Back-illuminated image sensor and method for manufacturing the same

Abstract

The present application relates to a back-illuminated image sensor and a method for preparing the same, including: providing a substrate, wherein the substrate includes a first region and a second region arranged along a first direction parallel to the top surface of the substrate; forming a first groove for isolating a photodiode in the first region and a second groove for isolating a buried wire in the second region based on the same photomask; after filling the first groove with a sacrificial barrier layer, forming a protective layer covering the inner surface of the second groove; after removing the sacrificial barrier layer in the first groove, using a target gas to selectively etch and remove part of the substrate at the bottom of the first groove; after removing the protective layer, forming a dielectric layer, the dielectric layer covers the inner surface of the second groove and fills the first groove; forming a buried wire in the second groove. The present application only requires one photomask to simultaneously produce deep isolation grooves between photodiodes and shallow grooves for metal wires, thereby saving the number of photomasks and reducing costs.

Description

Technical Field

[0001] The present application relates to the field of integrated circuit technology, and in particular to a back-illuminated image sensor and a method for preparing the same. Background Art

[0002] In the design of backside illuminated image sensors (BSI), two different types of trenches are usually required to achieve their functions. One is a narrow and deep trench, which is deep enough to ensure that the photodiodes inside the BSI work independently without interfering with each other, allowing the sensor to capture higher quality image data. The other is a wide and shallow trench, which has a moderate width and is used to arrange and connect metal wires, which are essential for signal transmission.

[0003] However, two special masks are usually required to complete the manufacture of such a double-depth groove structure. This not only increases the production cost, but also prolongs the production cycle due to the cumbersome process. The high manufacturing cost may limit the popularity and application of back-illuminated image sensors in the market. Summary of the invention

[0004] Based on this, it is necessary to provide a back-illuminated image sensor and a preparation method thereof to address the technical problems in the prior art, which can at least appropriately reduce the manufacturing cost.

[0005] In a first aspect, the present application provides a method for preparing a back-illuminated image sensor, comprising: providing a substrate, wherein the substrate comprises a first region and a second region arranged along a first direction parallel to a top surface of the substrate, wherein the first region is used to form a plurality of photodiodes, and the second region is used to form a plurality of buried wires; based on the same photomask, forming a first trench for isolating the photodiodes in the first region, and forming a second trench for isolating the buried wires in the second region;

[0006] After the sacrificial barrier layer is filled in the first trench, a protective layer covering the inner surface of the second trench is formed; after the sacrificial barrier layer in the first trench is removed, a target gas is used to selectively etch and remove part of the substrate at the bottom of the first trench; after removing the protective layer, a dielectric layer is formed, the dielectric layer covers the inner surface of the second trench and fills the first trench; and an embedded conductor is formed in the second trench.

[0007] In the method for preparing a back-illuminated image sensor in the above-mentioned embodiment, a first groove and a second groove are formed synchronously on a semiconductor substrate using the same photomask. Due to the morphological differences between the grooves, the first groove and the second groove have different filling rates for the sacrificial barrier layer, that is, when the first groove is completely filled, the second groove only fills its two sides and bottom, and the center of the groove remains empty. The different groove filling degrees help to form a protective layer on the inner surface of the second groove in a targeted manner. During the secondary etching process, the protective layer provides protection for the second groove and maintains its depth unchanged. At this time, part of the substrate at the bottom of the first groove is etched away, and the size in the substrate is deepened, ultimately achieving the purpose of preparing two groove areas with different widths and depths. After processes such as dielectric layers and buried conductors, a first groove for isolating photodiodes and a second groove for isolating buried conductors are finally obtained.

[0008] The present application can simultaneously form the first groove between the photodiodes and the second groove of the metal wire through a single photomask. In the improved process, the morphology difference is used to accurately realize the positioning and depth control of the grooves. Under the premise of ensuring the performance of the device, no redundant photomasks are required, which reduces the manufacturing cost.

[0009] In some embodiments, the target size of the first trench is smaller than the target size of the second trench, and the target size is at least used to characterize the size of the opening along the first direction.

[0010] In some embodiments, after forming the first trench and the second trench and before forming the sacrificial barrier layer, it also includes: using a first thermal oxidation process to form a sacrificial oxide layer of a preset thickness on the inner surface of the first trench and the second trench; forming the sacrificial barrier layer includes: using a deposition process to fill the sacrificial barrier layer in the first trench while forming a sacrificial barrier layer covering the sacrificial oxide layer in the second trench.

[0011] In some embodiments, before forming the protection layer covering the inner surface of the second trench, the method includes:

[0012] The sacrificial barrier layer in the second trench is removed by wet etching using a target solution; and a protective layer with a target thickness is formed on the inner surface of the second trench by a second thermal oxidation process.

[0013] In some embodiments, removing the sacrificial barrier layer in the first trench includes: wet etching and removing the sacrificial barrier layer in the first trench using a target solution; and before selectively etching and removing the substrate at the bottom of the first trench using a target gas, it also includes: pickling and removing the sacrificial oxide layer in the first trench.

[0014] In some embodiments, using a target gas to selectively etch and remove a portion of the substrate at the bottom of the first trench includes: using a target gas including hydrogen bromide and / or sulfur hexafluoride to anisotropically etch and remove a portion of the substrate at the bottom of the first trench.

[0015] In some embodiments, pickling and removing the sacrificial oxide layer in the first trench includes: removing the sacrificial oxide layer in the first trench using diluted hydrofluoric acid.

[0016] In some embodiments, forming a dielectric layer includes: simultaneously forming a first dielectric layer on the inner surface of the first trench, the inner surface of the second trench, and the exposed top surface of the substrate; simultaneously forming the first dielectric layer covering the second trench and a second dielectric layer at least filling the first trench; the first dielectric layer and the second dielectric layer are used to jointly constitute a dielectric layer, and the dielectric constant of the first dielectric layer is greater than the dielectric constant of the second dielectric layer.

[0017] In some embodiments, forming an embedded wire in the second trench includes: forming a metal layer that at least covers the dielectric layer in the second trench; patterning the metal layer to obtain an embedded wire at least partially located in the second trench, and the embedded wires in different second trenches are insulated from each other.

[0018] In some embodiments, the target solution includes sulfuric acid (H2SO4), hydrogen peroxide (H2O2), and water (H2O).

[0019] In a second aspect, the present application further provides a back-illuminated image sensor, including a back-illuminated image sensor prepared by any of the above back-illuminated image sensor preparation methods.

[0020] In the back-illuminated image sensor prepared by the above-mentioned back-illuminated image sensor preparation method, the improved preparation method only needs a single mask to simultaneously form the photodiode isolation groove and the metal wire isolation groove, while ensuring the precise control of the groove depth, simplifying the process flow and effectively reducing its manufacturing cost. Compared with the traditional preparation method, the simplified process flow can improve production efficiency. This new process brings new possibilities for the manufacture of back-illuminated image sensors. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0022] Figure 1 is a flow chart of a method for preparing a back-illuminated image sensor provided in an embodiment;

[0023] Figure 2 A schematic cross-sectional view of a structure obtained by forming a hard mask layer in step S202 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0024] Figure 3 It is a schematic cross-sectional view of a structure obtained after forming the first groove and the second groove in step S204 in the method for preparing a back-illuminated image sensor provided in an embodiment;

[0025] Figure 4 A schematic cross-sectional view of a structure obtained by forming a sacrificial oxide layer in step S2062 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0026] Figure 5 A schematic cross-sectional view of a structure obtained by forming a sacrificial barrier layer in step S2064 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0027] Figure 6 A schematic cross-sectional view of a structure obtained by removing the sacrificial barrier layer in the second trench in step S2066 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0028] Figure 7 A schematic cross-sectional view of a structure obtained by forming a protective layer in step S2068 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0029] Figure 8 A schematic cross-sectional view of a structure obtained by removing the sacrificial barrier layer in the first trench in step S2082 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0030] Fig. 9 A schematic cross-sectional view of a structure obtained by removing the sacrificial oxide layer in the first trench in step S2084 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0031] Fig.10 A schematic cross-sectional view of a structure obtained by removing a portion of the substrate at the bottom of the first trench in step S2086 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0032] Fig.11 A schematic cross-sectional view of a structure obtained by removing the hard mask layer and the protective layer in step S2102 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0033] Fig.12 A schematic cross-sectional view of a structure obtained by forming a dielectric layer in step S2106 in a method for preparing a back-illuminated image sensor provided in an embodiment;

[0034] Fig.13 A schematic cross-sectional view of a structure obtained by forming a metal layer in step S2122 of a method for preparing a back-illuminated image sensor provided in an embodiment;

[0035] Fig.14 FIG. 1 is a cross-sectional schematic diagram of a structure obtained by forming an embedded conductive line in step S2124 in a method for preparing a back-illuminated image sensor provided in an embodiment.

[0036] Description of reference numerals:

[0037] 10. substrate; 11. hard mask layer; 12. sacrificial oxide layer; 13. sacrificial barrier layer; 14. protective layer; 15. metal layer; 20. first groove; 20a. inner surface of the first groove; 30. second groove; 30a. inner surface of the second groove; 40. dielectric layer; 41. first dielectric layer; 42. second dielectric layer; 50. buried conductor. DETAILED DESCRIPTION

[0038] In order to facilitate understanding of the present application, the present application will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present application are given in the drawings. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0040] It should be understood that when an element or layer is referred to as being "on, adjacent to, connected to or coupled to other elements or layers, it may be directly on, adjacent to, connected to or coupled to other elements or layers, or there may be intervening elements or layers. On the contrary, when an element is referred to as being "directly on, directly adjacent to, directly connected to or directly coupled to other elements or layers, there are no intervening elements or layers. It should be understood that although the terms first, second, third, etc. may be used to describe various elements, components, regions, layers, doping types and / or parts, these elements, components, regions, layers, doping types and / or parts should not be limited by these terms. These terms are merely used to distinguish one element, component, region, layer, doping type or part from another element, component, region, layer, doping type or part. Therefore, without departing from the teachings of the present application, the first element, component, region, layer, doping type or portion discussed below may be represented as a second element, component, region, layer or portion; for example, the first doping type may be referred to as the second doping type, and similarly, the second doping type may be referred to as the first doping type; the first doping type and the second doping type are different doping types, for example, the first doping type may be P-type and the second doping type may be N-type, or the first doping type may be N-type and the second doping type may be P-type.

[0041] Spatially relative terms such as "under," "beneath," "below," "under," "above," "above," and the like may be used herein to describe the relationship of an element or feature shown in the figures to other elements or features. It should be understood that, in addition to the orientations shown in the figures, spatially relative terms also include different orientations of the device in use and operation. For example, if the device in the accompanying drawings is flipped, an element or feature described as "under other elements" or "under it" or "under it" will be oriented as being "above" the other elements or features. Thus, the exemplary terms "under" and "under" may include both upper and lower orientations. In addition, the device may also include additional orientations (e.g., rotated 90 degrees or other orientations), and the spatial descriptors used herein are interpreted accordingly.

[0042] When used herein, the singular forms "a", "an", and "said / the" may also include plural forms, unless the context clearly indicates otherwise. It should also be understood that when the terms "consisting of" and / or "comprising" are used in this specification, the presence of the features, integers, steps, operations, elements and / or parts can be determined, but the presence or addition of one or more other features, integers, steps, operations, elements, parts and / or groups is not excluded. At the same time, when used herein, the term "and / or" includes any and all combinations of the relevant listed items.

[0043] Embodiments of the invention are described herein with reference to cross-sectional views which are schematic diagrams of ideal embodiments (and intermediate structures) of the present application, so that variations in the shapes shown due to, for example, manufacturing techniques and / or tolerances can be expected. Therefore, embodiments of the present application should not be limited to the specific shapes of the regions shown herein, but rather include shape deviations due to, for example, manufacturing techniques. For example, an implanted region shown as a rectangle typically has rounded or curved features and / or an implant concentration gradient at its edges, rather than a binary change from an implanted region to a non-implanted region. Similarly, a buried region formed by implantation may result in some implantation in the region between the buried region and the surface through which the implantation is performed. Therefore, the regions shown in the figures are schematic in nature, their shapes do not represent the actual shape of the region of the device, and do not limit the scope of the present application.

[0044] See also Figure 1 The present application provides a method for preparing a back-illuminated image sensor, comprising: step S202 to step S212.

[0045] Step S202: providing a substrate, wherein the substrate comprises a first region and a second region arranged along a first direction on a top surface of the substrate, wherein the first region is used to form a plurality of photodiodes, and the second region is used to form a plurality of buried conductive lines.

[0046] For example, the substrate can be made of semiconductor material, insulating material, conductor material or any combination thereof. For example, the substrate can be any of the following materials: silicon (Si) substrate, silicon germanium (SiGe) substrate, silicon germanium carbon (SiGeC) substrate, silicon carbide (SiC) substrate, gallium arsenide (GaAs) substrate, indium arsenide (InAs) substrate, indium phosphide (InP) substrate or other III / V semiconductor substrate or II / VI semiconductor substrate. Or, for example, the substrate can be a layered substrate including Si / SiGe, Si / SiC, silicon on insulator (SOI) or silicon germanium on insulator. Therefore, the type and thickness of the substrate should not limit the scope of protection of the present disclosure.

[0047] Step S204: Based on the same photomask, a first trench for isolating the photodiode is formed in the first region, and a second trench for isolating the buried conductive line is formed in the second region.

[0048] For example, in the process of preparing a back-illuminated image sensor, a high-energy ion implantation process is usually used after preparing a trench isolation structure to form a photodiode between adjacent trench isolation structures. In this example, the process step of preparing the photodiode is arranged after filling the dielectric layer in the first trench, wherein the photodiode and the trench isolation structure are spaced apart and distributed in the substrate along the first direction.

[0049] Step S206: After the first trench is filled with the sacrificial barrier layer, a protection layer is formed to cover the inner surface of the second trench.

[0050] By way of example, in this embodiment, the material of the sacrificial barrier layer is titanium nitride (TiN), and the material of the protection layer is silicon oxide (SiO 2 ).

[0051] Step S208: After removing the sacrificial barrier layer in the first trench, a target gas is used to selectively etch and remove a portion of the substrate at the bottom of the first trench.

[0052] For example, compared with the second groove, the first groove obtained by the secondary etching has a larger size along the substrate. The longitudinal section of the first groove along the first direction may include a regular trapezoid, an inverted trapezoid, a rectangle, etc., or a combination of regular trapezoid, inverted trapezoid, rectangle, etc.

[0053] Step S210: After removing the protective layer, a dielectric layer is formed, and the dielectric layer covers the inner surface of the second trench and fills the first trench.

[0054] For example, the dielectric layer includes at least a first dielectric layer and a second dielectric layer. The material of the first dielectric layer includes, but is not limited to, one or more of aluminum oxide (Al2O3), hafnium oxide (HfO2), zirconium oxide (ZrO2), tantalum oxide (Ta2O5), titanium oxide (TiO2), or strontium titanium oxide (SrTiO3); the material of the second dielectric layer includes, but is not limited to, silicon oxide (SiO2), silicon nitride (Si3N4), silicon oxynitride (Si2N2O), and other insulating materials or a combination thereof.

[0055] For example, the first trench is filled with a dielectric layer to form a trench isolation structure, and the trench isolation structure is used to isolate electrons and light energy. The cross-sectional shape of the trench isolation structure along the first direction may include a regular trapezoid, an inverted trapezoid, a rectangle, etc., or may also be a combination of regular trapezoids, inverted trapezoids, rectangles, etc. In the embodiment of the present application, the trench isolation structure only needs to be able to isolate electrons and light energy, and the depth does not exceed the thickness of the substrate. In addition, the distance between adjacent trench isolation structures and the aspect ratio of the trench isolation structure are not specifically limited in this embodiment, and can be set according to actual needs.

[0056] Step S212: forming an embedded conductive line in the second trench.

[0057] For example, the material of the embedded wire includes but is not limited to single metal materials such as copper (Cu), nickel (Ni), gold (Au), and silver (Ag), and may also be an alloy composed of multiple metals. The material of the embedded wire can be selected according to factors such as the use environment, cost-effectiveness, and electrical performance, and is not specifically limited here.

[0058] The back-illuminated image sensor obtained after steps S202-S212 can be referred to as Fig.13 Of course, in order to facilitate the understanding of this application, Fig.13 An example of a back-illuminated image sensor prepared by the back-illuminated image sensor preparation method of the present application is given. There may be other suitable examples of the back-illuminated image sensor prepared by the present application, and the present application does not limit them here.

[0059] See also Figure 2 In some embodiments, step S202 further includes: forming a hard mask layer 11 on the substrate 10 to cover the top surface of the substrate 10 .

[0060] For example, the hard mask layer 11 may be formed by one or more deposition methods such as, but not limited to, chemical vapor deposition (CVD), physical vapor deposition (PVD), and atomic layer deposition (ALD). The hard mask layer 11 may be a single-layer structure or a multi-layer stacked structure, and its material includes but is not limited to silicon oxide; then, a photoresist is coated on the hard mask layer 11, and after a series of steps such as exposure and development, a self-aligned double patterning (SADP) process or a self-aligned quadruple patterning (SAQP) process is used to realize a patterned photoresist layer to define the position and shape of the first groove 20 and the second groove 30. In this embodiment, the hard mask layer 11 is a single layer of silicon oxide.

[0061] See also Figure 3 In some embodiments, step S204: forming a first trench 20 for isolating a photodiode in the first region and forming a second trench 30 for isolating a buried conductive line in the second region based on the same mask, further comprises:

[0062] The target size of the first groove 20 is smaller than the target size of the second groove 30 , and the target size is at least used to characterize the opening size along the first direction.

[0063] For example, any one of dry etching and wet etching processes can be used to form a first trench 20 and a second trench 30 that penetrate the hard mask layer 11 and extend into the substrate 10, wherein a target size of the first trench 20 is smaller than a target size of the second trench 30, and the depths of the first trench 20 and the second trench 30 are the same.

[0064] See also Figure 4-Figure 7 In some embodiments, step S206 includes:

[0065] Step S2062 : using a first thermal oxidation process to form a sacrificial oxide layer 12 with a preset thickness on the inner surfaces of the first trench 20 and the second trench 30 .

[0066] For example, see Figure 4 Thermal oxidation processes include wet oxygen oxidation and dry oxygen oxidation. In the dry oxygen oxidation process, a mixed gas (oxygen and nitrogen) needs to be introduced into the reactor, and the temperature is usually between 900 degrees Celsius and 1100 degrees Celsius. Wet oxygen oxidation, on the other hand, heats deionized water so that it carries water vapor into the reactor. Each method has its advantages and disadvantages, and the specific choice should be comprehensively considered based on the processing object, requirements and actual conditions.

[0067] In this embodiment, after the thermal oxidation process, a sacrificial oxide layer 12 with a thickness of 2-3 nanometers, such as 2 nanometers, 2.5 nanometers, 3 nanometers, etc. is formed on the inner surface of the first trench 20 and the second trench 30. The sacrificial oxide layer 12 is a silicon oxide layer.

[0068] Step S2064 : using a deposition process to fill the first trench 20 with the sacrificial barrier layer 13 , while forming the sacrificial barrier layer 13 covering the sacrificial oxide layer 12 in the second trench.

[0069] For example, see Figure 5 In this embodiment, the material used for the sacrificial barrier layer 13 is titanium nitride (TiN). Since the target size of the first trench 20 is smaller than the target size of the second trench 30, the filling rate of titanium nitride in the first trench 20 is higher than the filling rate in the second trench 30. When the titanium nitride film covers the sidewall and bottom of the second trench 30 and fails to be completely closed, the titanium nitride film completely fills the first trench 20, and the top surface of the formed sacrificial barrier layer 13 is higher than the top surface of the hard mask layer 11.

[0070] Step S2066: wet-etch and remove the sacrificial barrier layer 13 in the second trench 30 using the target solution.

[0071] For example, see Figure 6 The sacrificial barrier layer 13 in the second trench 30 is removed by wet etching, and the target solution is an SPM solution, including sulfuric acid (H2SO4), hydrogen peroxide (H2O2) and water (H2O). Since the titanium nitride film has different filling levels in the first trench 20 and the second trench 30, after removing the titanium nitride film in the second trench 30, the titanium nitride film in the first trench 20 is only reduced, but it can still completely fill the first trench 20, so that it is not affected.

[0072] Step S2068 : using a second thermal oxidation process to form a protection layer 14 with a target thickness on the inner surface of the second trench 30 .

[0073] For example, see Figure 7 , a protection layer 14 with a target thickness of 100 nanometers is formed on the inner surface of the second trench 30 by using either a dry oxygen oxidation process or a wet oxygen oxidation process.

[0074] Since the sacrificial barrier layer 13 itself does not contain oxygen, it will not cause oxidation of the inner surface of the first trench 20; and the titanium nitride film in the sacrificial barrier layer 13 has a dense texture, oxygen cannot penetrate the titanium nitride film to reach the inner surface of the first trench 20, so the inner surface of the first trench 20 is protected by the sacrificial barrier layer 13 and will not be oxidized.

[0075] See also Figure 8-Figure 10 In some embodiments, step S208 further includes:

[0076] Step S2082: wet-etching and removing the sacrificial barrier layer 13 in the first trench 20 using a target solution.

[0077] For example, see Figure 8 Step S2082 is substantially the same as step S2066, that is, the sacrificial barrier layer 13 in the first trench 20 is removed by wet method using the SPM target solution. The protection layer 14 in the second trench 30 is not affected.

[0078] Step S2084: pickling and removing the sacrificial oxide layer 12 in the first trench.

[0079] For example, see Fig. 9 , the sacrificial oxide layer 12 in the first groove 20 is removed by wet etching. The etching solution used in this step is diluted hydrofluoric acid (DHF). In this embodiment, the sacrificial oxide layer 12 and the protective layer are both silicon oxide layers, and the silicon hexafluoride (SiF6) generated by the reaction with hydrofluoric acid is soluble in water. Therefore, when the sacrificial oxide layer 12 is removed, the protective layer 14 in the second groove 30 will also be slightly thinned. However, since the thickness of the sacrificial oxide layer 12 is relatively thin, the protective layer 14 can still retain a thickness of about 100nm after the end of step S2084.

[0080] Step S2086: using a target gas including hydrogen bromide and / or sulfur hexafluoride to anisotropically etch and remove a portion of the substrate 10 at the bottom of the first trench 20 .

[0081] For example, see Fig.10, a reactive ion etching (RIE) method in dry etching can be used to utilize anisotropic etching to remove a portion of the substrate 10 at the bottom of the first trench 20. Among them, bromine-containing plasma can achieve vertical anisotropic etching of silicon; the steepness of the trench sidewall can be controlled by adjusting the proportion of sulfur hexafluoride (SF6) in the target gas.

[0082] See also Figure 11-Figure 12 In some embodiments, step S210 includes:

[0083] Step S2102 : removing the hard mask layer 11 and the protection layer 14 in the second trench 30 to expose the inner surface 20 a of the first trench 20 and the inner surface 30 a of the second trench 30 .

[0084] For example, see Fig.11 The hard mask layer 11 can be planarized and removed by using a chemical mechanical polishing (CMP) process, or any other planarization process can be used, and it should not be limited to only one method. The protective layer 14 in the second groove is pickled and removed by using the same steps as step S2084.

[0085] Step S2104 : simultaneously forming a first dielectric layer 41 (not shown) on the inner surface 20 a of the first trench 20 , the inner surface 30 a of the second trench 30 , and the exposed top surface of the substrate.

[0086] Step S2106 : simultaneously forming the first dielectric layer 41 covering the second trench 30 and the second dielectric layer 42 at least filling up the first trench 20 .

[0087] For example, see Fig.12 , the dielectric constant of the first dielectric layer 41 is greater than a preset value. In the present embodiment, the material of the second dielectric layer 42 is silicon oxide. The use of high-k dielectric material to replace the silicon oxide insulating material in part of the groove can have a larger capacitance under the condition of the same thickness and achieve a better insulation effect. The first dielectric layer 41 and the second dielectric layer 42 together constitute the dielectric layer 40. Due to the different target sizes of the first groove 20 and the second groove 30, there are differences in the filling rate of the dielectric layer 40. During synchronous filling, the first groove 20 is filled but the second groove 30 is not closed. This morphological difference helps to form an embedded conductor in the second groove 30 later.

[0088] See also Figure 13-Figure 14 In some embodiments, step S212 includes:

[0089] Step S2122 : forming a metal layer 15 at least covering the dielectric layer 40 in the second trench 30 .

[0090] For example, see Fig.13 , the metal layer 15 can be obtained by any deposition method.

[0091] Step S2124: patterning the metal layer 15 to obtain an embedded conductive line 50 at least partially located in the second trench 30 , wherein the embedded conductive lines 50 in different second trenches 30 are insulated from each other.

[0092] For example, see Fig.14 , the embedded conductor 50 is used for conducting electricity.

[0093] It should be understood that although Figure 1 The steps in the flowchart are shown in sequence as indicated by the arrows, but these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified in this document, there is no strict order restriction for the execution of these steps, and these steps can be executed in other orders. Moreover, Figure 1 At least part of the steps may include multiple steps or multiple stages. These steps or stages are not necessarily executed at the same time, but can be executed at different times. The execution order of these steps or stages is not necessarily sequential, but can be executed in turn or alternately with other steps or at least part of the steps or stages in other steps.

[0094] See also Fig.13 In some embodiments, a back-illuminated image sensor is provided, comprising a back-illuminated image sensor prepared by the back-illuminated image sensor preparation method described above.

[0095] In the above embodiments, the unexpected technical effects of the present application are:

[0096] By using the same photomask to simultaneously form the first trench and the second trench on the semiconductor substrate, and utilizing the different filling rates of the sacrificial barrier layer, the first trench is completely filled while the second trench is only filled on the sides and bottom. In the subsequent protective layer formation process, the protective layer only grows on the inner surface of the second trench, so that the second trench is not affected in the secondary etching and the depth remains unchanged, while part of the substrate at the bottom of the first trench is removed, forming two trench areas with different depths and widths. This process can simultaneously form photodiode and metal wire isolation trenches with a single photomask, and uses wet etching and anisotropic etching technology to achieve precise control of the trench depth, simplifying the process flow while ensuring the performance of the device.

[0097] Since this method can simultaneously form grooves with different functions through a single mask and accurately control their depth, this new preparation method brings new possibilities for the manufacture of back-illuminated image sensors and has potential application prospects and economic benefits.

[0098] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features of the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0099] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be construed as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent application shall be subject to the attached claims.

Claims

1. A method for preparing a back-illuminated image sensor, characterized in that: include: Providing a substrate, wherein the substrate includes a first region and a second region arranged along a first direction parallel to a top surface of the substrate, wherein the first region is used to form a plurality of photodiodes, and the second region is used to form a plurality of buried conductive lines; Based on the same photomask, a first trench for isolating the photodiode is formed in the first region, and a second trench for isolating the buried conductive line is formed in the second region at the same time; A first thermal oxidation process is used to form a sacrificial oxide layer of a preset thickness on the inner surfaces of the first trench and the second trench; the sacrificial oxide layer is a silicon oxide layer; Filling the first trench with a sacrificial barrier layer, wherein the sacrificial barrier layer is titanium nitride; forming a protection layer covering the sacrificial oxide layer in the second trench; After removing the sacrificial oxide layer in the first trench, selectively etching and removing a portion of the substrate at the bottom of the first trench using a target gas; removing the protection layer and the sacrificial oxide layer located in the second trench in the same process step; forming a dielectric layer, wherein the dielectric layer covers the inner surface of the second trench and fills the first trench; An embedded conductive line is formed in the second trench.

2. The method for preparing a back-illuminated image sensor according to claim 1, characterized in that: The target size of the first groove is smaller than the target size of the second groove, and the target size is at least used to characterize the opening size along the first direction.

3. The method for preparing a back-illuminated image sensor according to claim 2, characterized in that: Before forming a protection layer covering the inner surface of the second groove, the method includes: Wet etching and removing the sacrificial barrier layer in the second groove using a target solution; A second thermal oxidation process is adopted to form the protection layer with a target thickness on the inner surface of the second trench.

4. The method for preparing a back-illuminated image sensor according to claim 3, characterized in that: Removing the sacrificial barrier layer in the first trench includes: Wet etching and removing the sacrificial barrier layer in the first groove using a target solution; Before selectively etching and removing the substrate at the bottom of the first groove using the target gas, the method further includes: The sacrificial oxide layer in the first trench is pickled and removed.

5. The method for preparing a back-illuminated image sensor according to claim 4, characterized in that: Selectively etching and removing a portion of the substrate at the bottom of the first trench using a target gas, comprising: A target gas including hydrogen bromide and / or sulfur hexafluoride is used to anisotropically etch and remove a portion of the substrate at the bottom of the first trench.

6. The method for preparing a back-illuminated image sensor according to claim 4, characterized in that: Pickling and removing the sacrificial oxide layer in the first groove includes: The sacrificial oxide layer in the first trench is removed by using diluted hydrofluoric acid.

7. The method for preparing a back-illuminated image sensor according to any one of claims 1 to 6, characterized in that: Forming the dielectric layer includes: Synchronously forming a first dielectric layer on the inner surface of the first trench, the inner surface of the second trench, and the exposed top surface of the substrate; A first dielectric layer covering the second groove and a second dielectric layer at least filling the first groove are formed simultaneously; the first dielectric layer and the second dielectric layer are used to jointly constitute the dielectric layer, and the dielectric constant of the first dielectric layer is greater than the dielectric constant of the second dielectric layer.

8. The method for preparing a back-illuminated image sensor according to any one of claims 1 to 6, characterized in that: Forming an embedded conductive line in the second trench, comprising: forming a metal layer covering at least the dielectric layer in the second trench; The metal layer is patterned to obtain an embedded conductive line at least partially located in the second groove, wherein the embedded conductive lines in different second grooves are insulated from each other.

9. The method for preparing a back-illuminated image sensor according to claim 3 or 4, characterized in that: The target solution includes sulfuric acid (H2SO4), hydrogen peroxide (H2O2) and water (H2O).

10. A back-illuminated image sensor, characterized in that: include: A back-illuminated image sensor prepared by the method for preparing a back-illuminated image sensor according to any one of claims 1 to 9.

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