Preparation method of gallium nitride template on large-angle sapphire substrate

Abstract

The present invention provides a method for preparing a gallium nitride template on a large-angle sapphire substrate, comprising: step 1) providing a sapphire substrate, placing the sapphire substrate into an MOCVD reaction chamber, wherein the epitaxial surface of the sapphire substrate is oriented to the c-plane and tilted toward the a-plane at an angle greater than or equal to 0.2°; step 2) depositing a low-temperature buffer layer on the sapphire substrate; step 3) performing superlattice growth on the low-temperature buffer layer, wherein the superlattice is formed by alternating growth and stacking of two-dimensional growth layers and three-dimensional growth layers; and step 4) growing a gallium nitride template layer on the superlattice. The present invention can obtain a gallium nitride template having a smooth surface, high crystal quality, and a c-plane tilted toward the m-plane on a sapphire substrate with a c-plane tilted toward the a-plane by more than 0.2°. Using this gallium nitride template, a gallium nitride single crystal with a c-plane tilted toward the m-plane can be obtained, thereby obtaining a gallium nitride-based vertical structure power device with good performance.

Description

Technical Field

[0001] The present invention belongs to the field of semiconductor design and manufacturing, and in particular relates to a method for preparing a gallium nitride template on a large-angle sapphire substrate. Background Art

[0002] Wide bandgap semiconductor gallium nitride (GaN) has a high critical breakdown electric field (~3.3×10 6 V / cm), high electron mobility (~2000cm 2 / V·s) and other characteristics, and the heterojunction high electron mobility transistor (HEMT) based on GaN material also has high concentration (~10 13 cm -2 ) two-dimensional electron gas (2DEG) channel, which makes GaN-based HEMT devices have the characteristics of high reverse blocking voltage, low forward on-resistance, and high operating frequency, and has great application prospects in the field of high current, low power consumption, and high voltage switching devices.

[0003] However, GaN-based HEMT devices have a horizontal structure, and the device area is much larger than that of vertical structure devices, which is not conducive to improving the integration level.

[0004] The current lack of widespread adoption of vertically structured GaN-based power devices stems not only from the high cost of GaN single crystal substrates but also from the difficulty of homoepitaxial growth. Conventional GaN single crystal substrates feature epitaxial growth on the c-plane, tilted 0.2° toward the a-plane. GaN grows faster in the a-plane direction than in the m-plane direction. When epitaxially growing device structures on these GaN single crystal substrates, the density of steps in the a-plane direction is high, and the interval between steps is short. This accelerates the growth rate in the a-plane direction, making it difficult to maintain a flat surface and resulting in a rough surface. Summary of the Invention

[0005] In view of the shortcomings of the prior art described above, the object of the present invention is to provide a method for preparing a gallium nitride template on a sapphire substrate with a large deviation angle, which is used to solve the problem in the prior art that the gallium nitride template heteroepitaxially grown on a sapphire substrate with a c-plane deviation toward the a-plane has a rough surface, which is not conducive to subsequent HVPE (hydride vapor phase epitaxy) epitaxial growth.

[0006] To achieve the above-mentioned object and other related objects, the present invention provides a method for preparing a gallium nitride template on a large-angle sapphire substrate, the preparation method comprising: step 1), providing a sapphire substrate, and feeding the sapphire substrate into an MOCVD reaction chamber, wherein the epitaxial surface of the sapphire substrate is oriented as a c-plane and is tilted toward the a-plane at an angle greater than or equal to 0.2°; step 2), depositing a low-temperature buffer layer on the sapphire substrate; step 3), growing a superlattice on the low-temperature buffer layer, wherein the superlattice is formed by alternating growth and stacking of two-dimensional growth layers and three-dimensional growth layers; and step 4), growing a gallium nitride template layer on the superlattice.

[0007] Optionally, before step 2), the method further includes the steps of high-temperature purging and surface nitriding of the sapphire substrate.

[0008] Optionally, in step 2), when depositing the low-temperature buffer layer, the temperature of the sapphire substrate is between 450 and 600°C, the gas pressure is between 600 and 700 mbar, the molar ratio of the introduced group V elements to the group III elements is between 5000 and 6000, and the thickness is between 30 and 50 nm.

[0009] Optionally, after the low-temperature buffer layer is deposited, the MOCVD reaction chamber is heated to 1050-1100° C., and the low-temperature buffer layer is annealed during the heating process. The annealing time is between 500-700 s and the gas pressure is between 400-500 mbar.

[0010] Optionally, in step 3), the two-dimensional growth layer is a gallium nitride layer grown at low pressure and high temperature, and its growth conditions are: the gas pressure is between 200 and 300 mbar, the temperature is between 1050 and 1100°C, the rotation speed of the tray carrying the sapphire substrate is between 1100 and 1300 rpm, and the molar ratio of the nitrogen element to the gallium element is between 1100 and 1200; the three-dimensional growth layer is a gallium nitride layer grown at high pressure and low temperature, and its growth conditions are: the gas pressure is between 600 and 700 mbar, the temperature is between 1000 and 1050°C, the rotation speed of the tray carrying the sapphire substrate is between 500 and 700 rpm, and the molar ratio of the nitrogen element to the gallium element is between 1400 and 1600.

[0011] Optionally, in step 3), the thickness of the two-dimensional growth layer is between 90 and 110 nm, and the thickness of the three-dimensional growth layer is between 130 and 150 nm.

[0012] Optionally, in step 3), the two-dimensional growth layer and the three-dimensional production layer are alternately grown and stacked 4 to 8 times.

[0013] Optionally, step 4) includes the following steps: step 4-1), depositing a three-dimensional growth template layer on the superlattice, wherein the growth conditions are: the gas pressure is between 600 and 700 mbar, the temperature is between 1010 and 1050°C, the rotation speed of the tray carrying the sapphire substrate is between 500 and 700 rpm, and the molar ratio of the nitrogen element to the gallium element is between 1450 and 1600; step 4-2), depositing a two-dimensional growth template layer on the three-dimensional growth template layer, wherein the growth conditions are: the gas pressure is between 200 and 300 mbar, the temperature is between 1080 and 1110°C, the rotation speed of the tray carrying the sapphire substrate is between 1100 and 1300 rpm, and the molar ratio of the nitrogen element to the gallium element is between 900 and 1000.

[0014] Optionally, the growth thickness of the three-dimensional growth template layer is between 0.3 and 0.5 μm; the growth thickness of the two-dimensional growth template layer is between 3 and 4 μm.

[0015] Optionally, the epitaxial plane of the gallium nitride template layer is oriented as a c-plane and is tilted toward the m-plane at an off-angle greater than or equal to 0.2°.

[0016] As described above, the method for preparing a gallium nitride template on a large-angle sapphire substrate of the present invention has the following beneficial effects:

[0017] The present application provides a method for preparing a gallium nitride template on a large-angle sapphire substrate. Through this preparation method, a superlattice is grown on a low-temperature buffer layer, where the superlattice is formed by alternating growth and stacking of two-dimensional growth layers and three-dimensional growth layers, and then a gallium nitride template layer is grown on the superlattice. A gallium nitride template with a flat surface, high crystal quality, and a c-plane deflected toward the m-plane can be obtained on a sapphire substrate with a c-plane deflected toward the a-plane by more than 0.2°. Using this gallium nitride template, a gallium nitride single crystal with a c-plane deflected toward the m-plane can be obtained, thereby obtaining a gallium nitride-based vertical structure power device with good performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figures 1 to 4 Shown are structural schematic diagrams of the steps of a method for preparing a gallium nitride template on a high-angle sapphire substrate according to an embodiment of the present invention.

[0019] Figure 5 Shown is the morphology of the gallium nitride template obtained by conventional process.

[0020] Figure 6 Shown is the morphology of the gallium nitride template obtained by the method for preparing the gallium nitride template on a high-angle sapphire substrate of this embodiment.

[0021] Component number description

[0022] 101 Sapphire Substrate

[0023] 102 Low-temperature buffer layer

[0024] 20 Superlattice

[0025] 201 Two-dimensional growth layer

[0026] 202 Three-dimensional growth layer

[0027] 30 GaN template layer

[0028] 301 Three-dimensional growth template layer

[0029] 302 Two-dimensional growth template layer DETAILED DESCRIPTION

[0030] The following describes the embodiments of the present invention through specific examples. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention.

[0031] For example, when describing the embodiments of the present invention, cross-sectional views of device structures may be partially enlarged to scale for ease of explanation. Furthermore, these schematic views are merely illustrative and should not limit the scope of the present invention. Furthermore, in actual manufacturing, three-dimensional dimensions, including length, width, and depth, should be included.

[0032] For convenience, spatially relative terms such as "under," "below," "below," "below," "above," and "on" may be used herein to describe the relationship of one element or feature to other elements or features shown in the drawings. It will be understood that these spatially relative terms are intended to encompass orientations of the device in use or operation in addition to the orientation depicted in the drawings. Additionally, when a layer is referred to as being "between" two layers, it can be the only layer between the two layers, or one or more intervening layers may also be present.

[0033] In the context of the present application, a structure described as a first feature being "above" a second feature may include embodiments where the first and second features are formed in direct contact, and may also include embodiments where an additional feature is formed between the first and second features, such that the first and second features may not be in direct contact.

[0034] It should be noted that the illustrations provided in this embodiment are only used to schematically illustrate the basic concept of the present invention. Therefore, the illustrations only show components related to the present invention and are not drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component can be changed at will, and the component layout type may also be more complicated.

[0035] In order to obtain a flat homoepitaxial surface on a GaN single crystal substrate, GaN needs to have similar growth rates on the a-plane and m-plane during epitaxial growth. Therefore, the epitaxial growth surface of the GaN single crystal substrate is required to be the c-plane and tilted toward the m-plane by more than 0.2° to ensure that there are steps with a sufficiently short period in the m-direction, thereby increasing the growth rate in the m-direction to a level close to that in the a-direction.

[0036] Conventional gallium nitride single crystal substrates with c-plane biased to a-plane are obtained by stripping off a gallium nitride thick film heteroepitaxially grown on a sapphire substrate 101 with c-plane biased to m-plane. To obtain a gallium nitride single crystal substrate with c-plane biased to m-plane, it is necessary to strip off a gallium nitride thick film heteroepitaxially grown on a sapphire substrate with c-plane biased to a-plane. And in order to obtain a gallium nitride thick film heteroepitaxially grown on a sapphire substrate with c-plane biased to a-plane, it is necessary to provide a gallium nitride template heteroepitaxially grown on a sapphire substrate with c-plane (0001 plane) biased to a-plane. However, the gallium nitride template heteroepitaxially grown on a sapphire substrate with c-plane biased to a-plane obtained by conventional methods has a rough surface, which is not conducive to subsequent HVPE epitaxial growth.

[0037] like Figures 1 to 4 As shown, this embodiment provides a method for preparing a gallium nitride template on a large-angle sapphire substrate, the preparation method comprising:

[0038] like Figure 1 As shown, first, step 1) is performed to provide a sapphire substrate 101, and the sapphire substrate 101 is sent into the MOCVD reaction chamber. The epitaxial surface of the sapphire substrate 101 is oriented to the c-plane and tilted toward the a-plane at an angle greater than or equal to 0.2°.

[0039] Specifically, a sapphire substrate 101 is provided and sent into a MOCVD reaction chamber for high-temperature purging and surface nitridation to provide a good growth interface for the subsequent low-temperature buffer layer 102 .

[0040] like Figure 2 As shown, step 2) is then performed to deposit a low-temperature buffer layer 102 on the sapphire substrate 101 .

[0041] The low-temperature buffer layer may be, for example, a low-temperature gallium nitride layer.

[0042] Specifically, when depositing the low-temperature buffer layer 102, the temperature of the sapphire substrate 101 is between 450°C and 600°C, the pressure is between 600 and 700 mbar, the molar ratio of the introduced Group V elements (such as nitrogen, etc.) to the Group III elements (such as gallium, etc.) is between 5000 and 6000, and the thickness is between 30 and 50 nm. For example, in this embodiment, when depositing the low-temperature buffer layer 102, the temperature of the sapphire substrate 101 is 540°C, the pressure is 660 mbar, the molar ratio of the introduced Group V elements (such as nitrogen, etc.) to the Group III elements (such as gallium, etc.) is 5620, and the thickness is 40 nm.

[0043] After the low-temperature buffer layer 102 is deposited, the MOCVD reaction chamber is heated to 1050-1100°C, and the low-temperature buffer layer 102 is annealed during the heating process. The annealing time is between 500-700 seconds, and the pressure is between 400-500 mbar. For example, after the low-temperature buffer layer 102 is deposited, the MOCVD reaction chamber is heated to 1080°C, and the low-temperature buffer layer 102 is annealed during the heating process. The annealing time is between 600 seconds, and the pressure is 460 mbar.

[0044] like Figure 3 As shown, step 3 is then performed to grow a superlattice 20 on the low-temperature buffer layer 102. The superlattice 20 is formed by alternating growth and stacking of a two-dimensional growth layer 201 and a three-dimensional growth layer 202.

[0045] In this embodiment, the two-dimensional growth layer 201 is a gallium nitride layer grown at low pressure and high temperature, and its growth conditions are: gas pressure between 200 and 300 mbar, temperature between 1050 and 1100°C, the rotation speed of the tray carrying the sapphire substrate 101 is between 1100 and 1300 rpm, the molar ratio of the introduced nitrogen element to the gallium element is between 1100 and 1200, and the thickness of the two-dimensional growth layer 201 is between 90 and 110 nm; the three-dimensional growth layer 202 is a gallium nitride layer grown at high pressure and low temperature, and its growth conditions are: gas pressure between 600 and 700 mbar, temperature between 1000 and 1050°C, the rotation speed of the tray carrying the sapphire substrate 101 is between 500 and 700 rpm, the molar ratio of the introduced nitrogen element to the gallium element is between 1400 and 1600, and the thickness of the three-dimensional growth layer 202 is between 130 and 150 nm. In a specific implementation process, the two-dimensional growth layer 201 is a gallium nitride layer grown at low pressure and high temperature, and its growth conditions are: gas pressure of 260 mbar, temperature of 1080°C, the rotation speed of the tray carrying the sapphire substrate 101 is 1200 rpm, the molar ratio of the nitrogen element to the gallium element is 1130, and the thickness of the two-dimensional growth layer 201 is 100 nm; the three-dimensional growth layer 202 is a gallium nitride layer grown at high pressure and low temperature, and its growth conditions are: gas pressure of 660 mbar, temperature of 1030°C, the rotation speed of the tray carrying the sapphire substrate 101 is 660 rpm, the molar ratio of the nitrogen element to the gallium element is 1519, and the thickness of the three-dimensional growth layer 202 is 140 nm.

[0046] like Figure 3 As shown, the two-dimensional growth layer 201 and the three-dimensional production layer are alternately grown and stacked 4 to 8 times. In a specific embodiment, the two-dimensional growth layer 201 and the three-dimensional production layer are alternately grown and stacked 5 times. By arranging the two-dimensional growth layer 201 and the three-dimensional growth layer 202 for alternating growth and stacking, and by alternating the different crystal qualities and surface morphologies of the two-dimensional growth layer 201 and the three-dimensional growth layer 202, the superlattice 20 can gradually obtain an epitaxial surface inclined toward the m-plane through the superlattice 20, and can gradually reduce the lattice mismatch between the subsequent gallium nitride template layer 30 and the sapphire substrate 101, thereby obtaining a gallium nitride template layer 30 with good crystal quality.

[0047] like Figure 4 As shown, step 4) is finally performed to grow a gallium nitride template layer 30 on the superlattice 20 .

[0048] In this embodiment, the following steps are included: Step 4-1), depositing a three-dimensional growth template layer 301 on the superlattice 20, wherein the growth conditions are as follows: the pressure is between 600 and 700 mbar, the temperature is between 1010 and 1050° C., the rotation speed of the tray carrying the sapphire substrate 101 is between 500 and 700 rpm, the molar ratio of the nitrogen element to the gallium element is between 1450 and 1600, and the growth thickness of the three-dimensional growth template layer 301 is between 0.3 and 0.5. μm; step 4-2), depositing a two-dimensional growth template layer 302 on the three-dimensional growth template layer 301, the growth conditions are: the gas pressure is between 200 and 300 mbar, the temperature is between 1080 and 1110 ° C, the rotation speed of the tray carrying the sapphire substrate 101 is between 1100 and 1300 rpm, the molar ratio of the nitrogen element to the gallium element is between 900 and 1000, and the growth thickness of the two-dimensional growth template layer 302 is between 3 and 4 μm. In a specific implementation process, a three-dimensional growth template layer 301 is deposited on the superlattice 20, and its growth conditions are: gas pressure of 660 mbar, temperature of 1030°C, rotation speed of the tray carrying the sapphire substrate 101 is 600 rpm, the molar ratio of the nitrogen element to the gallium element is 1519, and the growth thickness of the three-dimensional growth template layer 301 is 0.4 μm; a two-dimensional growth template layer 302 is deposited on the three-dimensional growth template layer 301, and its growth conditions are: gas pressure of 260 mbar, temperature of 1095°C, rotation speed of the tray carrying the sapphire substrate 101 is 1200 rpm, the molar ratio of the nitrogen element to the gallium element is 955, and the growth thickness of the two-dimensional growth template layer 302 is 3.1 μm. By using the preparation method of the present invention, the epitaxial surface orientation of the obtained gallium nitride template layer 30 is that the c-plane is tilted toward the m-plane at an angle, and the angle is greater than or equal to 0.2°. That is, a gallium nitride template with a flat surface, high crystal quality, and a c-plane tilted toward the m-plane can be obtained on a sapphire substrate 101 with a c-plane tilted toward the a-plane by more than 0.2°. By using this gallium nitride template, a gallium nitride single crystal with a c-plane tilted toward the m-plane can be obtained, thereby obtaining a gallium nitride-based vertical structure power device.

[0049] Figure 5 The morphology of the gallium nitride template obtained by conventional process is shown. Its surface is relatively rough. Figure 6 The topography of the GaN template obtained by the method for preparing the GaN template on the high-angle sapphire substrate 101 according to this embodiment is shown. Obviously, the surface of the GaN template obtained by the improved process of this embodiment is very flat, and the surface flatness is greatly improved compared to the conventional process.

[0050] The following table is a comparison of the crystal quality of the gallium nitride template obtained by the preparation method of the gallium nitride template on the large-angle sapphire substrate 101 of this embodiment and the gallium nitride template obtained by the conventional process. Obviously, the FWHM of the 102 surface of the sample obtained in this application is significantly lower than that of the conventional process. Among them, F, C, and R in the table represent the values ​​of FWHM at several different positions, and Avg represents the average value of the values ​​at these positions.

[0051]

[0052] As described above, the method for preparing a gallium nitride template on a large-angle sapphire substrate of the present invention has the following beneficial effects:

[0053] The present application provides a method for preparing a gallium nitride template on a large-angle sapphire substrate 101. Through this preparation method, a superlattice 20 is grown on a low-temperature buffer layer 102, where the superlattice 20 is formed by alternating growth and stacking of two-dimensional growth layers 201 and three-dimensional growth layers 202. A gallium nitride template layer 30 is then grown on the superlattice 20. A gallium nitride template having a smooth surface, high crystal quality, and a c-plane deflected toward the m-plane can be obtained on the sapphire substrate 101, where the c-plane deflects toward the a-plane by more than 0.2°. Using this gallium nitride template, a gallium nitride single crystal with a c-plane deflected toward the m-plane can be obtained, thereby obtaining a gallium nitride-based vertical structure power device with good performance.

[0054] Therefore, the present invention effectively overcomes various shortcomings of the prior art and has high industrial utilization value.

[0055] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A method for preparing a gallium nitride template on a large-angle sapphire substrate, characterized in that: The preparation method comprises: Step 1) providing a sapphire substrate, and placing the sapphire substrate into an MOCVD reaction chamber, wherein the epitaxial surface of the sapphire substrate is oriented as a c-plane and tilted toward the a-plane at an angle greater than or equal to 0.2°; Step 2), depositing a buffer layer on the sapphire substrate; Step 3), growing a superlattice on the buffer layer, wherein the superlattice is formed by alternating growth and stacking of two-dimensional growth layers and three-dimensional growth layers; Step 4), growing a gallium nitride template layer on the superlattice; Step 4) comprises the following steps: Step 4-1), depositing a three-dimensional growth template layer on the superlattice, wherein the growth conditions are: a pressure between 600 and 700 mbar, a temperature between 1010 and 1050°C, a rotation speed of the tray carrying the sapphire substrate between 500 and 700 rpm, and a molar ratio of nitrogen to gallium between 1450 and 1600; Step 4-2), depositing a gallium nitride template layer on the three-dimensional growth template layer; A two-dimensional growth template layer is deposited on the substrate, and its growth conditions are as follows: gas pressure between 200 and 300 mbar, temperature between 1080 and 1110°C, rotation speed of a tray carrying the sapphire substrate between 1100 and 1300 rpm, and a molar ratio of nitrogen to gallium between 900 and 1000; the epitaxial surface orientation of the gallium nitride template layer is the c-plane and is tilted toward the m-plane at an angle greater than or equal to 0.2°, and the gallium nitride template layer is used to prepare a gallium nitride-based vertical structure power device.

2. The method for preparing a gallium nitride template on a high-angle sapphire substrate according to claim 1, wherein: Before step 2), the method further includes the steps of high-temperature purging and surface nitriding of the sapphire substrate.

3. The method for preparing a gallium nitride template on a high-angle sapphire substrate according to claim 1, wherein: In step 2), when depositing the buffer layer, the temperature of the sapphire substrate is between 450 and 600° C., the pressure is between 600 and 700 mbar, the molar ratio of the introduced group V elements to the group III elements is between 5000 and 6000, and the thickness is between 30 and 50 nm.

4. The method for preparing a gallium nitride template on a high-angle sapphire substrate according to claim 3, wherein: After the buffer layer is deposited, the temperature of the MOCVD reaction chamber is raised to 1050-1100° C., and the buffer layer is annealed during the heating process. The annealing time is between 500-700 seconds, and the gas pressure is between 400-500 mbar.

5. The method for preparing a gallium nitride template on a high-angle sapphire substrate according to claim 1, wherein: In step 3), the two-dimensional growth layer is a gallium nitride layer grown at low pressure and high temperature, and its growth conditions are: the gas pressure is between 200 and 300 mbar, the temperature is between 1050 and 1100°C, the rotation speed of the tray carrying the sapphire substrate is between 1100 and 1300 rpm, and the molar ratio of the nitrogen element to the gallium element is between 1100 and 1200; the three-dimensional growth layer is a gallium nitride layer grown at high pressure and low temperature, and its growth conditions are: the gas pressure is between 600 and 700 mbar, the temperature is between 1000 and 1050°C, the rotation speed of the sapphire substrate is between 500 and 700 rpm, and the molar ratio of the nitrogen element to the gallium element is between 1400 and 1600.

6. The method for preparing a gallium nitride template on a high-angle sapphire substrate according to claim 1, wherein: In step 3), the thickness of the two-dimensional growth layer is between 90 and 110 nm, and the thickness of the three-dimensional growth layer is between 130 and 150 nm.

7. The method for preparing a gallium nitride template on a high-angle sapphire substrate according to claim 1, wherein: In step 3), the two-dimensional growth layer and the three-dimensional production layer are alternately grown and stacked 4 to 8 times.

8. The method for preparing a gallium nitride template on a high-angle sapphire substrate according to claim 1, wherein: The growth thickness of the three-dimensional growth template layer is between 0.3 and 0.5 μm; the growth thickness of the two-dimensional growth template layer is between 3 and 4 μm.

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