Preparation method of double-depth groove and back-illuminated image sensor

Abstract

The invention provides a preparation method of a double-depth groove and a back-illuminated image sensor, and the method comprises the steps: forming a first groove and a second groove with different calibers through a photoetching technology, and in the process of deepening the first groove through etching, firstly filling a sacrificial layer in the first groove, and then filling a second groove in the second groove through a sacrificial layer in the process of deepening the first groove through etching; the oxide layer is formed in the second groove through the isolation effect of the sacrificial layer in combination with the thermal oxidation process to serve as an etching protection layer for the second groove when the first groove is deepened, and in addition, the sacrificial layer can be removed under the condition that etching damage to the oxide layer is as small as possible in combination with different material selections of the sacrificial layer and the oxide layer. And finally, the first groove is etched and deepened based on the oxide layer, and grooves with two depths are obtained. The problem of photoetching overlay errors of the two photomasks is avoided, and meanwhile, the management cost and the manufacturing cost of the photomasks are reduced; in addition, the process variation of the key sizes of the two grooves is relatively low on the whole, so that the product yield is effectively improved; finally, the process steps are simple, the efficiency is high, and more cost is saved.

Description

Technical Field

[0001] This invention relates to the field of integrated circuit manufacturing technology, and in particular to a method for fabricating a dual-deep trench and back-illuminated image sensor. Background Technology

[0002] Image sensors utilize the photoelectric conversion function of optoelectronic devices to convert a light image on a photosensitive surface into an electrical signal proportional to the light image. Based on the different components, they can be divided into two main categories: CCD (Charge-Coupled Device) and CMOS (Metal-Oxide-Semiconductor). With the continuous development of CMOS image sensor (CIS) design and manufacturing processes, CMOS image sensors have gradually replaced CCD image sensors and become the mainstream.

[0003] CMOS image sensors are divided into Figure 1 Front illumination type (i.e., front-illuminated image sensor) and such Figure 2 There are two types of back-illuminated (i.e., back-illuminated image sensors). The biggest optimization of the back-illuminated CMOS (BSI) image sensor lies in changing the internal structure of the element and reversing the element orientation of the photosensitive layer so that light can enter directly from the back and illuminate the photodiode 20, thereby avoiding the influence of the circuit and transistor 21 on the light and significantly improving the light efficiency.

[0004] 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 often used to lay metal wires. This method can increase the wire width, thereby reducing the wire resistance.

[0005] Existing trench fabrication methods typically require two specialized photomasks for etching to form dual-depth trenches. One photomask is used to jointly form the shallower trench, creating a wide and shallow trench initially, while the other is used to partially etch and deepen the shallower trench, creating a narrow and deep trench. This method uses two photomasks to pattern the shallow and deep trenches separately, resulting in lithographic overlay errors. Furthermore, the management and manufacturing costs of the two photomasks increase the overall process cost. Alternatively, dual-depth trenches can be fabricated using a single photomask, but this process is cumbersome, increases costs, and enlarges the critical dimensions of both trenches, thereby increasing process variability and reducing product yield.

[0006] It should be noted that the above introduction to the technical background is only for the purpose of providing a clear and complete explanation of the technical solutions of this application and facilitating understanding by those skilled in the art. It should not be assumed that these technical solutions are known to those skilled in the art simply because they have been described in the background section of this application. Summary of the Invention

[0007] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a method for fabricating a dual-depth trench and back-illuminated image sensor, which solves the problems in the fabrication of dual-depth trenches in the prior art. When two special photomasks are used for fabrication, there are photolithographic overlay errors, and the management and manufacturing costs of the two photomasks will increase the process cost. On the other hand, when a single photomask is used to fabricate dual-depth trenches, the process is cumbersome and increases the cost. It will also increase the critical dimensions of the two trenches, thereby increasing the process variability and reducing the product yield.

[0008] To achieve the above and other related objectives, the present invention provides a method for fabricating a dual-depth trench, the method comprising:

[0009] A substrate is provided, the material of which can be oxidized by a thermal oxidation process;

[0010] A plurality of first trenches and a plurality of second trenches are formed from the surface of the substrate inward using the same photolithography etching process; wherein the diameter of the first trench is smaller than the diameter of the second trench.

[0011] The sacrificial layer is filled only in the first trench;

[0012] An oxide layer is formed on the sidewalls and bottom wall of the second trench using a thermal oxidation process;

[0013] Remove the filling sacrificial layer in the first trench to expose the bottom wall of the first trench;

[0014] A dry etching process is used to continue etching the substrate downwards from the bottom wall of the first trench to a predetermined depth, in order to form a third trench of the required depth.

[0015] Optionally, the method for forming the first trench and the second trench includes:

[0016] A hard mask layer is formed on the surface of the substrate;

[0017] The hard mask layer is etched and patterned using the same photolithography etching process to obtain a patterned hard mask layer; wherein the patterned hard mask layer has the first trench and the second trench pattern formed in it;

[0018] The substrate is etched using the patterned hard mask layer as a mask to form the first trench and the second trench in the substrate.

[0019] Optionally, the method of filling the sacrificial layer only in the first trench includes:

[0020] A sacrificial material layer is formed on the substrate; wherein the sacrificial material layer at least fills the first trench, while the sacrificial material layer is formed on the sidewalls and bottom wall of the second trench but does not fill the second trench;

[0021] The sacrificial material layer is etched back to remove the sacrificial material layer from the sidewalls and bottom wall of the second trench, and the remaining sacrificial material layer in the first trench is formed as the sacrificial layer.

[0022] Optionally, the height of the upper surface of the sacrificial layer is not lower than the height of the upper surface of the substrate.

[0023] Optionally, the substrate is a silicon substrate, and the material of the sacrificial layer includes titanium nitride or tungsten.

[0024] Furthermore, the thickness of the oxide layer is

[0025] Furthermore, the sacrificial layer is formed using a CVD process.

[0026] Optionally, the sacrificial layer filling the first trench can be removed by dry etching.

[0027] The present invention also provides a method for fabricating a back-illuminated image sensor, including the method for fabricating a double-depth trench as described in any one of the above claims; wherein, the third trench is used to isolate a photodiode, and the second trench is used to isolate an embedded wire.

[0028] Optionally, it also includes:

[0029] A dielectric layer is formed on the substrate, the dielectric layer being formed on the bottom wall and sidewalls of the second trench and filling the third trench;

[0030] An embedded conductor is formed on the dielectric layer in the second trench.

[0031] As described above, the fabrication method of the dual-depth trench and back-illuminated image sensor of the present invention uses a single photolithography etching process to form a first trench and a second trench with different apertures using a photomask. During the etching process of deepening the first trench, a sacrificial layer is first filled into the first trench. Through the isolation effect of the sacrificial layer and combined with a thermal oxidation process, an oxide layer is formed in the second trench as an etching protection layer for the second trench when deepening the first trench. In addition, by combining the different material selections of the sacrificial layer and the oxide layer, the sacrificial layer can be removed with minimal etching damage to the oxide layer. Finally, the first trench is deepened based on the protective effect of the oxide layer on the second trench, thereby obtaining trenches of two depths. This fabrication method requires only one photomask to fabricate trenches of two depths, avoiding the problem of photolithographic overlay errors between the two photomasks, while reducing the management and manufacturing costs of the photomask. In addition, when etching to deepen the first trench, only one thermal oxidation process is used, and this thermal oxidation process is for the wide-diameter second trench. Generally, the tolerance requirements for wide-diameter trenches in semiconductor device structures are relatively low, so the overall process variation of the critical dimensions of the two trenches is low, effectively improving the product yield. Finally, the process steps of this invention are simple, efficient, and more cost-effective. Attached Figure Description

[0032] Figure 1 The diagram shown is a simplified cross-sectional view of a front-illuminated image sensor as an example.

[0033] Figure 2 The diagram shown is a simplified cross-sectional view of a back-illuminated image sensor as an example.

[0034] Figures 3 to 13 The diagram shows a cross-sectional view of each step in the preparation method of the double-depth trench according to Embodiment 1 of the present invention.

[0035] Figure 14 and Figure 15 The diagram shows a cross-sectional view of each step in the fabrication method of the back-illuminated image sensor according to Embodiment 2 of the present invention.

[0036] Component designation explanation

[0037] 10 Substrates

[0038] 100 hard mask layers

[0039] 101 Photoresist layer

[0040] 102 First trench pattern

[0041] 103 Second Groove Pattern

[0042] 11 First trench

[0043] 12 Second trench

[0044] 13 Sacrificial Layer

[0045] 130 Sacrificial Material Layer

[0046] 14 Oxide layer

[0047] 15 Third trench

[0048] 16 Dielectric Layer

[0049] 17. Embedded conductor

[0050] 20 Photodiode

[0051] 21 Circuits and Transistors Detailed Implementation

[0052] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0053] In the detailed description of embodiments of the present invention, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged and not to scale. Furthermore, the schematic diagrams are merely examples and should not limit the scope of protection of the present invention. In actual fabrication, the three-dimensional spatial dimensions of length, width, and depth should be included.

[0054] For ease of description, spatial relation terms such as “below,” “under,” “lower than,” “below,” “above,” and “upper” may be used herein to describe the relationship between one element or feature shown in the accompanying drawings and other elements or features. It will be understood that these spatial relation terms are intended to include orientations of the device in use or operation other than those depicted in the drawings, and may include embodiments in which the first and second features are formed in direct contact, or embodiments in which additional features are formed between the first and second features, such that the first and second features may not be in direct contact. Furthermore, when a layer is referred to as “between” two layers, it may be the only layer between the two layers, or there may be one or more layers in between.

[0055] Embodiments of the invention are described herein with reference to cross-sectional views illustrating preferred embodiments (and intermediate structures) of this application, thus allowing for variations in the illustrated shape due to, for example, fabrication methods and / or tolerances. Therefore, embodiments of this application should not be limited to the specific shapes shown herein, but include shape deviations due to, for example, manufacturing techniques. For example, implantation regions shown as rectangular typically have rounded or curved features at their edges and / or implantation concentration gradients, rather than a binary change from implantation regions to non-implantation regions. Similarly, the buried regions formed by implantation can result in some implantation in the region between the buried region and the surface traversed during implantation. Therefore, the regions shown in the figures are substantially schematic, and their shapes do not represent the actual shapes of regions of the device and do not limit the scope of this application.

[0056] Please see Figures 3 to 15 It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the illustrations only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0057] Example 1

[0058] This embodiment provides a method for fabricating dual-depth trenches, which can be applied to scenarios requiring the formation of two trenches of different depths in semiconductor devices. The fabrication method includes:

[0059] S1, providing a substrate, the material of which can be oxidized by a thermal oxidation process;

[0060] S2, a plurality of first trenches and a plurality of second trenches are formed from the surface of the substrate inward using the same photolithography etching process; wherein the diameter of the first trench is smaller than the diameter of the second trench;

[0061] S3, fill the sacrificial layer only in the first trench;

[0062] S4, using a thermal oxidation process to form an oxide layer on the sidewall and bottom wall of the second trench;

[0063] S5, Remove the filling sacrificial layer in the first trench to expose the bottom wall of the first trench;

[0064] S6, using a dry etching process, the substrate is etched downwards from the bottom wall of the first trench to a predetermined depth to form a third trench of the required depth.

[0065] The dual-depth trench fabrication method of this embodiment uses a single photolithography etching process to form a first trench and a second trench with different diameters using a photomask. During the etching process to deepen the first trench, a sacrificial layer is first filled into the first trench. Through the isolation effect of the sacrificial layer and combined with a thermal oxidation process, an oxide layer is formed in the second trench as an etching protection layer for the second trench when deepening the first trench. In addition, by choosing different materials for the sacrificial layer and the oxide layer, the sacrificial layer can be removed with minimal etching damage to the oxide layer. Finally, the first trench is deepened based on the protective effect of the oxide layer on the second trench, thus obtaining trenches of two depths. This fabrication method requires only one photomask to fabricate trenches of two depths, avoiding the problem of photolithographic overlay errors between the two photomasks, while reducing the management and manufacturing costs of the photomask. In addition, when etching to deepen the first trench, only one thermal oxidation process is used, and this thermal oxidation process is for the wide-diameter second trench. Generally, the tolerance requirements for wide-diameter trenches in semiconductor device structures are relatively low, so the overall process variation of the critical dimensions of the two trenches is low, effectively improving the product yield. Finally, the process steps in this embodiment are simple, efficient, and more cost-effective.

[0066] The method for preparing the double-depth trench in this embodiment will be described in detail below with reference to the specific accompanying drawings.

[0067] like Figure 3 As shown, step S1 is performed first, providing a substrate 10, the material of which can be oxidized by a thermal oxidation process.

[0068] Since a thermal oxidation process is required for substrate 10, the substrate 10 in this embodiment is suitable for being made of a material that can be oxidized by the thermal oxidation process. Exemplarily, the substrate 10 is generally selected as a semiconductor material to facilitate the fabrication of other semiconductor structures on the substrate 10. For example, the substrate 10 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 group III / V or group II / VI semiconductor substrates. Alternatively, for example, the substrate can be a layered substrate including materials such as Si / SiGe, Si / SiC, silicon on insulator (SOI), or silicon-germanium on insulator, selected specifically according to actual needs. As a specific example, when the fabrication method of this embodiment is used in the fabrication process of a back-illuminated image sensor, the material of the substrate 10 is generally selected as a single-material semiconductor material, such as a silicon substrate.

[0069] like Figure 7As shown, step S2 is then performed, forming a plurality of first trenches 11 and a plurality of second trenches 12 from the surface of the substrate 10 inward based on the same photolithography etching process; wherein, the diameter of the first trenches 11 is smaller than the diameter of the second trenches 12.

[0070] The specific diameters of the first trench 11 and the second trench 12 are selected according to actual needs and are not excessively restricted here. The required depth of the second trench 12 can be achieved in this step. Therefore, the etching depth of the first trench 11 and the trench 12 in this step is based on the required depth of the second trench 12.

[0071] As a specific example, the method for forming the first trench and the second trench includes the following steps:

[0072] like Figure 3 As shown, in step S20, a hard mask layer 100 is formed on the surface of the substrate 10. The material of the hard mask layer 100 can be any material suitable for use as a hard mask. It can be a single-layer structure or a stacked structure. For example, when the substrate 10 is a silicon substrate, the hard mask layer 100 is preferably a silicon nitride hard mask layer. The hard mask layer 100 can be formed using conventional deposition processes, such as CVD, PVD, ALD, etc.

[0073] like Figures 4 to 6 As shown, in step S21, the hard mask layer 100 is etched and patterned using the same photolithography etching process to obtain a patterned hard mask layer 100, as follows. Figure 6 As shown; wherein, the patterned hard mask layer 100 has the patterns of the first trench and the second trench formed therein, namely the first trench pattern 102 and the second trench pattern 103; specifically: as Figure 4 As shown, a photoresist layer 101 is coated on the hard mask layer 100, such as... Figure 5 As shown, the photoresist layer 101 is then exposed and developed to obtain a patterned photoresist layer 101, as shown. Figure 6 As shown, the hard mask layer 100 is then etched based on the patterned photoresist layer 101 to obtain the patterned hard mask layer 100, and finally the patterned photoresist layer is removed.

[0074] like Figure 7 As shown, in step S22, the substrate 10 is etched using the patterned hard mask layer 100 as a mask to form the first trench 11 and the second trench 12 in the substrate 10; generally, anisotropic dry etching is selected to form the first trench 11 and the second trench 12.

[0075] like Figure 9As shown, step S3 is then performed, in which the sacrificial layer 13 is filled only in the first trench 11.

[0076] As an example, the sacrificial layer 13 primarily functions to prevent the thermal oxidation process from occurring in the first trench 11 during subsequent steps. Specifically, it prevents oxygen ions from entering the first trench 11 and consuming the substrate to form an oxide layer. Therefore, the material of the sacrificial layer 13 is chosen to block oxygen ions from passing through during the thermal oxidation process. Furthermore, the thickness of the sacrificial layer 13 is chosen to at least completely cover the bottom wall of the first trench 11 to absolutely prevent the formation of an oxide layer on the bottom wall of the first trench 11, thus ensuring that the bottom wall of the first trench 11 can be exposed after the sacrificial layer 13 is removed. Preferably, the height of the upper surface of the sacrificial layer 13 is not lower than the height of the upper surface of the substrate 10 to absolutely prevent the formation of an oxide layer on the sidewalls and bottom wall of the first trench 11 during subsequent thermal oxidation processes.

[0077] As a specific example, the method of filling the sacrificial layer only in the first trench includes the following steps:

[0078] like Figure 8 As shown, in step S30, a sacrificial material layer 130 is formed on the substrate 10. The sacrificial material layer 130 at least fills the first trench 11, while the sacrificial material layer 130 is formed on the sidewalls and bottom wall of the second trench 12 but does not completely fill the second trench 12. Because the diameter of the first trench 11 is smaller than the diameter of the second trench 12, when the sacrificial material layer 130 is formed, the sacrificial material layers on the sidewalls of the first trench 11 will merge first, completing the full filling of the trench. However, because the diameter of the second trench 12 is larger, after the first trench 11 is filled, the sacrificial material layers 130 on the sidewalls of the second trench 12 will not merge, thus the sacrificial material layer 130 in the second trench 12 is formed on the sidewalls and bottom wall. The second trench 12 is formed without filling the second trench 12, thereby forming a groove-shaped sacrificial material layer 130 in the second trench 12. It should be noted that when the patterned hard mask layer 100 is formed on the substrate 10, the sacrificial material layer 130 is formed on the surface of the patterned hard mask layer. In this step, the material of the sacrificial material layer 130 is selected from materials with strong hole-filling ability and deposition processes with strong hole-filling ability, such as CVD deposition process with strong hole-filling ability, deposition of titanium nitride or tungsten materials with strong hole-filling ability, and titanium nitride and tungsten have a high etching selectivity with oxides, so that the sacrificial layer can be completely removed in subsequent processes while ensuring low oxide damage.

[0079] like Figure 9As shown, in step S31, the sacrificial material layer 130 is etched back to remove the sacrificial material layer 130 from the sidewall and bottom wall of the second trench 12, and the remaining sacrificial material layer 130 in the first trench 11 forms the sacrificial layer 13. It is preferable to choose dry etching for etching back, but it is not limited to this. If the etching rate can be effectively controlled, wet process can also be used for etching back.

[0080] like Figure 10 As shown, step S4 is then performed, in which an oxide layer 14 is formed on the sidewalls and bottom wall of the second trench 12 using a thermal oxidation process. Since the first trench 11 is filled with the sacrificial layer 13, the oxide layer 14 will not form on the bottom wall of the first trench 12 during the thermal oxidation process in this step, due to the blocking effect of the sacrificial layer 13, thus effectively ensuring the exposure of the bottom wall of the first trench 12 in the future.

[0081] Thermal oxidation processes include two methods: wet oxidation and dry oxidation. In dry oxidation, a mixed gas (oxygen and nitrogen) is introduced into the reactor, with the temperature typically between 900 and 1100 degrees Celsius. Wet oxidation, on the other hand, involves heating deionized water to carry water vapor into the reactor; the ISSG wet oxidation process is commonly used. Each method has its advantages and disadvantages, and the specific choice should be made based on a comprehensive consideration of the processing object, requirements, and actual conditions.

[0082] As an example, when the substrate 10 is selected as a silicon substrate, the thickness of the oxide layer 14 is selected as follows: For example etc.

[0083] like Figure 11 As shown, step S5 is then performed to remove the sacrificial layer 13 that fills the first trench 11, so that the bottom wall of the first trench 11 is exposed.

[0084] The sacrificial layer 13 can be removed using either wet or dry etching. The specific etching source is determined based on the materials of the sacrificial layer 13 and the oxide layer 14, as well as the chosen etching method; no excessive restrictions are imposed here. Preferably, dry etching is chosen to remove the sacrificial layer 13 filling the first trench. Because the diameter of the first trench 11 is small, wet etching solution does not easily flow into the bottom wall of the first trench 11, resulting in poor etching effect. Dry etching, based on its excellent anisotropic etching performance, can effectively and completely remove the sacrificial layer 13 from the bottom wall of the first trench 11.

[0085] like Figure 12As shown, in step S6, a dry etching process is used to continue etching the substrate 10 downwards from the bottom wall of the first trench 11 to a predetermined depth, in order to form a third trench 15 of the required depth. The predetermined depth of this further downward etching step can be set according to actual needs and is not excessively limited here.

[0086] As an example, such as Figure 13 As shown, when the patterned hard mask layer 100 is formed on the surface of the substrate 10, the step of removing the patterned hard mask layer 100 is included after forming the third trench 15.

[0087] Example 2

[0088] like Figure 13 As shown, this embodiment provides a method for fabricating a back-illuminated image sensor. The method includes the method for fabricating a dual-depth trench as described in Embodiment 1. The functions of the fabricated third trench 15 and second trench 12 in the back-illuminated image sensor are as follows: the third trench 15 is used to isolate photodiodes, providing physical isolation for each pixel to reduce light interference between photodiodes; the second trench 12 is used to isolate embedded wires to increase the wire width and thereby reduce the wire resistance.

[0089] After forming the third trench 15 and the second trench 12, the method further includes steps S7 and S8, specifically:

[0090] Step S7, as follows Figure 14 As shown, a dielectric layer 16 is formed on the substrate 10, the dielectric layer 16 is formed on the bottom wall and side wall of the second trench 12 and fills the third trench 15.

[0091] The oxide layer 14 may or may not be removed before the formation of the dielectric layer 16. The dielectric layer 16 may be a single layer of insulating material or a stack of multiple layers of different insulating materials, depending on the actual needs. In addition, the dielectric layer 16 may be formed using existing conventional deposition processes, such as CVD, PVD, sol-gel method or electrochemical deposition method, etc.

[0092] Step S8, as follows Figure 15 As shown, an embedded conductor 17 is formed on the dielectric layer 16 in the second trench 12.

[0093] As an example, a pixel electrode is formed on the dielectric layer 16 of the third trench 15 simultaneously with the formation of the embedded conductor 17. The embedded conductor 17 typically serves as a signal readout line in a back-illuminated image sensor to achieve charge transfer and signal readout.

[0094] As an example, the embedded wire 17 is made of a metal material with good electrical conductivity, such as aluminum, copper, gold, or tungsten.

[0095] In summary, this invention provides a method for fabricating a dual-depth trench and back-illuminated image sensor. Through a single photolithography etching process, a first trench and a second trench with different apertures are formed using a photomask. During the etching process to deepen the first trench, a sacrificial layer is first filled into the first trench. Through the isolation effect of the sacrificial layer and combined with a thermal oxidation process, an oxide layer is formed in the second trench as an etching protection layer for the second trench during the deepening of the first trench. Furthermore, by choosing different materials for the sacrificial layer and the oxide layer, the sacrificial layer can be removed with minimal etching damage to the oxide layer. Finally, the first trench is deepened based on the protective effect of the oxide layer on the second trench, thus obtaining trenches of two depths. This fabrication method requires only one photomask to fabricate trenches of two depths, avoiding the lithographic overlay error problem between the two photomasks and reducing photomask management and manufacturing costs. Furthermore, when etching to deepen the first trench, only one thermal oxidation process is used, specifically for the wide-aperture second trench. Since the tolerance requirements for wide-aperture trenches are generally low in semiconductor device structures, the overall process variation in the critical dimensions of the two trenches is low, effectively improving product yield. Finally, the process steps in this embodiment are simple, efficient, and cost-effective. Therefore, this invention effectively overcomes the various shortcomings of the prior art and has high industrial applicability.

[0096] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for fabricating a double-depth trench, characterized in that, The preparation method includes: A substrate is provided, the material of which can be oxidized by a thermal oxidation process; A plurality of first trenches and a plurality of second trenches are formed from the surface of the substrate inward using the same photolithography etching process; Wherein, the diameter of the first groove is smaller than the diameter of the second groove; The sacrificial layer is filled only in the first trench; An oxide layer is formed on the sidewalls and bottom wall of the second trench using a thermal oxidation process; Remove the filling sacrificial layer in the first trench to expose the bottom wall of the first trench; A dry etching process is used to continue etching the substrate downwards from the bottom wall of the first trench to a predetermined depth, in order to form a third trench of the required depth.

2. The method for preparing a double-depth trench according to claim 1, characterized in that: The method for forming the first trench and the second trench includes: A hard mask layer is formed on the surface of the substrate; The hard mask layer is etched and patterned using the same photolithography etching process to obtain a patterned hard mask layer; wherein the patterned hard mask layer has the first trench and the second trench pattern formed in it; The substrate is etched using the patterned hard mask layer as a mask to form the first trench and the second trench in the substrate.

3. The method for preparing a double-depth trench according to claim 1, characterized in that, The method of filling the sacrificial layer only in the first trench includes: A sacrificial material layer is formed on the substrate; wherein the sacrificial material layer at least fills the first trench, while the sacrificial material layer is formed on the sidewalls and bottom wall of the second trench but does not fill the second trench; The sacrificial material layer is etched back to remove the sacrificial material layer from the sidewalls and bottom wall of the second trench, and the remaining sacrificial material layer in the first trench is formed as the sacrificial layer.

4. The method for preparing a double-depth trench according to claim 1, characterized in that: The height of the upper surface of the sacrificial layer is not lower than the height of the upper surface of the substrate.

5. The method for preparing a double-depth trench according to claim 1, characterized in that: The substrate is a silicon substrate, and the material of the sacrificial layer includes titanium nitride or tungsten.

6. The method for preparing a double-depth trench according to claim 5, characterized in that: The thickness of the oxide layer is 7. The method for preparing a double-depth trench according to claim 5, characterized in that: The sacrificial layer is formed using a CVD process.

8. The method for preparing a double-depth trench according to claim 1, characterized in that: The sacrificial layer filling the first trench is removed by dry etching.

9. A method for fabricating a back-illuminated image sensor, characterized in that: The method includes the preparation method of a double-depth trench as described in any one of claims 1 to 8; wherein the third trench is used to isolate a photodiode and the second trench is used to isolate an embedded wire.

10. The method for fabricating a back-illuminated image sensor according to claim 9, characterized in that, Also includes: A dielectric layer is formed on the substrate, the dielectric layer being formed on the bottom wall and sidewalls of the second trench and filling the third trench; An embedded conductor is formed on the dielectric layer in the second trench.

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