Backside illuminated image sensor and preparation method thereof

Abstract

The invention 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 on the substrate at equal intervals; forming a side wall on the side wall of the sacrificial structure, removing the sacrificial structure, and forming a transition mask pattern formed by the side wall; part of the side walls in the transition mask pattern are removed, a first mask pattern is obtained, the first mask pattern is provided with a plurality of openings located between the side walls, and the width of at least one opening is different from the width of other openings; a plurality of grooves are formed in the substrate with the first mask pattern as a mask, and the depths of the grooves corresponding to the openings with different widths are different; removing the first mask pattern; forming an isolation structure in the groove; removing the part, between the adjacent isolation structures, of the substrate to form a plurality of device accommodating grooves; and forming a doping layer in the device accommodating groove, wherein the doping type of the doping layer is opposite to that of the substrate.

Description

Technical Field

[0001] The disclosed embodiments relate to the field of semiconductor technology, and in particular, to a back-illuminated image sensor and a method for preparing the same. Background Art

[0002] CMOS Image Sensor BSI includes multiple photodiodes and deep trench isolation structures (DTI) between the photodiodes. In the advanced manufacturing process of CMOS BSI, the typical DTI structures between multiple photodiodes have the same size, which cannot meet the different isolation requirements between multiple photodiodes in the BSI image sensor. Summary of the invention

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

[0004] A method for preparing a back-illuminated image sensor, comprising:

[0005] providing a substrate;

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

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

[0008] Removing part of the sidewalls in the transition mask pattern to obtain a first mask pattern, wherein 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;

[0009] Using the first mask pattern as a mask, a plurality of grooves are formed in the substrate, wherein openings with different widths correspond to different depths of the grooves;

[0010] removing the first mask pattern;

[0011] forming an isolation structure in the trench;

[0012] Removing a portion of the substrate between adjacent isolation structures to form a plurality of device accommodating grooves;

[0013] A doping layer is formed in the device receiving groove, wherein the doping type of the doping layer is opposite to the doping type of the substrate.

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

[0016] In one embodiment, the method for preparing a back-illuminated image sensor further includes:

[0017] A light shielding layer is formed on the surface of the isolation structure.

[0018] In one of the embodiments, the openings of the light shielding layer expose the doping layers, and the method for preparing a back-illuminated image sensor further includes:

[0019] A color filter layer is formed on the surface of each doping layer, and the color filter layer is filled in the corresponding opening of the light shielding layer.

[0020] In one embodiment, the sacrificial structure and the substrate are made of the same material; an etching protection layer is formed between the substrate and the sacrificial structure; after removing the first mask pattern and before forming the isolation structure in the trench, the preparation method further comprises:

[0021] The etching protection layer is removed.

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

[0023] Using the first mask pattern as a mask, and adopting an isotropic etching process, etching the substrate at the opening position;

[0024] Using the first mask pattern as a mask, an anisotropic etching process is used to etch the substrate at the opening position;

[0025] Wherein, the depth of the groove is negatively correlated with the width of the corresponding opening.

[0026] 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 anisotropic etching process includes methane and fluoromethane, and the bias power is greater than 0.

[0027] In one embodiment, forming an isolation structure in the trench includes:

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

[0029] Performing chemical mechanical planarization on the isolation material layer to obtain an isolation structure located in the trench;

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

[0031] A back-illuminated image sensor is manufactured by adopting the manufacturing method of the back-illuminated image sensor.

[0032] The unexpected technical effects that this application can produce are:

[0033] In the above-mentioned back-illuminated image sensor and its preparation method, by forming sacrificial structures with the same spacing on the substrate, the uniformity of the size of each side wall located on the side wall of the sacrificial structure is improved, the influence of the spacing 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 width of the opening between the side walls is different, thereby forming grooves with different depths corresponding to each opening, so that the size of the isolation structure in the groove is different, thereby meeting the different isolation requirements between the photosensitive devices located between adjacent isolation structures formed subsequently. In addition, in the present application, the isolation structure is formed first and then the doped layer located between the isolation structures is formed. The isolation structure serves as a self-aligned structure for forming the doped layer. In addition, in the present application, the isolation structure is formed first and then the doped layer located between the isolation structures is formed, which improves the accuracy of the shape and position of the doped layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure or related technologies, the drawings required for use in the embodiments or related technical descriptions will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present disclosure. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0035] FIG1 is a schematic flow diagram of a method for preparing a back-illuminated image sensor in some embodiments;

[0036] FIG2 is a cross-sectional schematic diagram of a back-illuminated image sensor after a photoresist pattern is formed in some embodiments;

[0037] Figure 3 is a schematic cross-sectional view of a back-illuminated image sensor after a sacrificial layer is formed in some embodiments;

[0038] Figure 4 is a schematic cross-sectional view of a back-illuminated image sensor after a spacer material layer is formed in some embodiments;

[0039] Figure 5 is a schematic cross-sectional view of a back-illuminated image sensor after sidewalls are formed in some embodiments;

[0040] Figure 6 is a schematic cross-sectional view of a back-illuminated image sensor after a second mask pattern is formed in some embodiments;

[0041] Figure 7 is a schematic cross-sectional view of a back-illuminated image sensor after a first mask pattern is formed in some embodiments;

[0042] Figure 8 is a schematic cross-sectional view of a back-illuminated image sensor after grooves are formed in some embodiments;

[0043] Fig. 9 is a schematic cross-sectional view of a back-illuminated image sensor after an isolation structure is formed in some embodiments;

[0044] Fig.10 is a schematic cross-sectional view of a back-illuminated image sensor after a device receiving groove is formed in some embodiments;

[0045] Fig.11 FIG. 4 is a schematic cross-sectional view of a back-illuminated image sensor after a light shielding layer is formed in some embodiments.

[0046] Description of reference numerals:

[0047] Substrate 102, hard mask layer 104, metal interconnect structure 106, etching protection layer 108, side wall 110, second mask pattern 112, first mask pattern 114, isolation structure 116, doping layer 118, light shielding layer 120, color filter layer 122, photoresist pattern 202, sacrificial structure 204, side wall material layer 206, opening 208, groove 210, device accommodating groove 212. DETAILED DESCRIPTION

[0048] In order to facilitate understanding of the embodiments of the present disclosure, the embodiments of the present disclosure will be described more fully below with reference to the relevant drawings. The preferred embodiments of the embodiments of the present disclosure are shown in the drawings. However, the embodiments of the present disclosure can be implemented 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 those commonly understood by those skilled in the art to which the disclosed embodiments belong. The terms used herein in the specification of the disclosed embodiments are only for the purpose of describing specific embodiments and are not intended to limit the disclosed embodiments. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0050] In the description of the embodiments of the present disclosure, it should be understood that the terms "upper", "lower", "vertical", "horizontal", "inside", "outside", etc. indicating orientations or positional relationships are based on the methods or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present disclosure and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present disclosure.

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

[0052] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of the present disclosure, the meaning of "multiple" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined. In the description of the present disclosure, the meaning of "several" is at least one, such as one, two, etc., unless otherwise clearly and specifically defined.

[0053] FIG. 1 is a schematic flow chart of a method for preparing a back-illuminated image sensor in some embodiments. As shown in FIG. 1 , in this embodiment, a method for preparing a back-illuminated image sensor is provided, comprising:

[0054] S102, providing a substrate.

[0055] Specifically, a substrate is provided, the substrate comprising a first surface and a second surface arranged opposite to each other, and a sacrificial structure formed subsequently is located on the first surface of the substrate. The constituent material of the substrate comprises single crystal silicon, silicon on insulator (SOI), stacked silicon on insulator (SSOI), stacked silicon germanium on insulator (S-SiGeOI), silicon germanium on insulator (SiGeOI), germanium on insulator (GeOI), gallium arsenide (GaAs), gallium nitride (GaN), silicon carbide (SiC), or any combination thereof. As an example, in this embodiment, the constituent material of the substrate is selected from single crystal silicon.

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

[0057] Specifically, a plurality of sacrificial structures are formed on the substrate and are arranged at intervals. In a plane parallel to the substrate, the intervals between two adjacent sacrificial structures are the same.

[0058] S106, forming a sidewall on the sidewall of the sacrificial structure, removing the sacrificial structure, and forming a transition mask pattern composed of the sidewall.

[0059] Specifically, a sidewall is formed on the sidewall of the sacrificial structure, the sidewall is adjacent to the sacrificial structure, the top surface of the sidewall away from the substrate is flush with the top surface of the sacrificial structure away from the substrate, and the bottom surface of the sidewall close to the substrate is flush with the bottom surface of the sacrificial structure close to the substrate, and the spacing between two adjacent sacrificial structures is the same, so that the size of the sidewalls of the sidewalls of each sacrificial structure is the same, thereby improving the uniformity of the sidewalls. Then, an etching process (such as a dry etching process) is used to remove the sacrificial structure to form a transition mask pattern composed of the sidewalls.

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

[0061] The sidewalls at some positions in the transition mask pattern are removed by photolithography and etching processes to obtain a first mask pattern composed of the remaining sidewalls. The first mask pattern has a plurality of openings located between adjacent sidewalls, and at least one opening has a width different from the widths of the other openings, which is the distance between adjacent sidewalls in a direction parallel to the substrate. By removing the sidewalls at some positions, the width of the openings located between adjacent sidewalls in the first mask pattern is adjusted to achieve the purpose of adjusting the width of the subsequently formed groove in a plane parallel to the substrate, and then adjusting the depth of the groove in a direction perpendicular to the substrate. At the same time, a doping layer is subsequently formed at the position covered by the first mask pattern, and the doping layer and the bottom substrate form a photosensitive device located between the isolation structure. The shape and position of the subsequently formed photosensitive device in a plane parallel to the substrate, as well as the shape and position of the isolation structure in a plane parallel to the substrate, are defined by the first mask pattern.

[0062] S110, using the first mask pattern as a mask, forming a plurality of grooves in the substrate.

[0063] Using the first mask pattern as a mask, etching is performed to remove the partial thickness of the substrate exposed by the opening to form a plurality of grooves in the substrate, wherein the plurality of grooves correspond to the plurality of openings respectively, and the grooves 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] S112, removing the first mask pattern.

[0065] S114, forming an isolation structure in the trench.

[0066] Specifically, an isolation structure is formed in the groove, the isolation structure fills the groove, the top surface of the isolation structure is flush with the first surface of the substrate, and the isolation structures corresponding to grooves of different depths have different sizes, thereby meeting the different isolation requirements between different photosensitive devices located between adjacent isolation structures that are subsequently formed.

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

[0068] Specifically, a portion of the thickness of the substrate between adjacent isolation structures is etched away to form a device accommodating groove between adjacent isolation structures, wherein the sidewalls of the device accommodating groove in a direction perpendicular to the substrate expose the adjacent isolation structure, and adjacent device accommodating grooves are separated by the isolation structure.

[0069] S118, forming a doping layer in the device receiving groove.

[0070] Specifically, a doping layer is formed in the device receiving groove, the doping layer has a first conductivity type, and the substrate has a second conductivity type, that is, the doping type of the doping 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 doping layer close to the first surface of the substrate is flush with the first surface of the substrate.

[0071] In the above-mentioned back-illuminated image sensor and its preparation method, by forming sacrificial structures with the same spacing on the substrate, the uniformity of the size of each side wall of the sacrificial structure side wall is improved, the influence of the spacing 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 width of the opening between the side walls is different, thereby forming grooves with different depths corresponding to each opening, so that the size of the isolation structure in the groove is different, thereby meeting the different isolation requirements between the photosensitive devices located between adjacent isolation structures formed subsequently. In addition, in the present application, the isolation structure is formed first and then the doped layer located between the isolation structures is formed. The isolation structure serves as a self-aligned structure for forming the doped layer. In addition, in the present application, the isolation structure is formed first and then the doped layer located between the isolation structures is formed, which improves the accuracy of the shape and position of the doped layer.

[0072] FIG. 2 is a cross-sectional schematic diagram of a back-illuminated image sensor after a photoresist pattern is formed in some embodiments. Figure 3 2 is a schematic cross-sectional view of a back-illuminated image sensor after a sacrificial layer is formed in some embodiments, as shown in FIG. Figure 3As shown, the step of forming a plurality of sacrificial structures 204 with the same spacing on the substrate includes steps S202 - S204 .

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

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

[0075] Specifically, in step S202-S204, in the first step, a hard mask layer 104 and a photoresist layer are sequentially formed on the first surface of the substrate 102 in a direction from the first surface of the substrate 102 to the direction away from the first surface of the substrate 102. In the second step, the hard mask layer 104 is patterned using the first mask plate to form a plurality of sacrificial structures 204 with the same spacing. The specific steps are: first, the photoresist layer is patterned using the first mask plate as a mask to form a photoresist pattern 202 located 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 and removed using the photoresist pattern 202 as a mask to form a plurality of spaced sacrificial structures 204 composed of the remaining hard mask layer 104 (the hard mask layer 104 covered by the photoresist pattern 202), and the spacing L1 between two adjacent sacrificial structures 204 is the same.

[0076] It is understandable that during the process of removing the hard mask layer 104 exposed by the photoresist pattern 202 through etching, the photoresist pattern 202 is removed; or after forming the sacrificial structure 204 , the method for preparing a back-illuminated image sensor includes the step of removing the photoresist pattern 202 .

[0077] Exemplarily, the material of the hard mask layer 104 includes silicon, amorphous silicon or amorphous carbon, and the hard mask layer 104 can be formed by epitaxial process, spin coating or spray coating. In this embodiment, silicon is selected as the material of the hard mask layer 104. At this time, the material of the hard mask layer 104 is the same as that of the substrate 102.

[0078] 2 , a metal interconnection structure 106 is formed on the second surface of the substrate 102, and the metal interconnection structure 106 is used to realize interconnection and conduction of devices in the substrate 102. For example, the first surface is the back side of the substrate 102, and the second surface is the back side of the substrate 102.

[0079] As shown in Fig. 2, an etch protection layer 108 covering the first surface of the substrate 102 is formed on the first surface of the substrate 102, and the hard mask layer 104 is located on the surface of the etch protection layer 108 away from the substrate 102. Exemplarily, the material of the etch protection layer 108 includes silicon oxide, and the etch 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 is a schematic cross-sectional view of a back-illuminated image sensor after a spacer material layer is formed in some embodiments, Figure 5 FIG. 4 is a cross-sectional schematic diagram of a back-illuminated image sensor after forming a sidewall in some embodiments. Figure 4 , Figure 5 As shown, in one embodiment, the step of forming the spacer 110 on the sidewall of the sacrificial structure 204 includes steps S302 - S304 .

[0081] S302 , forming a spacer material layer 206 on the top surface of the sacrificial structure 204 , wherein the spacer material layer 206 extends along the sidewall of the sacrificial structure 204 onto the substrate 102 .

[0082] S304 , removing the spacer material layer 206 on the top surface of the sacrificial structure 204 and a portion of the spacer material layer 206 on the substrate 102 , and retaining the spacer material layer 206 located on the sidewall of the sacrificial structure 204 as the spacer 110 .

[0083] Steps S302-S304 are specifically as follows: first, a chemical vapor deposition process or an atomic layer deposition process is used to form a spacer material layer 206 on the top surface of the sacrificial structure 204, the spacer material layer covers the sidewall of the sacrificial structure 204, and extends along the sidewall of the sacrificial structure 204 to cover the substrate 102, wherein the spacing L1 between two adjacent sacrificial structures 204 is the same, so that the size L2 of the spacer material layer 206 located on the sidewall of the sacrificial structure 204 in the direction parallel to the substrate 102 (the direction in the plane where the first direction X and the second direction Z are located) is the same, thereby improving the uniformity of the spacer 110 formed subsequently. Secondly, etching and removing part of the spacer material layer 206 on the top surface of the sacrificial structure 204 and the substrate 102, and retaining the spacer material layer 206 located on the sidewall of the sacrificial structure 204 as the spacer 110, wherein the etching protection layer 108 can be used as an etching stop layer for etching part of the spacer material layer 206 on the substrate 102.

[0084] Exemplarily, the material of the spacer 110 includes one or more of silicon oxide (eg, silicon dioxide), silicon nitride (eg, silicon oxynitride), and nitride (eg, silicon nitride). In this embodiment, the material of the spacer 110 is silicon nitride.

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

[0086] Figure 6 is a cross-sectional schematic diagram of a back-illuminated image sensor after a second mask pattern is formed in some embodiments, Figure 7FIG. 4 is a cross-sectional schematic diagram of a back-illuminated image sensor after forming a first mask pattern in some embodiments. Figure 6 , Figure 7 As shown, in one embodiment, the step of removing part of the sidewall spacer 110 in the transition mask pattern to obtain the first mask pattern includes steps S402-S404.

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

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

[0089] Steps S402-S404 are specifically as follows: first, a second mask material layer is formed on the substrate 102, and the second mask material layer is patterned using a second mask plate to form a second mask pattern 112 composed of the remaining second mask material layer, the second mask pattern 112 covers the sidewall 110 that needs to be retained, and exposes the sidewall 110 that needs to be removed. Exemplarily, the constituent material of the second mask material layer includes photoresist, nitride (silicon nitride), amorphous silicon or amorphous carbon. Secondly, using the second mask pattern 112 as a mask, the sidewall 110 exposed by the second mask pattern 112 is etched away to form a first mask pattern 114 composed of the 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 that is different from a width W2 of the other openings 208. The width is the distance between adjacent sidewalls 110 in the same direction parallel to the substrate 102 (any direction within the plane where the first direction X and the second direction Z are located). By removing the sidewalls 110 at some positions, the width of the openings 208 between adjacent sidewalls 110 in the first mask pattern 114 is adjusted.

[0090] Figure 8 FIG. 4 is a schematic cross-sectional view of a back-illuminated image sensor after grooves are formed in some embodiments. Figure 8 As shown, in one embodiment, the step of forming a plurality of trenches 210 in the substrate 102 using the first mask pattern 114 as a mask includes steps S502 - S504 .

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

[0092] S504 , using the first mask pattern 114 as a mask and adopting an isotropic etching process to etch the substrate 102 at the position of the opening 208 .

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

[0094] Exemplarily, 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, an isotropic etching process is first performed and then a 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, an isotropic etching process is first performed and then an 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 anisotropic etching process includes methane and fluoromethane, and the bias power is greater than 0.

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

[0097] In one embodiment, after removing the first mask pattern 110 and before forming an isolation structure in the trench 210 , the method for preparing a back-illuminated image sensor further includes: removing the etching protection layer 108 .

[0098] Fig. 9 FIG. 4 is a cross-sectional schematic diagram of a back-illuminated image sensor after an isolation structure is formed in some embodiments. Fig. 9 As shown, in one embodiment, the step of forming the isolation structure 116 in the trench 210 includes 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 an isolation structure 116 located in the trench 210 .

[0101] Steps S602-S604 are specifically to form an isolation material layer in the groove 210 by using a chemical vapor deposition process or an atomic layer deposition process, the isolation material layer fills the groove 210, and extends to the surface of the substrate 102 along the sidewall of the groove 210. Then, a chemical mechanical planarization process is used to planarize the isolation material layer, remove the isolation material layer above the surface of the substrate 102, and form an isolation structure 116 located in the groove 210, the top surface of the isolation structure 116 is flush with the surface (first surface) of the substrate 102, and the grooves 210 with different depths D correspond to different sizes of the isolation structure 116, so that the isolation structures 116 between the subsequently formed photosensitive devices are different, meeting the isolation requirements of the photosensitive devices. At the same time, 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] Exemplarily, the constituent material of the isolation structure 116 includes one or more of silicon oxide (eg, silicon dioxide), silicon nitride (eg, silicon oxynitride), and nitride (eg, silicon nitride). In the present embodiment, the constituent material of the isolation structure 116 is silicon dioxide.

[0103] Fig.10 FIG. 4 is a cross-sectional schematic diagram of a back-illuminated image sensor after forming a device receiving groove in some embodiments. Fig.10 As shown, the portion of the substrate 102 located between adjacent isolation structures 116 is etched away to form a plurality of device receiving grooves 212, and the side walls of the device receiving grooves 212 expose the adjacent isolation structures 116. Exemplarily, a dry etching process is used to etch away the portion of the substrate 102 located between adjacent isolation structures 116 to form the device receiving grooves 212, and photosensitive devices are subsequently formed between the doping layers formed in the device receiving grooves 212 and the substrate 102, and the isolation structures 116 between the device receiving grooves 212 isolate the photoelectrons generated by the photosensitive devices from flowing to adjacent photosensitive devices.

[0104] In one embodiment, the depth D of at least two of the device receiving grooves 212 is different, and the depth D of any of the device receiving grooves 212 is less than or equal to the minimum depth of the adjacent isolation structure 116. This setting enables the photosensitive device subsequently formed between the doping layer formed in the device receiving groove 212 and the substrate 102 at the bottom of the device receiving groove 212 to have different depths.

[0105] In one embodiment, the depth D of each device accommodating groove 212 is equal, and the depth D of the device accommodating groove 212 is less than or equal to the minimum depth of the isolation structure 116. The process of forming the device accommodating groove 212 is simple, and the isolation effect of the isolation structure 116 on photoelectrons is improved.

[0106] Fig.11 FIG. 4 is a cross-sectional schematic diagram of a back-illuminated image sensor after a light shielding layer is formed in some embodiments. Fig.11 As shown, a doping layer 118 is formed in the device receiving groove 212, and the doping type of the doping layer 118 is opposite to that of the substrate 102, wherein the doping layer 118 fills the device receiving groove 212. Exemplarily, the doping layer 118 is formed in the device receiving groove 212 by an in-situ doping process. In other embodiments, the doping layer 118 may be formed by deposition and ion implantation.

[0107] like Fig.11 As shown, in one embodiment, the method for preparing a back-illuminated image sensor further includes: forming a light shielding 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 shielding material layer covering the doping layer 118 and the isolation structure 116; then, the light shielding material layer on the surface of the doping layer 118 is etched and removed to form a light shielding layer 120 located on the surface of the isolation structure 116, and the opening of the light shielding layer 120 exposes each of the doping layers 118. Exemplarily, the constituent material of the light shielding material layer includes metal 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 same mask is used to form the first mask pattern and the light-shielding layer 120, thereby reducing the number of masks and reducing the manufacturing cost of the back-illuminated image sensor.

[0109] like Fig.11As shown, in one embodiment, the method for preparing a back-illuminated image sensor further includes: forming a color filter layer 122 on the surface of each of the doping layers 118, and the color filter layer 122 is filled in the corresponding opening of the light shielding layer 120. The color filter layer 122 is used for filtering light to match the imaging color of the photosensitive device formed by the corresponding doping layer 118 and the substrate 102. The color filter layer 122 on the surface of any doping 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 can be 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 the transmission of light.

[0110] The present disclosure also provides a back-illuminated image sensor, which is manufactured using the above-mentioned method for manufacturing the back-illuminated image sensor.

[0111] It should be understood that, although the various steps in the flowchart of FIG. 1 are shown in sequence according to the indication of the arrows, these steps are not necessarily executed in sequence according to the order indicated by the arrows. Unless there is a clear explanation in this article, the execution of these steps is not strictly limited in order, and these steps can be executed in other orders. Moreover, at least a part of the steps in FIG. 1 may include a plurality of sub-steps or a plurality of stages, and these sub-steps or stages are not necessarily executed at the same time, but can be executed at different times, and the execution order of these sub-steps or stages is not necessarily to be carried out in sequence, but can be executed in turn or alternately with other steps or at least a part of the sub-steps or stages of other steps.

[0112] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described 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-mentioned embodiments only express several implementation methods of the embodiments of the present disclosure, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the embodiments of the present disclosure, and these all belong to the protection scope of the embodiments of the present disclosure.

Claims

1. A method for preparing a back-illuminated image sensor, characterized in that: include: providing a substrate; forming a plurality of sacrificial structures with the same spacing 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 sidewalls in the transition mask pattern to obtain a first mask pattern, wherein 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; Using the first mask pattern as a mask, a plurality of grooves are formed in the substrate, wherein openings with different widths correspond to different depths of the grooves; removing the first mask pattern; forming an isolation structure in the trench; Removing a portion of the substrate between adjacent isolation structures to form a plurality of device accommodating grooves; A doping layer is formed in the device receiving groove, wherein the doping type of the doping layer is opposite to the doping type of the substrate.

2. The method for preparing a back-illuminated image sensor according to claim 1, characterized in that: The depths of at least two of the 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.

3. The method for preparing a back-illuminated image sensor according to claim 1, characterized in that: The depths of the device accommodating grooves are equal, and the depths of the device accommodating grooves are less than or equal to the minimum depth of the isolation structure.

4. The method for preparing a back-illuminated image sensor according to claim 1, characterized in that: Also includes: A light shielding layer is formed on the surface of the isolation structure.

5. The method for preparing a back-illuminated image sensor according to claim 4, characterized in that: The openings of the light shielding layer expose the doping layers; The preparation method further comprises: A color filter layer is formed on the surface of each doping layer, and the color filter layer is filled in the corresponding opening of the light shielding layer.

6. The method for preparing a back-illuminated image sensor according to claim 1, characterized in that: The sacrificial structure is made of the same material as the substrate; an etching protection layer is formed between the substrate and the sacrificial structure; After removing the first mask pattern and before forming an isolation structure in the trench, the preparation method further includes: The etching protection layer is removed.

7. The method for preparing a back-illuminated image sensor according to claim 1, characterized in that: The step of forming a plurality of grooves in the substrate using the first mask pattern as a mask comprises: Using the first mask pattern as a mask, and adopting an isotropic etching process, etching the substrate at the opening position; Using the first mask pattern as a mask, an anisotropic etching process is used to etch the substrate at the opening position; Wherein, the depth of the groove is negatively correlated with the width of the corresponding opening.

8. The method for preparing a back-illuminated image sensor according to claim 7, characterized in that: The process gas of the isotropic etching process includes methane and fluoromethane, and the bias power is 0; the process gas of the anisotropic etching process includes methane and fluoromethane, and the bias power is greater than 0.

9. The method for preparing a back-illuminated image sensor according to claim 1, characterized in that: The forming of the isolation structure in the trench comprises: forming an isolation material layer in the trench; Performing chemical mechanical planarization on the isolation material layer to obtain an isolation structure located in the trench; Wherein, the top surface of the isolation structure is flush with the surface of the substrate.

10. A back-illuminated image sensor, characterized in that: The back-illuminated image sensor is manufactured by the method for manufacturing the back-illuminated image sensor according to any one of claims 1 to 9.

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