Backside illuminated image sensing structure, sensor and preparation method

Abstract

The invention discloses a backside illuminated image sensing structure, a sensor and a preparation method, and belongs to the field of semiconductors, the backside of a substrate is thinned to form a laminated photosensitive structure through a deposition process, a deep trench isolation structure is prepared on the laminated photosensitive structure, a first section of metal grating is prepared, and ions of VA group elements are injected to form a second section of metal grating; an inclined reinforced doping belt is formed; then preparing a second section of metal grating to obtain a complete metal grating, obtaining a back-illuminated image sensing structure, and then performing the processes of activation, preparation of a filter layer and the like to obtain a complete back-illuminated image sensor; according to the invention, the stacked photosensitive structure and the reinforced doping band are combined, so that the crosstalk effect is greatly reduced while the problem of doping damage to the substrate is solved, and the performance of the image sensor is improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of semiconductor, and relates to a preparation technology of an image sensor, in particular to a back-illuminated image sensing structure, a sensor and a preparation method. BACKGROUND

[0002] An image sensor is a photoelectric conversion device widely used in many fields such as consumer electronics, security monitoring, automotive electronics, machine vision, etc. A back-illuminated (BSI) image sensor has higher sensitivity, better wiring layout and allows high-speed recording, and is often used in fields with high requirements for image sensor pixel performance.

[0003] However, in the conventional BSI front-end process, a diode structure needs to be prepared by high-energy ion implantation (IMP) to form a photosensitive region, which will cause damage to the substrate surface, and uneven ion implantation will also cause signal cross talk between different pixels, hindering the further improvement of the performance of the BSI image sensor.

[0004] The prior art CN119008646A discloses a preparation method of a back-illuminated image sensor, which forms a photosensitive region by epitaxy. However, the carrier migration rate of the photosensitive region formed only by the epitaxy process is difficult to meet the performance requirements of a high-sensitivity sensor, so the technology sets the photosensitive region as a direction away from the substrate, sequentially stacking an isolation layer, a SiAs layer, an intermediate photosensitive layer, and a SiP cover layer; while avoiding damage caused by ion implantation, the different VA group-doped photosensitive layers stacked and / or arranged alternately are used to improve the quantum efficiency of the photodiode, and a stacked trench isolation structure is used to obtain a high-performance image sensor; however, in this technology, an etching, deposition and planarization process needs to be performed once after the preparation of each photosensitive layer to form the stacked trench isolation structure, so the preparation process is relatively complex.

[0005] Therefore, it is necessary to conduct relevant research and development to find a new photosensitive region structure and formation process to reduce the difficulty of obtaining a high-sensitivity image sensor. SUMMARY

[0006] One of the purposes of the present application is to provide an enhanced back-illuminated image sensing structure, which uses a stacked photosensitive structure and ion implantation to form an inclined enhanced doping zone to increase the carrier concentration, thereby improving the sensitivity of the back-illuminated image sensing structure and achieving a better balance between the preparation process and high performance.

[0007] Another object of the present application is to provide a preparation method of the enhanced back-illuminated image sensing structure, which is prepared by a feasible and low-cost process.

[0008] Another object of the present application is to provide a preparation method of the enhanced back-illuminated image sensor, which is prepared by laser activation and preparation of the light filter layer on the basis of the preparation of the back-illuminated image sensing structure.

[0009] In order to solve the above technical problems, the technical means adopted by the present application are as follows: On the one hand, the present application provides an enhanced back-illuminated image sensing structure, which comprises a substrate, an isolation layer formed on the substrate, and a plurality of photodiodes formed on the isolation layer, wherein adjacent photodiodes are isolated by a deep trench isolation structure, and wherein the photodiode comprises a stacked light-sensitive structure and a tilted strengthening doped belt formed in the stacked light-sensitive structure by an ion implantation process, and wherein the stacked light-sensitive structure is formed by a plurality of first type light-sensitive layers and a plurality of second type light-sensitive layers stacked or alternately stacked.

[0010] Preferably, the element doped in the strengthening doped belt is a VA group element.

[0011] Preferably, the first type light-sensitive layer contains a VA group element, and the second type light-sensitive layer contains a IIIA group element; or The first type light-sensitive layer contains a IIIA group element, and the second type light-sensitive layer contains a VA group element.

[0012] Preferably, the stacked light-sensitive structure is formed by a first type light-sensitive layer, a second type light-sensitive layer, a first type light-sensitive layer, a second type light-sensitive layer, and a first type light-sensitive layer, wherein the first type light-sensitive layer is a silicon material layer doped with phosphorus (hereinafter referred to as Si-P), and the second type light-sensitive layer is a silicon material layer doped with boron (hereinafter referred to as Si-B).

[0013] Preferably, the strengthening doped belt is a cross-shaped tilted doped belt formed by setting an ion implantation angle and rotating the substrate several times during the ion implantation process.

[0014] Preferably, the substrate is rotated 4 times during the ion implantation process to form an X-shaped cross-shaped tilted doped belt.

[0015] On the other hand, the present application provides an enhanced back-illuminated image sensor, which comprises the above-mentioned back-illuminated image sensing structure, an oxide isolation layer formed on the stacked light-sensitive structure, and a metal grid formed on the oxide isolation layer, wherein the metal grid is located above the deep trench isolation structure.

[0016] Preferably, the metal grating comprises a first section of metal grating and a second section of metal grating wrapping the first section of metal grating, the first section of metal grating comprising a laminated insulating layer and a first metal layer.

[0017] Preferably, a filter layer is arranged above the photodiode between adjacent metal gratings.

[0018] In another aspect, the present application provides a preparation method of an enhanced back-illuminated image sensor structure, comprising the following steps: providing a substrate having a front surface and a back surface, the front surface of the substrate having a plurality of shallow trench isolation structures; forming an isolation layer under the shallow trench isolation structures by an ion implantation process; thinning the back surface of the substrate to expose the isolation layer; forming a laminated photosensitive structure on the isolation layer by depositing a first type of photosensitive layer and a second type of photosensitive layer; preparing a deep trench isolation structure in the laminated photosensitive structure to form a plurality of photosensitive regions; preparing an oxide isolation layer on the laminated photosensitive structure; preparing a first section of metal grating on the oxide isolation layer and corresponding to the deep trench isolation structure, the first section of metal grating comprising an insulating layer and a first metal layer; forming an inclined enhanced doping band by implanting ions of a VA group element into the laminated photosensitive structure of the photosensitive region through an ion implantation process; preparing a second section of metal grating wrapping the first section of metal grating on the insulating layer and the first metal layer, the first section of metal grating and the second section of metal grating together constituting a metal grating.

[0019] Preferably, the isolation layer is formed under the shallow trench isolation structures by implanting a IIIA group element through an ion implantation process.

[0020] Preferably, the laminated photosensitive structure is formed by sequentially depositing a first type of photosensitive layer, a second type of photosensitive layer, a first type of photosensitive layer, a second type of photosensitive layer, and a first type of photosensitive layer on the isolation layer, the first type of photosensitive layer containing a VA group element, and the second type of photosensitive layer containing a IIIA group element; or the first type of photosensitive layer contains a IIIA group element, and the second type of photosensitive layer contains a VA group element.

[0021] Preferably, during the ion implantation in the laminated photosensitive structure of the photosensitive region, the ion implantation inclination angle is maintained, and the substrate is rotated several times to form a cross-shaped inclined doping band.

[0022] Preferably, the substrate is rotated 4 times during the ion implantation in the laminated photosensitive structure of the photosensitive region to form an X-shaped cross-shaped inclined doping band.

[0023] In another aspect, the present application provides a preparation method of an enhanced back-illuminated image sensor, comprising the following steps: A substrate is provided, the substrate has a front surface and a back surface, the front surface of the substrate has a plurality of shallow trench isolation structures; An isolation layer is formed under the shallow trench isolation structures by an ion implantation process; The back surface of the substrate is thinned to expose the isolation layer; A laminated photosensitive structure is formed on the isolation layer by depositing a first type of photosensitive layer and a second type of photosensitive layer; Deep trench isolation structures are prepared in the laminated photosensitive structure to form a plurality of photosensitive regions; An oxide isolation layer is prepared on the laminated photosensitive structure; A first section of metal grating is prepared on the oxide isolation layer and in the region corresponding to the deep trench isolation structure, the first section of metal grating comprises an insulating layer and a first metal layer; Ions of a VA group element are implanted in the laminated photosensitive structure of the photosensitive region by an ion implantation process to form an inclined reinforced doping belt; A second section of metal grating is prepared to wrap the insulating layer and the first metal layer, and the first section of metal grating and the second section of metal grating together constitute a metal grating; The photosensitive region is activated by a laser annealing process; A light filtering layer is prepared above the photodiode between adjacent metal gratings.

[0024] Compared with the prior art, the present application has the following effects: Compared with the prior art, the present application combines the technical advantages of epitaxial formation of photodiodes and doping formation of photodiodes in the prior art, first forms a laminated photosensitive structure by deposition, and then forms an inclined reinforced doping belt by doping. The unexpected effect is that the present application not only obtains a photosensitive region with high carrier mobility, but also avoids the damage to the substrate surface caused by heavy doping in the prior art, and enables the present application to form an isolation structure with good isolation performance by the most mature process of deep trench isolation structure after epitaxial formation of all photosensitive layers, so that the present application has all the advantages of epitaxial photosensitive structure and heavy doping formation of photosensitive structure, and avoids the corresponding disadvantages, obtains a high-quality image sensor, and achieves an excellent balance between high-performance devices and low-cost processes, so that the present application has great production value. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The figure is a flowchart of the preparation method of the enhanced back-illuminated image sensor structure in embodiment 1 of the present application.

[0026] Figure 2 The figure is a schematic diagram of the substrate provided in embodiment 1 of the present application.

[0027] Figure 3 Schematic diagram for forming isolation layer on the back side of substrate by ion implantation in embodiment 1 of the present application.

[0028] Figure 4 Schematic diagram for thinning the back side of substrate to expose the isolation layer in embodiment 1 of the present application.

[0029] Figure 5 Schematic diagram for sequentially and alternately depositing first type of photosensitive layer and second type of photosensitive layer on the isolation layer to prepare a stacked photosensitive structure in embodiment 1 of the present application.

[0030] Figure 6 Schematic diagram for etching the stacked photosensitive structure to form a plurality of spaced-apart isolation trenches in embodiment 1 of the present application.

[0031] Figure 7 Schematic diagram for filling the isolation trenches with an isolation material in embodiment 1 of the present application.

[0032] Figure 8 Schematic diagram for planarizing the isolation material layer to form a deep trench isolation structure in embodiment 1 of the present application.

[0033] Figure 9 Schematic diagram for preparing a first segment of metal grating on the stacked photosensitive structure in embodiment 1 of the present application.

[0034] Figure 10 Schematic diagram for implanting VA group elements into the photosensitive region of the stacked photosensitive structure to form a reinforced doped band in embodiment 1 of the present application.

[0035] Figure 11 Schematic diagram for preparing a second segment of metal grating on the first segment of metal grating in embodiment 1 of the present application.

[0036] Figure 12 Schematic diagram for the preparation method of the enhanced back-illuminated image sensor in embodiment 2 of the present application.

[0037] Figure 13 Schematic diagram for activating the photosensitive region by laser annealing process in embodiment 2 of the present application.

[0038] Figure 14 Schematic diagram for preparing a filter layer in embodiment 2 of the present application.

[0039] 100-substrate, 110-front side, 120-back side, 130-shallow trench isolation structure, 140-etching stop layer, 150-metal interconnection layer, 160-isolation layer; 200-Layered photosensitive structure, 210-First type of photosensitive layer, 220-Second type of photosensitive layer, 230-Deep trench isolation structure, 231-Isolation trench, 232-Isolation material layer; 300 - Metal grid, 310 - First section of metal grid, 311 - Insulation layer, 312 - First metal layer, 320 - Second section of metal grid; 400-oxide isolation layer; 500-X type cross-tilted doped band; 610 - Blue filter element, 620 - Green filter element, 630 - Red filter element; 700 - Axis. Detailed Implementation

[0040] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0041] In the description of this invention, it should be noted that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0042] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0043] Example 1: As Figure 1 As shown, this embodiment provides a method for fabricating an enhanced back-illuminated image sensing structure, including the following steps: S100, a substrate 100 is provided, the substrate 100 having a front side 110 and a back side 120, the front side 110 of the substrate 100 having a plurality of shallow trench isolation structures 130; S200, An isolation layer 160 is formed below the shallow trench isolation structure 130 by ion implantation process; S300, the back side 120 of the substrate 100 is thinned to expose the isolation layer 160; S400, forming a laminated photosensitive structure 200 by depositing a plurality of first type photosensitive layers 210 and a plurality of second type photosensitive layers 220 on the isolation layer 160; S500, preparing a deep trench isolation structure 230 in the laminated photosensitive structure 200 to form a plurality of photosensitive regions; S600, preparing an oxide isolation layer 400 on the laminated photosensitive structure 200; S700, preparing a first section metal grid 310 on the oxide isolation layer 400 and corresponding regions of the deep trench isolation structure 230, the first section metal grid 310 comprising an insulating layer 311 and a first metal layer 312; S800, injecting ions of VA group elements into the laminated photosensitive structure 200 of the photosensitive regions by an ion implantation process to form a tilted reinforced doped band; S900, preparing a second section metal grid 320 on the insulating layer 311 and the first metal layer 312 to wrap the same, the first section metal grid 310 and the second section metal grid 320 together constituting a metal grid 300.

[0044] The present application does not form a photodiode by ion implantation, thus, the present application can avoid damage to other film structures caused by ion implantation, reduce the probability of signal crosstalk of the image sensor, and avoid dark current.

[0045] The present application injects ions of VA group elements into the laminated photosensitive structure 200 of the photosensitive regions by an ion implantation process to form a tilted reinforced doped band, which unexpectedly has the following effects: the present application avoids damage to the substrate caused by heavy doping, and additionally dopes more VA group elements on the basis of depositing a photosensitive layer containing VA group elements by reinforced doping, which greatly improves the concentration of VA group elements, thereby improving the carrier concentration of the photosensitive region, and providing a better electron flow channel in the photosensitive region, thereby greatly improving the electron flow concentration of the photodiode; the present application further forms a plurality of laminated photodiodes by laminating two photosensitive layers, which unexpectedly has the following effects: the laminating greatly improves the electron flow concentration, which can generate about 1E10 electrons more than non-laminated; further improves the electron concentration, reduces crosstalk effect by improving the electron concentration of the photosensitive region, improves the photosensitivity, and thus improves the sensitivity of the image sensor.

[0046] The present application forms a reinforced doping belt through the way of epitaxy and doping, so that there is no carrier concentration gradient interface on the reinforced doping belt between adjacent layers of the multi-layer photosensitive structure, and the carrier can migrate efficiently on the reinforced doping belt, and the contact area between the reinforced doping belt and each layer of the photosensitive structure is large enough, so that the present application can greatly improve the carrier migration rate of the multi-layer photosensitive structure by using a lower concentration of doping, and greatly improves the electrical performance of the photosensitive region.

[0047] The present application improves the contact area between the reinforced doping belt and the multi-layer photosensitive structure through the way of inclined doping, further improves the carrier migration rate, and ultimately makes the present application obtain a photosensitive region with high carrier migration rate by using a low-cost epitaxy combined with a deep trench isolation process, thereby providing a basis for the manufacture of high-performance image sensors.

[0048] In step S100, the substrate 100 can be made of a semiconductor material, an insulating material, a conductor 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, for example, 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 protection scope of the present disclosure.

[0049] As shown in FIG. 1, Figure 2 The substrate 100 has a front surface 110 and a back surface 120, and a shallow trench isolation structure 130 (STI) can be prepared by etching and deposition processes in a front-end-of-line (FEOL) process. Of course, the shallow trench isolation structure 130 (STI) 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), or a combination thereof.

[0050] As shown in FIG. 1, Figure 2 The front-end-of-line process further includes forming an etching stop layer 140 on the substrate 100 to cover the shallow trench isolation structure 130, and preparing a metal interconnection layer 150 on the etching stop layer 140. The metal interconnection layer 150 includes an interlayer dielectric layer (IMD) and metal lines formed in the interlayer dielectric layer. Figure 2(Not shown in the text) The signal of the photodiode is brought out using metal lines; specifically, an interlayer dielectric (IMD) is first prepared on the etch stop layer 140 by a deposition process. The interlayer dielectric can be a low dielectric material layer, such as tetraethyl orthosilicate (TEOS), undoped silicate glass or doped silicon oxide (such as borosilicate glass (BPSG), fused silica glass (FSG), phosphosilicate glass (PSG), boron-doped silicon glass (BSG), organosilicon glass (OSG), SiOC) and / or any suitable low-k dielectric material; then, metal lines are prepared in the interlayer dielectric layer as the metal connection part of the device, thereby forming the metal interconnect layer 150.

[0051] Of course, this embodiment only illustrates one method. As long as the metal interconnect structure can be formed reasonably, there are no restrictions on the thickness of the etch stop layer 140 and the interlayer dielectric layer. They can be adjusted according to specific process requirements.

[0052] like Figure 3 As shown, in step S200, an isolation layer 160 can be formed by ion implantation below the shallow trench isolation structure 130 in the substrate 100 (i.e., the shallow trench isolation structure 130 is away from the surface of the metal interconnect layer 150); the isolation layer 160 can serve as a push-stop layer in the thinning process; the material of the isolation layer 160 is a group IIIA element, including boron (B), aluminum (Al), gallium (Ga), indium (In), thallium (Tl), etc.; preferably, SiGa is formed by implanting Ga ions as the isolation layer 160; the thickness of the isolation layer 160 is not limited, and the implantation process is not limited; the optimal position is exactly at the bottom of the shallow trench isolation structure 130.

[0053] In step S300, such as Figure 4 As shown, at least one of the following processes can be used to thin the back side 120 of the substrate 100 to expose the isolation layer 160: dry etching, wet etching, chemical mechanical polishing, and planarization.

[0054] For example, chemical mechanical polishing relies primarily on mechanical polishing and chemical reactions. Dry etching includes at least one of reactive ion etching (RIE) or plasma etching. Wet etching processes can use a mixture of hydrofluoric acid and nitric acid as the etching solution. Each of the three processes has its advantages and disadvantages; the specific choice should be based on the different processing objects, requirements, and actual conditions.

[0055] In step S400, such as Figure 5As shown, at least 3 layers of the layered photosensitive structure 200 need to be prepared on the isolation layer 160 for the photosensitive layer to form a layered photodiode structure, thereby playing the effect of increasing the electron concentration of the layer. However, if the number of layers is too large, the cumulative effect of increasing the electron concentration will be weakened, but the cost will be greatly increased. Therefore, in general, the total number of layers is 3-20 layers, which has practical application value. For example, the 3-layer combination of the first type of photosensitive layer 210, the second type of photosensitive layer 220, and the first type of photosensitive layer 210; for example: the 5-layer combination of the first type of photosensitive layer 210, the second type of photosensitive layer 220, the first type of photosensitive layer 210, the second type of photosensitive layer 220, and the first type of photosensitive layer 210 (as shown in Figure 5 , etc. have good effects, among which the 5-layer combination has the best effect, which has been verified in practice.

[0056] For example, the first type of photosensitive layer 210 can be formed by any one of the deposition methods such as chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), etc. The deposition process can avoid the problems of crystal structure damage, temperature rise, and electric field effect caused by ion implantation. In this embodiment, the chemical vapor deposition method can be used to form the first type of photosensitive layer 210 on the isolation layer 160. The first type of photosensitive layer 210 is an N-type semiconductor containing VA group elements, including nitrogen N, phosphorus P, arsenic As, antimony Sb, bismuth Bi, etc. For example, the first type of photosensitive layer 210 is Si-P.

[0057] For example, the preparation process of the second type of photosensitive layer 220 can be the same as or different from that of the first type of photosensitive layer 210. The second type of photosensitive layer 220 can be a P-type semiconductor of group IIIA elements, including boron B, aluminum Al, gallium Ga, indium In, thallium Tl, etc. For example, the second type of photosensitive layer 220 is Si-B.

[0058] In step S500, as shown in Figure 8 , a deep trench isolation structure 230 (BDTI) is prepared in the layered photosensitive structure 200, forming a plurality of photosensitive regions (regions isolated by the deep trench isolation structure 230); the deep trench isolation structure 230 is used to isolate light energy, ions, electrons, etc. For example, the deep trench isolation structure 230 can be etched by lithography and dry etching. In other embodiments, the etching process can be selected according to actual needs.

[0059] For example, the preparation method of the deep trench isolation structure 230 is as follows: Step S510: etching the laminated photosensitive structure 200 to form a plurality of spaced apart isolation trenches 231.

[0060] For example, referring to Figure 6 The isolation trenches 231 can be formed by combining photolithography and dry etching. The isolation trenches 231 are arranged in correspondence with the shallow trench isolation structures 130, for example, one-to-one, that is, the center lines of the isolation trenches 231 and the shallow trench isolation structures 130 in the depth direction are located on the same straight line. In the above example, the larger the spacing between two adjacent isolation trenches 231, the larger the photosensitive area of the image sensor, that is, the better the photosensitive capability of the image sensor. However, too large spacing will result in too large pixels and reduced resolution.

[0061] Therefore, by setting the distance between the symmetrical axes of two adjacent isolation trenches 231 to 500-700 nm, the photosensitive capability of the image sensor is improved while the resolution is ensured.

[0062] Step S520: as Figure 7 shown, forming an isolation material layer 232 that at least fills the isolation trenches 231, wherein the top surface of the isolation material layer 232 is not lower than the top surface of the laminated photosensitive structure 200.

[0063] For example, referring to Figure 7 The isolation material layer 232 can be formed by deposition process. The material of the isolation material layer 232 can include oxide. In this embodiment, a liquid dielectric mixed by solvent and silicon dioxide dielectric is coated in the isolation trenches 231 in a spin coating manner (SOG process) to form the isolation material layer 232 whose top surface is not lower than the top surface of the laminated photosensitive structure 200. The filling performance of the flowing liquid material is good, which can avoid the problems such as early closure of the pore corner and internal void defects in the traditional deposition mode, and is helpful to form the target isolation structure with uniform filling and no void to ensure the isolation effect between pixels and avoid signal crosstalk.

[0064] Step S530: taking the first type of photosensitive layer 210 at the top of the laminated photosensitive structure 200 as a stop layer, planarizing the top surface of the isolation material layer 232 to obtain the deep trench isolation structure 230, as Figure 8 shown, the isolation material layer 232 is planarized by CMP process.

[0065] In step S600, an oxide isolation layer 400 is prepared on the laminated photosensitive structure 200. The oxide isolation layer 400 is silicon dioxide (SiO2) and is made by plasma enhanced chemical vapor deposition process.

[0066] In step S700, the method for preparing the first section metal grid 310 on the oxide isolation layer 400 corresponding to the deep trench isolation structure 230 is as follows: Depositing an insulating material layer and a first metal material layer on the oxide isolation layer 400 in sequence; Through the exposure, development and etching technology, taking the oxide isolation layer 400 as a stop layer, etching away the insulating material layer and the first metal material layer above the photosensitive region, obtaining the insulating layer 311 and the first metal layer 312 above the deep trench isolation structure 230 as the first section metal grid 310.

[0067] The insulating layer 311 prepared on the oxide isolation layer 400 corresponding to the deep trench isolation structure 230 is made of a material with high dielectric constant, such as one or more of aluminum oxide (Al2O3), hafnium oxide (HfO2), hafnium oxide nitride (HfON), zirconium oxide (ZrO2), tantalum oxide (Ta2O5), titanium oxide (TiO2) or strontium titanium oxide (SrTiO3); in this embodiment, the material is hafnium oxide (HfO2).

[0068] The first metal layer 312 prepared on the oxide isolation layer 400 corresponding to the deep trench isolation structure 230 is made of a metal material or a metal compound, such as a metal conductive material or a metal nitride, wherein 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 by 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.

[0069] The insulating layer 311 with a thickness too small or too large will result in poor isolation effect, and thus the insulating layer 311 with a thickness of about 30-50 nm has a better isolation effect.

[0070] In step S800, as shown in Figure 10 The implanted VA group elements for forming the reinforced doped belt include nitrogen N, phosphorus P, arsenic As, antimony Sb, bismuth Bi and the like, and in this embodiment, the implanted element is P with an implantation concentration of 1.5-2.5E 13 / cm 2 .

[0071] In this embodiment, during the ion implantation of P, the implantation direction has an angle (i.e. tilt angle) with the axis 700 of the wafer (substrate 100), and the angle is referred to as the implantation angle; the implantation angle θ is generally 25-40°.

[0072] For example, during the ion implantation in the layered photosensitive structure 200 of the photosensitive region, the ion implantation tilt angle is kept unchanged, and the substrate 100 is rotated several times, for example, as shown in Figure 10 the axis 700 to form a cross-shaped tilt doping zone. If the doping concentration is too low, the electron concentration is limited, and if the doping concentration is too high, the substrate and the metal grid structure will be damaged. Therefore, the cross-shaped tilt doping can improve the distribution concentration of the group VA elements in the layered photosensitive structure 200, thereby increasing the number of carriers.

[0073] For example, during the ion implantation in the layered photosensitive structure 200 of the photosensitive region, the ion implantation tilt angle is kept unchanged, and the substrate 100 is rotated several times (90 degrees each time), as shown in Figure 10 , an X-shaped cross-shaped tilt doping zone 500 is formed in a certain cross section. Compared with no rotation, a higher concentration of group VA elements can be obtained under the same dose, thereby increasing the carrier concentration, while avoiding substrate damage or metal grid structure failure caused by high-dose doping.

[0074] In step S900, the method for preparing the second metal grid 320 is as follows: First, a second metal layer is deposited on the first metal grid 310 and the oxide isolation layer 400. By using the exposure, development and etching technology, the oxide isolation layer 400 is used as a stop layer, the insulating layer 311 and the second metal layer above the photosensitive region are etched away, and the second metal layer above and on the side of the first metal grid 310 is reserved to form the second metal grid 320 wrapping the first metal grid 310, as shown in Figure 11 ; the insulating layer 311, the first metal layer 312 and the second metal grid 320 together constitute a complete metal grid 300 (CMG).

[0075] The material of the second metal layer is selected from at least one of the group consisting of Ti, Ta and Al. Moreover, the material of the second metal layer is different from that of the first metal layer 312. For example, the material of the second metal layer is Al.

[0076] The enhanced back-illuminated image sensor structure prepared by the above embodiment is as shown in Figure 11 . Since the layered photosensitive structure 200 is composed of multiple layers of different doping materials, a layered N-type region and a P-type region are formed. Therefore, the back-illuminated image sensor structure contains a multi-layer photodiode structure, which greatly improves the concentration of carriers in the quantum well. Further five-element implantation is performed to further improve the concentration of carriers in the quantum well, thereby improving the sensitivity of the photosensitive region, so that the back-illuminated image sensor structure has high precision and sensitivity.

[0077] Example 2: asFigure 12 As shown, the application also provides a preparation method of the enhanced back-illuminated image sensor, comprising the following steps: M100, on the basis of the enhanced back-illuminated image sensor structure prepared in Embodiment 1, the photosensitive region is activated by laser annealing process (Laser Annealing), such as Figure 13 As shown, Figure 13 The hollow arrow is a schematic diagram of laser activated annealing. For example, the laser annealing is performed in an oxygen-containing environment.

[0078] M200, a filter layer is prepared above the photodiode between the adjacent metal grids 300, and the filter layer is a plurality of filter elements.

[0079] After the formation of the metal grid 300, the filter elements are formed on the surface of the oxide isolation layer 400 between the metal grids 300. The filter elements can include blue filter elements 610, green filter elements 620 and red filter elements 630 as shown. Figure 14 It should be noted that the filter elements include color filters and microlenses on the surface of the color filters. Since the surface of the microlenses is convex, the Figure 14 As shown, the blue filter elements 610, the green filter elements 620 and the red filter elements 630 are all in a convex surface shape.

[0080] The above embodiments are only used to illustrate the application, but not to limit the application. Although the application is described in detail with reference to the embodiments, those skilled in the art should understand that various combinations, modifications or equivalent replacements of the technical solutions of the application do not deviate from the spirit and scope of the application, and should be covered in the scope of the claims of the application.

Claims

1. An enhanced back-illuminated image sensor structure, comprising a substrate, an isolation layer formed on the substrate, and a plurality of photodiodes formed on the isolation layer, adjacent photodiodes being isolated by a deep trench isolation structure, characterized in that, The photodiode comprises a laminated photosensitive structure and a tilted reinforced doped belt formed in the laminated photosensitive structure by an ion implantation process.

2. The enhanced back-illuminated image sensor structure of claim 1, wherein, The element doped in the reinforced doped belt is a VA group element.

3. The enhanced back-illuminated image sensor structure of claim 1, wherein, The first type of photosensitive layer comprises a VA group element, and the second type of photosensitive layer comprises a IIIA group element; or The first type of photosensitive layer comprises a IIIA group element, and the second type of photosensitive layer comprises a VA group element.

4. The enhanced back-illuminated image sensor structure of claim 1, wherein, The laminated photosensitive structure is formed by sequentially stacking a first type of photosensitive layer, a second type of photosensitive layer, a first type of photosensitive layer, a second type of photosensitive layer, and a first type of photosensitive layer, wherein the first type of photosensitive layer is a silicon material layer doped with phosphorus, and the second type of photosensitive layer is a silicon material layer doped with boron.

5. The enhanced back-illuminated image sensor structure of claim 1, wherein, The reinforced doped belt is a cross-shaped tilted doped belt formed by setting an ion implantation angle and rotating the substrate several times during the ion implantation process.

6. An enhanced back-illuminated image sensor, characterized by The back-illuminated image sensing structure, the oxide isolation layer formed on the laminated photosensitive structure, and the metal grid formed on the oxide isolation layer are included.

7. The enhanced backside illumination image sensor of claim 6, wherein, The metal grid comprises a first segment of the metal grid and a second segment of the metal grid wrapping the first segment of the metal grid, and the first segment of the metal grid comprises a laminated insulating layer and a first metal layer.

8. The enhanced backside illumination image sensor of claim 6, wherein, An optical filter layer is arranged above the photodiode between adjacent metal grids.

9. A method for fabricating an enhanced back-illuminated image sensing structure, characterized in that, The method comprises the following steps: A substrate is provided, the substrate has a front surface and a back surface, and the front surface of the substrate has a plurality of shallow trench isolation structures; An isolation layer is formed below the shallow trench isolation structures by an ion implantation process; The back surface of the substrate is thinned to expose the isolation layer; A laminated photosensitive structure is formed on the isolation layer by depositing a first type of photosensitive layer and a second type of photosensitive layer; Deep trench isolation structures are prepared in the laminated photosensitive structure to form a plurality of photosensitive regions; An oxide isolation layer is prepared on the laminated photosensitive structure; A first segment of the metal grid is prepared on the oxide isolation layer and in a region corresponding to the deep trench isolation structure, and the first segment of the metal grid comprises an insulating layer and a first metal layer; Ions of a VA group element are implanted in the laminated photosensitive structure of the photosensitive region by an ion implantation process to form a tilted reinforced doped belt; A second segment of the metal grid is prepared on the insulating layer and the first metal layer to wrap the first segment of the metal grid, and the first segment of the metal grid and the second segment of the metal grid together constitute the metal grid.

10. The method of claim 9, wherein the method further comprises: forming a plurality of metal pillars on the substrate; and forming a plurality of metal pillars on the substrate. A IIIA group element is implanted below the shallow trench isolation structures by an ion implantation process to form an isolation layer.

11. The method of claim 9, wherein the method further comprises: forming a plurality of metal pillars on the substrate; and forming a plurality of metal pillars on the substrate. A laminated photosensitive structure is formed by sequentially depositing a first type of photosensitive layer, a second type of photosensitive layer, a first type of photosensitive layer, a second type of photosensitive layer, and a first type of photosensitive layer on the isolation layer, wherein the first type of photosensitive layer comprises a VA group element, and the second type of photosensitive layer comprises a IIIA group element; or The first type of photosensitive layer comprises a IIIA group element, and the second type of photosensitive layer comprises a VA group element.

12. The method of claim 9, wherein the method further comprises: forming a plurality of metal pillars on the substrate; and forming a plurality of metal pillars on the substrate. During the ion implantation process in the laminated photosensitive structure of the photosensitive region, the ion implantation angle is kept and the substrate is rotated several times to form a cross-shaped tilted doped belt.

13. A method of fabricating an enhanced back-illuminated image sensor, comprising: The method comprises the following steps: A substrate is provided, the substrate has a front surface and a back surface, and the front surface of the substrate has a plurality of shallow trench isolation structures; Forming an isolation layer under the shallow trench isolation structure by an ion implantation process; Exposing the isolation layer by backside thinning of the substrate; Forming a laminated photosensitive structure on the isolation layer by depositing a first type of photosensitive layer and a second type of photosensitive layer; Preparing a deep trench isolation structure in the laminated photosensitive structure to form a plurality of photosensitive regions; Preparing an oxide isolation layer on the laminated photosensitive structure; Preparing a first segment of metal grating on the oxide isolation layer and in a region corresponding to the deep trench isolation structure, the first segment of metal grating including an insulating layer and a first metal layer; Forming an inclined reinforced doped band by implanting ions of a VA group element into the laminated photosensitive structure of the photosensitive region through an ion implantation process; Preparing a second segment of metal grating on the insulating layer and the first metal layer to wrap the same, the first segment of metal grating and the second segment of metal grating together forming a metal grating; Activating the photosensitive region by a laser annealing process; Preparing a filter layer above the photodiode between adjacent metal gratings.

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