A manufacturing method of double deep trenches

Abstract

The present invention discloses a manufacturing method for double-depth trenches, belonging to the technical field of semiconductor integrated circuit manufacturing. The method first manufactures at least two trenches with the same depth but different widths in a substrate and a hard mask layer, namely a narrow deep trench and a wide shallow trench, and then sequentially manufactures a first sacrificial layer and a protective layer on the hard mask layer. During this process, the narrow deep trench is sealed by the first sacrificial layer; when removing the sealing structure and the internal first sacrificial layer of the narrow deep trench, the protective layer can protect the wide shallow trench; further, the narrow deep trench is depth-expanded to form a target depth, and the internal material of the wide shallow trench is removed to form double-depth trenches. By using the method of the present invention, narrow deep trenches and wide shallow trenches with different depths can be simultaneously manufactured using only one photomask, significantly reducing the cost of manufacturing a back-illuminated image sensor.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor integrated circuit manufacturing, and particularly relates to a method for fabricating double-depth trenches. Background Art

[0002] A back-illuminated image sensor is a specially designed image sensor. Its characteristic is that light enters from the back of the sensor and directly irradiates the photosensitive device, thereby effectively improving the light utilization efficiency and image quality, especially performing better in low-light environments. In order to enable the back-illuminated image sensor to meet the isolation requirements between the photodiode and the charge storage area, the manufacturing process and product yield of the back-illuminated image sensor, and to improve the performance of the back-illuminated image sensor, during the manufacturing process of the back-illuminated image sensor, two different types of trenches need to be formed: narrow and deep narrow-deep trenches and wide and shallow wide-shallow trenches.

[0003] The narrow-deep trenches are used for isolation between photodiodes to ensure the photoelectric conversion efficiency and signal isolation of the back-illuminated image sensor, thereby avoiding mutual interference between signals, which is the basis for ensuring the imaging quality and performance stability of the back-illuminated image sensor. The wide-shallow trenches are used for arranging metal wires to increase the actual width of the wires, thereby reducing the wire resistance and improving the circuit performance. Therefore, the narrow-deep trenches and wide-shallow trenches are important structural components of the back-illuminated image sensor.

[0004] During the fabrication process of the narrow-deep trenches and wide-shallow trenches, a photomask needs to be introduced. The photomask (also known as a photomask or lithography mask) serves as a template during the manufacturing process of the back-illuminated image sensor, and forms a circuit pattern by controlling the transmission of light. Due to the different sizes of the narrow-deep trenches and wide-shallow trenches, two photomasks are required to fabricate the two types of trenches respectively during the manufacturing process, resulting in a high manufacturing cost. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above-mentioned drawbacks of the prior art and provide a method for fabricating double-depth trenches to solve the problem in the prior art that during the manufacturing process of the back-illuminated image sensor, due to the existence of two trenches with different depths and widths, two photomasks are required, resulting in a high manufacturing cost.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for fabricating double-depth trenches includes the following steps:

[0008] Fabricate a hard mask layer on the substrate;

[0009] At least two trenches with the same depth are fabricated in the substrate and the hard mask layer, namely the first process narrow and deep trench and the first process wide and shallow trench; on the same plane, the cross-sectional area of the first process narrow and deep trench is smaller than that of the first process wide and shallow trench;

[0010] A first sacrificial layer is fabricated on the surface of the first process narrow and deep trench and the surface of the first process wide and shallow trench, forming a second process narrow and deep trench and a second process wide and shallow trench; the upper end of the second process narrow and deep trench is a sealed structure, and the inside is a cavity;

[0011] A protective layer is fabricated on the first sacrificial layer, and the protective layer covers the inner sidewall of the second process wide and shallow trench;

[0012] Part of the hard mask layer is removed, the sealed structure is removed, and the upper end of the second process narrow and deep trench is opened;

[0013] The first sacrificial layer in the second process narrow and deep trench is removed, the second process narrow and deep trench is processed to the depth of the target narrow and deep trench, and the protective layer in the second process wide and shallow trench is removed;

[0014] After removing the remaining hard mask layer, a target narrow and deep trench and a target wide and shallow trench are formed.

[0015] A further improvement of the present invention lies in:

[0016] Preferably, the depth of the trenches with the same depth is equal to the depth of the target wide and shallow trench.

[0017] Preferably, the first sacrificial layer is a silicon oxide layer, and the protective layer is a silicon oxynitride layer.

[0018] Preferably, the first sacrificial layer includes a silicon oxide layer and a polysilicon layer, and the protective layer is a silicon oxide layer.

[0019] Preferably, the protective layer is obtained by converting a part of the thickness of the first sacrificial layer.

[0020] Preferably, the upper end of the cavity is higher than the upper surface of the substrate.

[0021] Preferably, before removing part of the hard mask layer, a second sacrificial layer is fabricated on the protective layer, and the second process wide and shallow trench is filled with the second sacrificial layer material.

[0022] Preferably, the second sacrificial layer is a silicon oxide layer or a silicon nitride layer.

[0023] Preferably, after removing part of the hard mask layer, the second process narrow and deep trench becomes a third process narrow and deep trench, and the second process wide and shallow trench becomes a third process wide and shallow trench;

[0024] After the first sacrificial layer in the third-process narrow and deep trench is removed, a fourth-process narrow and deep trench is formed, and the third-process wide and shallow trench becomes the fourth-process wide and shallow trench.

[0025] Preferably, the depth of the fourth-process narrow and deep trench is processed to the depth of the target narrow and deep trench to obtain the target narrow and deep trench.

[0026] Remove the second sacrificial layer and the protective layer in the fourth-process wide and shallow trench to obtain the target wide and shallow trench.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The present invention discloses a method for fabricating a dual-depth trench. The method first fabricates a first-process narrow and deep trench and a first-process wide and shallow trench with the same depth in a substrate and a hard mask layer through a single photomask. After sealing the upper end of the first-process narrow and deep trench with a first sacrificial layer, a protective layer and a second sacrificial layer are sequentially fabricated on the first sacrificial layer. The protective layer can protect the sidewalls of the active regions adjacent to the wide and shallow trenches from being exposed when removing the first sacrificial layer in the second-process narrow and deep trench. By using the method of the present invention, a target narrow and deep trench and a target wide and shallow trench that meet the requirements can be fabricated simultaneously using only a single photomask, significantly reducing the fabrication cost. In addition, the method also has the advantages of simple process and easy implementation, and is suitable for large-scale industrial production. The dual-depth trench structure can be used to fabricate a back-illuminated image sensor, which helps to improve the performance and reduce the cost of the back-illuminated image sensor. Description of the Drawings

[0029] Figure 1 It is a flowchart of a method for fabricating a dual-depth trench sensor according to the present invention;

[0030] Figure 2 It is a schematic structural diagram of fabricating a hard mask layer on a substrate according to the present invention;

[0031] Figure 3 It is a schematic structural diagram of fabricating a first-process narrow and deep trench and a first-process wide and shallow trench according to the present invention;

[0032] Figure 4 It is a schematic structural diagram of fabricating a first sacrificial layer on a hard mask layer according to the present invention;

[0033] Figure 5 It is a schematic structural diagram of fabricating a protective layer on a first sacrificial layer according to the present invention;

[0034] Figure 6 It is a schematic structural diagram of fabricating a second sacrificial layer on a protective layer according to the present invention;

[0035] Figure 7 It is a schematic structural diagram of removing a part of the hard mask layer according to the present invention;

[0036] Figure 8 Schematic structural diagram of removing the first sacrificial layer inside the narrow and deep trench in the third process of the present invention;

[0037] Figure 9 Schematic structural diagram of transforming the narrow and deep trench in the fourth process into the target narrow and deep trench of the present invention;

[0038] Figure 10 Schematic structural diagram of transforming the wide and shallow trench in the fourth process into the target wide and shallow trench of the present invention;

[0039] Figure 11 Schematic structural diagram of the double-depth trench after removing the hard mask layer of the present invention;

[0040] Wherein: 1. Substrate; 2. Hard mask layer; 3. First sacrificial layer; 4. Protective layer; 5. Second sacrificial layer; 301. Sealing structure; 601. Narrow and deep trench in the first process; 602. Narrow and deep trench in the second process; 603. Narrow and deep trench in the third process; 604. Narrow and deep trench in the fourth process; 605. Target narrow and deep trench; 701. Wide and shallow trench in the first process; 702. Wide and shallow trench in the second process; 703. Wide and shallow trench in the third process; 704. Wide and shallow trench in the fourth process; 705. Target wide and shallow trench. Detailed implementation manners

[0041] The embodiments of the present invention will be described in detail below. Examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention and should not be construed as a limitation of the present invention.

[0042] The back-illuminated image sensor improves the light utilization efficiency and image quality by allowing light to enter from the back and directly irradiate the photosensitive device. During its manufacturing process, it is necessary to form narrow and deep trenches for isolating photodiodes and wide and shallow trenches for arranging metal wires to reduce resistance; the narrow and deep trenches are trenches that are narrow and deep in size, and the wide and shallow trenches are trenches that are wide and shallow in size. A more specific structural description is that the cross-sectional area of the narrow and deep trenches on the same plane is smaller than that of the wide and shallow trenches, and the depth of the narrow and deep trenches is greater than that of the wide and shallow trenches. Due to the different sizes of these two types of trenches, traditionally two photomasks are required for separate manufacturing, increasing the manufacturing cost.

[0043] In view of the above problems, the present invention discloses a solution method. First, grooves with the same depth but different widths are formed on a hard mask layer and a substrate, namely a process narrow and deep groove and a process wide and shallow groove. A sacrificial layer is formed on the surface of each groove. At the same time, the upper end of the narrow and deep groove is sealed by the sacrificial layer to form a sealing structure. Further, a protective layer is formed on the sacrificial layer and then removed together with the sealing structure, so that the upper end of the process narrow and deep groove is exposed. At this time, there is still a protective layer on the surface of the process wide and shallow groove, so that when removing the sacrificial layer on the surface of the process narrow and deep groove, the sidewalls of the active regions adjacent to the process wide and shallow groove can be protected by the protective layer from being damaged and exposed; further, the sacrificial layer in the narrow and deep groove is removed, and at the same time, the narrow and deep groove is etched to the target depth. This method enables multiple grooves with two target sizes to be formed using only one photomask.

[0044] See Figure 1 , the present invention discloses a method for manufacturing double-depth grooves, which includes the following steps:

[0045] S1, fabricate a hard mask layer 2 on a substrate 1;

[0046] S2, place a photomask on the hard mask layer 2, and fabricate at least two grooves with the same depth in the substrate 1 and the hard mask layer 2, namely a first process narrow and deep groove 601 and a first process wide and shallow groove 701; on the same plane, the cross-sectional area of the first process narrow and deep groove 601 is smaller than that of the first process wide and shallow groove 701;

[0047] S3, fabricate a first sacrificial layer 3 on the surface of the first process narrow and deep groove 601 and the surface of the first process wide and shallow groove 701 to form a second process narrow and deep groove 602 and a second process wide and shallow groove 702; the upper end surface of the second process narrow and deep groove 602 is a sealing structure 301, and the inside is a cavity;

[0048] S4, fabricate a protective layer 4 on the first sacrificial layer 3, and the protective layer 4 covers the inner sidewalls of the second process wide and shallow groove 702;

[0049] S5, remove part of the hard mask layer 2, the sealing structure 301 is removed, and the upper end of the second process narrow and deep groove 602 is opened;

[0050] S6, remove the first sacrificial layer 3 in the second process narrow and deep groove 602, process the second process narrow and deep groove 602 to the depth of the target narrow and deep groove 605, and remove the protective layer 4 in the second process wide and shallow groove 702;

[0051] S7, after removing the remaining hard mask layer 2, the target narrow and deep groove 605 and the target wide and shallow groove 705 are formed.

[0052] The following will be introduced in detail by combining Figures 2 - 9 toFigure 1 The manufacturing method of double-depth trenches provided in some embodiments of the present invention as shown, the Figures 2 - 9 is a schematic structural diagram during the manufacturing process of the manufacturing method of double-depth trenches provided in some embodiments of the present invention.

[0053] Refer to Figure 2 , in S1, it is necessary to first provide a substrate 1, which serves as a platform for subsequently forming narrow deep trenches and wide shallow trenches. A hard mask layer 2 is formed on the substrate 1. The hard mask layer 2 is an inorganic thin film material mainly composed of a series of inorganic compounds, such as silicon oxynitride, silicon oxide, or amorphous carbon, etc. The hard mask layer 2, as an intermediate medium, can accurately transfer the pattern formed during the lithography process to the target material, and is particularly suitable for cases where high-precision pattern transfer is required.

[0054] Furthermore, when fabricating the hard mask layer 2 on the substrate 1, chemical vapor deposition (CVD) or physical vapor deposition (PVD), etc. are used. These methods can directly deposit the required thin film material from gas molecules through chemical reactions at high temperatures. In addition, plasma enhanced chemical vapor deposition (PECVD) can be used to further improve the deposition rate and film quality.

[0055] It should be understood that the hard mask layer 2 is used during the trench formation process. After the required double-depth trenches are formed, the hard mask layer 2 needs to be removed finally and will not be retained in the final back-illuminated image sensor.

[0056] It should be understood that the substrate 1 in the present invention can be selected from any suitable material well-known in the art as the substrate. For example, it can be composed of one or more of the following materials: silicon (Si), germanium (Ge), silicon-germanium alloy (SiGe), silicon-carbon alloy (SiC), silicon-germanium-carbon alloy (SiGeC), indium arsenide (InAs), gallium arsenide (GaAs), indium phosphide (InP), and also includes multi-layer composite structures composed of these semiconductor materials. In addition, it can also be a double-sided polished silicon wafer (DSP), an alumina ceramic substrate, a quartz substrate, or a glass substrate, etc. Specifically, in the embodiments of the present invention, the substrate 1 is exemplified by a silicon wafer as the substrate 1.

[0057] Refer to Figure 3, in S2, on the hard mask layer 2 and the substrate 1, the photomask is placed on the hard mask layer 2, and at least two grooves with the same depth are fabricated by etching, namely the first process narrow and deep groove 601 and the first process wide and shallow groove 701, which are used to prepare for the grooves with different depths finally. During the fabrication process of the grooves with the same depth, the specific quantity and arrangement are determined according to specific process requirements. In this step, the grooves with different final depths are first fabricated into process grooves with the same depth, which can avoid using two photomasks.

[0058] In some embodiments of the present invention, the depths of the first process narrow and deep groove 601 and the first process wide and shallow groove 701 are less than or equal to the depth of the target wide and shallow groove 705, leaving a processing margin for the subsequent further processing to form the final target narrow and deep groove 605 and target wide and shallow groove 705. More preferably, the depths of the first process narrow and deep groove 601 and the first process wide and shallow groove 701 fabricated in this step are the same as the depth of the final target wide and shallow groove 705, so that in the subsequent processing, only the first process narrow and deep groove 601 needs to be further processed, and there is no need to further process and improve the depth of the process wide and shallow groove, simplifying the process.

[0059] Furthermore, the first process narrow and deep groove 601 and the first process wide and shallow groove 701 are formed by plasma etching method.

[0060] Furthermore, the width of the first process narrow and deep groove 601 is equal to the width of the finally fabricated target narrow and deep groove 605, and the width of the first process wide and shallow groove 701 is equal to the width of the finally fabricated target wide and shallow groove 705, so that in the subsequent processing, only the depth of the groove needs to be further etched, and there is no need to adjust the width anymore.

[0061] In the embodiments of the present invention, for the sake of simplifying the expression, one narrow and deep groove and one wide and shallow groove are used as examples in the subsequent description and drawings.

[0062] See Figure 4 , in S3, a first sacrificial layer 3 is deposited on the upper surface of the hard mask layer 2. The inner surfaces of the first process narrow and deep groove 601 and the first process wide and shallow groove 701 are both covered by the first sacrificial layer 3. At the same time, the upper end of the first process narrow and deep groove 601 is covered and sealed by the material of the first sacrificial layer 3, forming a second process narrow and deep groove 602 and a second process wide and shallow groove 702. The upper end of the second process narrow and deep groove 602 is a sealing structure 301, and the inside is a cavity.

[0063] It should be understood that the height of the cavity is greater than the height of the upper surface of the substrate 1, ensuring that when the upper sealing structure 301 is removed subsequently, the sealing structure 301 will not remain.

[0064] It should be noted that the first sacrificial layer 3 mainly has two functions. One is to seal the upper end surface of the first-process narrow and deep trench 601 so that it is not affected when the protective layer 4 is formed subsequently. Only the inner surface of the second-process narrow and deep trench 602 is covered by the first sacrificial layer 3, reducing the complexity of removing the material inside the third-process narrow and deep trench 603 subsequently; the other function is to prepare for the subsequent protective layer 4.

[0065] In some embodiments of the present invention, the first sacrificial layer 3 is made of silicon oxide. Silicon oxide can be fabricated by conventional processes and is also convenient to be removed by subsequent etching methods, providing convenience for the entire process flow.

[0066] Furthermore, the silicon oxide is deposited by a high-density plasma (HDP, High Density Plasma) method, and only deposition and no etching are performed during this process to form the sealing structure 301, and the deposition stops after completely sealing the top of the first-process narrow and deep trench 601.

[0067] See Figure 4 , in S3, in some other embodiments of the present invention, the first sacrificial layer 3 is a composite film of silicon oxide and polysilicon, and the thickness of the polysilicon layer is much larger than that of the silicon oxide layer. During the fabrication process, first, a silicon oxide thin film layer with a thickness of 2 nm to 5 nm is deposited to isolate the substrate 1 and the subsequently deposited polysilicon layer. The thickness of the formed polysilicon layer needs to ensure that a sealing structure 301 can be formed at the upper end of the first-process narrow and deep trench 601, and the thickness is dozens or hundreds of times that of the silicon oxide thin film layer. Then, the polysilicon layer is deposited by a high-density plasma method, and only deposition and no etching are performed during this process to form the sealing structure 301. At this time, the inner sidewall of the first-process narrow and deep trench 601 is covered by a very thin silicon oxide thin film layer, and there is a polysilicon layer outside the silicon oxide thin film layer.

[0068] See Figure 5 , in S4, a protective layer 4 is formed on the upper surface of the first sacrificial layer 3. The protective layer 4 covers the upper surface of all the first sacrificial layer 3 and also covers the surface of the first sacrificial layer 3 inside the second-process wide and shallow trench 702. The protective layer 4 is mainly used to protect the inner surface of the third-process wide and shallow trench 703 from being affected when the first sacrificial layer 3 inside the third-process narrow and deep trench 603 is removed subsequently and the depth of the fourth-process narrow and deep trench 604 is deepened.

[0069] See Figure 5, in some embodiments of the present invention, based on the first sacrificial layer 3 being made of silicon oxide, the protective layer 4 is made of a silicon oxynitride layer, which is obtained by performing plasma nitridation treatment on the first sacrificial layer 3 made of silicon oxide. In this step, a part of the first sacrificial layer 3 is directly transformed into the protective layer 4. The protective layer 4 changes the covering material on the sidewalls of the second-process wide and shallow trench 702 from the first sacrificial layer 3 to the new material protective layer 4, while the covering material on the sidewalls of the second-process narrow and deep trench 602 remains the first sacrificial layer 3. That is, the covering materials on the sidewalls of the second-process wide and shallow trench 702 and the second-process narrow and deep trench 602 are no longer the same. In this way, when removing the covering layer on the sidewalls of the third-process narrow and deep trench 603 (i.e., the first sacrificial layer 3) subsequently, the covering layer on the sidewalls of the third-process wide and shallow trench 703 (i.e., the protective layer 4) is not affected, so that the sidewalls of the active region adjacent to the third-process wide and shallow trench 703 can be well protected from being exposed. At the same time, during the process of deepening the fourth-process narrow and deep trench 604 and forming the fourth-process wide and shallow trench 704, the active region adjacent to the fourth-process wide and shallow trench 704 is not damaged.

[0070] Further, in this step, as a preferred method, the process parameters of the plasma nitridation treatment are such that the first sacrificial layer 3 inside the second-process wide and shallow trench 702 is completely transformed into the protective layer 4 in the thickness direction, so that the thickness of the protective layer 4 can provide sufficient protection for the active region in subsequent processes.

[0071] Further, in this step, as a preferred method, when the first sacrificial layer 3 is a composite film of silicon oxide and polysilicon, at this time in S4, the protective layer 4 can be formed by oxidizing part of the polysilicon layer, and the material of the protective layer 4 is silicon oxide at this time.

[0072] See Figure 6 , in some embodiments of the present invention, a second sacrificial layer 5 is also fabricated on the protective layer 4. The second sacrificial layer 5 completely covers the upper surface of the protective layer 4 and completely fills the inside of the second-process wide and shallow trench 702.

[0073] Further, based on the protective layer 4 being silicon oxynitride, the second sacrificial layer 5 is a silicon oxide layer. Since the second sacrificial layer 5 is mainly filled in the second-process wide and shallow trench 702, and the inside of the second-process wide and shallow trench 702 is a concave structure, when fabricating the second sacrificial layer 5, the spin on glass coating (SOG) method is selected.

[0074] In some embodiments, based on the protective layer 4 being silicon oxide, the material of the second sacrificial layer 5 can be silicon nitride.

[0075] In a specific embodiment of the present invention, Figure 6In this case, a first sacrificial layer 3 made of silicon oxide, a protective layer 4 made of silicon oxynitride, and a second sacrificial layer 5 made of silicon oxide are sequentially stacked above the hard mask layer 2.

[0076] In a specific embodiment of the present invention, Figure 6 In this case, a first sacrificial layer 3 made of silicon oxide and polysilicon, a protective layer 4 made of silicon oxide, and a second sacrificial layer 5 made of silicon nitride are sequentially stacked above the hard mask layer 2; wherein, the silicon oxide in the first sacrificial layer 3 is at the lower part or inside of the polysilicon.

[0077] Refer to Figure 7 , in S5, the upper part of the hard mask layer 2 is removed, so that the sealing structure 301 at the upper end of the second-process narrow and deep trench 602 is removed, forming a third-process narrow and deep trench 603, and a part of the second-process wide and shallow trench 702 is removed, forming a third-process wide and shallow trench 703; the depth of the third-process narrow and deep trench 603 is equal to the depth of the target wide and shallow trench 705, and only the first sacrificial layer 3 is on the inner surface. The depth of the third-process wide and shallow trench 703 is the same as the depth of the target wide and shallow trench 705; the inner surface of the third-process wide and shallow trench 703 is covered by the protective layer 4, and the second sacrificial layer 5 is filled in the third-process wide and shallow trench 703, and the second sacrificial layer 5 is surrounded by the protective layer 4.

[0078] It should be understood that in this process, it is necessary to ensure that the sealing structure 301 can be completely removed, the upper surface of the third-process wide and shallow trench 703 is cut into a plane, and the second sacrificial layer 5 completely fills the inside of the third-process wide and shallow trench 703. This structure enables the second sacrificial layer 5 to fully protect the sidewalls of the inner surface of the third-process wide and shallow trench 703 and the adjacent active regions during the subsequent process of deepening the narrow and deep trench.

[0079] Preferably, the hard mask layer 2, the first sacrificial layer 3 in the second-process narrow and deep trench 602, the protective layer 4 and the second sacrificial layer 5 in the second-process wide and shallow trench 702 are processed by Chemical Mechanical Polishing (CMP), and the upper surface of the entire hard mask layer 2 and the internal structure after this process is flat.

[0080] In some embodiments of the present invention, selective etching is used to remove each sacrificial layer and the protective layer 4 subsequently, so that when etching and removing a certain layer, it will not affect other layers.

[0081] Refer to Figure 8, in S6, the first sacrificial layer 3 in the third - process narrow - deep trench 603 is removed to form a fourth - process narrow - deep trench 604. Meanwhile, during the removal process, it may affect the third - process wide - shallow trench 703 and remove a part of the second sacrificial layer 5. However, under the action of the protective layer 4, it can be avoided that the side walls of the third - process wide - shallow trench 703 are affected, and the third - process wide - shallow trench 703 is transformed into a fourth - process wide - shallow trench 704.

[0082] In some embodiments, when the material of the first sacrificial layer 3 is silicon oxide, it is removed by wet etching with a hydrofluoric acid solution in this process. When the material of the first sacrificial layer 3 is silicon oxide and polysilicon, the polysilicon is removed by etching with tetramethylammonium hydroxide, and the silicon oxide is removed by wet etching with a hydrofluoric acid solution. Exemplarily, the hydrofluoric acid solution is a mixed solution of hydrofluoric acid and water, where the volume ratio of hydrofluoric acid to water is 1:200.

[0083] In some embodiments, both the first sacrificial layer 3 and the second sacrificial layer 5 are silicon oxide, and the protective layer 4 is a silicon oxynitride layer. Therefore, when the first sacrificial layer 3 is removed by wet etching with a hydrofluoric acid solution, a part of the second sacrificial layer 5 will be removed, but the silicon oxynitride layer as the protective layer 4 will not be etched away. At this time, the upper end of the fourth - process wide - shallow trench 704 is stepped, and the protective layer 4 can protect the side walls of the active region of the fourth - process wide - shallow trench 704.

[0084] In some embodiments, the first sacrificial layer 3 is silicon oxide and polysilicon, the protective layer 4 is silicon oxide, and the second sacrificial layer 5 is silicon nitride. When removing the polysilicon, it basically has no influence on the protective layer 4 and the second sacrificial layer 5. When removing the silicon oxide in the first sacrificial layer 3, since the silicon oxide layer in the first sacrificial layer 3 is very thin, it has almost no influence on the protective layer 4 with a thickness of about dozens of nanometers. At this time, the shape and size of the fourth - process wide - shallow trench 704 are basically the same as those of the third - process wide - shallow trench 703.

[0085] See Figure 9 , in S6, the fourth - process narrow - deep trench 604 is continuously etched by plasma etching, so as to form a deeper trench in the fourth - process narrow - deep trench 604 to reach the target depth and form the final target narrow - deep trench 605. During this process, under the action of the protective layer 4, the side walls of the fourth - process wide - shallow trench 704 are still not affected.

[0086] See Figure 10 , in S6, the second sacrificial layer 5 and the protective layer 4 inside the fourth - process wide - shallow trench 704 are removed.

[0087] In some embodiments, when the protective layer 4 is a silicon oxynitride layer, a specific removal method can be to first use a hydrofluoric acid solution to remove the second sacrificial layer 5 made of silicon oxide, and then use a hot phosphoric acid solution to remove the protective layer 4 made of silicon oxynitride. Exemplarily, in the hydrofluoric acid, the volume ratio of hydrofluoric acid to water is 1:200, and the phosphoric acid solution is a mixed solution composed of phosphoric acid and water, wherein the concentration of the phosphoric acid solution is 85%.

[0088] In some embodiments, when the protective layer 4 is silicon oxide, first use an 85% phosphoric acid solution to remove the second sacrificial layer 5 made of silicon nitride, and then use a hydrofluoric acid solution to remove the protective layer 4 in the fourth process narrow and deep trench 604.

[0089] See Figure 11 , in S7, in the process of removing the remaining hard mask layer 2 to form the target narrow and deep trench 605 and the target wide and shallow trench 705, different methods need to be adopted according to the different compositions of the hard mask layer 2. For example, silicon oxynitride can be removed by a phosphoric acid solution, and silicon oxide can be removed by a hydrofluoric acid solution.

[0090] By using the above method, only one photomask is needed to simultaneously fabricate the narrow and deep trench and the wide and shallow trench, and the semiconductor with this trench structure can be used to fabricate a back-illuminated image sensor.

[0091] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation of the present invention. In addition, the features defined as "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise specified, the meaning of "a plurality" is two or more. In the description of the present invention, that the first feature is "above" or "below" the second feature may include direct contact between the first and second features, or may include that the first and second features are not in direct contact but in contact through other features therebetween.

[0092] In the description of the present invention, that the first feature is "above", "above" and "on" the second feature includes that the first feature is directly above and obliquely above the second feature, or merely means that the first feature is at a higher horizontal level than the second feature.

[0093] In the description of the present invention, it should be noted that, unless otherwise clearly specified and defined, the terms "installed", "connected", and "coupled" shall be construed in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0094] In the description of this specification, the descriptions referring to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic descriptions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0095] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and purposes of the present invention. The scope of the present invention is defined by the claims and their equivalents.

[0096] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for making a double-depth groove, characterized in that: The following steps are involved: forming a hard mask layer on the substrate; At least two trenches of the same depth are made in the substrate and the hard mask layer, which are a first process narrow deep trench and a first process wide shallow trench; on the same plane, the cross-sectional area of ​​the first process narrow deep trench is smaller than the cross-sectional area of ​​the first process wide shallow trench; A first sacrificial layer is formed on the surface of the first process narrow deep groove and the surface of the first process wide shallow groove to form a second process narrow deep groove and a second process wide shallow groove; the upper end of the second process narrow deep groove is a sealing structure, and the inside is a cavity; Forming a protection layer on the first sacrificial layer, wherein the protection layer covers the inner sidewall of the second process wide shallow trench; Removing part of the hard mask layer, the sealing structure is removed, and the upper end of the second process narrow deep trench is opened; Removing the first sacrificial layer in the second process narrow and deep trench, processing the second process narrow and deep trench to the depth of the target narrow and deep trench, and removing the protective layer in the second process wide and shallow trench; After removing the remaining hard mask layer, a target narrow deep trench and a target wide shallow trench are formed.

2. A method for manufacturing a double-depth groove according to claim 1, characterized in that: The depth of the grooves of the same depth is equal to the depth of the target wide shallow grooves.

3. The method for manufacturing a double-depth groove according to claim 1, characterized in that: The first sacrificial layer is a silicon oxide layer, and the protective layer is a silicon oxynitride layer.

4. The method for manufacturing a double-depth groove according to claim 1, characterized in that: The first sacrificial layer includes a silicon oxide layer and a polysilicon layer, and the protective layer is a silicon oxide layer.

5. A method for manufacturing a double-depth groove according to claim 3 or 4, characterized in that: The protective layer is obtained by converting a first sacrificial layer of partial thickness.

6. The method for manufacturing a double-depth groove according to claim 1, characterized in that: The upper end of the cavity is higher than the upper surface of the substrate.

7. The method for manufacturing a double-depth groove according to claim 1, characterized in that: Before removing part of the hard mask layer, a second sacrificial layer is formed on the protective layer, and the second process wide shallow trench is filled with the second sacrificial layer material.

8. The method for manufacturing a double-depth groove according to claim 7, characterized in that: The second sacrificial layer is a silicon oxide layer or a silicon nitride layer.

9. The method for manufacturing a double-depth groove according to claim 7, characterized in that: After removing part of the hard mask layer, the second process narrow deep trench becomes the third process narrow deep trench, and the second process wide shallow trench becomes the third process wide shallow trench; After the first sacrificial layer in the third process narrow and deep trench is removed, a fourth process narrow and deep trench is formed, and the third process wide and shallow trench becomes a fourth process wide and shallow trench.

10. The method for manufacturing a double-depth groove according to claim 9, characterized in that: Processing the fourth process narrow and deep groove to a depth of a target narrow and deep groove to obtain a target narrow and deep groove; The second sacrificial layer and the protective layer in the wide and shallow trench of the fourth process are removed to obtain the target wide and shallow trench.

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