Method for optimizing etching depth uniformity of deep groove
By forming a mask layer with a curved structure on the surface of a CMOS image sensor substrate and using a synchronous etching process to optimize the depth uniformity of deep trenches, the problem of depth difference caused by etching load effect is solved, thereby improving the performance and sensitivity of the image sensor.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-11
- Publication Date
- 2026-04-14
AI Technical Summary
In the deep trench etching process of existing CMOS image sensors, the etching load effect causes a large difference in trench depth between the cross-region and non-cross-region, which affects the performance of the image sensor.
A mask layer with a curved structure is formed on the substrate surface, and trenches in the cross and non-cross regions are formed by synchronous etching, so that the trench depth difference is within a preset range. The uniformity of depth is optimized by using a gray-tone mask or reflow etching process.
By optimizing the uniformity of deep trench etching depth, the difference in trench depth was reduced, thereby improving the performance and sensitivity of the image sensor.
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Figure CN121865719A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of image sensors, and more particularly to a method for optimizing the uniformity of deep trench etching depth. Background Technology
[0002] CMOS (Complementary Metal-Oxide-Semiconductor) image sensors offer advantages such as simple manufacturing processes, ease of integration with other devices, small size, light weight, low power consumption, and low cost. Therefore, with technological advancements, CMOS image sensors are increasingly replacing CCD (Charge-Coupled Device) image sensors in various electronic products. Currently, CMOS image sensors are widely used in still digital cameras, camera phones, digital camcorders, medical imaging devices (e.g., gastroscopes), and automotive imaging devices. CMOS image sensors can be categorized into FSI (Front Side Illumination) and BSI (Back Side Illumination).
[0003] However, as the pixel size of image sensors becomes smaller and smaller, crosstalk between adjacent photosensitive areas becomes more and more serious. Crosstalk can lead to more white pixels and reduce the sensitivity of image sensors. The industry usually uses DTI (deep trench isolation) structure to reduce crosstalk.
[0004] like Figure 1 As shown, DTI structures typically include deep trenches and isolation materials filling the trenches. These deep trenches are generally several micrometers deep and have a high aspect ratio. This makes it difficult to extract the polymer generated during the etching process to remove it from the trenches. The etching load effect makes the polymer in trench regions with larger feature sizes easier to extract than the polymer in trench regions with smaller feature sizes. This results in the trench depth formed by the smaller feature size trench regions being less than the trench depth of the larger feature size trench regions. In image sensor chips, deep trench isolation structures extend laterally around multiple pixel units. The deep trench isolation structure includes a first trench extending along a first direction and a second trench extending along a second direction. Multiple first trenches and multiple second trenches have multiple intersection regions, and the feature size of the intersection regions is larger than that of the non-intersection regions, making the etching depth of the intersection regions greater than that of the non-intersection regions. Figure 1 As can be seen, the depth difference between the two can reach more than 600 nanometers. Therefore, there is an urgent need for a process method that can optimize the uniformity of deep trench etching depth in order to improve the performance of CMOS image sensors. Summary of the Invention
[0005] To achieve the above objectives, the present invention aims to provide a method for optimizing the uniformity of deep trench etching depth, specifically including the following steps: Multiple first layers with curved structures are formed on the first surface of the substrate; The substrate and the first layer are simultaneously etched to form intersecting trenches, such that the difference in trench depth between the intersecting and non-intersecting regions is no greater than a preset value.
[0006] Furthermore, the curved surface structure is high in the middle and low around the edges, and is located in the intersection area.
[0007] Furthermore, the curved structure completely covers the intersection area on a projection plane perpendicular to the substrate.
[0008] Furthermore, the curved structure at least partially overlaps with the non-intersecting region on the projection plane perpendicular to the substrate.
[0009] Furthermore, the method for forming the curved structure specifically involves depositing a first layer on the substrate, spin-coating a first photoresist layer, using a gray-tone mask for exposure and development to form a first photoresist layer with a first pattern, etching the first layer to form the first layer with the curved structure, and removing the remaining first photoresist layer.
[0010] Furthermore, the method for forming the curved structure may also include depositing a first layer on the substrate, spin-coating a first photoresist layer, performing exposure and development, and reflowing the first photoresist layer to form a first pattern with a curved structure.
[0011] Furthermore, the method for forming the curved structure specifically involves spin-coating a first photoresist layer on the substrate, performing exposure and development, reflowing the first photoresist layer to form a first pattern, etching the first layer to form the first layer with the curved structure, and removing the remaining first photoresist layer.
[0012] Furthermore, after the curved structure is formed, a photoresist layer is spin-coated, and a second photoresist layer with a second pattern is formed by exposure and development using a second mask.
[0013] Furthermore, the first layer can be a hard mask layer, and the material of the hard mask layer is one or more of silicon oxide, silicon nitride, and silicon oxynitride.
[0014] Furthermore, the preset value is between -500 and 500 nm.
[0015] Furthermore, the curved surface structure is one or more of the following: a spherical table, a hemisphere, a semi-ellipsoid, a cone, and a polygon.
[0016] Furthermore, the groove depth difference between the intersecting and non-intersecting regions can be adjusted based on the thickness of the curved surface structure.
[0017] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: The present invention pre-forms a layer with a curved structure in the intersection area of deep trenches on the substrate surface with photosensitive areas by using a gray-tone mask or reflow etching process. Then, the intersection area and non-intersection area of the first layer with curved structure are simultaneously etched, thereby offsetting the difference in trench depth caused by the different opening sizes of the intersection area and non-intersection area. Finally, a deep trench with better uniformity of depth in each area is obtained, or a deep trench with shallower intersection area can be obtained. Attached Figure Description
[0018] The accompanying drawings, which form part of this specification, are used to further understand the invention. The drawings illustrate embodiments of the invention and, together with the specification, serve to explain the principles of the invention.
[0019] Figure 1 This is a cross-sectional view of the depth of a deep trench in the existing technology.
[0020] Figure 2 A-2G is a schematic diagram of the process flow of Embodiment 1 of this application.
[0021] Figure 3 A-3F is a schematic diagram of the process flow of Embodiment 3 of this application.
[0022] Figure 4 This is a schematic diagram of some of the photomasks used in the embodiments of this application.
[0023] Figure 5 This is a partial schematic diagram of the grayscale mask used in the embodiments of this application.
[0024] Figure 6 This is a cross-sectional view along the CC' direction of the deep trench in an embodiment of this application. Detailed Implementation
[0025] The following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.
[0026] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the present invention.
[0027] This invention proposes a method to optimize the uniformity of deep trench etching depth in order to reduce the impact of etching on the structure below the trench.
[0028] The following description uses some examples. It should be noted that, 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 top" 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. Example 1
[0029] As a preferred example, the present invention provides a method for optimizing the uniformity of deep trench etching depth, comprising the following steps: A substrate is provided, and a mask layer with a curved structure is formed on the substrate. The substrate and the mask layer are simultaneously etched to form trenches that intersect each other, such that the difference in trench depth between the intersecting and non-intersecting regions is not greater than a preset value.
[0030] In some embodiments, the curved structure is located at the intersection of intersecting grooves.
[0031] The following is combined with Figure 2 The detailed steps of the technical solution of this invention are described in detail.
[0032] like Figure 2 As shown in Figure A, a substrate 100 is provided, the substrate 100 having a first surface 100A and a second surface 100B. The surface of the second surface 100B has a connection layer 200 connected to a carrier wafer 300. In some embodiments, the connection layer 200 includes a metal interconnect layer and a dielectric layer. A hard mask layer 400 and a photoresist layer 500 are sequentially formed over the first surface 100A of the substrate 100. The photoresist layer 500 is a positive photoresist.
[0033] like Figure 2 As shown in Figure B, a grey tone mask 11A is used to expose and develop the photoresist layer 500 to form a photoresist layer 501 with a curved surface. The pattern of the grey tone mask 11A is as follows: Figure 5 As shown.
[0034] It should be pointed out that, although Figure 5 Mask 11A and Figure 4The mask 12A is similar in shape to the one in the photomask 11A, but the mask 11A uses a gray stone mask, while the mask 12A uses a regular photomask.
[0035] like Figure 2 As shown in Figure C, a photoresist layer 501 with a curved surface is used as a mask, and the hard mask layer is etched away to form a hard mask layer 401 with a curved surface.
[0036] like Figure 2 As shown in Figure D, a photoresist layer 600 is deposited on the surface of a hard mask layer 401 with a curved structure, completely covering the hard mask layer 401 and the substrate 100.
[0037] like Figure 2 As shown in Figure E, photoresist layer 600 is developed and exposed using photomask 11B as a mask, and the photoresist above the trench region is removed to form a patterned photoresist layer 601. The pattern of photomask 11B is illustrated below. Figure 4 As shown.
[0038] like Figure 2 As shown in Figure F, the substrate 100 is etched using the photoresist layer 601 as a mask. While etching the substrate 100, the hard mask layer 401 with a curved surface is removed to form an array of deep trenches with intersections. The difference between the depth of the intersection region 702 and the depth of the non-intersection region 701 is less than a preset value. In this embodiment, the depth of the intersection region 702 is slightly less than the depth of the non-intersection region 701, and the difference ranges from -500 to 500 nm, preferably -100 to 100 nm.
[0039] like Figure 2 As shown in G, in some embodiments, the depth of the cross region 702 is slightly greater than the depth of the non-cross region 701, with the difference ranging from -500 to 500 nm, preferably -100 to 100 nm. Example 2
[0040] Also refer to Figure 2 A substrate 100 is provided, the substrate 100 having a first surface 100A and a second surface 100B. The surface of the second surface 100B has a connection layer 200 connected to a carrier wafer 300. In some embodiments, the connection layer 200 includes a metal interconnect layer and a dielectric layer. A hard mask layer 400 and a photoresist layer 500 are sequentially formed over the first surface 100A of the substrate 100. The photoresist layer 500 is a positive photoresist.
[0041] After forming the photoresist layer 500, the photoresist is heated using a mask 12A. The heating temperature is gradually increased to eliminate bubbles generated during the baking process. The photoresist is heated to a certain temperature and held for a predetermined time, allowing some of the photoresist to melt and reflow, thus eliminating streaks. Heating can be performed using a hot plate or by baking with hot air. The heating temperature and holding time can be selected according to the photoresist material, and this invention is not limited to any specific values. Through the reflow process, a smooth, curved surface structure photoresist layer 501 can be obtained.
[0042] Except for the method of forming the photoresist layer 501 with curved structure, which is different from that in Example 1, all other steps are the same and will not be described again here. Example 3
[0043] The following is combined with Figure 3 Another embodiment of this application will be briefly described.
[0044] like Figure 3 As shown in Figure A, a substrate 100 is provided, the substrate 100 having a first surface 100A and a second surface 100B. The surface of the second surface 100B has a connection layer 200 connected to a carrier wafer 300. In some embodiments, the connection layer 200 includes a metal interconnect layer and a dielectric layer. A photoresist 410 is formed over the first surface 100A of the substrate 100. The photoresist 410 is a negative resist.
[0045] like Figure 3 As shown in Figure B, the photoresist 410 is exposed and developed using a mask 13A, and then cured using a reflow process to form a photoresist layer 411 with a curved surface structure.
[0046] like Figure 3 As shown in Figure C, a photoresist layer 610 is deposited on the surface of the photoresist layer 411 with a curved structure, and completely covers the photoresist layer 411 and the substrate 100.
[0047] like Figure 3 As shown in D, the photoresist layer 610 is developed and exposed using mask 11B as a mask, and the photoresist above the trench area is removed to form a patterned photoresist layer 611.
[0048] like Figure 3 As shown in Figure E, the substrate 100 is etched using the photoresist layer 601 as a mask. While etching the substrate 100, the hard mask layer 401 with a curved surface is removed to form an array of deep trenches with intersections. The difference between the depth of the intersection region 702 and the depth of the non-intersection region 701 is less than a preset value. In this embodiment, the depth of the intersection region 702 is slightly less than the depth of the non-intersection region 701, and the difference ranges from -500 to 500 nm, preferably -100 to 100 nm.
[0049] like Figure 3 As shown in F, in some embodiments, the depth of the cross region 702 is slightly greater than the depth of the non-cross region 701, with the difference ranging from -5000 to 500 nm, preferably from -100 to 100 nm.
[0050] In other embodiments, the shape of the mask for exposing the photoresist layer can also be as follows: Figure 4 As shown in 14A, it is not limited to the area above the intersection, but can also partially cover the non-intersection area, so that the trench depth of the intersection area and the non-intersection area boundary of the deep trench is smoothly transitioned.
[0051] Furthermore, the present invention also proposes an image sensor having a uniformly deep trench array prepared by the method described in any of the foregoing embodiments.
[0052] The basic concepts have been described above. It is clear that the detailed disclosure above is merely illustrative and does not constitute a limitation of the present invention. Although not explicitly stated herein, various modifications, improvements, and corrections may be made to the present invention by those skilled in the art. Such modifications, improvements, and corrections are suggested in this invention and therefore remain within the spirit and scope of the exemplary embodiments of the present invention.
[0053] It should be understood that the embodiments described in this invention are merely illustrative of the principles of the invention. Other modifications may also fall within the scope of this invention. Therefore, alternative configurations of the embodiments of this invention are considered as examples and not limitations, and are regarded as consistent with the teachings of this invention. Accordingly, the embodiments of this invention are not limited to those explicitly described and illustrated herein.
Claims
1. A method for forming an image sensor, the method comprising the following steps: Multiple first layers with curved structures are formed on the first surface of the substrate; The substrate and the first layer are simultaneously etched to form intersecting trenches, such that the difference in trench depth between the intersecting and non-intersecting regions is no greater than a preset value.
2. The method according to claim 1, wherein, The curved surface structure is high in the middle and low around the edges, and is located in the intersection area.
3. The method according to claim 1, wherein, The curved structure completely covers the intersection area on the projection plane perpendicular to the substrate.
4. The method according to claim 1, wherein, The curved structure at least partially overlaps with the non-intersecting region on the projection plane perpendicular to the substrate.
5. The method according to claim 1, wherein, The specific method for forming the curved surface structure is as follows: The first layer on the substrate, Spin coating is used to prepare the first photoresist layer. A gray-toned mask is used for exposure and development to form the first photoresist layer of the first pattern. The first layer is etched to form the first layer with the curved surface structure. Remove the remaining first photoresist layer.
6. The method according to claim 1, wherein, The specific method for forming the curved surface structure is as follows: The first layer on the substrate, Spin coating is used to prepare the first photoresist layer. Exposure and development are performed, and the first photoresist layer is reflowed to form the first pattern. The first layer is etched to form the first layer with the curved surface structure. Remove the remaining first photoresist layer.
7. The method according to claim 1, wherein, The specific method for forming the curved surface structure is as follows: A first photoresist layer is prepared by spin-coating on the substrate. Exposure and development are performed, and the first photoresist layer is reflowed to form a first pattern with a curved surface structure. Remove the remaining first photoresist layer.
8. The method according to claim 5, 6, or 7, wherein, After the curved surface structure is formed, a photoresist layer is also spin-coated. A second photoresist layer with a second pattern is formed by exposure and development using a second photomask.
9. The method according to claim 5 or 6, wherein, The first layer material is one or more of silicon oxide, silicon nitride, and silicon oxynitride.
10. The method according to claim 1, wherein, The preset value is -500 to 500 nm.
11. The method according to claim 1, wherein, The curved surface structure is one or more of the following: spherical, hemispherical, semi-ellipsoidal, conical, and polygonal.
12. The method according to claim 1 can adjust the groove depth difference between the intersecting region and the non-intersecting region according to the thickness of the curved surface structure.