500 at this time can provide an additional electric field force to the photosensitive region 201, the electric charge formed at the photosensitive region 201 is pushed to the substrate surface close to the transmission channel under the action of the additional electric field force, and is more easily pulled out of the substrate 200 after passing through the transmission channel and the floating diffusion region 203, so that the problem of electric charge residue is solved, and the performance of the formed image sensor is improved.
Accordingly, an embodiment of the present invention further provides an image sensor, please continue to refer to fig. 8, including: a substrate 200 including a first surface 210, a second surface 220, a photosensitive region 201, an isolation region 202, and a floating diffusion region 203; a first trench 300 located in the substrate 200 and extending from the first surface 210 to the second surface 220; an isolation layer 310 located in the first trench 300; a second trench 400 located in the isolation layer 310, wherein a distance from the bottom of the second trench 400 to the bottom of the first trench 300 is greater than 0; a conductive layer 500 located in the second trench 400; a second isolation layer 2021 located in the isolation region 202; a photo-electrically doped region 2011 located in the photosensitive region 201; the device layer 230 includes a transfer gate structure 232 and an interconnect structure 231, wherein the transfer gate structure 232 is located on the second surface 220, and the photodoping region 2011 and the isolation region 202 are respectively located on two sides of the transfer gate structure 232; and a carrier substrate 240 located on the surface of the device layer 230.
Correspondingly, the invention also provides a working method of the image sensor, which comprises the following steps: providing a graphic sensor as shown in FIG. 8; a negative bias voltage with respect to the potential of the substrate 200 is applied to the conductive layer 500.
In this embodiment, the negative bias voltage ranges from-0.5 volts to-0.3 volts.
In this embodiment, after receiving the optical signal, the photosensitive region 201 converts the optical signal into an electric charge through the photodiode, an equivalent capacitance structure is formed between the conductive layer 500, the first isolation layer 310 and the substrate 200, when a negative bias is applied to the conductive layer 500, an additional electric field force can be generated to the substrate 200, the electric field force accelerates the electric charge to be pushed to the surface of the substrate, and the electric charge is pulled out of the substrate 200 through the transfer channel and the floating diffusion region 203, so that the rate of electric charge generation and the speed of electric charge discharge are balanced, thereby reducing the problem of electric charge residue and improving the usability of the formed image sensor.
In this embodiment, the negative bias ranges from-0.5 v to-0.3 v, and when the negative bias is less than-0.5 v, it cannot generate enough electric field force to push the charges to the substrate surface close to the transfer channel, so that the charges cannot be pulled out of the substrate through the transfer channel and the floating diffusion region; when the negative bias voltage is greater than-0.3 v, the applied voltage is too large, which easily causes the breakdown of the first isolation layer, and causes the electrical crosstalk and optical crosstalk between the photoelectric doped regions, thereby affecting the performance of the formed image sensor.
Although the present invention is disclosed above, the present invention is not limited thereto. Various changes and modifications may be effected therein by one skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.

Claims (13)

1. A method of forming an image sensor, comprising:
providing a substrate, wherein the substrate is provided with a first surface and a second surface which are opposite to each other, and the substrate comprises a photosensitive area and an isolation area which surrounds the photosensitive area;
forming a device layer on the second surface, the device layer comprising: the transmission gate structure is positioned on the second surface;
forming a photoelectric doped region in the photosensitive region;
forming a floating diffusion region in the substrate, wherein the floating diffusion region is exposed out of the second surface, and the floating diffusion region and the photoelectric doped region are positioned on two sides of the transmission gate structure;
after the device layer is formed, etching is carried out from the first surface, and a first groove is formed in the substrate and is located in the isolation region, the width of the bottom of the first groove is 0.1-0.2 micrometer, and the width of the top of the first groove is 0.1-0.8 micrometer;
forming a first isolation layer in the first trench;
forming a second groove in the first isolation layer, wherein the distance from the bottom of the second groove to the bottom of the first groove is 0.01-0.2 microns;
and filling a conducting layer in the second groove, wherein the conducting layer is used for applying negative bias relative to the substrate potential.
2. The method of claim 1, wherein the first trench has a depth of 0.1 to 2 μm.
3. The method of claim 1, wherein the second trench has a depth of 0.09 to 1.8 microns and a width of 0.05 to 0.4 microns.
4. The method of claim 1, wherein the sidewall of the first trench forms an angle with the first surface in a range greater than 0 ° and less than or equal to 90 °.
5. The method of forming an image sensor of claim 1, further comprising: and forming a second isolation layer in the isolation region, wherein the second isolation layer is exposed out of the second surface.
6. The method of claim 1, wherein the material of the first spacer layer comprises silicon oxide, silicon nitride, or silicon oxynitride.
7. The method of forming an image sensor as claimed in claim 1, further comprising, before forming the first trench: and thinning the first surface.
8. The method of claim 7, wherein a carrier substrate is secured to the surface of the device layer prior to thinning.
9. The method of forming an image sensor of claim 1, further comprising: forming a barrier layer in the second trench before forming the conductive layer; the conductive layer is located on the surface of the barrier layer.
10. The method of claim 9, wherein the material of the barrier layer comprises one or more of titanium and titanium nitride.
11. The method of forming an image sensor as claimed in claim 10, wherein the method of forming the barrier layer and the conductive layer comprises: forming a barrier film on the first surface, the surface of the first isolation layer, and the side wall and the bottom surface of the second trench; forming a conductive film filling the second trench on the surface of the barrier film; and flattening the conductive film until the first surface is exposed, and forming the barrier layer and the conductive layer.
12. An image sensor formed by the method of any of claims 1 to 11, comprising:
the substrate comprises a first surface and a second surface, and the substrate comprises a photosensitive area and an isolation area surrounding the photosensitive area;
a device layer on the second surface, the device layer comprising: the transmission gate structure is positioned on the second surface;
a photoelectric doped region located in the photosensitive region;
the second surface exposes the floating diffusion region, and the floating diffusion region and the photoelectric doped region are positioned on two sides of the transmission grid structure;
the first groove is positioned in the isolation region and extends from the first surface to the second surface, the width of the bottom of the first groove is 0.1-0.2 micrometers, and the width of the top of the first groove is 0.1-0.8 micrometers;
a first isolation layer located in the first trench;
the second groove is positioned in the first isolation layer, and the distance from the bottom of the second groove to the bottom of the first groove is 0.01-0.2 microns;
a conductive layer within the second trench, the conductive layer for applying a negative bias with respect to the substrate potential.
13. The image sensor of claim 12, wherein the negative bias voltage is in a range of-0.5 volts to-0.3 volts.
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