Backside illuminated image sensor and method of making the same

Abstract

The application discloses a back-illuminated image sensor and a preparation method thereof. The method comprises the following steps: providing a substrate; forming a plurality of sacrificial structures with the same interval on the substrate; forming a sidewall on the sidewall of the sacrificial structure, removing the sacrificial structure, and forming a transition mask pattern composed of the sidewall; removing part of the sidewall in the transition mask pattern to obtain a first mask pattern, the first mask pattern has a plurality of openings between the sidewalls, and the width of at least one opening is different from the width of other openings; taking the first mask pattern as a mask, forming a plurality of grooves in the substrate, and the depth of the groove corresponding to the opening with different width is different; removing the first mask pattern; forming an isolation structure in the groove; removing part of the substrate between adjacent isolation structures to form a plurality of device accommodation grooves; forming a doped layer in the device accommodation groove, and the doping type of the doped layer is opposite to the doping type of the substrate.

Description

TECHNICAL FIELD

[0001] Embodiments of the present disclosure relate to the technical field of semiconductor technology, and particularly to a back-illuminated image sensor and a preparation method thereof. BACKGROUND

[0002] A CMOS back-illuminated image sensor (CMOS Image Sensor BSI) includes a plurality of photodiodes and a deep trench isolation structure (DTI) between the photodiodes. In an advanced process of the CMOS back-illuminated image sensor, the size of the deep trench isolation structure between the plurality of photodiodes is the same, which cannot meet the different isolation requirements between the plurality of photodiodes in the back-illuminated image sensor. SUMMARY

[0003] Embodiments of the present disclosure provide a back-illuminated image sensor and a preparation method thereof, which can optimize the size of the isolation structure between the photodiodes, and meet the different isolation requirements between the photodiodes in the back-illuminated image sensor without affecting the size of the photodiodes.

[0004] A preparation method of a back-illuminated image sensor, comprising:

[0005] providing a substrate;

[0006] forming a plurality of sacrificial structures with the same interval on the substrate;

[0007] forming a side wall on the side wall of the sacrificial structure, removing the sacrificial structure, and forming a transition mask pattern composed of the side wall;

[0008] removing part of the side wall in the transition mask pattern to obtain a first mask pattern, the first mask pattern has a plurality of openings between the side walls, and the width of at least one opening is different from the width of other openings;

[0009] forming a plurality of trenches in the substrate using the first mask pattern as a mask, and the depths of the trenches corresponding to the openings with different widths are different;

[0010] removing the first mask pattern;

[0011] forming an isolation structure in the trench;

[0012] removing part of the substrate between adjacent isolation structures to form a plurality of device accommodation grooves;

[0013] forming a doped layer in the device accommodation groove, and the doping type of the doped layer is opposite to the doping type of the substrate.

[0014] In one of the embodiments, the depths of the at least two device accommodating grooves are different, and the depth of any of the device accommodating grooves is less than or equal to the minimum depth of the adjacent isolation structure.

[0015] In one of the embodiments, the depths of the device accommodating grooves are equal, and the depth of the device accommodating grooves is less than or equal to the minimum depth of the isolation structure.

[0016] In one of the embodiments, the method for manufacturing the back-illuminated image sensor further comprises:

[0017] forming a light shielding layer on the surface of the isolation structure.

[0018] In one of the embodiments, the openings of the light shielding layer expose the doped layers, and the method for manufacturing the back-illuminated image sensor further comprises:

[0019] forming a color filter layer on the surface of each of the doped layers, respectively, the color filter layer being filled in the corresponding opening of the light shielding layer.

[0020] In one of the embodiments, the material of the sacrificial structure is the same as that of the substrate; an etching protection layer is further formed between the substrate and the sacrificial structure; after the first mask pattern is removed, before the isolation structure is formed in the trench, the method for manufacturing the back-illuminated image sensor further comprises:

[0021] removing the etching protection layer.

[0022] In one of the embodiments, the step of forming a plurality of trenches in the substrate using the first mask pattern as a mask comprises:

[0023] using an isotropic etching process to etch the substrate at the opening position using the first mask pattern as a mask;

[0024] using a non-isotropic etching process to etch the substrate at the opening position using the first mask pattern as a mask;

[0025] wherein the depth of the trench is negatively correlated with the width of the corresponding opening.

[0026] In one of the embodiments, the process gas of the isotropic etching process comprises methane and fluoromethane, and the bias power is 0; the process gas of the non-isotropic etching process comprises methane and fluoromethane, and the bias power is greater than 0.

[0027] In one of the embodiments, the step of forming an isolation structure in the trench comprises:

[0028] forming an isolation material layer in the trench;

[0029] Chemical mechanical planarization is performed on the isolation material layer to obtain an isolation structure in the trench.

[0030] The top surface of the isolation structure is flush with the surface of the substrate.

[0031] A back-illuminated image sensor is prepared by the method.

[0032] The unexpected technical effects that can be produced by the application are:

[0033] In the back-illuminated image sensor and the preparation method thereof, the uniformity of the size of each side wall located on the sidewall of the sacrificial structure is improved by forming the sacrificial structures with the same pitch on the substrate, the influence of the pitch between the sacrificial structures on the size of the doped layer in the back-illuminated image sensor is eliminated, and the performance of the back-illuminated image sensor is improved. By removing part of the side wall, the widths of the openings between the side walls are different, thereby forming trenches with different depths corresponding to each opening, so that the sizes of the isolation structures in the trenches are different, thereby meeting the different isolation requirements between the photoactive devices formed subsequently between adjacent isolation structures. In the application, the isolation structure is formed first, and then the doped layer between the isolation structures is formed, the isolation structure serves as a self-aligned structure for forming the doped layer, and the isolation structure is formed first, and then the doped layer between the isolation structures is formed, thereby improving the accuracy of the shape and position of the doped layer. BRIEF DESCRIPTION OF DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure or the related art, the following will briefly introduce the drawings needed to be used in the embodiments or related art descriptions. Obviously, the drawings in the following description are only some embodiments of the present disclosure, and for those skilled in the art, other drawings can also be obtained without creative labor based on these drawings.

[0035] Figure 1 A flowchart of the preparation method of the back-illuminated image sensor in some embodiments;

[0036] Figure 2 A cross-sectional view of the back-illuminated image sensor after forming a photoresist pattern in some embodiments;

[0037] Figure 3 A cross-sectional view of the back-illuminated image sensor after forming a sacrificial layer in some embodiments;

[0038] Figure 4 A cross-sectional view of the back-illuminated image sensor after forming a side wall material layer in some embodiments;

[0039] Figure 5A cross-sectional view of a backside illuminated image sensor after formation of a second mask pattern for some embodiments;

[0040] Figure 6 A cross-sectional view of a backside illuminated image sensor after formation of a second mask pattern for some embodiments;

[0041] Figure 7 A cross-sectional view of a backside illuminated image sensor after formation of a first mask pattern for some embodiments;

[0042] Figure 8 A cross-sectional view of a backside illuminated image sensor after formation of a trench for some embodiments;

[0043] Figure 9 A cross-sectional view of a backside illuminated image sensor after formation of an isolation structure for some embodiments;

[0044] Figure 10 A cross-sectional view of a backside illuminated image sensor after formation of a device receptacle for some embodiments;

[0045] Figure 11 A cross-sectional view of a backside illuminated image sensor after formation of a light blocking layer for some embodiments.

[0046] BRIEF DESCRIPTION OF DRAWINGS

[0047] substrate 102, hard mask layer 104, metal interconnect structure 106, etch stop layer 108, sidewall 110, second mask pattern 112, first mask pattern 114, isolation structure 116, doped layer 118, light blocking layer 120, color filter layer 122, photoresist pattern 202, sacrificial structure 204, sidewall material layer 206, opening 208, trench 210, device receptacle 212. DETAILED DESCRIPTION

[0048] In order to make the disclosure more comprehensively understood, the following will refer to the related drawings to make a more comprehensive description of the embodiments of the present disclosure. The preferred embodiments of the present disclosure are shown in the drawings. However, the embodiments of the present disclosure can be realized in many different forms, and are not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the embodiments of the present disclosure more thorough and comprehensive.

[0049] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the embodiments of the present disclosure belong. The terminology used in the description of the embodiments of the present disclosure herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the embodiments of the present disclosure. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0050] In the description of the embodiments of the present disclosure, it needs to be understood that the terms "upper", "lower", "vertical", "horizontal", "inner", "outer" and the like indicate the positional or positional relationship shown in the drawings based on the method or positional relationship, and are only for the convenience of describing the embodiments of the present disclosure and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the embodiments of the present disclosure.

[0051] It can be understood that the terms "first", "second" and the like used in the present disclosure can be used herein to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish the first element from another element. For example, without departing from the scope of the present disclosure, the first mask can be referred to as the second mask, and similarly, the second mask can be referred to as the first mask. The first mask and the second mask are both masks, but they are not the same mask.

[0052] In addition, the terms "first", "second" are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined with "first", "second" can explicitly or implicitly include at least one of the features. In the description of the present disclosure, the meaning of "a plurality of" is at least two, such as two, three, etc., unless otherwise explicitly and specifically limited. In the description of the present disclosure, the meaning of "several" is at least one, such as one, two, etc., unless otherwise explicitly and specifically limited.

[0053] Figure 1 For the flowchart of the preparation method of the back-illuminated image sensor in some embodiments, as shown in Figure 1 In the present embodiment, a preparation method of a back-illuminated image sensor is provided, comprising:

[0054] S102, providing a substrate.

[0055] Specifically, the substrate includes oppositely arranged first and second surfaces, and the subsequently formed sacrificial structure is located on the first surface of the substrate. The constituent material of the substrate includes single crystal silicon, silicon-on-insulator (SOI), silicon-on-insulator (SSOI), silicon-on-insulator (S-SiGeOI), silicon-on-insulator (SiGeOI), and germanium-on-insulator (GeOI), gallium arsenide (GaAs), gallium nitride (GaN), silicon carbide (SiC) or any combination thereof. As an example, in the present embodiment, the constituent material of the substrate is selected to be single crystal silicon.

[0056] S104, forming a plurality of sacrificial structures with the same pitch on the substrate.

[0057] Specifically, a plurality of spaced-apart sacrificial structures are formed on the substrate, and the distance between any two adjacent sacrificial structures is the same in a plane parallel to the substrate.

[0058] In S106, sidewalls are formed on the sidewalls of the sacrificial structures, and the sacrificial structures are removed to form a transition mask pattern composed of the sidewalls.

[0059] Specifically, the sidewalls are formed on the sidewalls of the sacrificial structures, and the sidewalls are contiguous to the sacrificial structures, the top surfaces of the sidewalls away from the substrate are flush with the top surfaces of the sacrificial structures away from the substrate, and the bottom surfaces of the sidewalls close to the substrate are flush with the bottom surfaces of the sacrificial structures close to the substrate. The distance between any two adjacent sacrificial structures is the same, so that the size of the sidewalls on the sidewalls of each sacrificial structure is the same, and the uniformity of the sidewalls is improved. Then, the sacrificial structures are removed by etching (for example, dry etching) to form a transition mask pattern composed of the sidewalls.

[0060] In S108, part of the sidewalls in the transition mask pattern is removed to obtain a first mask pattern.

[0061] The sidewalls in part of the positions of the transition mask pattern are removed by lithography and etching to obtain a first mask pattern composed of the remaining sidewalls. The first mask pattern has a plurality of openings between adjacent sidewalls, and at least one opening has a width different from the widths of the other openings. The width is the distance between the adjacent sidewalls in a direction parallel to the substrate. By removing the sidewalls in part of the positions, the width of the opening between the adjacent sidewalls in the first mask pattern is adjusted to achieve the purpose of adjusting the width of the trench formed subsequently in a plane parallel to the substrate, and further adjusting the depth of the trench in a direction perpendicular to the substrate. Meanwhile, the position covered by the first mask pattern is used to form a doped layer subsequently. The doped layer and the substrate at the bottom form a photosensitive device between the isolation structures. The shape and position of the photosensitive device in a plane parallel to the substrate, and the shape and position of the isolation structures in a plane parallel to the substrate are defined by the first mask pattern.

[0062] In S110, a plurality of trenches are formed in the substrate by taking the first mask pattern as a mask.

[0063] The substrate with a thickness exposed by the opening is removed by etching to form a plurality of trenches in the substrate by taking the first mask pattern as a mask. The plurality of trenches correspond to the plurality of openings respectively, and the trenches corresponding to the openings with different widths in a plane parallel to the substrate have different depths in a direction perpendicular to the substrate.

[0064] In S112, the first mask pattern is removed.

[0065] In S114, isolation structures are formed in the trenches.

[0066] Specifically, the isolation structure is formed in the trench, the isolation structure fills the trench, the top surface of the isolation structure is flush with the first surface of the substrate, and the sizes of the isolation structures corresponding to trenches with different depths are different, thereby meeting the requirement of different isolation between different photosensitive devices formed subsequently between adjacent isolation structures.

[0067] S116, removing the part of the substrate between adjacent isolation structures to form a plurality of device accommodation grooves.

[0068] Specifically, the part of the substrate between adjacent isolation structures is etched to form a device accommodation groove between adjacent isolation structures, and the sidewall of the device accommodation groove in the direction perpendicular to the substrate exposes the adjacent isolation structure, and adjacent device accommodation grooves are separated by the isolation structure.

[0069] S118, forming a doped layer in the device accommodation groove.

[0070] Specifically, the doped layer is formed in the device accommodation groove, the doped layer has a first conductivity type, and the substrate has a second conductivity type, i.e. the doping type of the doped layer is opposite to the doping type of the substrate. The doping type includes N-type doping and P-type doping, when the first conductivity type is P-type, the second conductivity type is N-type, and when the first conductivity type is N-type, the second conductivity type is P-type. In this embodiment, the first conductivity type is N-type, and the second conductivity type is P-type. Further, the top surface of the doped layer close to the first surface of the substrate is flush with the first surface of the substrate.

[0071] In the above back-illuminated image sensor and the preparation method thereof, the uniformity of the size of each sidewall of the sidewall of the sacrificial structure is improved by forming the sacrificial structures with the same pitch on the substrate, the influence of the pitch between the sacrificial structures on the size of the doped layer in the back-illuminated image sensor is eliminated, and the performance of the back-illuminated image sensor is improved. By removing part of the sidewall, the width of the opening between the sidewalls is different, thereby forming trenches with different depths corresponding to each opening, so that the sizes of the isolation structures in the trenches are different, thereby meeting the requirement of different isolation between photosensitive devices formed subsequently between adjacent isolation structures. In this application, the isolation structure is formed first, and then the doped layer between the isolation structures is formed, the isolation structure serves as a self-alignment structure for forming the doped layer, and the isolation structure is formed first, and then the doped layer between the isolation structures is formed, which improves the accuracy of the shape and position of the doped layer.

[0072] Figure 2 For some embodiments, a cross-sectional view of the back-illuminated image sensor after forming a photoresist pattern is shown, Figure 3 For some embodiments, a cross-sectional view of the back-illuminated image sensor after forming a sacrificial layer is shown, such as Figure 2 、 Figure 3As shown, the step of forming a plurality of equally spaced sacrificial structures 204 on the substrate includes steps S202-S204.

[0073] S202, a hard mask layer is formed on the substrate.

[0074] S204, the hard mask layer is patterned using the first mask to form the sacrificial structure 204.

[0075] Specifically, steps S202-S204 are as follows: First, a hard mask layer 104 and a photoresist layer are sequentially formed on the first surface of the substrate 102, extending from the first surface of the substrate 102 away from the first surface of the substrate 102. Second, the hard mask layer 104 is patterned using a first mask to form multiple sacrificial structures 204 with equal spacing. Specifically, the photoresist layer is patterned using the first mask to form a photoresist pattern 202 on the surface of the hard mask layer 104 away from the substrate 102. Second, the hard mask layer 104 exposed by the photoresist pattern 202 is etched away using the photoresist pattern 202 as a mask, forming multiple spaced sacrificial structures 204 composed of the remaining hard mask layer 104 (the hard mask layer 104 covered by the photoresist pattern 202), with the same spacing L1 between adjacent sacrificial structures 204.

[0076] It is understood that during the etching process to remove the hard mask layer 104 exposed by the photoresist pattern 202, or after forming the sacrificial structure 204, the fabrication method of the back-illuminated image sensor includes the step of removing the photoresist pattern 202.

[0077] For example, the hard mask layer 104 may be made of silicon, amorphous silicon, or amorphous carbon, and may be formed by processes such as epitaxy, spin coating, or spray coating. In this embodiment, silicon is selected as the material for the hard mask layer 104. In this case, the hard mask layer 104 is made of the same material as the substrate 102.

[0078] like Figure 2 As shown, a metal interconnect structure 106 is formed on the second surface of the substrate 102. The metal interconnect structure 106 is used to realize the interconnection of devices in the substrate 102. For example, the first surface is the back surface of the substrate 102, and the second surface is the back surface of the substrate 102.

[0079] like Figure 2As shown, the first surface of the substrate 102 is formed with an etching protection layer 108 covering the first surface of the substrate 102, and the hard mask layer 104 is located on the surface of the etching protection layer 108 away from the substrate 102. Exemplarily, the material of the etching protection layer 108 includes silicon oxide, and the etching protection layer 108 is formed on the first surface of the substrate 102 by a thermal oxidation process or a chemical vapor deposition process.

[0080] Figure 4 FIG. 6 is a schematic view of a cross section of a back-illuminated image sensor after forming a side wall material layer in some embodiments, Figure 5 FIG. 7 is a schematic view of a cross section of a back-illuminated image sensor after forming a side wall in some embodiments, as Figure 4 、 Figure 5 In one embodiment, as shown in FIG. 7, the step of forming the side wall 110 on the sidewall of the sacrificial structure 204 includes steps S302-S304.

[0081] S302, forming a side wall material layer 206 on the top surface of the sacrificial structure 204, the side wall material layer 206 extending along the sidewall of the sacrificial structure 204 to the substrate 102.

[0082] S304, removing the side wall material layer 206 on the top surface of the sacrificial structure 204 and part of the side wall material layer 206 on the substrate 102, and retaining the side wall material layer 206 on the sidewall of the sacrificial structure 204 as the side wall 110.

[0083] Specifically, first, a chemical vapor deposition process or an atomic layer deposition process is used to form the side wall material layer 206 on the top surface of the sacrificial structure 204, the side wall material layer covering the sidewall of the sacrificial structure 204 and extending along the sidewall of the sacrificial structure 204 to cover the substrate 102, wherein the interval L1 between two adjacent sacrificial structures 204 is the same, so that the size L2 of the side wall material layer 206 on the sidewall of the sacrificial structure 204 in the direction parallel to the substrate 102 (the direction in the plane of the first direction X and the second direction Z) is the same, improving the uniformity of the subsequently formed side wall 110. Second, part of the side wall material layer 206 on the top surface of the sacrificial structure 204 and the substrate 102 is etched and removed, and the side wall material layer 206 on the sidewall of the sacrificial structure 204 is retained as the side wall 110, wherein the etching protection layer 108 can be used as an etching stop layer for etching part of the side wall material layer 206 on the substrate 102.

[0084] Exemplarily, the material of the side wall 110 includes one or more of silicon oxide (e.g., silicon dioxide), silicon nitride (e.g., silicon oxynitride), and nitride (e.g., silicon nitride). In this embodiment, the material of the side wall 110 is selected as silicon nitride.

[0085] AsFigure 6 As shown, the method for preparing the back-illuminated image sensor further comprises a step of removing the sacrificial structure 204.

[0086] Figure 6 FIG. 6 is a schematic view of a cross section of a back-illuminated image sensor after forming a second mask pattern in some embodiments, Figure 7 FIG. 5 is a schematic view of a cross section of a back-illuminated image sensor after forming a first mask pattern in some embodiments, as shown in Figure 6 、 Figure 7 As shown in one of the embodiments, the step of removing part of the sidewall 110 in the transition mask pattern to obtain the first mask pattern comprises steps S402-S404.

[0087] S402, forming a second mask pattern 112 on the substrate 102, the second mask pattern 112 covering the sidewall 110 in the first mask pattern.

[0088] S404, etching to remove the exposed sidewall 110 with the second mask pattern 112 as a mask to form the first mask pattern.

[0089] Specifically, the steps S402-S404 are as follows: first, forming a second mask material layer on the substrate 102, and performing a patterning process on the second mask material layer by using a second mask plate to form a second mask pattern 112 composed of a remaining second mask material layer, the second mask pattern 112 covering the sidewall 110 to be retained and exposing the sidewall 110 to be removed, and exemplarily, the constituting material of the second mask material layer includes photoresist, nitride (silicon nitride), amorphous silicon or amorphous carbon. Second, etching to remove the exposed sidewall 110 with the second mask pattern 112 as a mask to form a first mask pattern 114 composed of a remaining sidewall 110, wherein the etching protection layer 108 can be used as an etching stop layer for removing the exposed sidewall 110. The first mask pattern 114 has a plurality of openings 208 between adjacent sidewalls 110, and at least one opening 208 has a width W1 different from the width W2 of the other openings 208, the width being the distance between the adjacent sidewalls 110 in the same direction (any direction in the plane of the first direction X and the second direction Z) parallel to the substrate 102. By removing part of the sidewall 110, the width of the opening 208 between the adjacent sidewalls 110 in the first mask pattern 114 is adjusted.

[0090] Figure 8 FIG. 4 is a schematic view of a cross section of a back-illuminated image sensor after forming a trench in some embodiments, as shown in Figure 8 As shown in one of the embodiments, the step of forming a plurality of trenches 210 in the substrate 102 with the first mask pattern 114 as a mask comprises steps S502-S504.

[0091] S502, using the first mask pattern 114 as a mask, using an isotropic etching process to etch the base 102 at the position of the opening 208.

[0092] S504, using the first mask pattern 114 as a mask, using a non-isotropic etching process to etch the base 102 at the position of the opening 208.

[0093] Steps S502-S504 are specifically, using the first mask pattern 114 as a mask, using an isotropic etching process and a non-isotropic etching process to etch the base 102 at the position of the opening 208, forming a groove 210 in the base 102, the depth D of the groove 210 is negatively related to the width W corresponding to the opening 208, that is, the depth of the groove 210 corresponding to the opening 208 with large width is small, and the depth of the groove 210 corresponding to the opening 208 with small width is large, the direction of the depth D is the third direction Y perpendicular to the base 102. It can be understood that when the base 102 has the etching protection layer 108, the etching protection layer 108 exposed by the opening 208 is removed, and then the base 102 is etched.

[0094] For example, when the ratio of the depth of the groove 210 to the width of the opening 208 is greater than or equal to 1:5 and less than or equal to 1:1, the isotropic etching process is performed first and then the non-isotropic etching process is performed in the process of forming the groove 210; when the ratio of the depth of the groove 210 to the width of the opening 208 is greater than or equal to 1:10 and less than 1:5, the non-isotropic etching process is performed first and then the isotropic etching process is performed in the process of forming the groove 210; when the ratio of the depth of the groove 210 to the width of the opening 208 is less than 1:10, the order of the isotropic etching process and the non-isotropic etching process is not limited.

[0095] In one of the embodiments, the process gas of the isotropic etching process includes methane and fluoromethane, and the bias power is 0; the process gas of the non-isotropic etching process includes methane and fluoromethane, and the bias power is greater than 0.

[0096] For example, in the isotropic etching process, the flow rate of the methane gas is greater than or equal to 100 sccm and less than or equal to 150 sccm, the flow rate of the fluoromethane gas is greater than or equal to 60 sccm and less than or equal to 100 sccm, and the process time of the isotropic etching process is greater than or equal to 15 s and less than or equal to 30 s. In the non-isotropic etching process, the flow rate of the methane gas is greater than or equal to 100 sccm and less than or equal to 150 sccm, the flow rate of the fluoromethane gas is greater than or equal to 60 sccm and less than or equal to 100 sccm, the process time of the non-isotropic etching process is greater than or equal to 15 s and less than or equal to 30 s, and the bias power in the non-isotropic etching process is 100 W.

[0097] In one of the embodiments, after the first mask pattern 110 is removed, before the isolation structure is formed in the trench 210, the method for manufacturing the back-illuminated image sensor further comprises: removing the etching protection layer 108.

[0098] Figure 9 A cross-sectional view of the back-illuminated image sensor after the isolation structure is formed in some embodiments is shown in FIG. 6B. Figure 9 As shown in one of the embodiments, the step of forming the isolation structure 116 in the trench 210 comprises steps S602-S604.

[0099] S602, forming an isolation material layer in the trench 210.

[0100] S604, performing chemical mechanical planarization on the isolation material layer to obtain the isolation structure 116 in the trench 210.

[0101] Specifically, the steps S602-S604 comprise: forming an isolation material layer in the trench 210 by using a chemical vapor deposition process or an atomic layer deposition process, the isolation material layer fills the trench 210 and extends along the sidewall of the trench 210 to the surface of the substrate 102. Then, performing planarization on the isolation material layer by using a chemical mechanical planarization process to remove the isolation material layer above the surface of the substrate 102, and to form the isolation structure 116 in the trench 210, the top surface of the isolation structure 116 is flush with the surface (the first surface) of the substrate 102, and the isolation structure 116 corresponding to the trench 210 with different depth D has different size, so that the isolation structures 116 between the subsequently formed photosensitive devices are different, which meets the requirement of the photosensitive device for isolation, and the isolation structure 116 defines the position and shape of the photosensitive device, and plays an alignment role in the process of forming the photosensitive device.

[0102] For example, the isolation structure 116 is composed of one or more of silicon oxide (e.g., silicon dioxide), silicon nitride (e.g., silicon oxynitride), and nitride (e.g., silicon nitride), and in this embodiment, the isolation structure 116 is composed of silicon dioxide.

[0103] Figure 10 A cross-sectional view of the back-illuminated image sensor after the device accommodating groove is formed in some embodiments is shown in FIG. 7B. Figure 10As shown, etching removes the portions of the substrate 102 between the adjacent isolation structures 116, forming a plurality of device accommodation grooves 212, the sidewalls of the device accommodation grooves 212 exposing the adjacent isolation structures 116. For example, a dry etching process is used to etch and remove the portions of the substrate 102 between the adjacent isolation structures 116, forming the device accommodation grooves 212. Subsequently, a doped layer is formed in the device accommodation grooves 212, and a photosensitive device is formed between the doped layer and the substrate 102 at the bottom of the device accommodation groove 212. The isolation structures 116 between the device accommodation grooves 212 isolate the photoelectron flow generated by the photosensitive device from the adjacent photosensitive device.

[0104] In one embodiment, the depths D of the at least two device accommodation grooves 212 are different, and the depth D of any of the device accommodation grooves 212 is less than or equal to the minimum depth of the adjacent isolation structure 116. This arrangement allows the photosensitive devices formed between the doped layer and the substrate 102 at the bottom of the device accommodation groove 212 to have different depths.

[0105] In one embodiment, the depths D of the device accommodation grooves 212 are equal, and the depth D of the device accommodation grooves 212 is less than or equal to the minimum depth of the isolation structure 116. This arrangement simplifies the process of forming the device accommodation grooves 212 and improves the isolation effect of the isolation structure 116 on photoelectrons.

[0106] Figure 11 For some embodiments, a cross-sectional view of the back-illuminated image sensor after forming the light-blocking layer is shown as follows. Figure 11 As shown, a doped layer 118 is formed in the device accommodation groove 212, and the doping type of the doped layer 118 is opposite to that of the substrate 102. For example, an in-situ doping process is used to form the doped layer 118 in the device accommodation groove 212. In other embodiments, the doped layer 118 can be formed by deposition and ion implantation.

[0107] As shown in the following figure, Figure 11 In one embodiment, the method for preparing the back-illuminated image sensor further includes forming a light-blocking layer 120 on the surface of the isolation structure 116. Specifically, a chemical vapor deposition process or an atomic layer deposition process is used to form a light-blocking material layer covering the doped layer 118 and the isolation structure 116. Then, the light-blocking material layer on the surface of the doped layer 118 is etched and removed, forming the light-blocking layer 120 on the surface of the isolation structure 116, and the openings of the light-blocking layer 120 expose the doped layers 118. For example, the constituent material of the light-blocking material layer includes aluminum.

[0108] In some embodiments, a second mask is used to pattern the light-shielding material layer to form a light-shielding layer 120 located on the surface of the isolation structure 116. That is, the first mask pattern and the light-shielding layer 120 are formed using the same mask, which reduces the number of masks and lowers the manufacturing cost of the back-illuminated image sensor.

[0109] like Figure 11 As shown, in one embodiment, the fabrication method of the back-illuminated image sensor further includes: forming color filter layers 122 on the surface of each of the doped layers 118, wherein the color filter layers 122 fill the corresponding openings of the light-shielding layer 120. The color filter layers 122 are used for filtering light to match the imaging color of the photosensitive device formed by the corresponding doped layer 118 and the substrate 102. The color filter layer 122 on the surface of any doped layer 118 can be one of a red filter layer, a green filter layer, or a blue filter layer to achieve color imaging. Exemplarily, the top surface of the color filter layer 122 away from the substrate 102 is flush with the top surface of the light-shielding layer 120 away from the substrate 102. It is understood that the light-shielding layer 120 between the color filter layers 122 and the isolation structure 116 located at the bottom of the light-shielding layer 120 also have the function of filtering light and blocking light transmission.

[0110] This disclosure also provides a back-illuminated image sensor, which is manufactured using the aforementioned method for fabricating a back-illuminated image sensor.

[0111] It should be understood that, although Figure 1 The steps in the flowchart are shown sequentially as indicated by the arrows, but these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified herein, there is no strict order in which these steps are executed, and they can be performed in other orders. Figure 1 At least some of the steps in the process may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be executed in turn or alternately with other steps or at least some of the sub-steps or stages of other steps.

[0112] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0113] The above-described embodiments only express several implementation manners of the present disclosure, the description is relatively specific and detailed, but it cannot be understood as a limitation on the scope of the patent. It should be noted that, for those skilled in the art, without departing from the concept of the present disclosure, several modifications and improvements can be made, which are within the protection scope of the present disclosure.

Claims

1. A method of fabricating a backside illuminated image sensor, comprising: The method comprises the following steps: providing a substrate; forming a plurality of sacrificial structures with same interval on the substrate; forming a sidewall on the sidewall of the sacrificial structure, removing the sacrificial structure, and forming a transition mask pattern composed of the sidewall; removing part of the sidewall in the transition mask pattern to obtain a first mask pattern, the first mask pattern has a plurality of openings between the sidewalls, and at least one opening has a width different from that of the other openings; forming a plurality of trenches in the substrate using the first mask pattern as a mask, and the depth of the trench corresponding to the opening with different width is different; removing the first mask pattern; forming an isolation structure in the trench; the surface of the isolation structure is flush with the surface of the substrate; removing part of the thickness of the substrate between adjacent isolation structures to form a plurality of device accommodation grooves; at least two device accommodation grooves have different depths, the depth of the device accommodation groove is less than or equal to the minimum depth of the isolation structure, and the bottom of the device accommodation groove exposes the substrate; forming a doped layer in the device accommodation groove, the doping type of the doped layer is opposite to the doping type of the substrate, and the doped layer and the substrate exposed by the bottom of the device accommodation groove form a photosensitive device.

2. The method of manufacturing a backside illumination image sensor according to claim 1, wherein The step of forming a plurality of sacrificial structures with same interval on the substrate comprises: forming a hard mask layer on the substrate; using a first mask to perform patterned processing on the hard mask layer to form the sacrificial structure.

3. The method of manufacturing a backside illumination image sensor according to claim 1, wherein The step of forming a sidewall on the sidewall of the sacrificial structure comprises: forming a sidewall material layer on the top surface of the sacrificial structure, the sidewall material layer extends along the sidewall of the sacrificial structure to the substrate; removing the sidewall material layer on the top surface of the sacrificial structure and part of the sidewall material layer on the substrate, and retaining the sidewall material layer on the sidewall of the sacrificial structure as the sidewall.

4. The method of producing a backside illumination type image sensor according to claim 1, wherein Further comprising: forming a light shielding layer on the surface of the isolation structure.

5. The method of producing a backside illumination image sensor according to claim 4, wherein The opening of the light shielding layer exposes each doped layer; The preparation method further comprises: forming a color filter layer on the surface of each doped layer, respectively, the color filter layer is filled in the corresponding opening of the light shielding layer.

6. The method of producing a backside illumination type image sensor according to claim 1, wherein The material of the sacrificial structure is the same as that of the substrate; an etching protection layer is further formed between the substrate and the sacrificial structure; After removing the first mask pattern, before forming an isolation structure in the trench, the preparation method further comprises: removing the etching protection layer.

7. The method of producing a backside illumination type image sensor according to claim 1, wherein The step of forming a plurality of trenches in the substrate using the first mask pattern as a mask comprises: using the first mask pattern as a mask, and using an isotropic etching process to etch the substrate at the opening position; using the first mask pattern as a mask, and using a non-isotropic etching process to etch the substrate at the opening position; wherein the depth of the trench is negatively correlated with the width of the corresponding opening.

8. The method of producing a backside illumination image sensor according to claim 7, wherein The process gas of the isotropic etching process comprises methane and fluoromethane, and the bias power is 0; the process gas of the non-isotropic etching process comprises methane and fluoromethane, and the bias power is greater than 0.

9. The method of producing a backside illumination image sensor according to claim 1, wherein The step of forming an isolation structure in the trench comprises: forming an isolation material layer in the trench; Chemical mechanical planarization is performed on the isolation material layer to obtain an isolation structure in the trench; The top surface of the isolation structure is flush with the surface of the substrate.

10. A backside illuminated image sensor, comprising: The backside illuminated image sensor is prepared by the method according to any one of claims 1-9.

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