Single-crystalline AlN thin film on silicon-on-insulator substrate and preparation method thereof

Abstract

The present invention provides a single-crystal AlN thin film on a silicon-on-insulator substrate and a preparation method thereof. The preparation method includes: providing a silicon-on-insulator substrate, the silicon-on-insulator substrate including a plurality of cavities located at an interface in any one of a top layer silicon, a buried oxide layer, and a back substrate or between any two adjacent ones; epitaxially growing an AlN buffer layer on the top layer silicon at a first growth temperature; epitaxially growing a first AlN layer on the AlN buffer layer at a second growth temperature; and epitaxially growing a second AlN layer on the first AlN layer at a third growth temperature. The present invention utilizes a silicon-on-insulator substrate with embedded cavities to reduce the influence brought by lattice mismatch and thermal mismatch during the growth of a single-crystal AlN thin film at high temperature, thereby enabling the growth of a crack-free single-crystal AlN thin film.

Description

Technical Field

[0001] The present invention relates to the manufacturing technology of MEMS device structures, and particularly to a piezoelectric thin film and a preparation method thereof. Background Art

[0002] With the rapid development of wireless communication technology towards high frequency and high performance, more and more requirements are put forward for high-performance frequency control devices. In particular, the role of filters in the front end in improving the anti-interference ability and signal-to-noise ratio of signals has become increasingly prominent. Related devices prepared using single-crystal high-quality AlN have shown broad application prospects in the fields of high-frequency communication, sensing, etc.

[0003] Taking the radio frequency front end as an example, at present, most of the radio frequency front-end filtering devices with the most mature commercial applications, such as bulk acoustic wave resonators (BAW), mostly use polycrystalline AlN piezoelectric thin film materials. The polycrystalline thin film structure has a large number of grain boundaries and defects. When acoustic waves propagate in it, they will be scattered by the grain boundaries and defects, resulting in energy loss, reducing the effective electromechanical coupling efficiency, and it is difficult to improve the quality factor Q value. On the contrary, single-crystal piezoelectric thin films have good crystal quality and few defects. BAW resonators with higher frequencies and Q values prepared using single-crystal piezoelectric thin films have gradually become a research hotspot for further improving the resonance frequency and performance of resonators. However, the preparation of single-crystal AlN thin films is relatively difficult, and cracking and other situations are likely to occur on the surface, which restricts the use of single-crystal piezoelectric thin films in BAW resonators.

[0004] Therefore, the present invention provides a single-crystal AlN thin film material with good crystal quality and few defects and a preparation method thereof. Summary of the Invention

[0005] In view of the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a single-crystal AlN thin film on a silicon-on-insulator substrate and a preparation method thereof, which are used to solve the problems such as excessive stress leading to fracture during the growth of single-crystal AlN in the prior art.

[0006] To achieve the above purpose and other related purposes, the present invention provides a preparation method of a single-crystal AlN thin film on a silicon-on-insulator substrate, and the preparation method includes the following steps:

[0007] Provide a silicon-on-insulator substrate, and the silicon-on-insulator substrate includes a plurality of cavities located in any one of the top silicon, buried oxide layer, back substrate or at the interface between any two adjacent ones;

[0008] Epitaxially grow an AlN buffer layer above the silicon-on-insulator substrate at a first growth temperature;

[0009] Epitaxially grow the first AlN layer on the AlN buffer layer at a second growth temperature;

[0010] Epitaxially grow a second AlN layer on the first AlN layer at a third growth temperature;

[0011] wherein the first growth temperature is lower than the second growth temperature and the third growth temperature.

[0012] Optionally, the cavity has a depth in the range of 0.1 μm - 20 μm, the cavity has a circular cross-section with a diameter in the range of 0.2 μm - 100 μm, or has a rectangular cross-section with side dimensions in the range of 0.2 μm - 100 μm, and the spacing between any two adjacent cavities is 1 to 5 times the size of a single cavity;

[0013] Optionally, the preparation method further includes: pretreating the surface of the silicon-on-insulator substrate before epitaxially growing the AlN buffer layer.

[0014] Optionally, the step of pretreating the silicon-on-insulator substrate includes: introducing an aluminum source at a chamber pressure of 20 mbar - 150 mbar and a temperature of 600 °C - 1200 °C for 1 s - 50 s to grow a pre-deposited aluminum layer on the top silicon, wherein the growth thickness of the pre-deposited aluminum layer is 0.5 nm - 5 nm.

[0015] Optionally, at a chamber pressure of 30 mbar - 150 mbar and a first growth temperature in the range of 800 °C - 1200 °C, introduce a first gas mixture containing a group V element source and a group III element source for 150 s - 450 s to epitaxially grow the AlN buffer layer on the top silicon, and at the same time at least a part of the pre-deposited aluminum layer is transformed into aluminum nitride, wherein the first gas mixture contains a group V element source and a group III element source with a molar flow ratio of 100:1 - 1000:1.

[0016] Optionally, at a chamber pressure of 10 mbar - 100 mbar and a second growth temperature in the range of 1200 °C - 1400 °C, introduce a second gas mixture containing a group V element source and a group III element source for 1000 s - 2000 s to epitaxially grow the first AlN layer on the AlN buffer layer, wherein the second gas mixture contains a group V element source and a group III element source with a molar flow ratio of 1000:1 - 10000:1.

[0017] Optionally, at a chamber pressure of 10 mbar - 100 mbar and a third growth temperature in the range of 1200 °C - 1400 °C, a third gas mixture containing a group V element source and a group III element source is introduced for 200 s - 2000 s to epitaxially grow the second AlN layer on the first AlN layer, wherein the third gas mixture contains the group V element source and the group III element source with a molar flow rate ratio of 100:1 - 1000:1, the growth rate of the first AlN layer is less than that of the second AlN layer, the first AlN layer grows in a three-dimensional island mode, and the second AlN layer grows in a two-dimensional layer mode.

[0018] Optionally, the thickness range of the first AlN layer is 10 nm - 200 nm, and the thickness range of the second AlN layer is 100 nm - 1000 nm.

[0019] Optionally, each of the first gas mixture, the second gas mixture, and the third gas mixture includes H2 or a combination of H2 and N2.

[0020] Optionally, the AlN buffer layer, the first AlN layer, and the second AlN layer are grown by an epitaxial process, and the epitaxial process includes a metalorganic chemical vapor deposition process, a molecular beam epitaxy process, an atomic layer deposition process, or a pulsed laser deposition process.

[0021] Optionally, the top silicon is a (111) crystal plane.

[0022] The present invention also provides a method for manufacturing a semiconductor device, and the manufacturing method includes the method for manufacturing a single-crystal AlN thin film on a silicon-on-insulator substrate described above.

[0023] Optionally, the semiconductor device includes one of a light-emitting diode, a laser diode, a high electron mobility transistor, a radio frequency device, a power device, and a piezoelectric device.

[0024] In the present invention, by epitaxially growing an AlN piezoelectric thin film on an SOI substrate with an embedded cavity, the cavity in the substrate can reduce the influence brought by lattice mismatch and thermal mismatch during the growth of a single-crystal AlN thin film at high temperature, thereby realizing a crack-free single-crystal AlN thin film.

[0025] The crack-free single-crystal AlN thin film of the present invention is suitable for manufacturing various semiconductor devices, and the semiconductor devices include a light-emitting diode, a laser diode, a high electron mobility transistor, a radio frequency device, a power device, and a piezoelectric device, so it has broad application prospects. Description of the Drawings

[0026] Figure 1 It shows a process flow chart for manufacturing a single-crystal AlN thin film on a silicon-on-insulator substrate in an embodiment of the present invention.

[0027] Figure 2 It shows a schematic structural diagram of the SOI substrate with an embedded cavity in the embodiment of the present invention.

[0028] Figures 3A - 3D It shows a schematic diagram of the structures obtained in each step of preparing a single-crystal AlN thin film on an insulator-on-silicon substrate in the embodiment of the present invention.

[0029] Description of component labels

[0030] 100 SOI substrate

[0031] 105 Cavity

[0032] 110 Back substrate

[0033] 120 Buried oxide layer

[0034] 130 Top silicon

[0035] 210 AlN buffer layer

[0036] 220 First AlN layer

[0037] 230 Second AlN layer

[0038] Steps S1 to S4 Detailed implementation manners

[0039] The following uses specific specific examples to illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0040] When detailing the embodiments of the present invention, for ease of explanation, the cross-sectional views showing the device structure will be enlarged locally in a non-general proportion, and the schematic diagrams are only examples and should not limit the scope of protection of the present invention here. In addition, in actual production, three-dimensional spatial dimensions including length, width, and depth should be included.

[0041] For convenience of description, spatial relationship terms such as "under", "below", "lower than", "beneath", "above", "on", etc. may be used herein to describe the relationship between one element or feature shown in the drawings and other elements or features. It will be understood that these spatial relationship terms are intended to encompass other directions of the device in use or operation, in addition to the directions depicted in the drawings. Further, when a layer is referred to as being "between" two layers, it can be the only layer between the two layers, or there can also be one or more intervening layers.

[0042] In the context of the present application, the structure in which the first feature described is "above" the second feature may include embodiments where the first and second features are formed in direct contact, and may also include embodiments where additional features are formed between the first and second features, such that the first and second features may not be in direct contact.

[0043] To grow high-quality single-crystal AlN thin films, it is necessary to consider both the preparation process and the growth substrate. Since the diffusion barrier of Al adsorbed atoms on the growth surface is relatively high during the growth of AlN, AlN tends to grow in a three-dimensional (3D) island mode on the growth surface, and Al atoms tend to remain at the initial surface positions, which is likely to cause extended defects such as high-density grain boundaries and dislocations. Moreover, internal tensile stress is generated when the 3D islands merge, and this tensile stress accumulates as the film thickness increases, which is likely to form dislocations or cause cracking of the AlN thin film. This situation will limit the growth thickness of the single-crystal AlN thin film.

[0044] In addition, since the selection of the growth substrate will affect the dislocation density formed in the AlN epitaxy, and even a too high thermal mismatch between the substrate and the epitaxial layer will cause cracks during the cooling process, thus affecting the material quality; on the other hand, at high temperatures, especially at temperatures above 1000 °C, to grow high-quality AlN crystals, the substrate used for epitaxial growth of AlN thin films is also required to have excellent thermal conductivity.

[0045] The present invention utilizes a void embedded silicon on insulator (VESOI) substrate structure. As a customizable substrate with a three-dimensional structure, the SOI material includes a top silicon layer, a buried oxide layer, and a back substrate to form a sandwich structure, which can meet the process requirements of devices such as MEMS. The void embedded silicon on insulator (VESOI) substrate structure has a flexible void position, which can be located in any one of the top silicon layer, the buried oxide layer, and the back substrate or at the interface between the two. Such a VESOI substrate structure can be applied to fields such as CMOS devices, MEMS, and silicon photonics.

[0046] By epitaxially growing AlN on the VESOI substrate, the voids in the substrate can reduce the effects of lattice mismatch and thermal mismatch during the growth of single-crystal AlN thin films at high temperatures. Moreover, silicon materials have good thermal conductivity, providing growth conditions for performing high-temperature epitaxial growth of AlN.

[0047] To promote stress release of the single-crystal AlN thin film heteroepitaxially grown on the substrate and achieve a crack-free single-crystal AlN thin film, the present invention provides a method for preparing a single-crystal AlN thin film on a silicon-on-insulator substrate, and the preparation method includes the following steps:

[0048] Provide a silicon-on-insulator substrate, the silicon-on-insulator substrate including a plurality of cavities located in any one of the top silicon layer, the buried oxide layer, the back substrate or at the interface between any two adjacent ones thereof;

[0049] Grow an AlN buffer layer on the silicon-on-insulator substrate above the embedded cavities at a first growth temperature;

[0050] Epitaxially grow a first AlN layer on the AlN buffer layer at a second growth temperature;

[0051] Epitaxially grow a second AlN layer on the first AlN layer at a third growth temperature;

[0052] Wherein the first growth temperature is lower than the second growth temperature and the third growth temperature.

[0053] The following will be combined with Figure 1 - Figure 3 to describe the specific details of the method for preparing a single-crystal AlN thin film on a silicon-on-insulator substrate of the present invention.

[0054] It should be noted that the drawings provided in this embodiment only illustrate the basic concept of the present invention in a schematic manner. Therefore, only the components related to the present invention are shown in the drawings, rather than being drawn according to the number, shape and size of the components in actual implementation. The types, quantities and proportions of the components in actual implementation can be arbitrarily changed, and the component layout type may also be more complex.

[0055] Figure 1 Show a process flow chart for preparing a single-crystal AlN thin film on a silicon-on-insulator substrate according to an embodiment of the present invention.

[0056] In step S1, refer to Figure 3A , provide a silicon-on-insulator substrate 100, the silicon-on-insulator substrate 100 sequentially including a back substrate 110, a buried oxide layer 120 and a top silicon layer 130 from bottom to top, wherein a plurality of cavities 105 are provided in the silicon-on-insulator substrate 100, and the cavities 105 are located in any one of the top silicon layer 130, the buried oxide layer 120 and the back substrate 110 or at the interface between any two adjacent ones thereof. Figure 2 Show a schematic structural diagram of the silicon-on-insulator substrate with embedded cavities in an embodiment of the present invention. Specifically, a plurality of cavities can be located on the side of the back substrate 110 or the top silicon layer 130 adjacent to the buried oxide layer 120, such as Figure 2 the structures shown in a and 2j; a plurality of cavities can be located in any one of the back substrate 110, the buried oxide layer 120 and the top silicon layer 130, such as Figure 2 the structures shown in e, 2k and 2l; a plurality of cavities can be located in the buried oxide layer 120 and extend into the back substrate 110 or the top silicon layer 130, such as Figure 2the structures shown in b, 2c, 2h, and 2i; a plurality of cavities may be located in the buried oxide layer 120 and adjacent to the back substrate 110 and / or the top silicon layer 130, as Figure 2 the structures shown in d and 2g; and a plurality of cavities may be arranged to penetrate through the buried oxide layer 120, as Figure 2 the structure shown in f, or penetrate through the buried oxide layer 120 and further extend into the back substrate 110 and the top silicon layer 130, as Figure 2 the structure shown in m. The formation process of the silicon-on-insulator substrate with embedded cavities can refer to relevant technical literature (for example, Qiang Liu, Zhiqiang Mu, Chenhe Liu, Lantian Zhao, etc., "Gate-All-Around MOSFET Built on Void Embedded Silicon on Insulator Substrate", IEEE Electron Device Letters, 2021, 42(5): 657-660, and Lantian Zhao, Qiang Liu, Chenhe Liu, etc., "Total Ionizing Dose Effects on Nanosheet Gate-All-Around MOSFETs Built on Void Embedded Silicon on Insulator Substrate", IEEE Electron Device Letters, 2021, 42(10): 1428-1431), which will not be elaborated here.

[0057] Specifically, the thickness range of the buried oxide layer 120 is 0.1 μm - 10 μm, and the thickness range of the top silicon layer is 0.1 μm - 10 μm. The plurality of cavities 105 are arranged at equal intervals in the same horizontal plane, and the distance between any two adjacent cavities is 1 to 5 times the cavity size. The cavity 105 may have a depth in the range of 0.11 μm - 20 μm and a circular or rectangular cross-section; in particular, the cavity may have a circular cross-section with a diameter in the range of 0.2 μm - 100 μm, or a rectangular cross-section with side length dimensions in the range of 0.2 μm - 100 μm.

[0058] As an example, the top silicon layer 130 is selected to be silicon with a (111) orientation; correspondingly, a c-axis oriented AlN thin film can be grown with Si(111) as the epitaxial surface.

[0059] Subsequently, in step S2, refer to Figure 3B, an AlN buffer layer 210 is epitaxially grown and deposited on a silicon-on-insulator substrate 100 in an embedded cavity 105 at a first growth temperature.

[0060] As an example, before epitaxially growing the AlN buffer layer 210, the silicon-on-insulator substrate 100 is pre-treated, including: cleaning the silicon-on-insulator substrate 100 in the embedded cavity, and then moving it into a reaction chamber to grow a pre-deposited aluminum layer (not shown) on the top silicon 130 of the silicon-on-insulator substrate.

[0061] Specifically, at a chamber pressure of 20 mbar - 150 mbar and a temperature of 600 °C - 1200 °C, an aluminum source is introduced into the reaction chamber at a flow rate of 150 sccm - 250 sccm for 1 s - 50 s, wherein the growth thickness of the pre-deposited aluminum layer is 0.5 nm - 5 nm. Introducing the aluminum source before introducing the nitrogen source for pre-depositing aluminum on the substrate can prevent the top silicon from reacting with NH3 to form Si3N4, avoiding the influence of Si-N preferential bonding on the nucleation of AlN. The pre-deposited aluminum layer can also enhance the surface wettability and improve the diffusion and migration ability of Al atoms, thereby effectively improving the quality of the AlN epitaxial film on the substrate. The aluminum source includes but is not limited to trialkylaluminum, trialkoxyaluminum, aluminum diketonate, derivatives thereof, or any combination of them. In some examples, the growth temperature of the pre-deposited aluminum layer is 1100 °C, the chamber pressure is 100 mbar, the flow rate of trimethylaluminum is 200 sccm, the introduction time is 5 s, and the growth thickness is about 2 nm.

[0062] Subsequently, step S2 is continued. Specifically, at a chamber pressure of 30 mbar - 150 mbar and a first growth temperature of 800 °C - 1200 °C, a first gas mixture is introduced into the reaction chamber for 150 s - 450 s to epitaxially grow an AlN buffer layer 210 on the top silicon 130, and at the same time at least a part of the pre-laid aluminum layer is transformed into aluminum nitride, wherein the first gas mixture contains a group V element source and a group III element source, and the growth thickness of the AlN buffer layer is 25 nm - 35 nm. Due to multiple cavities being embedded in the silicon-on-insulator substrate, silicon atoms slip on the surface during the epitaxial growth of AlN, so that the stress caused by the lattice mismatch between the epitaxial layer and the substrate is partially released through the slip. Preferably, the first gas mixture contains a group V element source and a group III element source with a molar flow ratio of 100:1 - 1000:1. In this embodiment, the group V element source for epitaxially growing the AlN thin film includes NH3, and the group III element source includes trimethylaluminum (TMAl), wherein the flow rate of trimethylaluminum is 50 sccm - 250 sccm. In some examples, the growth temperature of the aluminum nitride buffer layer 210 is 1100 °C, the chamber pressure is 100 mbar, the molar ratio of the group V element source to the group III element source is 700:1, the flow rate of trimethylaluminum is 200 sccm, the introduction time is 200 s, and the growth thickness of the aluminum nitride buffer layer 210 is about 30 nm, thereby obtaining a high-quality aluminum nitride buffer layer 210.

[0063] Next, in step S3, refer to Figure 3C, the first AlN layer 220 is epitaxially grown on the AlN buffer layer 210 at a second growth temperature. Specifically, at a chamber pressure of 10 mbar - 100 mbar and a second growth temperature of 1200 °C - 1400 °C, a second gas mixture is introduced into the reaction chamber for 1000 s - 2000 s to epitaxially grow the first AlN layer 220; wherein, the second gas mixture contains a group V element source and a group III element source, and the growth thickness of the first aluminum nitride layer is 10 nm - 200 nm. As an example, the second gas mixture contains a group V element source and a group III element source with a molar flow rate ratio of 1000:1 - 10000:1. The group V element source for epitaxially growing the first AlN layer includes NH3, and the group III element source includes trimethylaluminum (TMAl), wherein the trimethylaluminum flow rate is 50 sccm - 250 sccm. In some examples, the growth temperature of the first AlN layer 220 is 1300 °C, the chamber pressure is 55 mbar, the molar ratio of the group V element source to the group III element source is 3000:1, the flow rate of trimethylaluminum is 100 sccm, the introduction time is 1500 s, and the growth thickness of the first AlN layer 220 is about 100 nm, thereby obtaining a high-quality first AlN layer 220. By appropriately adjusting the process parameters in the multi-step epitaxial process, the growth mode and surface morphology of AlN can be optimized; in particular, when the growth temperature is lower and / or the molar flow rate ratio of the group V element source to the group III element source is higher, AlN tends to grow in a three-dimensional island mode. As the growth temperature increases, the diffusion ability of Al adatoms increases, and / or as the molar flow rate ratio of the group V element source to the group III element source decreases, the growth mode of AlN gradually changes from a three-dimensional island mode to a two-dimensional layer mode.

[0064] After epitaxially growing the first AlN layer 220, see Figure 3D, step S4 is performed to epitaxially grow a second AlN layer 230 on the first AlN layer 220 at a third growth temperature. Specifically, at a chamber pressure of 10 mbar - 100 mbar and a third growth temperature of 1200 °C - 1400 °C, a third gas mixture is introduced into the reaction chamber for 200 s - 2000 s to epitaxially grow the second AlN layer 230; wherein, the second gas mixture contains a group V element source and a group III element source, and the growth thickness of the second AlN layer is 100 nm - 1000 nm. As an example, the third gas mixture contains a group V element source and a group III element source with a molar flow rate ratio of 100:1 - 1000:1. The group V element source for epitaxially growing the second AlN layer includes NH3, and the group III element source includes trimethylaluminum (TMAl), where the flow rate of trimethylaluminum is 200 sccm - 800 sccm. In this embodiment, the molar flow rate ratio of the group V element source to the group III element source contained in the second gas mixture is higher than the molar flow rate ratio of the group V element source to the group III element source contained in the third gas mixture. The growth rate of the first AlN layer 220 is less than the growth rate of the second AlN layer 230, and the first AlN layer grows in a three-dimensional island mode, while the second AlN layer grows in a two-dimensional layer mode. Further, when the molar flow rate ratio of the group V element source to the group III element source is high, the AlN nucleation density is high, the longitudinal growth rate is large, it is easy to present a three-dimensional island mode of growth, and the dislocation density is high, which is used to release the mismatch stress; when the molar flow rate ratio of the group V element source to the group III element source is low, the AlN nucleation density is low, the grain size and the lateral growth size are larger, the growth rate of AlN is high, and it is easy to present a two-dimensional layer growth mode to guide the dislocation closure. By sequentially setting the first AlN layer with a high molar flow rate ratio of the group V element source to the group III element source and the second AlN layer with a low molar flow rate ratio of the group V element source to the group III element source, the dislocation density of the epitaxial layer can be reduced, and the crystal quality of the grown second AlN layer can be improved.

[0065] In some examples, the temperature for epitaxially growing the second AlN layer 230 on the first AlN layer 220 is 1300 °C, the chamber pressure is 50 mbar, the molar flow rate ratio of the group V element source to the group III element source is 300:1, the flow rate of trimethylaluminum is 300 sccm, the introduction time is 2000 s, and the thickness of the second AlN layer 230 is about 350 nm. As an example, each of the first gas mixture, the second gas mixture, and the third gas mixture further includes H2 or a combination of H2 and N2 to provide a reducing atmosphere suitable for epitaxial growth of AlN.

[0066] In this embodiment, an AlN buffer layer 210, a first AlN layer 220, and a second AlN layer 230 are sequentially grown by an epitaxial process, and the epitaxial process includes, but is not limited to, a metalorganic chemical vapor deposition process (MOCVD), a molecular beam epitaxy process (MBE), an atomic layer deposition process (ALD), or a pulsed laser deposition process (PLD), wherein trimethylaluminum (TMAl) can be used as a group V element source and NH3 can be used as a group III element source to perform the epitaxial process.

[0067] This embodiment also provides a method for manufacturing a semiconductor device, and the manufacturing method includes the method for manufacturing a single-crystal AlN thin film on a silicon-on-insulator substrate described above. Specifically, the semiconductor device includes, but is not limited to: a light-emitting diode, a laser diode, a high electron mobility transistor, a radio frequency device, a power device, and / or a piezoelectric device.

[0068] In summary, for the method for manufacturing a single-crystal AlN piezoelectric thin film on an SOI substrate with an embedded cavity according to the present invention, the cavity in the substrate can reduce the influence brought by lattice mismatch and thermal mismatch during the growth of the single-crystal AlN thin film at high temperature, so as to realize the growth of a crack-free single-crystal AlN thin film and improve the growth thickness and quality of the single-crystal AlN thin film.

[0069] The above embodiments are only illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical ideas disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing a single-crystalline AlN thin film on a silicon-on-insulator substrate, characterized in that, The preparation method comprises the following steps: Providing a silicon-on-insulator substrate, the silicon-on-insulator substrate comprising a plurality of cavities located at an interface in any one of the top silicon, the buried oxide layer, and the back substrate or between any two adjacent ones thereof; Growing a pre-deposited aluminum layer on the top silicon; Epitaxially growing an AlN buffer layer above the silicon-on-insulator substrate at a first growth temperature, and at the same time, at least a part of the pre-deposited aluminum layer is transformed into aluminum nitride; At a second growth temperature, introducing a second gas mixture comprising a group V element source and a group III element source to epitaxially grow a first AlN layer on the AlN buffer layer, wherein the second gas mixture comprises the group V element source and the group III element source with a molar flow ratio of 1000:1 - 10000:1, and the first AlN layer grows in a three-dimensional island mode; At a third growth temperature, introducing a third gas mixture comprising a group V element source and a group III element source to epitaxially grow a second AlN layer on the first AlN layer, wherein the third gas mixture comprises the group V element source and the group III element source with a molar flow ratio of 100:1 - 1000:1, the second AlN layer grows in a two-dimensional layer mode, and the first growth temperature is lower than the second growth temperature and the third growth temperature.

2. The method for preparing a single-crystalline AlN thin film on a silicon-on-insulator substrate according to claim 1, wherein: The cavity has a depth in the range of 0.1 μm - 20 μm, the cavity has a circular cross-section and a diameter in the range of 0.2 μm - 100 μm, or has a rectangular cross-section and side length dimensions in the range of 0.2 μm - 100 μm, and the interval between any two adjacent cavities is 1 to 5 times the size of a single cavity.

3. The method for preparing a single-crystalline AlN thin film on a silicon-on-insulator substrate according to claim 1, wherein: The preparation method further comprises: pre-treating the surface of the silicon-on-insulator substrate before performing the epitaxial growth of the AlN buffer layer.

4. The method for preparing a single-crystalline AlN thin film on a silicon-on-insulator substrate according to claim 3, wherein, The step of pre-treating the silicon-on-insulator substrate comprises: introducing an aluminum source at a chamber pressure of 20 mbar - 150 mbar and a temperature of 600 °C - 1200 °C for 1 s - 50 s to grow a pre-deposited aluminum layer on the top silicon, wherein the growth thickness of the pre-deposited aluminum layer is 0.5 nm - 5 nm.

5. The method for preparing a single-crystalline AlN thin film on a silicon-on-insulator substrate according to claim 1, wherein: At a chamber pressure of 30 mbar - 150 mbar and a first growth temperature in the range of 800 °C - 1200 °C, introducing a first gas mixture comprising a group V element source and a group III element source for 150 s - 450 s to epitaxially grow the AlN buffer layer on the top silicon, and at the same time, at least a part of the pre-deposited aluminum layer is transformed into aluminum nitride, wherein the first gas mixture comprises the group V element source and the group III element source with a molar flow ratio of 100:1 - 1000:

1.

6. The method for preparing a single-crystalline AlN thin film on a silicon-on-insulator substrate according to claim 1, wherein: At a chamber pressure of 10 mbar - 100 mbar and a second growth temperature in the range of 1200 °C - 1400 °C, introducing a second gas mixture comprising a group V element source and a group III element source for 1000 s - 2000 s to epitaxially grow the first AlN layer on the AlN buffer layer.

7. The method for preparing a single-crystalline AlN thin film on a silicon-on-insulator substrate according to claim 1, characterized in that: At a chamber pressure of 10 mbar - 100 mbar and a third growth temperature in the range of 1200 °C - 1400 °C, a third gas mixture containing a group V element source and a group III element source is introduced for 200 s - 2000 s to epitaxially grow the second AlN layer on the first AlN layer, wherein the growth rate of the first AlN layer is less than the growth rate of the second AlN layer.

8. The method for preparing a single-crystalline AlN thin film on a silicon-on-insulator substrate according to claim 1, characterized in that: The thickness range of the first AlN layer is 10 nm - 200 nm, and the thickness range of the second AlN layer is 100 nm - 1000 nm.

9. The method for growing a single crystal AlN thin film on a silicon-on-insulator substrate according to claim 5, characterized in that: The first gas mixture, the second gas mixture, and the third gas mixture each include H2 or a combination of H2 and N2.

10. The method for preparing a single-crystalline AlN thin film on a silicon-on-insulator substrate according to claim 1, wherein: The AlN buffer layer, the first AlN layer, and the second AlN layer are grown by an epitaxial process, and the epitaxial process includes a metalorganic chemical vapor deposition process, a molecular beam epitaxy process, an atomic layer deposition process, or a pulsed laser deposition process.

11. The method for preparing a single-crystalline AlN thin film on a silicon-on-insulator substrate according to claim 1, characterized in that: The top silicon layer has a (111) crystal plane.

12. A method for manufacturing a semiconductor device, characterized in that: The preparation method includes the method for preparing a single-crystal AlN thin film on a silicon-on-insulator substrate as described in any one of claims 1 - 11.

13. The manufacturing method of the semiconductor device according to claim 12, characterized in that: The semiconductor device includes one of a light-emitting diode, a laser diode, a high electron mobility transistor, a radio frequency device, a power device, and a piezoelectric device.

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