Method for preparing back-illuminated image sensor and back-illuminated image sensor

Abstract

The present invention provides a method for preparing a back-illuminated image sensor and a back-illuminated image sensor, and specifically relates to the field of semiconductor technology. The method for preparing the back-illuminated image sensor comprises: providing a substrate, and forming a plurality of grooves in the substrate; forming a nitride isolation layer on the inner walls of the plurality of grooves and on both sides of the grooves; filling the grooves with the nitride isolation layer with semiconductor material to form a photoelectric sensing area; forming a metal interconnection structure on the substrate, and the metal interconnection structure covers the photoelectric sensing area; thinning the side of the substrate away from the metal interconnection structure; and forming a grid structure on the side of the substrate away from the metal interconnection structure. The preparation method of the present invention can effectively improve the problems of ion damage and optical crosstalk.

Description

Technical Field

[0001] The present invention belongs to the field of semiconductor technology, and in particular relates to a method for preparing a back-illuminated image sensor and the back-illuminated image sensor. Background Art

[0002] An image sensor is a semiconductor device that converts light signals into electrical signals. According to the difference in photosensitive elements and photosensitive principles, it can be divided into charge-coupled device (CCD) image sensors and complementary metal-oxide-semiconductor (CMOS) image sensors. Among them, CMOS image sensors have gradually replaced CCD image sensors and are used in various electronic products, such as still digital cameras, digital video cameras, medical cameras (such as gastroscopes), and automotive cameras, due to their advantages such as simple process, easy integration with other devices, small size, light weight, low power consumption, and low cost.

[0003] CMOS image sensors can be divided into front-side illumination image sensors (FSI) and back-side illumination image sensors (BSI) according to the position of receiving light. In comparison, back-side illumination image sensors have higher sensitivity, use better wiring layout, and allow high-speed recording. They are used in fields that require high pixel performance of image sensors. In traditional BSI processes, high-energy ion implantation (IMP) is mostly used to form photodiodes (PDs), and the PD isolation method is mainly isolation by non-isotropic ions or trenches. High-energy ion implantation will cause damage to the substrate, and single ion implantation isolation also has the problem of optical crosstalk. Summary of the invention

[0004] In view of the above shortcomings of the prior art, the present invention provides a method for preparing a back-illuminated image sensor and a back-illuminated image sensor to improve the damage and optical crosstalk problems caused by ion implantation.

[0005] To achieve the above object and other related objects, the present invention provides a method for preparing a back-illuminated image sensor, comprising the following steps:

[0006] providing a substrate, and forming a plurality of grooves in the substrate;

[0007] forming a nitride isolation layer on the inner walls of the plurality of trenches and the substrate at both sides of the trenches;

[0008] Filling the trench with the nitride isolation layer with semiconductor material to form a photoelectric sensing region;

[0009] forming a metal interconnection structure on the substrate, wherein the metal interconnection structure covers the photoelectric sensing area;

[0010] Thinning a side of the substrate facing away from the metal interconnect structure;

[0011] A grid structure is formed on a side of the substrate facing away from the metal interconnect structure.

[0012] In one embodiment of the present invention, the material of the nitride isolation layer includes silicon nitride, and the thickness of the nitride isolation layer is 50 to 150 angstroms.

[0013] In one embodiment of the present invention, the step of filling the trench with the nitride isolation layer with a semiconductor material to form a photoelectric sensing region includes:

[0014] epitaxially forming a first type of silicon material in the trench;

[0015] A second type of silicon material is epitaxially formed on the first type of silicon material; wherein the first type of silicon material and the second type of silicon material have different doping types.

[0016] In one embodiment of the present invention, the step of filling the trench with the nitride isolation layer with a semiconductor material to form a photoelectric sensing region includes:

[0017] epitaxially forming a first type of silicon material in the trench;

[0018] Implanting second type doping ions into the first type silicon material to transform a portion of the first type silicon material into second type silicon material; wherein the first type silicon material and the second type silicon material have different doping types.

[0019] In one embodiment of the present invention, the step of thinning a side of the substrate away from the metal interconnect structure comprises:

[0020] Bonding a side of the substrate provided with the metal interconnect structure to a carrier wafer;

[0021] Using the nitride isolation layer at the bottom of the trench as a stop layer, thinning the side of the substrate away from the metal interconnect structure;

[0022] The nitride isolation layer at the bottom of the trench is removed.

[0023] In one embodiment of the present invention, before forming the metal interconnect structure on the substrate, the method further includes: planarizing the semiconductor material and removing the nitride isolation layer on the substrate at both sides of the trench.

[0024] In one embodiment of the present invention, a grid structure is formed on a side of the substrate away from the photoelectric sensing region, comprising:

[0025] Forming a stacked structure on a side of the substrate away from the photoelectric sensing region, the stacked structure comprising a first grid material layer, a second grid material layer and a third grid material layer;

[0026] Forming a photoresist layer having a grid pattern on the stacked structure, wherein the photoresist layer has an opening exposing a portion of the stacked structure, and the opening corresponds to a region between adjacent photoelectric sensing regions;

[0027] The photoresist layer with the grid pattern is used as a mask to remove the stacked structure exposed by the opening to form a grid structure.

[0028] In an embodiment of the present invention, after the grid structure is formed, the method further includes: forming a filter element between adjacent grid structures, wherein the filter element is disposed corresponding to the photoelectric sensing area.

[0029] Another aspect of the present invention provides a back-illuminated image sensor, the back-illuminated image sensor comprising:

[0030] a substrate having a plurality of grooves formed therein;

[0031] A nitride isolation layer is disposed on the sidewalls of the plurality of trenches;

[0032] A photoelectric sensing region filled in the groove;

[0033] A metal interconnection structure, disposed on the substrate and covering the photoelectric sensing area;

[0034] The grid structure is arranged on a side of the substrate away from the metal interconnection structure.

[0035] In summary, the preparation method of the back-illuminated sensor of the present invention forms a groove on the substrate before the photoelectric sensing area is formed, and forms a nitride isolation layer on the inner wall of the groove, and uses the nitride isolation layer as an isolation structure between adjacent photoelectric sensing areas. The unexpected effect is that the excellent isolation performance of the nitride isolation layer can effectively improve the optical crosstalk between the photoelectric sensing areas, thereby improving the optical performance of the device; and, the present application adopts the method of epitaxial semiconductor material to fill the groove to form the photoelectric sensing area, which can avoid the ion damage caused by the ion implantation of the traditional photoelectric sensing area.

[0036] Furthermore, when the substrate is thinned, the nitride isolation layer can also serve as a hard mask stop layer to prevent over-grinding of the wafer edge, effectively improving product quality and yield, and reducing process difficulty.

[0037] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative work.

[0039] Figure 1 is a flow chart of a method for preparing a back-illuminated image sensor in one embodiment of the present invention;

[0040] Figure 2 A schematic diagram of the structure of a substrate in one embodiment of the present invention;

[0041] Figure 3 A schematic diagram of a structure for forming a nitride isolation layer in one embodiment of the present invention;

[0042] Figure 4 It is a schematic diagram of a structure in which a semiconductor material is filled in a trench in one embodiment of the present invention;

[0043] Figure 5 A schematic diagram of a structure for forming a photoelectric sensing area in one embodiment of the present invention;

[0044] Figure 6 A schematic diagram of a structure for forming a metal interconnection structure in one embodiment of the present invention;

[0045] Figure 7 It is a schematic diagram of the structure after bonding with a carrier wafer in one embodiment of the present invention;

[0046] Figure 8 It is a schematic diagram of the structure after the substrate is thinned in one embodiment of the present invention;

[0047] Fig. 9 FIG. 4 is a schematic structural diagram of a back-illuminated image sensor according to an embodiment of the present invention.

[0048] Description of labels:

[0049] 100, substrate; 101, groove; 110, nitride isolation layer; 120, photoelectric sensing area; 130, metal interconnection structure; 140, bonding layer; 150, grid structure; 160, filter element; 200, carrier wafer. DETAILED DESCRIPTION

[0050] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0051] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0052] In the present invention, if the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. appear, the orientation or position relationship indicated is based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limiting the present application. In addition, if the terms "first" and "second" appear, they are only used for description and distinction purposes, and cannot be understood as indicating or implying relative importance.

[0053] Back Side Illumination (BSI) is a new type of CMOS image sensor. After thinning the silicon wafer, a color filter (CF) and a micro lens are built on the back of the photodiode. Light enters from the back, which increases the photosensitive area of ​​the photoelectric element and reduces the loss of light when passing through the wiring. It can greatly improve the photosensitivity of CIS in low-light environments. BSI technology has brought the sensitivity of CMOS imaging to a new level.

[0054] In traditional BSI processes, high-energy ion implantation is mostly used to form a photodiode (PD), and the PD isolation method is mainly isolation by non-homogeneous ions or trenches. In addition, single ion implantation isolation also has the problem of optical crosstalk.

[0055] In order to improve the above-mentioned problem, the present invention provides a method for preparing a back-illuminated image sensor and a back-illuminated image sensor. Before the photoelectric sensing area is formed, a groove is first formed on the substrate, and a nitride isolation layer is formed on the inner wall of the groove. The excellent isolation performance of the nitride isolation layer can effectively improve the optical crosstalk problem between the photoelectric sensing areas.

[0056] See also Figure 1 The present invention provides a method for preparing a back-illuminated image sensor, comprising the following steps:

[0057] S1, providing a substrate 100, and forming a plurality of grooves 101 in the substrate 100 (see Figure 2 );

[0058] S2, forming a nitride isolation layer 110 on the inner walls of the plurality of trenches 101 and on the substrate 100 at both sides of the trenches 101 (see Figure 3 );

[0059] S3, filling the trench 101 with the nitride isolation layer 110 with semiconductor material to form a photoelectric sensing region 120 (see Figure 4 and Figure 5 );

[0060] S4, forming a metal interconnection structure 130 on the substrate 100, wherein the metal interconnection structure 130 covers the photoelectric sensing area 120 (see Figure 6 );

[0061] S5, thinning the side of the substrate 100 away from the metal interconnect structure 130 (see Figure 8 );

[0062] S6, forming a grid structure 150 on a side of the substrate 100 away from the metal interconnect structure 130 (see Fig. 9 ).

[0063] Combine the following Figures 2 to 9 The steps of the preparation method of the back-illuminated image sensor are introduced in detail.

[0064] See also Figure 2The substrate 100 in step S1 may be any material suitable for forming a semiconductor device, such as silicon (Si), germanium (Ge), silicon germanium (SiGe), silicon carbide (SiC), gallium arsenide (GaAs), gallium phosphide (GaP), indium phosphide (InP), indium arsenide (InAs), indium antimonide (InSb), indium nitride (InN), gallium nitride (GaN), silicon germanium (GeSi), sapphire or other semiconductor materials formed by III / V compounds; the substrate 100 may also be a stacked structure, such as silicon / germanium / silicon stacking; the substrate 100 may also be silicon-on-insulator (SOI for short), germanium-on-insulator (GOI for short), etc. The type of the substrate 100 may be selected according to actual production, and may be a P-type substrate or an N-type substrate. In this embodiment, the substrate 100 uses a P-type silicon substrate.

[0065] A plurality of grooves 101 are formed on the substrate 100 to define a plurality of photoelectric sensing regions 120, and the number of the grooves 101 is equal to the number of the photoelectric sensing regions 120 to be formed. For example, if three photoelectric sensing regions 120 are to be formed, corresponding to the three regions of red, green and blue, three grooves 101 are formed on the substrate 100. The substrate 100 has a front side and a back side arranged opposite to each other in the thickness direction, the front side is used to form the device layer, and the back side is used to form the grid structure 150 and the filter element 160, etc. The groove 101 is formed on the front side of the substrate 100, that is, it is formed by extending from the front side of the substrate 100 to the inside. The groove 101 can be formed by conventional technical means in the art. In one embodiment, the formation process of the groove 101 is exemplified as follows: a pad oxide layer is first formed on the substrate 100. The pad oxide layer, as a buffer layer, can improve the stress between the substrate 100 and the pad nitride layer formed subsequently. The pad oxide layer is, for example, a dense silicon oxide material. The pad oxide layer can be formed by a thermal oxidation method, such as dry oxidation, wet oxidation or in-situ steam growth (ISSG). Then a pad nitride layer is formed on the pad oxide layer. The pad nitride layer is, for example, silicon nitride (SiN). The pad nitride layer can be used as a hard mask when the groove 101 is etched to protect the substrate 100 from damage. The pad nitride layer can be formed by a low pressure chemical vapor deposition method (LPCVD), a plasma enhanced chemical vapor deposition method (PECVD) and the like. Then, a PD pattern for defining the photoelectric sensing area 120 is formed on the pad nitride layer. For example, a photoresist is first spin-coated on the pad nitride layer to cover the upper surface of the pad nitride layer. After exposure and development, a plurality of openings exposing the pad nitride layer are formed on the photoresist. The number of openings is the same as the number of the grooves 101. Then, using the photoresist layer with the PD pattern as a mask, the pad nitride layer, the pad oxide layer and part of the substrate 100 are sequentially etched downward to form a groove 101; in this embodiment, for example, the groove 101 is formed by dry etching and / or wet etching, wherein the depth of the groove 101 is selected according to actual production needs and is not limited here. After the groove 101 is formed, the photoresist is removed by ashing or wet cleaning, and then the pad nitride layer and the pad oxide layer are removed by wet etching.

[0066] See also Figure 3, perform step S2 to form a nitride isolation layer 110 on the inner wall of the trench 101. The material of the nitride isolation layer 110 may be, for example, silicon nitride (SiN). Silicon nitride has excellent isolation performance. The lining silicon nitride layer formed on the inner wall of the trench 101 can serve as an isolation structure between adjacent photoelectric sensing regions 120, effectively improving the optical crosstalk problem. If the thickness of the nitride isolation layer 110 in the trench 101 is too thick, it may affect the formation of the photoelectric sensing region 120 and the photoelectric performance of the photoelectric sensing region 120. If the thickness of the nitride isolation layer 110 is too thin, its isolation performance cannot be fully exerted, and thus the optical crosstalk problem between the photoelectric sensing regions 120 cannot be improved. Therefore, in the present application, the thickness of the nitride isolation layer 110 is 50 angstroms to 150 angstroms. Specifically, the thickness of the nitride isolation layer 110 may be 50 angstroms, 80 angstroms, 100 angstroms, 120 angstroms or 150 angstroms, etc.

[0067] In some embodiments, the nitride isolation layer 110 can be formed by low pressure chemical vapor deposition (LPCVD), plasma enhanced chemical vapor deposition (PECVD) or the like. Specifically, the substrate 100 having the groove 101 is placed in a liquid filled with a silicon source such as silane (SiH 4 ) and nitrogen sources such as ammonia (NH 3 ) in a chamber of a CVD machine, react at a low pressure of, for example, 2T~10T, and a temperature of, for example, 300°C~500°C to deposit silicon nitride on the substrate 100, and the thickness of the silicon nitride can be adjusted by controlling the reaction time. Since the substrate 100 is placed in a furnace tube during the deposition of the nitride isolation layer 110, nitride is deposited on the exposed areas of the substrate 100, i.e., the bottom wall and side wall of the groove 101 and the surface of the substrate 100 on both sides of the groove 101. Therefore, in the subsequent process, the nitride isolation layer 110 on the surface of the substrate 100 on both sides of the groove 101 needs to be removed, and the removal step will be described in detail below.

[0068] See also Figure 4 and Figure 5 After the nitride isolation layer 110 is formed, it is necessary to fill the groove 101 with semiconductor material to form a photoelectric sensing area 120, that is, perform step S3. The photoelectric sensing area 120 is used to convert optical signals into electrical signals. The photoelectric sensing area 120 is, for example, a photodiode, which is a PN junction composed of different types of semiconductor materials. The traditional process of the photoelectric sensing area 120 is through high-energy ion implantation, which will cause serious ion damage to the substrate 100. In order to improve the ion damage, the present application adopts an epitaxial method to fill different types of semiconductor materials into the groove 101 to form the photoelectric sensing area 120.

[0069] In one embodiment, a first type of silicon material is first formed in the trench 101 where the nitride isolation layer 110 is formed by epitaxy, wherein the first type of silicon material does not fill the trench 101, so as to leave sufficient space for the subsequent formation of the second type of silicon material; and then the second type of silicon material is epitaxially formed on the first type of silicon material. It should be noted that the first type of silicon material and the second type of silicon material have different doping types, for example, the first type of silicon material is doped with P-type ions, such as boron (B), aluminum (Al), etc., and the second type of silicon material is doped with N-type ions, such as phosphorus (P), arsenic (As), antimony (Sb), etc. On the contrary, the first type of silicon material is doped with N-type ions and the second type of silicon material is doped with P-type ions.

[0070] In other embodiments, the first type of silicon material may be filled in the trench 101 formed with the nitride isolation layer 110 by epitaxy, the first type of silicon material fills the trench 101, and then the second type of doping ions are implanted into the first type of silicon material by ion implantation to transform part of the first type of silicon material into the second type of silicon material. The first type of silicon material and the second type of silicon material have different doping types. For example, the first type of silicon material is doped with P-type ions, such as boron (B), aluminum (Al), etc., and the second type of doping ions include but are not limited to phosphorus (P), arsenic (As), antimony (Sb), etc. On the contrary, the first type of silicon material is doped with N-type ions, and the second type of doping ions include but are not limited to boron (B), aluminum (Al), etc.

[0071] Furthermore, in order to improve the quality of epitaxial silicon, before the epitaxial step, a buffer layer (not shown in the figure) needs to be deposited on the nitride isolation layer 110 as a transition layer to reduce microcracks and dislocations caused by lattice mismatch and thermal expansion coefficient mismatch between silicon nitride and epitaxial silicon, thereby improving the crystal quality of epitaxial silicon. The material of the buffer layer can be, for example, single crystal silicon, polycrystalline silicon, etc. The thickness of the buffer layer is not particularly limited, as long as it can play a mitigating role. As an example, the thickness of the buffer layer is 5 angstroms to 100 angstroms, such as 5 angstroms, 20 angstroms, 50 angstroms, 80 angstroms or 100 angstroms.

[0072] Since the semiconductor material is filled in an epitaxial manner, its upper surface is not flat, and there will also be some semiconductor material on the substrate 100 on both sides of the trench 101. Therefore, after the filling is completed, the filling material needs to be flattened to remove the semiconductor material on the substrate 100 to obtain a flat photoelectric sensing area 120. In this embodiment, the nitride isolation layer 110 on the substrate 100 is used as a stop layer, and a chemical mechanical polishing (CMP) process is used to flatten the epitaxial semiconductor material to obtain a photoelectric sensing area 120 with a smooth and flat surface.

[0073] Furthermore, before executing the next step, the nitride isolation layer 110 on the substrate 100 needs to be removed by, for example, chemical mechanical polishing (CMP) or wet etching. The wet etching method, for example, uses hot phosphoric acid to etch the nitride isolation layer 110 until the front side of the substrate 100 is exposed.

[0074] See also Figure 6 , perform step S4, form a metal interconnection structure 130 on the substrate 100, and the metal interconnection structure 130 covers the photoelectric sensing area 120. The metal interconnection structure 130 is used to connect the functional units of the back-illuminated image sensor to achieve signal transmission and circuit connection. The metal interconnection structure 130 includes a dielectric layer and interconnection metal wires embedded in the dielectric layer, wherein the dielectric layer is used to support and protect the interconnection metal wires, and can also prepare for subsequent bonding. The material of the dielectric layer is, for example, silicon oxide or other low-dielectric material layer, and the dielectric layer can be formed by chemical vapor deposition (CVD), physical vapor deposition (PVD) and other processes. The interconnection metal wires can be made of metal materials with low resistance, such as aluminum (Al), copper (Cu), tungsten (W), etc. The interconnection metal wires can be formed, for example, by a Damascus inlay process. The metal interconnection structure 130 can also be formed by other suitable conventional processes in the art, which will not be repeated here.

[0075] See also Figure 7 and Figure 8 After the metal interconnection structure 130 is formed, step S5 is performed to thin the substrate 100 to increase the utilization of light and improve the photoelectric conversion efficiency of the sensor.

[0076] The specific process is as follows: the side of the substrate 100 provided with the metal interconnection structure 130 is bonded to the carrier wafer 200, wherein the carrier wafer 200 is a wafer without devices, and mainly serves to carry and assist in subsequent process processing. In the bonding step, a bonding layer 140 is provided on the bonding surface of the carrier wafer 200, and the material of the bonding layer 140 is, for example, silicon oxide, and the carrier wafer 200 is bonded to the dielectric layer of the metal interconnection structure 130 through the bonding layer 140. Afterwards, the bonded wafer structure is turned over, and the back side of the substrate 100 (the side away from the metal interconnection structure 130) is thinned. During thinning, the nitride isolation layer 110 at the bottom of the groove 101 is used as a stop layer, and the back of the substrate 100 is thinned by chemical mechanical polishing (CMP) and / or wet etching to obtain a back-illuminated image sensor that meets actual production requirements. Afterwards, CMP or wet etching is used to remove the nitride isolation layer 110 at the bottom of the trench 101. In this step, the nitride isolation layer 110 is used as a hard mask stop layer to improve the problem of wafer edge over-grinding, improve product yield, and reduce manufacturing difficulty.

[0077] See also Fig. 9 , then perform step S6 to form a grid structure 150 on the back side of the substrate 100. The grid structure 150 corresponds to the area formed between adjacent photoelectric sensing areas 120. The grid structure 150 helps to isolate each photoelectric sensing area, reduce light crosstalk between pixels, and improve imaging quality. The grid structure 150 can adopt a conventional structure in the art. As an example, the grid structure 150 includes a multi-layer structure, which is respectively recorded as a first grid layer, a second grid layer, and a third grid layer. The first grid layer is located on the back side of the substrate 100, and a material with a high dielectric constant (high K) can be selected, such as hafnium dioxide (HfO 2 ), the second grid layer is located on the first grid layer, and the second grid layer can be made of metal material, such as aluminum (Al), and the third grid layer is located on the second grid layer as a protective layer of the second grid layer, for example, it can be titanium nitride (TiN). The grid structure 150 adopts a multi-layer structure, which can reduce the generation of dark current and improve the product yield. In this embodiment, the formation process of the grid structure 150 is as follows: first, a first grid material layer, a second grid material layer and a third grid material layer are sequentially formed on the back of the substrate 100 to form a stacked structure, and the formation method is, for example, chemical vapor deposition or physical vapor deposition, etc., and a photoresist layer with a grid pattern is formed on the third grid material layer, and the photoresist layer has an opening that exposes part of the stacked structure, and the opening corresponds to the area between adjacent photoelectric sensing areas; then, the photoresist layer with a grid pattern is used as a mask to sequentially etch the third grid material layer, the second grid material layer and the first grid material layer to form a multi-layer grid structure 150, which can be specifically carried out by dry etching, wet etching or a combination of dry etching and wet etching.

[0078] See also Fig. 9 , further, after forming the grid structure 150, the method for preparing the image sensor of the present application also includes: forming a filter element 160 between the grid structures 150. The filter element 160, for example, includes a plurality of color filters, and the plurality of color filters form a color filter array. Each color filter corresponds to a photoelectric sensing area 120. In this embodiment, the filter element 160 includes at least three primary color color filters, and they can be arranged in any suitable combination. Among them, the color filter can be a polymer material, such as a negative photoresist with an acrylic polymer as a substrate, and can contain a color dye. When light passes through the color filter, it can change color, maintain a high transmittance in a certain band, and thus enhance the effect of photoelectric conversion. Furthermore, a microlens structure is also provided on the color filter. Since the surface of the microlens is convex, it can focus the incident light on the photoelectric sensing area 120. According to the focusing requirements, the curvature of the surface of the filter element 160 can be changed to improve the photosensitivity efficiency.

[0079] See also Fig. 9 Based on the same inventive concept, the present invention also provides a back-illuminated image sensor, which is prepared by the above-mentioned preparation method. The back-illuminated image sensor includes: a substrate 100, a nitride isolation layer 110, a photoelectric sensing region 120, a metal interconnection structure 130 and a grid structure 150.

[0080] Specifically, the substrate 100, as the base of the back-illuminated image sensor, can be any material suitable for forming a semiconductor device, such as silicon (Si), germanium (Ge), silicon germanium (SiGe), silicon carbide (SiC), gallium arsenide (GaAs), gallium phosphide (GaP), indium phosphide (InP), indium arsenide (InAs), indium antimonide (InSb), indium nitride (InN), gallium nitride (GaN), silicon germanium (GeSi), sapphire or other semiconductor materials formed by III / V compounds, etc.; it can also be a stacked structure, such as silicon / germanium / silicon stacked, etc.; and silicon-on-insulator (SOI for short), germanium-on-insulator (GOI for short), etc. The type of the substrate 100 can be selected according to actual production, and a P-type substrate or an N-type substrate can be used. In this embodiment, the substrate 100 uses a P-type silicon substrate.

[0081] A plurality of grooves 101 are formed in the substrate 100 to define the photoelectric sensing regions 120. The number of the grooves 101 is equal to the number of the photoelectric sensing regions 120 to be formed. In one embodiment, the photoelectric sensing regions 120 include at least three photoelectric sensing regions 120 of red, green and blue, and at least three grooves 101 are formed in the substrate 100.

[0082] The nitride isolation layer 110 is disposed on the inner walls of the plurality of trenches 101; the material of the nitride isolation layer 110 may be, for example, silicon nitride (SiN), which has excellent isolation performance. The linear silicon nitride formed on the inner walls of the trenches 101 may serve as an isolation structure between adjacent photoelectric sensing regions 120, effectively improving the optical crosstalk problem. Further, the thickness of the nitride isolation layer 110 is 50 angstroms to 150 angstroms, and specifically, the thickness of the nitride isolation layer 110 may be 50 angstroms, 80 angstroms, 100 angstroms, 120 angstroms, or 150 angstroms, etc.

[0083] The photoelectric sensing region 120 is filled in the trench 101 formed with the nitride isolation layer 110, and the photoelectric sensing region 120 is used to convert the optical signal into an electrical signal. The photoelectric sensing region 120 is, for example, a photodiode, which is a PN junction composed of different types of semiconductor materials. In one embodiment, the photoelectric sensing region 120 includes a first type silicon material and a second type silicon material, wherein the first type silicon material and the second type silicon material have different doping types, for example, the first type silicon material is a P-type doped silicon material, and the second type silicon material is an N-type doped silicon material, or vice versa.

[0084] The metal interconnection structure 130 is disposed on the substrate 100 and covers the photoelectric sensing area 120. The metal interconnection structure 130 is used to connect the functional units of the back-illuminated image sensor to achieve signal transmission and circuit connection. The metal interconnection structure 130 includes a dielectric layer and interconnection metal wires embedded in the dielectric layer, wherein the dielectric layer is used to support and protect the interconnection metal wires, and the material of the dielectric layer is, for example, silicon oxide or other low-dielectric material layers, and the interconnection metal wires can be made of metal materials with low resistance, such as aluminum (Al), copper (Cu), tungsten (W), etc.

[0085] The grid structure 150 is disposed on the side of the substrate 100 away from the interconnection metal structure 130. The grid structure 150 is formed corresponding to the area between adjacent photoelectric sensing areas 120. The grid structure 150 helps to isolate each photoelectric sensing area, reduce light crosstalk between pixels, and improve imaging quality. The grid structure 150 can adopt a conventional structure in the art. As an example, the grid structure 150 includes a first grid layer, a second grid layer, and a third grid layer. The first grid layer is located on the back of the substrate 100, and a material with a high dielectric constant (high K) can be selected, such as hafnium dioxide (HfO 2 ), the second grid layer is located on the first grid layer, the second grid layer can be made of metal material, such as aluminum (Al), the third grid layer is located on the second grid layer, and serves as a protective layer for the second grid layer, such as titanium nitride (TiN).

[0086] Further, the back-illuminated image sensor also includes a filter element 160, which is arranged between adjacent grid structures 150 and corresponds to the photoelectric sensing area 120. The filter element 160, for example, includes a plurality of color filters, and the plurality of color filters form a color filter array. Each color filter corresponds to a photoelectric sensing area 120. In this embodiment, the filter element 160 includes at least three primary color color filters, and they can be arranged in any suitable combination. Among them, the color filter can be a polymer material, such as a negative photoresist with an acrylic polymer as a substrate, and can contain a color dye. When light passes through the color filter, it can change color, maintain a high transmittance in a certain band, and thus enhance the effect of photoelectric conversion. Furthermore, a microlens structure is also provided on the color filter. Since the surface of the microlens is convex, it can focus the incident light on the photoelectric sensing area 120. According to the focusing requirements, the curvature of the surface of the filter element 160 can be changed to improve the photosensitivity efficiency.

[0087] It should be noted that the structures and processes of the present invention not described in detail above can all be manufactured according to conventional technical means in the art.

[0088] The preparation method of the back-illuminated sensor of the present invention forms a groove on the substrate before the photoelectric sensing area is formed, and forms a nitride isolation layer on the inner wall of the groove, and uses the nitride isolation layer as an isolation structure between adjacent photoelectric sensing areas. The excellent isolation performance of the nitride isolation layer can effectively improve the optical crosstalk between the photoelectric sensing areas, thereby improving the optical performance of the device; and, the use of epitaxial semiconductor materials to fill the groove to form the photoelectric sensing area can avoid ion damage caused by ion implantation in the traditional photoelectric sensing area. When the substrate is thinned, the nitride isolation layer can also be used as a hard mask stop layer to prevent over-grinding of the wafer edge, effectively improve product quality and increase yield, and reduce process difficulty. Therefore, the present invention effectively overcomes some practical problems in the prior art and has high utilization value and use significance.

[0089] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A method for preparing a back-illuminated image sensor, characterized in that: The following steps are involved: providing a substrate, and forming a plurality of grooves in the substrate; forming a nitride isolation layer on the inner walls of the plurality of trenches and the substrate at both sides of the trenches; Filling the trench with the nitride isolation layer with semiconductor material to form a photoelectric sensing region; forming a metal interconnection structure on the substrate, wherein the metal interconnection structure covers the photoelectric sensing area; Turning the substrate over, using the nitride isolation layer at the bottom of the trench as a stop layer, thinning the side of the substrate away from the metal interconnect structure, and removing the nitride isolation layer at the bottom of the trench; forming a grid structure on a side of the substrate facing away from the metal interconnect structure; Among them, different types of semiconductor materials are filled into the groove by epitaxy to form a photoelectric sensing area. Before the epitaxy step, it also includes: depositing a buffer layer on the nitride isolation layer, and the material of the buffer layer is single crystal silicon or polycrystalline silicon.

2. The method for preparing a back-illuminated image sensor according to claim 1, characterized in that: The material of the nitride isolation layer includes silicon nitride, and the thickness of the nitride isolation layer is 50 to 150 angstroms.

3. The method for preparing a back-illuminated image sensor according to claim 1, characterized in that: The step of filling the trench with the nitride isolation layer with a semiconductor material to form a photoelectric sensing region comprises: epitaxially forming a first type of silicon material in the trench; A second type of silicon material is epitaxially formed on the first type of silicon material; wherein the first type of silicon material and the second type of silicon material have different doping types.

4. The method for preparing a back-illuminated image sensor according to claim 1, characterized in that: The step of filling the trench with the nitride isolation layer with a semiconductor material to form a photoelectric sensing region comprises: epitaxially forming a first type of silicon material in the trench; Implanting second type doping ions into the first type silicon material to transform a portion of the first type silicon material into second type silicon material; wherein the first type silicon material and the second type silicon material have different doping types.

5. The method for preparing a back-illuminated image sensor according to claim 1, characterized in that: The step of thinning the side of the substrate facing away from the metal interconnect structure comprises: Bonding a side of the substrate provided with the metal interconnect structure to a carrier wafer; Using the nitride isolation layer at the bottom of the trench as a stop layer, thinning the side of the substrate away from the metal interconnect structure; The nitride isolation layer at the bottom of the trench is removed.

6. The method for preparing a back-illuminated image sensor according to claim 1, characterized in that: Before forming the metal interconnection structure on the substrate, the method further includes: planarizing the semiconductor material and removing the nitride isolation layer on the substrate at both sides of the trench.

7. The method for preparing a back-illuminated image sensor according to claim 1, characterized in that: The step of forming a grid structure on a side of the substrate away from the metal interconnect structure comprises: Forming a stacked structure on a side of the substrate away from the photoelectric sensing region, the stacked structure comprising a first grid material layer, a second grid material layer and a third grid material layer; Forming a photoresist layer having a grid pattern on the stacked structure, wherein the photoresist layer has an opening exposing a portion of the stacked structure, and the opening corresponds to a region between adjacent photoelectric sensing regions; The photoresist layer with the grid pattern is used as a mask to remove the stacked structure exposed by the opening to form a grid structure.

8. The method for preparing a back-illuminated image sensor according to claim 1, characterized in that: After the grid structure is formed, the method further includes: forming a filter element between adjacent grid structures, wherein the filter element is arranged corresponding to the photoelectric sensing area.

9. A back-illuminated image sensor, characterized in that: The back-illuminated image sensor is manufactured by the manufacturing method according to any one of claims 1 to 8, and comprises: a substrate having a plurality of grooves formed therein; A nitride isolation layer is disposed on the sidewalls of the plurality of trenches; A photoelectric sensing region filled in the groove; A metal interconnection structure, disposed on the substrate and covering the photoelectric sensing area; The grid structure is arranged on a side of the substrate away from the metal interconnection structure.

10. The back-illuminated image sensor according to claim 9, wherein: It also includes a filter element, which is arranged between adjacent grid structures and corresponds to the photoelectric sensing area.

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