Separated terminal structure and preparation method thereof

Abstract

The invention provides a separated terminal structure and a preparation method thereof, and the method comprises the steps: forming a first field plate and a second field plate in a first groove and a second groove respectively through a substrate, a first groove disposed in the substrate, and a second groove spaced from the first groove by a preset distance; the first field plate comprises a first oxide layer and a first polycrystalline silicon layer which are sequentially deposited in the first groove, the second field plate comprises a second polycrystalline silicon layer located in the middle area of the second groove and a third polycrystalline silicon layer symmetrical about the second polycrystalline silicon layer, and the second polycrystalline silicon layer, the third polycrystalline silicon layer and the substrate are isolated through isolation parts. The isolation part is an oxide, and in the epitaxial growth direction, the length of the second polycrystalline silicon layer is smaller than that of the third polycrystalline silicon layer, specifically, the second polycrystalline silicon layer is connected with the source electrode to work, so that the field intensity of a trench oxide layer of a terminal field plate can be effectively reduced, the depletion effect is improved, and a depletion line in a terminal region is smoother.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a separate terminal structure and a preparation method thereof. Background Art

[0002] As a key component of electronic systems, the performance and reliability of power devices directly affect the operating efficiency and stability of the entire system. Among them, the terminal electric field distribution problem of power devices has always been an important factor restricting their performance improvement.

[0003] As electronic devices continue to pursue higher power density, higher operating voltage and higher reliability, the shortcomings of traditional power devices in terminal electric field distribution are becoming increasingly prominent. In the prior art, there is often an electric field concentration phenomenon in the terminal area of ​​power devices, which may cause the device to break down prematurely under high voltage, reducing the device's voltage resistance and reliability.

[0004] In the prior art, trench field plates are often used as terminal structures. One near the edge of the cell is usually connected to the source terminal to reduce the potential difference at the edge of the cell. If the others are left floating, the depletion region cannot be enlarged and the curvature cannot be increased; if they are connected to a low potential, the depletion region will be enlarged, but the trench oxide layer will be subjected to high field strength, resulting in insufficient withstand voltage of the device. Summary of the invention

[0005] Based on this, the purpose of the present invention is to provide a separate terminal structure and a preparation method thereof, which aims to reduce the field strength of the terminal field plate trench oxide layer while enhancing the depletion effect to make the depletion line in the terminal area smoother.

[0006] A separate terminal structure according to an embodiment of the present invention includes a substrate, a first trench provided in the substrate, and a second trench spaced apart from the first trench by a preset distance, wherein a first field plate and a second field plate are formed in the first trench and the second trench respectively; The first field plate includes a first oxide layer and a first polysilicon layer deposited in sequence in the first trench, the second field plate includes a second polysilicon layer located in the middle area of ​​the second trench, and a third polysilicon layer symmetrical about the second polysilicon layer, the second polysilicon layer, the third polysilicon layer and the substrate are isolated by an isolation part, the isolation part is oxide, wherein in the epitaxial growth direction, the length of the second polysilicon layer is shorter than the length of the third polysilicon layer.

[0007] Furthermore, the depth of the first groove and the second groove are both 2 μm to 5 μm.

[0008] Furthermore, the thickness of the first oxide layer is 1500Å~2000Å.

[0009] Furthermore, the thickness of the third polysilicon layer is one quarter of the width of the second trench.

[0010] Furthermore, the second polysilicon layer and the third polysilicon layer have the same thickness, which is 0.4 μm to 0.8 μm.

[0011] Furthermore, the isolation portion includes a first isolation sub-portion, a second isolation sub-portion, a third isolation sub-portion and a fourth isolation sub-portion, the first isolation sub-portion is used to isolate the third polysilicon layer from the substrate, the second isolation sub-portion extends from the first isolation sub-portion in a direction away from the substrate, and is used to arrange the second polysilicon layer in the middle area of ​​the second trench, the third isolation sub-portion extends from the second isolation sub-portion in a direction away from the substrate, and is used to isolate the third polysilicon layer from the second polysilicon layer, and the fourth isolation sub-portion is connected to the third isolation sub-portion and the second polysilicon layer, and is used to seal the second polysilicon layer.

[0012] Furthermore, the thickness of the first isolation sub-portion is 1500Å~2000Å.

[0013] Furthermore, the upper surface of the second polysilicon layer is located at a depth that is two-thirds of the depth of the second trench. A method for preparing a separate terminal structure according to an embodiment of the present invention is used to prepare the separate terminal structure, and the method includes: Providing a substrate, and etching a first groove and a second groove on the substrate; By thermal oxidation treatment, an oxide layer is grown on the surface of the first trench and the second trench, and then polysilicon is filled and CMP polishing is performed; Etching the polysilicon in the second trench to obtain a third polysilicon layer; Filling the groove formed by the third polysilicon layer with an oxide layer, and performing back etching to obtain a second isolation sub-portion, and then performing a thermal oxidation process to form an oxide layer on the inner sidewall of the groove; Filling polysilicon, CMP grinding and etching back, to obtain the second polysilicon layer; The oxide layer is filled and CMP polished to obtain the fourth isolation sub-portion to complete the preparation of the separated terminal structure.

[0014] The beneficial effects of the present invention are: A first field plate and a second field plate are formed in the first trench and the second trench respectively through a substrate, a first trench provided in the substrate, and a second trench spaced a preset distance from the first trench; the first field plate comprises a first oxide layer and a first polysilicon layer sequentially deposited in the first trench, the second field plate comprises a second polysilicon layer located in the middle area of ​​the second trench, and a third polysilicon layer symmetrical with respect to the second polysilicon layer, the second polysilicon layer, the third polysilicon layer and the substrate are isolated by an isolation portion, the isolation portion is an oxide, wherein in the epitaxial growth direction, the length of the second polysilicon layer is shorter than the length of the third polysilicon layer, specifically, the second polysilicon layer is connected to the source electrode and then operated, which can effectively reduce the field strength of the oxide layer in the terminal field plate trench while enhancing the depletion effect, so that the depletion line in the terminal area is smoother. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 A schematic diagram of a separate terminal structure provided by an embodiment of the present invention; Figure 2 A flowchart of a method for preparing a separate terminal structure provided by an embodiment of the present invention; Figure 3 A schematic diagram of a process flow for preparing a separate terminal structure provided by an embodiment of the present invention; Figure 4 A schematic diagram of a depletion line of a separate terminal structure in an embodiment of the present invention; Figure 5 A schematic diagram of a depletion line of a trench field plate structure in prior art 1; Figure 6 A schematic diagram of a depletion line of a trench field plate structure in prior art 2; Figure 7 Schematic diagram of the electric field strength at the oxide layer on the right sidewall of the trench.

[0016] Description of main component symbols:

[0017] The following specific implementation methods will further illustrate the present application in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0018] In order to facilitate the understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. Several embodiments of the present invention are given in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive.

[0019] It should be noted that when an element is referred to as being "fixed to" another element, it may be directly on the other element or there may be a central element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0021] The embodiment of the present invention provides a separate terminal structure, please refer to Figure 1 , is a schematic structural diagram of a separation terminal structure provided by an embodiment of the present invention. Specifically, the separation terminal structure includes a substrate 1, a first groove 11 provided in the substrate 1, and a second groove 12 spaced apart from the first groove 11 by a preset distance. A first field plate and a second field plate are formed in the first groove 11 and the second groove 12, respectively. Since the first groove 11 and the second groove 12 are prepared at the same time, the depths of the first groove 11 and the second groove 12 are the same, both of which are 2μm to 5μm. Exemplarily, the depths of the first groove 11 and the second groove 12 are 2μm, 3μm, 4μm or 5μm, but are not limited thereto; The first field plate includes a first oxide layer 21 and a first polysilicon layer 3 deposited in sequence in the first trench 11, the thickness of the first oxide layer 21 is 1500Å~2000Å, and exemplarily, the thickness of the first oxide layer 21 is 1500Å, 1600Å, 1700Å, 1800Å, 1900Å or 2000Å, but is not limited thereto. The second field plate includes a second polysilicon layer 4 located in the middle area of ​​the second trench 12, and a third polysilicon layer 5 symmetrical about the second polysilicon layer 4, the second polysilicon layer 4, the third polysilicon layer 5 and the substrate 1 are isolated by an isolation portion, and the isolation portion is an oxide, wherein, in the epitaxial growth direction, the length of the second polysilicon layer 4 is shorter than the length of the third polysilicon layer 5.

[0022] It should be noted that the thickness of the third polysilicon layer 5 is one quarter of the width of the second groove 12, and the thickness of the second polysilicon layer 4 and the third polysilicon layer 5 are the same, and are both 0.4μm~0.8μm. Exemplarily, the thickness of the second polysilicon layer 4 and the third polysilicon layer 5 are both 0.4μm, 0.5μm, 0.6μm, 0.7μm or 0.8μm, but not limited to this. It can be understood that the thickness here refers to the lateral length, that is, the direction perpendicular to the epitaxial growth direction.

[0023] In the present embodiment, the isolation portion includes a first isolation sub-portion 22, a second isolation sub-portion 31, a third isolation sub-portion 32 and a fourth isolation sub-portion 33. The first isolation sub-portion 22 is used to isolate the third polysilicon layer 5 from the substrate 1. It can be understood that the first isolation sub-portion 22 and the first oxide layer 21 are actually prepared at the same time and have the same thickness, that is, the thickness of the first isolation sub-portion 22 is 1500Å~2000Å. The second isolation sub-portion 31 extends from the first isolation sub-portion 22 in a direction away from the substrate 1, and is used to set the second polysilicon layer 4 in the middle area of ​​the second groove 12. The third isolation sub-portion 32 extends from the second isolation sub-portion 31 in a direction away from the substrate 1, and is used to isolate the third polysilicon layer 5 from the second polysilicon layer 4. The fourth isolation sub-portion 33 is connected to the third isolation sub-portion 32 and the second polysilicon layer 4, and is used to seal the second polysilicon layer 4. Specifically, the upper surface of the second polysilicon layer 4 is located at a depth that is two-thirds of the depth of the second trench 12 , and finally a second field plate structure with long polysilicon on both sides and short polysilicon in the middle is obtained.

[0024] In order to prepare the above-mentioned separate terminal structure, the embodiment of the present invention provides a method for preparing the separate terminal structure, please refer to Figure 2 and Figure 3 , Figure 2 A flowchart of a method for preparing a separate terminal structure provided by an embodiment of the present invention is provided. Figure 3 A schematic diagram of a process flow for preparing a separate terminal structure provided by an embodiment of the present invention, the method specifically comprises the following steps: S100: providing a substrate, and etching a first groove and a second groove on the substrate.

[0025] Specifically, the depths of the etched first groove 11 and the second groove 12 are both 2 μm to 5 μm.

[0026] S200: growing an oxide layer on the surface of the first trench and the second trench through thermal oxidation treatment, then filling with polysilicon, and performing CMP polishing.

[0027] Specifically, oxygen is introduced at a high temperature of 800°C~1100°C to grow a high-quality oxide layer as a dielectric layer for the sidewalls of the field plate polysilicon, with a thickness of 1500Å~2000Å. It can be understood that the oxide layer located on the surface of the first groove 11 is the first oxide layer 21, and the oxide layer located on the surface of the second groove 12 is the first isolation sub-portion 22, and the polysilicon is isolated from the substrate 1 by the oxide layer.

[0028] Subsequently, polysilicon is deposited on the first oxide layer 21 and the first isolation sub-portion 22 , respectively, and then CMP polishing is performed. The polysilicon located in the first trench 11 is the first polysilicon layer 3 .

[0029] S300: etching the polysilicon in the second trench to obtain a third polysilicon layer.

[0030] Specifically, one half of the polysilicon in the middle region of the second trench 12 is etched away to obtain the third polysilicon layer 5, which provides a position for forming the middle short field plate.

[0031] S400: filling the groove formed by the third polysilicon layer with an oxide layer, and performing back etching to obtain a second isolation sub-portion, and then performing thermal oxidation treatment to form an oxide layer on the inner sidewall of the groove.

[0032] It should be noted that an oxide layer is filled in the groove formed in the third polysilicon layer 5 and etched back to one-third of the depth of the second groove 12, and then oxygen is introduced at a high temperature of 800°C~1100°C to form an oxide layer on the inner side wall of the groove, that is, the third isolation sub-portion 32, with a thickness of 1500Å~2000Å.

[0033] S500: filling polysilicon, and performing CMP grinding and etching to obtain a second polysilicon layer.

[0034] The upper surface of the second polysilicon layer 4 is located at a depth that is two-thirds of the depth of the second trench 12 .

[0035] S600: Fill the oxide layer, and after CMP polishing, obtain the fourth isolation sub-portion to complete the preparation of the separated terminal structure.

[0036] It should be noted that the first field plate is actually a single integral polysilicon. The first polysilicon layer 3 and the second polysilicon layer 4 in the second field plate are respectively connected to the source. During actual operation, the field strength between the field plate trench oxide layer and the substrate can be reduced, thereby improving the withstand voltage and reliability of the device. The curvature of the depletion line in the terminal area can also be increased to make the depletion line smoother, thereby improving the electric field distribution and further improving the withstand voltage of the device.

[0037] The present invention will be further described below with specific embodiments: See also Figure 4 , Figure 5 as well as Figure 6 , Figure 4 is a schematic diagram of a depletion line of a separate terminal structure in an embodiment of the present invention, Figure 5 is a schematic diagram of the depletion line of the trench field plate structure in the prior art 1, Figure 6 It is a schematic diagram of the depletion line of the trench field plate structure in the prior art 2. Specifically, Figure 5 The field plate on the middle right is floating. The advantage is that when a positive voltage is applied to the drain, a positive voltage smaller than the drain voltage will be coupled to the floating field plate. In this way, the field strength borne by the oxide layer in the trench is small, and it will not break down prematurely and affect reliability. However, the depletion effect of the field plate is small, the white depletion line at the bottom is less extrapolated, and the curvature is small, resulting in low withstand voltage. Figure 6 The field plate on the right side of the middle is connected to the source and is at a low potential. When a positive voltage is applied to the drain, the voltage difference between the field plate and the substrate is greater than Figure 5 Therefore, the field strength borne by the trench oxide layer is relatively large. Although the depletion effect of the field plate is strong due to the large pressure difference, the bottom depletion line is extrapolated a lot and the curvature is small, but due to the large field strength borne by the trench oxide layer, it will also break down in advance, resulting in the inability to effectively improve the withstand voltage.

[0038] And as Figure 4 As shown in the figure, the short polysilicon field plate is located in the middle. Since it is connected to the source at a low potential, the voltage difference between the low potential and the substrate is large, and the field strength is high, it is placed in the middle of the trench, away from the upper surface of the substrate and the bottom of the trench, to reduce the field strength at these two places. Then the long field plates on the left and right sides of the trench are floating. In this way, when a positive voltage is applied to the drain, a positive voltage will be coupled to the floating field plates on the left and right sides of the trench. Due to the existence of the short field plate in the middle, it is connected to a low potential, so the voltage coupled to the floating field plates on the left and right sides is higher than Figure 6 Therefore, the field strength between the field plate and the substrate, and between the field plates are small, and the field strength borne by the oxide layer between the trench and the substrate is also small. In addition, since the voltage coupled between the left and right field plates in the trench is smaller than that on the right and left field plates in the trench, Figure 5 The depletion effect is lower than Figure 5 The curvature of the bottom depletion line becomes larger. It can be seen from the figure that the curvature of the depletion line of the separated terminal structure in the embodiment of the present invention is between the two prior arts. Compared with the prior art, the present invention not only increases the curvature of the depletion line, but also reduces the field strength of the trench oxide layer. Using 40V SGT for simulation, the terminal withstand voltage can be increased by about 10%, which greatly increases the reliability and competitiveness of the device. This invention is not limited to SGT, but is also compatible with other trench power devices.

[0039] For further information, see Figure 7, is a schematic diagram of the electric field strength at the oxide layer on the right sidewall of the trench, wherein a represents the electric field strength curve of the separate terminal structure provided by the present invention, b represents the electric field strength curve of the trench field plate structure in the prior art 1, and c represents the electric field strength curve of the trench field plate structure in the prior art 2. It can be found that in the separate terminal structure in the embodiment of the present invention, the electric field strength at the left sidewall oxide layer of the second field plate is the lowest, and the electric field strength at the right sidewall oxide layer is in the middle position. The advantages of the prior art are combined to improve the distribution of the electric field, reduce the electric field strength of the trench oxide layer, and the field plate effect is not weak, which can effectively increase the depletion line curvature.

[0040] In summary, the separated terminal structure and the preparation method thereof in the embodiments of the present invention are formed with a substrate, a first groove provided in the substrate, and a second groove spaced a preset distance from the first groove, and a first field plate and a second field plate are respectively formed in the first groove and the second groove; the first field plate includes a first oxide layer and a first polysilicon layer deposited in the first groove in sequence, the second field plate includes a second polysilicon layer located in the middle area of ​​the second groove, and a third polysilicon layer symmetrical about the second polysilicon layer, the second polysilicon layer, the third polysilicon layer and the substrate are isolated by an isolation part, the isolation part is an oxide, wherein in the epitaxial growth direction, the length of the second polysilicon layer is shorter than the length of the third polysilicon layer, specifically, the second polysilicon layer is connected to the source electrode and then works, which can effectively reduce the field strength of the oxide layer in the terminal field plate groove, while enhancing the depletion effect, so that the depletion line in the terminal area is smoother.

[0041] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A separate terminal structure, characterized in that: It comprises a substrate, a first trench provided in the substrate, and a second trench spaced apart from the first trench by a preset distance, wherein a first field plate and a second field plate are formed in the first trench and the second trench respectively; The first field plate includes a first oxide layer and a first polysilicon layer deposited in sequence in the first trench, the second field plate includes a second polysilicon layer located in the middle area of ​​the second trench, and a third polysilicon layer symmetrical about the second polysilicon layer, the second polysilicon layer, the third polysilicon layer and the substrate are isolated by an isolation part, the isolation part is oxide, wherein in the epitaxial growth direction, the length of the second polysilicon layer is shorter than the length of the third polysilicon layer.

2. The separate terminal structure according to claim 1, characterized in that: The depths of the first groove and the second groove are both 2 μm to 5 μm.

3. The separate terminal structure according to claim 1, characterized in that: The thickness of the first oxide layer is 1500Å~2000Å.

4. The separate terminal structure according to claim 1, characterized in that: The thickness of the third polysilicon layer is one quarter of the width of the second trench.

5. The separate terminal structure according to claim 4, characterized in that: The second polysilicon layer and the third polysilicon layer have the same thickness, which is 0.4 μm to 0.8 μm.

6. The separate terminal structure according to claim 1, characterized in that: The isolation portion includes a first isolation sub-portion, a second isolation sub-portion, a third isolation sub-portion and a fourth isolation sub-portion. The first isolation sub-portion is used to isolate the third polysilicon layer from the substrate. The second isolation sub-portion extends from the first isolation sub-portion in a direction away from the substrate, and is used to arrange the second polysilicon layer in the middle area of ​​the second trench. The third isolation sub-portion extends from the second isolation sub-portion in a direction away from the substrate, and is used to isolate the third polysilicon layer from the second polysilicon layer. The fourth isolation sub-portion is connected to the third isolation sub-portion and the second polysilicon layer, and is used to seal the second polysilicon layer.

7. The separate terminal structure according to claim 6, characterized in that: The thickness of the first isolation sub-portion is 1500Å~2000Å.

8. The separate terminal structure according to claim 6, characterized in that: The upper surface of the second polysilicon layer is located at a depth that is two-thirds of the depth of the second trench.

9. A method for preparing a separate terminal structure, characterized in that: For preparing the separate terminal structure according to any one of claims 1 to 8, the method comprises: Providing a substrate, and etching a first groove and a second groove on the substrate; By thermal oxidation treatment, an oxide layer is grown on the surface of the first trench and the second trench, and then polysilicon is filled and CMP polishing is performed; Etching the polysilicon in the second trench to obtain a third polysilicon layer; Filling the groove formed by the third polysilicon layer with an oxide layer, and performing back etching to obtain a second isolation sub-portion, and then performing a thermal oxidation process to form an oxide layer on the inner sidewall of the groove; Filling polysilicon, CMP grinding and etching back, to obtain the second polysilicon layer; The oxide layer is filled and CMP polished to obtain the fourth isolation sub-portion to complete the preparation of the separated terminal structure.

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