BCD device structure and forming method thereof

Abstract

The invention 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, the two sides of the N-type region and the two sides of a P-type region participate in depletion, and therefore the depletion area of the N-type region can be increased; and a slowly changing junction is formed between the first isolation buried layer and the substrate, so that the breakdown voltage between the first isolation buried layer and the substrate is improved. A first isolation buried layer is formed in the first epitaxial layer, 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 trap is formed in the second epitaxial layer, when the deep trap is formed, the first isolation buried layer is diffused into the second epitaxial layer, and the deep trap is electrically connected with the second isolation buried layer through the first isolation buried layer to form an isolation structure. The first isolation buried layer is diffused into the second epitaxial layer, so that the connection between the deep trap and the second isolation buried layer is enhanced, and the process difficulty or the production cost of the deep trap is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of integrated circuits, and in particular to a BCD device structure and a forming method thereof. Background Art

[0002] Conventional isolation devices use an N-type buried layer (NBL) to isolate on a P-type substrate, are connected by an N-type deep well (DNW), and form contact plugs 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 depth of withstand voltage becomes deeper and deeper, and the N-type isolation buried layer needs to be buried deeper, which will make it more difficult for the N-type deep well to connect to the N-type isolation buried layer. The conventional method is to perform N-type deep well injection in multiple epitaxy and epitaxial layers, or use a strong thermal process to push the well (thermal drive-in) to push the N-type deep well deeper, but these methods will greatly increase the production cost.

[0004] At the same time, higher application voltages place higher pressure resistance and punch-through resistance requirements on N-type isolation buried layers. N-type isolation buried layers that can prevent high-voltage punch-through require sufficiently high peak concentrations, but high-concentration N-type isolation buried layers are difficult to provide sufficiently high pressure resistance.

[0005] Also, some BCD (bipolar, CMOS and DMOS devices are made on the same chip) process platforms require a P+ type substrate (sub). In this case, it is difficult to increase the breakdown voltage (BV) of the junction from the N-type isolation buried layer to the P+ type substrate. Summary of the invention

[0006] The object of the present 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 isolation buried layer and the P+ type substrate in the BCD device structure and to enhance the connection between the deep well and the isolation buried layer.

[0007] In order to solve the above technical problems, the present invention provides a BCD device structure, comprising:

[0008] a substrate, on which a first epitaxial layer and a second epitaxial layer are formed;

[0009] A first isolation buried layer, wherein the first isolation buried layer is formed in the first epitaxial layer and diffused into the second epitaxial layer, and a graded junction is formed between the first isolation buried layer and the substrate;

[0010] a second isolation buried layer, wherein the second isolation buried layer is located in the first epitaxial layer and in the first isolation buried layer;

[0011] A deep well is located in 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.

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

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

[0014] Optionally, the doping element of the first isolation buried layer and the deep well is phosphorus, and the doping element of the second isolation buried layer is 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 percent to one tenth of the doping dose of the second isolation buried layer.

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

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

[0019] Providing a substrate, on which a first epitaxial layer is formed;

[0020] Performing a first ion implantation process to form a first isolation buried layer in the first epitaxial layer, wherein a graded junction is formed between the first isolation buried layer and the substrate;

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

[0022] Performing an epitaxial growth process to form a second epitaxial layer, wherein the second epitaxial layer is located on the first isolation buried layer;

[0023] A third ion implantation process and a thermal process well-driving process are performed in sequence to form a deep well in the second epitaxial layer. In the thermal process well-driving 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 doping element of the first isolation buried layer and the deep well is phosphorus, and the doping element of the second isolation buried layer is 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 the present invention, a first epitaxial layer and a second epitaxial layer are formed on a substrate, and a first isolation buried layer is formed in the first epitaxial layer. By adding the first isolation buried layer, the phosphorus in the first isolation buried layer can increase the depletion area of ​​the N-type region, and both sides of the N-type region and the P-type region participate in depletion. A gradual junction is formed between the first isolation buried layer and the substrate, thereby increasing the breakdown voltage between the first isolation buried layer and the substrate. A second isolation buried layer is formed in the first epitaxial layer, and the second isolation buried layer is located in the first isolation buried layer. A deep well is formed in the second epitaxial layer. When the deep well is formed, the first isolation buried layer diffuses into the second epitaxial layer. The deep well is electrically connected to the second isolation buried layer through the first isolation buried layer to form an isolation structure. 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, thereby reducing the process difficulty or production cost of the deep well. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Those skilled in the art will appreciate that the accompanying drawings are provided for a better understanding of the present invention and do not constitute any limitation on the scope of the present invention.

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

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

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

[0031] Figure 5 4 is a doping curve diagram in the BCD device structure of an embodiment of the present invention.

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

[0033] In the attached figure:

[0034] 10 - substrate; 11 - first epitaxial layer; 12 - first isolation buried layer; 13 - second isolation buried layer; 14 - second epitaxial layer; 15 - deep well; 16 - conductive contact region. DETAILED DESCRIPTION

[0035] In order to make the purpose, advantages and features of the present invention clearer, the present invention is further described in detail below in conjunction with 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 conveniently and clearly assist in explaining the purpose of the embodiments of the present invention. In addition, the structure shown in the drawings is often a part of the actual structure. In particular, the emphasis of each drawing is different, and sometimes different scales are used.

[0036] As used in the present invention, the singular forms "one", "an" and "the" include plural objects, the term "or" is usually used to include the meaning of "and / or", the term "several" is usually used to include the meaning of "at least one", and the term "at least two" is usually used to include the meaning of "two or more". In addition, the terms "first", "second" and "third" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Therefore, the features defined as "first", "second" and "third" can explicitly or implicitly include one or at least two of the features. In addition, as used in the present invention, an element is arranged on another element, which usually only indicates that there is a connection, coupling, matching or transmission relationship between the two elements, and the connection, coupling, matching or transmission between the two elements can be direct or indirect through an intermediate element, and cannot be understood as indicating or implying the spatial position relationship between the two elements, that is, an element can be in any orientation such as inside, outside, above, below or on one side of another element, unless the content clearly indicates otherwise. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

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

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

[0039] A first isolation buried layer 12, wherein the first isolation buried layer 12 is formed in the first epitaxial layer 11 and diffused into the second epitaxial layer 14, and a graded junction is formed between the first isolation buried layer 12 and the substrate 10;

[0040] a second isolation buried layer 13, wherein the second isolation buried layer 13 is located in the first epitaxial layer 11 and in the first isolation buried layer 12;

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

[0042] Please continue to refer to Figure 1 The substrate 10 can provide an operating platform for subsequent processes. It can be any substrate for carrying semiconductor integrated circuit components known to those skilled in the art, and can be a bare chip or a wafer processed by an epitaxial growth process. In detail, 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 doping type of the substrate 10 is a first doping type, and the first doping type is, for example, a P type. In some embodiments, the substrate 10 is, for example, a P+ type. A first epitaxial layer 11 is formed on the substrate 10, and the doping type of the first epitaxial layer 11 is a first doping type, that is, the first epitaxial layer 11 is a P type. The first isolation buried layer 12 and the second isolation buried layer 13 are formed in the first epitaxial layer 11, and the second isolation buried layer 13 is located in the first isolation buried layer 12. The doping types of the first isolation buried layer 12 and the second isolation buried layer 13 are both the second doping type, that is, the first isolation buried layer 12 and the second isolation buried layer 13 are N-type isolation buried layers (NBL). Specifically, the doping element of the first isolation buried layer 12 is phosphorus, and the doping element of the second isolation buried layer 13 is antimony. Higher applied voltages put forward higher withstand voltage and anti-punch-through requirements for the isolation of the N-type isolation buried layer. The N-type isolation buried layer that can prevent high-voltage punch-through requires a sufficiently high peak concentration. Therefore, the antimony doping amount of the second isolation buried layer 13 is, for example, 10 14 cm -3 . Compared with antimony, phosphorus diffuses faster and farther, so the doping dose of the first isolation buried layer 12 is less than the doping dose of the second isolation buried layer 13. Exemplarily, the doping dose of the first isolation buried layer 12 is one hundredth to one tenth of the doping dose of the second isolation buried layer 13. Since phosphorus diffuses faster and farther, in order not to affect the devices in the upper isolation region, phosphorus is implanted deeper. Therefore, the implantation depth of the first isolation buried layer 12 is greater than the implantation depth of the second isolation buried layer 13.

[0043] Please continue to refer to Figure 1, a second epitaxial layer 14 is formed on the second isolation buried layer 13, and a deep well 15 is formed in the second epitaxial layer 14. 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. The doping type of the deep well 15 is the second doping type, that is, the doping type of the deep well 15 is N type. Exemplarily, the doping element of the deep well 15 is phosphorus. In the process of forming the deep well 15, the first isolation buried 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, and the isolation region is used to form a MOS device. The isolation structure is used to isolate adjacent MOS devices and isolate the MOS device from the substrate 10. A conductive contact region 16 is also formed in the deep well 15. The conductive contact region 16 is, for example, N+ type ions, which are 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 isolation buried layer 13 by forming the first isolation buried layer 12, does not require a higher temperature and longer time push-well process, or does not require multiple epitaxial processes, reducing the process difficulty and process cost. In addition, in the prior art, when there is only the second buried layer 13, the concentration of antimony in the N-type isolation buried layer is too high and does not diffuse, the formed N-type isolation buried layer and the substrate (NBL-to-Psub) are a single-sided mutation junction, the depletion region is concentrated on the P-type substrate side, and the breakdown voltage between the N-type isolation buried layer and the substrate is difficult to increase; this embodiment forms the first isolation buried layer 12, the phosphorus in the first isolation buried layer 12 diffuses to increase the depletion area of ​​the N-type region, both sides of the N-type region and the P-type region participate in depletion, and a graded junction is formed between the first isolation buried layer 12 and the substrate 10, and the graded junction increases the breakdown voltage between the first isolation buried layer 12 and the substrate 10.

[0044] Figure 2 FIG. 1 is a flow chart of a 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, providing a substrate, on which a first epitaxial layer is formed;

[0046] Step S20, performing a first ion implantation process to form a first isolation buried layer in the first epitaxial layer, wherein a graded junction is formed between the first isolation buried layer and the substrate;

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

[0048] Step S40, performing an epitaxial growth process to form a second epitaxial layer, wherein the second epitaxial layer is located on the first isolation buried layer;

[0049] Step S50, sequentially performing a third ion implantation process and a thermal process well-driving process to form a deep well in the second epitaxial layer. In the thermal process well-driving 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] Figure 3 to Figure 4 1 is a schematic diagram of the structure corresponding to the steps of the method for forming the BCD device structure of the embodiment of the present invention. In order to make the above-mentioned purpose, features and beneficial effects of the present invention more obvious and easy to understand, the following is a schematic diagram of the structure corresponding to the steps of the method for forming the BCD device structure of the embodiment of the present invention. Figure 3 to Figure 4 The specific embodiments of the present invention are described in detail.

[0051] Please refer to Figure 3 , a substrate 10 is provided. The substrate 10 can provide an operating platform for subsequent processes. The substrate 10 can be any substrate for carrying semiconductor integrated circuit components known to those skilled in the art, and can be a bare chip or a wafer processed by an epitaxial growth process. In detail, 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 doping type of the substrate 10 is a first doping type, and the first doping type is, for example, a P type. In some embodiments, the substrate 10 is, for example, a P+ type. A first epitaxial layer 11 is formed on the substrate 10, and the doping type of the first epitaxial layer 11 is a first doping type, that is, the first epitaxial layer 11 is a P type.

[0052] Please continue to refer to Figure 3 , performing a first ion implantation process to form a first isolation buried layer 12 in the first epitaxial layer 11, and forming a graded junction between the first isolation buried layer 12 and the substrate 10. The doping type of the first isolation buried layer 12 is the second doping type, that is, the first isolation buried layer 12 is an N-type isolation buried layer (NBL). Specifically, the doping element of the first isolation buried layer 12 is phosphorus.

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

[0054] Compared with antimony, phosphorus diffuses faster and farther, so the doping dose of the first isolation buried layer 12 is less than the doping dose of the second isolation buried layer 13. Exemplarily, the doping dose of the first isolation buried layer 12 is one hundredth to one tenth of the doping dose of the second isolation buried layer 13. Since phosphorus diffuses faster and farther, in order not to affect the devices in the upper isolation region, phosphorus is implanted deeper. Therefore, the implantation depth of the first isolation buried layer 12 is greater than the implantation depth of the second isolation buried layer 13.

[0055] Please refer to Figure 4 , performing an epitaxial growth process to form a second epitaxial layer 14, wherein the second epitaxial layer 14 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 , perform a third ion implantation process and a thermal process well-pushing process to form a deep well 15 in the second epitaxial layer 14. In the thermal process well-pushing process, the first isolation buried layer 12 extends into the second epitaxial layer 14, and the deep well 15 is electrically connected to the second isolation buried layer 13 through the first isolation buried layer 12 to form an isolation structure. The doping type of the deep well 15 is the second doping type, that is, the doping type of the deep well 15 is N-type. Exemplarily, the doping element of the deep well 15 is phosphorus. In the thermal process well-pushing process for forming the deep well 15, the first isolation buried 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, and the isolation region is used to form a MOS device. The isolation structure is used to isolate adjacent MOS devices and isolate MOS devices from the substrate 10.

[0057] Please continue to refer to Figure 1 A conductive contact region 16 is formed in the deep well 15 and 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 isolation buried layer 13 by forming the first isolation buried layer 12, does not require a higher temperature and longer time push-well process, or does not require multiple epitaxial processes, reducing the process difficulty and process cost. In addition, in the prior art, when there is only the second buried layer 13, the concentration of antimony in the N-type isolation buried layer is too high and does not diffuse, the formed N-type isolation buried layer and the substrate (NBL-to-Psub) are a single-sided mutation junction, the depletion region is concentrated on the P-type substrate side, and the breakdown voltage between the N-type isolation buried layer and the substrate is difficult to increase; this embodiment forms the first isolation buried layer 12, the phosphorus in the first isolation buried layer 12 diffuses to increase the depletion area of ​​the N-type region, both sides of the N-type region and the P-type region participate in depletion, and a graded junction is formed between the first isolation buried layer 12 and the substrate 10, and the graded junction increases the breakdown voltage between the first isolation buried layer 12 and the substrate 10.

[0059] Figure 5 is a doping curve diagram of the BCD device structure in the embodiment of the present invention. Figure 5 As shown in the figure, the horizontal axis is the depth from the silicon substrate surface (Depth from Si top), the unit is micrometer (um). The vertical axis is the doping concentration of each doping element, the unit is the number of impurity atoms per cubic centimeter (cm -3). The boron doping curve (blue curve) indicates that the doping concentration increases from the silicon surface to the silicon interior, that is, the boron doping concentration in the second epitaxial layer 14 and the first epitaxial layer 11 is less than the boron doping concentration in the substrate 10. In this embodiment, the substrate 10 is of P+ type. The antimony doping curve (yellow) is 6um-7um away from the silicon surface, and the second isolation buried layer 13 is located in the first epitaxial layer 11. The antimony doping curve rises and falls sharply. It can be seen that the antimony concentration in the second isolation buried layer 13 is too high and does not diffuse. Therefore, when there is only the second isolation buried layer 13, the second isolation buried layer 13 and the substrate 10 (NBL-to-Psub) are a single-sided mutation junction, and the depletion region is concentrated on one side of the substrate 10. It is difficult to increase the breakdown voltage between the second isolation buried layer 13 and the substrate 10. The phosphorus-1 doping curve (orange curve) is the doping curve of the N-type deep well in the prior art. As the depth of silicon increases, the phosphorus doping concentration decreases sharply, and it is difficult to connect phosphorus and antimony. Since the N-type deep well needs to be pushed very deep in the high-voltage device, as the applied voltage increases, the depth required for the withstand voltage of the high-voltage device becomes deeper and deeper, and the N-type isolation buried layer isolation layer needs to be buried deeper, which will increase the difficulty of connecting the N-type deep well to the N-type isolation buried layer isolation layer. The conventional method is to perform multiple epitaxy and epitaxial layer N-type deep well injections, or use a strong thermal process to push the well (thermal drive-in) to push the N-type deep well deeper, but these methods will greatly increase the production cost. In this embodiment, a first isolation buried layer 12 is added. Since the doping element of the first isolation buried layer 12 is phosphorus, phosphorus is easy to diffuse. The phosphorus in the first isolation buried layer 12 diffuses upward during the thermal process of the N-type deep well, which effectively increases the connection between the first isolation buried layer 12 and the N-type deep well. The phosphorus-2 curve (gray curve) is on the silicon surface, and the doping concentration of phosphorus decreases as the depth of silicon goes deeper. After reaching the first isolation buried layer 12, the concentration of phosphorus first increases and then decreases, and extends 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, does not require a well-pushing process with a higher temperature and a longer time, or does not require multiple epitaxial processes, thereby reducing the process difficulty and process cost; at the same time, increasing the first isolation buried layer 12, that is, increasing phosphorus injection, the diffused phosphorus can increase the depletion area of ​​the N-type region, and both sides of the N-type region and the P-type region 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 : is a breakdown voltage curve diagram between the N-type isolation buried layer and the P-type substrate of the BCD device structure of the embodiment of the present invention. The horizontal axis is voltage (Voltage), the unit is volt (V). The vertical axis is current (Current), the unit is ampere (A). Figure 6As shown, the yellow curve is the breakdown voltage curve between the N-type isolation buried layer and the P-type substrate of the BCD device structure of the technical solution in the prior art, and the blue curve is the breakdown voltage curve between the N-type isolation buried layer and the P-type substrate of the BCD device structure in 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 isolation buried layer and the P-type substrate is increased by 30%, that is, the junction withstand voltage between the N-type isolation buried layer and the P-type substrate is increased.

[0061] In summary, in a BCD device structure and a method for forming the same provided in an embodiment of the present invention, a first epitaxial layer and a second epitaxial layer are formed on a substrate in the BCD device structure, and a first isolation buried layer is formed in the first epitaxial layer. By adding the first isolation buried layer, the phosphorus in the first isolation buried layer can increase the depletion area of ​​the N-type region, and both sides of the N-type region and the P-type region participate in depletion. A gradual junction is formed between the first isolation buried layer and the substrate, thereby increasing the breakdown voltage between the first isolation buried layer and the substrate. A second isolation buried layer is formed in the first epitaxial layer, and the second isolation buried layer is located in the first isolation buried layer. A deep well is formed in the second epitaxial layer. When the deep well is formed, the first isolation buried layer diffuses into the second epitaxial layer. The deep well is electrically connected to the second isolation buried layer through the first isolation buried layer to form an isolation structure. 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, thereby 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, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other. In addition, the different parts between the various embodiments can also be used in combination with each other, and the present invention is not limited to this.

[0063] In addition, it should be recognized that although the present invention has been disclosed as a preferred embodiment, the above embodiment is not intended to limit the present invention. For any technician familiar with the art, without departing from the scope of the technical solution of the present invention, the technical content disclosed above can be used to make many possible changes and modifications to the technical solution of the present invention, or modified into equivalent embodiments of equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still belongs to the scope of protection of the technical solution of the present invention.

Claims

1. A BCD device structure, characterized in that: include: a substrate, on which a first epitaxial layer and a second epitaxial layer are formed; A first isolation buried layer, wherein the first isolation buried layer is formed in the first epitaxial layer and diffused into the second epitaxial layer, and a graded junction is formed between the first isolation buried layer and the substrate; a second isolation buried layer, wherein the second isolation buried layer is located in the first epitaxial layer and in the first isolation buried layer; A deep well is located in 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.

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

3. The BCD device structure according to claim 1, 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 doping element of the first isolation buried layer and the deep well is phosphorus, and the doping element of the second isolation buried layer is 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 1% to 10% of the doping dose of the second isolation buried layer.

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

8. A method for forming a BCD device structure, characterized in that: include: Providing a substrate, on which a first epitaxial layer is formed; Performing a first ion implantation process to form a first isolation buried layer in the first epitaxial layer, wherein a graded junction is formed between the first isolation buried layer and the substrate; Performing a second ion implantation process to form a second isolation buried layer in the first epitaxial layer, wherein the second isolation buried layer is located in the first isolation buried layer; Performing an epitaxial growth process to form a second epitaxial layer, wherein the second epitaxial layer is located on the first isolation buried layer; A third ion implantation process and a thermal process well-driving process are performed in sequence to form a deep well in the second epitaxial layer. In the thermal process well-driving 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 doping element of the first isolation buried layer and the deep well is phosphorus, and the doping element of the second isolation buried layer is 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 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.

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