Method for manufacturing epitaxial structure, epitaxial structure and applications thereof

Abstract

The application relates to a preparation method of an epitaxial structure, the epitaxial structure and application thereof. The preparation method of the epitaxial structure comprises the following steps: providing a substrate; introducing a nitrogen source and a group III source, and epitaxially growing at least one dislocation blocking layer on the substrate by adopting a molecular beam epitaxy process; the dislocation blocking layer comprises a first growth layer and a second growth layer which are stacked in sequence, the first growth layer has a three-dimensional island-shaped morphology, the bottom surface of the second growth layer is in contact with the surface of the first growth layer which is away from the substrate, and the surface of the second growth layer which is away from the substrate has a planar structure; during the growth of the first growth layer, the stoichiometric ratio of the flow rates of the nitrogen source and the group III source is greater than 1, and during the growth of the second growth layer, the stoichiometric ratio of the flow rates of the nitrogen source and the group III source is less than 1; and a group III nitride material layer is epitaxially grown on the dislocation blocking layer by adopting the molecular beam epitaxy process. In this way, part of the dislocations can be terminated in the dislocation blocking layer, so that the dislocation density in the epitaxial structure is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor technology, in particular to a preparation method of an epitaxial structure, an epitaxial structure and application thereof. BACKGROUND

[0002] With the rapid development of semiconductor technology, the demand for high-quality semiconductor thin films is increasing. Molecular beam epitaxy (MBE) technology has become one of the key technologies for preparing high-performance semiconductor devices due to its advantages of being able to precisely control the film growth thickness, composition and doping concentration at the atomic scale. Among many semiconductor material systems, thin film materials based on molecular beam epitaxy have important application prospects in the fields of optoelectronics and microelectronics. Compared with metal-organic chemical vapor deposition (MOCVD), MBE has the advantages of low impurity pollution, low growth temperature and real-time in-situ monitoring, and can be used to grow high-purity, high-crystalline quality and interface mutant semiconductor materials.

[0003] In the traditional molecular beam epitaxy growth process, when growing a heterostructure with lattice mismatch, due to the difference in lattice constant between the substrate and the epitaxial layer, a large number of dislocations will be generated at the interface and will extend to the entire thin film layer as the epitaxial layer grows. The existence of dislocations will seriously affect the electrical, optical and other properties of semiconductor materials, such as reducing electron mobility, increasing carrier scattering probability and introducing non-radiative recombination centers, etc., which in turn leads to problems such as performance degradation, reliability reduction and power consumption increase of devices prepared based on these semiconductor materials. Therefore, how to reduce the dislocation density in the epitaxial layer grown by molecular beam epitaxy process is a technical problem that needs to be solved at present. SUMMARY

[0004] Therefore, the embodiments of the present application provide a preparation method of an epitaxial structure, an epitaxial structure and application thereof to solve at least one problem in the background art.

[0005] In a first aspect, the embodiments of the present application provide a preparation method of an epitaxial structure, comprising:

[0006] providing a substrate;

[0007] introducing a nitrogen source and a group III source, and growing at least one dislocation blocking layer on the substrate by a molecular beam epitaxy process; the dislocation blocking layer comprises a first growth layer and a second growth layer stacked in sequence, the first growth layer has a three-dimensional island morphology, a bottom surface of the second growth layer is in contact with a surface of the first growth layer away from the substrate, and a surface of the second growth layer away from the substrate has a planar structure; wherein, a stoichiometric ratio of flow rates of the nitrogen source and the group III source during growth of the first growth layer is greater than 1, and a stoichiometric ratio of flow rates of the nitrogen source and the group III source during growth of the second growth layer is less than 1;

[0008] growing a group III nitride material layer on the dislocation blocking layer by a molecular beam epitaxy process.

[0009] With reference to the first aspect of the present application, in an optional implementation, the number of layers of the dislocation blocking layer is greater than or equal to 3.

[0010] With reference to the first aspect of the present application, in an optional implementation, during growth of the first growth layer, the flow rate of the nitrogen source is 5-7 sccm, the radio frequency plasma source power is 300-450 W, and the growth temperature is 600-900 ℃.

[0011] With reference to the first aspect of the present application, in an optional implementation, during growth of the second growth layer, the flow rate of the nitrogen source is 3-5 sccm, the radio frequency plasma source power is 300-450 W, and the growth temperature is 600-900 ℃.

[0012] With reference to the first aspect of the present application, in an optional implementation, the thickness of the first growth layer is 10-20 nm.

[0013] With reference to the first aspect of the present application, in an optional implementation, the thickness of the second growth layer is 10-70 nm.

[0014] With reference to the first aspect of the present application, in an optional implementation, the dislocation density in the group III nitride material layer is less than or equal to 4.2E9 / cm -2 .

[0015] With reference to the first aspect of the present application, in an optional implementation, before growing the dislocation blocking layer by epitaxy, the method further comprises:

[0016] growing an AlN nucleation layer on the substrate.

[0017] In a second aspect, the embodiments of the present application provide an epitaxial structure prepared by the preparation method of the epitaxial structure according to any one of the first aspect.

[0018] Secondly, embodiments of this application provide the application of the epitaxial structure as described in the second aspect in the fabrication of semiconductor devices.

[0019] The epitaxial structure preparation method, epitaxial structure, and its application provided in this application embodiment employ molecular beam epitaxy (MBE) to epitaxially grow at least one dislocation blocking layer on a substrate. During the epitaxial growth process, by controlling the stoichiometric ratio of the nitrogen source and the group III source to be greater than 1, a first growth layer with a three-dimensional island morphology is grown. By controlling the stoichiometric ratio of the nitrogen source and the group III source to be less than 1, a second growth layer is grown with its bottom surface in contact with the surface of the first growth layer in the direction away from the substrate, and the surface in the direction away from the substrate has a planar structure. By changing the epitaxial growth process, different growth modes are controlled to grow the dislocation blocking layer composed of the first growth layer and the second growth layer. During the growth of the dislocation blocking layer, the propagation direction of dislocations in the material can be changed, causing dislocations to bend and some dislocations to terminate in the dislocation blocking layer, reducing the number of dislocations propagating in the epitaxial growth direction. This effectively reduces the number of dislocations entering the subsequently grown group III nitride material layer, thereby reducing the dislocation density in the group III nitride material layer and improving the quality and performance of the epitaxial structure.

[0020] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0021] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments of this application and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0022] Figure 1 A schematic flowchart illustrating the method for preparing the epitaxial structure provided in this application embodiment;

[0023] Figures 2 to 5 A cross-sectional structural diagram of the preparation process of the epitaxial structure provided in the embodiments of this application;

[0024] Figure 6 for Figure 5 Enlarged view of point A in the middle;

[0025] Figure 7 This is a diagram showing the changes in the RHEED pattern during the growth of the dislocation barrier layer in Example 1.

[0026] Figure 8 The rocking curves of the (002) crystal plane in the epitaxial structures obtained in Examples 1 to 3 and Comparative Example 1 are shown.

[0027] Figure 9The curves show the relationship between dislocation density, full width at half maximum (FWHM), and the number of dislocation blocking layers. Detailed Implementation

[0028] Exemplary embodiments of the present application will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present application are shown in the drawings, it should be understood that the present application may be implemented in various forms and should not be limited to the specific embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present application and to fully convey the scope of the disclosure of the present application to those skilled in the art.

[0029] In the following description, numerous specific details are set forth in order to provide a more thorough understanding of this application. However, it will be apparent to those skilled in the art that this application can be practiced without one or more of these details. In other instances, to avoid confusion with this application, some technical features well-known in the art have not been described; that is, not all features of actual embodiments are described herein, nor are well-known functions and structures described in detail.

[0030] In the accompanying drawings, for clarity, the dimensions of layers, areas, and elements, as well as their relative dimensions, may be exaggerated. The same reference numerals denote the same elements throughout.

[0031] It should be understood that when an element or layer is referred to as "on," "adjacent to," "connected to," or "coupled to" other elements or layers, it may be directly on, adjacent to, connected to, or coupled to other elements or layers, or there may be intervening elements or layers. Conversely, when an element is referred to as "directly on," "directly adjacent to," "directly connected to," or "directly coupled to" other elements or layers, there are no intervening elements or layers. It should be understood that although the terms first, second, third, etc., may be used to describe various elements, components, areas, layers, and / or portions, these elements, components, areas, layers, and / or portions should not be limited by these terms. These terms are only used to distinguish one element, component, area, layer, or portion from another element, component, area, layer, or portion. Therefore, without departing from the teachings of this application, the first element, component, area, layer, or portion discussed below may be referred to as a second element, component, area, layer, or portion. And the discussion of a second element, component, area, layer, or portion does not imply that the first element, component, area, layer, or portion necessarily exists in this application.

[0032] Spatial relation terms such as “below,” “under,” “below,” “under,” “above,” “above,” etc., are used herein for convenience of description to describe the relationship between one element or feature shown in the figure and other elements or features. It should be understood that, in addition to the orientation shown in the figure, spatial relation terms are intended to also include different orientations of the device in use and operation. For example, if the device in the figure is flipped, then the element or feature described as “below,” “under,” or “below” other elements or features will be oriented “above” other elements or features. Therefore, the exemplary terms “below” and “under” can include both above and below orientations. The device may be otherwise oriented (rotated 90 degrees or otherwise) and the spatial descriptive terms used herein will be interpreted accordingly.

[0033] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. When used herein, the singular forms “a,” “an,” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising” and / or “including,” when used in this specification, identify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups. When used herein, the term “and / or” includes any and all combinations of the associated listed items.

[0034] To fully understand this application, detailed steps and structures will be presented in the following description to illustrate the technical solution of this application. Preferred embodiments of this application are described in detail below; however, in addition to these detailed descriptions, this application may have other implementation methods.

[0035] Different types of substrates have been explored for growing high-quality group III nitride materials. Sapphire, with its relatively economical price and hexagonal crystal structure similar to nitrides, is widely used for the epitaxial growth of nitrides (such as AlN and GaN). Taking GaN as an example, sapphire and GaN exhibit approximately 14% lattice mismatch and 33% thermal mismatch, resulting in a high dislocation density in GaN films epitaxially grown on sapphire substrates. This significantly impacts the optoelectronic and other performance characteristics of semiconductor devices manufactured using this material. Similar to sapphire substrates, silicon substrates also exhibit significant lattice and thermal mismatches with GaN. Furthermore, silicon undergoes melt-back etching with Ga, necessitating the introduction of an AlN intercalation layer. Despite the aid of the AlN nucleation layer, AlN struggles to align precisely on the silicon lattice during the initial growth stages, leading to the generation and propagation of numerous mismatch dislocations into the GaN layer.

[0036] One feasible method to reduce dislocations is to increase the thickness of the buffer layer. As the buffer layer thickness increases, dislocations fuse and annihilate each other. MOCVD technology can leverage its relatively fast growth rate to utilize a thick buffer layer to reduce dislocations. However, in MBE technology, especially plasma-assisted molecular beam epitaxy (PA-MBE), the slow growth rate is a weakness; due to the use of group III-rich growth mode, the growth rate is only 0.4 μm / h. Therefore, increasing the thickness of the buffer layer to reduce dislocations is not applicable to MBE technology. Furthermore, in related technologies, special structures are created on the substrate or epitaxial layer surface using techniques such as photolithography and etching. For example, etching patterned structures on a sapphire substrate for epitaxial growth can change the dislocation vector direction through lateral growth, thereby reducing dislocation density. However, this method is generally only suitable for thick-film growth in MOCVD and not for MBE technology because the grown film needs to be thick enough to eliminate the influence of the patterned substrate on the surface morphology of the epitaxial layer, which places certain requirements on the growth rate.

[0037] Introducing intercalation layers during epitaxial growth can alter the stress distribution and dislocation propagation direction in the crystal structure, thereby reducing dislocation density. However, intercalation layers typically introduce compressive or tensile stress at the interface, affecting the quality of the subsequently grown film and making the final product prone to warping or cracking. Simultaneously, some intercalation layer materials introduce impurity elements (such as silicon impurities), affecting the material's band structure and consequently the optoelectronic performance of the device. Furthermore, in molecular beam epitaxy, low-temperature growth can reduce atomic surface mobility, lower thermal stress, and decrease dislocation nucleation, but this affects the growth rate and film quality.

[0038] Based on this, the present application provides a method for preparing an epitaxial structure. Figure 1 This is a schematic flowchart of the method for preparing the epitaxial structure provided in the embodiments of this application; as shown below. Figure 1 As shown, the method includes:

[0039] Step S101: Provide a substrate;

[0040] Step S102: Introduce a nitrogen source and a group III source, and use molecular beam epitaxy to epitaxially grow at least one dislocation blocking layer on the substrate. The dislocation blocking layer includes a first growth layer and a second growth layer stacked sequentially. The first growth layer has a three-dimensional island-like morphology, and the bottom surface of the second growth layer is in contact with the surface of the first growth layer away from the substrate. The surface of the second growth layer away from the substrate has a planar structure. During the growth of the first growth layer, the stoichiometric ratio of the flow rates of the nitrogen source and the group III source is greater than 1, and during the growth of the second growth layer, the stoichiometric ratio of the flow rates of the nitrogen source and the group III source is less than 1.

[0041] Step S103: A group III nitride material layer is epitaxially grown on the dislocation blocking layer using molecular beam epitaxy.

[0042] Understandably, by employing molecular beam epitaxy (MBE) as described above, at least one dislocation barrier layer is epitaxially grown on a substrate. During the epitaxial growth process, by controlling the stoichiometric ratio of the nitrogen source and the group III source to be greater than 1, a first growth layer with a three-dimensional island morphology is grown. By controlling the stoichiometric ratio of the nitrogen source and the group III source to be less than 1, a second growth layer is grown with its bottom surface in contact with the surface of the first growth layer in the direction away from the substrate, and the surface in the direction away from the substrate has a planar structure. By changing the epitaxial growth process and controlling different growth modes, a dislocation barrier layer composed of the first and second growth layers can be grown. During the growth of the dislocation barrier layer, the propagation direction of dislocations in the material can be changed, causing dislocations to bend and some dislocations to terminate within the dislocation barrier layer, reducing the number of dislocations propagating in the epitaxial growth direction. This effectively reduces the number of dislocations entering the subsequently grown group III nitride material layer, thereby reducing the dislocation density in the group III nitride material layer and improving the quality and performance of the epitaxial structure.

[0043] Below, in conjunction with Figures 2 to 5 The preparation method of the epitaxial structure provided in the embodiments of this application and its beneficial effects will be further described in detail.

[0044] First, please refer to Figure 2 Step S101 is executed to provide substrate 100.

[0045] The material of the substrate 100 may include, for example, sapphire, silicon, silicon carbide, or diamond. Of course, the material of the substrate 100 may also include other materials capable of epitaxially growing group III nitrides.

[0046] In some embodiments, please refer to Figure 2 Before the epitaxial growth of the dislocation blocking layer, the method for preparing the epitaxial structure also includes: growing an AlN nucleation layer 200 on a substrate 100.

[0047] Growing an AlN nucleation layer 200 on substrate 100 is beneficial for the subsequent epitaxial growth of the dislocation barrier layer, reduces the lattice mismatch and interface stress between the dislocation barrier layer and substrate 100, and improves the quality of the dislocation barrier layer and the entire epitaxial layer.

[0048] Next, please refer to Figure 3 and Figure 4 In step S102, a nitrogen source and a group III source are introduced, and at least one dislocation barrier layer 300 is epitaxially grown on the substrate 100 using molecular beam epitaxy. The dislocation barrier layer 300 includes a first growth layer 301 and a second growth layer 302 stacked sequentially.

[0049] Specifically, performing step S102 may include the following steps:

[0050] First, please refer to Figure 3 A nitrogen source and a group III source are introduced, and a first growth layer 301 is epitaxially grown on a substrate 100 using molecular beam epitaxy. During the growth of the first growth layer 301, the stoichiometric ratio of the flow rates of the nitrogen source and the group III source is greater than 1, and the first growth layer 301 has a three-dimensional island morphology.

[0051] Next, please refer to Figure 4 Nitrogen source and group III source are continuously introduced, and molecular beam epitaxy is used to epitaxially grow a second growth layer 302. The bottom surface of the second growth layer 302 is in contact with the surface of the first growth layer 301 in the direction away from the substrate 100. The surface of the second growth layer 302 in the direction away from the substrate 100 has a planar structure. During the growth of the second growth layer 302, the stoichiometric ratio of the flow rates of the nitrogen source and the group III source is less than 1.

[0052] In this embodiment, the group III source may include, for example, an aluminum source or a gallium source (specifically, including Al atoms or Ga atoms). During the growth of the first growth layer 301, the stoichiometric ratio of the nitrogen source and the group III source is controlled to be greater than 1. This growth condition can be called a nitrogen-rich condition. In a nitrogen-rich atmosphere, nitrogen is more abundant than group III elements, and the stoichiometric ratio of nitrogen to group III elements is greater than 1. The migration of group III atoms (e.g., Al atoms or Ga atoms) on the surface of the substrate 100 is restricted, making it difficult to distribute them uniformly on the surface of the substrate 100. Therefore, multiple independent growth centers are formed, resulting in island-like growth, thus making the morphology of the first growth layer 301 three-dimensional island-like (e.g., Figure 3(As shown). Further optionally, during the growth of the first growth layer 301, while maintaining the background vacuum, the stoichiometric ratio of the nitrogen source and the group III source can be 3-10, or the stoichiometric ratio of N element to group III element can be considered to be 3-10; in this way, the growth morphology of the first growth layer 301 can be better controlled, and it is easier to form a three-dimensional island morphology. During the growth of the second growth layer 302, the stoichiometric ratio of the nitrogen source and the group III source is controlled to be less than 1. This growth condition can be called the group III source-rich condition. Under this condition, group III elements are more abundant than N elements, and the stoichiometric ratio of N elements to group III elements is less than 1. Group III atoms can migrate sufficiently and be evenly distributed on the surface of the substrate 100 and the first growth layer 301, realizing the transformation from island-shaped growth mode to lateral growth. This causes multiple island-shaped structures to gradually merge. During this growth stage, the propagation direction of some dislocations generated at the interface between the substrate 100 and the epitaxial layer will be bent and will no longer propagate along the epitaxial growth direction (i.e., the thickness direction of the substrate 100). After the bent dislocations merge, they will annihilate, causing some dislocations to terminate in the dislocation blocking layer 300. This can reduce the number of dislocations entering the subsequent epitaxial layer. In other words, the dislocation blocking layer 300 can achieve the function of blocking dislocation propagation. After the island structures merge, molecular beam epitaxy transitions to a stable step-flow growth mode. Step-flow growth is the optimal epitaxial growth mode for achieving a complete lattice structure and a smooth surface, thus allowing the surface of the second growth layer 302 away from the substrate 100 to exhibit a planar structure (e.g., Figure 4 (As shown). Further optionally, during the growth of the second growth layer 302, the stoichiometric ratio of the flow rates of the nitrogen source and the group III source can be 1:(2-2.3), or the stoichiometric ratio of N element to group III element can be considered to be 1:(2-2.3); in this way, the growth mode can be better controlled to change from the island growth mode to the stable step flow growth mode, thereby better controlling the growth morphology of the second growth layer 302.

[0053] In this embodiment, by changing the epitaxial growth mode of the material, the dislocation vector direction is changed in the process of "island growth mode → lateral growth → island merging → step flow growth mode", causing dislocations to bend and annihilate, thereby reducing the propagation of dislocations to the epitaxial growth direction. This can effectively reduce the number of dislocations entering the subsequent epitaxial layer, thus reducing the dislocation density in the group III nitride material layer, thereby improving the quality of the epitaxial layer and the optoelectronic properties of the epitaxial structure.

[0054] It should be noted that, Figure 3The island-like structure morphology of the first growth layer 301 shown is only a schematic diagram. In the actual fabrication process, the morphology of the first growth layer 301 is a three-dimensional island. This can be understood as follows: in the direction away from the substrate 100, the cross-section of the island-like structure in the first growth layer 301 gradually decreases, and the top and side morphologies of the island-like structure are not necessarily flat and regular planes.

[0055] Molecular beam epitaxy (MBE) equipment mainly comprises a sample loading chamber, a transport chamber, a pretreatment chamber, a storage chamber, and an ultra-high vacuum growth chamber. Except for the transport and storage chambers, which are directly connected, the other chambers are separated by vacuum valves. To ensure the system operates in an ultra-high vacuum environment, each chamber is equipped with an independently operating vacuum pump, including mechanical pumps, molecular pumps, and condenser pumps. Additionally, the system is equipped with a gas analysis and detection system and an in-situ monitoring system, including a quadrupole mass spectrometer, a high-energy electron diffractometer, and beam current measurement instruments.

[0056] Before epitaxial growth, the liquid nitrogen circulation system in the molecular beam epitaxy (MBE) equipment must first be activated to adjust the pressure in the growth chamber to a suitable level and raise the source furnace temperature to the required value. The source furnace provides the group III source molecular beam (e.g., Al or Ga beam) required for growth. Then, the nitrogen source (e.g., nitrogen gas) plasma-assisted system is activated. Nitrogen gas cannot be directly used for epitaxial layer growth; instead, it enters the radio frequency plasma equipment through a dedicated gas path, is excited into a plasma composed of ions and atoms, and then flows into the growth chamber to participate in the epitaxial layer growth. During epitaxial growth, a reflective high-energy electron diffractometer can be used to monitor the substrate 100 surface in real time. Information about the growth front end can be obtained through the diffraction image on the fluorescent screen, and the temperature of the substrate 100 can be measured using a temperature measurement system.

[0057] In some embodiments, during the growth of the first growth layer 301, the flow rate of the nitrogen source can be 5 sccm-7 sccm, for example, 5 sccm, 5.5 sccm, 6 sccm, 6.5 sccm, 7 sccm or any value between any two of the above ranges, and the power of the radio frequency plasma source can be 300W-450W, for example, 300W, 350W, 400W, 450W or any value between any two of the above ranges.

[0058] For example, the nitrogen source in the growth process of the first growth layer 301 may include nitrogen and / or ammonia. As described above, the nitrogen source is first introduced into a radio frequency plasma device and excited into a plasma composed of ions and atoms, and then introduced into the growth chamber to participate in the growth of the epitaxial layer. In the embodiments of this application, controlling the flow rate of the nitrogen source (e.g., the flow rate of nitrogen and / or ammonia introduced into the radio frequency plasma device) and the power of the radio frequency plasma source within the above-mentioned range is beneficial to controlling the flow rate of the nitrogen source participating in the growth of the epitaxial layer, and thus facilitates the control of the stoichiometric ratio of the flow rates of the nitrogen source and the group III source. In a specific embodiment, the flow rate of the group III source, such as the group III source beam (Al beam or Ga beam), can be 6.6E-8 Torr. In this way, it is possible to better control the stoichiometric ratio of the flow rates of the nitrogen source and the group III source to be greater than 1, that is, to control the nitrogen-rich growth conditions.

[0059] It is understood that during the growth of the first growth layer 301, a lower growth temperature will affect the growth rate and film quality of the first growth layer 301; a higher growth temperature will result in a faster growth rate, which will also affect the quality of the grown film and make it difficult to control the growth morphology (three-dimensional island morphology) of the first growth layer 301. Therefore, in some specific embodiments, the growth temperature during the growth of the first growth layer 301 can be 600℃-900℃, for example, 600℃, 700℃, 800℃, 900℃, or any value between any two of the above ranges.

[0060] It should be noted that in the actual fabrication process, the growth temperature in molecular beam epitaxy can be the temperature of the substrate 100. In this way, the temperature of the substrate 100 can be measured and controlled by the temperature measurement system in the molecular beam epitaxy equipment, which is convenient for operation.

[0061] When the thickness of the first growth layer 301 is relatively thin, it not only places higher demands on the growth process and increases the difficulty of the process, but also limits the ability to change the direction of dislocation propagation during subsequent growth, which affects the effect of dislocation bending and annihilation. When the thickness of the first growth layer 301 is relatively thick, it not only increases the processing time and cost, but also makes it difficult to control the three-dimensional island-like growth morphology of the first growth layer 301. Therefore, in some specific embodiments, the thickness of the first growth layer 301 can be 10nm-20nm, for example, it can be 10nm, 15nm, 20nm or any value between any two of the above ranges.

[0062] In some embodiments, during the growth of the second growth layer 302, the flow rate of the nitrogen source can be 3 sccm-5 sccm, for example, 3 sccm, 3.5 sccm, 4 sccm, 4.5 sccm, 5 sccm or any value between any two of the above ranges, and the power of the radio frequency plasma source can be 300W-450W, for example, 300W, 350W, 400W, 450W or any value between any two of the above ranges.

[0063] For example, the nitrogen source in the growth process of the second growth layer 302 may include nitrogen and / or ammonia. In this embodiment, controlling the flow rate of the nitrogen source (e.g., the flow rate of nitrogen and / or ammonia introduced into the radio frequency plasma device) and the power of the radio frequency plasma source within the aforementioned range is beneficial for controlling the flow rate of the nitrogen source participating in the epitaxial layer growth, thereby facilitating the control of the stoichiometric ratio of the nitrogen source and the group III source flow rates. In a specific embodiment, the flow rate of the group III source, such as the group III source beam (Al beam or Ga beam), can be 6.6E-8 Torr. In this way, it is possible to better control the stoichiometric ratio of the nitrogen source and the group III source flow rates to be less than 1, that is, to control the group III source-rich growth conditions.

[0064] It should be noted that the nitrogen source used in the growth process of the first growth layer 301 and the second growth layer 302 can be the same or different. In some specific embodiments, the nitrogen source used in the growth process of the first growth layer 301 and the second growth layer 302 is the same. In this way, it is not necessary to switch the nitrogen source during the growth process of the dislocation blocking layer 300, which simplifies the process.

[0065] In the actual preparation process, during the growth of the first growth layer 301 and the second growth layer 302, the group III source beam current can be kept constant. By adjusting the flow rate of the nitrogen source, such as by adjusting the flow rate of nitrogen and / or ammonia into the radio frequency plasma device, the stoichiometric ratio of the flow rates of the nitrogen source and the group III source can be adjusted and controlled more conveniently and accurately.

[0066] It is understood that during the growth of the second growth layer 302, a lower growth temperature will affect the growth rate and film quality of the second growth layer 302, as well as the change in dislocation propagation direction; a higher growth temperature will result in a faster growth rate, which will also affect the quality of the grown film and the change in dislocation propagation direction, thus affecting the effects of dislocation bending and annihilation. Therefore, in some specific embodiments, the growth temperature during the growth of the second growth layer 302 can be 600℃-900℃, for example, 600℃, 700℃, 800℃, 900℃, or any value between any two of the above ranges.

[0067] When the thickness of the second growth layer 302 is too thin, it may affect the dislocation bending and annihilation effects; when the thickness of the second growth layer 302 is too thick, it will not only increase the processing time and cost, but also make it difficult to control the overall thickness of the epitaxial structure. Therefore, in some specific embodiments, the thickness of the second growth layer 302 can be 10nm-70nm, for example, it can be 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm or any value between any two of the above ranges.

[0068] like Figure 4 As shown, since the bottom surface of the second growth layer 302 is in contact with the surface of the first growth layer 301 in the direction away from the substrate 100, and the surface of the second growth layer 302 in the direction away from the substrate 100 has a planar structure, the thickness of the second growth layer 302 is greater than or equal to the thickness of the first growth layer 301. More preferably, the thickness of the second growth layer 302 is greater than the thickness of the first growth layer 301. This allows for better control of the surface morphology of the second growth layer 302 in the direction away from the substrate 100, which is beneficial for the high-quality growth of subsequent epitaxial layers. It can be understood that, considering both process time and material cost, the difference between the thickness of the second growth layer 302 and the thickness of the first growth layer 301 can be 10nm-50nm.

[0069] It should be noted that the thickness of the first growth layer 301 refers to the vertical distance from the highest point of its surface away from the substrate 100 to the bottom surface, and the thickness of the second growth layer 302 refers to the vertical distance between its surface and bottom surface away from the substrate 100. Here, the vertical direction refers to the thickness direction of the substrate 100.

[0070] Figure 4 This example only illustrates the case of epitaxial growth of a single dislocation blocking layer 300. Of course, the number of dislocation blocking layers 300 in this embodiment can be greater than or equal to two, and the specific number can be adjusted according to the requirements for the quality of the epitaxial structure. When the number of dislocation blocking layers 300 is greater than or equal to two, in adjacent dislocation blocking layers 300, the first growth layer 301 in the upper dislocation blocking layer 300 is in contact with the second growth layer 302 in the lower dislocation blocking layer 300; that is, in a multi-layered structure of dislocation blocking layers 300, the first and second growth layers are arranged alternately. It can be understood that the more dislocation blocking layers 300 there are, the more times the propagation direction of dislocations can be changed. After multiple bends, the number of dislocations propagating in the epitaxial growth direction decreases step by step, thereby further reducing the number of dislocations in the subsequently grown epitaxial layers and further improving the performance of the epitaxial structure.

[0071] In some specific embodiments, the number of dislocation blocking layers 300 can be greater than or equal to 3. This allows for better dislocation blocking through three or more dislocation blocking layers 300, enabling more dislocations to bend and annihilate within the dislocation blocking layers 300 and terminate there. This significantly reduces the number of dislocations entering the subsequently grown epitaxial layers, thereby reducing the dislocation density in the epitaxial layers and further improving the quality and performance of the epitaxial structure.

[0072] Finally, please refer to Figure 5 In step S103, a group III nitride material layer 400 is epitaxially grown on the dislocation blocking layer 300 using molecular beam epitaxy.

[0073] Because the dislocation blocking layer 300 effectively blocks dislocations, some dislocations bend and annihilate within it, terminating within the layer. Therefore, the number of dislocations entering the group III nitride material layer 400 is reduced, effectively lowering the dislocation density and thus significantly improving the quality and optoelectronic properties of the epitaxial structure. Since the group III nitride material layer 400 is typically used as the target epitaxial layer to function in semiconductor devices, reducing the dislocation density in it significantly improves the performance and reliability of semiconductor devices fabricated using the epitaxial structure prepared according to the embodiments of this application. In actual fabrication processes, the group III nitride material layer 400 may also include a buffer layer.

[0074] In some embodiments, the dislocation density in the group III nitride material layer 400 may be less than or equal to 4.2E9 / cm². -2 .

[0075] In this embodiment, by effectively blocking dislocation propagation through the dislocation blocking layer 300, the dislocation density in the group III nitride material layer 400 can be reduced to a low level, thereby ensuring that the prepared epitaxial structure has high performance.

[0076] Here we combine Figure 6 The principle by which the dislocation blocking layer 300 in the embodiments of this application blocks dislocations is further explained, wherein, Figure 6 for Figure 5 Enlarged view at point A. When the crystal growth mode transitions from two-dimensional to three-dimensional island growth, strain energy release is a crucial factor. In the two-dimensional growth stage (e.g., the growth stage of AlN nucleation layer 200 and the second growth layer 302), strain caused by lattice mismatch gradually accumulates. However, in the three-dimensional island growth stage (the growth stage of the first growth layer 301), when forming a three-dimensional island structure, these island structures can release strain energy through lattice relaxation at the island edges. Dislocations will bend under this strain environment (e.g., ...). Figure 6As indicated by the solid arrows, dislocations propagate along the path of lowest strain energy. With the growth and merging of island structures, dislocations in adjacent island structures approach each other. When they meet, the dislocation lines connect to form closed loops. Some bent dislocations terminate at grain boundaries and interfaces between different materials, resulting in dislocation annihilation, thus reducing the growth in the epitaxial growth direction (e.g., ...). Figure 6 The number of dislocations propagating (as indicated by the dashed arrow) can reduce the dislocation density in the group III nitride material layer 400. It can be understood that when the dislocation blocking layer 300 has two or more layers, after multiple bending and annihilation processes as described above, the number of dislocations propagating in the epitaxial growth direction is greatly reduced, thus significantly reducing the dislocation density in the group III nitride material layer 400.

[0077] This application also provides an epitaxial structure, which is prepared using the preparation method of the epitaxial structure provided in any of the foregoing embodiments.

[0078] This application also provides the application of the epitaxial structure described in the above embodiments in the fabrication of semiconductor devices.

[0079] It should be understood that, due to the low dislocation density in the epitaxial structure prepared in any of the foregoing embodiments, the semiconductor devices prepared using this epitaxial structure have high performance and reliability.

[0080] In practical applications, the epitaxial structure prepared in any of the foregoing embodiments can be directly used to prepare semiconductor devices; alternatively, the epitaxial structure prepared in any of the foregoing embodiments can be processed before being used to prepare semiconductor devices, such as thinning or removing the substrate in the epitaxial structure.

[0081] The technical solution of this application will be further described below with reference to several embodiments and comparative examples.

[0082] Example 1

[0083] The method for preparing the epitaxial structure in this embodiment includes the following steps:

[0084] Step S1: An AlN nucleation layer is epitaxially grown on a sapphire substrate using molecular beam epitaxy.

[0085] Step S2: Introducing nitrogen and aluminum sources, and using molecular beam epitaxy, an AlN layer (first growth layer) with a three-dimensional island morphology is epitaxially grown on the AlN nucleation layer. The growth conditions for the first growth layer are nitrogen-rich conditions; specifically, the Al beam current is 6.6E-8 Torr, the nitrogen flow rate in the radio frequency plasma equipment is 6 sccm, the radio frequency plasma source power is 380W, the growth temperature is 850℃, and the thickness of the first growth layer is 20nm. Introducing nitrogen and aluminum sources, and using molecular beam epitaxy, an AlN layer with a planar surface structure is epitaxially grown on the first growth layer. The second growth layer (lN layer) is grown under aluminum-rich conditions (also known as micro-aluminum-rich conditions). Specifically, the Al beam current is 6.6E-8 Torr, the nitrogen flow rate introduced into the radio frequency plasma equipment is 4 sccm, the radio frequency plasma source power is 380W, the growth temperature is 780℃, and the thickness of the second growth layer is 30nm (here, the thickness of the second growth layer refers to the thickness of the part of the second growth layer above the highest point of the first growth layer). The first and second growth layers together constitute a dislocation blocking layer with a thickness of 50nm.

[0086] Step S3: Continue to introduce nitrogen and aluminum sources, and use molecular beam epitaxy to epitaxially grow an AlN layer (Group III nitride material layer) with a thickness of 500 nm on the dislocation blocking layer.

[0087] Example 2

[0088] The preparation method of the epitaxial structure in this embodiment is basically the same as that in Example 1, except that:

[0089] In step S2, the first growth layer and the second growth layer are alternately grown in a cyclical manner to form two dislocation barrier layers.

[0090] The thickness of the AlN layer in step S3 is 450 nm.

[0091] Example 3

[0092] The preparation method of the epitaxial structure in this embodiment is basically the same as that in Example 1, except that:

[0093] In step S2, the first growth layer and the second growth layer are alternately grown to form 10 dislocation barrier layers.

[0094] The thickness of the AlN layer in step S3 is 50 nm.

[0095] Comparative Example 1

[0096] The preparation method of the epitaxial structure in this comparative example includes the following steps:

[0097] Step S10: An AlN nucleation layer is epitaxially grown on a sapphire substrate using molecular beam epitaxy.

[0098] Step S20: Using molecular beam epitaxy, an AlN layer (also known as an AlN buffer layer) with a thickness of 550 nm is epitaxially grown on the AlN nucleation layer.

[0099] It should be noted that, for the sake of consistency, the total thickness of the epitaxial layer in the above embodiments and comparative examples is 550 nm.

[0100] During the growth process, the substrate surface is monitored in real time using a Reflection High-Energy Electron Diffraction (RHEED) instrument. Information about the growth front end can be obtained through the diffraction images displayed on the fluorescent screen. Figure 7 This is a diagram showing the changes in the RHEED pattern during the growth of the dislocation barrier layer in Example 1. Figure 7 The RHEED pattern in (a) is the RHEED pattern after nitrogen-rich growth, corresponding to the RHEED pattern after the growth of the first growth layer. The RHEED pattern is a "swallowtail" dot pattern, indicating that the surface morphology of the first growth layer away from the substrate is a three-dimensional island. Figure 7 Images (b)-(d) in the diagram show the RHEED patterns during the growth of the second growth layer. As the second growth layer grows under micro-aluminum conditions, Figure 7 In the RHEED patterns (b)-(d) shown in the diagram, the pattern gradually changes from dots to lines, indicating that the AlN film growth begins to transition to a two-dimensional layered growth mode. The three-dimensional island structures begin to merge, eventually forming a second growth layer with a planar surface structure away from the substrate. This further proves that in the embodiments of this application, different growth modes can indeed be controlled by changing the epitaxial growth process, transforming the growth mode from an island-like mode to lateral growth, island merging, and then to a step-flow growth mode, thus realizing the transformation of the first and second growth layers from an island-like surface morphology to a layered surface morphology.

[0101] Next, the dislocation density in the epitaxial structures prepared in Examples 1 to 3 and Comparative Example 1 was measured by X-ray diffraction rocking curves.

[0102] Figure 8 The rocking curves are for the (002) crystal plane in the epitaxial structures prepared in Examples 1 to 3 and Comparative Example 1. The screw dislocation density results in the epitaxial structures obtained from the full width at half maximum (FWHM) of the rocking curves are shown in Table 1.

[0103] Table 1

[0104] Half width of swing curve / arc seconds Screw dislocation density / cm -2 ]] Example 1 1008 4.2E9 Example 2 801 2.6E9 Example 3 463 8.8E8 Comparative Example 1 1809 1.3E10

[0105] As can be seen from the data in Table 1, at least one dislocation blocking layer was introduced into the epitaxial structures prepared in Examples 1 to 3. The full width at half maximum (FWHM) of the rocking curves was significantly reduced compared to Comparative Example 1, and the corresponding screw dislocation density in the epitaxial structure was also significantly reduced. This indicates that in this application, by changing the molecular beam epitaxy growth process and growing a dislocation blocking layer, the propagation direction of dislocations in the material can be changed during the growth of the dislocation blocking layer, causing dislocations to bend and some dislocations to terminate within the dislocation blocking layer. This reduces the number of dislocations propagating in the epitaxial growth direction, thereby effectively reducing the number of dislocations entering the subsequently grown Group III nitride material layer. This reduces the dislocation density in the Group III nitride material layer, which in turn reduces the dislocation density in the epitaxial structure, thus effectively improving the quality and performance of the epitaxial structure.

[0106] In Comparative Example 1, an AlN buffer layer was directly grown on the AlN nucleation layer without introducing a dislocation blocking layer. Compared to Examples 1 to 3, the screw dislocation density in the epitaxial structure obtained in Comparative Example 1 was significantly higher. As can be seen from the data in Table 1, the dislocation density in the epitaxial structure obtained in Comparative Example 1 was three times that of the epitaxial structure obtained in Example 1. This demonstrates that growing a dislocation blocking layer can effectively reduce the dislocation density in the epitaxial structure.

[0107] As can be seen from the data in Table 1 for Examples 1 to 3, the dislocation density in the epitaxial structure decreases with the increase in the number of dislocation blocking layers. The epitaxial structure prepared in Example 3 contains 10 dislocation blocking layers, and the screw dislocation density has been reduced by an order of magnitude compared to Comparative Example 1.

[0108] Figure 9 This is a curve showing the relationship between dislocation density, full width at half maximum (FWHM), and the number of dislocation blocking layers. Figure 9 It can be seen that in the epitaxial structure, as the number of dislocation blocking layers increases, the dislocation density gradually decreases, but the rate of decrease gradually diminishes, which is consistent with crystallographic principles. In actual materials, when the dislocation density decreases to a certain level, the material's own structure and external environmental factors will still lead to the generation of new dislocations, preventing the dislocation density from continuously decreasing significantly. Therefore, in this application, a number of dislocation blocking layers greater than or equal to 3 is a preferred approach, as this can significantly reduce the dislocation density in the epitaxial structure. Considering the time and cost of the process, the number of dislocation blocking layers can be controlled to within 10 layers.

[0109] In this application, by altering the growth mode of group III nitrides (e.g., N-rich and Al-rich growth modes) during MBE growth, a first growth layer with a nano-three-dimensional island structure is first grown, followed by a second growth layer. This allows the islands to gradually merge, enabling dislocations to bend and annihilate within the dislocation blocking layer. MOCVD, however, requires a nitrogen-rich growth mode. Taking AlN growth via MOCVD as an example, the N / Al ratio can reach over 1000. Due to the high growth temperature of MOCVD, nitrogen-rich conditions can address issues such as AlN decomposition, Al droplet formation, and low ammonia efficiency during high-temperature growth. Changing the growth mode would severely impact the quality of MOCVD epitaxial films. Therefore, the preparation method in this application is suitable for MBE but not for MOCVD.

[0110] Compared to methods such as introducing intercalation layers and using patterned substrates to reduce dislocation density during epitaxial growth, the dislocation blocking layer in this application can form a good interface with the target epitaxial layer (Group III nitride material layer), without introducing additional impurities, thus improving crystal quality. Furthermore, the thickness of the entire epitaxial layer can be controlled within a smaller range; the thinner overall structure can reduce the series resistance of semiconductor devices fabricated using epitaxial structures, improve the heat dissipation efficiency of the material, and also reduce production costs. In addition, the nitrogen-sealed ends of nitrogen-polar materials give them higher surface activity than metallic polar materials, making them easier to bond with impurity atoms. These impurities interfere with normal atomic arrangement, forming defects. Simultaneously, the nitrogen-sealed ends of nitrogen-polar materials make it difficult for Group III atoms to migrate, causing atomic accumulation and affecting crystal growth quality. Therefore, in this application, by introducing dislocation blocking layer technology during the growth of nitrogen-polar materials, the growth quality of nitrogen-polar materials can be significantly improved.

[0111] Furthermore, the preparation method in this application does not use any additional equipment or apparatus, fully utilizes the in-situ monitoring advantages of the MBE equipment itself, and does not add any material source, nor generate any toxic or harmful gases or waste that may pollute the environment. It has significant advantages in terms of cost and environmental protection, and has high practical application value.

[0112] It should be noted that the epitaxial structure embodiments, epitaxial structure preparation method embodiments, and application embodiments provided in this application belong to the same concept; the technical features in the technical solutions described in each embodiment can be arbitrarily combined without conflict.

[0113] It should be understood that the above embodiments are exemplary and not intended to encompass all possible implementations. Various modifications and changes can be made to the above embodiments without departing from the scope of this disclosure. Similarly, the various technical features of the above embodiments can be arbitrarily combined to form other embodiments of this application that may not be explicitly described. Therefore, the above embodiments only illustrate several implementations of this application and do not limit the scope of protection of this patent application.

Claims

1. A method for preparing an epitaxial structure, characterized in that, include: Provide substrate; A nitrogen source and a group III source are introduced, and at least one dislocation blocking layer is epitaxially grown on the substrate using molecular beam epitaxy. The dislocation blocking layer includes a first growth layer and a second growth layer stacked sequentially. The first growth layer has a three-dimensional island-like morphology, and the bottom surface of the second growth layer is in contact with the surface of the first growth layer away from the substrate. The thickness of the second growth layer is greater than or equal to the thickness of the first growth layer, and the surface of the second growth layer away from the substrate has a planar structure. During the growth of the first growth layer, the stoichiometric ratio of the flow rates of the nitrogen source and the group III source is greater than 1, and during the growth of the second growth layer, the stoichiometric ratio of the flow rates of the nitrogen source and the group III source is less than 1. A group III nitride material layer was epitaxially grown on the dislocation blocking layer using molecular beam epitaxy.

2. The method for preparing the epitaxial structure according to claim 1, characterized in that, The number of dislocation blocking layers is greater than or equal to 3.

3. The method for preparing the epitaxial structure according to claim 1, characterized in that, During the growth of the first growth layer, the flow rate of the nitrogen source is 5 sccm-7 sccm, the power of the radio frequency plasma source is 300W-450W, and the growth temperature is 600℃-900℃.

4. The method for preparing the epitaxial structure according to claim 1, characterized in that, During the growth of the second growth layer, the flow rate of the nitrogen source is 3 sccm-5 sccm, the power of the radio frequency plasma source is 300W-450W, and the growth temperature is 600℃-900℃.

5. The method for preparing the epitaxial structure according to claim 1, characterized in that, The thickness of the first growth layer is 10nm-20nm.

6. The method for preparing the epitaxial structure according to claim 1, characterized in that, The thickness of the second growth layer is 10nm-70nm.

7. The method for preparing the epitaxial structure according to claim 1, characterized in that, The dislocation density in the group III nitride material layer is less than or equal to 4.2E9 / cm². -2 .

8. The method for preparing the epitaxial structure according to any one of claims 1 to 7, characterized in that, Before epitaxially growing the dislocation blocking layer, the method further includes: An AlN nucleation layer is grown on the substrate.

9. An epitaxial structure, characterized in that, The epitaxial structure is prepared using the preparation method described in any one of claims 1 to 8.

10. The application of the epitaxial structure as described in claim 9 in the fabrication of semiconductor devices.

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