Preparation method of epitaxial structure, epitaxial structure and application of epitaxial structure

Abstract

The invention relates to a preparation method of an epitaxial structure, the epitaxial structure and application of the epitaxial structure. 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 barrier layer on the substrate by adopting a molecular beam epitaxy process; the dislocation barrier 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, away from the substrate direction, of the first growth layer, and the surface, away from the substrate direction, of the second growth layer is of a plane structure; in the growth process of the first growth layer, the stoichiometric ratio of the flow of the nitrogen source to the flow of the III-family source is larger than 1, and in the growth process of the second growth layer, the stoichiometric ratio of the flow of the nitrogen source to the flow of the III-family source is smaller than 1; and epitaxially growing a group III nitride material layer on the dislocation barrier layer by adopting a molecular beam epitaxy process. In this way, part of dislocation can be terminated in the dislocation barrier layer, so that the dislocation density in the epitaxial structure is reduced.

Description

Technical Field

[0001] The present application relates to the field of semiconductor technology, and in particular, to a method for preparing an epitaxial structure, an epitaxial structure and its application. Background Art

[0002] With the rapid development of semiconductor technology, the demand for high-quality semiconductor thin films is increasing day by day. Molecular Beam Epitaxy (MBE) technology has become one of the key technologies for preparing high-performance semiconductor devices due to its advantages of precisely controlling the growth thickness, composition, and doping concentration of thin films at the atomic scale. Among many semiconductor material systems, thin film materials grown by molecular beam epitaxy have important application prospects in the fields of optoelectronics, microelectronics, etc. Compared with Metal-Organic Chemical Vapor Deposition (MOCVD), MBE has the advantages of low impurity contamination, low growth temperature, and real-time in-situ monitoring, and can be used to grow semiconductor materials with high purity, high crystal quality, and abrupt interfaces.

[0003] In the traditional molecular beam epitaxy growth process, when growing a heterostructure with lattice mismatch, due to the difference in lattice constants between the substrate and the epitaxial layer, a large number of dislocations will be generated at the interface and 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 the electron mobility, increasing the carrier scattering probability, and introducing non-radiative recombination centers, etc., which will in turn lead to problems such as the 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 the molecular beam epitaxy process is a technical problem that needs to be solved urgently at present. Summary of the Invention

[0004] In view of this, embodiments of the present application provide a method for preparing an epitaxial structure, an epitaxial structure and its application to solve at least one problem in the background art.

[0005] In a first aspect, embodiments of the present application provide a method for preparing an epitaxial structure, including:

[0006] Providing a substrate;

[0007] A nitrogen source and a group III source are introduced, and at least one dislocation blocking layer is epitaxially grown on the substrate by using a molecular beam epitaxy process; the dislocation blocking layer includes a first growth layer and a second growth layer stacked in sequence, the first growth layer has a three-dimensional island-like morphology, the bottom surface of the second growth layer is in contact with the surface of the first growth layer away from the substrate, and the surface of the second growth layer away from the substrate is a planar structure; wherein, 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;

[0008] A group III nitride material layer is epitaxially grown on the dislocation blocking layer by using a molecular beam epitaxy process.

[0009] Combined with the first aspect of the present application, in an alternative embodiment, the number of layers of the dislocation blocking layer is greater than or equal to 3.

[0010] Combined with the first aspect of the present application, in an alternative embodiment, 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 300 W - 450 W, and the growth temperature is 600 °C - 900 °C.

[0011] Combined with the first aspect of the present application, in an alternative embodiment, 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 300 W - 450 W, and the growth temperature is 600 °C - 900 °C.

[0012] Combined with the first aspect of the present application, in an alternative embodiment, the thickness of the first growth layer is 10 nm - 20 nm.

[0013] Combined with the first aspect of the present application, in an alternative embodiment, the thickness of the second growth layer is 10 nm - 70 nm.

[0014] Combined with the first aspect of the present application, in an alternative embodiment, the dislocation density in the group III nitride material layer is less than or equal to 4.2E9 / cm -2 。

[0015] Combined with the first aspect of the present application, in an alternative embodiment, before epitaxially growing the dislocation blocking layer, the method further includes:

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

[0017] In a second aspect, an epitaxial structure provided by an embodiment of the present application is prepared by using the preparation method of the epitaxial structure according to any one of the first aspects.

[0018] In a second aspect, an embodiment of the present application provides an application of the epitaxial structure as described in the second aspect in the preparation of semiconductor devices.

[0019] In the preparation method of the epitaxial structure provided by the embodiment of the present application, the epitaxial structure and its application, a molecular beam epitaxy process is adopted to epitaxially grow at least one dislocation blocking layer on a substrate. During the epitaxial growth process, by controlling the stoichiometric ratio of the flow rates of the nitrogen source and the group III source to be greater than 1, a first growth layer with a three-dimensional island-like morphology is grown. By controlling the stoichiometric ratio of the flow rates of the nitrogen source and the group III source to be less than 1, a second growth layer is grown, the bottom surface of which is in contact with the surface of the first growth layer away from the substrate, and the surface away from the substrate is a planar structure. By changing the epitaxial growth process, different growth modes are controlled to grow a dislocation blocking layer composed of the first growth layer and the second growth layer. During the growth process of the dislocation blocking layer, the propagation direction of dislocations in the material can be changed, so that the dislocations are bent, and some dislocations terminate within the dislocation blocking layer, reducing the number of dislocations transmitted in the epitaxial growth direction, thereby effectively reducing the number of dislocations entering the subsequent grown group III nitride material layer, reducing the dislocation density in the group III nitride material layer, and further improving the quality and performance of the epitaxial structure.

[0020] Additional aspects and advantages of the present application will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present application. Description of the Drawings

[0021] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The schematic embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation of the present application. In the drawings:

[0022] Figure 1 is a schematic flow chart of the preparation method of the epitaxial structure provided by the embodiment of the present application;

[0023] Figures 2 to 5 is a schematic cross-sectional structure diagram during the preparation of the preparation method of the epitaxial structure provided by the embodiment of the present application;

[0024] Figure 6 is Figure 5 an enlarged view of part A in

[0025] Figure 7 is a diagram of the change in the RHEED pattern during the growth process of the dislocation blocking layer in Example 1;

[0026] Figure 8 is the rocking curve of the (002) crystal plane in the epitaxial structures prepared in Examples 1 to 3 and Comparative Example 1;

[0027] Figure 9It is a relationship curve of dislocation density and full width at half maximum with the number of dislocation blocking layers. Specific Embodiments

[0028] Exemplary embodiments disclosed in the present application will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present application are shown in the drawings, it should be understood that the present application can be implemented in various forms and should not be limited by the specific embodiments set forth herein. On the contrary, these embodiments are provided so that the present application can be more thoroughly understood and the scope of the present application disclosed can be fully conveyed to those skilled in the art.

[0029] In the following description, numerous specific details are given to provide a more thorough understanding of the present application. However, it will be apparent to one of ordinary skill in the art that the present application can be practiced without one or more of these details. In other instances, some well-known technical features are not described to avoid obscuring the present application; that is, not all features of the actual embodiments are described here, and the well-known functions and structures are not described in detail.

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

[0031] It should be understood that when an element or layer is referred to as being "on", "adjacent to", "connected to" or "coupled to" another element or layer, it can be directly on, adjacent to, connected or coupled to the other element or layer, or there may be intervening elements or layers. In contrast, when an element is referred to as being "directly on", "directly adjacent to", "directly connected to" or "directly coupled to" another element or layer, 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, regions, layers and / or portions, these elements, components, regions, layers and / or portions should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or portion from another element, component, region, layer or portion. Thus, a first element, component, region, layer or portion discussed below may be denoted as a second element, component, region, layer or portion without departing from the teachings of the present application. And when discussing a second element, component, region, layer or portion, it does not necessarily imply that there is a first element, component, region, layer or portion in the present application.

[0032] Spatial relationship terms such as "under", "below", "lower", "beneath", "above", "upper", etc. may be used herein for convenience of description to describe the relationship of one element or feature shown in the figures with other elements or features. It should be understood that, in addition to the orientation shown in the figures, spatial relationship terms are also intended to include different orientations of the device in use and operation. For example, if the device in the drawings is flipped, then an element or feature described as "under other elements" or "beneath them" or "below them" will be oriented "above" the other elements or features. Thus, the exemplary terms "under" and "beneath" can include both an upper and a lower orientation. The device may be otherwise oriented (rotated 90 degrees or other orientations) and the spatial descriptors used herein are to be interpreted accordingly.

[0033] The purpose of the terms used herein is only to describe specific embodiments and not to limit the present application. As used herein, the singular forms "a", "an" and "the" are also intended to include the plural forms unless the context clearly dictates otherwise. It should also be understood that the terms "comprising" and / or "including", when used in this specification, specify the presence of the stated features, integers, steps, operations, elements and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups. As used herein, the term "and / or" includes any and all combinations of the related listed items.

[0034] To fully understand the present application, detailed steps and detailed structures will be presented in the following description to illustrate the technical solutions of the present application. The preferred embodiments of the present application are described in detail below. However, in addition to these detailed descriptions, the present application may have other embodiments.

[0035] Different types of substrates have been tried for growing high-quality group III nitride materials. Sapphire, with a relatively economical price and a hexagonal crystal structure similar to that of nitrides, is widely used in the epitaxial growth of nitrides (such as AlN, GaN). Taking GaN as an example, there is a lattice mismatch of about 14% and a thermal mismatch of about 33% between sapphire and GaN, which makes the GaN thin film grown on the sapphire substrate have a high dislocation density, and further seriously affects the optoelectronic and other properties of semiconductor devices fabricated using this material. Similar to the sapphire substrate, the silicon substrate also has a large lattice mismatch and thermal mismatch with GaN, and moreover, silicon will undergo melt-back etching with Ga, and an AlN insertion layer needs to be introduced. Despite the help of the AlN nucleation layer, it is difficult for AlN to be precisely arranged on the silicon lattice at the initial stage of growth, resulting in a large number of misfit dislocations being generated and propagated to the GaN layer.

[0036] A feasible method to reduce dislocations is to increase the thickness of the buffer layer. As the thickness of the buffer layer increases, dislocations merge and annihilate with each other. In the MOCVD technology, the advantage of its relatively fast growth rate can be utilized, and a thick buffer layer can be used to achieve the purpose of reducing dislocations. However, in the MBE technology, especially plasma-assisted molecular beam epitaxy (PA-MBE), the slow growth rate is its weakness. Due to the use of the 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 the MBE technology. In addition, in related technologies, special structures are fabricated on the surface of the substrate or epitaxial layer through technologies such as photolithography and etching. For example, a patterned structure is etched on a sapphire substrate for epitaxial growth, and the dislocation vector direction is changed through lateral growth to achieve the purpose of reducing the dislocation density. However, this method is usually only applicable to the thick film growth of MOCVD and is also not applicable to the MBE technology because the grown thin film needs to be thick enough to eliminate the influence of the patterned substrate on the surface morphology of the epitaxial layer, which has certain requirements for the growth rate.

[0037] Introducing an insertion layer during the epitaxial growth process can change the stress distribution in the crystal structure and the propagation direction of dislocations, thereby reducing the dislocation density. However, the insertion layer usually introduces compressive stress or tensile stress at the interface, which affects the quality of the subsequently grown thin film, making the finally prepared product prone to warping or cracking. At the same time, some insertion layer materials introduce impurity elements (such as silicon impurities), which will affect the energy band structure of the material and thus affect the optoelectronic properties of the device. In addition, in molecular beam epitaxial growth, low-temperature growth can reduce the surface mobility of atoms, reduce thermal stress, and reduce the nucleation of dislocations, but this will affect the growth rate and the quality of the thin film.

[0038] Based on this, an embodiment of the present application provides a method for preparing an epitaxial structure. Figure 1 It is a schematic flow chart of the method for preparing the epitaxial structure provided by the embodiment of the present application; as Figure 1 shown, the method includes:

[0039] Step S101, providing a substrate;

[0040] Step S102, introducing a nitrogen source and a group-III source, and using the molecular beam epitaxy process 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 in sequence. The first growth layer has a three-dimensional island-like morphology. The bottom surface of the second growth layer is in contact with the surface of the first growth layer away from the substrate, and the surface of the second growth layer away from the substrate is a planar structure; wherein, 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: Using molecular beam epitaxy, grow a group-III nitride material layer on the dislocation blocking layer.

[0042] It can be understood that by the above method, using molecular beam epitaxy, at least one dislocation blocking layer is grown epitaxially on the 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-like 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 whose bottom surface is in contact with the surface of the first growth layer away from the substrate, and the surface away from the substrate is a planar structure. By changing the epitaxial growth process, different growth modes are controlled to grow a 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 the dislocations to bend, and some dislocations terminate within the dislocation blocking layer, reducing the number of dislocations transmitted in the epitaxial growth direction, thereby effectively reducing the number of dislocations entering the subsequent grown group-III nitride material layer, reducing the dislocation density in the group-III nitride material layer, and thus improving the quality and performance of the epitaxial structure.

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

[0044] First, please refer to Figure 2 , and perform step S101: Provide a substrate 100.

[0045] Here, the material of the substrate 100 may include, for example, sapphire, silicon, silicon carbide, or diamond, etc. 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 continue to refer to Figure 2 , before epitaxially growing the dislocation blocking layer, the preparation method of the epitaxial structure further includes: growing an AlN nucleation layer 200 on the substrate 100.

[0047] Growing the AlN nucleation layer 200 on the substrate 100 is beneficial to the subsequent epitaxial growth of the dislocation blocking layer, reducing the lattice mismatch and interface stress between the dislocation blocking layer and the substrate 100, and improving the quality of the dislocation blocking layer and the entire epitaxial layer.

[0048] Next, please refer to Figure 3 and Figure 4 , and perform 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 300 on the substrate 100; the dislocation blocking layer 300 includes a first growth layer 301 and a second growth layer 302 stacked in sequence.

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

[0050] First, please refer to Figure 3 , introduce a nitrogen source and a group III source, and use molecular beam epitaxy technology to epitaxially grow a first growth layer 301 on the substrate 100. During the growth process 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-like morphology;

[0051] Next, please refer to Figure 4 , continue to introduce a nitrogen source and a group III source, and use molecular beam epitaxy technology 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 away from the substrate 100, and the surface of the second growth layer 302 away from the substrate 100 is a planar structure. During the growth process 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 the embodiments of the present application, the group III source may include, for example, an aluminum source or a gallium source (specifically, including Al atoms or Ga atoms, etc.). During the growth process of the first growth layer 301, the stoichiometric ratio of the flow rates 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, there are more N elements than group III elements, and the stoichiometric ratio of N elements to group III elements is greater than 1. The migration of group III atoms (such as Al atoms or Ga atoms) on the surface of the substrate 100 is restricted and it is difficult to be evenly distributed on the surface of the substrate 100. Therefore, multiple independent growth centers will be formed and island growth will occur, so that the morphology of the first growth layer 301 is three-dimensional island-like (as Figure 3as shown). Further optionally, during the growth of the first growth layer 301, while maintaining the background vacuum degree, the stoichiometric ratio of the flow rates of the nitrogen source and the group III source can be 3-10, and it can also be considered that the stoichiometric ratio of the N element to the group III element is 3-10; in this way, the growth morphology of the first growth layer 301 can be better controlled, and it is more convenient to form a three-dimensional island-like morphology. 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 controlled to be less than 1. This growth condition can be called a group III source-rich condition. Under this condition, there are more group III elements than N elements, and the stoichiometric ratio of the N element to the group III element is less than 1. The 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 change from the island growth mode to the lateral growth mode, so that multiple island-like structures are gradually merged. At this growth stage, the propagation direction of some of the dislocations generated at the interface between the substrate 100 and the epitaxial layer will bend and 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 within the dislocation blocking layer 300, thereby reducing the number of dislocations entering the subsequent grown epitaxial layer. That is, the dislocation blocking layer 300 can play the role of blocking the propagation of dislocations. After the island-like structures are merged, the molecular beam epitaxial growth will turn into a stable step flow growth mode. The step flow growth is a better epitaxial growth mode for obtaining a complete lattice structure and a flat surface, so that the surface of the second growth layer 302 away from the substrate 100 direction is a planar structure (such as 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), and it can also be considered that the stoichiometric ratio of the N element to the group III element is 1:(2-2.3); in this way, the growth mode can be better controlled to switch from the island growth mode to the stable step flow growth mode, so that the growth morphology of the second growth layer 302 can be better controlled.

[0053] In the embodiments of the present application, by changing the material epitaxial growth mode, the dislocation vector direction is changed during the process of "island growth mode → lateral growth → island merging → step flow growth mode", so that the dislocations bend and annihilate, thereby reducing the transmission of dislocations in the epitaxial growth direction, and further effectively reducing the number of dislocations entering the subsequent grown epitaxial layer. Therefore, the dislocation density in the group III nitride material layer can be reduced, and the quality of the epitaxial layer and the optoelectronic and other properties of the epitaxial structure can be better improved.

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

[0055] The molecular beam epitaxy equipment mainly includes a sample loading chamber, a transfer chamber, a pretreatment chamber, a storage chamber, and an ultra-high vacuum growth chamber. Among them, except that the transfer chamber and the storage chamber are directly connected, the other chambers are separated from each other by vacuum valves. To ensure that the system is in an ultra-high vacuum environment, each chamber is equipped with an independently operating vacuum pump, including a mechanical pump, a molecular pump, a cryopump, etc. In addition, the system is also equipped with a gas analysis and detection system and an in-situ monitoring system, including a quadrupole mass spectrometer, a high-energy electron diffractometer, a beam current measuring instrument, etc.

[0056] Before epitaxial growth, first, the liquid nitrogen circulation system in the molecular beam epitaxy equipment needs to be turned on, the pressure in the growth chamber of the molecular beam epitaxy equipment is adjusted to an appropriate pressure, and the temperature of the source furnace is raised to the required value. The source furnace is used to provide the group III source molecular beam current required for growth (such as Al beam current or Ga beam current); then, the nitrogen source (such as nitrogen) plasma-assisted system is turned on. Since nitrogen cannot be directly used for the growth of the epitaxial layer, it enters the radio frequency plasma equipment through a dedicated gas pipeline, is excited into a plasma composed of ions and atoms, and then is introduced into the growth chamber to participate in the growth of the epitaxial layer. During the epitaxial growth process, the surface of the substrate 100 can be monitored in real time by a reflection high-energy electron diffractometer, and the growth front-end information can be obtained through the diffraction image on the fluorescent screen, and the temperature of the substrate 100 can be measured by 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, it can be 5 sccm, 5.5 sccm, 6 sccm, 6.5 sccm, 7 sccm, or any value between any two of the above numerical ranges, and the radio frequency plasma source power can be 300 W - 450 W, for example, it can be 300 W, 350 W, 400 W, 450 W, or any value between any two of the above numerical ranges.

[0058] Exemplarily, the nitrogen source during the growth of the first growth layer 301 may include nitrogen gas and / or ammonia gas. As described above, the nitrogen source is first introduced into the radio frequency plasma device, 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 the present application, controlling the flow rate of the nitrogen source (for example, the flow rate of nitrogen gas and / or ammonia gas introduced into the radio frequency plasma device) and the radio frequency plasma source power within the above ranges is beneficial to controlling the flow rate of the nitrogen source participating in the growth of the epitaxial layer, and thus facilitating 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), may be 6.6E-8 Torr. In this way, it is possible to preferably 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 can be understood that during the growth of the first growth layer 301, when the growth temperature is relatively low, it will affect the growth rate and film quality of the first growth layer 301; when the growth temperature is relatively high, the growth rate is relatively fast, which will also affect the film quality of the growth and is not conducive to controlling the growth morphology (three-dimensional island-like morphology) of the first growth layer 301. Therefore, in some specific embodiments, during the growth of the first growth layer 301, the growth temperature may be 600°C - 900°C, for example, it may be 600°C, 700°C, 800°C, 900°C, or any value between any two of the above numerical ranges.

[0060] It should be noted that in the actual preparation process, the growth temperature in the molecular beam epitaxy process may be the temperature of the substrate 100. In this way, the temperature measurement system in the molecular beam epitaxy device can be used to measure and control the temperature of the substrate 100, which is convenient for operation.

[0061] When the thickness of the first growth layer 301 is relatively thin, it not only requires higher growth process requirements, increases the process difficulty, but also makes the change in the dislocation propagation direction limited during the subsequent growth process, which will affect the effect of dislocation bending and annihilation; when the thickness of the first growth layer 301 is relatively thick, it not only increases the process time and cost, but also is not conducive to controlling 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 may be 10 nm - 20 nm, for example, it may be 10 nm, 15 nm, 20 nm, or any value between any two of the above numerical ranges.

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

[0063] Exemplarily, the nitrogen source during the growth of the second growth layer 302 may include nitrogen and / or ammonia. In the embodiments of the present application, controlling the flow rate of the nitrogen source (for example, the flow rate of nitrogen and / or ammonia into the radio frequency plasma device) and the power of the radio frequency plasma source within the above ranges is beneficial to controlling the flow rate of the nitrogen source participating in the growth of the epitaxial layer, and thus facilitating 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, for example, the group III source beam current (Al beam current or Ga beam current) may be 6.6E - 8 Torr. In this way, the stoichiometric ratio of the flow rates of the nitrogen source and the group III source can be better controlled to be less than 1, that is, the growth conditions of the group III source-rich are controlled.

[0064] It should be noted that the nitrogen source during the growth of the first growth layer 301 and the second growth layer 302 may be the same or different. In some specific embodiments, the nitrogen source during the growth of the first growth layer 301 and the second growth layer 302 is the same. In this way, there is no need to switch the nitrogen source during the growth of the dislocation blocking layer 300, which can simplify 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 unchanged, and the flow rate of the nitrogen source can be adjusted, for example, by adjusting the flow rate of nitrogen and / or ammonia into the radio frequency plasma device, to more conveniently and accurately adjust and control the stoichiometric ratio of the flow rates of the nitrogen source and the group III source.

[0066] It can be understood that during the growth of the second growth layer 302, when the growth temperature is low, it will affect the growth rate and film quality of the second growth layer 302 and the change in the dislocation propagation direction; when the growth temperature is high, the growth rate is fast, which will also affect the film quality of the growth and the change in the dislocation propagation direction, and thus will affect the effect of dislocation bending and annihilation. Therefore, in some specific embodiments, during the growth of the second growth layer 302, the growth temperature may be 600 °C - 900 °C. For example, it may be 600 °C, 700 °C, 800 °C, 900 °C, or any value between any two of the above numerical ranges.

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

[0068] As Figure 4 shown, since the bottom surface of the second growth layer 302 is in contact with the surface of the first growth layer 301 away from the substrate 100, the surface of the second growth layer 302 away from the substrate 100 is a planar structure. Therefore, 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. In this way, the surface morphology of the second growth layer 302 away from the substrate 100 can be better controlled, which is beneficial to the high-quality growth of the subsequent epitaxial layer. It can be understood that considering the process time and material cost comprehensively, the difference between the thickness of the second growth layer 302 and the thickness of the first growth layer 301 can be 10 nm - 50 nm.

[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 away from the substrate 100 and the bottom surface. The vertical direction here refers to the thickness direction of the substrate 100.

[0070] Figure 4 In

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

[0072] Finally, please refer to Figure 5 and perform step S103 to epitaxially grow a group-III nitride material layer 400 on the dislocation blocking layer 300 by using molecular beam epitaxy.

[0073] Since the dislocation blocking layer 300 can achieve good blocking of dislocations, causing some dislocations to bend and annihilate in the dislocation blocking layer 300 and terminate within the dislocation blocking layer 300, the number of dislocations entering the group-III nitride material layer 400 is reduced. As a result, the dislocation density in the group-III nitride material layer 400 can be effectively decreased, and further the quality and optoelectronic properties of the epitaxial structure can be effectively improved. Since the group-III nitride material layer 400 is usually used as the target epitaxial layer to play a functional role in semiconductor devices, a reduction in the dislocation density in the group-III nitride material layer 400 can better improve the performance and reliability of semiconductor devices fabricated using the epitaxial structure prepared in the embodiments of the present application. In the actual fabrication process, the group-III nitride material layer 400 may further include a buffer layer.

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

[0075] In the embodiments of the present application, through the effective blocking of dislocation propagation by the dislocation blocking layer 300, the dislocation density in the group-III nitride material layer 400 can be reduced to a relatively low level, and further the prepared epitaxial structure can be ensured to have high performance.

[0076] Here, in combination with Figure 6 , the principle of the dislocation blocking layer 300 in the embodiments of the present application achieving dislocation blocking is further explained. Among them, Figure 6 is the enlarged view of point A in Figure 5 . When the crystal growth mode changes from two-dimensional growth to three-dimensional island growth, the release of strain energy is a key factor. In the two-dimensional growth stage (such as the growth stages of the AlN nucleation layer 200 and the second growth layer 302), the strain generated by lattice mismatch gradually accumulates. In the three-dimensional island growth stage (the growth stage of the first growth layer 301), when forming three-dimensional island structures, these island structures can release strain energy through lattice relaxation at the island edges, and dislocations will bend in this strain environment (as shown in Figure 6 Figure 6As shown by the solid arrows, dislocations will propagate along the path with the lowest strain energy. As the island structures grow and merge, the dislocations in adjacent island structures approach each other. When they meet, the dislocation lines connect to form closed loops, and some bent dislocations will terminate at grain boundaries and interfaces of different materials, resulting in dislocation annihilation, thereby reducing the number of dislocations propagating in the direction of epitaxial growth (such as Figure 6 as shown by the dashed arrows). Therefore, the dislocation density in the group-III nitride material layer 400 can be reduced. It can be understood that when the number of layers of the dislocation blocking layer 300 is more than two, after the dislocations undergo multiple bendings and annihilations as described above, the number of dislocations propagating in the direction of epitaxial growth is greatly reduced, thereby being able to more significantly reduce the dislocation density in the group-III nitride material layer 400.

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

[0078] The embodiment of the present application also provides an application of the epitaxial structure described in the foregoing embodiment in the preparation of semiconductor devices.

[0079] It should be understood that since the dislocation density in the epitaxial structure prepared in any of the foregoing embodiments is relatively low, therefore, the performance and reliability of the semiconductor device prepared by using this epitaxial structure are both relatively high.

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

[0081] The technical solution of the present application will be further described below in combination with multiple embodiments and comparative examples.

[0082] Example 1

[0083] The preparation method of the epitaxial structure in this embodiment includes the following steps:

[0084] Step S1: Use molecular beam epitaxy technology to epitaxially grow an AlN nucleation layer on a sapphire substrate;

[0085] Step S2: Introduce a nitrogen source and an aluminum source, and use molecular beam epitaxy to epitaxially grow an AlN layer (the first growth layer) with a three-dimensional island-like morphology on the AlN nucleation layer. The growth conditions of the first growth layer are nitrogen-rich conditions. Specifically, the Al beam current is 6.6E-8 Torr, the nitrogen flow rate into the radio frequency plasma equipment is 6 sccm, the radio frequency plasma source power is 380 W, the growth temperature is 850 °C, and the thickness of the first growth layer is 20 nm; introduce a nitrogen source and an aluminum source, and use molecular beam epitaxy to epitaxially grow an AlN layer (the second growth layer) with a planar surface structure on the first growth layer. The growth conditions of the second growth layer are aluminum-rich conditions (which can also be called slightly aluminum-rich conditions). Specifically, the Al beam current is 6.6E-8 Torr, the nitrogen flow rate into the radio frequency plasma equipment is 4 sccm, the radio frequency plasma source power is 380 W, the growth temperature is 780 °C, and the thickness of the second growth layer is 30 nm (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 growth layer and the second growth layer together constitute a dislocation blocking layer, and the thickness of the dislocation blocking layer is 50 nm;

[0086] Step S3: Continuously introduce a nitrogen source and an aluminum source, 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 example 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 cycles to form 2 dislocation blocking 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 example 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 in cycles to form 10 dislocation blocking 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: Use molecular beam epitaxy to epitaxially grow an AlN nucleation layer on a sapphire substrate;

[0098] Step S20: Using molecular beam epitaxy, an AlN layer (which can also be referred to 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 layers in the above-mentioned embodiments and comparative examples is 550 nm.

[0100] During the growth process, a reflection high-energy electron diffraction (RHEED) instrument is used to monitor the substrate surface in real time. Growth front-end information can be obtained through the diffraction images on the fluorescent screen. Figure 7 It is a diagram showing the change of the RHEED pattern during the growth of the dislocation blocking layer in Example 1. Figure 7 The RHEED pattern in (a) is the RHEED pattern corresponding to after nitrogen-rich growth and after the growth of the first growth layer. The RHEED pattern is a "swallowtail-shaped" dot pattern, indicating that the surface morphology of the first growth layer far from the substrate is three-dimensional island-like. Figure 7 (b)-(d) in it are the RHEED patterns during the growth of the second growth layer. As the growth of the second growth layer proceeds under slightly aluminum-rich conditions, Figure 7 the RHEED patterns in (b)-(d) gradually change from dot patterns to line patterns, indicating that the growth of the AlN thin film begins to transform into a two-dimensional layer growth mode, and the three-dimensional island structures start to merge slowly, and finally a second growth layer with a planar structure on the surface far from the substrate is formed. This further proves that in the embodiments of the present application, by changing the epitaxial growth process, different growth modes can indeed be controlled, enabling the transformation from an island growth mode to lateral growth, island merging, and then to a step-flow growth mode, realizing the transformation of the surface morphology of the first growth layer and the second growth layer from island-like to layer-like.

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

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

[0103] Table 1

[0104] Full width at half maximum of rocking curve / arc second <![CDATA[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 is introduced into the epitaxial structures prepared in Examples 1 to 3. The full width at half maximum (FWHM) of the rocking curve is significantly reduced compared to Comparative Example 1, and the corresponding screw dislocation density in the epitaxial structure is also significantly reduced. This indicates that in the present application, by changing the molecular beam epitaxy growth process to grow a dislocation blocking layer, the propagation direction of dislocations in the material can be changed during the growth of the dislocation blocking layer, causing the dislocations to bend, and some dislocations terminate within the dislocation blocking layer, reducing the number of dislocations transmitted in the epitaxial growth direction, thereby effectively reducing the number of dislocations entering the subsequent grown group III nitride material layer, reducing the dislocation density in the group III nitride material layer, that is, reducing the dislocation density in the epitaxial structure, and 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. The screw dislocation density in the epitaxial structure prepared in Comparative Example 1 is significantly higher than that in Examples 1 to 3. As can be seen from the data in Table 1, the dislocation density in the epitaxial structure prepared in Comparative Example 1 is three times that in the epitaxial structure prepared in Example 1. It can be seen that growing one dislocation blocking layer can already effectively reduce the dislocation density in the epitaxial structure.

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

[0108] Figure 9 is the relationship curve of dislocation density and full width at half maximum with the number of dislocation blocking layers. As Figure 9 can be seen, in the epitaxial structure, as the number of dislocation blocking layers increases, the dislocation density gradually decreases, but the decreasing amplitude of the dislocation density gradually decreases, which is consistent with the crystallographic law. In actual materials, when the dislocation density is reduced to a certain extent, the self-structure of the material and external environmental factors will still cause new dislocations to be generated, so that the dislocation density will not continue to decrease significantly. It can also be obtained from this that in the present application, it is a preferable scheme that the number of dislocation blocking layers is greater than or equal to 3, so that the dislocation density in the epitaxial structure can be significantly reduced. Considering the time and cost of the process, the number of dislocation blocking layers can be controlled within 10 layers.

[0109] In this application, by changing the growth mode of group III nitrides (such as N-rich and Al-rich growth modes) during MBE growth, a first growth layer with a nano three-dimensional island structure is grown first, and then a second growth layer is grown, enabling the islands to gradually merge, so that dislocations can bend and annihilate in the dislocation blocking layer. While MOCVD needs to use an N-rich growth mode. Taking the growth of AlN by MOCVD as an example, the N / Al (nitrogen-aluminum element ratio) can reach more than 1000. Due to the relatively high growth temperature of MOCVD, the N-rich condition can solve problems such as the decomposition of AlN, the formation of Al droplets, and the low ammonia efficiency during high-temperature growth. Changing the growth mode will seriously affect the quality of the MOCVD epitaxial thin film. Therefore, the preparation method in this application is applicable to MBE but not to MOCVD.

[0110] Compared with the methods of introducing an insertion layer and reducing the dislocation density in epitaxial growth by patterning the substrate, the dislocation blocking layer in this application can form a good interfacial bond with the target epitaxial layer (group III nitride material layer), will not introduce additional impurities, can improve the crystal quality, and the thickness of the entire epitaxial layer can be controlled within a relatively small range. The thinner overall structure can reduce the series resistance of semiconductor devices prepared using the epitaxial structure, improve the heat dissipation efficiency of the material, and can also reduce production costs. In addition, the N-termination of the nitrogen-polarity material makes it have higher surface activity compared with the metal polarity, and it is easier to bond with impurity atoms, which will interfere with the normal atomic arrangement and form defects. At the same time, the N-termination of the nitrogen-polarity material makes the migration of group III atoms difficult, resulting in atomic accumulation, thus affecting the crystal growth quality. Therefore, in this application, by introducing the dislocation blocking layer technology during the growth of the nitrogen-polarity material, the growth quality of the nitrogen-polarity material can be significantly improved.

[0111] Furthermore, the preparation method in this application does not use any additional equipment and devices, makes full use of the in-situ monitoring advantages of the MBE equipment itself, does not add any material sources, does not generate any toxic and harmful gases or waste that may pollute the environment, and has obvious advantages in terms of cost and environmental protection, and has high practical application value.

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

[0113] It should be understood that the above embodiments are all exemplary and do not cover all possible implementation manners. Without departing from the scope of the present disclosure, various deformations and changes can be made on the basis of the above embodiments. Similarly, any combination of the technical features of the above embodiments can be made to form additional embodiments of the present application that may not be clearly described. Therefore, the above embodiments only represent several implementation manners of the present application and do not limit the protection scope of the patent of the present application.

Claims

1. A method for preparing an epitaxial structure, characterized in that: include: providing a substrate; A nitrogen source and a group III source are introduced, and at least one dislocation barrier layer is epitaxially grown on the substrate by a molecular beam epitaxy process; the dislocation barrier layer comprises a first growth layer and a second growth layer stacked in sequence, the first growth layer has a three-dimensional island morphology, the bottom surface of the second growth layer is in contact with a surface of the first growth layer away from the substrate, and the surface of the second growth layer away from the substrate is in a planar structure; wherein, 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 molecular beam epitaxy process is adopted to epitaxially grow a group III nitride material layer on the dislocation barrier layer.

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

3. The method for preparing an 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 RF plasma source is 300W-450W, and the growth temperature is 600°C-900°C.

4. The method for preparing an 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 RF plasma source is 300W-450W, and the growth temperature is 600°C-900°C.

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

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

7. The method for preparing an 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 / cm -2 .

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

9. An epitaxial structure, characterized in that: The epitaxial structure is prepared by the method for preparing the epitaxial structure according to any one of claims 1 to 8.

10. Use of the epitaxial structure according to claim 9 in preparing a semiconductor device.

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