Diamond-based GaN device preparation method and diamond-based GaN device

Abstract

The invention discloses a diamond-based GaN device preparation method and a diamond-based GaN device. The method comprises the following steps: growing a polycrystalline diamond thick film on the back surface of a single crystal substrate through chemical vapor deposition; carrying out first temporary bonding on the polycrystalline diamond thick film and the first temporary bonding substrate; thinning the front surface of the single crystal substrate to complete the preparation of the diamond composite substrate; epitaxially growing a GaN epitaxial structure on the surface of the single crystal substrate; performing a front process of the GaN device on the surface of the GaN epitaxial structure to complete processing of a front electrode structure; carrying out second temporary bonding on the front electrode structure and a second temporary bonding substrate; the first temporary bonding substrate is removed, and thinning of the diamond composite substrate is completed; performing a back hole and back metallization process on the diamond composite substrate; and removing the second temporary substrate through de-bonding to complete the preparation of the diamond-based GaN device. Bonding of GaN and diamond can be effectively achieved, the diamond substrate is thinned, the cost is reduced, and the device performance is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor materials and devices, and in particular relates to a diamond-based GaN device preparation method and a diamond-based GaN device. Background Art

[0002] As a third-generation semiconductor material, GaN has a wide bandgap (3.39 eV at room temperature), a high electron saturation rate (2.5×10 7 The excellent properties of GaN RF power devices, such as high power consumption (up to 200 MW) and high breakdown field strength (3.3 MV / cm), make it superior to silicon and gallium arsenide materials in RF high-power electronic applications. It is very suitable for the development of high-frequency, high-power microwave and millimeter-wave devices and circuits, and has extremely high application value in 5G communications, aerospace, national defense and other fields. However, as the power density of GaN RF power devices increases, the heat accumulation effect in the active area of ​​the chip increases rapidly, resulting in the degradation of its various performance indicators. Its reliability and stability are also seriously challenged, which restricts the full use of its high-power advantages. Therefore, the heat dissipation problem has become one of the main technical bottlenecks restricting the further development and widespread application of GaN RF power devices.

[0003] GaN RF devices are mainly prepared on sapphire, Si and SiC substrates. The thermal conductivities of these three substrates are 50, 150 and 400 W / (m·K) respectively, which makes it difficult to meet the heat dissipation requirements under high-power conditions, severely limiting the release of the potential of GaN-based power devices. Chemical vapor deposited diamond, with a thermal conductivity of up to 2000 W / (m·K), can provide superior heat dissipation performance than other substrate materials such as SiC. Therefore, diamond has gradually become the first choice for thermal management of GaN RF power devices due to its ultra-high thermal conductivity.

[0004] There are three main methods for preparing diamond-based GaN devices: epitaxial growth of GaN on diamond, growth of diamond on GaN, and bonding of GaN and diamond. Due to the large lattice mismatch and thermal mismatch between GaN and diamond, it is very difficult to grow high-quality GaN on diamond or grow diamond on GaN. The bonding process of GaN and diamond has extremely high requirements on the surface parameters of diamond, the roughness of the bonding surface and the bonding process. Generally, the surface roughness below the nanometer level is required, the grinding and polishing process is complex, the cost is extremely high, and due to the surface shape and roughness problems, the effective bonding rate is not high. Summary of the invention

[0005] The purpose of the present invention is to provide a diamond-based GaN device preparation method and a diamond-based GaN device, which can effectively realize the bonding of GaN and diamond, thin the diamond substrate, reduce the cost and improve the device performance.

[0006] One aspect of the present invention provides a method for preparing a diamond-based GaN device, comprising:

[0007] Step S1, providing a single crystal substrate;

[0008] Step S2, growing a polycrystalline diamond thick film on the back side of the single crystal substrate by chemical vapor deposition;

[0009] Step S3, performing a first temporary bonding of the polycrystalline diamond thick film and the first temporary bonding substrate by using the bonding auxiliary layer to achieve temporary support for the polycrystalline diamond thick film;

[0010] Step S4, thinning the front side of the single crystal substrate to complete the preparation of the diamond composite substrate;

[0011] Step S5, epitaxially growing a GaN epitaxial structure on the surface of the single crystal substrate of the diamond composite substrate, thereby completing the preparation of a diamond-based GaN epitaxial wafer based on the diamond composite substrate;

[0012] Step S6, performing a front process of the GaN device on the surface of the GaN epitaxial structure to complete the processing of the front electrode structure;

[0013] Step S7, temporarily bonding the front electrode structure to the second temporary bonding substrate for a second time using a bonding medium to temporarily protect the front electrode structure;

[0014] Step S8, removing the first temporary bonding substrate and the bonding auxiliary layer to complete the thinning of the diamond composite substrate;

[0015] Step S9, performing back hole and back metallization processes on the thinned diamond composite substrate;

[0016] Step S10, removing the second temporary substrate and the bonding medium by debonding, thereby completing the preparation of the diamond-based GaN device.

[0017] Preferably, in step S1, the single crystal substrate is any one of silicon carbide, aluminum nitride, gallium nitride or silicon single crystal substrate, and has a thickness of 300um to 700um.

[0018] Preferably, in step S2, the thickness of the polycrystalline diamond thick film is 50 um to 500 um, and the chemical vapor deposition growth is performed by microwave plasma chemical vapor deposition.

[0019] Preferably, in step S3, the thickness of the first temporary bonding substrate is 300um-1mm, the first temporary bonding substrate is a Si or SiC single crystal substrate, and the bonding auxiliary layer includes one or more of silicon, silicon oxide, silicon nitride, aluminum nitride, aluminum oxide, and silicon carbide.

[0020] Preferably, in step S4, the thinning method includes a combination of any one or more methods of mechanical grinding, chemical mechanical polishing, plasma etching, and laser lift-off, and the thickness of the front side of the single crystal substrate after thinning is 50 nm to 50 um.

[0021] Preferably, a combined method of mechanical grinding and chemical mechanical polishing is used, wherein mechanical grinding is first used to thin the thickness of the single crystal substrate to 10 to 50 um, and then chemical mechanical polishing is used to process the surface of the single crystal substrate, the surface roughness after mechanical grinding is polished to less than 0.5 nm, and the thickness is further precisely thinned to a thickness of 50 nm to 50 um.

[0022] Preferably, a laser lift-off method is adopted to form a stress damage layer inside the single crystal substrate by irradiating the surface of the single crystal substrate with laser, and then the single crystal substrate is annealed to achieve wafer-level lift-off at the position of the stress damage layer, and then the surface of the single crystal substrate is processed by chemical mechanical polishing to polish the surface roughness after laser lift-off to less than 0.5nm, and the thickness is further accurately thinned to a thickness of 50nm to 50um.

[0023] Preferably, in step S7, an organic polymer is used as a bonding medium, and the second temporary bonding substrate is any one of Si, SiC and sapphire.

[0024] Preferably, in step S8, the method for removing the first temporary bonding substrate and the bonding auxiliary layer is a combination of any one or more methods of mechanical grinding, chemical mechanical polishing, plasma etching, laser stripping, and wet etching; in step S10, the debonding method is thermal sliding or laser debonding.

[0025] Another aspect of the present invention provides a diamond-based GaN device, which is prepared using the above method.

[0026] The diamond-based GaN device preparation method and diamond-based GaN device according to the above aspects of the present invention can effectively realize a diamond composite substrate, perform GaN epitaxial growth based on the diamond composite substrate, and achieve thinning of the diamond composite substrate, thereby reducing costs and improving device performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings used in the description of the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work:

[0028] Figure 1 is a flow chart of a method for preparing a diamond-based GaN device according to an embodiment of the present invention;

[0029] Figure 2 is a schematic diagram of providing a single crystal substrate according to an embodiment of the present invention;

[0030] Figure 3 is a schematic diagram of growing a polycrystalline diamond thick film on a single crystal substrate according to an embodiment of the present invention;

[0031] Figure 4 is a schematic diagram of a first temporary wafer bonding between a polycrystalline diamond thick film and a first temporary bonding substrate according to an embodiment of the present invention;

[0032] Figure 5 It is a schematic diagram of thinning the front side of a single crystal substrate to complete the preparation of a diamond composite substrate according to an embodiment of the present invention;

[0033] Figure 6 It is a schematic diagram of epitaxially growing a GaN epitaxial structure on the surface of a single crystal substrate to complete the preparation of a GaN epitaxial wafer with a diamond composite substrate according to an embodiment of the present invention;

[0034] Figure 7 It is a schematic diagram of performing a front process of a GaN device on the surface of a GaN epitaxial structure to complete the processing of a front electrode structure according to an embodiment of the present invention;

[0035] Figure 8 It is a schematic diagram of performing a second temporary bonding with a second temporary bonding substrate and protecting the front electrode structure of the GaN device according to an embodiment of the present invention;

[0036] Fig. 9 It is a schematic diagram of removing the first temporary bonding substrate and the bonding auxiliary layer to complete the thinning of the composite diamond substrate of the GaN device wafer according to an embodiment of the present invention;

[0037] Fig.10 is a schematic diagram of performing back hole and back metal processing on a composite diamond substrate according to an embodiment of the present invention;

[0038] Fig.11 It is a schematic diagram of completing the preparation of a diamond-based GaN device by removing the second temporary substrate through debonding according to an embodiment of the present invention. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] An embodiment of the present invention provides a method for preparing a diamond-based GaN device. Figure 1 FIG. 1 is a flow chart of a method for preparing a diamond-based GaN device according to an embodiment of the present invention. Figure 1 As shown, the method for preparing a diamond-based GaN device according to an embodiment of the present invention includes steps S1 to S10.

[0041] In step S1, if Figure 2 As shown, a single crystal substrate 100 is provided. The single crystal substrate 100 can be any one of silicon carbide (SiC), aluminum nitride (AlN), gallium nitride (GaN) or silicon (Si) single crystal substrates. The back side of the SiC single crystal substrate is a carbon side, and the back side of the AlN and GaN single crystal substrates are nitrogen sides.

[0042] In a specific embodiment, a silicon carbide (SiC) single crystal substrate 100 is provided, with a thickness ranging from 300um to 700um, and a more preferred thickness ranging from 400um to 650um. The front side of the SiC single crystal substrate 100 is a silicon (Si) side, and the back side is a carbon (C) side. The single crystal substrate 100 is a double-sided polished substrate, and the substrate is clean and free of contamination. In order to ensure the subsequent epitaxial quality, the thickness uniformity and surface parameters such as warpage of the single crystal substrate 100 should be controlled as small as possible. In order to ensure the RF performance of the device, the single crystal substrate 100 is a semi-insulating substrate.

[0043] In step S2, if Figure 3 As shown, on the back of the single crystal substrate 100, a polycrystalline diamond thick film 101 is grown by CVD (Chemical Vapor Deposition), and the thickness of the polycrystalline diamond thick film 101 is 50um to 500um, and the more preferred thickness range is 50um to 100um. After the polycrystalline diamond thick film 101 is grown, the surface of the polycrystalline diamond thick film 101 can be ground and polished to reduce the roughness of the diamond surface. The thickness of the polycrystalline diamond thick film 101 can be determined according to the thickness of the final GaN device and the thickness consumed by diamond grinding and polishing. The CVD growth method adopts a microwave plasma chemical vapor deposition (MPCVD) method.

[0044] In step S3, if Figure 4As shown, the polycrystalline diamond thick film 101 is subjected to the first temporary wafer bonding with the first temporary bonding substrate 102, so as to realize the temporary substrate support for the polycrystalline diamond thick film 101. The thickness of the first temporary bonding substrate 102 is 300um to 1mm. The first temporary bonding substrate 102 is a Si or SiC single crystal substrate. In this embodiment, a silicon substrate is used. In order to achieve a better bonding effect, the first temporary wafer bonding is realized by depositing a bonding auxiliary layer 103. The bonding auxiliary layer 103 includes one or more materials such as silicon, silicon oxide, silicon nitride, aluminum nitride, aluminum oxide, and silicon carbide. The temporary bonding can be a high-temperature melt bonding of silicon-silicon or silicon-silicon oxide, or a room temperature surface activation bonding based on the bonding auxiliary layer 103. The bonding auxiliary layer 103 of this embodiment is made of silicon, and the bonding method is a silicon-silicon high-temperature melt bonding.

[0045] In step S4, if Figure 5 As shown, the front side of the single crystal substrate 100 is thinned to reduce the thickness of the single crystal substrate 100 to 50nm-50um. In this embodiment, the thickness is thinned to 1um-5um. The thinning method can be a combination of any one or more methods of mechanical grinding, chemical mechanical polishing, plasma etching, and laser stripping. For example, a method of combining mechanical grinding and chemical mechanical polishing can be used. First, mechanical grinding is used to reduce the thickness of the single crystal substrate 100 to near the target thickness, such as 10-50um. Then, chemical mechanical polishing is used to process the surface of the single crystal substrate 100. The surface roughness after mechanical grinding is polished to less than 0.5nm, and the thickness is further accurately thinned to the required thickness of 50nm-50um, so as to meet the smooth surface required for epitaxial growth, and the preparation of the diamond composite substrate 104 is completed. At this time, the diamond composite substrate 104 includes a polycrystalline diamond thick film 101, a first temporary bonding substrate 102, a bonding auxiliary layer 103 and a single crystal substrate 100. Laser stripping can also be used, whereby the surface of the single crystal substrate 100 is irradiated with laser to form a stress damage layer inside, and then annealing is performed to achieve wafer-level stripping of the single crystal substrate 100 at the location of the stress damage layer. The surface of the single crystal substrate 100 is then processed using chemical mechanical polishing, and the surface roughness after laser stripping is polished to less than 0.5 nm, and the thickness is further precisely thinned to the required thickness of 50 nm to 50 um, so as to meet the smooth surface requirements of epitaxial growth and complete the preparation of the diamond composite substrate 104.

[0046] In step S5, Figure 6As shown, a GaN epitaxial structure 105 is epitaxially grown on the surface of a single crystal substrate 100 of a diamond composite substrate 104 (in the case of a SiC substrate, that is, the Si surface of the SiC substrate), and a diamond-based GaN epitaxial wafer 106 based on the diamond composite substrate 104 is prepared, and the diamond-based GaN epitaxial wafer 106 includes the diamond composite substrate 104 and the GaN epitaxial structure 105. The GaN epitaxial structure 105 generally includes an AlN nucleation layer, a GaN buffer layer, a GaN channel layer, an AlN insertion layer, an AlGaN barrier layer, and a GaN cap layer.

[0047] In step S6, if Figure 7 As shown, the front process of the GaN device is performed on the surface of the GaN epitaxial structure 105 of the diamond-based GaN epitaxial wafer 106 to complete the processing of the front electrode structure 107. The basic structure of the front electrode structure 107 includes a source, a gate and a drain, and may also include a field plate, a multi-layer interconnect metal, a passivation dielectric layer of the electrode, etc.

[0048] In step S7, Figure 8 As shown, the front electrode structure 107 is temporarily bonded to the second temporary bonding substrate 109 using an organic polymer as a bonding medium 108 to temporarily protect the front electrode structure 107 of the GaN device. The second temporary bonding substrate 109 is any one of Si, SiC, and sapphire. In this embodiment, a sapphire substrate is used as the second temporary bonding substrate 109.

[0049] In step S8, Fig. 9 As shown, the first temporary bonding substrate 102 and the bonding auxiliary layer 103 are removed. The method for removing the first temporary bonding substrate 102 and the bonding auxiliary layer may be a combination of any one or more methods of mechanical grinding, chemical mechanical polishing, plasma etching, laser stripping, and wet etching. In this embodiment, a solution containing hydrofluoric acid is used to wet-etch and remove the first temporary bonding substrate 102 and the bonding auxiliary layer 103. After removing the first temporary bonding substrate 102 and the bonding auxiliary layer 103, only the polycrystalline diamond thick film 101 and the thinned single crystal substrate 100 remain on the composite diamond substrate 104. Since the thickness of the polycrystalline diamond thick film 101 is determined by CVD growth, the thickness of the polycrystalline diamond thick film 101 grown by CVD can be determined according to the requirements of the GaN device for the thickness of the diamond substrate, without the need to thin the diamond substrate, thereby avoiding the extremely difficult problem of thinning the diamond substrate, thereby completing the substrate thinning of the diamond-based GaN device.

[0050] In step S9, if Fig.10As shown, the thinned diamond composite substrate is subjected to back hole and back metallization processes to complete the production of back hole 110 and back metal layer 111. The back hole 110 is produced by plasma etching or laser drilling, and the back metal layer 111 is produced by sputtering and electroplating processes.

[0051] In step S10, Fig.11 As shown, the second temporary substrate 109 and the bonding medium 108 are removed by debonding. The debonding method may be thermal slip or laser debonding. The present embodiment uses thermal slip to achieve debonding. After debonding, the preparation of the diamond-based GaN device wafer is completed.

[0052] An embodiment of the present invention further provides a diamond-based GaN device, which is prepared by the above method.

[0053] In summary, the method for preparing a diamond-based GaN device according to an embodiment of the present invention has the following beneficial effects:

[0054] (1) Avoiding material growth problems such as lattice mismatch and thermal mismatch in epitaxial growth of GaN on diamond or growth of diamond on GaN;

[0055] (2) It avoids the process difficulties of GaN original substrate stripping, diamond nano-level polishing, and low-stress bonding between GaN and diamond in the diamond and GaN bonding process route;

[0056] (3) Since the diamond thickness of the present invention is adjustable, there is no need for a diamond substrate thinning process, and thus the process problem of thinning the back side of the diamond substrate can be effectively solved.

[0057] The above description is only by way of illustration of certain exemplary embodiments of the present invention. It is undoubted that those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a diamond-based GaN device, characterized in that: include: Step S1, providing a single crystal substrate; Step S2, growing a polycrystalline diamond thick film on the back side of the single crystal substrate by chemical vapor deposition; Step S3, performing a first temporary bonding of the polycrystalline diamond thick film and the first temporary bonding substrate by using the bonding auxiliary layer to achieve temporary support for the polycrystalline diamond thick film; Step S4, thinning the front side of the single crystal substrate to complete the preparation of the diamond composite substrate; Step S5, epitaxially growing a GaN epitaxial structure on the surface of the single crystal substrate of the diamond composite substrate, thereby completing the preparation of a diamond-based GaN epitaxial wafer based on the diamond composite substrate; Step S6, performing a front process of the GaN device on the surface of the GaN epitaxial structure to complete the processing of the front electrode structure; Step S7, temporarily bonding the front electrode structure to the second temporary bonding substrate for a second time using a bonding medium to temporarily protect the front electrode structure; Step S8, removing the first temporary bonding substrate and the bonding auxiliary layer to complete the thinning of the diamond composite substrate; Step S9, performing back hole and back metallization processes on the thinned diamond composite substrate; Step S10, removing the second temporary substrate and the bonding medium by debonding, thereby completing the preparation of the diamond-based GaN device.

2. The method according to claim 1, characterized in that In step S1, the single crystal substrate is any one of silicon carbide, aluminum nitride, gallium nitride or silicon single crystal substrate, and has a thickness of 300um to 700um.

3. The method according to claim 1 or 2, characterized in that In step S2, the thickness of the polycrystalline diamond thick film is 50 um to 500 um, and the film is grown by chemical vapor deposition using microwave plasma chemical vapor deposition.

4. The method according to claim 1 or 2, characterized in that: In step S3, the thickness of the first temporary bonding substrate is 300um-1mm, the first temporary bonding substrate is a Si or SiC single crystal substrate, and the bonding auxiliary layer includes one or more of silicon, silicon oxide, silicon nitride, aluminum nitride, aluminum oxide, and silicon carbide.

5. The method according to claim 1 or 2, characterized in that: In step S4, the thinning method includes a combination of any one or more methods of mechanical grinding, chemical mechanical polishing, plasma etching, and laser lift-off, and the thickness of the front side of the single crystal substrate after thinning is 50nm-50um.

6. The method according to claim 5, characterized in that A combined method of mechanical grinding and chemical mechanical polishing is used to first thin the thickness of the single crystal substrate to 10-50um by mechanical grinding, and then the surface of the single crystal substrate is processed by chemical mechanical polishing, the surface roughness after mechanical grinding is polished to less than 0.5nm, and the thickness is further accurately thinned to 50nm-50um.

7. The method according to claim 5, characterized in that The laser lift-off method is adopted to form a stress damage layer inside by irradiating the surface of the single crystal substrate with laser, and then the single crystal substrate is peeled off at the position of the stress damage layer through annealing. The surface of the single crystal substrate is then processed by chemical mechanical polishing, and the surface roughness after laser lift-off is polished to less than 0.5nm, and the thickness is further accurately thinned to 50nm~50um.

8. The method according to claim 1 or 2, characterized in that: In step S7, an organic polymer is used as a bonding medium, and the second temporary bonding substrate is any one of Si, SiC, and sapphire.

9. The method according to claim 1 or 2, characterized in that: In step S8, the method for removing the first temporary bonding substrate and the bonding auxiliary layer is a combination of any one or more methods of mechanical grinding, chemical mechanical polishing, plasma etching, laser stripping, and wet etching; in step S10, the debonding method is thermal sliding or laser debonding.

10. A diamond-based GaN device, characterized in that: Prepared by the method according to any one of claims 1 to 9.

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