Trench structure preparation method and trench structure

Abstract

The invention discloses a trench structure preparation method and a trench structure, and belongs to the field of semiconductor manufacturing, and the method comprises the steps: forming a patterned mask layer on the surface of a wafer; the patterned mask layer is provided with a groove pattern; etching the wafer along the thickness direction according to the groove pattern to form an initial groove; forming a first groove of which the inner surface is covered with a protective layer based on the initial groove; the depth of the first groove is equal to that of the initial groove; the width of the first groove is greater than that of the initial groove; etching the protective layer at the bottom of the first groove along the thickness direction according to the groove pattern to expose the wafer; etching the exposed wafer along the thickness direction to form a second groove; the width of the second groove is smaller than that of the first groove; and removing the patterned mask layer and the residual protective layer to form a groove structure. According to the method, the bowl-mouth-shaped groove structure is prepared through the step of forming the groove twice, and polycrystalline silicon can be better filled in the groove.

Description

Technical Field

[0001] The present application relates to the field of semiconductor manufacturing, and in particular to a method for preparing a trench structure and a trench structure. Background Art

[0002] In the existing trench structures, especially the SGT (Shield Gate Trench) structures with a large trench depth-width ratio, the problem of polysilicon filling closing is prone to occur when filling polysilicon in the trench, forming filling gaps inside the polysilicon, causing the length of the polysilicon to be uneven in the subsequent polysilicon etching, and the top of the polysilicon to form a sharp corner. This affects the electrical performance of the device, reduces the device's withstand voltage, and increases leakage between oxide layers. Summary of the invention

[0003] The purpose of this application is to provide a trench structure preparation method and a trench structure. Under the same device size, an improved process preparation method can be used to form a new trench structure, which can solve the closing problem during polysilicon filling, ensure that the polysilicon is filled intact without gaps, and solve the problem of device performance failure.

[0004] To achieve the above objectives, the present application provides a method for preparing a groove structure, comprising:

[0005] Forming a patterned mask layer on the surface of the wafer; the patterned mask layer has a groove pattern;

[0006] Etching the wafer along the thickness direction according to the groove pattern to form an initial groove;

[0007] A first groove whose inner surface is covered with a protective layer is formed based on the initial groove; the depth of the first groove is equal to the depth of the initial groove; and the width of the first groove is greater than the width of the initial groove;

[0008] Etching the protective layer at the bottom of the first groove along the thickness direction according to the groove pattern to expose the wafer;

[0009] Etching the exposed wafer along the thickness direction to form a second groove; the width of the second groove is smaller than the width of the first groove;

[0010] The patterned mask layer and the remaining protection layer are removed to form a trench structure.

[0011] Optionally, after removing the patterned mask layer and the remaining protection layer to form a trench structure, the method further includes:

[0012] forming an isolation layer on the surface of the wafer having the groove structure formed thereon;

[0013] The trench structure covered with the isolation layer is filled with polysilicon.

[0014] Optionally, forming an isolation layer on the surface of the wafer having the groove structure formed thereon comprises:

[0015] forming the isolation layer on the surface of the wafer having the groove structure formed thereon by oxidation;

[0016] Alternatively, the isolation layer is formed on the surface of the wafer having the groove structure formed thereon by deposition.

[0017] Optionally, forming an isolation layer on the surface of the wafer having the groove structure formed thereon comprises:

[0018] forming a first isolation layer on the surface of the wafer having the groove structure formed thereon by oxidation;

[0019] A second isolation layer is formed on a surface of the first isolation layer facing away from the wafer by deposition.

[0020] Optionally, forming a patterned mask layer on the surface of the wafer includes:

[0021] Depositing the mask layer on the surface of the wafer;

[0022] Coating a photoresist layer on the surface of the mask layer facing away from the wafer, and using a photomask for exposure and development to form a photolithography pattern;

[0023] After etching the mask layer along the thickness direction according to the photolithography pattern, the photoresist layer is removed to form the patterned mask layer.

[0024] Optionally, removing the patterned mask layer and the remaining protection layer to form a trench structure includes:

[0025] The patterned mask layer and the remaining protection layer are removed by wet etching to form the trench structure.

[0026] Optionally, the step of forming a first groove having an inner surface covered with a protective layer based on the initial groove includes:

[0027] The wafer with a preset thickness at the periphery of the initial groove undergoes an oxidation reaction through an oxidation process to form the first groove whose inner surface is covered with the protective layer; the protective layer is an oxide layer.

[0028] Optionally, the step of forming a first groove having an inner surface covered with a protective layer based on the initial groove includes:

[0029] Etching the sidewall of the initial trench using isotropic dry etching to form the first trench;

[0030] The protection layer is formed on the inner surface of the first groove.

[0031] Optionally, the protective layer includes an oxide layer or a nitride layer.

[0032] To achieve the above objectives, the present application also provides a groove structure, including: a wafer; a groove structure formed on the surface of the wafer; the groove structure includes a second groove and a first groove connected in sequence along the thickness direction; the width of the second groove is smaller than the width of the first groove.

[0033] The present application provides a method for preparing a groove structure, comprising: forming a patterned mask layer on the surface of a wafer; the patterned mask layer has a groove pattern; etching the wafer along the thickness direction according to the groove pattern to form an initial groove; forming a first groove whose inner surface is covered with a protective layer based on the initial groove; the depth of the first groove is equal to the depth of the initial groove; the width of the first groove is greater than the width of the initial groove; etching the protective layer at the bottom of the first groove along the thickness direction according to the groove pattern to expose the wafer; etching the exposed wafer along the thickness direction to form a second groove; the width of the second groove is less than the width of the first groove; removing the patterned mask layer and the remaining protective layer to form a groove structure. Obviously, the present application obtains the second groove and the first groove connected in sequence along the thickness direction through two steps of forming the groove, and the width of the second groove is smaller than the width of the first groove, so that in the groove with the same depth as the traditional groove, a groove structure with a large opening size and a small depth-to-width ratio is formed, and a bowl-shaped groove structure is prepared, so that polysilicon can be better filled in the groove under the same polysilicon filling technology. The present application also provides a groove structure with the above-mentioned beneficial effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0035] Figure 1 This is a physical picture of an existing groove structure;

[0036] Figure 2 A flow chart of a method for preparing a groove structure provided in an embodiment of the present application;

[0037] Figures 3 to 12 A schematic diagram of a process for preparing a groove structure provided in an embodiment of the present application;

[0038] Fig.13 A physical diagram of a groove structure provided in an embodiment of the present application.

[0039] The following are the descriptions of the reference numerals:

[0040] 1-wafer; 2-mask layer; 3-photoresist; 4-initial trench; 5-first trench; 6-protective layer; 7-second trench; 8-isolation layer; 9-polysilicon. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings 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 ordinary technicians in this field without creative work are within the scope of protection of this application.

[0042] Please refer to Figure 1 The arrow indicates the polysilicon filling gap that occurs during the polysilicon filling process of the existing trench structure. The filling gap of polysilicon causes failure in the performance of the device, especially in the SGT MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) device, which has a polysilicon etching step after polysilicon filling, resulting in uneven lengths of polysilicon etching and a concave shape on the top of the polysilicon, which affects the electrical performance of the device, reduces the withstand voltage of the device and increases leakage between oxide layers.

[0043] Therefore, the present application provides a method for preparing a groove structure. Using the new groove structure preparation method, a bowl-shaped groove structure with a large upper opening size and a small lower size can be formed. When filling with polysilicon, the groove structure can be better filled due to the large opening size above the groove structure, which can solve the problem of polysilicon filling gaps existing in the existing structure and improve the performance of the device.

[0044] Please refer to Figure 2 , Figure 2 A flow chart of a method for preparing a groove structure provided in an embodiment of the present application, the method may include:

[0045] S101: forming a patterned mask layer on the surface of the wafer; the patterned mask layer has a groove pattern.

[0046] This embodiment does not limit the specific method of forming the patterned mask layer 2, and may be but is not limited to the following methods:

[0047] Depositing a mask layer 2 on the surface of the wafer 1;

[0048] A photoresist layer is coated on the surface of the mask layer 2 facing away from the wafer 1, and a photomask is used for exposure and development to form a photolithography pattern;

[0049] After the mask layer 2 is etched along the thickness direction according to the photolithography pattern, the photoresist layer is removed to form a patterned mask layer 2.

[0050] It should be noted that in this embodiment, the width of the photolithography pattern is the same as the width of the groove pattern. The mask layer 2 is etched along the thickness direction according to the photolithography pattern to form a groove pattern in the mask layer 2. The obtained mask layer 2 with the groove pattern is a patterned mask layer 2.

[0051] This embodiment does not limit the specific material of the mask layer 2, and the mask layer 2 may be an oxide layer or other types of materials. Accordingly, the patterned mask layer 2 may be an oxide layer or other types of materials.

[0052] This embodiment does not limit the specific material of the photoresist layer. For example, the photoresist layer may be photoresist 3 or other types of photoresist materials.

[0053] This embodiment does not limit the specific material of the wafer 1. For example, the wafer 1 may be silicon or other types of materials.

[0054] S102: Etching the wafer along the thickness direction according to the groove pattern to form an initial groove.

[0055] This embodiment does not limit the specific depth of the initial groove 4, and the specific depth of the initial groove 4 can be set according to product requirements.

[0056] S103: forming a first groove whose inner surface is covered with a protective layer based on the initial groove; the depth of the first groove is equal to the depth of the initial groove; and the width of the first groove is greater than the width of the initial groove.

[0057] This embodiment does not limit the specific method of forming the first groove 5 with the inner surface covered with the protective layer 6, for example, the following method can be used:

[0058] (1) The wafer 1 with a preset thickness at the periphery of the initial groove 4 is oxidized by an oxidation process to form a first groove 5 with an inner surface covered with a protective layer 6; the protective layer 6 is an oxide layer.

[0059] The present embodiment does not limit the specific material of the protective layer 6 , and the specific material of the protective layer 6 may be determined according to the specific material of the wafer 1 . For example, when the wafer 1 is silicon, the protective layer 6 may be silicon oxide.

[0060] It should be noted that the oxide layer in this embodiment serves to consume the wafer 1 by oxidation reaction during the oxidation process, so that the size of the opening of the initial groove 4 is slightly larger than the size of the opening of the mask layer 2, forming the final bowl-shaped shape. Another function is that the oxide layer can serve as a protective layer 6 to protect the sidewalls of the first groove 5 and avoid damage to the sidewalls during the second groove etching process. This embodiment adopts two groove etching steps, and uses an oxidation process in the first groove etching to consume the original wafer 1 and form an oxide layer on the sidewalls of the groove. The oxidized and consumed wafer 1 enlarges the size of the upper opening of the groove, which can effectively improve the filling problem of polysilicon 9.

[0061] (2) Etching the sidewall of the initial trench 4 by isotropic dry etching to form a first trench 5; and forming a protective layer 6 on the inner surface of the first trench 5.

[0062] The present embodiment does not limit the specific material of the protection layer 6 . For example, the protection layer 6 may include an oxide layer or a nitride layer, or other types of materials.

[0063] It should be noted that, in this embodiment, isotropic dry etching can be used instead of the above-mentioned oxidation process. In this dry etching process, the etching selectivity ratio of the wafer 1 and the mask layer 2 needs to be very large, and when isotropic dry etching is used as a substitute, an additional protective layer 6 is required to protect the side wall to prevent the second trench etching from damaging the side wall of the first trench 5.

[0064] S104: etching the protection layer at the bottom of the first groove along the thickness direction according to the groove pattern to expose the wafer.

[0065] It should be noted that, since the present embodiment etches the protective layer 6 at the bottom of the first groove 5 along the thickness direction according to the groove pattern, the width of the exposed wafer 1 is equal to the width of the groove pattern, and the exposed wafer 1 is further etched along the thickness direction, the width of the formed second groove 7 is also equal to the width of the groove pattern.

[0066] S105: etching the exposed wafer along the thickness direction to form a second groove; the width of the second groove is smaller than the width of the first groove.

[0067] This embodiment does not limit the specific depth of the second groove 7, and the specific depth of the second groove 7 can be set according to product requirements. It should be noted that in this embodiment, the sum of the depth of the first groove 5 (or initial groove 4) and the depth of the second groove 7 is equal to the depth of the traditional groove.

[0068] S106: removing the patterned mask layer and the remaining protection layer to form a trench structure.

[0069] This embodiment does not limit the specific method of removing the patterned mask layer 2 and the protective layer 6. The specific method of removing the patterned mask layer 2 and the protective layer 6 can be determined according to the specific materials of the patterned mask layer 2 and the protective layer 6. For example, when the patterned mask layer 2 is an oxide layer and the protective layer 6 is an oxide layer, the following method can be used: use wet etching to remove the patterned mask layer 2 and the remaining protective layer 6 to form a groove structure.

[0070] Furthermore, after step S106, this embodiment may further include:

[0071] Forming an isolation layer 8 on the surface of the wafer 1 having the groove structure;

[0072] The trench structure covered with the isolation layer 8 is filled with polysilicon 9 .

[0073] It should be noted that the isolation layer 8 covers both the inner surface of the trench structure and the surface of the wafer 1 other than the inner surface of the trench structure. The isolation layer 8 is located between the polysilicon 9 and the inner surface of the trench structure, and is used to isolate the wafer 1 from the polysilicon 9.

[0074] The present embodiment does not limit the specific material of the isolation layer 8 . For example, the isolation layer 8 may be an oxide layer or other types of materials.

[0075] This embodiment does not limit the specific method of forming the isolation layer 8, and the specific method of forming the isolation layer 8 can be determined according to the specific material of the isolation layer 8. For example, when the isolation layer 8 is an oxide layer, the following method can be used:

[0076] (1) forming an isolation layer 8 on the surface of the wafer 1 having the groove structure by oxidation;

[0077] (2) An isolation layer 8 is formed on the surface of the wafer 1 having the groove structure by deposition.

[0078] (3) forming a first isolation layer 8 on the surface of the wafer 1 having the groove structure by oxidation; and forming a second isolation layer 8 on the surface of the first isolation layer 8 facing away from the wafer 1 by deposition. The first isolation layer 8 and the second isolation layer 8 are both oxide layers.

[0079] Based on the above embodiments, the present application obtains a second groove and a first groove that are connected in sequence along the thickness direction through two steps of forming grooves, and the width of the second groove is smaller than the width of the first groove, thereby forming a groove structure with a large opening size and a relatively small depth to width in the groove with the same depth as the traditional groove, and preparing a bowl-shaped groove structure, thereby better filling polysilicon in the groove under the same polysilicon filling technology.

[0080] Please refer to Figures 3 to 13A groove structure provided in an embodiment of the present application may include: a wafer 1; a groove structure is formed on the surface of the wafer 1; the groove structure includes a second groove 7 and a first groove 5 connected in sequence along the thickness direction; the width of the second groove 7 is smaller than the width of the first groove 5.

[0081] Furthermore, in this embodiment, the inner surface of the trench structure and the surface of the wafer 1 other than the inner surface of the trench structure may be covered with a protective layer 6 ; and the interior of the trench structure may be filled with polysilicon 9 .

[0082] Based on the above embodiments, the present application can be prepared by the above groove structure preparation method, so it also has the above beneficial effects.

[0083] The following is a specific example to illustrate the above groove structure preparation process. Please refer to Figures 3 to 13 , the process is as follows:

[0084] Step 1: Deposit an oxide layer or other type of material on the surface of wafer 1 as a mask layer 2 for etching wafer 1 in step 3, such as Figure 3 As shown;

[0085] Step 2: Apply photoresist 3, use a mask to expose and develop to form a photolithography pattern, such as Figure 4 As shown;

[0086] Step 3: Etching the mask layer 2 and removing the photoresist 3 to form a groove pattern in the mask layer 2, such as Figure 5 As shown;

[0087] Step 4: Etching the wafer 1 for the first time to form an initial groove 4. The depth of the initial groove 4 can be set according to the requirements of the product, such as Figure 6 As shown;

[0088] Step 5: Oxidation process: an oxide layer is formed on the side wall of the initial trench 4 through the oxidation process. The oxide layer consumes the wafer 1 during the oxidation reaction, so that the opening size of the initial trench 4 is slightly larger than the opening size of the mask layer 2, forming the final bowl-shaped shape. Another function of the oxide layer is that it can serve as a protective layer 6 to protect the side wall of the first trench 5 and avoid damage to the side wall during the second trench etching process. Figure 7 As shown;

[0089] Step 6: Dry etching of the oxide layer at the bottom of the first trench 5 facilitates etching of the second trench 7. Figure 8 As shown;

[0090] Step 7: Etch the wafer 1 for the second time to form a second groove 7. The depth of the second groove 7 can be set according to product requirements, such as Fig. 9 As shown;

[0091] Step 8: Wet etching is performed to remove the mask layer 2 and the oxide layer on the sidewall of the first trench 5 to obtain a trench structure, such as Fig.10 As shown;

[0092] Step 9: The isolation layer 8 in the trench structure is an oxide layer. The isolation layer 8 can be formed by deposition, oxidation or a combination of the two to form the isolation layer 8 in the trench structure, isolating the wafer 1 from the polysilicon 9 to be filled in the next step. Fig.11 As shown;

[0093] Step 10: Fill the trench structure with polysilicon 9, such as Fig.12 and Fig.13 shown. Fig.13 A physical diagram of a groove structure provided in an embodiment of the present application, Fig.13 A bowl-shaped groove structure with a large upper opening and a small lower opening is formed. When the polysilicon 9 is filled, the larger opening at the upper end of the groove structure allows for better filling, thereby solving the polysilicon 9 filling gap problem existing in the existing structure and improving device performance.

[0094] Specific examples are used herein to illustrate the principles and implementation methods of the present application, and the embodiments are in a progressive relationship, each embodiment focuses on the differences from other embodiments, and the same and similar parts between the embodiments can be referred to each other. The description of the above embodiments is only used to help understand the method and core ideas of the present application. For ordinary technicians in this technical field, without departing from the principles of the present application, several improvements and modifications can be made to the present application, and these improvements and modifications also fall within the scope of protection of the claims of the present application.

[0095] It should also be noted that, in this specification, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprise", "include" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or equipment. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or equipment including the elements.

Claims

1. A method for preparing a groove structure, characterized in that: include: forming a patterned mask layer on the surface of the wafer; The patterned mask layer has a groove pattern; Etching the wafer along the thickness direction according to the groove pattern to form an initial groove; forming a first groove having an inner surface covered with a protective layer based on the initial groove; The depth of the first groove is equal to the depth of the initial groove; the width of the first groove is greater than the width of the initial groove; Etching the protective layer at the bottom of the first groove along the thickness direction according to the groove pattern to expose the wafer; Etching the exposed wafer along the thickness direction to form a second groove; The width of the second groove is smaller than the width of the first groove; The patterned mask layer and the remaining protection layer are removed to form a trench structure.

2. The method for preparing a groove structure according to claim 1, characterized in that: After removing the patterned mask layer and the remaining protection layer to form a trench structure, the method further includes: forming an isolation layer on the surface of the wafer having the groove structure formed thereon; The trench structure covered with the isolation layer is filled with polysilicon.

3. The method for preparing a groove structure according to claim 2, characterized in that: The step of forming an isolation layer on the surface of the wafer having the groove structure formed thereon comprises: forming the isolation layer on the surface of the wafer having the groove structure formed thereon by oxidation; Alternatively, the isolation layer is formed on the surface of the wafer having the groove structure formed thereon by deposition.

4. The method for preparing a groove structure according to claim 2, characterized in that: The step of forming an isolation layer on the surface of the wafer having the groove structure formed thereon comprises: forming a first isolation layer on the surface of the wafer having the groove structure formed thereon by oxidation; A second isolation layer is formed on a surface of the first isolation layer facing away from the wafer by deposition.

5. The method for preparing a groove structure according to claim 1, characterized in that: The step of forming a patterned mask layer on the surface of the wafer comprises: Depositing the mask layer on the surface of the wafer; Coating a photoresist layer on the surface of the mask layer facing away from the wafer, and using a photomask for exposure and development to form a photolithography pattern; After etching the mask layer along the thickness direction according to the photolithography pattern, the photoresist layer is removed to form the patterned mask layer.

6. The method for preparing a groove structure according to claim 1, characterized in that: The step of removing the patterned mask layer and the remaining protection layer to form a trench structure includes: The patterned mask layer and the remaining protection layer are removed by wet etching to form the trench structure.

7. The method for preparing a groove structure according to any one of claims 1 to 6, characterized in that: The forming of a first groove having an inner surface covered with a protective layer based on the initial groove comprises: The wafer with a preset thickness at the periphery of the initial groove undergoes an oxidation reaction through an oxidation process to form the first groove whose inner surface is covered with the protective layer; the protective layer is an oxide layer.

8. The method for preparing a groove structure according to any one of claims 1 to 6, characterized in that: The forming of a first groove having an inner surface covered with a protective layer based on the initial groove comprises: Etching the sidewall of the initial trench using isotropic dry etching to form the first trench; The protection layer is formed on the inner surface of the first groove.

9. The method for preparing a groove structure according to claim 8, characterized in that: The protection layer includes an oxide layer or a nitride layer.

10. A groove structure, characterized in that: include: Wafer; A groove structure is formed on the surface of the wafer; the groove structure comprises a second groove and a first groove that are sequentially connected along the thickness direction; The width of the second trench is smaller than the width of the first trench.

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