JP7205233B2 - Semiconductor device, method for manufacturing semiconductor device, and method for bonding substrate - Google Patents

Description

The present invention relates to a semiconductor device, a semiconductor device manufacturing method, and a substrate bonding method.

Due to the characteristics of the semiconductor, the operation of the semiconductor device becomes unstable and the characteristics change when the temperature rises. In particular, semiconductor devices used in high-output/high-efficiency amplifiers, high-power switching devices, and the like are subject to large amounts of heat and are likely to reach high temperatures due to the flow of large currents, so heat dissipation is particularly important.

For this reason, a semiconductor having a heat dissipation structure in which a semiconductor element is directly bonded to one surface of a diamond base material, which serves as a diamond heat spreader with high thermal conductivity, and a metallic heat conductor is bonded to the other surface for heat dissipation. An apparatus is disclosed.

Japanese Patent No. 4654389 JP 2018-120963 A

Jean-Paul Crocombette and Lionel Gelebart，‘Multiscale modeling of the thermal conductivity of polycrystalline silicon Carbide’JOURNAL OF APPLIED PHYSICS 106，083520 2009

In direct bonding, one surface of the diamond substrate and the surface of the semiconductor element to be bonded to this surface are flattened and brought into contact with each other for bonding. As the diamond base material, a single crystal diamond base material is often used, but since the single crystal diamond base material is extremely expensive, it is being considered to use a lower cost polycrystalline diamond base material. However, it is extremely difficult to flatten the surface of a polycrystalline diamond base material because diamond is ground differently depending on the crystal face during polishing. For this reason, direct bonding could not be achieved using a polycrystalline diamond base material.

Therefore, there is a demand for a semiconductor device in which a polycrystalline diamond base material, which serves as a diamond heat spreader, and a semiconductor substrate are bonded with low thermal resistance.

According to one aspect of the present embodiment, a semiconductor device comprises a polycrystalline diamond base, a semiconductor element formed on a semiconductor substrate, and SiC provided between the polycrystalline diamond base and the semiconductor element. and a metal layer provided between the polycrystalline diamond base material and the semiconductor layer .

According to the disclosed semiconductor device, it is possible to provide a semiconductor device in which a polycrystalline diamond base material and a semiconductor substrate are bonded with low thermal resistance.

Structural drawing of the semiconductor device in the first embodiment Process drawing (1) of the manufacturing method of the semiconductor device in the first embodiment Process drawing (2) of the manufacturing method of the semiconductor device in the first embodiment Process drawing (3) of the manufacturing method of the semiconductor device in the first embodiment Process drawing (4) of the manufacturing method of the semiconductor device in the first embodiment Process drawing (5) of the manufacturing method of the semiconductor device in the first embodiment Process drawing (6) of the manufacturing method of the semiconductor device in the first embodiment Structural drawing of the semiconductor device in the second embodiment Process drawing (1) of the manufacturing method of the semiconductor device in the second embodiment Process drawing (2) of the manufacturing method of the semiconductor device in the second embodiment Process drawing (3) of the manufacturing method of the semiconductor device in the second embodiment Process drawing (4) of the manufacturing method of the semiconductor device in the second embodiment Process drawing (5) of the manufacturing method of the semiconductor device in the second embodiment Process drawing (6) of the manufacturing method of the semiconductor device in the second embodiment Process drawing (7) of the manufacturing method of the semiconductor device in the second embodiment Structural drawing of the semiconductor device in the third embodiment Process drawing (1) of the manufacturing method of the semiconductor device in the third embodiment Process drawing (2) of the manufacturing method of the semiconductor device in the third embodiment Process drawing (3) of the manufacturing method of the semiconductor device in the third embodiment Process drawing (4) of the manufacturing method of the semiconductor device in the third embodiment Process drawing (5) of the manufacturing method of the semiconductor device in the third embodiment Process drawing (6) of the manufacturing method of the semiconductor device in the third embodiment Process drawing (7) of the manufacturing method of the semiconductor device in the third embodiment

The form for carrying out is demonstrated below. In addition, the same reference numerals are assigned to the same members and the description thereof is omitted.

[First Embodiment]
A heat sink and heat spreader using a diamond base material will be described in more detail. Since diamond has extremely high thermal conductivity, it is effective to use it as a heat sink or heat spreader. For this reason, a semiconductor device is conceivable in which a semiconductor element is joined to a diamond base material that serves as a heat sink or heat spreader. However, when the semiconductor element and the diamond base material are bonded using an adhesive or the like, heat cannot be efficiently transferred from the semiconductor element to the diamond base material because the adhesive does not conduct heat well. Otherwise, the advantage of using a diamond substrate is lost.

Therefore, a method of flattening one surface of the single-crystal diamond substrate and one surface of the semiconductor element and directly bonding the one surface of the single-crystal diamond substrate and the one surface of the semiconductor element is conceivable. ing. In direct bonding, for example, the surface roughness Ra of the bonding surface is required to be 1 nm or less as measured by an atomic force microscope (AFM). Since one surface of the single crystal diamond substrate has the same plane orientation, it is possible to polish one surface flat to the surface roughness required for direct bonding. Diamond substrates are extremely expensive.

Therefore, it is conceivable to use a polycrystalline diamond base material, which is cheaper than a single crystal diamond base material. There is Therefore, even if the surface of the polycrystalline diamond base material is polished, irregularities corresponding to the crystal grains are generated, and the surface roughness Ra becomes 10 nm or more, and the surface roughness Ra required for direct bonding cannot be flattened. . Therefore, the surface of the polycrystalline diamond base material and the surface of the semiconductor element cannot be directly bonded.

The present embodiment is in such a situation, and has been made by the inventor's earnest study.

(semiconductor device)
A semiconductor device according to the first embodiment will be described. As shown in FIG. 1, the semiconductor device according to the present embodiment has a semiconductor layer 20 formed on one surface 10a of a polycrystalline diamond substrate 10, and a semiconductor element 30 is formed on the semiconductor layer 20. One surface 30a is directly joined. In the present embodiment, semiconductor element 30 is formed on a single-crystal SiC substrate, which is a semiconductor substrate, and semiconductor layer 20 is polycrystalline SiC. are made of the same SiC, although they have different crystal structures. Polycrystalline SiC is preferable as a material for the semiconductor layer 20 because it has relatively high thermal conductivity and is relatively easy to planarize by CMP.

Also, on the other surface 30b of the semiconductor element, although not shown, a device is formed of a nitride semiconductor such as GaN. A package substrate or the like made of Cu, CuMo, CuW, or the like may be bonded to the other surface of the polycrystalline diamond base material 10 as necessary.

(Method for manufacturing semiconductor device)
Next, a method for manufacturing a semiconductor device according to this embodiment will be described with reference to FIGS.

First, as shown in FIG. 2, one surface 10a of the polycrystalline diamond substrate 10 is polished by CMP (chemical mechanical polishing). Since the polycrystalline diamond substrate 10 contains a plurality of crystal grains with different plane orientations, one surface 10a of the polycrystalline diamond substrate 10 polished by CMP is not flat and uneven. . Therefore, one surface 10a of the polycrystalline diamond substrate 10 polished by CMP has a surface roughness Ra of 10 nm or more by AFM.

Next, as shown in FIG. 3, a semiconductor layer 20 is formed on one surface 10a of the polycrystalline diamond substrate 10 polished by CMP. The semiconductor layer 20 is made of polycrystalline SiC, has a film thickness of about 15 nm, and is formed by sputtering or CVD (Chemical Vapor Deposition). Film formation by sputtering does not require heating of the polycrystalline diamond substrate 10, which is preferable because film peeling due to thermal expansion is less likely to occur.

Next, as shown in FIG. 4, the semiconductor layer 20 formed on one surface 10a of the polycrystalline diamond substrate 10 is polished by CMP and flattened until the surface roughness Ra becomes 1 nm or less. A flat surface 20a is formed. The semiconductor layer 20 is made of polycrystalline SiC, which is not harder than diamond and has little dependence on the degree of abrasion due to the plane orientation. The thickness Ra can be 1 nm or less.

Similarly, as shown in FIG. 5, one surface 30a of the semiconductor element 30, which is to be bonded to the flat surface 20a of the semiconductor layer 20, is polished and flattened to a surface roughness of 1 nm or less. On the other surface 30b of the semiconductor element 30, although not shown, a device is formed of a nitride semiconductor such as GaN. The thickness of the semiconductor element 30 is, for example, approximately 300 μm.

Next, as shown in FIG. 6, in a high vacuum, a rare A gas beam (for example, an Ar beam or a Xe beam) is applied. As a result, dangling bonds are generated and activated on the surface by removing the contamination layer and the oxide layer on the surface. For the Ar beam, for example, an Ar fast atom beam (Ar-FAB) or the like can be used.

Next, as shown in FIG. 7, the activated surfaces are brought into contact with the flat surface 20a of the semiconductor layer 20 irradiated with the rare gas beam and the one surface 30a of the semiconductor element 30 in a high vacuum. are brought into close contact with each other and joined by direct joining. In this method, the dangling bonds in the semiconductor layer 20 and the semiconductor element 30 are bonded to each other, so that the thermal resistance at the interface can be extremely reduced.

Direct bonding as described above is called Surface Activating Bonding (SAB), and does not require the use of an adhesive material. can be lowered. Moreover, although the crystal structures are different, since the semiconductor layer 20 and the semiconductor element 30 are made of the same SiC, they can be easily bonded by direct bonding.

In the above description, the semiconductor device manufacturing method has been described, but in the present embodiment, the semiconductor element 30 can be simply considered as a substrate, and in this case, the above embodiment can also be considered as a substrate bonding method. be able to. Specifically, the semiconductor layer 20 formed on one surface 10a of the polycrystalline diamond substrate 10 is polished by CMP, one surface of the substrate bonded thereto is polished by CMP, and the semiconductor layer 20 is flattened. The surface 20a and one polished surface of the substrate are directly bonded. A substrate to be bonded is a single-crystal semiconductor substrate such as SiC when applied to a semiconductor device.

(Semiconductor layer 20)
In the semiconductor device of the present embodiment, a semiconductor layer 20 made of polycrystalline SiC is provided between a polycrystalline diamond substrate 10 and a semiconductor element 30 . The thermal conductivity of polycrystalline SiC varies greatly depending on the size of the crystal grains that are formed. If the crystal grain size is small, the thermal conductivity is low, and if the crystal grain size is large, the thermal conductivity is high. . Therefore, it is preferable that the crystal grain size of the polycrystalline SiC forming the semiconductor layer 20 is 70 nm or more. If the crystal grain size of polycrystalline SiC is 70 nm or more, the thermal conductivity is 100 W/m K or more. The heat resistance can be remarkably reduced as compared with the case where the thickness is about 3 μm. From the viewpoint of heat conduction between the polycrystalline diamond substrate 10 and the semiconductor element 30, the thickness of the semiconductor layer 20 is preferably thin. Therefore, the film thickness of the semiconductor layer 20 is preferably 20 nm or less, more preferably 10 nm or less, and even more preferably 5 nm or less.

[Second embodiment]
Next, a semiconductor device according to the second embodiment will be described. In the semiconductor device according to the present embodiment, as shown in FIG. 8, a metal layer 110 made of Ti or Ta is formed on one surface 10a of a polycrystalline diamond substrate 10, and the metal layer A semiconductor layer 120 is formed over 110 . One surface 30a of the semiconductor element is bonded to the flat surface 120a of the semiconductor layer 120 by direct bonding. The semiconductor element 30 is formed on a single crystal SiC substrate which is a semiconductor substrate, the semiconductor layer 120 is polycrystalline SiC, and the semiconductor substrate forming the semiconductor element 30 and the semiconductor layer 120 have different crystal structures. However, they are made of the same SiC.

In this embodiment, by forming the metal layer 110 of Ti or Ta, it is possible to prevent the polycrystalline diamond substrate 10 from being damaged by the Ar beam irradiated during direct bonding. When diamond is directly irradiated with an Ar beam, the irradiated portion becomes amorphous, which may result in a decrease in physical strength or a decrease in bonding strength. However, in the present embodiment, it is possible to prevent the polycrystalline diamond base material 10 from becoming amorphous, thereby improving the reliability of the semiconductor device.

(Method for manufacturing semiconductor device)
Next, a method for manufacturing a semiconductor device according to this embodiment will be described with reference to FIGS. 9 to 14. FIG.

First, as shown in FIG. 9, one surface 10a of the polycrystalline diamond substrate 10 is polished by CMP.

Next, as shown in FIG. 10, a metal layer 110 is formed on one surface 10a of the polycrystalline diamond substrate 10 polished by CMP. The metal layer 110 is made of Ti or Ta deposited by sputtering.

Next, as shown in FIG. 11, a semiconductor layer 120 is deposited on the metal layer 110 . The semiconductor layer 120 is made of polycrystalline SiC and is formed by sputtering or CVD.

Next, as shown in FIG. 12, the semiconductor layer 120 formed on the metal layer 110 on one surface 10a of the polycrystalline diamond substrate 10 is polished by CMP to obtain a surface roughness Ra of 1 nm. It is flattened to form a flat surface 120a.

Similarly, as shown in FIG. 13, one surface 30a of the semiconductor element 30, which is to be bonded to the flat surface 20a of the semiconductor layer 20, is polished and flattened to a surface roughness of 1 nm or less.

Next, as shown in FIG. 14, in a high vacuum, the flat surface 120a of the semiconductor layer 120 and the one surface 30a of the semiconductor element 30 on the metal layer 110 on the one surface 10a of the polycrystalline diamond substrate 10 are separated. is irradiated with a rare gas beam (for example, an Ar beam or a Xe beam). As a result, dangling bonds are generated and activated on the surface by removing the contamination layer and the oxide layer on the surface. In the present embodiment, since the metal layer 110 is made of Ti or Ta, it is possible to prevent the polycrystalline diamond substrate 10 from being damaged when it is irradiated with an Ar beam.

Next, as shown in FIG. 15, in a high vacuum, the flat surface 120a of the semiconductor layer 120 irradiated with the rare gas beam and the one surface 30a of the semiconductor element 30 are brought into contact with each other to activate the activated surfaces. are brought into close contact with each other and joined by direct joining. In this method, the dangling bonds in the semiconductor layer 20 and the semiconductor element 30 are bonded to each other, so that the thermal resistance at the interface can be extremely reduced.

Contents other than the above are the same as in the first embodiment.

[Third Embodiment]
Next, a semiconductor device according to a third embodiment will be described.
In the semiconductor device according to the present embodiment, as shown in FIG. 16, a semiconductor layer 20 is formed of polycrystalline SiC on one surface 10a of a polycrystalline diamond substrate 10, and the semiconductor layer 20 is flat. A metal layer 230 is formed on the surface 20a. The metal layer 230 is made of Ti or Ta, and one surface 30a of the semiconductor element 30 is directly bonded to the surface 230a of the metal layer 230 .

In this embodiment, by forming the metal layer 230 of Ti or Ta, it is possible to prevent the polycrystalline diamond substrate 10 from being damaged by the Ar beam irradiated during direct bonding. Since Ti and Ta forming the metal layer 230 are hardly scraped off even when the Ar beam is irradiated, the one surface 10a of the polycrystalline diamond substrate 10 can be prevented from becoming amorphous.

(Method for manufacturing semiconductor device)
Next, a method for manufacturing a semiconductor device according to this embodiment will be described with reference to FIGS. 17 to 23. FIG.

First, as shown in FIG. 17, one surface 10a of the polycrystalline diamond substrate 10 is polished by CMP.

Next, as shown in FIG. 18, a semiconductor layer 20 is formed on one surface 10a of the polycrystalline diamond substrate 10 polished by CMP.

Next, as shown in FIG. 19, the semiconductor layer 20 formed on one surface 10a of the polycrystalline diamond substrate 10 is polished by CMP and planarized until the surface roughness Ra becomes 1 nm or less. A flat surface 20a is formed.

Next, as shown in FIG. 20, a metal layer 230 is deposited on the flat surface 20a of the semiconductor layer 20. Next, as shown in FIG. The metal layer 230 is made of Ti or Ta deposited by sputtering.

Similarly, as shown in FIG. 21, one surface 30a of the semiconductor element 30 to be bonded to the metal layer 230 is polished and flattened until the surface roughness becomes 1 nm or less.

Next, as shown in FIG. 22, in a high vacuum, the surface 230a of the metal layer 230 on the semiconductor layer 120 on the one side 10a of the polycrystalline diamond substrate 10 and the one side 30a of the semiconductor element 30 are subjected to , a rare gas beam (for example, an Ar beam or a Xe beam) is applied. As a result, dangling bonds are generated and activated on the surface by removing the contamination layer and the oxide layer on the surface. In the present embodiment, since the metal layer 230 is made of Ti or Ta, it is possible to prevent the polycrystalline diamond substrate 10 from being damaged when the Ar beam is irradiated.

Next, as shown in FIG. 23, the surface 230a of the metal layer 230 irradiated with the rare gas beam is brought into contact with the one surface 30a of the semiconductor element 30 in a high vacuum to separate the activated surfaces. They are brought into close contact and joined by direct joining. In this method, the dangling bonds in the metal layer 230 and the semiconductor element 30 are bonded to each other, so that the thermal resistance at the interface can be extremely reduced.

Contents other than the above are the same as in the first embodiment.

Although the embodiment has been described in detail above, it is not limited to a specific embodiment, and various modifications and changes are possible within the scope described in the claims.

With respect to the above description, the following notes are further disclosed.
(Appendix 1)
a polycrystalline diamond substrate;
a semiconductor element formed on a semiconductor substrate;
a semiconductor layer formed of SiC provided between the polycrystalline diamond base material and the semiconductor element;
A semiconductor device comprising:
(Appendix 2)
The semiconductor device according to appendix 1, further comprising a metal layer between the polycrystalline diamond base material and the semiconductor layer.
(Appendix 3)
The semiconductor device according to appendix 1, further comprising a metal layer between the semiconductor layer and the semiconductor element.
(Appendix 4)
4. The semiconductor device according to appendix 2 or 3, wherein the metal layer is made of a material containing Ti or Ta.
(Appendix 5)
5. The semiconductor device according to any one of appendices 1 to 4, wherein the semiconductor element is formed on a SiC substrate.
(Appendix 6)
6. The semiconductor device according to any one of appendices 1 to 5, wherein the semiconductor layer is made of polycrystalline SiC.
(Appendix 7)
7. The semiconductor device according to claim 6, wherein the polycrystalline SiC forming the semiconductor layer has a crystal grain size of 70 μm or more.
(Appendix 8)
8. The semiconductor device according to any one of appendices 1 to 7, wherein the semiconductor layer has a thickness of 20 nm or less.
(Appendix 9)
polishing one surface of the polycrystalline diamond substrate;
forming a film of SiC on one surface of the polycrystalline diamond base material to form a semiconductor layer;
polishing the surface of the semiconductor layer to form a flat surface;
polishing one surface of the semiconductor element;
a step of directly bonding the flat surface of the semiconductor layer and one surface of the semiconductor element;
A method of manufacturing a semiconductor device, comprising:
(Appendix 10)
Between the step of polishing one surface of the polycrystalline diamond substrate and the step of forming the semiconductor layer,
forming a metal layer on one surface of the polycrystalline diamond substrate;
10. The method of manufacturing a semiconductor device according to claim 9, wherein a film of SiC is formed on the metal layer to form the semiconductor layer.
(Appendix 11)
polishing one surface of the polycrystalline diamond substrate;
forming a film of SiC on one surface of the polycrystalline diamond base material to form a semiconductor layer;
polishing the surface of the semiconductor layer to form a flat surface;
forming a metal layer on the flat surface of the semiconductor layer;
polishing one surface of the semiconductor element;
a step of directly bonding the surface of the metal layer and one surface of the semiconductor element;
A method of manufacturing a semiconductor device, comprising:
(Appendix 12)
12. The method of manufacturing a semiconductor device according to appendix 10 or 11, wherein the metal layer is made of a material containing Ti or Ta.
(Appendix 13)
13. The method of manufacturing a semiconductor device according to claim 12, wherein the metal layer is formed by sputtering.
(Appendix 14)
The direct bonding is
irradiating a flat surface of the semiconductor layer and one surface of the semiconductor element with a rare gas beam;
a step of contacting and bonding the flat surface of the semiconductor layer irradiated with the rare gas beam and one surface of the semiconductor element;
11. The method of manufacturing a semiconductor device according to appendix 9 or 10, characterized by comprising:
(Appendix 15)
The direct bonding is
irradiating the surface of the metal layer and one surface of the semiconductor element with a rare gas beam;
a step of contacting and bonding the surface of the metal layer irradiated with the rare gas beam and one surface of the semiconductor element;
12. The method of manufacturing a semiconductor device according to appendix 11, characterized by comprising:
(Appendix 16)
polishing one surface of the polycrystalline diamond substrate;
forming a film of SiC on one surface of the polycrystalline diamond base material to form a semiconductor layer;
polishing the surface of the semiconductor layer to form a flat surface;
polishing one side of the substrate;
a step of directly bonding the flat surface of the semiconductor layer and one surface of the substrate;
A substrate bonding method, comprising:
(Appendix 17)
Between the step of polishing one surface of the polycrystalline diamond substrate and the step of forming the semiconductor layer,
forming a metal layer on one surface of the polycrystalline diamond substrate;
17. The substrate bonding method according to appendix 16, wherein a film of SiC is formed on the metal layer to form the semiconductor layer.
(Appendix 18)
polishing one surface of the polycrystalline diamond substrate;
forming a film of SiC on one surface of the polycrystalline diamond base material to form a semiconductor layer;
polishing the surface of the semiconductor layer to form a flat surface;
forming a metal layer on the flat surface of the semiconductor layer;
polishing one side of the substrate;
a step of directly bonding the surface of the metal layer and one surface of the substrate;
A substrate bonding method, comprising:
(Appendix 19)
The direct bonding is
irradiating a flat surface of the semiconductor layer and one surface of the substrate with a rare gas beam;
a step of contacting and bonding the flat surface of the semiconductor layer irradiated with the rare gas beam and one surface of the substrate;
18. The substrate bonding method according to appendix 16 or 17, characterized by having
(Appendix 20)
The direct bonding is
irradiating the surface of the metal layer and one surface of the substrate with a rare gas beam;
a step of contacting and bonding the surface of the metal layer irradiated with the rare gas beam and one surface of the substrate;
19. The substrate bonding method according to appendix 18, characterized by comprising:

10 polycrystalline diamond substrate 10a one surface 20 semiconductor layer 20a flat surface 30 semiconductor element 30a one surface 30b the other surface

Claims (11)

a polycrystalline diamond substrate;
a semiconductor element formed on a semiconductor substrate;
a semiconductor layer formed of SiC provided between the polycrystalline diamond base material and the semiconductor element;
a metal layer provided between the polycrystalline diamond base material and the semiconductor layer ;
A semiconductor device comprising: a polycrystalline diamond substrate;
a semiconductor element formed on a semiconductor substrate;
a semiconductor layer formed of SiC provided between the polycrystalline diamond base material and the semiconductor substrate;
a metal layer provided between the semiconductor layer and the semiconductor substrate ;
A semiconductor device comprising: The semiconductor substrate is a single crystal SiC substrate,
3. The semiconductor device according to claim 2, wherein the semiconductor layer is made of polycrystalline SiC. 4. The semiconductor device according to claim 1 , wherein said metal layer is made of a material containing Ti or Ta. 5. The semiconductor device according to claim 4, wherein the crystal grain size of polycrystalline SiC forming said semiconductor layer is 70 nm or more. 6. The semiconductor device according to claim 1, wherein said semiconductor layer has a thickness of 20 nm or less. polishing one surface of the polycrystalline diamond substrate;
forming a film of SiC on one surface of the polycrystalline diamond base material to form a semiconductor layer;
polishing the surface of the semiconductor layer to form a flat surface;
polishing one surface of the semiconductor element;
a step of directly bonding the flat surface of the semiconductor layer and one surface of the semiconductor element;
A method of manufacturing a semiconductor device, comprising: Between the step of polishing one surface of the polycrystalline diamond base material and the step of forming the semiconductor layer,
forming a metal layer on one surface of the polycrystalline diamond substrate;
8. The method of manufacturing a semiconductor device according to claim 7, wherein a film of SiC is formed on said metal layer to form said semiconductor layer. polishing one surface of the polycrystalline diamond substrate;
forming a film of SiC on one surface of the polycrystalline diamond base material to form a semiconductor layer;
polishing the surface of the semiconductor layer to form a flat surface;
forming a metal layer on the flat surface of the semiconductor layer;
polishing one surface of the semiconductor element;
a step of directly bonding the surface of the metal layer and one surface of the semiconductor element;
A method of manufacturing a semiconductor device, comprising: polishing one surface of the polycrystalline diamond substrate;
forming a film of SiC on one surface of the polycrystalline diamond base material to form a semiconductor layer;
polishing the surface of the semiconductor layer to form a flat surface;
polishing one side of the substrate;
a step of directly bonding the flat surface of the semiconductor layer and one surface of the substrate;
A substrate bonding method, comprising: polishing one surface of the polycrystalline diamond substrate;
forming a film of SiC on one surface of the polycrystalline diamond base material to form a semiconductor layer;
polishing the surface of the semiconductor layer to form a flat surface;
forming a metal layer on the flat surface of the semiconductor layer;
polishing one side of the substrate;
a step of directly bonding the surface of the metal layer and one surface of the substrate;
A substrate bonding method, comprising:

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