Image sensor and manufacturing method thereof
By using dual deep trench isolation technology, the problems of electrical signal conduction and quantum efficiency caused by traditional deep trench isolation have been solved, enabling more efficient image sensor manufacturing and improving production capacity and photoelectric conversion performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-12
- Publication Date
- 2026-04-07
AI Technical Summary
Traditional deep trench isolation technology results in complete isolation between pixels at the silicon substrate interface, which is not conducive to the design of three transistors and floating diffusers, and also absorbs additional photons, affecting conversion gain and quantum efficiency.
The dual-depth trench isolation technology is adopted. By depositing a hard mask layer before etching and adding a photomask, the thickness difference between full-depth trenches and partial-depth trenches is achieved. They share a single trench etching process to form full-depth and partial-depth trench isolation.
It saves process time, increases production capacity, ensures electrical signal conduction and quantum efficiency within pixel units, reduces metal winding, and improves photoelectric conversion efficiency.
Smart Images
Figure CN121815781A_ABST
Abstract
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, security cameras, and in medical, automotive, and other applications. As image sensors have evolved, pixel sizes have become increasingly smaller while maintaining high full-well capacity. Deep trench isolation technology is widely used in small-sized image sensor products to improve full-well capacity and achieve better pixel-to-pixel isolation. Traditional deep trench isolation uses a silicon substrate that penetrates the entire thickness of the image sensor to achieve isolation between adjacent pixels and / or adjacent pixel units. However, completely penetrating the silicon substrate results in complete pixel-to-pixel isolation at the silicon substrate interface, which is detrimental to the design of three transistors and floating diffusers (FDs).
[0003] A common design employs a single inner perimeter for each pixel to share a floating diffuser located in the central region. This design requires electrical signal conduction between pixels within the silicon substrate. However, traditional deep trench isolation, which penetrates the entire silicon substrate, results in complete isolation between pixels at the silicon substrate interface, hindering electrical signal conduction between pixels within the silicon substrate. Therefore, more metal wires are needed to facilitate electrical signal conduction, which is detrimental to improving conversion gain. Conversion gain is a key parameter for measuring the photoelectric conversion efficiency of a sensor. Furthermore, the deep trenches, which require polycrystalline silicon to fill their entire depth, absorb additional photons, leading to a decrease in quantum efficiency.
[0004] One type of floating diffuser (FD) structure on the market has a shared central region for peripheral pixels. The central region has no isolation structure and requires high-depth ion implantation to achieve isolation, which also requires an additional ion implantation process. Summary of the Invention
[0005] The purpose of this invention is to provide a method for fabricating an image sensor. First, a hard mask layer is deposited, and only one photomask is added. The hard mask layer is patterned using this photomask, achieving a thickness difference between the full-depth trench isolation and partial-depth trench isolation regions. This allows a single trench etching process to be used, transferring this thickness difference to both the full-depth and partial-depth trench isolation regions. This avoids the need for two separate photomasks to form the full-depth and partial-depth trenches, saving process time and increasing production capacity.
[0006] This invention provides a method for manufacturing an image sensor, comprising:
[0007] S11. A substrate is provided, the substrate having opposing first and second surfaces;
[0008] S12. A patterned hard mask layer is formed on the first surface of the substrate, wherein the removal area of the patterned hard mask layer corresponds to the area of a full-depth trench.
[0009] S13. Form a patterned photoresist, the patterned photoresist covering the substrate and the patterned hard mask layer, the patterned photoresist including a first opening corresponding to the full-depth trench and a second opening corresponding to a partial-depth trench; the first opening corresponds to the removal area of the patterned hard mask layer, and the second opening corresponds to the retention area of the patterned hard mask layer.
[0010] S14. Perform a first etching process to etch the substrate at a predetermined depth directly below the first opening, and simultaneously etch the patterned hard mask layer directly below the second opening.
[0011] S15. Perform a second etching process to continue etching the substrate directly below the first opening until the substrate is completely etched through to form a full-depth trench, and at the same time etch a portion of the substrate directly below the second opening to form a partial-depth trench.
[0012] S16. Fill the full-depth trench and the partial-depth trench in the substrate with isolation layers to form full-depth trench isolation and partial-depth trench isolation, respectively.
[0013] Furthermore, after step S12 and before step S13, the method further includes: forming an anti-reflective layer that covers the substrate and the patterned hard mask layer, wherein the top surface of the anti-reflective layer is flush with and higher than the top surface of the patterned hard mask layer.
[0014] Furthermore, the full-depth trench isolation completely penetrates the entire thickness of the substrate or penetrates more than 90% of the substrate thickness; the partial-depth trench isolation penetrates 40% to 70% of the substrate thickness.
[0015] Furthermore, the full-depth trench isolation is located in the outer frame region of the pixel unit of the image sensor; the pixel unit includes peripheral pixels and a floating diffuser located in the central region; the peripheral pixels share the floating diffuser; the row spacing between adjacent rows and the column spacing between adjacent columns in the pixel unit are isolated by the partial-depth trench isolation.
[0016] The present invention also provides another method for manufacturing an image sensor, comprising:
[0017] S21. A substrate is provided, the substrate having opposing first and second surfaces;
[0018] S22, A patterned first hard mask layer is formed on the first surface of the substrate; the removal area of the patterned first hard mask layer corresponds to the area of a full-depth trench; a second hard mask layer is formed covering the substrate and the patterned first hard mask layer;
[0019] S23. Form a patterned photoresist covering the second hard mask layer, the patterned photoresist including a third opening corresponding to the full-depth trench and a fourth opening corresponding to the partial-depth trench; the third opening corresponds to the removal area of the patterned first hard mask layer, and the fourth opening corresponds to the retention area of the patterned first hard mask layer.
[0020] S24. Perform etching process one to etch the second hard mask layer directly below the third opening and the substrate at a preset depth, and simultaneously etch the second hard mask layer directly below the fourth opening.
[0021] S25. Perform etching process two, continue etching the substrate directly below the third opening until the substrate is completely etched through to form a full-depth trench, and simultaneously etch the patterned first hard mask layer directly below the fourth opening and the substrate at a partial depth to form a partial-depth trench.
[0022] S26. Fill the full-depth trench and the partial-depth trench in the substrate with isolation layers to form full-depth trench isolation and partial-depth trench isolation, respectively.
[0023] Furthermore, after step S22 and before step S23, the method further includes: forming an anti-reflective layer that covers the second hard mask layer, wherein the top surface of the anti-reflective layer is flush with and higher than the top surface of the second hard mask layer located above the reserved area of the first hard mask layer.
[0024] Furthermore, in the first etching process, the second hard mask layer directly below the fourth opening is etched, stopping at the upper surface of the first hard mask layer.
[0025] The present invention also provides an image sensor, comprising:
[0026] A substrate having opposing first and second surfaces;
[0027] Multiple pixel units are formed on the substrate, and each pixel unit includes M rows * N columns of pixels;
[0028] Full-depth trench isolation is provided in the outer frame area of the pixel unit; the row spacing between adjacent rows and the column spacing between adjacent columns within the pixel unit are partially-depth trench isolation.
[0029] Both the full-depth trench isolation and the partial-depth trench isolation extend from the first surface into the substrate in a direction perpendicular to the upper surface of the substrate.
[0030] Furthermore, a floating diffusion portion is formed in the central region of the pixel unit on the side of the substrate near the second surface, and a transmission gate is formed around the floating diffusion portion;
[0031] The region where the pixel is located in the substrate includes, from the second surface to the first surface, the following in sequence: the transmission gate 30, DNPPD, and a deep N-well; the pixels around the periphery share the floating diffusion section, and the central region includes, from the second surface to the first surface, the following in sequence: the floating diffusion section, a shallow P-well, a deep P-well, and the partial depth trench isolation.
[0032] Furthermore, the deep P-well and the partial depth trench isolation have an overlapping region in depth; the deep P-well and the partial depth trench isolation are spaced apart between the DNPPDs of adjacent pixel regions.
[0033] Compared with the prior art, the present invention has the following beneficial effects:
[0034] This invention provides an image sensor and its fabrication method, employing a dual-depth trench isolation technology, namely, full-depth trench isolation combined with partial-depth trench isolation. Before trench etching, this invention first deposits a hard mask layer and adds only one photomask. The hard mask layer is patterned using this photomask, achieving a thickness difference between the full-depth and partial-depth trench isolation regions. This allows a single trench etching process to be used, transferring this thickness difference to both the full-depth and partial-depth trench isolation regions. This avoids the need for two separate photomasks to form the full-depth and partial-depth trenches, saving process time and increasing production capacity.
[0035] Furthermore, full-depth trench isolation is located in the outer frame region of the pixel unit of the image sensor; the pixel unit includes peripheral pixels and a floating diffuser located in the central region; the peripheral pixels share the floating diffuser; the row spacing between adjacent rows and the column spacing between adjacent columns within the pixel unit adopts partial-depth trench isolation. This invention employs dual-depth trench isolation technology, namely, full-depth trench isolation combined with partial-depth trench isolation. A full-depth trench isolation structure is used in the outer frame region of the pixel unit to achieve better isolation. The row spacing and column spacing within the pixel unit adopt a partial-depth trench isolation structure; thus ensuring that the substrate silicon interface within the pixel unit remains intact, the design of the three transistors and the floating diffuser (FD) is not constrained, and electrical signal conduction between pixels within the pixel unit is achieved in the silicon substrate, reducing metal wiring. In addition, the reduced depth of the partial-depth trench isolation structure reduces the filling of polysilicon in the trenches, which helps to improve quantum efficiency. Attached Figure Description
[0036] Figure 1 This is a schematic diagram of the manufacturing process of the first image sensor of the present invention.
[0037] Figures 2 to 7 This is a schematic diagram of the steps in the manufacturing method of the first image sensor of the present invention.
[0038] Figure 8 This is a top view of a pixel unit of the image sensor of the present invention. Figure 9 For along Figure 8 A cross-sectional diagram of the diagonal Aa.
[0039] Figures 10 to 14 This is a schematic diagram of the steps in the manufacturing method of the second image sensor of the present invention.
[0040] The accompanying figure is labeled as follows:
[0041] 10-Substrate; 101-First surface; 102-Second surface; 11-Hard mask layer; 12-Antireflective layer; 13-Patterned photoresist; K1-First opening; K2-Second opening; V1-Full depth trench; V2-Partial depth trench; C-Pixel unit; P-Pixel; I1-Full depth trench isolation;
[0042] I2 - Partial depth trench isolation; 21 - First hard mask layer; 22 - Second hard mask layer; 23 - Anti-reflective layer; 24 - Patterned photoresist; K3 - Third aperture; K4 - Fourth aperture; 30 - Transmission gate. Detailed Implementation
[0043] 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 drawings are in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of the present invention.
[0044] 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, 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.
[0045] This invention provides a first method for manufacturing an image sensor, such as... Figure 1 As shown, it includes:
[0046] S11. A substrate is provided, the substrate having opposing first and second surfaces;
[0047] S12. A patterned hard mask layer is formed on the first surface of the substrate, and the removal area of the patterned hard mask layer corresponds to the area of the full-depth trench.
[0048] S13. Form a patterned photoresist, the patterned photoresist covering the substrate and the patterned hard mask layer, the patterned photoresist including a first opening corresponding to a full-depth trench and a second opening corresponding to a partial-depth trench; the first opening corresponds to the removal area of the patterned hard mask layer, and the second opening corresponds to the retention area of the patterned hard mask layer.
[0049] S14. Perform the first etching process to etch the substrate at a preset depth directly below the first opening, and simultaneously etch the patterned hard mask layer directly below the second opening.
[0050] S15. Perform the second etching process to continue etching the substrate directly below the first opening until the substrate is completely etched through to form a full-depth trench, and at the same time etch a portion of the substrate directly below the second opening to form a partial-depth trench.
[0051] S16. Fill the full-depth trench and partial-depth trench in the substrate with isolation layers to form full-depth trench isolation and partial-depth trench isolation, respectively.
[0052] The following describes in detail the steps of the manufacturing method of the first image sensor of the present invention with reference to the accompanying drawings.
[0053] Step S11, as follows Figure 2As shown, a substrate 10 is provided, having a first surface 101 and a second surface 102 opposite to each other. Specifically, the substrate 10 can be any suitable substrate known in the art, such as at least one of the following materials: silicon, germanium, silicon germanium, silicon carbon, silicon germanium carbon, indium arsenide, gallium arsenide, indium phosphide, or other III / V compound semiconductors, including multilayer structures composed of these semiconductors, or silicon-on-insulator, silicon-on-insulator stacked, silicon-on-insulator stacked, silicon-on-insulator, and germanium-on-insulator, or it can also be a double-sided polished silicon wafer, etc. In this embodiment, the substrate 10 is, for example, a silicon wafer. Depending on the distribution range within the surface of the substrate 10, the image sensor can include a pixel area and a peripheral circuit area, wherein the pixel area can include multiple pixels distributed in an array. The peripheral circuit area can specifically be divided into areas for horizontal driving circuits, vertical driving circuits, column signal processing circuits, and control circuits, etc.
[0054] Step S12, as follows Figure 3 As shown, a patterned hard mask layer 11 is formed on the first surface of the substrate 10, and the removal area of the patterned hard mask layer 11 corresponds to the area of the full-depth trench. Optionally, as... Figure 4 As shown, after step S2, the method further includes: forming an anti-reflection layer 12, which covers the substrate 10 and the patterned hard mask layer 11, with the top surface of the anti-reflection layer 12 flush with and higher than the top surface of the patterned hard mask layer 11.
[0055] Step S13, as follows Figure 4 As shown, a patterned photoresist 13 is formed, which covers an anti-reflective layer 12. The patterned photoresist 13 includes a first opening K1 corresponding to a full-depth trench and a second opening K2 corresponding to a partial-depth trench; the first opening K1 corresponds to the removal area of the patterned hard mask layer 11, and the second opening K2 corresponds to the retention area of the patterned hard mask layer 11.
[0056] Step S14, as follows Figure 5 As shown, a first etching process is performed to etch the substrate 10 at a predetermined depth directly below the first opening K1, and simultaneously etch the patterned hard mask layer 11 directly below the second opening K2.
[0057] Step S15, as follows Figure 6 As shown, a second etching process is performed to continue etching the substrate 10 directly below the first opening K1 until it is completely etched through to form a full-depth trench V1, and at the same time, a portion of the substrate 10 directly below the second opening K2 is etched to form a partial-depth trench V2.
[0058] like Figure 6 and Figure 7 As shown, the patterned photoresist 13, anti-reflection layer 12, and patterned hard mask layer 11 are removed.
[0059] Figure 8 This is a top view of the structure of a pixel unit in an image sensor. Figure 9 For along Figure 8 A cross-sectional view of the diagonal Aa. Step S16, as shown... Figures 7 to 9 As shown, isolation layers are filled in the full-depth trench V1 and partial-depth trench V2 of the substrate 10 to form full-depth trench isolation I1 and partial-depth trench isolation I2, respectively. The isolation layer material can be polysilicon, oxide, or other suitable materials.
[0060] Specifically, the image sensor includes multiple pixel units C, and each pixel unit C includes M rows * N columns of pixels P; the values of M and N can be set according to actual needs and are not limited; the figure shows the case where the pixel unit C includes 2 rows * 2 columns of pixels P.
[0061] This invention employs a dual-depth trench isolation technology, combining full-depth trench isolation I1 with partial-depth trench isolation I2. The full-depth trench isolation I1 structure is used in the outer frame region of the pixel unit C to achieve better isolation. The pixel unit C includes M rows * N columns of pixels; the row spacing between adjacent rows and the column spacing between adjacent columns within the pixel unit C utilize a partial-depth trench isolation I2 structure. This ensures that the substrate silicon interface within the pixel unit C remains intact, and the design of the three transistors and the floating diffuser (FD) is not constrained. The design of pixels on the inner periphery of the pixel unit C sharing the floating diffuser (FD) located in the central region can be retained, reducing metal wiring. Furthermore, the reduced depth of the partial-depth trench isolation I2 structure decreases the polysilicon filling in the trenches, contributing to improved quantum efficiency, which measures the efficiency of an image sensor in converting incident photons into collectable electrons.
[0062] Dual-depth trenches, namely full-depth trenches V1 and partial-depth trenches V2, have disadvantages such as two photomasks to form full-depth trenches V1 and partial-depth trenches V2 respectively, due to the different depths of the two trenches. The conventional method involves adding two photomasks to form full-depth trenches V1 and partial-depth trenches V2 respectively. These disadvantages include two photolithography alignment misalignments, repeated etching of the overlapping areas of full-depth trenches V1 and partial-depth trenches V2, and a long etching process time for the two trenches, which is a bottleneck for the production capacity of manufacturing plants.
[0063] The first method for fabricating an image sensor of this invention involves depositing a hard mask layer 11 of a specific thickness before etching the full-depth trench V1 and partial-depth trench V2. Using a single photomask, photolithography is employed to remove the thin film from the isolation region of the full-depth trench, thereby achieving a thickness difference between the top of the full-depth trench isolation region and the partial-depth trench isolation region. This thickness difference can be transferred to both the full-depth trench isolation and the partial-depth trench isolation through a single trench etching process. During subsequent etching of the full-depth trench and the partial-depth trench, the different selectivity ratios of the hard mask layer 11 and the substrate 10 further facilitate this thickness difference, thus realizing the full-depth trench isolation and partial-depth trench isolation structures. This avoids the need for two separate photomasks to form the full-depth trench V1 and the partial-depth trench V2, saving process time and increasing production capacity.
[0064] The present invention also provides an image sensor, such as Figure 8 and Figure 9 As shown, it includes:
[0065] Substrate 10, having opposing first surface 101 and second surface 102;
[0066] Multiple pixel units C are formed on the substrate, and each pixel unit C includes M rows * N columns of pixels P;
[0067] Full-depth trench isolation I1 is used in the outer frame area of pixel unit C; the row spacing between adjacent rows and the column spacing between adjacent columns within pixel unit C adopt a partial-depth trench isolation I2 structure.
[0068] Both full-depth trench isolation I1 and partial-depth trench isolation I2 extend from the first surface 101 into the substrate in a direction perpendicular to the upper surface of the substrate.
[0069] Specifically, a floating diffuser (FD) is formed in the central region of pixel cell C on the side of substrate 10 near the second surface 102, and a transmission gate 30 is formed around the floating diffuser. The region where pixel P is located in substrate 10, from the second surface 102 to the first surface 101, sequentially includes: the transmission gate 30, a DNPPD (deep n-type pinned photodiode), and a DNW (deep N-well). The surrounding pixels share the floating diffuser (FD) in the central region, which, from the second surface to the first surface 101, sequentially includes: the floating diffuser (FD), a CPW (shallow P-well), a DPW (deep P-well), and a partial deep trench isolation I2. The DPW (deep P-well) and the partial deep trench isolation I2 overlap in depth. The DNPPDs in adjacent pixel P regions are separated by DPWs (deep P-wells) and partial deep trench isolation I2. The transmission gate 30 is T-shaped, with the vertical portion of the T-shape located in the substrate and the horizontal portion located on the surface of substrate 10. The transfer gate 30 can achieve deeper charge storage in a smaller pixel space, thereby improving photoelectric conversion efficiency and signal transmission capability.
[0070] The image sensor of the present invention can be manufactured using either the first image sensor manufacturing method described above or the second image sensor manufacturing method described below, and there is no limitation.
[0071] The present invention also provides a second method for manufacturing an image sensor, comprising:
[0072] S21. A substrate is provided, the substrate having opposing first and second surfaces;
[0073] S22. A patterned first hard mask layer is formed on the first surface of the substrate; the removal area of the patterned first hard mask layer corresponds to the area of the full-depth trench; a second hard mask layer is formed covering the substrate and the patterned first hard mask layer.
[0074] S23. Form a patterned photoresist covering the second hard mask layer. The patterned photoresist includes a third opening corresponding to a full-depth trench and a fourth opening corresponding to a partial-depth trench. The third opening corresponds to the removal area of the patterned first hard mask layer, and the fourth opening corresponds to the retention area of the patterned first hard mask layer.
[0075] S24. Perform etching process one, etching the second hard mask layer directly below the third opening and the substrate at a preset depth, and simultaneously etching the second hard mask layer directly below the fourth opening.
[0076] S25. Perform etching process two, continue etching the substrate directly below the third opening until the substrate is completely etched through to form a full-depth trench, and at the same time etch the patterned first hard mask layer and the substrate at a partial depth directly below the fourth opening to form a partial-depth trench.
[0077] S26. Fill the full-depth trench and partial-depth trench in the substrate with isolation layers to form full-depth trench isolation and partial-depth trench isolation, respectively.
[0078] The following describes in detail the steps of the manufacturing method of the second image sensor of the present invention with reference to the accompanying drawings.
[0079] Step S21, as follows Figure 10 As shown, a substrate 10 is provided, the substrate having a first surface and a second surface opposite to each other.
[0080] Step S22, as follows Figure 11 As shown, a patterned first hard mask layer 21 is formed on the first surface of the substrate 10; the removal area of the patterned first hard mask layer 21 corresponds to the area of a full-depth trench; a second hard mask layer 22 is formed covering the substrate 10 and the patterned first hard mask layer 21. Optionally, after step S22, an anti-reflective layer 23 is further formed, which covers the second hard mask layer 22. The top surface of the anti-reflective layer 23 is flush with and higher than the top surface of the second hard mask layer 22 located above the retention area of the first hard mask layer 21.
[0081] Step S23, as follows Figure 11 As shown, a patterned photoresist 24 is formed covering the anti-reflective layer 23. The patterned photoresist 24 includes a third opening K3 corresponding to a full-depth trench and a fourth opening K4 corresponding to a partial-depth trench. The third opening K3 is located above the removal area of the patterned first hard mask layer 21, and the fourth opening K4 is located above the retention area of the patterned first hard mask layer 21.
[0082] Step S24, as follows Figure 12 As shown, etching process one is performed, etching the second hard mask layer 22 directly below the third opening K3 and the substrate 10 at a preset depth, and simultaneously etching the second hard mask layer 22 directly below the fourth opening K4.
[0083] Step S25, as follows Figure 13 As shown, etching process two is performed, and the substrate 10 directly below the third opening K3 is etched until the substrate is completely etched through to form a full-depth trench V1. At the same time, the patterned first hard mask layer 21 directly below the fourth opening K4 and the substrate 10 at a partial depth are etched to form a partial-depth trench V2.
[0084] Step S26: Fill the full-depth trench V1 and partial-depth trench V2 in the substrate with isolation layers to form full-depth trench isolation I1 and partial-depth trench isolation I2.
[0085] like Figures 12 to 14 As shown, the patterned photoresist 24, anti-reflective layer 23, second hard mask layer 22 and first hard mask layer 21 are removed.
[0086] The second image sensor fabrication method of the present invention involves first depositing a first hard mask layer 21 of a specific thickness over the entire surface before etching the full-depth trench V1 and the partial-depth trench V2. A photomask is then added to pattern the first hard mask layer 21, and photolithography is used to remove the first hard mask layer 21 corresponding to the full-depth trench isolation region. Next, a second hard mask layer 22 is uniformly deposited over the entire surface. This achieves a thickness difference in the first hard mask layer 21 at the top of the full-depth trench isolation region and the partial-depth trench isolation region. During subsequent etching of the full-depth trench and the partial-depth trench, the thickness difference can be propagated due to the different selection ratios of the first hard mask layer 21 and the substrate 10, thus achieving full-depth trench isolation I1 and partial-depth trench isolation I2. The material selection and corresponding deposition thickness of the first hard mask layer 21 and the second hard mask layer 22, as well as subsequent etching, can be adjusted by selecting materials and changing different etching ratios to achieve different height differences as required.
[0087] In summary, this invention provides an image sensor and its fabrication method, employing a dual-depth trench isolation technology, namely, full-depth trench isolation combined with partial-depth trench isolation. Before trench etching, this invention first deposits a hard mask layer and adds only one photomask. The hard mask layer is patterned using this photomask, achieving the thickness difference between the full-depth trench isolation and partial-depth trench isolation regions. This allows a single trench etching process to be used, transferring this thickness difference to both the full-depth and partial-depth trench isolation regions. This avoids the need for two separate photomasks to form the full-depth and partial-depth trenches, saving process time and increasing production capacity.
[0088] Furthermore, full-depth trench isolation is located in the outer frame region of the pixel unit of the image sensor; the pixel unit includes peripheral pixels and a floating diffuser located in the central region; the peripheral pixels share the floating diffuser; the row spacing between adjacent rows and the column spacing between adjacent columns within the pixel unit adopts partial-depth trench isolation. This invention employs dual-depth trench isolation technology, namely, full-depth trench isolation combined with partial-depth trench isolation. A full-depth trench isolation structure is used in the outer frame region of the pixel unit to achieve better isolation. The row spacing and column spacing within the pixel unit adopt a partial-depth trench isolation structure; thus ensuring that the substrate silicon interface within the pixel unit remains intact, the design of the three transistors and the floating diffuser (FD) is not constrained, and electrical signal conduction between pixels within the pixel unit is achieved in the silicon substrate, reducing metal wiring. In addition, the reduced depth of the partial-depth trench isolation structure reduces the filling of polysilicon in the trenches, which helps to improve quantum efficiency.
[0089] 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.
[0090] 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. A method for manufacturing an image sensor, characterized in that, include: S11. A substrate is provided, the substrate having opposing first and second surfaces; S12. A patterned hard mask layer is formed on the first surface of the substrate, wherein the removal area of the patterned hard mask layer corresponds to the area of a full-depth trench. S13. Form a patterned photoresist, the patterned photoresist covering the substrate and the patterned hard mask layer, the patterned photoresist including a first opening corresponding to the full-depth trench and a second opening corresponding to a partial-depth trench; the first opening corresponds to the removal area of the patterned hard mask layer, and the second opening corresponds to the retention area of the patterned hard mask layer. S14. Perform a first etching process to etch the substrate at a predetermined depth directly below the first opening, and simultaneously etch the patterned hard mask layer directly below the second opening. S15. Perform a second etching process to continue etching the substrate directly below the first opening until the substrate is completely etched through to form a full-depth trench, and at the same time etch a portion of the substrate directly below the second opening to form a partial-depth trench. S16. Fill the full-depth trench and the partial-depth trench in the substrate with isolation layers to form full-depth trench isolation and partial-depth trench isolation, respectively.
2. The method for manufacturing an image sensor as described in claim 1, characterized in that, After step S12 and before step S13, the method further includes: forming an anti-reflective layer that covers the substrate and the patterned hard mask layer, wherein the top surface of the anti-reflective layer is flush with and higher than the top surface of the patterned hard mask layer.
3. The method for manufacturing an image sensor as described in claim 1, characterized in that, The full-depth trench isolation completely penetrates the entire thickness of the substrate or penetrates more than 90% of the substrate thickness; the partial-depth trench isolation penetrates 40% to 70% of the substrate thickness.
4. The method for manufacturing an image sensor as described in claim 1, characterized in that, The full-depth trench isolation is located in the outer frame region of the pixel unit of the image sensor; the pixel unit includes peripheral pixels and a floating diffuser located in the central region; The pixels around the perimeter share the floating diffuser; the row spacing between adjacent rows and the column spacing between adjacent columns within the pixel unit are isolated by the partial depth trench.
5. A method for manufacturing an image sensor, characterized in that, include: S21. A substrate is provided, the substrate having opposing first and second surfaces; S22. A patterned first hard mask layer is formed on the first surface of the substrate; The removal area of the patterned first hard mask layer corresponds to the area of the full-depth trench; a second hard mask layer is formed covering the substrate and the patterned first hard mask layer; S23. Form a patterned photoresist covering the second hard mask layer, the patterned photoresist including a third opening corresponding to the full-depth trench and a fourth opening corresponding to the partial-depth trench; the third opening corresponds to the removal area of the patterned first hard mask layer, and the fourth opening corresponds to the retention area of the patterned first hard mask layer. S24. Perform etching process one to etch the second hard mask layer directly below the third opening and the substrate at a preset depth, and simultaneously etch the second hard mask layer directly below the fourth opening. S25. Perform etching process two, continue etching the substrate directly below the third opening until the substrate is completely etched through to form a full-depth trench, and simultaneously etch the patterned first hard mask layer directly below the fourth opening and the substrate at a partial depth to form a partial-depth trench. S26. Fill the full-depth trench and the partial-depth trench in the substrate with isolation layers to form full-depth trench isolation and partial-depth trench isolation, respectively.
6. The method for manufacturing an image sensor as described in claim 5, characterized in that, After step S22 and before step S23, the method further includes: forming an anti-reflective layer that covers the second hard mask layer, wherein the top surface of the anti-reflective layer is flush with and higher than the top surface of the second hard mask layer located above the reserved area of the first hard mask layer.
7. The method for manufacturing an image sensor as described in claim 5, characterized in that, In the first etching process, the second hard mask layer directly below the fourth opening is etched, stopping at the upper surface of the first hard mask layer.
8. An image sensor, comprising: A substrate having opposing first and second surfaces; Multiple pixel units are formed on the substrate, and each pixel unit includes M rows * N columns of pixels; A full-depth trench isolation is provided in the outer frame area of the pixel unit; The row spacing between adjacent rows and the column spacing between adjacent columns within the pixel unit are partially isolated by depth trenches. Both the full-depth trench isolation and the partial-depth trench isolation extend from the first surface into the substrate in a direction perpendicular to the upper surface of the substrate.
9. The image sensor as claimed in claim 8, characterized in that, A floating diffusion portion is formed in the central region of the pixel unit on the side of the substrate near the second surface, and a transmission gate is formed around the floating diffusion portion. The region where the pixel is located in the substrate includes, from the second surface to the first surface, the following in sequence: the transmission gate 30, DNPPD, and a deep N-well; the pixels around the periphery share the floating diffusion section, and the central region includes, from the second surface to the first surface, the following in sequence: the floating diffusion section, a shallow P-well, a deep P-well, and the partial depth trench isolation.
10. The image sensor as claimed in claim 9, characterized in that, The deep P-well and the partial depth trench isolation have an overlapping region in depth; the deep P-well and the partial depth trench isolation are spaced apart between the DNPPDs of adjacent pixels.