BCD device structure and method of forming the same

Abstract

The application provides a BCD device structure and a forming method thereof, a first epitaxial layer and a second epitaxial layer are formed on a substrate in the BCD device structure, a first isolation buried layer is formed in the first epitaxial layer, phosphorus diffusion in the first isolation buried layer can increase the depletion area of an N-type region, both sides of the N-type region and a P-type region participate in depletion, a gradual junction is formed between the first isolation buried layer and the substrate, and the breakdown voltage between the first isolation buried layer and the substrate is improved. A second isolation buried layer is formed in the first epitaxial layer, the second isolation buried layer is located in the first isolation buried layer, a deep well is formed in the second epitaxial layer, the first isolation buried layer diffuses into the second epitaxial layer when the deep well is formed, the deep well is electrically connected with the second isolation buried layer through the first isolation buried layer to form an isolation structure, and since the first isolation buried layer diffuses into the second epitaxial layer when the deep well is formed, the connection between the deep well and the second isolation buried layer is enhanced, and the process difficulty or production cost of the deep well is reduced.

Description

Technical Field

[0001] This invention relates to the field of integrated circuit technology, and in particular to a BCD device structure and its formation method. Background Technology

[0002] Conventional isolation devices use an N-type buried layer (NBL) to create isolation on a P-type substrate, connected by an N-type deep well (DNW), and form a contact plug on the silicon surface to provide a stable potential.

[0003] However, in the design of high-voltage devices, as the applied voltage increases, the required withstand voltage depth becomes deeper, necessitating deeper burial of the N-type isolation layer. This increases the difficulty of connecting the N-type deep well to the N-type isolation layer. Conventional methods involve multiple epitaxial cycles and epitaxial layers to implant the N-type deep well, or using a thermal drive-in process to push the N-type deep well deeper. However, these methods significantly increase production costs.

[0004] Meanwhile, higher application voltages place higher demands on the withstand voltage and punch-through protection of N-type buried isolation layers. N-type buried isolation layers capable of preventing high-voltage punch-through require sufficiently high peak concentrations, but high-concentration N-type buried isolation layers often fail to provide sufficiently high withstand voltage capabilities.

[0005] In addition, some BCD (bipolar, CMOS and DMOS devices fabricated on the same chip) process platforms require a P+ type substrate, in which case it is difficult to achieve a high breakdown voltage (BV) at the junction from the N-type buried isolation layer to the P+ type substrate. Summary of the Invention

[0006] The purpose of this invention is to provide a BCD device structure and a method for forming the same, so as to improve the breakdown voltage of the junction between the buried isolation layer and the P+ type substrate in the BCD device structure and enhance the connection between the deep well and the buried isolation layer.

[0007] To solve the above-mentioned technical problems, the present invention provides a BCD device structure, comprising:

[0008] A substrate, wherein a first epitaxial layer and a second epitaxial layer are formed on the substrate;

[0009] A first isolation buried layer is formed within the first epitaxial layer and diffuses into the second epitaxial layer, and a gradual junction is formed between the first isolation buried layer and the substrate;

[0010] The second isolation layer is located within the first epitaxial layer and within the first isolation layer;

[0011] A deep well is located within the second epitaxial layer, and the deep well is electrically connected to the second isolation layer through the first isolation layer to form an isolation structure.

[0012] Optionally, the substrate is doped with a first doping type, and the first buried isolation layer, the second buried isolation layer, and the deep well are all doped with a second doping type.

[0013] Optionally, the first doping type is P-type, and the second doping type is N-type.

[0014] Optionally, the first isolation buried layer and the deep trap are doped with phosphorus, and the second isolation buried layer is doped with antimony.

[0015] Optionally, the doping dose of the first isolation buried layer is less than the doping dose of the second isolation buried layer.

[0016] Optionally, the doping dose of the first isolation buried layer is one-hundredth to one-tenth of the doping dose of the second isolation buried layer.

[0017] Optionally, the injection depth of the first isolation layer is greater than the injection depth of the second isolation layer.

[0018] Based on the same inventive concept, the present invention also provides a method for forming a BCD device structure, comprising:

[0019] A substrate is provided on which a first epitaxial layer is formed;

[0020] A first ion implantation process is performed to form a first isolation buried layer within the first epitaxial layer, and a gradual junction is formed between the first isolation buried layer and the substrate;

[0021] A second ion implantation process is performed to form a second isolation buried layer within the first epitaxial layer, wherein the second isolation buried layer is located within the first isolation buried layer;

[0022] An epitaxial growth process is performed to form a second epitaxial layer, which is located on the first isolation buried layer;

[0023] The third ion implantation process and the thermal push-well process are executed sequentially to form a deep well in the second epitaxial layer. In the thermal push-well process, the first isolation buried layer extends into the second epitaxial layer, and the deep well is electrically connected to the second isolation buried layer through the first isolation buried layer to form an isolation structure.

[0024] Optionally, the first isolation buried layer and the deep trap are doped with phosphorus, and the second isolation buried layer is doped with antimony.

[0025] Optionally, the doping dose of the first isolation buried layer is less than the doping dose of the second isolation buried layer, and the implantation depth of the first isolation buried layer is greater than the implantation depth of the second isolation buried layer.

[0026] In a BCD device structure provided by this invention, a first epitaxial layer and a second epitaxial layer are formed on a substrate. A first buried isolation layer is formed within the first epitaxial layer. By adding the first buried isolation layer, the phosphorus diffusion in the first buried isolation layer increases the depletion area of ​​the N-type region. Both the N-type and P-type regions participate in depletion. A gradual junction is formed between the first buried isolation layer and the substrate, increasing the breakdown voltage between the first buried isolation layer and the substrate. A second buried isolation layer is formed within the first buried isolation layer. A deep well is formed within the second epitaxial layer. During the formation of the deep well, the first buried isolation layer diffuses into the second epitaxial layer. The deep well is electrically connected to the second buried isolation layer through the first buried isolation layer to form an isolation structure. Because the first buried isolation layer diffuses into the second epitaxial layer during the formation of the deep well, the connection between the deep well and the second buried isolation layer is enhanced, reducing the process difficulty or production cost of the deep well. Attached Figure Description

[0027] Those skilled in the art will understand that the accompanying drawings are provided to better understand the invention and do not constitute any limitation on the scope of the invention. Wherein:

[0028] Figure 1 This is a schematic diagram of the BCD device structure according to an embodiment of the present invention.

[0029] Figure 2 This is a flowchart of the method for forming the BCD device structure according to an embodiment of the present invention.

[0030] Figures 3 to 4 This is a schematic diagram of the structural steps corresponding to the method for forming the BCD device structure according to an embodiment of the present invention.

[0031] Figure 5 This is a doping curve diagram of the BCD device structure in an embodiment of the present invention.

[0032] Figure 6 This is a breakdown voltage curve between the N-type isolation buried layer and the P-type substrate of the BCD device structure according to an embodiment of the present invention.

[0033] In the attached image:

[0034] 10-Substrate; 11-First epitaxial layer; 12-First buried isolation layer; 13-Second buried isolation layer; 14-Second epitaxial layer; 15-Deep well; 16-Conductive contact region. Detailed Implementation

[0035] To make the objectives, advantages, and features of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that the drawings are all in a very simplified form and are not drawn to scale, and are only used to facilitate and clarify the explanation of the embodiments of this invention. Furthermore, the structures shown in the drawings are often part of the actual structures. In particular, different figures may emphasize different aspects and may sometimes use different scales.

[0036] As used in this invention, the singular forms “a,” “an,” and “the” include plural objects; the term “or” is generally used to mean “and / or”; the term “a number” is generally used to mean “at least one”; and the term “at least two” is generally used to mean “two or more”. Furthermore, the terms “first,” “second,” and “third” are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with “first,” “second,” or “third” may explicitly or implicitly include one or at least two of that feature. Additionally, as used in this invention, the placement of one element on another element generally only indicates a connection, coupling, cooperation, or transmission relationship between the two elements, which can be direct or indirect through an intermediate element. It should not be construed as indicating or implying a spatial positional relationship between the two elements, i.e., one element can be located arbitrarily inside, outside, above, below, or to one side of the other element, unless otherwise explicitly stated. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0037] Figure 1 This is a schematic diagram of the BCD device structure according to an embodiment of the present invention. Figure 1 As shown, this embodiment provides a BCD device structure, including:

[0038] Substrate 10, on which a first epitaxial layer 11 and a second epitaxial layer 14 are formed;

[0039] A first isolation buried layer 12 is formed in the first epitaxial layer 11 and diffuses into the second epitaxial layer 14. A gradual junction is formed between the first isolation buried layer 12 and the substrate 10.

[0040] The second isolation layer 13 is located within the first epitaxial layer 11 and within the first isolation layer 12;

[0041] The deep well 15 is located within the second epitaxial layer 14, and the deep well 15 is electrically connected to the second isolation layer 13 through the first isolation layer 12 to form an isolation structure.

[0042] Please continue to refer to this. Figure 1 The substrate 10 provides an operating platform for subsequent processes. It can be any substrate known to those skilled in the art for supporting semiconductor integrated circuit components, such as a bare die or a wafer processed by epitaxial growth. Specifically, the substrate 10 is, for example, a silicon-on-insulator (SOI) substrate, a bulk silicon substrate, a germanium substrate, a germanium-silicon substrate, an indium phosphide (InP) substrate, a gallium arsenide (GaAs) substrate, or a germanium-on-insulator substrate. In this embodiment, the substrate 10 is a silicon substrate. The substrate 10 is doped with a first doping type, such as P-type. In some embodiments, the substrate 10 is, for example, P+ type. A first epitaxial layer 11 is formed on the substrate 10, and the first epitaxial layer 11 is doped with the first doping type, that is, the first epitaxial layer 11 is P-type. A first buried isolation layer 12 and a second buried isolation layer 13 are formed within the first epitaxial layer 11, with the second buried isolation layer 13 located within the first buried isolation layer 12. Both the first buried isolation layer 12 and the second buried isolation layer 13 are doped with the second doping type, meaning they are N-type buried isolation layers (NBL). Specifically, the first buried isolation layer 12 is doped with phosphorus, and the second buried isolation layer 13 is doped with antimony. Higher application voltages place higher demands on the isolation of N-type buried isolation layers for voltage withstand and punch-through protection. N-type buried isolation layers capable of preventing high-voltage punch-through require sufficiently high peak concentrations; therefore, the antimony doping level in the second buried isolation layer 13 is, for example, 10. 14 cm -3 Compared to antimony, phosphorus diffuses faster and farther; therefore, the doping dose of the first buried isolation layer 12 is less than that of the second buried isolation layer 13. For example, the doping dose of the first buried isolation layer 12 is one-hundredth to one-tenth of the doping dose of the second buried isolation layer 13. Because phosphorus diffuses faster and farther, it is implanted deeper to avoid affecting devices within the upper isolation region. Therefore, the implantation depth of the first buried isolation layer 12 is greater than that of the second buried isolation layer 13.

[0043] Please continue to refer to this. Figure 1A second epitaxial layer 14 is formed on the second buried isolation layer 13, and a deep well 15 is formed within the second epitaxial layer 14. The second epitaxial layer 14 is doped with a first doping type, that is, P-type. The deep well 15 is doped with a second doping type, that is, N-type. For example, the doping element of the deep well 15 is phosphorus. In the process of forming the deep well 15, the first buried isolation layer 12 diffuses upward into the second epitaxial layer 14 and electrically connects with the deep well 15 to form an isolation structure. The isolation structure surrounds an isolation region, within which a MOS device is formed. The isolation structure is used to isolate adjacent MOS devices and to isolate the MOS device from the substrate 10. A conductive contact region 16 is also formed within the deep well 15. The conductive contact region 16 is, for example, N+ type ions, used to reduce the contact resistance between the deep well 15 and the conductive layer. This embodiment effectively enhances the connection between the deep well 15 and the second buried isolation layer 13 by forming a first buried isolation layer 12. It eliminates the need for a higher-temperature, longer-time push-well process or multiple epitaxial processes, reducing process difficulty and cost. Furthermore, in the prior art, with only the second buried layer 13, the antimony concentration in the N-type buried isolation layer is too high and does not diffuse. The resulting N-type buried isolation layer and substrate (NBL-to-Psub) form a single-sided abrupt junction, with the depletion region concentrated on the P-type substrate side, making it difficult to increase the breakdown voltage between the N-type buried isolation layer and the substrate. In this embodiment, by forming the first buried isolation layer 12, the phosphorus in the first buried isolation layer 12 diffuses, increasing the depletion area of ​​the N-type region. Both the N-type and P-type regions participate in depletion, forming a gradual junction between the first buried isolation layer 12 and the substrate 10. This gradual junction improves the breakdown voltage between the first buried isolation layer 12 and the substrate 10.

[0044] Figure 2 This is a flowchart illustrating the method for forming a BCD device structure according to an embodiment of the present invention. Figure 2 As shown, this embodiment also provides a method for forming a BCD device structure, including:

[0045] Step S10: Provide a substrate on which a first epitaxial layer is formed;

[0046] Step S20: Perform a first ion implantation process to form a first isolation buried layer in the first epitaxial layer, and form a gradual junction between the first isolation buried layer and the substrate;

[0047] Step S30: Perform a second ion implantation process to form a second isolation buried layer within the first epitaxial layer, wherein the second isolation buried layer is located within the first isolation buried layer;

[0048] Step S40: Perform an epitaxial growth process to form a second epitaxial layer, the second epitaxial layer being located on the first isolation buried layer;

[0049] Step S50: The third ion implantation process and the thermal push-well process are executed sequentially to form a deep well in the second epitaxial layer. In the thermal push-well process, the first isolation buried layer extends into the second epitaxial layer, and the deep well is electrically connected to the second isolation buried layer through the first isolation buried layer to form an isolation structure.

[0050] Figures 3 to 4 This is a schematic diagram corresponding to the steps of the method for forming the BCD device structure according to an embodiment of the present invention. To make the above-mentioned objectives, features, and beneficial effects of the present invention more apparent and understandable, the following description is provided in conjunction with the appendix to the specification. Figures 3 to 4 Specific embodiments of the present invention will be described in detail below.

[0051] Please refer to Figure 3 A substrate 10 is provided, which serves as an operating platform for subsequent processes. The substrate 10 can be any substrate known to those skilled in the art for supporting semiconductor integrated circuit components, such as a bare die or a wafer processed by epitaxial growth. Specifically, the substrate 10 can be, for example, a silicon-on-insulator (SOI) substrate, a bulk silicon substrate, a germanium substrate, a germanium-silicon substrate, an indium phosphide (InP) substrate, a gallium arsenide (GaAs) substrate, or a germanium-on-insulator substrate. In this embodiment, the substrate 10 is a silicon substrate. The substrate 10 is doped with a first doping type, such as P-type. In some embodiments, the substrate 10 is, for example, P+ type. A first epitaxial layer 11 is formed on the substrate 10, and the first epitaxial layer 11 is doped with the first doping type, i.e., the first epitaxial layer 11 is P-type.

[0052] Please continue to refer to this. Figure 3 A first ion implantation process is performed to form a first buried isolation layer 12 within the first epitaxial layer 11, and a gradient junction is formed between the first buried isolation layer 12 and the substrate 10. The first buried isolation layer 12 is doped with a second doping type, that is, the first buried isolation layer 12 is an N-type buried isolation layer (NBL). Specifically, the doping element of the first buried isolation layer 12 is phosphorus.

[0053] Please continue to refer to this. Figure 3 A second ion implantation process is performed to form a second buried isolation layer 13 within the first epitaxial layer 11. The second buried isolation layer 13 is located within the first buried isolation layer 12. The doping type of the second buried isolation layer 13 is a second doping type, that is, the second buried isolation layer 13 is an N-type buried isolation layer (NBL). Specifically, the doping element of the second buried isolation layer 13 is antimony, and the antimony doping amount of the second buried isolation layer 13 is, for example, 10. 14 cm -3 .

[0054] Compared to antimony, phosphorus diffuses faster and farther; therefore, the doping dose of the first buried isolation layer 12 is less than that of the second buried isolation layer 13. For example, the doping dose of the first buried isolation layer 12 is one-hundredth to one-tenth of the doping dose of the second buried isolation layer 13. Because phosphorus diffuses faster and farther, it is implanted deeper to avoid affecting devices within the upper isolation region. Therefore, the implantation depth of the first buried isolation layer 12 is greater than that of the second buried isolation layer 13.

[0055] Please refer to Figure 4 An epitaxial growth process is performed to form a second epitaxial layer 14, which is located on the first isolation buried layer 12. The doping type of the second epitaxial layer 14 is the first doping type, that is, the doping type of the second epitaxial layer 14 is P-type.

[0056] Please refer to Figure 1 A third ion implantation process and a thermal push-in process are performed to form a deep well 15 within the second epitaxial layer 14. In the thermal push-in process, the first buried isolation layer 12 extends into the second epitaxial layer 14, and the deep well 15 is electrically connected to the second buried isolation layer 13 through the first buried isolation layer 12 to form an isolation structure. The deep well 15 is doped with the second doping type, i.e., N-type. For example, the doping element of the deep well 15 is phosphorus. In the thermal push-in process forming the deep well 15, the first buried isolation layer 12 diffuses upward into the second epitaxial layer 14 and is electrically connected to the deep well 15 to form an isolation structure. The isolation structure encloses an isolation region, within which a MOS device is formed. The isolation structure is used to isolate adjacent MOS devices and to isolate the MOS devices from the substrate 10.

[0057] Please continue to refer to this. Figure 1 A conductive contact region 16 is formed within the deep well 15, which can be formed by implanting N+ type ions through an ion implantation process to reduce the contact resistance between the deep well 15 and the conductive layer.

[0058] This embodiment effectively enhances the connection between the deep well 15 and the second buried isolation layer 13 by forming a first buried isolation layer 12. It eliminates the need for a higher-temperature, longer-time push-well process or multiple epitaxial processes, reducing process difficulty and cost. Furthermore, in the prior art, with only the second buried layer 13, the antimony concentration in the N-type buried isolation layer is too high and does not diffuse. The resulting N-type buried isolation layer and substrate (NBL-to-Psub) form a single-sided abrupt junction, with the depletion region concentrated on the P-type substrate side, making it difficult to increase the breakdown voltage between the N-type buried isolation layer and the substrate. In this embodiment, by forming the first buried isolation layer 12, the phosphorus in the first buried isolation layer 12 diffuses, increasing the depletion area of ​​the N-type region. Both the N-type and P-type regions participate in depletion, forming a gradual junction between the first buried isolation layer 12 and the substrate 10. This gradual junction improves the breakdown voltage between the first buried isolation layer 12 and the substrate 10.

[0059] Figure 5 This is a doping curve diagram of the BCD device structure in an embodiment of the present invention. Figure 5 As shown, the horizontal axis represents the depth from the silicon substrate surface (Depth from Si top), in micrometers (µm). The vertical axis represents the doping concentration of each dopant element, in the number of impurity atoms per cubic centimeter (cm³). -3The boron doping curve (blue curve) indicates that the doping concentration increases from the silicon surface to the silicon interior. Specifically, the boron doping concentration in the second epitaxial layer 14 and the first epitaxial layer 11 is lower than that in the substrate 10. In this embodiment, the substrate 10 is P+ type. The antimony doping curve (yellow curve) is located 6-7 μm from the silicon surface, where the second buried isolation layer 13 is located within the first epitaxial layer 11. The antimony doping curve rises and falls sharply, indicating that the antimony concentration in the second buried isolation layer 13 is too high and does not diffuse. Therefore, with only the second buried isolation layer 13, the junction between the second buried isolation layer 13 and the substrate 10 (NBL-to-Psub) is a single-sided abrupt junction, with the depletion region concentrated on one side of the substrate 10. This makes it difficult to increase the breakdown voltage between the second buried isolation layer 13 and the substrate 10. The phosphorus-1 doping curve (orange curve) is the doping curve for an N-type deep well in the prior art. As the silicon depth increases, the phosphorus doping concentration decreases sharply, making the connection between phosphorus and antimony difficult. Because high-voltage devices require deep N-type deep wells, and as the applied voltage increases, the required depth for the withstand voltage of high-voltage devices becomes increasingly deeper, the N-type buried isolation layer needs to be buried even deeper. This increases the difficulty of connecting the N-type deep wells to the N-type buried isolation layers. Conventional methods include multiple epitaxial layers and N-type deep well implantation, or using a strong thermal drive-in process to push the N-type deep wells deeper. However, these methods significantly increase production costs. In this embodiment, a first buried isolation layer 12 is added. Since the doping element of the first buried isolation layer 12 is phosphorus, phosphorus diffuses easily. During the thermal drive-in process of the N-type deep well, the phosphorus in the first buried isolation layer 12 diffuses upwards, effectively increasing the connection between the first buried isolation layer 12 and the N-type deep well. The phosphorus-2 curve (gray curve) shows that on the silicon surface, the phosphorus doping concentration decreases with increasing silicon depth. After reaching the first buried isolation layer 12, the phosphorus concentration first increases and then decreases, extending to the edge of the first epitaxial layer 11. Therefore, the first isolation buried layer 12 in this embodiment effectively enhances the connection between the second isolation buried layer 13 and the deep well 15, eliminating the need for a push-well process with higher temperatures and longer time, or multiple epitaxial processes, thus reducing the process difficulty and cost. At the same time, the addition of the first isolation buried layer 12, i.e., the addition of phosphorus implantation, allows the diffused phosphorus to increase the depletion area of ​​the N-type region. Both sides of the N-type and P-type regions participate in the depletion, and a gradual junction is formed between the first isolation buried layer 12 and the substrate 10, thereby improving the breakdown voltage between the first isolation buried layer 12 and the substrate 10.

[0060] Figure 6 This is a breakdown voltage curve between the N-type buried isolation layer and the P-type substrate of the BCD device structure according to an embodiment of the present invention. The horizontal axis represents voltage (V), and the vertical axis represents current (A). Figure 6As shown, the yellow curve represents the breakdown voltage curve between the N-type buried isolation layer and the P-type substrate in the BCD device structure of the prior art, while the blue curve represents the breakdown voltage curve between the N-type buried isolation layer and the P-type substrate in the BCD device structure of this embodiment. The breakdown voltage of the yellow curve is 165V to 175V, and the breakdown voltage of the blue curve is 210V to 220V. The breakdown voltage between the N-type buried isolation layer and the P-type substrate is increased by 30%, which means that the junction breakdown voltage between the N-type buried isolation layer and the P-type substrate is improved.

[0061] In summary, in the BCD device structure and its formation method provided in this embodiment of the invention, a first epitaxial layer and a second epitaxial layer are formed on the substrate of the BCD device structure. A first buried isolation layer is formed within the first epitaxial layer. By adding the first buried isolation layer, the phosphorus diffusion in the first buried isolation layer can increase the depletion area of ​​the N-type region. Both the N-type and P-type regions participate in depletion. A gradual junction is formed between the first buried isolation layer and the substrate, which improves the breakdown voltage between the first buried isolation layer and the substrate. A second buried isolation layer is formed within the first buried isolation layer. A deep well is formed within the second epitaxial layer. When forming the deep well, the first buried isolation layer diffuses into the second epitaxial layer. The deep well is electrically connected to the second buried isolation layer through the first buried isolation layer to form an isolation structure. Since the first buried isolation layer diffuses into the second epitaxial layer when forming the deep well, the connection between the deep well and the second buried isolation layer is enhanced, reducing the process difficulty and production cost of the deep well.

[0062] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Similar or identical parts between embodiments can be referred to mutually. In addition, different parts between embodiments can also be combined with each other, and this invention does not limit this.

[0063] Furthermore, it should be understood that although the present invention has been disclosed above with reference to preferred embodiments, these embodiments are not intended to limit the present invention. For any person skilled in the art, many possible variations and modifications can be made to the technical solutions of the present invention based on the disclosed technical content, or equivalent embodiments can be modified accordingly, without departing from the scope of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the content of the present invention, shall still fall within the scope of protection of the present invention.

Claims

1. A BCD device structure, characterized in that, include: A substrate, wherein a first epitaxial layer and a second epitaxial layer are formed on the substrate; A first isolation buried layer is formed within the first epitaxial layer and diffuses into the second epitaxial layer, and a gradual junction is formed between the first isolation buried layer and the substrate; The second isolation layer is located within the first epitaxial layer and within the first isolation layer; A deep well is located within the second epitaxial layer, and the deep well is electrically connected to the second isolation layer through the first isolation layer to form an isolation structure.

2. The BCD device structure according to claim 1, characterized in that, The substrate is doped with a first doping type, and the first buried isolation layer, the second buried isolation layer, and the deep well are all doped with a second doping type.

3. The BCD device structure according to claim 2, characterized in that, The first doping type is P-type, and the second doping type is N-type.

4. The BCD device structure according to claim 3, characterized in that, The first isolation buried layer and the deep trap are doped with phosphorus, and the second isolation buried layer is doped with antimony.

5. The BCD device structure according to claim 1, characterized in that, The doping dose of the first isolation buried layer is less than the doping dose of the second isolation buried layer.

6. The BCD device structure according to claim 5, characterized in that, The doping dose of the first isolation buried layer is one-hundredth to one-tenth of the doping dose of the second isolation buried layer.

7. The BCD device structure according to claim 1, characterized in that, The injection depth of the first isolation layer is greater than the injection depth of the second isolation layer.

8. A method for forming a BCD device structure, characterized in that, include: A substrate is provided, on which a first epitaxial layer is formed; A first ion implantation process is performed to form a first isolation buried layer within the first epitaxial layer, and a gradual junction is formed between the first isolation buried layer and the substrate; A second ion implantation process is performed to form a second isolation buried layer within the first epitaxial layer, wherein the second isolation buried layer is located within the first isolation buried layer; An epitaxial growth process is performed to form a second epitaxial layer, which is located on the first isolation buried layer; The third ion implantation process and the thermal push-well process are executed sequentially to form a deep well in the second epitaxial layer. In the thermal push-well process, the first isolation buried layer extends into the second epitaxial layer, and the deep well is electrically connected to the second isolation buried layer through the first isolation buried layer to form an isolation structure.

9. The method for forming a BCD device structure according to claim 8, characterized in that, The first isolation buried layer and the deep trap are doped with phosphorus, and the second isolation buried layer is doped with antimony.

10. The method for forming a BCD device structure according to claim 8, characterized in that, The doping dose of the first isolation buried layer is less than that of the second isolation buried layer, and the implantation depth of the first isolation buried layer is greater than that of the second isolation buried layer.

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