A vertical Schottky diode and its preparation method

Abstract

The present invention discloses a vertical Schottky diode and a method for preparing the same, which relates to semiconductor devices. This solution addresses the contradiction between reverse breakdown voltage and forward conduction resistance in the prior art. An oxide layer is provided outside the drift layer and substrate to electrically isolate the anode; the bottom thickness of the oxide layer is greater than the sidewall thickness. This has the advantage of utilizing only N-type doping materials to implement the device, avoiding the introduction of P-type doping and resulting in a relatively simple process. The trench depth is sufficiently large, reaching a depth of 1 to 20 μm, forming a deep trench structure. The deep trench structure extends the electric field during reverse blocking to the entire drift layer, making the breakdown characteristics primarily dependent on the drift layer thickness and reducing dependence on doping concentration. Therefore, a higher concentration drift layer can be further selected to ensure better forward conduction characteristics, ultimately achieving a nearly rectangular uniform electric field distribution and maximizing device characteristics. The average electric field during breakdown can reach 2.34 MV / cm, exceeding existing levels.

Description

Technical Field

[0001] The present invention relates to a semiconductor device, in particular to a vertical Schottky diode and a preparation method thereof. Background Art

[0002] Gallium nitride (GaN), silicon carbide (SiC), gallium oxide (Ga2O3), and other materials as third-generation semiconductors have wide band gaps, high saturated electron mobility, high critical breakdown fields, and good thermal conductivity, making them very suitable for the manufacture of high-power devices. Therefore, devices using these materials as N-type doped substrates have become the best choice for high-frequency, high-power, and high-temperature applications in various future environments.

[0003] With the commercialization of large-scale, independent substrates, vertical Schottky barrier diodes have become possible. These devices not only offer high withstand voltage and high switching speed, but also low on-resistance, making them a leader in the power device field. Vertical Schottky barrier diodes demonstrate exceptional performance and reliability, providing strong support for future power electronics systems.

[0004] Disadvantages of these vertical Schottky diodes:

[0005] 1. Difficulties in P-type doping of devices. Taking GaN as an example, due to the low activation rate of Mg, the traditional P-doped terminal structure is difficult to directly apply to the vertical structure, which limits the performance optimization and large-scale application of the device.

[0006] Second, there is an electric field concentration effect at the bottom of the trench. This effect not only causes leakage in the MOS structure, thereby increasing the leakage current, but also may cause premature breakdown of the device. Taking GaN as an example, although there have been studies on GaN TMBS (Trench MOS Barrier Schottky Diode) devices, there are relatively few reports of high performance. The average breakdown electric field of the reported actual devices at breakdown is difficult to exceed 1MV / cm, and the average breakdown electric field of the reported simulated devices at breakdown does not exceed 2MV / cm. These values ​​are far lower than the theoretical limit of 3.3MV / cm for GaN materials.

[0007] Third, while the introduction of a termination structure improves the device's reverse breakdown voltage capability, it often comes at the expense of forward conduction characteristics. Consequently, there is a constant competition between reverse breakdown voltage and forward resistance. To balance these two, a quality factor is often introduced as an evaluation metric. However, this trade-off limits device performance in high-power applications, making it difficult to meet growing power demands. Summary of the Invention

[0008] The present invention aims to provide a vertical Schottky diode and a method for manufacturing the same, so as to solve the problems existing in the above-mentioned prior art.

[0009] In the vertical Schottky diode described in the present invention, an oxide layer is provided outside the drift layer and the substrate to electrically isolate the anode; the bottom thickness of the oxide layer is greater than the side wall thickness.

[0010] The specific structure includes a top metal layer, a drift layer, a substrate and a bottom metal layer stacked in sequence from top to bottom; the bottom metal layer is in ohmic contact with the substrate, and the top metal layer is in Schottky contact with the drift layer; a plurality of longitudinally extending grooves are provided in the drift layer, and the grooves completely penetrate the top metal layer and the drift layer from top to bottom and extend into the substrate, so as to isolate and separate the drift layer into a plurality of longitudinally extending sub-channels; an oxide layer is provided to cover the exposed surfaces of the top metal layer, the drift layer and the substrate, and a skylight is provided in the oxide layer above the top metal layer to expose all or part of the area of ​​the upper end surface of the top metal layer; a current spreading layer is provided to cover the exposed surfaces of the oxide layer and the top metal layer.

[0011] The current spreading layers on the sides of adjacent sub-channels are isolated from each other to form air grooves, or the current spreading layers on the sides of adjacent sub-channels are in contact with each other to completely fill the space.

[0012] The substrate and the drift layer are both gallium nitride-based, silicon carbide-based, or gallium oxide-based N-type doped, and the doping concentration of the substrate is higher than that of the drift layer. The doping concentration of the substrate is 1×10 18 to 5×10 19 cm -3 Optional, preferably 5×10 18 cm -3 The drift layer doping concentration is 8×10 15 to 5×10 16 cm -3 Optional, preferably 3×10 16 cm -3 .

[0013] The thickness of the substrate can be selected from 1 to 500 μm. The thickness of the drift layer can be selected from 1 to 100 μm, preferably 7 μm.

[0014] The oxide layer material may be silicon oxide, silicon nitride, aluminum oxide, hafnium oxide or other materials of high-k dielectric layers, preferably silicon oxide.

[0015] The thickness of the bottom is greater than 0.1 μm and less than or equal to 7 μm; the thickness of the sidewall is greater than or equal to 0.1 μm and less than 7 μm.

[0016] The depth of the trench extending into the substrate is greater than zero and less than 0.5 μm.

[0017] The method for preparing a vertical Schottky diode described in the present invention comprises the following steps:

[0018] S1. Preparing a drift layer on a substrate;

[0019] S2. Preparing a patterned top metal layer on the drift layer;

[0020] S3. Using the top metal layer as a first mask to etch a longitudinally extending trench;

[0021] S4. Preparing an oxide layer having a bottom thickness greater than that of the sidewalls;

[0022] S5. Prepare a current spreading layer and a bottom metal layer.

[0023] The step S4 includes the following sub-steps:

[0024] S411. An oxide material having a thickness of h0 is deposited at the bottom of the trench;

[0025] S412. Depositing an oxide material with a thickness of d on the upper surface of the oxide material obtained in step S411 and on the sides of the trench to form an oxide layer; the bottom thickness of the oxide layer is h1=h0+d, and the sidewall thickness is d; the oxide layer does not cover or partially covers the upper surface of the top metal layer;

[0026] In step S5 , when preparing the current spreading layer, the thickness of the current spreading layer is kept uniform so that the current spreading layers at the sides of adjacent sub-channels are isolated from each other to form air grooves.

[0027] or,

[0028] The step S4 includes the following sub-steps:

[0029] S421. Depositing an oxide material on the sample prepared in step S3, wherein the oxide material is vertically higher than the top metal layer by a distance d;

[0030] S422. A patterned second mask is provided on the upper surface of the oxide material obtained in step S421; the second mask has a lateral width extending beyond both sides of the drift layer by a distance d;

[0031] S423. Using a second mask, longitudinally etch the oxide material to control the etching depth to obtain an oxide layer; the bottom thickness of the oxide layer is h1, and the sidewall thickness is d;

[0032] S424. Remove the second mask;

[0033] S425. Etching the oxide material above the top metal layer to completely expose or partially expose the upper surface of the top metal layer;

[0034] In step S5, when preparing the current spreading layer, the space in the groove is completely filled.

[0035] The vertical Schottky diode and its preparation method described in the present invention have the following advantages:

[0036] Only N-type doping materials are used to realize the device, thus avoiding the introduction of P-type doping, and the process method is relatively simple.

[0037] The trench depth is large enough, reaching 1 to 20 μm, forming a deep trench structure. This deep trench structure extends the reverse blocking electric field throughout the drift layer, making the breakdown characteristics primarily dependent on drift layer thickness and less dependent on doping concentration. This allows for the selection of a higher concentration drift layer to ensure even better forward conduction characteristics, ultimately achieving a near-rectangular uniform electric field distribution and maximizing device performance. The average electric field during breakdown can reach 2.34 MV / cm, exceeding existing standards.

[0038] The top height of the oxide layer can exceed the top metal layer, but it has no significant impact on the forward and reverse characteristics, thereby reducing the process requirements and difficulty.

[0039] Deliberate alignment design can be omitted at the edges of the substrate, oxide layer, and current spreading layer. The presence of unintentional offset δ does not affect the forward or reverse characteristics of the device, but can greatly reduce process complexity. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Schematic diagram of the vertical Schottky diode structure in comparison.

[0041] Figure 2 It is a structural schematic diagram of a first embodiment of a vertical Schottky diode described in the present invention.

[0042] Figure 3 yes Figure 2 A partial enlarged view of point A in the middle.

[0043] Figure 4 It is a schematic diagram of the preparation process of Example 1 of the present invention.

[0044] Figure 5 1 is a graph showing forward conduction characteristic curves when the structures shown in Example 1 and Comparative Example 1 of the present invention are implemented with gallium nitride-based materials.

[0045] Figure 6 1 is a graph showing forward conduction characteristics when the structures shown in Example 1 and Comparative Example 1 of the present invention are implemented with silicon carbide-based materials.

[0046] Figure 7 1 is a graph showing forward conduction characteristics when the structures shown in Example 1 and Comparative Example 1 of the present invention are implemented with gallium oxide-based materials.

[0047] Figure 8 1 is a graph showing the relationship between the reverse breakdown voltage and the bottom thickness of the oxide layer when the structures shown in Example 1 and Comparative Example 1 of the present invention are implemented with gallium nitride-based materials.

[0048] Figure 9 1 is a graph showing the relationship between the reverse breakdown voltage and the bottom thickness of the oxide layer when the structures shown in Example 1 and Comparative Example 1 of the present invention are implemented with silicon carbide-based materials.

[0049] Figure 10 1 is a graph showing the relationship between the reverse breakdown voltage and the bottom thickness of the oxide layer when the structures shown in Example 1 and Comparative Example 1 of the present invention are implemented with gallium oxide-based materials.

[0050] Figure 11 1 is an electric field distribution curve diagram when the structures shown in Example 1 and Comparative Example 1 of the present invention are implemented with gallium nitride-based materials, and the electric field tangent coincides with the vertical line in the drift layer.

[0051] Figure 12 1 is an electric field distribution curve diagram of the structures shown in Example 1 and Comparative Example 1 of the present invention when they are implemented with gallium nitride-based materials, and the electric field tangent is parallel to the vertical line in the drift layer and close to the sidewall.

[0052] Figure 13 It is a structural schematic diagram of a second embodiment of a vertical Schottky diode described in the present invention.

[0053] Figure 14 It is a schematic diagram of the preparation process of Example 2 of the present invention.

[0054] Reference numerals:

[0055] 101 - air groove, 110 - bottom metal layer, 120 - substrate, 130 - oxide layer, 131 - bottom, 132 - sidewall, 140 - current spreading layer, 150 - drift layer, 160 - top metal layer. DETAILED DESCRIPTION

[0056] Example 1

[0057] like Figure 2 As shown, the vertical Schottky diode of the present invention is provided with an oxide layer 130 outside the drift layer 150 and the substrate 120 to electrically isolate the anode. The sidewall 132 of the oxide layer 130 is thinner than the bottom 131 .

[0058] The specific structure includes a top metal layer 160, a drift layer 150, a substrate 120, and a bottom metal layer 110 stacked sequentially from top to bottom. The bottom metal layer 110, serving as the device's cathode, makes ohmic contact with the substrate 120, while the top metal layer 160 makes Schottky contact with the drift layer 150. A plurality of longitudinally extending trenches are provided within the drift layer 150. These trenches completely penetrate the top metal layer 160 and the drift layer 150 from top to bottom and extend into the substrate 120, isolating and separating the drift layer 150 into a plurality of longitudinally extending sub-channels. An oxide layer 130 is provided to cover the exposed surfaces of the top metal layer 160, the drift layer 150, and the substrate 120. A skylight is provided above the top metal layer 160 to expose all or part of the upper surface of the top metal layer 160. A current spreading layer 140 is provided to cover the exposed surfaces of the oxide layer 130 and the top metal layer 160. The current spreading layer 140 is in electrical contact with the top metal layer 160 and serves as the anode of the device.

[0059] In particular, if Figure 3 As shown, there is an unintentional offset δ1 between the edge of the substrate 120 and the edge of the oxide layer 130, and another unintentional offset δ2 between the edge of the oxide layer 130 and the edge of the current spreading layer 140. The distance between the current spreading layer 140 and the edge of the substrate 120 is offset by a total amount of δ=δ1+δ2. In contrast, the TMBS structure in the prior art requires that the edges of the substrate 120, the oxide layer 130, and the current spreading layer 140 be deliberately made to overlap as much as possible, otherwise it will lead to an increase in edge MOS leakage. In the present invention, by increasing the thickness of the bottom 131, the breakdown voltage is increased without affecting the forward on-resistance, and the MOS leakage at the bottom is also reduced. Therefore, δ1 and δ2 can be left at the very edge of the device without deliberate intervention, and the MOS leakage will basically not change significantly, which significantly reduces the process requirements and difficulty.

[0060] In this embodiment, the current spreading layers 140 on the sides of adjacent sub-channels are isolated from each other to form air grooves 101. The advantage of allowing the air grooves 101 is that the process difficulty is reduced, and the oxide layer 130 can be prepared by deposition.

[0061] In this embodiment, the doping concentration of the substrate 120 is 5×10 18 cm -3 The drift layer 150 has a doping concentration of 3×10 16 cm -3, the thickness is 7μm. The material of the oxide layer 130 is silicon oxide. The depth of the groove extending into the substrate 120 is greater than zero and less than 0.5μm. The thickness of the bottom 131 is greater than 0.1μm and less than or equal to 7μm. The thickness of the sidewall 132 is greater than or equal to 0.1μm and less than 7μm. As the thickness of the sidewall 132 increases, the thickness of the bottom 131 also increases. Those skilled in the art can conduct a limited number of tests based on the technical principles and various graphs described in the present invention to obtain the specific thickness value of the oxide layer 130 of the required device.

[0062] The present invention also provides a method for preparing the vertical Schottky diode, which specifically comprises the following steps:

[0063] S1. Prepare a drift layer 150 on the substrate 120 .

[0064] S2 . Forming a patterned top metal layer 160 on the drift layer 150 .

[0065] S3. Using the top metal layer 160 as a first mask, a longitudinally extending trench is etched.

[0066] S4 . Prepare an oxide layer 130 with a bottom 131 having a thickness greater than that of the sidewall 132 .

[0067] S5. Prepare the current spreading layer 140 and the bottom metal layer 110.

[0068] In order to facilitate the preparation in this embodiment, the existence of the air groove 101 is allowed. Accordingly, step S4 includes the following sub-steps:

[0069] S411. Deposit an oxide material with a thickness of h0 at the bottom of the trench.

[0070] S412. Deposit an oxide material with a thickness of d on the upper surface of the oxide material obtained in step S411 and on the sides of the trench to form an oxide layer 130. The bottom 131 of the oxide layer 130 has a thickness of h1 = h0 + d, and the sidewalls 132 have a thickness of d. The oxide layer 130 does not cover or partially covers the upper surface of the top metal layer 160.

[0071] In step S5 , when preparing the current spreading layer 140 , the thickness of the current spreading layer 140 is kept uniform, so that the current spreading layers 140 on the sides of adjacent sub-channels are isolated from each other to form air grooves 101 .

[0072] Comparative Example 1

[0073] The vertical Schottky diode structure described in this invention can utilize a variety of N-type doped substrate materials. To ensure sufficient disclosure and support for the claims, this comparative example and Example 1 each utilize gallium nitride-based, silicon carbide-based, and gallium oxide-based N-type doping for comparison and demonstration of their effects. Gallium nitride-based N-type doping means both the substrate 120 and the drift layer 150 are N-type doped gallium nitride materials. Similarly, silicon carbide-based N-type doping means both the substrate 120 and the drift layer 150 are N-type doped silicon carbide materials. Gallium oxide-based N-type doping means both the substrate 120 and the drift layer 150 are N-type doped gallium oxide materials.

[0074] In this comparative example, the structure Figure 1 As shown, the main difference from the first embodiment is that the thickness of the bottom 131 and the sidewall 132 are the same, and the oxide layer 130 is evenly distributed.

[0075] Figures 5 to 7 The TMBS forward characteristics of uniform oxide layer and non-uniform oxide layer thickness are shown respectively:

[0076] like Figure 5 As shown in Figure 1, the uniform oxide layer thickness of the GaN-based TMBS is 1.8 μm; the sidewall thickness of the non-uniform oxide layer is 1.4 μm, and the bottom thickness is selected as 1.8 μm and 2.5 μm respectively. Figure 6 As shown in Figure 2, the thickness of the uniform oxide layer of the SiC-based TMBS is 1.4 μm; the sidewall thickness of the non-uniform oxide layer is 1 μm, and the bottom thickness is selected as 1.4 μm and 3 μm respectively. Figure 7 As shown in the figure, the uniform oxide layer thickness of the gallium oxide-based TMBS is 3μm; the sidewall thickness of the non-uniform oxide layer is 2μm, and the bottom thickness is selected as 3μm and 3.5μm respectively. It can be seen that the non-uniform oxide layer structure reduces the specific on-resistance by reducing the thickness of the sidewall, while increasing the bottom thickness does not affect the on-resistance. Figure 5 The specific on-resistance shown is from 0.72mΩ·cm 2 Reduced to 0.67 mΩ·cm 2 , this changing trend also exists in silicon carbide-based and gallium oxide-based TMBS.

[0077] Figures 8 to 10 The TMBS reverse characteristics of uniform and non-uniform oxide layer thickness are shown respectively:

[0078] like Figure 8 As shown, the sidewall thickness is maintained at 1.4μm while the bottom thickness gradually increases. When the oxide layer of the GaN-based TMBS is uniformly distributed, as indicated by the dots in the figure, the breakdown voltage is 1231V. When the oxide layer is non-uniformly distributed, the breakdown voltage increases with increasing bottom thickness, reaching a maximum breakdown voltage of 1640V at a bottom thickness of 2.5μm, as indicated by the star in the figure.

[0079] like Figure 9 As shown in Figure 1, the sidewall thickness is kept at 1μm while the bottom thickness is gradually increased. The breakdown voltage of the SiC-based TMBS is 915V when the oxide layer is uniformly distributed, and the maximum breakdown voltage is 1277V when the oxide layer is non-uniformly distributed.

[0080] like Figure 10 As shown in the figure, the sidewall thickness is kept at 2μm while the bottom thickness is gradually increased. The breakdown voltage of the gallium oxide-based TMBS is 2515V when the oxide layer is uniformly distributed, and the maximum breakdown voltage is 3382V when the oxide layer is non-uniformly distributed.

[0081] It can be seen that the traditional uniform oxide layer structure will break down prematurely, and the reason for the increased leakage current is the oxide layer leakage at the bottom of the trench. Since the thinner oxide layer thickness causes the electric field to concentrate at the corner of the bottom of the trench, it will cause greater MOS leakage. Increasing the bottom thickness directly solves the MOS leakage problem.

[0082] However, the bottom thickness cannot be too large. The selection of the bottom thickness is related to the sidewall thickness to ensure that the charge coupling effect of the MOS structure completely depletes the interior of the drift region. If the charge coupling effect is insufficient, breakdown will occur at the Schottky interface, while if it is too strong, it will occur at the bottom corner of the trench. Reducing the oxide layer sidewall thickness will enhance the charge coupling effect, so the bottom oxide layer thickness must be increased to balance it out.

[0083] Figure 11 and Figure 12 The electric field distribution of GaN TMBS with uniform and non-uniform oxide layer structures during breakdown is shown. Whether viewed from the middle of the drift layer or from the side of the drift layer, the electric field distribution inside and on the side of the drift layer with the non-uniform oxide layer structure is more uniform and close to a rectangle. Figure 11 and Figure 12 A person skilled in the art knows that the larger the area of ​​the curve envelope is, the closer the device condition is to the ideal.

[0084] like Figure 12 As shown, by increasing the bottom oxide layer thickness, the electric field peak can be shifted inward, thereby reducing the electric field concentration effect at the bottom of the trench and improving the device's withstand voltage. Therefore, increasing the bottom oxide layer thickness helps reduce the electric field concentration at the bottom of the trench and increase the breakdown voltage. The preferred non-uniform oxide layer GaN TMBS diode achieves an average electric field of up to 2.34 MV / cm at breakdown, demonstrating excellent performance. The variation in this electric field distribution is generally consistent with that of silicon carbide- and gallium oxide-based TMBS and is not further detailed here.

[0085] Example 2

[0086] The vertical Schottky diode structure described in the present invention is as follows Figure 13 As shown, the main difference from the first embodiment is that the current spreading layers 140 on the sides of adjacent sub-channels contact each other to completely fill the space, completely eliminating the air groove 101. The advantage is that the lateral spacing between the sub-channels of the drift layer 150 can be greatly reduced, thereby reducing the size of the device.

[0087] The preparation method provided in this embodiment also includes steps S1 to S5 described in the first embodiment, but due to the disappearance of the air groove 101, the corresponding steps S4 and S5 are slightly different.

[0088] Specifically, step S4 includes the following sub-steps:

[0089] S421 . Deposit an oxide material on the sample prepared in step S3 , with the oxide material vertically protruding above the top metal layer 160 by a distance d.

[0090] S422: A patterned second mask is placed on the upper surface of the oxide material prepared in step S421. The second mask has a lateral width that exceeds both sides of the drift layer 150 by a distance d.

[0091] S423. Use the second mask to longitudinally etch the oxide material, controlling the etching depth to obtain an oxide layer 130. The bottom 131 of the oxide layer 130 has a thickness of h1 and the sidewall 132 has a thickness of d.

[0092] S424. Remove the second mask.

[0093] S425 . Etch the oxide material above the top metal layer 160 to completely or partially expose the upper surface of the top metal layer 160 .

[0094] In step S5 , when preparing the current spreading layer 140 , the space in the trench is completely filled.

[0095] Those skilled in the art can make various other corresponding changes and deformations based on the technical solutions and concepts described above, and all of these changes and deformations should fall within the scope of protection of the claims of the present invention.

Claims

1. A vertical Schottky diode, wherein an oxide layer (130) is provided outside a drift layer (150) and a substrate (120) to electrically isolate an anode; characterized in that: The thickness of the sidewall (132) of the oxide layer (130) is smaller than the thickness of the bottom (131); The specific structure includes a top metal layer (160), a drift layer (150), a substrate (120) and a bottom metal layer (110) stacked in sequence from top to bottom; the bottom metal layer (110) is in ohmic contact with the substrate (120), and the top metal layer (160) is in Schottky contact with the drift layer (150); a plurality of longitudinally extending grooves are provided in the drift layer (150), and the grooves completely penetrate the top metal layer (160) and the drift layer (150) from top to bottom and extend into the substrate (1 20) so as to isolate and separate the drift layer (150) into a plurality of longitudinally extending sub-channels; arranging an oxide layer (130) to cover the exposed surfaces of the top metal layer (160), the drift layer (150) and the substrate (120); and opening a skylight in the oxide layer (130) above the top metal layer (160) to expose all or part of the upper end surface of the top metal layer (160); and arranging a current spreading layer (140) to cover the exposed surfaces of the oxide layer (130) and the top metal layer (160); The substrate (120) and the drift layer (150) are both gallium nitride-based, silicon carbide-based, or gallium oxide-based N-type doped, and the doping concentration of the substrate (120) is higher than that of the drift layer (150).

2. A vertical Schottky diode according to claim 1, characterized in that: The current spreading layers (140) at the sides of adjacent sub-channels are isolated from each other to form air grooves (101).

3. A vertical Schottky diode according to claim 1, characterized in that: The current spreading layers (140) at the sides of adjacent sub-channels contact each other to completely fill the space.

4. A vertical Schottky diode according to claim 1, characterized in that: The thickness of the bottom (131) is greater than 0.1 μm and less than or equal to 7 μm; the thickness of the side wall (132) is greater than or equal to 0.1 μm and less than 7 μm.

5. The vertical Schottky diode according to claim 1, characterized in that: The depth of the trench extending into the substrate (120) is greater than zero and less than 0.5 μm.

6. The method for preparing a vertical Schottky diode according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1. Preparing a drift layer (150) on a substrate (120); S2. Preparing a patterned top metal layer (160) on the drift layer (150); S3. using the top metal layer (160) as a first mask to etch a longitudinally extending groove; S4. Preparing an oxide layer (130) having a bottom (131) having a thickness greater than that of the sidewall (132); S5. Prepare a current spreading layer (140) and a bottom metal layer (110).

7. The preparation method according to claim 6, characterized in that: The step S4 includes the following sub-steps: S411. An oxide material having a thickness of h0 is deposited at the bottom of the trench; S412. Depositing oxide material with a thickness of d on the upper surface of the oxide material obtained in step S411 and on the sides of the groove to obtain an oxide layer (130); the bottom (131) of the oxide layer (130) has a thickness of h1=h0+d, and the sidewall (132) has a thickness of d; the oxide layer (130) does not cover or partially covers the upper surface of the top metal layer (160); In step S5, when preparing the current spreading layer (140), the thickness of the current spreading layer (140) is kept uniform, so that the current spreading layers (140) at the sides of adjacent sub-channels are isolated from each other to form air grooves (101).

8. The preparation method according to claim 6, characterized in that: The step S4 includes the following sub-steps: S421. Depositing an oxide material on the sample prepared in step S3, wherein the oxide material is vertically higher than the top metal layer (160) by a distance d; S422. A second patterned mask is provided on the upper surface of the oxide material obtained in step S421; the second mask has a lateral width that exceeds the distance d on both sides of the drift layer (150); S423. Using a second mask, longitudinally etching the oxide material, controlling the etching depth to obtain an oxide layer (130); the bottom (131) of the oxide layer (130) has a thickness of h1, and the sidewall (132) has a thickness of d; S424. Remove the second mask; S425. Etching the oxide material above the top metal layer (160) to completely or partially expose the upper surface of the top metal layer (160); In step S5, when preparing the current spreading layer (140), the space in the groove is completely filled.

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