Power semiconductor device and back gold method thereof

Abstract

The invention provides a power semiconductor device and a back metal plating method thereof, and belongs to the technical field of power electronic manufacturing. The back gold plating method comprises the following steps: attaching a hard film on a first surface of a substrate; the second surface is polished so that the substrate can be thinned, and the first surface and the second surface are the two opposite faces of the substrate; and evaporating metal on the second surface to form a back gold layer. According to the embodiment of the invention, the problem of non-uniform thickness of subsequent back gold caused by warping of the thinned substrate can be improved.

Description

Technical Field

[0001] The present disclosure relates to the technical field of power electronics manufacturing, and in particular to a power semiconductor device and a back-metal processing method thereof. Background Art

[0002] In power semiconductor devices, it is usually necessary to use a combination of back gold and conductive adhesive to increase the adhesion between the chip and the substrate during packaging, prevent the two from separating, and enhance the heat dissipation performance while improving product reliability.

[0003] In the related art, a back-gold process is usually used to evaporate and form a metal layer on the surface of a substrate of a power device.

[0004] Before forming a metal layer on the substrate, the substrate needs to be polished and thinned to a set thickness. However, after the substrate is thinned, the substrate will experience tensile stress warping; and when the substrate is evaporated in the plating pot, the ambient temperature in the plating pot is high, which will cause the substrate to further warp, resulting in uneven thickness of the evaporated metal layer. Summary of the invention

[0005] The disclosed embodiment provides a power semiconductor device and a back-metal method thereof, which can improve the problem of uneven thickness of the subsequent back-metal due to warping of the substrate after thinning. The technical solution is as follows:

[0006] In one aspect, an embodiment of the present disclosure provides a back-metallization method for a power semiconductor device, the back-metallization method comprising:

[0007] A hard film is attached to the first surface of the substrate; the second surface is polished to thin the substrate, the first surface and the second surface are opposite sides of the substrate; and metal is evaporated on the second surface to form a back gold layer.

[0008] In one implementation of the present disclosure, attaching a hard film on the first surface of the substrate includes: coating a UV-curable adhesive on a transparent tape; attaching a surface of the transparent tape having the UV-curable adhesive to the first surface; and curing the UV-curable adhesive to form the hard film on the first surface.

[0009] In another implementation of the present disclosure, evaporating metal on the second surface to form a back gold layer includes: providing an evaporation device, the evaporation device including a plating pot and a cover plate, the surface of the plating pot has an evaporation hole, the evaporation hole has a cover plate for sealing the evaporation hole, and the cover plate is detachably connected to the evaporation hole; fixing the side of the substrate formed with the hard film on the cover plate; fixing the cover plate on the evaporation hole so that the second surface of the substrate is located in the evaporation hole; turning on the evaporation source to evaporate metal on the second surface to form the back gold layer.

[0010] In another implementation of the present disclosure, grinding the second surface to thin the substrate includes: using a thinning machine to perform rough grinding on the second surface of the substrate so that the substrate is ground to 115μm to 205μm; using a grinder to perform fine grinding on the substrate so that the substrate is ground to 74μm to 101μm.

[0011] In another implementation of the present disclosure, after fine grinding the substrate with a grinder, the method further includes: grinding the second surface of the substrate with a grinding wheel to control the roughness Ra of the second surface to be 0.1 nm to 15 nm.

[0012] In another implementation of the present disclosure, the second surface is ground using a grinding wheel with a mesh size of 300 to 6000.

[0013] In another implementation of the present disclosure, when evaporating metal on the second surface, the operating temperature in the evaporation equipment is controlled to be lower than 150°C.

[0014] In another implementation of the present disclosure, after metal is evaporated on the second surface, the method further includes: adhering the surface of the substrate with the back gold layer formed on it to a blue film, and removing the hard film on the first surface of the substrate.

[0015] In another implementation of the present disclosure, attaching a hard film to the first surface of the substrate further includes: allowing the hard film to cover the first surface and allowing the hard film to extend to the side wall of the substrate.

[0016] On the other hand, an embodiment of the present disclosure provides a power semiconductor device, which includes: a substrate, a circuit board and at least one chip; the chip is located on the first surface of the substrate, and the second surface of the substrate has a back gold layer formed by the back gold method described above, and the back gold layer is located on the circuit board and electrically connected to the circuit board.

[0017] The beneficial effects brought by the technical solution provided by the embodiments of the present disclosure include at least:

[0018] The back-gold method provided by the embodiment of the present disclosure first attaches a hard film to the first surface of the substrate, and uses the hard film to attach to the first surface to improve the overall hardness of the substrate. Then, the second surface of the substrate is polished to thin the substrate. Since the first surface of the substrate is attached with a hard film with greater hardness, on the one hand, attaching the hard film can greatly reduce the risk of substrate breakage, and at the same time can effectively protect the first surface of the substrate; on the other hand, after the substrate is thinned, it is not easy to cause tensile stress warping under the constraint of the hard film, thereby ensuring the flatness of the substrate. Then, metal is evaporated on the second surface of the substrate to form a back-gold layer. In the process of evaporating metal, even if the ambient temperature is too high, the warping of the substrate caused by temperature can still be effectively weakened under the constraint of the hard film, thereby preventing the substrate from warping to a large extent during the evaporation process, which leads to uneven thickness of the metal layer evaporated on the second surface, and improving the preparation quality of the back-gold layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present disclosure. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0020] Figure 1 It is a flow chart of a back-metal method for a power semiconductor device provided by an embodiment of the present disclosure;

[0021] Figure 2 is a flow chart of another method for back-metallization of a power semiconductor device provided by an embodiment of the present disclosure;

[0022] Figure 3 is a structural schematic diagram of an evaporation device provided by an embodiment of the present disclosure;

[0023] Figure 4 is a schematic diagram of connection between a cover plate and a substrate provided by an embodiment of the present disclosure;

[0024] Figure 5 It is a schematic diagram of a power semiconductor device provided by an embodiment of the present disclosure.

[0025] The descriptions of the marks in the figure are as follows:

[0026] 10. substrate; 11. first surface; 12. second surface;

[0027] 20. Hard film;

[0028] 30. Back gold layer;

[0029] 40. Evaporation equipment;

[0030] 41. plating pot; 410. evaporation hole;

[0031] 42. Cover plate;

[0032] 43. Evaporation source;

[0033] 50. Circuit board;

[0034] 60. Chip. DETAILED DESCRIPTION

[0035] In order to make the objectives, technical solutions and advantages of the present disclosure more clear, the embodiments of the present disclosure will be further described in detail below with reference to the accompanying drawings.

[0036] Unless otherwise defined, the technical terms or scientific terms used herein shall have the usual meanings understood by persons with ordinary skills in the field to which the present disclosure belongs. The words "first", "second", "third" and similar words used in the patent application specification and claims of the present disclosure do not indicate any order, quantity or importance, but are only used to distinguish different components. Similarly, words such as "one" or "one" do not indicate a quantity limitation, but indicate the existence of at least one. Words such as "include" or "comprise" and similar words mean that the elements or objects appearing before "include" or "comprise" include the elements or objects listed after "include" or "comprise" and their equivalents, and do not exclude other elements or objects. Words such as "connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right", "top", "bottom" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0037] Figure 1 1 is a flow chart of a method for back-metallization of a power semiconductor device provided by an embodiment of the present disclosure. Figure 1 As shown, the back-gold method includes:

[0038] Step 101 : attaching a hard film 20 to the first surface 11 of the substrate 10 .

[0039] The hardness of the hard film 20 may be greater than the hardness of the substrate 10 , thereby compensating for the hardness lost after the substrate 10 is thinned and preventing the substrate 10 from being easily warped.

[0040] Step 102 : grinding the second surface 12 to thin the substrate 10 .

[0041] The first surface 11 and the second surface 12 are opposite surfaces of the substrate 10 .

[0042] Step 103 : evaporating metal on the second surface 12 to form a back gold layer 30 .

[0043] In the back-gold method provided in the embodiment of the present disclosure, a hard film 20 is firstly attached to the first surface 11 of the substrate 10 , and the hardness of the entire substrate 10 is improved by attaching the hard film 20 to the first surface 11 .

[0044] Then, the second surface 12 of the substrate 10 is polished to thin the substrate 10. Since a hard film 20 with relatively high hardness is attached to the first surface 11 of the substrate 10, on the one hand, the attachment of the hard film can greatly reduce the risk of substrate breakage and can effectively protect the first surface of the substrate; on the other hand, after the substrate 10 is thinned, it is not easy to cause tensile stress warping under the constraint of the hard film 20, thereby ensuring the flatness of the substrate 10.

[0045] Then, metal is evaporated on the second surface 12 of the substrate 10 to form a back gold layer 30. During the metal evaporation process, even if the ambient temperature is too high, the substrate 10 can still be effectively weakened due to the temperature under the restriction of the hard film 20, thereby preventing the substrate 10 from being warped to a large extent during the evaporation process, which causes the problem of uneven thickness of the metal layer evaporated on the second surface 12, thereby improving the preparation quality of the back gold layer 30.

[0046] Figure 2 It is a flow chart of another back-metal method for a power semiconductor device provided in an embodiment of the present disclosure.

[0047] like Figure 2 As shown, the back-gold method includes:

[0048] Step 201 : attaching a hard film 20 to the first surface 11 of the substrate 10 .

[0049] The specific steps may include:

[0050] First, apply UV curing glue on the transparent tape.

[0051] Exemplarily, the transparent tape may be a biaxially oriented polypropylene (BOPP) film.

[0052] The BOPP film has good physical stability, mechanical strength, and air tightness, high transparency and glossiness, and is tough and wear-resistant. The first surface 11 of the substrate 10 attached thereto can better restrict the tensile stress of the substrate 10 .

[0053] Exemplarily, the thickness of the transparent tape is 20 μm to 40 μm, for example, the thickness of the transparent tape is 20 μm.

[0054] Then, a surface of the transparent tape having the UV curing adhesive is attached to the first surface 11 .

[0055] Using the transparent tape as a carrier of the UV-curing adhesive can allow the UV-curing adhesive to be more evenly attached to the first surface 11 , and also make the thickness of the UV-curing adhesive subsequently formed at various locations on the transparent tape more uniform.

[0056] Next, the UV curable adhesive is cured to form a hard film 20 on the first surface 11 .

[0057] In the disclosed embodiment, after the transparent tape carrying the UV curing adhesive is attached to the first surface 11 , the UV curing adhesive can be irradiated with UV light to cure the UV curing adhesive on the transparent tape to form a hard film 20 with a certain hardness.

[0058] In some other implementations, a UV curing tape may be adhered to the first surface 11 of the substrate 10 , and then the UV curing tape is cured to adhere to the substrate 10 .

[0059] Optionally, when the transparent tape is attached to the first surface 11 of the substrate 10 in step 201 , the hard film 20 may cover the first surface 11 and extend to the sidewall of the substrate 10 .

[0060] In this way, the edge of the hard film 20 wraps around the side wall of the substrate 10. When the substrate 10 tends to warp, the hard film 20 attached to the side wall of the substrate 10 can more effectively restrain the warping tendency of the substrate 10, thereby preventing the substrate 10 from warping and deforming.

[0061] Step 202: Roughly grind the second surface 12 of the substrate 10 using a thinning machine.

[0062] In the disclosed embodiment, the substrate 10 may be a sapphire substrate 10. The sapphire substrate 10 has a relatively high light transmittance, that is, the substrate 10 is a transparent substrate 10. In addition, the sapphire material is relatively hard and has relatively stable chemical properties, so that the light-emitting diode has good light-emitting effect and stability.

[0063] Exemplarily, the thickness of the substrate 10 is 1000 μm.

[0064] Since the thickness of the substrate 10 before thinning is relatively large, a thinning machine is first used to roughly grind the second surface 12 of the substrate 10, so that the thickness of the substrate 10 can be reduced to near the required thickness more quickly.

[0065] Exemplarily, after the second surface 12 of the substrate 10 is roughly ground, the thickness of the substrate 10 is reduced to 115 μm to 205 μm.

[0066] As an example, in the embodiment of the present disclosure, the thickness of the substrate 10 after rough grinding is 200 μm.

[0067] Step 203: Use a grinder to perform fine grinding on the substrate 10.

[0068] After the substrate 10 is roughly ground by a thinning machine, the substrate 10 may be finely ground by a grinder so that the thickness of the substrate 10 reaches the thickness required by the design.

[0069] Exemplarily, the second surface 12 of the substrate 10 is further ground to a thickness of the substrate 10 of 74 μm to 101 μm.

[0070] As an example, in the embodiment of the present disclosure, the thickness of the substrate 10 after fine grinding is 100 μm.

[0071] Step 204: Grind the second surface 12 of the substrate 10 using a grinding wheel.

[0072] Optionally, the second surface 12 is ground using a grinding wheel with a mesh number of 300 to 6000. For example, the second surface 12 of the substrate 10 is ground using a grinding wheel with a mesh number of 3000, so that the roughness Ra of the second surface 12 of the substrate 10 is 0.1 nm to 15 nm.

[0073] Exemplarily, the roughness of the second surface 12 of the substrate 10 is Ra 1 μm.

[0074] The roughness of the second surface 12 of the substrate 10 is controlled within the above range, so that the second surface 12 has a certain roughness, which can increase the adhesion between the back gold layer 30 and the second surface 12 and prevent the back gold layer 30 from falling off.

[0075] Step 205: Provide an evaporation device 40.

[0076] Figure 3 Schematic diagram of the structure of a vapor deposition device 40 provided in an embodiment of the present disclosure. Figure 3 As shown, the evaporation device 40 includes a plating pot 41 and a cover plate 42. The surface of the plating pot 41 has an evaporation hole 410. The evaporation hole 410 has a cover plate 42 for sealing the evaporation hole 410. The cover plate 42 is detachably connected to the evaporation hole 410.

[0077] This type of evaporation equipment 40 has an evaporation hole 410 on the plating pot 41. During evaporation, the wafer to be evaporated is installed on the cover plate 42 and then fixed in the evaporation hole 410 through the cover plate 42, so that the wafer to be evaporated can be completely located in the plating pot 41 and fully receive the metal material evaporated by the evaporation source 43.

[0078] Step 206 : Fix the side of the substrate 10 on which the hard film 20 is formed on the cover plate 42 .

[0079] Figure 4 FIG. 4 is a schematic diagram of a connection between a cover plate 42 and a substrate 10 provided in an embodiment of the present disclosure. Figure 4 As shown, the hard film 20 is sandwiched between the cover plate 42 and the substrate 10 .

[0080] In this way, when the substrate 10 warps due to tensile stress generated after thinning, the warping of the substrate 10 will exert a force on the hard film 20 toward the cover plate 42, so that the hard film 20 can better fit the surface of the cover plate 42. This not only prevents the substrate 10 from warping, but also makes the hard film 20 and the substrate 10 smoother with the help of the cover plate 42, thereby improving the uniformity of the subsequent evaporated back gold layer 30.

[0081] In the disclosed embodiment, in order to ensure the uniformity of the coating, the substrate is required to be as flat as possible. However, after the substrate is thinned, there will be a convex phenomenon caused by tensile stress. This phenomenon can be effectively utilized to improve the problem of uneven coating. By setting a relatively flat cover plate on the surface of the hard film, the warping phenomenon of the substrate is used to achieve automatic adhesion between the front of the substrate and the surface of the cover plate. Because the edge of the substrate is pressed, the two can be effectively fitted, thereby achieving an automatic calibration effect and ultimately improving the quality of the coating.

[0082] Step 207 : fix the cover plate 42 on the evaporation hole 410 so that the second surface 12 of the substrate 10 is located in the evaporation hole 410 .

[0083] Step 208 : Turn on the evaporation source 43 to evaporate metal on the second surface 12 to form the back gold layer 30 .

[0084] When metal is evaporated on the second surface 12 , the working temperature in the evaporation device 40 is controlled to be lower than 150° C.

[0085] When evaporating metal, controlling the working temperature of the evaporation device 40 within the above range can avoid the working temperature in the evaporation device 40 being too high, which may cause the hard film 20 to soften, reduce the adhesion of the hard film 20, and cause the hard film 20 to fall off the substrate 10.

[0086] At the same time, the substrate 10 will also be heated during the evaporation process, causing the substrate 10 to expand and contract, so that the tensile stress on the substrate 10 that causes the substrate 10 to warp is further amplified, so that the substrate 10 exerts a greater force on the hard film 20 toward the cover plate 42, so that the hard film 20 can be more closely attached to the surface of the cover plate 42. Not only can the substrate 10 be prevented from warping, but the cover plate 42 can also be used to make the hard film 20 and the substrate 10 more flat, thereby improving the uniformity of the subsequent evaporation of the back gold layer 30.

[0087] Step 209 : Adhere the surface of the substrate 10 on which the back gold layer 30 is formed on the blue film, and remove the hard film 20 on the first surface 11 of the substrate 10 .

[0088] After the back-gold process is completed, the surface of the substrate 10 with the back-gold layer 30 is attached to the blue film using a film laminating machine. Then, the viscosity of the hard film 20 is reduced by heating, so that the hard film 20 can be directly torn off from the blue film to complete the film inversion process. Finally, the conventional process flow can be normally added, and the scratching operation can be completed by grinding wheel cutting or laser cutting.

[0089] The back-gold method firstly attaches a hard film 20 to the first surface 11 of the substrate 10 , and utilizes the hard film 20 to adhere to the first surface 11 to improve the overall hardness of the substrate 10 .

[0090] Then, the second surface 12 of the substrate 10 is polished to thin the substrate 10. Since a hard film 20 with relatively high hardness is attached to the first surface 11 of the substrate 10, the substrate 10 is not prone to tensile stress warping after being thinned under the constraint of the hard film 20, thereby ensuring the flatness of the substrate 10.

[0091] Then, metal is evaporated on the second surface 12 of the substrate 10 to form a back gold layer 30. During the metal evaporation process, even if the ambient temperature is too high, the substrate 10 can still be effectively prevented from warping due to temperature under the restriction of the hard film 20, thereby preventing the substrate 10 from warping during the evaporation process, which causes the problem of uneven thickness of the metal layer evaporated on the second surface 12, thereby improving the preparation quality of the back gold layer 30.

[0092] Figure 5 Schematic diagram of a power semiconductor device provided by an embodiment of the present disclosure. Figure 5 As shown, the power semiconductor device includes: a substrate 10 , a circuit board 50 and at least one chip 60 .

[0093] like Figure 5 As shown, the chip 60 is located on the first surface 11 of the substrate 10 , and the second surface 12 of the substrate 10 has a back gold layer 30 formed by the back gold method as described above, and the back gold layer 30 is located on the circuit board 50 , and the back gold layer 30 is electrically connected to the circuit board 50 .

[0094] When preparing the back gold layer 30 , the hard film 20 is first attached to the first surface 11 of the substrate 10 . The hard film 20 is attached to the first surface 11 to improve the overall hardness of the substrate 10 .

[0095] Then, the second surface 12 of the substrate 10 is polished to thin the substrate 10. Since a hard film 20 with relatively high hardness is attached to the first surface 11 of the substrate 10, the substrate 10 is not prone to tensile stress warping after being thinned under the constraint of the hard film 20, thereby ensuring the flatness of the substrate 10.

[0096] Then, metal is evaporated on the second surface 12 of the substrate 10 to form a back gold layer 30. During the metal evaporation process, even if the ambient temperature is too high, the substrate 10 can still be effectively prevented from warping due to temperature under the restriction of the hard film 20, thereby preventing the substrate 10 from warping during the evaporation process, which causes the problem of uneven thickness of the metal layer evaporated on the second surface 12, thereby improving the preparation quality of the back gold layer 30.

[0097] Optionally, the substrate 10 may be a sapphire substrate 10. The sapphire material is relatively hard and has relatively stable chemical properties, so that the power semiconductor device has good stability.

[0098] Optionally, the chip 60 may include a first GaN layer, a second GaN layer, an AlGaN layer, an ohmic electrode, and a Schottky electrode.

[0099] The first GaN layer and the second GaN layer are sequentially stacked on the substrate 10. The ohmic electrode is connected to the first GaN layer, and the Schottky electrode is connected to the second GaN layer.

[0100] Optionally, the power semiconductor device further includes a third GaN layer, and the third GaN layer is located on the surface of the AlGaN layer.

[0101] The first GaN layer, the second GaN layer and the third GaN layer are all doped with Si, and the doping concentration of the first GaN layer and the doping concentration of the third GaN layer are both higher than that of the second GaN layer.

[0102] Exemplarily, the doping concentration of the first GaN layer is higher than the doping concentration of the third GaN layer, and the doping concentration of the third GaN layer is higher than the doping concentration of the second GaN layer.

[0103] By providing a third GaN layer and making the doping concentration of Si doped in the third GaN layer higher than the doping concentration of Si doped in the second GaN layer, carriers can quickly enter the AlGaN layer and the first GaN layer from the third GaN layer, thereby improving carrier transmission efficiency.

[0104] Furthermore, the doping concentration of Si doped in the first GaN layer is higher than that in the second GaN layer and the third GaN layer, so that carriers can only flow from the first GaN layer to the second GaN layer and the third GaN layer to form unidirectional conduction and constitute a diode device.

[0105] Optionally, the doping concentration of the first GaN layer is 10 17 cm -3 Up to 10 19 cm -3 , the doping concentration of the second GaN layer is 10 15 cm -3 Up to 10 17cm -3 , the doping concentration of the third GaN layer is 5×10 15 cm -3 Up to 5×10 17 cm -3 .

[0106] As an example, in the embodiment of the present disclosure, the doping concentration of the first GaN layer is 10 18 cm -3 , the doping concentration of the second GaN layer is 10 17 cm -3 , the doping concentration of the third GaN layer is 5×10 17 cm -3 .

[0107] In the embodiment of the present disclosure, the first GaN layer, the second GaN layer and the third GaN layer are all doped with Si, that is, the first GaN layer, the second GaN layer and the third GaN layer are all n-type layers.

[0108] Optionally, the thickness of the AlGaN layer is 5 nm to 20 nm, and the thickness of the third GaN layer is greater than 75 nm.

[0109] By setting the thickness of the AlGaN layer within the above range, it is possible to avoid setting the AlGaN layer too thin to reduce the performance of the AlGaN layer in spreading current, and it is also possible to avoid setting the AlGaN layer too late to increase the manufacturing cost.

[0110] As an example, in the embodiment of the present disclosure, the thickness of the AlGaN layer is 10 nm, and the thickness of the third GaN layer may be 100 nm.

[0111] Optionally, the thickness of the first GaN layer is 1 μm to 5 μm, and the thickness of the second GaN layer is 1 μm to 5 μm.

[0112] As an example, in the embodiment of the present disclosure, the thickness of the first GaN layer is 3 μm, and the thickness of the second GaN layer is 3 μm.

[0113] In the embodiment of the present disclosure, a buffer layer and a u-type GaN layer stacked in sequence are further included between the substrate 10 and the first GaN layer.

[0114] Providing a buffer layer is beneficial to the growth of the GaN layer in the subsequent film layer, and can further improve the crystal quality of the GaN layer and ensure the performance of the power semiconductor device.

[0115] Optionally, the buffer layer may be a GaN layer. Exemplarily, the thickness of the buffer layer may be 15 nm to 35 nm. For example, the thickness of the buffer layer is 20 nm.

[0116] Exemplarily, the thickness of the u-type GaN layer may be 0.5 μm to 2 μm. For example, the thickness of the u-type GaN layer may be 1 μm.

[0117] In the disclosed embodiment, the Schottky electrode and the ohmic electrode may be made of aluminum, copper, tungsten, molybdenum, gold, titanium, neodymium, palladium or cesium.

[0118] Exemplarily, the Schottky electrode and the ohmic electrode are made of gold with a thickness of 50 nm to 500 nm.

[0119] The above description is only an optional embodiment of the present disclosure and is not intended to limit the present disclosure. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present disclosure shall be included in the protection scope of the present disclosure.

Claims

1. A back-metal method for a power semiconductor device, characterized in that: The back-gold method comprises: A hard film (20) is attached to a first surface (11) of a substrate (10); grinding the second surface (12) to thin the substrate (10), wherein the first surface (11) and the second surface (12) are opposite surfaces of the substrate (10); Metal is evaporated on the second surface (12) to form a back gold layer (30).

2. The back-metal method according to claim 1, characterized in that: Attaching a hard film (20) to a first surface (11) of a substrate (10) comprises: Applying UV curing adhesive on the transparent tape; Attaching a surface of the transparent tape having the ultraviolet curing adhesive to the first surface (11); The ultraviolet curing adhesive is cured to form the hard film (20) on the first surface (11).

3. The back-metal method according to claim 1, characterized in that: Vapor depositing metal on the second surface (12) to form a back gold layer (30) comprises: Provided is an evaporation device (40), the evaporation device (40) comprising a plating pot (41) and a cover plate (42), the surface of the plating pot (41) having an evaporation hole (410), the evaporation hole (410) having a cover plate (42) for sealing the evaporation hole (410), the cover plate (42) being detachably connected to the evaporation hole (410); Fixing the side of the substrate (10) on which the hard film (20) is formed on the cover plate (42); Fixing the cover plate (42) on the evaporation hole (410) so that the second surface (12) of the substrate (10) is located in the evaporation hole (410); The evaporation source (43) is turned on to evaporate metal on the second surface (12) to form the back gold layer (30).

4. The back-metal method according to any one of claims 1 to 3, characterized in that: Grinding the second surface (12) to thin the substrate (10) comprises: Using a thinning machine to perform rough grinding on the second surface (12) of the substrate (10), so that the substrate (10) is ground to 115 μm to 205 μm; The substrate (10) is finely ground using a grinder, so that the substrate (10) is ground to a thickness of 74 μm to 101 μm.

5. The back-metal method according to claim 4, characterized in that: After fine grinding the substrate (10) by a grinder, the method further comprises: The second surface (12) of the substrate (10) is ground using a grinding wheel, and the roughness Ra of the second surface (12) is controlled to be 0.1 nm to 15 nm.

6. The back-metal method according to claim 5, characterized in that: The second surface (12) is ground using a grinding wheel with a mesh size of 300 to 6000.

7. The back-metal method according to any one of claims 1 to 3, characterized in that: When metal is evaporated on the second surface (12), the operating temperature in the evaporation device (40) is controlled to be lower than 150°C.

8. The back-metal method according to any one of claims 1 to 3, characterized in that: After the second surface (12) is evaporated with metal, the method further comprises: The surface of the substrate (10) formed with the back gold layer (30) is adhered to a blue film, and the hard film (20) on the first surface (11) of the substrate (10) is removed.

9. The back-metal method according to any one of claims 1 to 3, characterized in that: A hard film (20) is attached to a first surface (11) of a substrate (10), and further comprises: The hard film (20) covers the first surface (11), and the hard film (20) extends to the side wall of the substrate (10).

10. A power semiconductor device, characterized in that: The power semiconductor device comprises: a substrate (10), a circuit board (50) and at least one chip (60); The chip (60) is located on the first surface (11) of the substrate (10), and the second surface (12) of the substrate (10) has a back-gold layer (30) formed by the back-gold method according to any one of claims 1 to 9, and the back-gold layer (30) is located on the circuit board (50) and is electrically connected to the circuit board (50).

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