Stacked back-illuminated anti-radiation pixel reinforcing structure and preparation method thereof

Abstract

The invention discloses a stacked back-illuminated anti-radiation pixel reinforcing structure and a preparation method thereof. The preparation method comprises the following steps: taking a semiconductor substrate with an epitaxial layer; an ST I structure, an ST I isolation well injection region and an N-type PD injection region are formed on the epitaxial layer, the ST I isolation well injection region is located on the periphery of the N-type PD injection region, and the ST I structure is located in the ST I isolation well injection region; forming a buried trench epitaxial region above the middle region of the epitaxial layer; forming a P-type clamping layer injection region around the buried trench epitaxial region on the epitaxial layer; forming a transmission tube channel isolation injection region on the outer side of the buried channel epitaxial region through injection; forming an FD region above the buried trench epitaxial region; forming a gate stack structure and a gate above the epitaxial layer; an FD contact structure is formed over the FD region. According to the invention, the buried channel structure is introduced into the transmission tube channel, and the electron barrier formed in the isolation injection region of the transmission tube channel is combined, so that the separation of the photoelectron transmission channel and the gate oxide layer is realized, and the anti-radiation capability of the pixel is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of image sensors, and in particular to a stacked back-illuminated anti-radiation pixel reinforcement structure and a preparation method thereof. Background Art

[0002] The pixel unit (abbreviated as pixel) plays a pivotal role in the entire sensor system. It is responsible for converting optical image signals into electrical signals. It is the unit that truly realizes "sensing" and is also the core component of the image sensor. Therefore, in-depth and comprehensive research based on the pixel unit is of great significance and value to the development of image sensors.

[0003] With the urgent need for human beings to explore unknown areas of space, CIS has also been applied in the field of aerospace technology. Artificial satellites are the core of aerospace technology, and image sensors are the "eyes" of artificial satellites. Image sensors play an important role in deep space exploration and surface environment monitoring. However, the aerospace environment is more complex than the ground environment. Space is full of various radiations. Space radiation can easily damage the performance of semiconductor devices, causing microelectronic systems to have varying degrees of failure, resulting in their inability to work properly. For CIS, a sophisticated microelectronic system, radiation will cause damage to its pixel devices, resulting in a significant decrease in imaging quality. Therefore, the exploration of CIS anti-irradiation pixel reinforcement design is of great practical significance.

[0004] When the pixel is in a radiation environment, the incident particles interact with the atoms in the material and transfer part of the energy to the electrons outside the nucleus. When the energy obtained by the electron is greater than the binding energy, it can break away from the bondage of the nucleus to form a free electron and generate a positive ion (hole) at the original position, which eventually changes the electrical properties of the material. In silicon dioxide, only a small number of electron-hole pairs are recombined, and most of the rest are separated by the electric field loaded on the oxide layer. Due to the high electron mobility, the time to drift out of silicon dioxide at room temperature is only picoseconds, while the escape time of holes can reach seconds. Therefore, the main effect of radiation is caused by the capture of non-equilibrium holes by traps to form positive charges on the oxide layer. Holes slowly transition to the silicon / silicon dioxide interface through the localized state in silicon dioxide, and are captured by the interface state defect center to form a fixed positive charge on the oxide layer, causing changes in the local energy band and electrical properties of the semiconductor.

[0005] Especially in stacked small-size PPD pixels, the vertical transmission channel adds an additional radiation damage mechanism, which not only complicates the radiation damage mechanism of PPD pixels, but also has a more serious impact on pixel characteristics. In the conventional back-illuminated pixel structure, there is an epitaxial layer or well under the gate of the transmission tube. After the photodiode in the pixel completes the collection of photogenerated electrons after exposure, the transmission tube is turned on, and the photoelectrons are transported along the channel at the gate oxide layer / semiconductor interface of the transmission tube to the FD area to wait for signal readout. Under the influence of the irradiation effect, the defects generated inside the gate oxide layer and at the gate oxide layer / semiconductor interface will be close to or in the transport channel of the photoelectrons, or in the transport path, causing recombination of the photoelectrons in the transport process, seriously affecting the conversion gain of the pixel and limiting the photoelectric conversion efficiency. How to effectively improve the radiation resistance while ensuring the performance of the pixel is still a hot spot and difficulty in current research. Summary of the invention

[0006] In view of the above-mentioned deficiencies in the prior art, the technical problem to be solved by the present invention is to provide a stacked back-illuminated anti-radiation pixel reinforcement structure and a preparation method thereof, which can improve the anti-radiation performance of the pixel.

[0007] In order to solve the above technical problems, a technical solution adopted by the present invention is: to provide a method for preparing a stacked back-illuminated anti-irradiation pixel reinforcement structure, comprising the following steps:

[0008] Taking a semiconductor substrate having an epitaxial layer;

[0009] forming an STI structure, an STI isolation well injection region and an N-type PD injection region in the epitaxial layer, wherein the STI isolation well injection region is located at the periphery of the N-type PD injection region, and the STI structure is located in the STI isolation well injection region;

[0010] forming a buried trench epitaxial region above the middle region of the epitaxial layer;

[0011] A P-type clamping layer injection region is formed in the epitaxial layer around the buried channel epitaxial region, and an outer end of the P-type clamping layer injection region is connected to the STI structure;

[0012] Forming a transmission pipe channel isolation implantation region by implantation outside the buried channel epitaxial region;

[0013] forming an FD region above the buried channel epitaxial region;

[0014] forming a gate stack structure and a gate on the epitaxial layer;

[0015] An FD contact structure is formed over the FD region.

[0016] Furthermore, after the step of forming the FD contact structure above the FD region, the method further includes the following step: depositing a passivation layer on the surface of the pixel.

[0017] Furthermore, the method of forming the STI structure, the STI isolation well injection region and the N-type PD injection region in the epitaxial layer includes:

[0018] forming an N-type PD implantation region in the epitaxial layer by ion implantation;

[0019] Etching a shallow groove at the periphery of the N-type PD implantation region;

[0020] Filling the shallow groove with silicon dioxide to form an STI structure;

[0021] An isolation well implantation is performed on the epitaxial layer to form an STI isolation well implantation region surrounding the STI structure.

[0022] Furthermore, the step of forming a buried trench epitaxial region above the middle region of the epitaxial layer includes the following sub-steps:

[0023] Performing in-situ doping epitaxial growth above the N-type PD implantation region to form a buried channel epitaxial layer;

[0024] The buried channel epitaxial layer is etched to form a buried channel epitaxial region in the shape of a nano-column.

[0025] Furthermore, the method of forming the transmission pipe channel isolation implantation region by implantation outside the buried channel epitaxial region is:

[0026] Boron ions were set as implanted ions in the ion implantation equipment; the implantation energy was set to 5-7 keV and the implantation dose was set to 1×10 12 ~3×10 12 cm -2 , the tilt angle is set to 30°~40°; the rotation angle and the number of rotations are controlled to perform ion implantation to ensure that the transmission pipe channel isolation implantation area is evenly distributed around the buried channel epitaxial area, the rotation angle is 90°, and the number of rotations is 4 times; after the implantation is completed, annealing is performed to activate the implanted ions.

[0027] Further, the gate stack structure includes a gate oxide layer and an FD electrode isolation layer;

[0028] The step of forming a gate stack structure and a gate on the epitaxial layer includes the following sub-steps:

[0029] isotropically depositing a gate oxide layer on the surface of the transmission pipe channel isolation implantation region and above the epitaxial layer;

[0030] Depositing an FD electrode isolation layer on the surface of the gate oxide layer and etching the FD electrode isolation layer to leave a portion covering the upper surface of the gate oxide layer;

[0031] Polysilicon is deposited on the surface of the gate oxide layer and a gate is formed by selective etching, and the upper surface of the gate is flush with the upper surface of the FD electrode isolation layer.

[0032] Furthermore, the step of forming an FD contact structure above the FD region includes the following sub-steps:

[0033] A contact hole is formed above the FD region, wherein the contact hole penetrates the gate oxide layer and the FD electrode isolation layer;

[0034] Metal is deposited in the contact hole to form an FD contact structure.

[0035] Further, the FD contact structure is configured as a T-shaped structure, the vertical portion of the FD contact structure is within the contact hole, and the horizontal portion of the FD contact structure is above the FD electrode isolation layer.

[0036] In order to solve the above technical problems, another technical solution adopted by the present invention is: to provide a stacked back-illuminated anti-irradiation pixel reinforcement structure, including an epitaxial layer, an N-type PD injection region formed in the epitaxial layer, an STI isolation well injection region located outside the N-type PD injection region, an STI structure located in the STI isolation well injection region, a buried channel epitaxial region located above the middle area of ​​the epitaxial layer, a P-type clamping layer injection region arranged in the epitaxial layer around the buried channel epitaxial region, a transmission pipe channel isolation injection region located outside the buried channel epitaxial region, an FD region located above the buried channel epitaxial region, a gate stack structure and a gate located above the epitaxial layer, and an FD contact structure located above the FD region; the STI isolation well injection region is formed by several boron ion implantations, the outer end of the P-type clamping layer injection region is connected to the STI structure, the gate stack structure is arranged on the surface of the transmission pipe channel isolation injection region, and the gate stack structure is located above the epitaxial region, the gate is located on the surface of the gate stack structure, and the FD contact structure is located above the FD region.

[0037] Furthermore, the epitaxial layer is of P type with a doping concentration of 1×10 15 ~5×10 15 cm -3 , thickness is 2 to 8 μm;

[0038] The STI isolation well injection region is formed by three boron ion injections, with the first injection energy of 140-160 keV and the injection dose of 1×10 13 ~2×10 13cm -2 The second injection energy is 290-310 keV, and the injection dose is 1×10 12 ~3×10 12 cm -2 The third injection energy is 70-90 keV and the injection dose is 1×10 12 ~3×10 12 cm -2 ;

[0039] The dopant of the N-type PD implantation region is arsenic, with an implantation energy of 60-70 keV and an implantation dose of 4×10 12 ~6×10 12 cm -2 ;

[0040] The buried channel epitaxial region is in-situ doped with boron at a doping concentration of 1×10 15 ~1×10 16 cm -3 , thickness is 0.1~2μm;

[0041] The dopant in the P-type clamping layer injection region is boron ions, with an injection energy of 5-7 keV and an injection dose of 8×10 12 ~1×10 13 cm -2 ;

[0042] The transmission pipe channel isolation injection region is formed by injecting boron ions in a tilted rotation manner, with an injection energy of 5 to 7 keV and an injection dose of 1×10 12 ~3×10 12 cm -2 ;

[0043] The dopant in the FD region is phosphorus, with a doping concentration of 1×10 18 ~1×10 19 cm -3 .

[0044] The stacked back-illuminated radiation-resistant pixel reinforcement structure and the preparation method thereof of the present invention have at least the following beneficial effects: the present invention successfully realizes the separation of the photoelectron transmission channel and the gate oxide layer / semiconductor interface by introducing a buried channel structure in the transmission pipe channel and combining the electron potential barrier formed by the transmission pipe channel isolation injection region, thereby reducing the composite influence of the radiation effect inside the gate oxide layer and the defects introduced by the gate oxide layer / semiconductor interface on the photoelectron transmission, which not only optimizes the transmission path of the photoelectrons, but also significantly improves the radiation resistance of the pixel; in the vertical structure of the stacking process, the buried channel outside is The extended area is etched into a nano-column structure, and the use of a ring gate structure enhances the gate's control over the channel, so that when a low level is applied to the transmission tube gate, the buried channel epitaxial area can be more effectively shut down, thereby reducing the dark current of the pixel and improving the signal-to-noise ratio and overall performance of the image sensor; through the design of the buried channel structure, the transmission path of photoelectrons from the photodiode injection area to the FD epitaxial area is optimized. The improvement of this path not only improves the transmission efficiency of photoelectrons, but also reduces energy loss and noise interference during the transmission process, further improving the photoelectric conversion efficiency and image quality of the image sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0046] Figure 1 The present invention is a flow chart of an embodiment of a method for preparing a stacked back-illuminated anti-irradiation pixel reinforcement structure.

[0047] Figure 2 for Figure 1 Schematic diagram of the cross-section of the structure obtained in step S2.

[0048] Figure 3 for Figure 1 Flow chart of step S3 in FIG.

[0049] Figure 4 for Figure 1 Schematic diagram of the cross section of the structure obtained in step S3.

[0050] Figure 5 for Figure 1 Schematic diagram of the cross section of the structure obtained in step S4.

[0051] Figure 6 for Figure 1 Schematic diagram of the cross-section of the structure obtained in step S5.

[0052] Figure 7 for Figure 1 Schematic diagram of the cross-section of the structure obtained in step S6.

[0053] Figure 8 for Figure 1 Flow chart of step S7 in FIG.

[0054] Fig. 9 for Figure 1 Schematic diagram of the cross-section of the structure obtained in step S6.

[0055] Fig.10 for Figure 1 Flowchart of step S8 in FIG.

[0056] Fig.11 for Figure 1 Schematic diagram of the cross-section of the structure obtained in step S8.

[0057] Fig.12 for Figure 1 Schematic diagram of the cross-section of the structure obtained in step S9.

[0058] The meanings of the symbols in the accompanying drawings are:

[0059] Epitaxial layer 10, STI structure 11, STI isolation well implantation region 12, N-type PD implantation region 13, buried channel epitaxial region 14, P-type clamping layer implantation region 15, transmission pipe channel isolation implantation region 16, FD region 17, gate oxide layer 18, FD electrode isolation layer 19, gate 20, FD contact structure 21, passivation layer 22. DETAILED DESCRIPTION

[0060] The present invention will be further described below in conjunction with the accompanying drawings.

[0061] See also Figure 1 , is a flow chart of an embodiment of a method for preparing a stacked back-illuminated anti-radiation pixel reinforcement structure of the present invention. This embodiment specifically includes the following steps:

[0062] S1. Take a semiconductor substrate having an epitaxial layer 10.

[0063] Specifically, the epitaxial layer 10 can be formed by epitaxial growth on a semiconductor substrate, or the semiconductor substrate of the specific epitaxial layer 10 can be directly taken, and the semiconductor substrate can be such as a silicon substrate, a silicon germanium substrate, a silicon germanium carbon substrate, a silicon carbide substrate, a gallium arsenide substrate, an indium arsenide substrate, an indium phosphide substrate or other III / V semiconductor substrates or II / VI semiconductor substrates. Therefore, the type of semiconductor substrate does not limit the protection scope of this application.

[0064] S2 , forming an STI structure 11 , an STI isolation well implantation region 12 and an N-type PD implantation region 13 in the epitaxial layer 10 .

[0065] See also Figure 2Specifically, the STI isolation well implantation region 12 is located at the periphery of the N-type PD implantation region 13, and the STI structure 11 is located in the STI isolation well implantation region 12. Specifically, firstly, the N-type PD implantation region 13 is formed in the epitaxial layer 10 by ion implantation, the dopant may be arsenic, the implantation energy may be 60-70 keV, and the implantation dose may be 4×10 12 ~6×10 12 cm -2 Secondly, a shallow groove is formed by etching the periphery of the N-type PD implantation region 13, and the shallow groove is filled with silicon dioxide to form an STI structure 11. Thirdly, an isolation well implantation is performed on the epitaxial layer 10 to form an STI isolation well implantation region 12 surrounding the STI structure 11. The STI isolation well implantation region 12 is formed by several boron ion implantations. In this embodiment, the STI isolation well implantation region 12 is formed by three boron ion implantations, with the first implantation energy of 140-160 keV and the implantation dose of 1×10 13 ~2×10 13 cm -2 The second injection energy is 290-310 keV, and the injection dose is 1×10 12 ~3×10 12 cm -2 The third injection energy is 70-90 keV and the injection dose is 1×10 12 ~3×10 12 cm -2 Finally, after the implantation is completed, annealing is performed to activate the implanted ions. The annealing temperature is set to 1050° C. and the annealing time is 10 seconds. It should be understood that the specific formation process of the STI structure 11, the STI isolation well implantation region 12 and the N-type PD implantation region 13 is not limited to the above-mentioned embodiment.

[0066] S3 , forming a buried channel epitaxial region 14 above the middle region of the epitaxial layer 10 .

[0067] See also Figure 3 , this step S3 includes the following sub-steps:

[0068] S31 , performing in-situ doping epitaxial growth above the N-type PD implantation region 13 to form a buried channel epitaxial layer.

[0069] Specifically, in this embodiment, the buried channel epitaxial layer is in-situ doped with boron at a doping concentration of 1×10 15 ~1×10 16 cm -3This concentration range is chosen to ensure sufficient conductivity while avoiding excessive doping concentration that leads to a decrease in crystal quality and an increase in defects; the thickness is 0.1 to 2 μm, and this thickness is chosen to ensure that the device has sufficient channel conductivity and good radiation resistance.

[0070] S32, etching the buried channel epitaxial layer to form a buried channel epitaxial region 14 in the shape of a nano-column.

[0071] See also Figure 4 After forming the buried channel epitaxial layer, it is processed into a nano-column shape by an etching process to form a buried channel epitaxial region 14. The design of the nano-column shape can improve the channel conductivity of the device, while reducing the capacitance effect and improving the response speed and sensitivity of the device.

[0072] S4 , forming a P-type clamping layer implantation region 15 in the epitaxial layer 10 around the buried channel epitaxial region 14 .

[0073] See also Figure 5 The outer end of the P-type clamping layer injection region 15 is connected to the STI structure 11. Specifically, the dopant of the P-type clamping layer injection region 15 can be boron ions, the injection energy can be controlled at 5-7 keV, and the injection dose can be controlled at 8×10 12 ~1×10 13 cm -2 .

[0074] S5 , forming a transmission pipe channel isolation implantation region 16 on the outer side of the buried channel epitaxial region 14 by implantation.

[0075] See also Figure 6 The transmission tube channel isolation implantation region 16 is arranged around the buried channel epitaxial region 14 and above the epitaxial layer 10 to isolate the channel region of the transmission tube, which effectively reinforces the transmission tube and improves the radiation resistance of the pixel. Specifically, boron ions are set as implantation ions in the ion implantation equipment; the implantation energy can be set to 5-7 keV, and the implantation dose can be 1×10 12 ~3×10 12 cm -2 , the tilt angle is generally set to 30° to 40°; the boron ion implantation is performed by controlling the rotation angle and the number of rotations to ensure that the transmission pipe channel isolation implantation region 16 is evenly distributed around the buried channel epitaxial region 14. In this embodiment, the rotation angle is 90° and the number of rotations is 4 times. It should be understood that the formation process of the transmission pipe channel isolation implantation region 16 is not limited to the above-mentioned embodiment. For example, in some embodiments, the rotation angle is 180° and the number of rotations is 2 times.

[0076] S6 , forming an FD region 17 above the buried-channel epitaxial region 14 .

[0077] Please see Figure 7 The FD region 17 is formed above the buried channel epitaxial region 14 and is used to collect the photogenerated charges converted by the photodiode and transfer them to the subsequent circuit for processing. Specifically, in this embodiment, the dopant of the FD region 17 is phosphorus, and the doping concentration is controlled to be 1×10 18 ~1×10 19 cm -3 within the range.

[0078] S7 . Form a gate stack structure and a gate 20 above the epitaxial layer 10 .

[0079] Specifically, the gate stack structure includes a gate oxide layer 18 and an FD electrode isolation layer 19, which are used to protect the gate 20 and provide good point contact. The gate 20 is a key structure for controlling the switching of the device.

[0080] See also Figure 8 , this step S7 includes the following sub-steps:

[0081] S71, depositing a gate oxide layer 18.

[0082] For details, please refer to Fig. 9 A gate oxide layer 18 is isotropically deposited on the surface of the transmission pipe channel isolation implantation region 16 and on the epitaxial layer 10. In this embodiment, the gate oxide layer 18 can be selected from silicon dioxide, and the thickness can be controlled within the range of 7 to 10 nm.

[0083] S72, depositing the FD electrode isolation layer 19.

[0084] Specifically, an FD electrode isolation layer 19 is deposited on the surface of the gate oxide layer 18 and the FD electrode isolation layer 19 is etched to leave a portion covering the upper surface of the gate oxide layer 18. In this embodiment, the FD electrode isolation layer can be selected as silicon nitride, and the thickness of silicon nitride can be controlled within the range of 30 to 50 nm.

[0085] S73 , forming the gate 20 .

[0086] Specifically, polysilicon is deposited on the surface of the gate oxide layer 18 and the gate 20 is formed by selective etching. The upper surface of the gate 20 is flush with the upper surface of the FD electrode isolation layer 19. The thickness of the gate 20 can be flexibly determined according to the specific process node.

[0087] S8 , forming an FD contact structure 21 above the FD region 17 .

[0088] See also Fig.10, this step S8 includes the following sub-steps:

[0089] S81 , opening a contact hole above the FD region 17 .

[0090] For details, please refer to Fig.11 , a contact hole is opened above the FD region 17, and the contact hole penetrates the gate oxide layer 18 and the.

[0091] S82 , depositing metal in the contact hole to form an FD contact structure 21 .

[0092] Specifically, metal is deposited in the contact hole to form an FD contact structure 21, which is used to establish an electrical connection with the FD region 17 to transfer the photogenerated charges to the subsequent circuit. In order to increase the contact area, improve the electrical contact performance, reduce the capacitance effect, and improve the response speed and sensitivity of the device, in this embodiment, the FD contact structure 21 is set to a T-shaped structure, the vertical part of the FD contact structure 21 is in the contact hole, and the horizontal part of the FD contact structure 21 is above the FD electrode isolation layer 19.

[0093] S9. Deposit a passivation layer 22 on the surface of the pixel.

[0094] In order to protect the device from damage by environmental factors, as a preferred embodiment, the present embodiment has a step of depositing a passivation layer 22. For details, please refer to Fig.12 The passivation layer 22 is deposited on the surface of the pixel to protect the device from environmental damage, such as oxidation, corrosion, etc. In this embodiment, the material of the passivation layer 22 can be a combination of silicon nitride and silicon oxide, and the thickness can be controlled within the range of 0.5-1 μm.

[0095] See also Fig.12The present invention also discloses a stacked back-illuminated anti-radiation pixel reinforcement structure, which is made by the above method, and includes an epitaxial layer 10, an N-type PD injection region 13 formed in the epitaxial layer 10, an STI isolation well injection region 12 located outside the N-type PD injection region 13, an STI structure 11 located in the STI isolation well injection region 12, a buried channel epitaxial region 14 located above the middle region of the epitaxial layer 10, a P-type clamping layer injection region 15 arranged in the epitaxial layer 10 around the buried channel epitaxial region 14, a transmission pipe channel isolation injection region 16 located outside the buried channel epitaxial region 14, an FD region 17 located above the buried channel epitaxial region 14, a gate stack structure and a gate 20 located above the epitaxial layer 10, and an FD contact structure 21 located above the FD region 17; the STI isolation well injection region 12 is formed by several boron ion implantations, the outer end of the P-type clamping layer injection region 15 is connected to the STI isolation well injection region 12, and the gate 20 is connected to the gate 20. I structure 11 is connected, the gate stack structure is arranged on the surface of the transmission pipe channel isolation injection area 16, and the gate stack structure is located above the epitaxial area, the gate 20 is located on the surface of the gate stack structure, and the FD contact structure 21 is located above the FD area 17.

[0096] In this embodiment, the epitaxial layer 10 is of P type with a doping concentration of 1×10 15 ~5×10 15 cm -3 , with a thickness of 2 to 8 μm; the ST I isolation well injection region 12 is formed by three boron ion injections, the first injection energy is 140 to 160 keV, the injection dose is 1×10 13 ~2×10 13 cm -2 The second injection energy is 290-310 keV, and the injection dose is 1×10 12 ~3×10 12 cm -2 The third injection energy is 70-90 keV and the injection dose is 1×10 12 ~3×10 12 cm -2 The dopant of the N-type PD implantation region 13 is arsenic, the implantation energy is 60-70 keV, and the implantation dose is 4×10 12 ~6×10 12 cm -2 The buried channel epitaxial region 14 is in-situ doped with boron at a doping concentration of 1×10 15 ~1×10 16 cm -3 The dopant of the P-type clamping layer injection region 15 is boron ions, with an injection energy of 5 to 7 keV and an injection dose of 8×10 12 ~1×1013 cm -2 The transmission pipe channel isolation injection region 16 is formed by injecting boron ions in a tilted rotation manner, with an injection energy of 5 to 7 keV and an injection dose of 1×10 12 ~3×10 12 cm -2 The dopant of the FD region 17 is phosphorus, and the doping concentration is 1×10 18 ~1×10 19 cm -3 .

[0097] The present invention successfully realizes the separation of the photoelectron transmission channel and the gate oxide layer / semiconductor interface by introducing a buried channel structure into the transmission tube channel and combining the electron potential barrier formed by the transmission tube channel isolation injection region, thereby reducing the composite influence of the radiation effect inside the gate oxide layer and the defects introduced by the gate oxide layer / semiconductor interface on the photoelectron transmission, not only optimizing the transmission path of the photoelectrons, but also significantly improving the radiation resistance of the pixel; in the longitudinal structure of the stacking process, the present invention etches the buried channel epitaxial region into a nano-column structure, and cooperates with the use of the ring gate structure to enhance the control ability of the gate over the channel, so that when a low level is applied to the transmission tube gate, the buried channel epitaxial region can be more effectively turned off, thereby reducing the dark current of the pixel and improving the signal-to-noise ratio and overall performance of the image sensor; through the design of the buried channel structure, the transmission path of the photoelectrons from the photodiode injection region to the FD epitaxial region is optimized, and the improvement of this path not only improves the transmission efficiency of the photoelectrons, but also reduces the energy loss and noise interference in the transmission process, further improving the photoelectric conversion efficiency and image quality of the image sensor.

Claims

1. A method for preparing a stacked back-illuminated anti-radiation pixel reinforcement structure, characterized in that: The following steps are involved: Taking a semiconductor substrate having an epitaxial layer; forming an STI structure, an STI isolation well injection region and an N-type PD injection region in the epitaxial layer, wherein the STI isolation well injection region is located at the periphery of the N-type PD injection region, and the STI structure is located in the STI isolation well injection region; forming a buried trench epitaxial region above the middle region of the epitaxial layer; A P-type clamping layer injection region is formed in the epitaxial layer around the buried channel epitaxial region, and an outer end of the P-type clamping layer injection region is connected to the STI structure; Forming a transmission pipe channel isolation implantation region by implantation outside the buried channel epitaxial region; forming an FD region above the buried channel epitaxial region; forming a gate stack structure and a gate on the epitaxial layer; An FD contact structure is formed over the FD region.

2. The method for preparing the stacked back-illuminated anti-irradiation pixel reinforcement structure according to claim 1, characterized in that: After the step of forming the FD contact structure above the FD region, the method further includes the following step: depositing a passivation layer on the surface of the pixel.

3. The method for preparing the stacked back-illuminated anti-irradiation pixel reinforcement structure according to claim 1, characterized in that: The method for forming an STI structure, an STI isolation well implantation region and an N-type PD implantation region in an epitaxial layer comprises: forming an N-type PD implantation region in the epitaxial layer by ion implantation; Etching a shallow groove at the periphery of the N-type PD implantation region; Filling the shallow trench with silicon dioxide to form an STI structure; An isolation well implantation is performed on the epitaxial layer to form an STI isolation well implantation region surrounding the STI structure.

4. The method for preparing the stacked back-illuminated anti-irradiation pixel reinforcement structure according to claim 1, characterized in that: The step of forming a buried trench epitaxial region above the middle region of the epitaxial layer includes the following sub-steps: Performing in-situ doping epitaxial growth above the N-type PD implantation region to form a buried channel epitaxial layer; The buried channel epitaxial layer is etched to form a buried channel epitaxial region in the shape of a nano-column.

5. The method for preparing the stacked back-illuminated anti-irradiation pixel reinforcement structure according to claim 1, characterized in that: The method for forming a transmission pipe channel isolation implantation region by implantation outside the buried channel epitaxial region is: Boron ions were set as implanted ions in the ion implantation equipment; the implantation energy was set to 5-7 keV and the implantation dose was set to 1×10 12 ~3×10 12 cm -2 , the tilt angle is set to 30°~40°; the rotation angle and the number of rotations are controlled to perform ion implantation to ensure that the transmission pipe channel isolation implantation area is evenly distributed around the buried channel epitaxial area, the rotation angle is 90°, and the number of rotations is 4 times; after the implantation is completed, annealing is performed to activate the implanted ions.

6. The method for preparing the stacked back-illuminated anti-irradiation pixel reinforcement structure according to claim 1, characterized in that: The gate stack structure includes a gate oxide layer and an FD electrode isolation layer; The step of forming a gate stack structure and a gate on the epitaxial layer includes the following sub-steps: isotropically depositing a gate oxide layer on the surface of the transmission pipe channel isolation implantation region and above the epitaxial layer; Depositing an FD electrode isolation layer on the surface of the gate oxide layer and etching the FD electrode isolation layer to leave a portion covering the upper surface of the gate oxide layer; Polysilicon is deposited on the surface of the gate oxide layer and a gate is formed by selective etching, and the upper surface of the gate is flush with the upper surface of the FD electrode isolation layer.

7. The method for preparing the stacked back-illuminated anti-irradiation pixel reinforcement structure according to claim 1, characterized in that: The step of forming an FD contact structure above the FD region includes the following sub-steps: A contact hole is formed above the FD region, wherein the contact hole penetrates the gate oxide layer and the FD electrode isolation layer; Metal is deposited in the contact hole to form an FD contact structure.

8. The method for preparing the stacked back-illuminated anti-irradiation pixel reinforcement structure according to claim 7, characterized in that: The FD contact structure is configured as a T-shaped structure, a vertical portion of the FD contact structure is within the contact hole, and a horizontal portion of the FD contact structure is above the FD electrode isolation layer.

9. A stacked back-illuminated anti-radiation pixel reinforcement structure, characterized in that: It includes an epitaxial layer, an N-type PD injection region formed in the epitaxial layer, an STI isolation well injection region located outside the N-type PD injection region, an STI structure located in the STI isolation well injection region, a buried channel epitaxial region located above the middle region of the epitaxial layer, a P-type clamping layer injection region arranged in the epitaxial layer around the buried channel epitaxial region, a transmission pipe channel isolation injection region located outside the buried channel epitaxial region, an FD region located above the buried channel epitaxial region, a gate stack structure and a gate located above the epitaxial layer, and an FD contact structure located above the FD region; the STI isolation well injection region is formed by several boron ion implantations, the outer end of the P-type clamping layer injection region is connected to the STI structure, the gate stack structure is arranged on the surface of the transmission pipe channel isolation injection region, and the gate stack structure is located above the epitaxial region, the gate is located on the surface of the gate stack structure, and the FD contact structure is located above the FD region.

10. The stacked back-illuminated anti-radiation pixel reinforcement structure according to claim 9, characterized in that: The epitaxial layer is of P type with a doping concentration of 1×10 15 ~5×10 15 cm -3 , thickness is 2 to 8 μm; The STI isolation well injection region is formed by three boron ion injections, with the first injection energy of 140-160 keV and the injection dose of 1×10 13 ~2×10 13 cm -2 The second injection energy is 290-310 keV, and the injection dose is 1×10 12 ~3×10 12 cm -2 The third injection energy is 70-90 keV and the injection dose is 1×10 12 ~3×10 12 cm -2 ; The dopant of the N-type PD implantation region is arsenic, with an implantation energy of 60-70 keV and an implantation dose of 4×10 12 ~6×10 12 cm -2 ; The buried channel epitaxial region is in-situ doped with boron at a doping concentration of 1×10 15 ~1×10 16 cm -3 , thickness is 0.1~2μm; The dopant in the P-type clamping layer injection region is boron ions, with an injection energy of 5-7 keV and an injection dose of 8×10 12 ~1×10 13 cm -2 ; The transmission pipe channel isolation injection region is formed by injecting boron ions in a tilted rotation manner, with an injection energy of 5 to 7 keV and an injection dose of 1×10 12 ~3×10 12 cm -2 ; The dopant in the FD region is phosphorus, with a doping concentration of 1×10 18 ~1×10 19 cm -3 .

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