Self-isolation type image sensing structure, sensor and preparation method

Abstract

The invention discloses a self-isolation type image sensing structure, a sensor and a preparation method, and belongs to the field of semiconductors, the self-isolation type image sensing structure is characterized in that a shallow trench isolation structure is exposed after the back surface of a substrate is thinned, then a first semiconductor layer is extended on the back surface of the substrate, and a first isolation structure is prepared in the first semiconductor layer; sequentially depositing a second semiconductor material layer and a metal grating material layer on the first semiconductor layer; sequentially etching the metal grating material layer and the second semiconductor material layer to form a plurality of metal grating structures distributed at intervals and corresponding self-isolation structures; extending a plurality of photosensitive layers in the photosensitive region groove between the adjacent self-isolation structures to form a photosensitive region; and then activating, preparing a filter layer and the like are carried out to obtain a complete back-illuminated image sensor. The self-isolation photodiode is obtained by changing the structural distribution of the photodiode, unexpectedly, the problem that the substrate is damaged by doping is solved, meanwhile, the crosstalk effect is greatly reduced, and the performance of the image sensor is improved.

Description

Technical Field

[0001] The present invention belongs to the field of semiconductors and relates to a technology for preparing an image sensor, in particular to a self-isolating image sensing structure, a sensor and a preparation method thereof. Background Art

[0002] Image sensors are photoelectric conversion devices widely used in consumer electronics, security monitoring, automotive electronics, machine vision, and other fields. Backside illuminated (BSI) image sensors offer advantages such as higher sensitivity, improved wiring layout, and high-speed recording, making them commonly used in applications requiring high pixel performance.

[0003] However, in traditional BSI front-end processes, high-energy ion implantation (IMP) is required to create the diode structure and photosensitive region, which can damage the substrate surface. Uneven ion implantation can also lead to signal crosstalk between different pixels, hindering further improvement in BSI image sensor performance. Therefore, further research and development of new photosensitive region structures and formation processes is necessary. Summary of the Invention

[0004] One of the objectives of the present invention is to provide a self-isolating image sensor structure. This structure alters the conventional layout of photodiodes, using the photodiode's P-type semiconductor as an isolation structure. This self-isolating structure achieves segmentation of the photosensitive region without the need for additional isolation structures, resulting in lower crosstalk compared to existing technologies. The present invention also utilizes stacked N-type semiconductors to form multiple photosensitive layers. This stacked structure creates a gradient distribution of electron concentration in the photosensitive region, which helps improve photoelectric conversion efficiency.

[0005] Another object of the present invention is to provide a method for preparing a self-isolating image sensing structure, which adopts a feasible and low-cost process to prepare the above-mentioned self-isolating image sensing structure.

[0006] Another object of the present invention is to provide a method for preparing a self-isolating image sensor, wherein laser activation and filter layer are performed on the basis of the above-mentioned self-isolating image sensing structure to form a back-illuminated image sensor.

[0007] In order to solve the above technical problems, the technical means adopted by the present invention are as follows: In one aspect, the present invention provides a method for preparing a self-isolating image sensing structure, comprising the following steps: Providing a substrate, the substrate having a front side and a back side, wherein the front side of the substrate has a plurality of shallow trench isolation structures; Thinning the back side of the substrate to expose a shallow trench isolation structure; epitaxially growing a first semiconductor layer on the back side of the thinned substrate; Preparing a first isolation structure at a position corresponding to the shallow trench isolation structure in the first semiconductor layer; sequentially depositing a second semiconductor material layer and a metal grid material layer on the first semiconductor layer; The metal grid material layer and the second semiconductor material layer are sequentially etched to form a plurality of spaced metal grid structures and self-isolating structures located thereunder, wherein the self-isolating structures are arranged correspondingly to the first isolating structures, and a photosensitive region groove is formed between adjacent self-isolating structures; Multiple photosensitive layers are epitaxially formed inside and outside the groove of the photosensitive area to form a photosensitive area.

[0008] Preferably, the first semiconductor layer is an N-type semiconductor layer, and the second semiconductor material layer is a P-type semiconductor material layer.

[0009] Preferably, the multilayer photosensitive layer includes a first photosensitive layer, a second photosensitive layer, a third photosensitive layer and a fourth photosensitive layer deposited in sequence by epitaxial deposition, wherein the first photosensitive layer and the second photosensitive layer are epitaxially deposited on the bottom and inner wall of the groove in the photosensitive area in sequence, the third photosensitive layer is epitaxially filled in the middle inner hole of the second photosensitive layer, and the fourth photosensitive layer is epitaxially deposited above the first to third photosensitive layers.

[0010] Preferably, the first to fourth photosensitive layers are all made of N-type semiconductor materials, wherein the materials of the first to third photosensitive layers are different, and the material of the fourth photosensitive layer is the same as that of the first photosensitive layer.

[0011] Preferably, preparing the first isolation structure at a position corresponding to the shallow trench isolation structure in the first semiconductor layer includes the following steps: Etching an isolation trench corresponding to the shallow trench isolation structure in the first semiconductor layer through an etching process; The isolation trench is filled with a P-type semiconductor material and then planarized to obtain a first isolation structure.

[0012] Preferably, the metal grid material layer includes an insulating layer, a first metal layer and a second metal layer.

[0013] On the other hand, the present invention provides a self-isolation image sensing structure, including a substrate having a shallow trench isolation structure, a first semiconductor layer formed on the substrate, and a plurality of photosensitive regions formed on the first semiconductor layer, wherein adjacent photosensitive regions are isolated by the self-isolation structure; the first semiconductor layer is an N-type semiconductor material layer, a first isolation structure corresponding to the shallow trench isolation structure is provided in the first semiconductor layer, the self-isolation structure is a P-type semiconductor material layer, and the photosensitive region is a multilayer photosensitive layer formed by stacking a plurality of N-type semiconductor materials.

[0014] Preferably, the material of the first isolation structure is a P-type semiconductor material, and is different from the material type of the self-isolation structure.

[0015] Preferably, the multi-layer photosensitive layer has four layers, wherein the first to third photosensitive layers are wrapped sequentially from the outside to the inside and are open and flush at the top; and the fourth photosensitive layer covers the top of the first to third photosensitive layers.

[0016] Preferably, the first to fourth photosensitive layers are all made of N-type semiconductor materials, wherein the materials of the first to third photosensitive layers are different, and the material of the fourth photosensitive layer is the same as that of the first photosensitive layer.

[0017] Preferably, a metal grid is provided on the self-isolating structure.

[0018] In another aspect, the present invention provides a method for preparing a self-isolating image sensor, comprising the following steps: Providing a substrate, the substrate having a front side and a back side, wherein the front side of the substrate has a plurality of shallow trench isolation structures; Thinning the back side of the substrate to expose a shallow trench isolation structure; epitaxially growing a first semiconductor layer on the back side of the thinned substrate; Preparing a first isolation structure at a position corresponding to the shallow trench isolation structure in the first semiconductor layer; sequentially depositing a second semiconductor material layer and a metal grid material layer on the first semiconductor layer; The metal grid material layer and the second semiconductor material layer are sequentially etched to form a plurality of spaced metal grid structures and self-isolating structures located thereunder, wherein the self-isolating structures are arranged correspondingly to the first isolating structures, and a photosensitive region groove is formed between adjacent self-isolating structures; Multiple photosensitive layers are formed inside and outside the groove of the photosensitive area to form a photosensitive area; Laser annealing process is used to activate the photosensitive area; A filter layer is prepared in the photosensitive area.

[0019] In another aspect, the present invention provides a self-isolated image sensor, comprising a substrate having a shallow trench isolation structure, a first semiconductor layer formed on the substrate, and a plurality of photosensitive regions formed on the first semiconductor layer, wherein adjacent photosensitive regions are isolated by the self-isolation structure; the first semiconductor layer is an N-type semiconductor material layer, a first isolation structure corresponding to the shallow trench isolation structure is provided within the first semiconductor layer, the self-isolation structure is a P-type semiconductor material layer, and the photosensitive regions are a multi-layer photosensitive layer formed by stacking a plurality of N-type semiconductor materials; A metal grid is provided on the self-isolating structure; and a filter layer is provided on the multi-layer photosensitive layer between adjacent metal grids.

[0020] Compared with the prior art, the present invention has the following effects: Compared with the prior art, the present invention changes the doping route used in the prior art to form a photodiode, and adopts a selective epitaxial method to form a stacked and wrapped multi-layer photosensitive layer. The unexpected technical effect is that a carrier concentration gradient is formed in the multi-layer photosensitive layer, thereby improving the photoelectric conversion efficiency. The present invention also changes the basic structure of the photodiode and creatively combines the isolation structure of the photosensitive region with the P-type region of the photodiode, that is, the P-type region of the photodiode serves as the isolation structure of the photosensitive region to form a self-isolation structure. Unexpectedly, the present invention not only fully realizes the basic function of the photodiode, but also greatly reduces the crosstalk effect through the self-isolation effect. In addition, compared with the self-isolation structure of silicon dioxide, it can be made in a smaller size while meeting the isolation requirements, thereby indirectly improving the pixel accuracy of the image sensor. The present invention also creatively changes the manufacturing process sequence, depositing the metal grid structure and the self-isolation structure material together. Unexpectedly, not only the production of the self-isolation structure is achieved, but also the process is saved and the cost is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the process for preparing the self-isolating image sensing structure in Example 1 of the present invention.

[0022] Figure 2 Schematic diagram of the substrate provided in Example 1 of the present invention.

[0023] Figure 3 This is a schematic diagram of thinning the back side of the substrate to expose the shallow trench isolation structure in Example 1 of the present invention.

[0024] Figure 4 This is a schematic diagram of epitaxially growing a first semiconductor layer on the back side of a thinned substrate in Example 1 of the present invention.

[0025] Figure 5 This is a schematic diagram of sequentially depositing a second semiconductor material layer and a metal grid material layer on the first semiconductor layer in Example 1 of the present invention.

[0026] Figure 6 Schematic diagram of etching to form a metal grid structure and a self-isolation structure in Example 1 of the present invention.

[0027] Figure 7 This is a schematic diagram of the first photosensitive layer epitaxially formed in the groove of the photosensitive area in Example 1 of the present invention.

[0028] Figure 8 This is a schematic diagram of epitaxially forming a second photosensitive layer in the groove of the photosensitive area in Example 1 of the present invention.

[0029] Figure 9 Schematic diagram of filling the third photosensitive layer in the photosensitive area groove in Example 1 of the present invention.

[0030] Figure 10 This is a schematic diagram of epitaxially depositing a fourth photosensitive layer on the first to third photosensitive layers in Example 1 of the present invention.

[0031] Figure 11 Schematic diagram of the process of preparing the self-isolating image sensor in Example 2 of the present invention.

[0032] Figure 12 Schematic diagram of activating the photosensitive area by laser annealing process in Example 2 of the present invention.

[0033] Figure 13 Schematic diagram of preparing the filter layer in Example 2 of the present invention.

[0034] 100 - substrate, 110 - front side, 120 - back side, 130 - shallow trench isolation structure, 140 - etch stop layer, 150 - metal interconnect layer, 160 - first semiconductor layer, 161 - first isolation structure; 200 - second semiconductor material layer, 210 - self-isolation structure; 300 - metal grid material layer, 310 - metal grid structure, 311 - insulation layer, 312 - first metal layer, 313 - second metal layer; 400 - photosensitive area, 410 - photosensitive area groove, 420 - multi-layer photosensitive layer, 421 - first photosensitive layer, 422 - second photosensitive layer, 423 - third photosensitive layer, 424 - fourth photosensitive layer; 510 - blue filter element, 520 - green filter element, 530 - red filter element. DETAILED DESCRIPTION

[0035] The following embodiments of the present invention are described in further detail with reference to the accompanying drawings and examples. The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0036] In the description of the present invention, it should be noted that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "back," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer" and the like, indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limiting the present invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0037] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "connected" and "connection" should be understood in a broad sense. For example, they can refer to fixed connection, detachable connection, or integral connection; mechanical connection, electrical connection; direct connection, or indirect connection through an intermediary. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0038] Example 1: Figure 1 As shown, a method for preparing a self-isolating image sensing structure includes the following steps: S100 , providing a substrate 100 , wherein the substrate 100 has a front surface 110 and a back surface 120 , and the front surface 110 of the substrate 100 has a plurality of shallow trench isolation structures 130 ; S200 , thinning the back surface 120 of the substrate 100 to expose the shallow trench isolation structure 130 ; S300 , epitaxially growing a first semiconductor layer 160 on the back surface 120 of the thinned substrate 100 , where the first semiconductor layer 160 is an N-type semiconductor; S400 , preparing a first isolation structure 161 in the first semiconductor layer 160 at a position corresponding to the shallow trench isolation structure 130 ; S500, depositing a second semiconductor material layer 200 and a metal grid material layer 300 in sequence on the first semiconductor layer 160, wherein the second semiconductor material layer 200 is a P-type semiconductor; S600, sequentially etching the metal grid material layer 300 and the second semiconductor material layer 200 to form a plurality of spaced metal grid structures 310 and self-isolating structures 210 located thereunder. The self-isolating structures 210 are positioned corresponding to the first isolation structures 161, and a photosensitive region groove 410 is formed between adjacent self-isolating structures 210; S700 , epitaxially forming a multi-layer photosensitive layer 420 in the photosensitive region groove 410 to form the photosensitive region 400 , wherein the multi-layer photosensitive layer 420 is a multi-layer N-type semiconductor layer.

[0039] The present invention does not use ion implantation to form a photodiode. Therefore, the present invention can avoid damage to other film structures caused by ion implantation, thereby reducing the probability of signal crosstalk in the image sensor and avoiding dark current.

[0040] The present invention changes the existing photosensitive region isolation structure. After fabricating an N-type semiconductor on the back surface 120 of the substrate 100, a P-type semiconductor is used to fabricate an isolation structure. This structure, combined with the N-type semiconductor in the photosensitive region 400, forms a photodiode. Surprisingly, the present invention redesigns the photodiode structure, avoiding crosstalk and forming a self-isolation technique that confines the electron flow from the photoelectric effect to the photosensitive region 400. Furthermore, compared to silicon dioxide self-isolation structures, while meeting isolation requirements, the structure can be made smaller, thereby indirectly improving the pixel accuracy of the image sensor. By modifying the manufacturing process, the present invention simultaneously fabricates the self-isolation structure material and the metal grid material, and then etches them together to form the metal grid structure 310 and the self-isolation structure 210. This makes the structure feasible, simplifies the process steps, and reduces costs.

[0041] In step S100, the substrate 100 can be made of a semiconductor material, an insulating material, a conductive material, or any combination thereof. For example, the substrate 100 can be a silicon (Si) substrate, a silicon germanium (SiGe) substrate, a silicon germanium carbon (SiGeC) substrate, a silicon carbide (SiC) substrate, a gallium arsenide (GaAs) substrate, an indium arsenide (InAs) substrate, an indium phosphide (InP) substrate, or other III / V semiconductor substrates or II / VI semiconductor substrates. Alternatively, for example, the substrate 100 can be a layered substrate including Si / SiGe, Si / SiC, silicon on insulator (SOI), or silicon germanium on insulator. Therefore, the type and thickness of the substrate 100 should not limit the scope of protection of the present disclosure.

[0042] like Figure 2 As shown, the substrate 100 has a front side 110 and a back side 120. The shallow trench isolation structure 130 (STI) can be prepared in the front end of line (FEOL) process by combining an etching process and a deposition process. Of course, it can also be prepared by other methods known to those skilled in the art. The filling material of the shallow trench isolation structure 130 (STI) can include but is not limited to silicon oxide (SiO2), silicon nitride (Si3N4), silicon oxynitride (Si2N2O), etc. or a combination thereof.

[0043] like Figure 2 As shown, the front-end process further includes forming an etch stop layer 140 covering the shallow trench isolation structure 130 on the substrate 100, and preparing a metal interconnect layer 150 after forming the etch stop layer 140. The metal interconnect layer 150 includes an interlayer dielectric layer (IMD) and a metal line ( Figure 2(not shown), the signal of the photodiode is led out using a metal line; specifically, an interlayer dielectric layer (IMD) is first formed on the etch stop layer 140 by a deposition process. The interlayer dielectric layer can be a low-k material layer, such as tetraethyl orthosilicate (TEOS), undoped silicate glass or doped silicon oxide (such as borophosphosilicate glass (BPSG), fused silica glass (FSG), phosphosilicate glass (PSG), boron-doped silica glass (BSG), organosilicate glass (OSG), SiOC) and / or any suitable low-k dielectric material; then, a metal line is formed in the interlayer dielectric layer as the metal connection part of the device.

[0044] Of course, this embodiment only shows one of the methods. As long as the metal interconnect structure can be reasonably formed, there is no restriction on the thickness of the etch stop layer 140 and the interlayer dielectric layer, and they can be adjusted according to specific process requirements.

[0045] like Figure 3 As shown, in step S200, at least one of a dry etching process, a wet etching process, a chemical mechanical polishing process and a push-on process can be used to thin the back side 120 of the substrate 100 to expose the shallow trench isolation structure 130. The best thinning is to just expose the bottom of the shallow trench isolation structure 130. The shallow trench isolation structure 130 itself can be prepared according to the existing technology without special limitations. The spacing between the shallow trench isolation structures 130 is determined according to the size of the photosensitive area 400 designed subsequently.

[0046] Exemplarily, in step S300, the first semiconductor layer 160 is used as an isolation structure, has a thickness of 20 to 30 nanometers, and is formed by any one of deposition methods including but not limited to chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), etc.; the first semiconductor layer 160 is a silicon-based semiconductor, specifically a silicon material doped with any one of nitrogen N, phosphorus P, arsenic As, antimony Sb, bismuth Bi, etc. Exemplarily, the first semiconductor layer 160 is a silicon material doped with phosphorus (P) (abbreviated as Si-P).

[0047] like Figure 4 As shown, in step S400, the position corresponding to the shallow trench isolation structure 130 means that the first isolation structure 161 is located just above the shallow trench isolation structure 130, or the center lines of the two are substantially coincident. The method for manufacturing the first isolation structure 161 is as follows: An isolation trench is etched at a corresponding position in the first semiconductor layer 160 through an etching process (dry etching process, wet etching process), and then an isolation material is filled in the isolation trench. The isolation material is a P-type semiconductor material, including a silicon material doped with any one of the elements such as boron B, aluminum Al, gallium Ga, indium In, thallium Tl, etc., and the best is a silicon material doped with thallium (Tl) (abbreviated as Si-Tl).

[0048] After the isolation material is deposited, planarization is performed using a process such as CMP to obtain a first isolation structure 161 .

[0049] like Figure 5 As shown, in step S500, the second semiconductor material layer 200 can be deposited by any one of the deposition methods including but not limited to chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), etc. The deposition process can avoid problems such as crystal structure damage, temperature increase, and electric field effect caused by ion implantation. In this embodiment, the second semiconductor material layer 200 can be formed on the first semiconductor layer 160 by chemical vapor deposition. The second semiconductor material layer 200 is a P-type semiconductor and can be a silicon material doped with any one of the elements such as boron B, aluminum Al, gallium Ga, indium In, thallium Tl, etc. Exemplarily, the second semiconductor material layer 200 is a silicon material doped with boron (B) (abbreviated as Si-B).

[0050] like Figure 5 As shown, in step S500, the metal grid material layer 300 deposited on the second semiconductor material layer 200 includes an insulating layer 311, a first metal layer 312 and a second metal layer 313 deposited in sequence, and the thickness of each layer is about 50~60nm, which can obtain the best isolation reflection effect; the insulating layer 311 is a material with a high-k dielectric constant, such as aluminum oxide (Al2O3), hafnium oxide (HfO2), hafnium oxynitride (HfON), zirconium oxide (ZrO2), tantalum oxide (Ta2O5), titanium oxide (TiO2) or strontium titanium oxide (SrTiO3); illustratively, in this embodiment, it is hafnium oxide (HfO2).

[0051] The first metal layer 312 is a metal material or a metal compound, such as a conductive metal material or a metal nitride. The metal material includes at least one selected from the group consisting of Ti, Ta, Ni, Cu, W, Hf, Zr, Nb, Y, Zn, Co, Al, Si, and Ge. The metal nitride includes a nitride formed from at least one metal selected from the group consisting of Ti, Ta, Ni, Cu, W, Hf, Zr, Nb, Y, Zn, Co, Al, Si, and Ge. In this embodiment, the first metal layer 312 is preferably TiN.

[0052] The material of the second metal layer 313 is at least one selected from the group consisting of Ti, Ta, and Al, and the material of the second metal layer 313 is different from that of the first metal layer 312. For example, the material of the second metal layer 313 is Al.

[0053] The insulating layer 311, the first metal layer 312 and the second metal layer 313 can be deposited using the best process that matches their respective materials, including but not limited to any one of chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), etc.

[0054] like Figure 6 As shown, in step S600, for example, the metal grid material layer 300 can be etched using a combination of photolithography and dry etching to form a plurality of metal grid structures 310. The metal grid structures 310 are arranged corresponding to the first isolation structures 161, for example, in a one-to-one arrangement, that is, the center lines of the metal grid structures 310 and the first isolation structures 161 in the depth direction are located on the same straight line. For example, the metal grid material layer 300 can be etched using carbon tetrafluoride to form the plurality of metal grid structures 310, or dry etching can be used to form the plurality of metal grid structures 310.

[0055] like Figure 6 As shown, in step S600, after etching the metal grid material layer 300, the second semiconductor material layer 200 is continuously etched using the first semiconductor layer 160 as a stop layer to form a plurality of self-isolating structures 210 located below the metal grid structure 310. It should be noted that the second semiconductor material layer 200 can be etched after waiting for etching the metal grid material layer 300, or can be etched simultaneously, depending on the process requirements and the size of the photosensitive area groove 410. If the etching can be completed in one go and the yield of forming the metal grid structure 310 and the photosensitive area groove 410 is high, the etching can be performed in one go or in two steps, without any specific limitation.

[0056] The spacing between adjacent self-isolation structures 210 determines the width of the photosensitive area groove 410, which also determines the width of the photosensitive area 400. In the above example, the larger the spacing between two adjacent self-isolation structures 210, the larger the photosensitive area of ​​the image sensor, that is, the better the photosensitivity of the image sensor. However, too large a spacing will result in excessively large pixels and reduced resolution.

[0057] Therefore, by setting the distance between the central axes of two adjacent self-isolating structures 210 to be 500 nanometers to 700 nanometers, the photosensitivity of the image sensor can be improved while ensuring the resolution.

[0058] Illustratively, in step S700, the multilayer photosensitive layer 420 includes several photosensitive layers stacked inside and outside, and the photosensitive layer is a silicon-based N-type semiconductor material layer, specifically a silicon material doped with any one of nitrogen N, phosphorus P, arsenic As, antimony Sb, bismuth Bi, etc., and is deposited by a selective epitaxial process; from the outside to the inside, the ordinal number of the doping element gradually increases, and the larger the ordinal number of the element, the stronger the ability to release electrons, that is, under the same lighting conditions, more carriers are generated. The gradient distribution of the ordinal number of the doping element provides carriers with a concentration gradient distribution, which is beneficial to improving the overall photoelectric conversion efficiency of the multilayer photosensitive layer 420.

[0059] like Figure 10 As shown, exemplarily, in step S700, the multilayer photosensitive layer 420 includes a first photosensitive layer 421, a second photosensitive layer 422, a third photosensitive layer 423 and a fourth photosensitive layer 424 that are epitaxially deposited in sequence, wherein the first photosensitive layer 421 and the second photosensitive layer 422 are epitaxially deposited on the bottom and inner wall of the photosensitive area groove 410 in sequence, the third photosensitive layer 423 is epitaxially filled in the middle inner hole of the second photosensitive layer 422, and the fourth photosensitive layer 424 is epitaxially deposited above the first photosensitive layer 421 to the third photosensitive layer 423.

[0060] Exemplarily, the materials of the first to third photosensitive layers 421 to 423 are different, and the material of the fourth photosensitive layer 424 is the same as that of the first photosensitive layer 421 , so as to obtain better photoelectric conversion efficiency and sensitivity.

[0061] like Figure 7 As shown, illustratively, the first photosensitive layer 421 uses Si-P, and the first photosensitive layer 421 is epitaxially grown in the photosensitive area groove 410 using a selective epitaxial process. When Si-P is deposited using the selective epitaxial deposition process, Si-P forms crystal nuclei on the top of the first semiconductor layer 160 and the surface exposed by the side wall of the self-isolation structure 210, that is, Si-P will only be formed on the inner side wall and bottom surface of the photosensitive area groove 410.

[0062] For example, Figure 8As shown, the second photosensitive layer 422 is made of Si-As (silicon material doped with arsenic) and is epitaxially grown on the surface of the first photosensitive layer 421 using a selective epitaxial process. When the Si-As is deposited using the selective epitaxial deposition process, Si-As forms crystal nuclei on the surface exposed by the internal groove of the first photosensitive layer 421, that is, Si-As is only formed on the inner sidewalls and bottom surface of the internal groove of the first photosensitive layer 421.

[0063] For example, Figure 8 As shown, after the second photosensitive layer 422 is deposited, a groove is still present in the middle area of ​​the second photosensitive layer 422. The groove can be filled with Si-Sb (silicon material doped with antimony) by spin coating (SOG process) to form a third photosensitive layer 423. Figure 9 As shown, the tops of the first photosensitive layer 421 to the third photosensitive layer 423 are substantially flush.

[0064] For example, Figure 10 As shown, Si-P is deposited on top of the first photosensitive layer 421 to the third photosensitive layer 423 by any one of the deposition methods including but not limited to chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), etc. to form a fourth photosensitive layer 424, thereby obtaining a multi-layer photosensitive layer 420 with an inner and outer stacked distribution. By selecting element numbers of different sizes, a gradient carrier concentration is formed in the multi-layer photosensitive layer 420, which unexpectedly greatly improves the photoelectric conversion efficiency of the photosensitive area 400.

[0065] Example 2: Figure 11 As shown, the present invention also provides a method for preparing a self-isolating image sensor, comprising the following steps: M100, based on the self-isolation type image sensor structure prepared in Example 1, the photosensitive area 400 is activated by laser annealing process, such as Figure 12 As shown, Figure 12 The hollow arrow is a schematic diagram of laser activation annealing; illustratively, the laser annealing is performed in an oxygen-containing environment.

[0066] M200 , preparing a filter layer on the photosensitive area 400 between adjacent metal grid structures 310 , wherein the filter layer includes a plurality of filter elements.

[0067] After forming the metal grid structure 310, a filter element is formed between the metal grid structures 310 and located on the surface of the photosensitive area 400. The filter element may include Figure 13The blue filter element 510, the green filter element 520 and the red filter element 530 are shown. It should be noted that the filter element includes a color filter and a micro lens located on the surface of the color filter. Since the surface of the micro lens is convex, Figure 13 The blue filter element 510 , the green filter element 520 , and the red filter element 530 are all convex in shape.

[0068] The above embodiments are intended to illustrate the present invention only and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, it should be understood by those skilled in the art that various combinations, modifications, or equivalent substitutions of the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention and should be encompassed by the scope of the claims of the present invention.

Claims

1. A method for preparing a self-isolating image sensing structure, characterized in that: The following steps are involved: Providing a substrate, the substrate having a front side and a back side, wherein the front side of the substrate has a plurality of shallow trench isolation structures; Thinning the back side of the substrate to expose a shallow trench isolation structure; epitaxially growing a first semiconductor layer on the back side of the thinned substrate; Preparing a first isolation structure at a position corresponding to the shallow trench isolation structure in the first semiconductor layer; sequentially depositing a second semiconductor material layer and a metal grid material layer on the first semiconductor layer; The metal grid material layer and the second semiconductor material layer are sequentially etched to form a plurality of spaced metal grid structures and self-isolating structures located thereunder, wherein the self-isolating structures are arranged correspondingly to the first isolating structures, and a photosensitive region groove is formed between adjacent self-isolating structures; Multiple photosensitive layers are epitaxially formed inside and outside the groove of the photosensitive area to form a photosensitive area.

2. The method for preparing the self-isolating image sensing structure according to claim 1, wherein: The first semiconductor layer is an N-type semiconductor layer, and the second semiconductor material layer is a P-type semiconductor material layer.

3. The method for preparing the self-isolating image sensing structure according to claim 2, wherein: The multilayer photosensitive layer includes a first photosensitive layer, a second photosensitive layer, a third photosensitive layer and a fourth photosensitive layer which are epitaxially deposited in sequence, wherein the first photosensitive layer and the second photosensitive layer are epitaxially deposited on the bottom and inner wall of the groove in the photosensitive area in sequence, the third photosensitive layer is epitaxially filled in the middle inner hole of the second photosensitive layer, and the fourth photosensitive layer is epitaxially deposited above the first to third photosensitive layers.

4. The method for preparing the self-isolating image sensing structure according to claim 3, wherein: The first to fourth photosensitive layers are all made of N-type semiconductor materials, wherein the materials of the first to third photosensitive layers are different, and the material of the fourth photosensitive layer is the same as that of the first photosensitive layer.

5. The method for preparing the self-isolating image sensing structure according to claim 1, wherein: Preparing a first isolation structure at a position corresponding to the shallow trench isolation structure in the first semiconductor layer includes the following steps: Etching an isolation trench corresponding to the shallow trench isolation structure in the first semiconductor layer through an etching process; The isolation trench is filled with a P-type semiconductor material and then planarized to obtain a first isolation structure.

6. The method for preparing the self-isolating image sensing structure according to claim 1, wherein: The metal grid material layer includes an insulating layer, a first metal layer and a second metal layer.

7. A self-isolating image sensing structure, characterized in that: It includes a substrate with a shallow trench isolation structure, a first semiconductor layer formed on the substrate, and several photosensitive areas formed on the first semiconductor layer, and adjacent photosensitive areas are isolated by a self-isolation structure; the first semiconductor layer is an N-type semiconductor material layer, and a first isolation structure corresponding to the shallow trench isolation structure is provided in the first semiconductor layer. The self-isolation structure is a P-type semiconductor material layer, and the photosensitive area is a multi-layer photosensitive layer formed by stacking several N-type semiconductor materials.

8. The self-isolating image sensing structure according to claim 7, wherein: The material of the first isolation structure is a P-type semiconductor material, and is different from the material type of the self-isolation structure.

9. The self-isolating image sensing structure according to claim 8, characterized in that: The multi-layer photosensitive layer has four layers, wherein the first to third photosensitive layers are wrapped in sequence from the outside to the inside and are open and flush on the top; the fourth photosensitive layer covers the top of the first to third photosensitive layers.

10. The self-isolating image sensing structure according to claim 9, characterized in that: The first to fourth photosensitive layers are all made of N-type semiconductor materials, wherein the materials of the first to third photosensitive layers are different, and the material of the fourth photosensitive layer is the same as that of the first photosensitive layer.

11. A method for preparing a self-isolating image sensor, characterized in that: The following steps are involved: Providing a substrate, the substrate having a front side and a back side, wherein the front side of the substrate has a plurality of shallow trench isolation structures; Thinning the back side of the substrate to expose a shallow trench isolation structure; epitaxially growing a first semiconductor layer on the back side of the thinned substrate; Preparing a first isolation structure at a position corresponding to the shallow trench isolation structure in the first semiconductor layer; sequentially depositing a second semiconductor material layer and a metal grid material layer on the first semiconductor layer; The metal grid material layer and the second semiconductor material layer are sequentially etched to form a plurality of spaced metal grid structures and self-isolating structures located thereunder, wherein the self-isolating structures are arranged correspondingly to the first isolating structures, and a photosensitive region groove is formed between adjacent self-isolating structures; Multiple photosensitive layers are formed inside and outside the groove of the photosensitive area to form a photosensitive area; The photosensitive area is activated by laser annealing process; A filter layer is prepared in the photosensitive area.

12. A self-isolating image sensor, characterized in that: The invention comprises a substrate having a shallow trench isolation structure, a first semiconductor layer formed on the substrate, and a plurality of photosensitive regions formed on the first semiconductor layer, wherein adjacent photosensitive regions are isolated by a self-isolation structure; the first semiconductor layer is an N-type semiconductor material layer, a first isolation structure corresponding to the shallow trench isolation structure is provided in the first semiconductor layer, the self-isolation structure is a P-type semiconductor material layer, and the photosensitive regions are multi-layer photosensitive layers formed by stacking a plurality of N-type semiconductor materials; A metal grid is provided on the self-isolating structure; and a filter layer is provided on the multi-layer photosensitive layer between adjacent metal grids.

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