Method for preparing multi-size grooves and method for preparing back-illuminated image sensor

Abstract

The present application discloses a method for preparing multi-size grooves and a method for preparing a back-illuminated image sensor. The method includes: providing a substrate, wherein the substrate has a first groove and a second groove, and the width of the first groove is smaller than that of the second groove; depositing an oxide layer on the substrate, the oxide layer including: a filling area filling the first groove, and a groove area covering the sidewall and bottom of the second groove; removing the groove area by an isotropic etching process and retaining part of the filling area; depositing an isolation layer to cover part of the filling area and the second groove; removing the isolation layer on the part of the filling area by an angled plasma etching process and retaining the isolation layer on the second groove; etching and removing part of the filling area to expose the bottom of the first groove; removing the exposed substrate at the bottom of the first groove by an anisotropic etching process, so that the depth of the first groove is greater than that of the second groove. Through the solution of the present application, the specified groove can be deepened without using a second mask, thereby reducing the product preparation cost.

Description

Technical Field

[0001] The present application generally relates to the field of semiconductor technology. More specifically, the present application relates to a method for preparing multi-sized trenches and a method for preparing a back-illuminated image sensor. Background Art

[0002] Backside Illumination (BSI) is an image sensor technology used in digital cameras, mobile phones and other imaging devices. In this technology, the photodiode array is designed to face the back of the camera lens, allowing light to directly hit the photodiodes, providing excellent low-light performance and image quality.

[0003] In BSI image sensors, two types of trenches are used to improve image quality and performance. One type of trench is narrower and deeper, and is usually used to isolate photodiodes, providing physical isolation for each pixel to reduce light interference between photodiodes. The other type of trench is wider and shallower, and is used to arrange metal wires. This method can increase the wire width and thus reduce wire resistance.

[0004] However, the existing trench preparation scheme usually requires two masks when preparing trenches of two depths, one of which is used to form the trench outline and the other is used for the etching deepening process of part of the trench. If the required trench size parameters change, the number of masks that need to be remade increases exponentially. The increased mask management cost and mask preparation cost make the existing trench preparation scheme more expensive.

[0005] In view of this, there is an urgent need to provide a multi-size groove preparation solution to reduce the number of masks required for multi-size groove preparation, thereby reducing the preparation cost of the multi-size groove. Summary of the invention

[0006] In order to at least solve one or more of the technical problems mentioned above, the present application proposes multi-size groove preparation solutions in multiple aspects.

[0007] In a first aspect, the present application provides a method for preparing multi-size grooves, including: providing a substrate, the substrate having a first groove and a second groove, the width of the first groove being smaller than that of the second groove; depositing an oxide layer above the substrate, the oxide layer including: a filling area filling the first groove, and a recessed area covering the sidewall and bottom of the second groove; removing the recessed area and retaining a portion of the filling area by an isotropic etching process; depositing an isolation layer to cover a portion of the filling area and the second groove; removing the isolation layer on the portion of the filling area and retaining the isolation layer on the second groove by an angled plasma etching process; etching away a portion of the filling area to expose the bottom of the first groove; removing the exposed substrate at the bottom of the first groove by an anisotropic etching process, so that the depth of the first groove is greater than that of the second groove.

[0008] In some embodiments, depositing an oxide layer on the substrate includes: calculating a deposition time according to a width of the first trench and a deposition rate; and performing deposition on the substrate according to the deposition time to obtain the oxide layer.

[0009] In some embodiments, calculating the deposition time according to the width of the first groove and the deposition rate includes: calculating the deposition time according to the formula t1=D / (2×v1), where t1 represents the deposition time, D represents the width of the first groove, and v1 represents the deposition rate.

[0010] In some embodiments, using an isotropic etching process to remove the groove area and retain a portion of the filling area includes: calculating the isotropic etching time based on the thickness of the oxide layer and the isotropic etching rate; and performing isotropic etching according to the isotropic etching time to remove the groove area of ​​the oxide layer and retain a portion of the filling area.

[0011] In some embodiments, the thickness of the oxide layer is half the width of the first groove; calculating the isotropic etching time according to the thickness of the oxide layer and the isotropic etching rate includes: calculating the isotropic etching time according to the formula t2=H / v2=D / (2×v2), wherein t2 represents the isotropic etching time, H represents the thickness of the oxide layer, D represents the width of the first groove, and v2 represents the isotropic etching rate.

[0012] In some embodiments, etching to remove a portion of the filling region includes: performing etching using a solution or plasma having an etching selectivity to the oxide layer greater than a threshold value to remove the portion of the filling region.

[0013] In some embodiments, removing the exposed substrate at the bottom of the first trench using an anisotropic etching process includes: performing etching using a gas having an etching selectivity to the substrate greater than a threshold value to remove a portion of the substrate exposed at the bottom of the first trench.

[0014] In some embodiments, the substrate includes: a substrate layer and a mask layer stacked from bottom to top, the mask layer having a first groove and a second groove penetrating into the substrate layer; providing the substrate includes: depositing the mask layer on the substrate layer; forming a first groove pattern and a second groove pattern on the mask layer using a mask having groove patterns of different widths; and removing the mask layer and a portion of the substrate layer under the first groove pattern and the second groove pattern using an anisotropic etching process to form a substrate having the first groove and the second groove.

[0015] In a second aspect, the present application provides a back-illuminated image sensor comprising: a substrate layer, a dielectric layer, an insulating layer and a metal layer stacked in sequence, the substrate layer having a first groove and a second groove; wherein the width of the first groove is smaller than the second groove, the depth of the first groove is greater than the second groove, the first groove is located in the pixel area of ​​the back-illuminated image sensor to isolate the photodiode, and the second groove is used to arrange the metal wire; the first groove and the second groove are prepared by executing any method as described in the first aspect.

[0016] In a third aspect, the present application provides a method for preparing a back-illuminated image sensor, comprising: executing the method as described in any one of the first aspects to form a substrate having a first groove and a second groove; wherein the width of the first groove is smaller than the second groove, the depth of the first groove is greater than the second groove, the substrate comprises a substrate layer and a mask layer stacked from bottom to top, the first groove and the second groove both penetrate the mask layer into the substrate layer, and the bottom of the second groove is covered with an isolation layer; etching to remove the mask layer and the isolation layer at the bottom of the second groove; sequentially depositing a dielectric layer and an insulating layer on the substrate layer; and forming a metal layer on the insulating layer to obtain a back-illuminated image sensor.

[0017] The unexpected technical effect of the present invention is: through the method for preparing multi-sized grooves as provided above, the embodiment of the present application first etches two grooves of different widths, the first groove and the second groove, on the substrate, and then etches to deepen the depth of the first groove, thereby obtaining a first groove with a narrower width and a deeper depth and a second groove with a wider width and a shallower depth. In the process of etching and deepening the first groove, the embodiment of the present application utilizes the different widths of the first groove and the second groove to achieve different deposition effects at the first groove and the second groove, and combines the etching characteristics of the isotropic etching process and the tilted plasma etching process in various directions to achieve different degrees of removal of the oxide layer and the isolation layer deposited at the first groove and the second groove, so that the bottom of the first groove and the bottom of the second groove are protected by different materials. Therefore, when the protective material at the bottom of the first groove is removed to etch and deepen its depth, it can be ensured that the bottom of the second groove is not affected by etching, thereby forming multi-sized grooves. In the above process, only one mask is needed in the process of etching the substrate. In the whole process of deepening the depth of the first groove, the effect of partition deepening can be achieved without using a second mask, thereby reducing the number of masks required and the preparation cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] By reading the detailed description below with reference to the accompanying drawings, the above and other purposes, features and advantages of the exemplary embodiments of the present application will become easy to understand. In the accompanying drawings, several embodiments of the present application are shown in an exemplary and non-limiting manner, and the same or corresponding reference numerals represent the same or corresponding parts, wherein:

[0019] Figure 1 An exemplary flow chart showing a method for preparing multi-sized grooves according to some embodiments of the present application;

[0020] Figure 2 An exemplary process diagram showing a substrate preparation method according to some embodiments of the present application;

[0021] Figure 3 A schematic diagram showing a multi-size groove preparation process according to some embodiments of the present application;

[0022] Figure 4 An exemplary flow chart showing a method for preparing multi-size grooves according to other embodiments of the present application;

[0023] Figure 5 An exemplary flow chart showing a method for preparing a back-illuminated image sensor according to some embodiments of the present application;

[0024] Figure 6 A schematic diagram showing a process for preparing a back-illuminated image sensor according to some embodiments of the present application is shown;

[0025] Figure 7An exemplary structural diagram of a back-illuminated image sensor according to some embodiments of the present application is shown. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0027] It should be understood that the terms "include" and "comprising" used in the specification and claims of the present application indicate the presence of described features, wholes, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or collections thereof.

[0028] It should also be understood that the terms used in this application specification are only for the purpose of describing specific embodiments and are not intended to limit the present application. As used in this application specification and claims, unless the context clearly indicates otherwise, the singular forms of "a", "an" and "the" are intended to include plural forms. It should also be further understood that the term "and / or" used in this application specification and claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes these combinations.

[0029] As used in this specification and claims, the term "if" can be interpreted as "when" or "upon" or "in response to determining" or "in response to detecting," depending on the context. Similarly, the phrases "if it is determined" or "if [described condition or event] is detected" can be interpreted as meaning "upon determination" or "in response to determining" or "upon detection of [described condition or event]" or "in response to detecting [described condition or event]," depending on the context.

[0030] The specific implementation of the present application is described in detail below with reference to the accompanying drawings.

[0031] Exemplary application scenarios

[0032] In the field of semiconductor memory manufacturing, the memory circuit may include a logic circuit area and a memory cell array area, and each cell in the memory cell array area and each semiconductor device are insulated and isolated by a trench isolation structure. Due to different usage environments, the line width of the memory cell array area is smaller than that of the peripheral logic circuit area, and the device density is higher. Therefore, the size of the trench isolation on the memory cell array area is smaller than that of the logic circuit area, and the depth is also shallower.

[0033] Taking the back-illuminated image sensor as an example, in order to improve image quality and performance, two types of grooves are usually used. One type of groove with a narrower width and a deeper depth is usually used to isolate the photodiode, providing physical isolation for each pixel to reduce light interference between photodiodes; the other type of groove with a wider width and a shallower depth is used to arrange metal wires, thereby reducing wire resistance by increasing wire width.

[0034] However, existing groove preparation schemes usually require the use of two masks when preparing grooves of two depths, one of which is used to form the groove profile and the other is used for the etching deepening process of part of the groove. This results in a high preparation cost for multi-sized grooves in back-illuminated image sensors.

[0035] Exemplary Application Scenarios

[0036] In view of this, an embodiment of the present application provides a multi-size groove preparation scheme, which utilizes the different widths of the first groove and the second groove to achieve different deposition effects, and then combines the etching characteristics of the isotropic etching process and the angled plasma etching process in different directions to achieve different degrees of removal of the protective material at the first groove and the second groove, thereby ensuring that the bottom of the second groove is not affected by etching during the deepening of the first groove, reducing the mask required in the etching deepening process, and reducing the preparation cost of multi-size grooves.

[0037] Figure 1 An exemplary flow chart of a method 100 for preparing multi-size grooves according to some embodiments of the present application is shown. Figure 1 As shown, in step S101, a substrate is provided. In this embodiment, a first groove and a second groove are provided in the substrate, and the width of the first groove is smaller than the width of the second groove.

[0038] In some embodiments, the first groove and the second groove can be prepared by using a photomask through a photolithography process and an etching process. The photomask is also called a mask, which is a light shielding plate with a specific pattern, which can ensure that the specific pattern designated area can be etched and removed.

[0039] As an example, Figure 2 An exemplary process diagram of a substrate preparation method 200 according to some embodiments of the present application is shown. Figure 2 As shown, in step S201, a mask layer is deposited on the substrate layer. In this embodiment, the mask layer can be formed by methods such as physical vapor deposition, chemical vapor deposition, sol-gel method or electrochemical deposition, and the mask layer can also be prepared by epitaxial growth, which is not too limited here.

[0040] Furthermore, in this step, the mask layer may be a hard mask layer made of a high dielectric constant material, silicon nitride or silicon carbide, etc., which can better resist deformation or damage of the photolithography pattern caused by stress or chemical attack during the etching process.

[0041] In step S202, a first groove pattern and a second groove pattern are formed on the mask layer using a mask having groove patterns of different widths. In this embodiment, the mask has a first groove pattern and a second groove pattern, and the widths of the first groove pattern and the second groove pattern are different. Specifically, the width of the first groove pattern is smaller than the width of the second groove pattern. In this step, the mask is attached to the mask layer, and the mask layer in other areas except under the first groove pattern and the second groove pattern is solidified, so that the mask layer in these areas will not be etched away.

[0042] In step S203, the mask layer and part of the substrate layer below the first groove pattern and the second groove pattern are removed by an anisotropic etching process to form a substrate having the first groove and the second groove. In the anisotropic etching process, the etching rates in different directions can be different, for example, different etching rates in the vertical direction and the horizontal direction, so this step can etch groove shapes with different aspect ratios on the substrate layer and the mask layer.

[0043] As an example, in step S203 , plasma may be used as an etching medium to dry-etch the mask layer below the first trench pattern and the second trench pattern, so that the mask layer and a portion of the substrate layer below the first trench pattern and the second trench pattern are completely removed.

[0044] use Figure 2 The substrate preparation method shown can prepare the following substrate: the substrate includes a substrate layer and a mask layer stacked from bottom to top, wherein the mask layer has a first groove and a second groove penetrating to the substrate layer, and the width of the first groove is smaller than the width of the second groove. Furthermore, the depth of the first groove can be consistent with the depth of the second groove.

[0045] In the process of preparing the substrate, a plurality of grooves of different widths can be prepared by using one photomask, thereby obtaining a substrate with different groove profiles for subsequent use in preparing multi-sized grooves of different depths and widths.

[0046] Back to Figure 1In step S102, an oxide layer is deposited on the substrate. In this embodiment, since the widths of the first trench and the second trench are different, after the same deposition time, the oxide layers on the two sidewalls of the first trench are merged to form a filling area filled in the first trench. Since the width of the second trench is wider, the oxide layer covers the sidewalls and bottom of the second trench, and the center of the second trench is still empty, thereby forming a recessed area covering the surface of the second trench.

[0047] In order to facilitate understanding by those skilled in the art, Figure 3 A schematic diagram showing a multi-size groove preparation process according to some embodiments of the present application is shown. Figure 3 Steps a and b in the figure respectively show the preparation process of the mask layer 2, the first trench 3 and the second trench 4 above the substrate layer 1. Figure 3 As shown in step c in FIG. 1 , the oxide layer 5 formed by deposition includes a filling area filling the first trench and a recessed area covering the sidewall and bottom of the second trench, and may also include a flat area covering the surface of the mask layer.

[0048] It should be noted that this embodiment has no strict restrictions on the deposition process of the oxide layer. Similar to the mask layer, the oxide layer can be formed by methods such as physical vapor deposition, chemical vapor deposition, sol-gel method or electrochemical deposition, or can be prepared by epitaxial growth, and no excessive restrictions are imposed here.

[0049] It should also be noted that the oxide layer in this embodiment can block current and effectively isolate charges between different photodiodes, thereby reducing leakage current and increasing the switching speed of the photodiode. As an example, the oxide layer can be made of oxide materials such as silicon dioxide.

[0050] In step S103, an isotropic etching process is used to remove part of the oxide layer. In the isotropic etching process, the etching rate is the same in all directions. Since the oxide layers on the two side walls in the first groove in step S102 are combined to form a filling area filled in the first groove, the filling area has different thicknesses of the material to be etched in the vertical and horizontal directions. Under the same etching rate and etching time, after the oxide layer is completely etched and removed in the horizontal direction, part of the oxide layer still remains in the first groove in the vertical direction. Unlike the first groove, the oxide layer in the second groove is in the shape of a groove. In step S103, the oxide layers on the side walls and bottom of the second groove can be removed together at the same etching rate and etching time.

[0051] like Figure 3 As shown in step d, after step S103 is completed, the recessed area and the flat area of ​​the oxide layer are completely removed, so that the bottom of the second trench is exposed, and part of the filling area is retained inside the first trench, and the bottom of the first trench is covered and protected by the oxide layer.

[0052] In step S104, an isolation layer is deposited. In this embodiment, the isolation layer is made of a material different from the oxide layer, so as to be distinguished from the protective material used to protect the bottom of the first trench. Similar to the oxide layer, the isolation layer is made of a non-conductive insulating material to isolate the charges between the photodiodes. As an example, the isolation layer can be made of an insulating material such as silicon nitride.

[0053] like Figure 3 As shown in step e in FIG. 1 , after step S104 is completed, the isolation layer 6 covers the partially filled area retained in the first trench and the sidewall and bottom of the second trench.

[0054] It should be noted that this embodiment has no strict restrictions on the deposition process of the isolation layer. Similar to the oxide layer, the isolation layer can be formed by methods such as physical vapor deposition, chemical vapor deposition, sol-gel method or electrochemical deposition, and can also be prepared by epitaxial growth, and no excessive restrictions are imposed here.

[0055] In step S105, a portion of the isolation layer is removed using an angled plasma etching process. The angled plasma etching process uses plasma to remove the surface of the material, and the process can form an inclined or angled etching profile on the surface of the material. Figure 3 As shown in step f in FIG. 1 , by controlling the tilt angle of the plasma, the isolation layer above a specific height in the first trench and the second trench can be etched and removed. Since the partial oxide layer retained in the first trench raises the height of the isolation layer at the first trench, the plasma in step S105 can remove all the isolation layers at the first trench, that is, remove the isolation layer on the partial filling area in step S103. The isolation layer at the second trench directly covers the sidewall and bottom of the second trench. Due to the certain tilt angle of the plasma, the isolation layer on the partial sidewall and the isolation layer at the bottom are retained.

[0056] like Figure 3 As shown in step f, after step S105 is completed, the bottom of the first trench is covered and protected by the oxide layer, and the bottom of the second trench is covered and protected by the isolation layer. At this point, the bottom of the first trench and the bottom of the second trench are protected by different materials, and the second trench will not be affected when the protective material at the bottom of the first trench is removed, thereby ensuring that the bottom of the second trench is not affected by the subsequent etching process. While the depth of the first trench is deepened, the second trench can maintain its original depth.

[0057] In step S106, the remaining oxide layer is removed by etching, so that the bottom of the first trench is exposed. Figure 3As shown in step g in FIG, since the bottom of the first trench and the bottom of the second trench are protected by different materials, in this embodiment, a solution or plasma having an etching selectivity to the oxide layer greater than a threshold can be used for etching to remove part of the filling area. The etching selectivity reflects the ratio of the removal rate of the etched material to the etching rate of other materials during etching. The etching medium with high etching selectivity can ensure that the etched layer is completely removed while causing less damage or corrosion to other material layers.

[0058] As an example, the oxide layer can be made of silicon dioxide. In this case, a diluted hydrofluoric acid solution, a mixed plasma of ammonia and hydrofluoric acid, or a plasma containing hydrogen fluoride can be selected as the etching medium to etch away the portion of the oxide layer retained in the first groove, i.e., the partial filling area described above, and prevent the isolation layer at the bottom of the second groove from being etched, thereby avoiding exposure of the bottom of the second groove.

[0059] It should be noted that the thresholds described above can be adjusted according to actual conditions and needs, and no excessive restrictions are imposed here.

[0060] In practical applications, although the dry etching process using plasma with high etching selectivity has a lower etching rate for other materials, there is still a certain amount of damage. Therefore, in some embodiments, a wet etching process is preferably used to remove part of the oxide layer retained in the first groove using a solution with high etching selectivity.

[0061] In step S107, the first trench is deepened by an anisotropic etching process. In this embodiment, after the partial oxide layer retained in the first trench is removed, the bottom of the first trench is exposed, and the bottom of the second trench is covered and protected by the isolation layer. Therefore, the substrate at the bottom of the first trench can be etched by an anisotropic etching process. Specifically, the substrate includes a substrate layer and a mask layer stacked from bottom to top, and the first trench and the second trench both penetrate the mask layer to the substrate layer, such as Figure 3 As shown in step h in FIG. 1 , step S107 can remove a portion of the substrate layer exposed at the bottom of the first trench, so that the depth of the first trench is greater than that of the second trench.

[0062] In the anisotropic etching process, the etching rates in different directions may be different. In this step, the etching rate in the vertical direction is greater than the etching rate in the horizontal direction, so that the etching degree of the sidewall of the first trench is less than the etching degree of the bottom of the first trench, thereby achieving the effect of deepening the depth of the first trench.

[0063] Furthermore, this step can be performed by etching with a gas having an etching selectivity to the substrate greater than a threshold value to remove a portion of the substrate exposed at the bottom of the first trench. As an example, in the anisotropic etching process of step S107, an etching gas including hydrobromic acid or sulfur hexafluoride can be used to etch and remove a portion of the substrate at the bottom of the first trench.

[0064] It should be noted that the thresholds described above can be adjusted according to actual conditions and needs, and no excessive restrictions are imposed here.

[0065] Combined with the previous article Figure 1 and Figure 3 In the described method, the present invention utilizes the narrow width of the first trench to completely fill the first trench with an oxide layer through a deposition process, while the second trench is only covered with an oxide layer on its sidewalls and bottom, thereby forming a groove-shaped oxide layer structure at the second trench.

[0066] On this basis, the isotropic etching process is used to achieve the complete removal of the groove-shaped oxide layer structure at the second trench and retain a portion of the oxide layer filled in the first trench by using the characteristic of the consistent etching rate in all directions. At this time, the bottom of the second trench is protected by depositing an isolation layer. Since the oxide layer retained in the first trench raises the height of the isolation layer at the first trench, the angled plasma etching process can remove the isolation layer at the first trench while retaining the isolation layer at the bottom of the second trench. At this point, the bottom of the first trench and the bottom of the second trench are protected by different materials.

[0067] Since the bottom of the first trench and the bottom of the second trench are covered with different material layers, the second trench will not be affected when the protective material at the bottom of the first trench is removed, so that when the first trench is etched in the depth direction using an anisotropic etching process, the bottom of the second trench can be guaranteed not to be affected by the etching medium, thereby achieving the effect of deepening the designated trench. In the above process, the first trench can be deepened without using a mask, so the number of masks required in the preparation process of multi-size trenches can be reduced, thereby reducing the preparation cost.

[0068] In the oxide layer deposition process and the oxide layer etching process described in the above embodiments, different deposition effects and etching effects at the first trench and the second trench can be achieved by controlling the operation duration.

[0069] Figure 4 An exemplary flow chart of a method 400 for preparing multi-size grooves according to other embodiments of the present application is shown. Figure 4 As shown, in step S401, a substrate is provided. In this embodiment, the content of step S401 is consistent with step S101 in the above embodiment, and will not be repeated here.

[0070] In step S402, the deposition time is calculated according to the width of the first trench and the deposition rate. In this embodiment, in order to merge the oxide layers on the two side walls of the first trench, there is a certain gap between the oxide layers on the two side walls of the second trench, thereby forming a filling area filled in the first trench and a recessed area covering the side walls and bottom of the second trench, it is necessary to control the thickness of the deposited oxide layer to be greater than or equal to half of the width of the first trench and the thickness of the deposited oxide layer to be less than half of the width of the second trench.

[0071] In order to shorten the time required for the deposition process as much as possible and improve the preparation efficiency, in some embodiments, the thickness of the deposited oxide layer can be controlled to be equal to half the width of the first groove. Specifically, in step S402, the deposition time can be calculated according to the formula t1=D / (2×v1), where t1 represents the deposition time, D represents the width of the first groove, and v1 represents the deposition rate.

[0072] In step S403, deposition is performed on the substrate according to the deposition time to obtain an oxide layer. In some embodiments, the thickness of the oxide layer is equal to half of the width of the first trench.

[0073] In step S404, the isotropic etching time is calculated according to the thickness of the oxide layer and the isotropic etching rate. In order to completely remove the oxide layer covering the second groove, it is necessary to calculate the isotropic etching time according to the thickness of the oxide layer and the isotropic etching rate. Specifically, step S404 can calculate the isotropic etching time according to the formula t2=H / v2=D / (2×v2), where t2 represents the isotropic etching time, H represents the thickness of the oxide layer, and v2 represents the isotropic etching rate.

[0074] In some embodiments, the thickness H of the oxide layer deposited in step S402 is equal to half of the first trench width D. In this case, the isotropic etching time in step S404 can be calculated according to the formula t2=D / (2×v2).

[0075] In step S405, isotropic etching is performed according to the isotropic etching time to remove the groove area of ​​the oxide layer and retain a portion of the filling area. By controlling the isotropic etching time, the oxide layer at the bottom of the second groove can be completely removed, and by controlling the deposition time, the thickness of the oxide layer can be controlled to the minimum value within the allowable range, thereby reducing the isotropic etching time as much as possible and improving the preparation efficiency.

[0076] In step S406, an isolation layer is deposited. In this embodiment, the content of step S406 is consistent with step S104 in the above embodiment, and will not be repeated here.

[0077] In step S407, a portion of the isolation layer is removed by using an angled plasma etching process. In this embodiment, the content of step S407 is consistent with step S105 in the above embodiment, and will not be repeated here.

[0078] In step S408, the remaining oxide layer is removed by etching to expose the bottom of the first trench. In this embodiment, the content of step S408 is consistent with step S106 in the above embodiment, and will not be repeated here.

[0079] In step S409, the first trench is deepened by an anisotropic etching process. In this embodiment, the content of step S409 is consistent with step S107 in the above embodiment, and will not be repeated here.

[0080] Based on any of the methods for preparing multi-size grooves described above, the present application also provides a method for preparing a back-illuminated image sensor.

[0081] Figure 5 An exemplary flow chart of a method 500 for preparing a back-illuminated image sensor according to some embodiments of the present application is shown. Figure 5 As shown, in step S501, a substrate is provided. The substrate includes a substrate layer and a mask layer stacked from bottom to top, wherein the mask layer has a first groove and a second groove penetrating to the substrate layer, and the width of the first groove is smaller than the width of the second groove.

[0082] It should be noted that, in this embodiment, the content of step S501 is consistent with step S101 in the previous embodiment, and will not be repeated here.

[0083] In step S502, an oxide layer is deposited on the substrate. In this embodiment, the content of step S502 is consistent with step S102 in the above embodiment, and will not be repeated here.

[0084] In step S503, a portion of the oxide layer is removed by an isotropic etching process. In this embodiment, the content of step S503 is consistent with step S103 in the above embodiment, and will not be repeated here.

[0085] In step S504, an isolation layer is deposited. In this embodiment, the content of step S504 is consistent with step S104 in the above embodiment, and will not be repeated here.

[0086] In step S505, a portion of the isolation layer is removed by using an angled plasma etching process. In this embodiment, the content of step S505 is consistent with step S105 in the above embodiment, and will not be repeated here.

[0087] In step S506, the remaining oxide layer is removed by etching to expose the bottom of the first trench. In this embodiment, the content of step S506 is consistent with step S106 in the above embodiment, and will not be repeated here.

[0088] In step S507, the first trench is deepened by an anisotropic etching process. In this embodiment, the content of step S507 is consistent with step S107 in the above embodiment, and will not be repeated here.

[0089] In step S508, the mask layer and the isolation layer at the bottom of the second trench are removed by etching. Figure 6 A schematic diagram showing a process for preparing a back-illuminated image sensor according to some embodiments of the present application is shown. Figure 6 The process ah and Figure 3 The process in ah is the same as that in ah, and will not be repeated here. Figure 6 As shown in step h in the figure, after the first trench is deepened by anisotropic etching process, part of the isolation layer is still retained in the second trench. At this time, the remaining part of the isolation layer in the second trench is removed by etching process, so that the bottom of the second trench is exposed.

[0090] like Figure 6 As shown in process i, in addition to removing the isolation layer at the bottom of the second groove, step S508 also requires removing the mask layer used to protect part of the substrate layer area when preparing the substrate, thereby obtaining a substrate layer having a first groove and a second groove, in which the width of the first groove is smaller than the width of the second groove and the depth of the first groove is greater than the depth of the second groove.

[0091] In step S509, a dielectric layer and an insulating layer are sequentially deposited on the substrate layer. Figure 6 As shown in step j in the embodiment, the dielectric layer 7 covers the first trench sidewall, the first trench bottom, the second trench sidewall, the second trench bottom and the exposed substrate layer at the same time, and the insulating layer 8 completely covers the dielectric layer.

[0092] It should be noted that the dielectric layer can be made of high dielectric constant materials to play the role of insulation and isolation, and can also protect the substrate layer from the external environment. The insulating layer can be made of insulating materials such as silicon dioxide to effectively block charge carriers, prevent charge leakage, ensure the stability of the electrical performance of the back-illuminated image sensor, and passivate the surface, reduce surface defects, and improve the optical performance of the back-illuminated image sensor.

[0093] It should be further explained that this embodiment has no strict restrictions on the deposition process of the dielectric layer and the insulating layer. The dielectric layer and the insulating layer can be formed by methods such as physical vapor deposition, chemical vapor deposition, sol-gel method or electrochemical deposition, and can also be prepared by epitaxial growth, and no excessive restrictions are imposed here.

[0094] In step S510, a metal layer is formed on the insulating layer to obtain a back-illuminated image sensor. Figure 6 As shown in step k in the figure, the metal layer is distributed above the first groove and above the second groove. In a back-illuminated image sensor, the metal layer is used to form a pixel electrode and a signal reading line to realize the transmission of charge and the reading of signal. As an example, the metal layer can be made of aluminum, copper or other metals with good conductivity.

[0095] It should be further explained that, in the back-illuminated image sensor prepared in this embodiment, the first trench is located in the pixel region of the back-illuminated image sensor to isolate the photodiode, and the second trench is used to arrange the metal wire.

[0096] Based on the method for preparing a back-illuminated image sensor described in the above embodiment, a back-illuminated image sensor can be prepared as follows: Figure 7 The back-illuminated image sensor shown, Figure 7 An exemplary structural diagram of a back-illuminated image sensor according to some embodiments of the present application is shown.

[0097] The back-illuminated image sensor includes: a substrate layer 1, a dielectric layer 7, an insulating layer 8 and a metal layer 9, wherein the substrate layer 1, the dielectric layer 7, the insulating layer 8 and the metal layer 9 are stacked in sequence, and the substrate layer 1 has a first groove and a second groove, the width of the first groove is smaller than the width of the second groove and the depth of the first groove is greater than the depth of the second groove.

[0098] In the back-illuminated image sensor, the first trench is located in the pixel region of the back-illuminated image sensor to isolate the photodiode, and the second trench is used to arrange the metal wire.

[0099] In the method for preparing a back-illuminated image sensor described above, the first groove and the second groove can be prepared by executing the method for preparing multi-sized grooves in any of the above embodiments.

[0100] As an example, the first groove and the second groove can be obtained by performing the following steps: first, a substrate is provided, the substrate having the first groove and the second groove, the width of the first groove is smaller than that of the second groove; then, an oxide layer is deposited on the substrate, and the deposited oxide layer includes a filling area filling the first groove and a groove area covering the sidewall and bottom of the second groove; then, an isotropic etching process is used to remove the groove area and retain part of the filling area; then, an isolation layer is deposited to cover part of the filling area and the second groove; thereafter, an angled plasma etching process is used to remove the isolation layer on the part of the filling area and retain the isolation layer on the second groove; then, the part of the filling area is etched away to expose the bottom of the first groove; finally, an anisotropic etching process is used to remove the exposed substrate at the bottom of the first groove, so that the depth of the first groove is greater than that of the second groove.

[0101] In summary, the present invention provides a method for preparing multi-sized grooves. The unexpected technical effect of the present invention is that in the process of etching and deepening the first groove, the method can use the different widths of the first groove and the second groove to achieve different deposition effects at the positions of the two grooves, and combine the etching characteristics of the isotropic etching process and the angled plasma etching process in various directions to achieve different degrees of removal of the oxide layer and the isolation layer deposited at the first groove and the second groove, thereby achieving protection of the bottom of the first groove and the bottom of the second groove by different material layers. Based on this, when removing the protective material at the bottom of the first groove to etch and deepen its depth, it can ensure that the bottom of the second groove is not affected by etching. In the above process, the effect of partition deepening can be achieved without using another mask, which reduces the number of masks required and reduces the preparation cost.

[0102] Some embodiments of the present invention also provide a method for preparing multi-size grooves, which can achieve different deposition effects at the first groove and the second groove by controlling the deposition time, and completely remove the protective material at the bottom of the second groove by controlling the isotropic etching time, while retaining part of the material to protect the bottom of the first groove, thereby facilitating the subsequent distinction between the protective materials at the bottom of the first groove and the bottom of the second groove, so as to achieve the effect of deepening one of the grooves without the need for a mask.

[0103] The present invention also provides a method for preparing a back-illuminated image sensor. The method can use only one photomask to etch two grooves with different depths and widths, and achieve isolation of photodiodes in the back-illuminated image sensor by controlling the arrangement positions of the grooves of two different sizes, thereby reducing light interference between photodiodes. At the same time, the grooves with wider width and shallower depth are used to arrange metal wires, thereby reducing wire resistance by increasing the wire width.

[0104] Although multiple embodiments of the present application have been shown and described herein, it is obvious to those skilled in the art that such embodiments are provided only by way of example. Those skilled in the art can think of many changes, modifications and alternatives without departing from the thought and spirit of the present application. It should be understood that in the process of practicing the present application, various alternatives to the embodiments of the present application described herein can be adopted. The attached claims are intended to limit the scope of protection of the present application, and therefore cover equivalents or alternatives within the scope of these claims.

Claims

1. A method for preparing multi-size grooves, characterized in that: include: Providing a substrate, wherein the substrate has a first groove and a second groove, wherein the width of the first groove is smaller than that of the second groove; Depositing an oxide layer on the substrate, the oxide layer comprising: a filling region filling the first trench, and a recessed region covering the sidewall and bottom of the second trench; Using an isotropic etching process to remove the groove area and retain a portion of the filling area; depositing an isolation layer to cover the partially filled region and the second trench; Using an angled plasma etching process to remove the isolation layer on the partial filling area and retain the isolation layer on the second trench; Etching and removing the part of the filling area so that the bottom of the first trench is exposed; An anisotropic etching process is used to remove the exposed substrate at the bottom of the first trench, so that the depth of the first trench is greater than that of the second trench.

2. The method according to claim 1, characterized in that Wherein depositing an oxide layer on the substrate comprises: calculating the deposition time according to the width of the first groove and the deposition rate; and Deposition is performed on the substrate according to the deposition time to obtain the oxide layer.

3. The method according to claim 2, characterized in that Calculating the deposition time according to the width of the first groove and the deposition rate includes: The deposition time is calculated according to the formula t1=D / (2×v1), where t1 represents the deposition time, D represents the width of the first groove, and v1 represents the deposition rate.

4. The method according to claim 1, characterized in that: The method of removing the groove area and retaining a part of the filling area by using an isotropic etching process comprises: Calculating the isotropic etching time according to the thickness of the oxide layer and the isotropic etching rate; and Isotropic etching is performed according to the isotropic etching time to remove the groove area of ​​the oxide layer and retain a part of the filling area.

5. The method according to claim 4, characterized in that wherein the thickness of the oxide layer is half the width of the first trench; Calculating the isotropic etching time according to the thickness of the oxide layer and the isotropic etching rate includes: The isotropic etching time is calculated according to the formula t2=H / v2=D / (2×v2), wherein t2 represents the isotropic etching time, H represents the thickness of the oxide layer, D represents the width of the first groove, and v2 represents the isotropic etching rate.

6. The method according to claim 1, characterized in that The etching to remove the part of the filling area comprises: Etching is performed using a solution or plasma having an etching selectivity to the oxide layer greater than a threshold value to remove the partial filling area.

7. The method according to claim 1, characterized in that The method of removing the exposed substrate at the bottom of the first trench by using an anisotropic etching process comprises: Etching is performed using a gas having an etching selectivity to the substrate greater than a threshold value to remove a portion of the substrate exposed at the bottom of the first trench.

8. The method according to claim 1, characterized in that The substrate comprises: a substrate layer and a mask layer stacked from bottom to top, wherein the mask layer has the first groove and the second groove penetrating to the substrate layer; Substrates include: depositing the mask layer on the substrate layer; forming a first groove pattern and a second groove pattern on the mask layer using a photomask having groove patterns with different widths; and The mask layer and a portion of the substrate layer below the first trench pattern and the second trench pattern are removed by an anisotropic etching process to form the substrate having the first trench and the second trench.

9. A method for preparing a back-illuminated image sensor, characterized in that: include: Executing the method according to any one of claims 1 to 8 to form the substrate having the first trench and the second trench; wherein the width of the first trench is smaller than that of the second trench, the depth of the first trench is greater than that of the second trench, the substrate comprises a substrate layer and a mask layer stacked from bottom to top, the first trench and the second trench both penetrate the mask layer to the substrate layer, and the bottom of the second trench is covered with an isolation layer; Etching and removing the mask layer and the isolation layer at the bottom of the second trench; Depositing a dielectric layer and an insulating layer in sequence on the substrate layer; and A metal layer is formed on the insulating layer to obtain a back-illuminated image sensor.

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