Image sensor and method of manufacturing the same

Abstract

This invention provides an image sensor and its fabrication method. The projections of multiple photodiodes in the photodiode group on a substrate surround the projection of a floating diffuser on the substrate. Intra-group deep trench isolation is provided between adjacent photodiodes within the photodiode group. The intra-group deep trench isolation includes a linear pattern structure obtained by removing the intersection region of a first line trench isolation along a first direction and a second line trench isolation along a second direction. The intra-group deep trench isolation removes the intersection region, and the projection of the intersection region on the substrate covers the projection of the floating diffuser on the substrate. That is, the intra-group deep trench isolation is not provided in the intersection region of the line trench isolation on the substrate above the floating diffuser to avoid damaging the floating diffuser and causing white pixel problems, thus improving pixel quality. The deeper intra-group deep trench isolation reduces or avoids crosstalk and overflow between photodiodes.

Description

Technical Field

[0001] This invention belongs to the field of integrated circuit manufacturing technology, specifically relating to an image sensor and its manufacturing method. Background Technology

[0002] Image sensors are widely used in digital still cameras, cellular phones, surveillance cameras, and applications in the medical and automotive industries. The technology used to manufacture image sensors continues to advance significantly, and the demand for higher resolution and lower power consumption has driven further miniaturization and high integration of image sensors. High integration results in a reduction in the size of each pixel in the image sensor. However, as the pixel size of image sensors decreases, crosstalk between neighboring pixels becomes severe. Crosstalk can increase the number of white pixels and reduce the sensitivity of the image sensor. Deep trench isolation (DTI) structures are often used to reduce crosstalk.

[0003] The DTI structure includes deep trenches and isolation layers filling the trenches. The deep trenches are positioned between adjacent pixels. Due to the high aspect ratio of the deep trenches, the polymer generated during the etching process is difficult to extract from the trenches. Due to the etching load effect, polymer in trench regions with larger feature sizes is easier to extract than polymer in trench regions with smaller feature sizes. Therefore, under the same etching process, trench regions with larger feature sizes form deeper trenches than those with smaller feature sizes. Ideally, the trench depth should be the same across all regions of the deep trenches. However, if the trench depth formed by the smaller feature size regions reaches the target depth of the DTI structure, the trench depth formed by the larger feature size regions will exceed the target depth, potentially damaging the image sensor structure (e.g., floating diffuser) beneath the larger feature size regions. Summary of the Invention

[0004] The purpose of this invention is to provide an image sensor and its manufacturing method. In this method, the intersecting region of the line trench isolation on the substrate above the floating diffuser is not provided with intra-group deep trench isolation to avoid damage to the floating diffuser and resulting in white pixel issues, thus improving pixel quality. The deeper intra-group deep trench isolation reduces or avoids crosstalk and overflow between photodiodes.

[0005] This invention provides an image sensor, comprising:

[0006] A substrate having opposing first and second sides; a photodiode group and a floating diffuser are disposed in the substrate; the photodiode group includes a plurality of photodiodes extending from the first side of the substrate into the substrate; the floating diffuser extends from the second side of the substrate into the substrate; the projections of the plurality of photodiodes included in the photodiode group on the substrate surround the projection of the floating diffuser on the substrate;

[0007] The intra-group deep trench isolation is disposed between adjacent photodiodes within the photodiode group and extends from a first side surface of the substrate to the substrate or a second side surface; the intra-group deep trench isolation includes a linear pattern structure obtained by removing the intersection region of a structure formed by the intersection of a first line trench isolation disposed along a first direction and a second line trench isolation disposed along a second direction; the projection of the intersection region on the substrate covers the projection of the floating diffuser on the substrate.

[0008] Furthermore, the plurality of photodiodes in the photodiode group includes four photodiodes arranged in a 2×2 pattern or nine photodiodes arranged in a 3×3 pattern.

[0009] Furthermore, the photodiode groups and the floating diffusion section are arranged in a regular repeating pattern, and deep trench isolation between adjacent photodiode groups is provided. The deep trench isolation between groups extends from the first side surface of the substrate to the substrate or the second side surface.

[0010] Furthermore, the photodiode group can be any one of a red photodiode group, a green photodiode group, and a blue photodiode group.

[0011] Furthermore, the inter-group deep trench isolation includes a first inter-group deep trench isolation disposed along the first direction and a second inter-group deep trench isolation disposed along the second direction. The first inter-group deep trench isolation intersects with the second line trench isolations located in the two photodiode groups on both sides to form a first intersection region. The first inter-group deep trench isolation intersects with the second inter-group deep trench isolation to form a second intersection region. The second inter-group deep trench isolation intersects with the first line trench isolations located in the two photodiode groups on both sides to form a third intersection region. The floating diffusion portion is not disposed in the first intersection region, the second intersection region, and the third intersection region within the projection range of the substrate.

[0012] Furthermore, the image sensor also includes a transfer transistor that extends from the second side surface of the substrate into the substrate and at least partially surrounds the floating diffusion portion.

[0013] The present invention also provides a method for manufacturing an image sensor, comprising:

[0014] A substrate is provided having a first side and a second side opposite to each other; a photodiode group and a floating diffuser are disposed in the substrate; the photodiode group includes a plurality of photodiodes extending from the first side of the substrate into the substrate; the floating diffuser extends from the second side of the substrate into the substrate; the projections of the plurality of photodiodes included in the photodiode group on the substrate surround the projection of the floating diffuser on the substrate;

[0015] A deep trench is formed, the deep trench including an intra-group deep trench disposed between adjacent photodiodes within the photodiode group; the intra-group deep trench extends from a first side surface of the substrate to the substrate or a second side surface; the intra-group deep trench includes a linear pattern structure obtained by removing the intersection region of a structure formed by the intersection of a first line trench disposed along a first direction and a second line trench disposed along a second direction; the projection of the intersection region on the substrate covers the projection of the floating diffuser on the substrate;

[0016] An isolation layer is formed, which fills the deep trenches within the group to form an intra-group deep trench isolation.

[0017] Furthermore, the photodiode groups and the floating diffusion section are arranged in a regular repeating pattern, and the deep trench also includes inter-group deep trenches disposed between adjacent photodiode groups, as well as outer ring deep trenches surrounding a plurality of photodiode groups.

[0018] Furthermore, the inter-group deep trench isolation includes a first inter-group deep trench isolation disposed along the first direction and a second inter-group deep trench isolation disposed along the second direction.

[0019] Furthermore, the deep trenches are formed using a dry etching process, and the etching reaction gases include fluorine-based gases, O2, and Ar.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] This invention provides an image sensor and its fabrication method. The projections of multiple photodiodes in the photodiode group onto a substrate surround the projection of a floating diffuser onto the substrate. Intra-group deep trench isolation is provided between adjacent photodiodes within the photodiode group. The intra-group deep trench isolation includes a linear pattern structure obtained by removing the intersection region of a first line trench isolation along a first direction and a second line trench isolation along a second direction. The intra-group deep trench isolation removes the intersection region, and the projection of the intersection region onto the substrate covers the projection of the floating diffuser onto the substrate. That is, the intersection region of the substrate above the floating diffuser in the photodiode group remains unetched, and no intra-group deep trench isolation is provided above the floating diffuser. This avoids the depth difference between the etched substrate intersection region and the linear pattern region caused by the loading effect, which could easily damage the floating diffuser. Furthermore, the depth of intra-group deep trench isolation is not limited by the depth of the deep trench in the cross region. The depth of intra-group deep trench isolation can be etched deeper. Deeper intra-group deep trench isolation can better isolate the photodiodes within the photodiode group, reduce or avoid crosstalk and overflow between photodiodes within the photodiode group, avoid damage to the floating diffusion part causing white pixel problems, and improve the pixel quality of the image sensor. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the manufacturing process of an image sensor according to an embodiment of the present invention.

[0023] Figure 2 This is a top view of the image sensor manufacturing method according to an embodiment of the present invention after forming a deep trench.

[0024] Figure 3 For along Figure 2 A cross-sectional view at point AA'.

[0025] Figure 4 This is a three-dimensional view of the image sensor fabrication method according to an embodiment of the present invention after forming deep trenches.

[0026] Figure 5 for Figure 2 A magnified view of a portion of the photodiode group area.

[0027] Figure 6 This is a schematic cross-sectional view of the depth containing the floating diffusion portion along the upper surface of the substrate after the isolation layer is formed in the image sensor manufacturing method of this embodiment of the invention.

[0028] Figure 7 For along Figure 6 A cross-sectional view at point AA'.

[0029] Figure 8A reverse example of forming a deep trench in the cross-shaped region within the photodiode array of an image sensor, shown in the cross-sectional view along AA'.

[0030] Figure 9 A three-dimensional schematic diagram of a reverse example of forming a deep trench in the cross-shaped area within the photodiode array of an image sensor.

[0031] The reference numerals in the attached figures are as follows:

[0032] 10-Substrate; 10a-Substrate in the cross region; 101-First side; 102-Second side; 20-Dielectric layer; 21-Metal layer; 30-Photodiode group; 31-Photodiode; 40-Floating diffuser; 50-Transfer transistor; 60-Isolation layer; 70-Deep trench; 71-Intra-group deep trench; 711-First line trench; 712-Second line trench; 72-Inter-group deep trench; 721-First inter-group deep trench; 722-Second inter-group deep trench; G1L2-First cross region; G1G2-Second cross region; G2L1-Third cross region; V1-First trench; V2-Second trench; V3-Third trench; 80-Deep opening. Detailed Implementation

[0033] Based on the above research, embodiments of the present invention provide an image sensor and a method for manufacturing the same. The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The advantages and features of the present invention will become clearer from the following description. It should be noted that the accompanying drawings are in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the explanation of the embodiments of the present invention.

[0034] For ease of description, some embodiments of this application may use spatially relative terms such as “above,” “below,” “top,” and “under” to describe the relationship between one element or component and another (or more) elements or components as shown in the accompanying drawings. It should be understood that, in addition to the orientations described in the drawings, the spatially relative terms are also intended to include different orientations of the device during use or operation. For example, if the device in the drawings is flipped, it is described as an element or component “below” or “under” other elements or components, and will subsequently be positioned “above” or “on” other elements or components. The terms “first,” “second,” etc., used below are used to distinguish between similar elements and are not necessarily used to describe a particular order or temporal sequence. It should be understood that these terms, as used, may be replaced where appropriate.

[0035] This invention provides a method for manufacturing an image sensor, such as... Figure 1 As shown, it includes:

[0036] Step S1: Provide a substrate having a first side and a second side opposite to each other; a photodiode group and a floating diffuser are disposed in the substrate; the photodiode group includes a plurality of photodiodes, which extend from the first side of the substrate into the substrate; the floating diffuser extends from the second side of the substrate into the substrate; the projections of the plurality of photodiodes included in the photodiode group on the substrate surround the projection of the floating diffuser on the substrate.

[0037] Step S2: Forming a deep trench, the deep trench including an intra-group deep trench disposed between adjacent photodiodes within the photodiode group; the intra-group deep trench extends from a first side surface of the substrate to the substrate or a second side surface; the intra-group deep trench includes a linear pattern structure obtained by removing the intersection region of a first line trench disposed along a first direction and a second line trench disposed along a second direction; the projection of the intersection region on the substrate covers the projection of the floating diffuser on the substrate;

[0038] Step S3: Form an isolation layer, wherein the isolation layer fills the deep trench within the group to form an intra-group deep trench isolation.

[0039] The following is combined Figures 2 to 7 The following details each step of the method for manufacturing the image sensor according to an embodiment of the present invention.

[0040] Step S1, as follows Figure 2 and Figure 3 As shown, a substrate 10 is provided, having a first side 101 and a second side 102 opposite to each other. The substrate 10 can be any substrate known to those skilled in the art for carrying components of a semiconductor integrated circuit; it can be a bare die or a wafer processed by epitaxial growth. The substrate 10 includes silicon-on-insulator (SOI) substrates, bulk silicon substrates, germanium substrates, germanium-silicon substrates, indium phosphide substrates, gallium arsenide substrates, or germanium-on-insulator substrates, etc. If the image sensor is, for example, a back-illuminated image sensor, light is incident from the first side 101 (e.g., the back side) of the substrate 10. In other examples, the image sensor can also be a front-illuminated image sensor, configured as needed, without limitation. A dielectric layer 20 is formed on the surface of the second side 102 of the substrate 10, and a metal layer 21 is embedded in the dielectric layer 20.

[0041] A photodiode array 30 and a floating diffuser 40 are disposed in a substrate 10. The photodiode array 30 includes a plurality of photodiodes 31. Exemplarily, the plurality of photodiodes 31 extend into the substrate 10 from a position near the first side 101 along a direction perpendicular to the first side surface (substrate thickness) of the substrate 10. The floating diffuser 40 extends into the substrate 10 from the second side 102 surface. The photodiode array 30 may be arranged in an array within the substrate 10. The projections of the plurality of photodiodes 31 included in the photodiode array 30 onto the substrate 10 surround the projection of the floating diffuser 40 onto the substrate 10. Exemplarily, the photodiode array 30 may include, for example, four photodiodes 31 arranged in a 2×2 pattern. In other examples, a photodiode array 30 may also include a greater number of photodiodes 31. The number of photodiodes 31 included in a photodiode array 30 is not limited and can be configured as needed. Photodiode array 30 may include, for example, nine photodiodes 31 arranged in a 3×3 pattern, or sixteen photodiodes 31 arranged in a 4×4 pattern. The photodiodes 31 are formed in the substrate 10 by implanting phosphorus or arsenic into the substrate 10. Image sensors may include hundreds, thousands, or even tens of thousands of photodiode arrays 30. Figure 2 Four photodiode groups 30 are schematically shown.

[0042] Multiple photodiodes 31 are arranged in a regular, repeating pattern, such that the multiple photodiodes 31 are positioned at regular intervals or otherwise disposed within the semiconductor material to form a square or rectangular photodiode array. For example, four photodiode groups 30 may include a red photodiode group, two diagonally distributed green photodiode groups, and a blue photodiode group. A red photodiode group may contain, for example, four red photodiodes, a green photodiode group may contain, for example, four green photodiodes, and a blue photodiode group may contain, for example, four blue photodiodes.

[0043] Figure 2 This is a top view of the image sensor manufacturing method according to an embodiment of the present invention after forming a deep trench. Figure 3 For along Figure 2 A cross-sectional view at point AA'. Figure 4 This is a three-dimensional view of the image sensor fabrication method according to an embodiment of the present invention after forming deep trenches. Figure 5 for Figure 2 A magnified view of a portion of the photodiode group area. Figure 6 This is a schematic cross-sectional view of the image sensor fabrication method according to an embodiment of the present invention, after the isolation layer is formed, at a depth (e.g., h1 depth) containing the floating diffusion portion, parallel to the upper surface of the substrate. Figure 7 For along Figure 6A cross-sectional view at point AA'.

[0044] Step S2, as follows Figures 2 to 7 As shown, a deep trench 70 is formed, including an inter-group deep trench 72 disposed between adjacent photodiode groups 30, an intra-group deep trench 71 disposed between adjacent photodiodes 31 within a photodiode group 30, and an outer ring deep trench surrounding the plurality of photodiode groups 30. The deep trench 70 extends from the surface of a first side 101 of the substrate 10 to the surface of a second side 102 of the substrate 10.

[0045] Specifically, an intra-group deep trench 71 is disposed between adjacent photodiodes 31 within the photodiode group 30 and extends from the surface of the first side 101 of the substrate 10 to the surface of the second side 102 of the substrate 10. The intra-group deep trench 71 includes a first line trench 711 disposed along a first direction (e.g., the X direction) between adjacent photodiodes 31 and a second line trench 712 disposed along a second direction (e.g., the Y direction) between adjacent photodiodes 31. The projection of the intra-group deep trench 71 onto the substrate 10 does not overlap with the projection of the floating diffusion portion 40 onto the substrate 10. For example, the intra-group deep trench 71 is generally a cross-shaped trench consisting of four line trenches left after removing the portion of the cross intersection area. The four line trenches include two first line trenches 711 and two second line trenches 712. The substrate 10a in the intersection area within the photodiode group 30 is retained; that is, the substrate 10a directly above the floating diffusion portion 40 is left unetched to form a deep trench. The deep trench 71 within the group separates the photodiodes 31 within the photodiode group 30, preventing charge leakage between the photodiodes 31 (when it is not the image charge that is to be leaked).

[0046] Inter-group deep trenches 72 are disposed between adjacent photodiode groups 30 and extend from the surface of the first side 101 of the substrate 10 to the surface of the second side 102 of the substrate 10. Outer ring deep trenches (not shown) may be disposed around the periphery of a plurality of photodiode groups 30. The inter-group deep trenches 72 include a first inter-group deep trench 721 disposed between adjacent photodiode groups 30 along a first direction and a second inter-group deep trench 722 disposed between adjacent photodiode groups 30 along a second direction.

[0047] The first inter-group deep trench 721 intersects with the second line trenches 712 located within the two photodiode groups 30 along the second direction on both sides, forming a first intersection region G1L2. The first inter-group deep trench 721 also intersects with the second inter-group deep trench 722, forming a second intersection region G1G2. Similarly, the second inter-group deep trench 722 intersects with the first line trenches 711 located within the two photodiode groups 30 along the first direction on both sides, forming a third intersection region G2L1. The first intersection region G1L2, the second intersection region G1G2, and the third intersection region G2L1 in the deep trench 70 do not have floating diffusion portions 40 within the projection range of the substrate 10. Therefore, the trench depth of the intersection region between the photodiode groups 30 in the deep trench 70 can be etched deeper, and an isolation layer can be filled in it to form a deep trench isolation, which better isolates adjacent photodiode groups 30 and adjacent photodiodes 31, reducing or avoiding crosstalk and overflow of the image sensor.

[0048] like Figure 2 and Figure 3 As shown, in a cross section perpendicular to the substrate 10 along the diagonal AA', the intersection area between the photodiode groups 30 in the deep trench 70 is etched to form a first trench V1, a second trench V2 (corresponding to the second intersection area G1G2) and a third trench V3.

[0049] The substrate 10a of the cross-region within the photodiode group 30 is left unetched to form a deep trench. The first cross-region G1L2, the second cross-region G1G2, and the third cross-region G2L1 all form deep trenches and are part of the inter-group deep trench 72.

[0050] Multiple photodiodes 31 are disposed in the substrate 10 and configured to generate image charge in response to incident light. A floating diffuser 40 is disposed close to the multiple photodiodes 31 to receive image charge from the multiple photodiodes 31. Multiple transfer transistors 50 are coupled to transfer image charge from the multiple photodiodes 31 to the floating diffuser 40. The multiple transfer transistors 50 may have vertical transfer gates.

[0051] In some instances, the image sensor is coupled to control circuitry to control the operation of a plurality of photodiodes 31, and to readout circuitry to read image charge from the plurality of photodiodes 31. In one instance, dielectric layer 20 may at least partially contain the control circuitry and the readout circuitry. The control circuitry may adjust the voltage applied to the gate terminal of transfer transistor 50 to substantially confine the image charge within the individual photodiodes 31.

[0052] The transfer transistor 50 extends from the surface of the second side 102 of the substrate 10 into the substrate 10. The transfer transistor 50 at least partially surrounds the floating diffusion portion 40. The transfer transistor 50 extends from the surface of the second side 102 of the substrate 10 into the substrate 10 to a first depth, and the floating diffusion portion 40 extends from the surface of the second side 102 of the substrate 10 into the substrate 10 to a second depth, and the first depth is greater than the second depth.

[0053] The deep trench is formed through processes such as exposure, development, and etching. Specifically, a patterned photoresist layer (not shown) is formed on the surface of the first side 101 of the substrate 10. The patterned photoresist layer covers the photodiode 31 region and the cross-shaped region within the photodiode group 30, exposing the deep trench 70 region.

[0054] Using an imaged photoresist layer as a mask, the substrate 10 is etched to form deep trenches 70. Specifically, the width of the first line trench 711 and the width of the second line trench 712 can be the same or different. The widths of the first inter-group deep trench 721 and the second inter-group deep trench 722 can be the same or different.

[0055] Deep trenches 70 can be formed using dry etching processes. Dry etching methods include photoelectrolysis, vapor phase etching, sputtering and ion beam milling, plasma etching, high-voltage plasma etching, high-density plasma etching, reactive ion etching, and inductively coupled plasma etching. Specifically, using a patterned photoresist layer as a mask, the etching gas can be a mixture of fluorocarbon gas, hydrocarbon or fluorinated hydrocarbon gas, and nitrogen-oxygen gas to generate plasma. The reactive gases used in etching are mainly fluorine-based gases, such as CF4, SF6, and NF3. During reactive ion etching of the substrate 10, fluorine or chlorine atoms decomposed in the glow discharge react with atoms on the substrate 10 surface to generate gaseous products, achieving the etching purpose. The mechanism of reactive ion etching is that fluorocarbons form CF polymers on the surface of the substrate 10 material. Under the energy provided by ion physical bombardment, the CF polymers react with the substrate 10 material (e.g., Si) to form volatile SiFx, which is then extracted from the reaction chamber by the vacuum system. To achieve high etching rates, in addition to fluorocarbon gases with a high C / F ratio, auxiliary gases such as O2 and Ar are also required. Under low-pressure, high-power conditions, energy is provided by high-energy Ar+ bombardment, and the fluorocarbon gas and the substrate material to be etched undergo a chemical reaction.

[0056] like Figures 2 to 5As shown, the characteristic dimension (i.e., the width of the first trench 711) is b, the characteristic dimension (i.e., the width of the second trench 712) is a, and the characteristic dimension (diagonal length) of the cross-shaped region within the photodiode group 30 is e. The characteristic dimensions (b and a) of both the first trench 711 and the second trench 712 are smaller than the characteristic dimension of the cross-shaped region within the photodiode group 30. Due to the high aspect ratio of the deep trench 70, the polymer generated during the etching process is more difficult to extract from the deep trench 70. Due to the etching load effect, polymer in trench regions with larger characteristic dimensions is easier to extract than polymer in trench regions with smaller characteristic dimensions.

[0057] Figure 8 A reverse example of a deep opening 80 formed in the cross-shaped region within a photodiode array of an image sensor, shown in a cross-sectional view along AA'. Figure 9 A three-dimensional schematic diagram illustrating a reverse example of forming a deep trench in the cross-shaped region within the photodiode array of an image sensor. (Example) Figure 2 , Figure 8 and Figure 9As shown, if a deep aperture 80 is also etched in the cross-shaped region within the photodiode group 30, the polymer in the first line trench 711 and the second line trench 712 is more difficult to extract than the polymer in the deep aperture 80 in the cross-shaped region within the photodiode group 30. Therefore, in the same etching process, at the same etching time, the trench etching depth of the first line trench 711 and the second line trench 712 is relatively shallow, while the etching depth of the deep aperture 80 formed in the cross-shaped region within the photodiode group 30 is relatively deep. Consequently, when the trench depth of the first line trench 711 and the second line trench 712 reaches the target depth of the DTI structure, the depth of the deep aperture 80 in the cross-shaped region within the photodiode group 30 is greater than the target depth of the DTI structure, which can easily damage the image sensor structure (e.g., the floating diffuser 40) below the cross-shaped region within the photodiode group 30, causing white pixel problems. Therefore, the deep trench etching process is difficult to control, and when the deep trench etching process is unstable, the floating diffuser 40 is easily damaged. When the depth of the deep opening 80 in the cross-shaped region within the photodiode array 30 is relatively shallow to ensure no damage to the floating diffuser 40 below, the depth of the first line trench 711 and the second line trench 712 must be even shallower than the depth of the deep opening 80 in the cross-shaped region within the photodiode array 30. Because the deep trenches are not deep enough, the isolation structure ultimately formed by the first line trench 711 and the second line trench 712 results in crosstalk and highlight overflow issues in the image sensor. Highlight overflow occurs when, under strong light conditions, a large number of electrons flow from the photodiode area to neighboring pixel photodiodes. Crosstalk is a significant noise source for photodiode arrays. Crosstalk is defined as the activity of noise injected into adjacent pixels of the image sensor. Essentially, it is interference noise generated by the coupling of one signal to another. The presence of crosstalk reduces image sharpness and severely affects the quality of the final output image.

[0058] like Figures 2 to 4 As shown, in this embodiment of the invention, the substrate 10a in the cross region within the photodiode group 30 is retained, that is, the substrate 10 directly above the floating diffusion portion 40 is retained without being etched to form a deep trench 70. In this way, the depth of the first line trench 711 and the second line trench 712 within the photodiode group 30 is not limited by the depth of the deep trench 70 in the cross region within the photodiode group 30. The depth of the first line trench 711 and the second line trench 712 can be etched deeper. The deeper first line trench 711 and the second line trench 712 are filled with an isolation layer to form a deep trench isolation, which can better isolate the photodiodes 31 within the photodiode group 30, reduce or avoid crosstalk and overflow between the photodiodes 31 within the photodiode group 30, avoid white pixel problems caused by damage to the floating diffusion portion 40, and improve the pixel quality of the image sensor.

[0059] Similarly, the non-crossing regions of the inter-group deep trench 72 can also be made deeper. The inter-group deep trench 72 is disposed between adjacent photodiode groups 30 and extends from the surface of the first side 101 of the substrate 10 to the surface of the second side 102 of the substrate 10. The crossing regions between photodiode groups 30 in the deep trench 70 include a first crossing region G1L2, a second crossing region G1G2, and a third crossing region G2L1. Since there is no floating diffuser 40 directly below the crossing regions between photodiode groups 30 in the deep trench 70, the trench 70 depth of the crossing regions between photodiode groups 30 in the deep trench 70 can also be etched deeper. Filling it with an isolation layer to form a deep trench isolation provides better isolation between adjacent photodiode groups 30 and adjacent photodiodes 31, reducing or avoiding crosstalk and overflow of the image sensor.

[0060] Step S3, as follows Figure 6 and Figure 7 As shown, an isolation layer 60 is formed, and the isolation layer 60 fills a deep trench 70 to form a deep trench isolation. The isolation layer materials of the intra-group deep trench 71 and the inter-group deep trench 72 can be the same or different. The isolation layer 60 can be a high-k dielectric layer or silicon oxide. The high-k dielectric layer material includes at least one of Al2O3, HfO2, Ta2O5, ZrO2, and TiO2. Since the image sensor contains an array of multiple photodiodes 31, the formed deep trench isolation presents a grid-like structure. The isolation layer 60 in the deep trench 70 can be formed using physical vapor deposition (PVD), chemical vapor deposition (CVD), or atomic layer deposition (ALD) processes. Deep trench isolation (DTI) includes the deep trench 70 and the isolation layer 60 filled in the deep trench 70. The DTI structure at least partially surrounds the photodiode 31, and further, the deep trench isolation can enclose the photodiode 31. The main function of the deep trench isolation is to prevent optical interference or crosstalk between adjacent photodiodes 31.

[0061] This embodiment also provides an image sensor, such as... Figure 2 , Figure 6 and Figure 7 As shown, it includes:

[0062] The substrate 10 has a first side 101 and a second side 102 opposite to each other; a photodiode group 30 and a floating diffusion section 40 are disposed in the substrate 10; the photodiode group 30 includes a plurality of photodiodes 31, which extend from the first side 101 of the substrate into the substrate 10; the floating diffusion section 40 extends from the second side 102 of the substrate into the substrate 10; the projections of the plurality of photodiodes 31 included in the photodiode group 30 on the substrate 10 surround the projection of the floating diffusion section 40 on the substrate 10.

[0063] The deep trench isolation within the group is disposed between adjacent photodiodes 31 within the photodiode group 30 and extends from the surface of the first side 101 of the substrate to the surface of the substrate 10 or the surface of the second side 102. The deep trench isolation within the group includes a linear pattern structure obtained by removing the intersection region of a first line trench isolation disposed along a first direction and a second line trench isolation disposed along a second direction. The projection of the intersection region on the substrate 10 covers the projection of the floating diffusion portion 40 on the substrate 10.

[0064] The photodiode group 30 comprises multiple photodiodes, including four photodiodes 31 arranged in a 2×2 pattern or nine photodiodes 31 arranged in a 3×3 pattern. The photodiode groups 30 and the floating diffuser 40 are arranged in a regular repeating pattern. Deep trench isolation is provided between adjacent photodiode groups 30, extending from the surface of the first side 101 of the substrate to the surface of the substrate 10 or the second side 102. The photodiode group 30 can be any one of a red photodiode group, a green photodiode group, or a blue photodiode group. The inter-group deep trench isolation includes a first inter-group deep trench isolation disposed along a first direction and a second inter-group deep trench isolation disposed along a second direction. The first inter-group deep trench isolation and the second line trench isolation located in the two photodiode groups 30 on both sides intersect to form a first cross region G1L2. The first inter-group deep trench isolation and the second inter-group deep trench isolation intersect to form a second cross region G1G2. The second inter-group deep trench isolation and the first line trench isolation located in the two photodiode groups 30 on both sides intersect to form a third cross region G2L1. The first cross region G1L2, the second cross region G1G2 and the third cross region G2L1 do not have floating diffusion portions 40 disposed within the projection range of the substrate 10.

[0065] The image sensor also includes a transfer transistor 50 that extends from the surface of the second side 102 of the substrate into the substrate 10, and the transfer transistor 50 at least partially surrounds the floating diffusion portion 40.

[0066] In summary, this invention provides an image sensor and its fabrication method. The projections of multiple photodiodes in the photodiode group of this invention onto the substrate surround the projection of a floating diffuser onto the substrate. Intra-group deep trench isolation is provided between adjacent photodiodes within the photodiode group. The intra-group deep trench isolation includes a linear pattern structure obtained by removing the intersection region of a first line trench isolation along a first direction and a second line trench isolation along a second direction. The intra-group deep trench isolation removes the intersection region, and the projection of the intersection region onto the substrate covers the projection of the floating diffuser onto the substrate. That is, the substrate intersection region above the floating diffuser in the photodiode group remains unetched, and no intra-group deep trench isolation is provided above the floating diffuser. This avoids the depth difference between the etched substrate intersection region and the linear pattern region caused by the loading effect, which could easily damage the floating diffuser. Furthermore, the depth of intra-group deep trench isolation is not limited by the depth of the deep trench in the cross region. The depth of intra-group deep trench isolation can be etched deeper. Deeper intra-group deep trench isolation can better isolate the photodiodes within the photodiode group, reduce or avoid crosstalk and overflow between photodiodes within the photodiode group, avoid white pixel problems caused by damage to the floating diffusion part, and improve the pixel quality of the image sensor.

[0067] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. The methods disclosed in the embodiments are described simply because they correspond to the devices disclosed in the embodiments; relevant details can be found in the method section.

[0068] The above description is merely a description of preferred embodiments of the present invention and is not intended to limit the scope of the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

Claims

1. An image sensor, characterized by, include: A substrate having opposing first and second sides; a group of photodiodes and a floating diffuser are disposed in the substrate; The photodiode group includes a plurality of photodiodes, which extend from a first side of the substrate into the substrate; the floating diffusion portion extends from a second side of the substrate into the substrate; The projections of the plurality of photodiodes included in the photodiode group on the substrate surround the projection of the floating diffuser on the substrate; The photodiode group includes an intra-group deep trench isolation structure. This deep trench isolation is disposed between adjacent photodiodes within the photodiode group and extends from a first side surface of the substrate to the substrate or a second side surface. The intra-group deep trench isolation includes a linear pattern structure obtained by removing the intersection region of a first line trench isolation along a first direction and a second line trench isolation along a second direction. The intra-group deep trench isolation removes the intersection region portion, and the projection of the intersection region onto the substrate covers the projection of the floating diffusion portion onto the substrate. That is, the intersection region of the substrate above the floating diffusion portion in the photodiode group remains unetched, and the intra-group deep trench isolation is not disposed above the floating diffusion portion.

2. The image sensor of claim 1, wherein, The plurality of photodiodes in the photodiode group includes four photodiodes arranged in a 2×2 pattern or nine photodiodes arranged in a 3×3 pattern.

3. The image sensor of claim 1, wherein, The photodiode groups and the floating diffuser are arranged in a regular repeating pattern, and deep trench isolation is provided between adjacent photodiode groups. The deep trench isolation extends from the first side surface of the substrate to the substrate or the second side surface.

4. The image sensor of claim 3, wherein, The photodiode group can be any one of red photodiode group, green photodiode group, and blue photodiode group.

5. The image sensor of claim 3, wherein, The inter-group deep trench isolation includes a first inter-group deep trench isolation disposed along the first direction and a second inter-group deep trench isolation disposed along the second direction. The first inter-group deep trench isolation intersects with the second line trench isolation located in the two photodiode groups on both sides to form a first intersection region. The first inter-group deep trench isolation intersects with the second inter-group deep trench isolation to form a second intersection region. The second inter-group deep trench isolation intersects with the first line trench isolation located in the two photodiode groups on both sides to form a third intersection region. The floating diffusion portion is not disposed in the first intersection region, the second intersection region, and the third intersection region within the projection range of the substrate.

6. The image sensor according to any one of claims 1 to 5, wherein The image sensor also includes a transfer transistor that extends from a second side surface of the substrate into the substrate and at least partially surrounds the floating diffuser.

7. A method of fabricating an image sensor, comprising: include: A substrate is provided, the substrate having opposing first and second sides; a group of photodiodes and a floating diffuser are disposed in the substrate; The photodiode group includes multiple photodiodes, which extend from a first side of the substrate into the substrate; the floating diffusion portion extends from a second side of the substrate into the substrate; The projections of the plurality of photodiodes included in the photodiode group on the substrate surround the projection of the floating diffuser on the substrate; Forming deep trenches, the deep trenches including intra-group deep trenches disposed between adjacent photodiodes within the photodiode group; The deep trench within the group extends from the first side surface of the substrate to the middle or the second side surface of the substrate; the deep trench within the group includes a linear pattern structure obtained by removing the intersection region of a first line trench disposed along a first direction and a second line trench disposed along a second direction; the deep trench within the group isolates and removes the intersection region portion, and the projection of the intersection region on the substrate covers the projection of the floating diffusion portion on the substrate, that is, the intersection region of the substrate above the floating diffusion portion in the photodiode group is retained without being etched, and the deep trench within the group is not provided above the floating diffusion portion for isolation; An isolation layer is formed, which fills the deep trenches within the group to form an intra-group deep trench isolation.

8. The method of manufacturing an image sensor according to claim 7, wherein The photodiode groups and the floating diffuser are arranged in a regular repeating pattern. The deep trench also includes inter-group deep trenches disposed between adjacent photodiode groups and outer ring deep trenches surrounding a plurality of photodiode groups.

9. The method for manufacturing an image sensor as described in claim 8, characterized in that, The inter-group deep trench isolation includes a first inter-group deep trench isolation disposed along the first direction and a second inter-group deep trench isolation disposed along the second direction.

10. The method of fabricating an image sensor of claim 7, wherein, The deep trenches are formed using a dry etching process, and the etching reaction gases include fluorine-based gases, O2, and Ar.

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