Epitaxial structure and preparation method, HEMT device and preparation method

Abstract

Embodiments of the present application relate to a preparation method of an epitaxial structure, an epitaxial structure, a preparation method of a HEMT device and the HEMT device, wherein the method comprises: providing a substrate; epitaxially growing a B x Al 1‑x N nucleation layer on the substrate, wherein 0 x Al 1‑x N nucleation layer, wherein 0 y Al 1‑y N graded buffer layer, wherein 0 y Al 1‑y N graded buffer layer, wherein 0 z Ga 1‑z N epitaxial layer, wherein 0 y1 Al 1‑y1 N and M z Ga 1‑z N is less than B y2 Al 1‑y2 N or B y3 Al 1‑y3 N and M z Ga 1‑z N. In this way, it is beneficial to form a high-quality M z Ga 1‑z N epitaxial layer, thereby effectively guaranteeing the quality of the GaN device.

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, a preparation method of an HEMT device and the HEMT device. BACKGROUND

[0002] GaN (gallium nitride) is widely used in optoelectronic devices, semiconductor laser devices, light-emitting diodes, high electron mobility transistors and other semiconductor devices due to its high thermal conductivity, high electron saturation drift speed, high breakdown electric field, strong radiation resistance and chemical stability.

[0003] GaN single crystals cannot be obtained from nature and need to be artificially manufactured. The preparation of GaN single crystal substrates is very difficult, so most GaN-based devices are currently prepared on hetero-substrates by hetero-epitaxy. These hetero-substrates mainly include Si (silicon), SiC (silicon carbide) and sapphire. Since the materials of the epitaxial layer and the substrate are different, the lattices cannot be perfectly matched, and cracks are prone to occur during thermal expansion. Dislocations of the substrate material will be brought into the GaN epitaxial layer and amplified, so the existing GaN epitaxy technology proposes to grow an AlN layer in the middle to solve the above problems. Specifically, taking a Si substrate as an example, in order to grow a high-quality GaN layer, an AlN nucleation layer is first epitaxially grown on the Si substrate, then a buffer layer is epitaxially grown on the AlN nucleation layer, and finally the required GaN layer is grown. However, due to the high lattice and thermal mismatch between the Si substrate and the AlN layer, the GaN grown from the AlN layer has poor quality, ultimately resulting in poor quality of GaN devices.

[0004] How to grow a high-quality GaN layer to improve the quality of GaN devices is still a technical problem that the field is committed to solving. SUMMARY

[0005] Therefore, the embodiments of the present application provide a preparation method of an epitaxial structure, an epitaxial structure, a preparation method of an HEMT device and the HEMT device to solve at least one problem in the background art.

[0006] In a first aspect, the embodiments of the present application provide a preparation method of an epitaxial structure, which comprises:

[0007] providing a substrate;

[0008] epitaxially growing a B x Al 1-x N nucleation layer on the substrate, wherein 0 < x ≤ 1;

[0009] epitaxially growing a B x Al 1-xepitaxially growing B y Al 1-y N graded buffer layer, wherein 0≤y≤1, y decreases from y0 to y2 and then increases to y1 or increases from y0 to y3 and then decreases to y1 along a direction away from the substrate;

[0010] epitaxially growing B y Al 1-y M z Ga 1-z N epitaxial layer, wherein 0≤z<1, M comprises at least one of B, Al, In, Ti, the lattice constant of B y1 Al 1-y1 N and M z Ga 1-z N is less than the difference between the lattice constant of B y2 Al 1-y2 N or B y3 Al 1-y3 N and M z Ga 1-z N.

[0011] With reference to the first aspect of the present application, in an optional implementation, the lattice constant of B y1 Al 1-y1 N and M z Ga 1-z N is equal; and y2≤1 / 2y1 or y3≥2y1.

[0012] With reference to the first aspect of the present application, in an optional implementation, before epitaxially growing the M z Ga 1-z N epitaxial layer, the method further comprises:

[0013] epitaxially growing a superlattice structure layer on the B y Al 1-y N graded buffer layer, wherein the superlattice structure layer comprises B y1 Al 1-y1 N sub-layers and M z Ga 1-z N sub-layers arranged periodically.

[0014] With reference to the first aspect of the present application, in an optional implementation, before epitaxially growing the B x Al 1-x N nucleation layer, the method further comprises:

[0015] epitaxially growing a B k Al 1-k N transition layer on the substrate, wherein 0<k≤1, the B k Al 1-kThe growth temperature of the N transition layer is 300℃~800℃ to achieve a 3D island-like growth pattern.

[0016] In conjunction with the first aspect of this application, in an alternative embodiment, during the epitaxial growth of the B... k Al 1-k Following the N transition layer, the method further includes:

[0017] For the B k Al 1-k The N-transition layer is subjected to high-temperature annealing.

[0018] In conjunction with the first aspect of this application, in an alternative embodiment, the B x Al 1-x The thickness of the N nucleation layer is greater than that of B. k Al 1-k The thickness of the N transition layer.

[0019] In conjunction with the first aspect of this application, in an alternative embodiment, the B x Al 1-x The growth temperature of the N nucleation layer is 800℃~1300℃ to ensure that the growth mode is 2D.

[0020] Secondly, embodiments of this application provide an extensional structure, including:

[0021] Substrate;

[0022] B located on the substrate x Al 1-x N is a nucleation layer, where 0 < x ≤ 1;

[0023] Located in B x Al 1-x B on the N nucleation layer y Al 1-y N-gradient buffer layer, wherein 0≤y≤1, and along the direction away from the substrate, y first decreases from y0 to y2 and then increases to y1 or first increases to y3 and then decreases to y1;

[0024] Located in B y Al 1-y M on the N gradient buffer layer z Ga 1-z N is an epitaxial layer, where 0 ≤ z < 1, and M includes at least one of B, Al, In, and Ti, where B y1 Al 1-y1 N and M z Ga 1-z The difference in lattice constant of N is smaller than that of B. y2 Al 1-y2 N or B y3 Al1-y3 N and M z Ga 1- z Difference of lattice constant of N.

[0025] In combination with the second aspect of the present application, in an optional implementation, B y1 Al 1-y1 N and M z Ga 1-z Lattice constant of N is equal; y2≤1 / 2y1 or y3≥2y1.

[0026] In combination with the second aspect of the present application, in an optional implementation, further comprising:

[0027] B y Al 1-y N graded buffer layer and the M z Ga 1-z N epitaxial layer, wherein the superlattice structure layer comprises periodically arranged B y1 Al 1-y1 N sublayer and M z Ga 1-z N sublayer.

[0028] In combination with the second aspect of the present application, in an optional implementation, further comprising:

[0029] B x Al 1-x N nucleation layer and the B k Al 1-k N transition layer, wherein 0 k Al 1-k The growth mode of the B x Al 1-x N transition layer is 3D island mode.

[0030] In combination with the second aspect of the present application, in an optional implementation, the thickness of the B x Al 1-x N nucleation layer is greater than the thickness of the B k Al 1-k N transition layer.

[0031] In combination with the second aspect of the present application, in an optional implementation, the growth mode of the B x Al 1-x N nucleation layer is 2D mode.

[0032] Thirdly, the embodiments of the present application provide a preparation method of a HEMT device, which comprises the steps in the preparation method of the epitaxial structure in any one of the first aspect, or comprises the preparation of the HEMT device by using the epitaxial structure in any one of the second aspect.

[0033] In a fourth aspect, the embodiments of the present application provide a HEMT device, comprising: the epitaxial structure according to any one of the second aspect; and a source electrode, a drain electrode and a gate electrode located on the epitaxial structure.

[0034] The epitaxial structure, the preparation method of the epitaxial structure, the preparation method of the HEMT device and the HEMT device provided by the embodiments of the present application effectively reduce the stress difference between the substrate and the M x Al 1-x N nucleation layer and the B y Al 1-y N graded buffer layer, effectively reduce the stress difference between the substrate and the M z Ga 1-z N epitaxial layer; the B y Al 1-y N graded buffer layer, y is first reduced to y2 and then increased to y1 or first increased to y3 and then reduced to y1 from y0, and the B y1 Al 1-y1 N and the M z Ga 1-z N lattice constant difference is less than the B y2 Al 1-y2 N or the B y3 Al 1-y3 N and the M z Ga 1-z N lattice constant difference, so that the internal stress is fully released by twice opposite buffer adjustment; finally, it is beneficial to form a high-quality M z Ga 1-z N epitaxial layer (not only can be used to form a GaN layer, but also can be used to form a GaN-based alloy layer), thereby effectively guaranteeing the quality of the GaN device.

[0035] Additional aspects and advantages of the present application will be made apparent by the following description and the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0036] The accompanying drawings, which are included to provide a further understanding of the present application, constitute a part of the present application, and the illustrative embodiments of the present application and their description serve to explain the present application, and do not constitute improper limitations on the present application. In the drawings:

[0037] Figure 1 The flowchart of the preparation method of the epitaxial structure provided by the embodiments of the present application is shown;

[0038] Figures 2 to 9 The cross-sectional structure schematic diagram of the epitaxial structure provided by the embodiments of the present application in the preparation process is shown;

[0039] Figure 10 A cross-sectional structure schematic diagram of a HEMT device provided by an embodiment of the present application is shown in FIG. 1.

[0040] Explanation of reference numerals:

[0041] 100, substrate; 110, B k Al 1-k N transition layer; 120, B x Al 1-x N nucleation layer; 130, B y Al 1-y N graded buffer layer; 131, first graded buffer layer; 132, second graded buffer layer; 140, superlattice structure layer; 140a, B y1 Al 1-y1 N sublayer; 140b, M z Ga 1-z N sublayer; 150, M z Ga 1-z N epitaxial layer; 160, barrier layer; 171, source electrode; 172, drain electrode; 173, gate electrode. DETAILED DESCRIPTION

[0042] Exemplary embodiments of the present application will be described in detail with reference to the drawings. Although 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 to the specific embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present application to those skilled in the art.

[0043] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. It will be apparent, however, to one skilled in the art that the present application can be practiced without one or more of these specific details. In other instances, well-known features have not been described in detail so as not to unnecessarily obscure the present application.

[0044] In the drawings, the size of layers, regions, elements and the relative sizes among them can be exaggerated for clarity. Like reference numerals refer to like elements throughout.

[0045] 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. 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.

[0046] Spatial relation terms such as “below,” “under,” “below,” “under,” “above,” “above,” etc., are used herein for convenience of description to describe the relationship of one element or feature shown in the figure to other elements or features. 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” or “under” the other element or feature will be oriented “above” the other element or feature. Therefore, the exemplary terms “below” and “under” can include both upper and lower orientations. The device may be otherwise oriented (rotated 90 degrees or otherwise) and the spatial descriptive terms used herein will be interpreted accordingly.

[0047] 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.

[0048] 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.

[0049] This application provides a method for preparing an epitaxial structure. Please refer to [link / reference]. Figure 1 The method includes:

[0050] Step S01, providing a substrate;

[0051] Step S02, epitaxially grow B on the substrate x Al 1-x N is a nucleation layer, where 0 < x ≤ 1;

[0052] Step S03, in B x Al 1-x B epitaxial growth on N nucleation layer y Al 1-y N graded buffer layer, where 0≤y≤1, and along the direction away from the substrate, y first decreases from y0 to y2 and then increases to y1 or first increases to y3 and then decreases to y1;

[0053] Step S04, in B y Al 1-y M epitaxially grows on N gradient buffer layer z Ga 1-z N is an epitaxial layer, where 0 ≤ z < 1, and M includes at least one of B, Al, In, and Ti, where B y1 Al 1-y1 N and M z Ga 1-z The difference in lattice constant of N is smaller than that of B. y2 Al 1-y2 N or B y3 Al 1- y3 N and M z Ga 1-z The difference in the lattice constant of N.

[0054] It is understood that the preparation method provided in the embodiments of this application is applicable to the epitaxial growth of high-quality GaN layers, wherein the GaN layer can be broadly understood as a GaN-based material layer. Specifically, M... z Ga 1-z N (0≤z<1) means that it includes both the GaN layer in the narrow sense (when Z=0) and the GaN-based alloy layer (when Z>0, specifically such as BGaN layer, AlGaN layer, BAlGaN layer, InAlGaN layer, etc.).

[0055] This application embodiment introduces B atoms to form B x Al 1-x N nucleation layer and B y Al 1-y N-gradient buffer layer effectively mitigates substrate and M z Ga1-z Stress difference between N epitaxial layers; B y Al 1-y In the N-gradient buffer layer, y decreases from y0 to y2 and then increases to y1, or increases to y3 and then decreases to y1, and B y1 Al 1-y1 N and M z Ga 1-z The difference in lattice constant of N is smaller than that of B. y2 Al 1-y2 N or B y3 Al 1-y3 N and M z Ga 1-z The difference in the lattice constant of N allows the internal stress to be fully released through two opposite buffering adjustments; ultimately, this is beneficial for the formation of high-quality M. z Ga 1-z The N-epitaxial layer (which can be used not only to form GaN layers but also to form GaN-based alloy layers) effectively ensures the quality of GaN devices.

[0056] Below, we will combine Figures 2 to 9 The schematic diagram of the cross-sectional structure of the epitaxial structure shown in the preparation process provides a further detailed explanation of the embodiments and beneficial effects of this application.

[0057] First, please refer to Figure 2 Substrate 100 is provided.

[0058] The substrate 100 can be made of any suitable material known to those skilled in the art, such as a range of semiconductor materials including Si, SiC, and sapphire. As a specific example, the substrate 100 is a Si substrate.

[0059] Substrate 100 serves as the growth substrate for the subsequently formed epitaxial layer. The material of substrate 100 is similar to that of the M layer to be formed. z Ga 1-z The N epitaxial layer is made of a different material; in other words, substrate 100 is a heterogeneous substrate. The thickness direction of substrate 100 is the direction of epitaxial growth, or the stacking direction of subsequent layers.

[0060] In actual fabrication, before performing the epitaxial growth process, a step of cleaning the surface of the substrate 100 with HF may also be included.

[0061] Next, please refer to Figure 3 In epitaxial growth B x Al 1-x Before the N nucleation layer, the method may further include: epitaxially growing B on the substrate 100. k Al 1-k N transition layer 110, where 0 < k ≤ 1.

[0062] Understandably, the transition layer used in this embodiment is a transition layer containing B.

[0063] B k Al 1-k The N-transition layer 110 is grown at a temperature of 300℃~800℃ to achieve a 3D island-like growth pattern. The transition layer formed under this growth pattern can also be called a low-temperature transition layer. The 3D island-like pattern typically involves rapid growth in the longitudinal direction, while being discontinuous in the transverse direction; this can be achieved by setting a relatively low growth temperature.

[0064] Optionally, B k Al 1-k The growth thickness of the N transition layer 110 is less than or equal to 10 nm.

[0065] In actual preparation, B k Al 1-k The N transition layer 110 can be grown directly on the substrate 100.

[0066] Optionally, during epitaxial growth of B k Al 1-k Following the N transition layer 110, the method further includes: [addressing B] k Al 1-k The N transition layer 110 is subjected to high-temperature annealing (for easy differentiation, the B layer can be annealed). k Al 1-k The high-temperature annealing of the N transition layer 110 is referred to as the "first high-temperature annealing". Thus, by introducing boron atoms, a BAlN transition layer is grown at a low temperature, followed by high-temperature annealing to form a barrier oxide / nitride layer, preventing deterioration of the nucleation layer quality. Specifically, taking a Si substrate 100 as an example, performing high-temperature annealing directly after the transition layer growth can prevent oxygen in the substrate from overflowing upwards or combining with external nitrogen, thereby preventing the formation of a silicon oxide / silicon nitride layer.

[0067] Optionally, the temperature of the first high-temperature annealing is 800℃~1300℃; the time of the first high-temperature annealing is 5min~60min.

[0068] Next, please refer to Figure 4 Epitaxial growth B x Al 1-x N has 120 nucleation layers, where 0 < x ≤ 1.

[0069] Understandably, the nucleation layer used in this embodiment is a nucleation layer containing B.

[0070] Furthermore, the components of B can be 0 < x ≤ 0.3. k Al 1-k The lattice constant of the N transition layer 110 can be related to that of the B layer.x Al 1- x The lattice constants of N nucleation layers 120 are equal, or B x Al 1-x The lattice constant of the N nucleation layer 120 is compared to that of B. k Al 1-k N transition layer 110 is closer to B y0 Al 1-y0 The lattice constant of N; in other words, k can be equal to x, or the absolute value of x-y0 can be less than the absolute value of k-y0, thus gradually achieving a lattice transition and reducing stress. Optionally, k=x=y0; therefore, B k Al 1-k The lattice constant of the N-transition layer 110 and the B x Al 1-x The lattice constant of N nucleation layer 120 and B y0 Al 1-y0 N(B) y Al 1-y N gradient buffer layer 130 is closest to B x Al 1-x The lattice constants of the material on the N nucleation layer 120 side are all equal.

[0071] B x Al 1-x The growth temperature of the N nucleation layer 120 is 800℃~1300℃ to ensure that its growth mode is 2D. In this embodiment, B is first grown using a 3D island pattern. k Al 1-k N transition layer 110; in the formation of B k Al 1-k After the N transition layer 110, the temperature can be increased to convert the growth mode to a 2D mode, thereby forming B. x Al 1-x The surface of the N nucleation layer 120 gradually becomes smoother, and the problem of poor lattice matching of the material at the growth interface gradually diminishes.

[0072] In actual preparation, B x Al 1-x The thickness of the N nucleation layer 120 can be greater than that of B. k Al 1-k The thickness of the N transition layer 110.

[0073] B x Al 1-x The thickness of the N nucleation layer 120 can range from 10 nm to 500 nm. B x Al 1-x The thickness of the N nucleation layer 120 can be B k Al 1-kThe thickness of the N transition layer 110 is several times or even tens of times greater.

[0074] In actual preparation, B x Al 1-x N nucleation layer 120 can grow directly on B k Al 1-k On the N transition layer 110.

[0075] Optionally, during epitaxial growth of B x Al 1-x After N nucleation layer 120, the method further includes: for B x Al 1-x The N nucleation layer 120 is subjected to high-temperature annealing (for easy differentiation, the B layer can be annealed at high temperature). x Al 1-x The high-temperature annealing of the N nucleation layer 120 is called "second high-temperature annealing". Specifically, in B x Al 1-x After the N nucleation layer 120 is grown, in-situ annealing is performed to improve crystal quality.

[0076] Optionally, the temperature of the second high-temperature annealing is 800℃~1300℃; the time of the second high-temperature annealing is 5min~60min.

[0077] Although the temperature of the second high-temperature annealing is similar to B x Al 1-x The growth temperature range for the N nucleation layer 120 is 800℃~1300℃, but in actual preparation, the temperature of the second high-temperature annealing is higher than that of the B layer. x Al 1-x The growth temperature of the N nucleation layer is 120°C; for example, B... x Al 1-x The growth temperature of the N nucleation layer 120 is 800℃, and the temperature of the second high-temperature annealing is 1200℃.

[0078] Next, please refer to Figure 5 and Figure 6 In B x Al 1-x B epitaxial growth on N nucleation layer 120 y Al 1-y N is a gradient buffer layer of 130, where 0 ≤ y ≤ 1.

[0079] Along the direction away from the substrate 100, y first decreases from y0 to y2 and then increases to y1, or first increases to y3 and then decreases to y1; B y1 Al 1-y1 N and M z Ga 1-z The difference in lattice constant of N is smaller than that of B. y2 Al 1-y2 N or By3 Al 1-y3 N and M z Ga 1-z The difference in the lattice constant of N.

[0080] Understandably, y is B y Al 1-y In the N-gradient buffer layer 130, the component B has a value of y ranging from 0 to 1. y Al 1- y The B component in the N-gradient buffer layer 130 is in the range of 0 to 1, therefore y0, y1, y2, and y3 are obviously also in the range of 0 to 1.

[0081] In the scheme where y decreases from y0 to y2 and then increases to y1, y0 is greater than 0 and y2 can be equal to 0; in the scheme where y increases from y0 to y3 and then decreases to y1, y0 can be equal to 0 and y3 is greater than 0.

[0082] Along the direction away from the substrate 100, the change in composition B makes B y Al 1-y The N-gradient buffer layer 130 is adjusted to match the M to be formed. z Ga 1-z The N epitaxial layer has a large difference in lattice constant, and then it is reversed to be adjusted to match the M layer to be formed. z Ga 1-z The N-epitaxial layers have small (or even equal) lattice constant differences, thus releasing stress between tension and compression.

[0083] As one optional specific implementation method, B y1 Al 1-y1 N and M z Ga 1-z The lattice constant of N is equal. y1 can also be called the target B component. By changing the B component, B... x Al 1-x The N nucleation layer 120 eventually gradually transitions to a lattice constant that matches the M layer to be grown. z Ga 1-z N is equal (actually basically equal), thus providing M for epitaxial growth. z Ga 1-z Layer N provides preparation.

[0084] As an optional implementation, y2 ≤ 1 / 2y1 or y3 ≥ 2y1. In this way, a relatively large change in the y value achieves sufficient buffering and adjustment, which helps to ensure the stress release effect.

[0085] In actual preparation, you can first refer to Figure 5 In B x Al1-x A first gradient buffer layer 131 is epitaxially grown on the N nucleation layer 120. The first gradient buffer layer 131 corresponds to the portion where y decreases from y0 to y2 or increases from y0 to y3.

[0086] The first gradient buffer layer 131 can be directly grown on B. x Al 1-x The N nucleation layer 120 is applied. The thickness of the first gradient buffer layer 131 can be 10 nm to 2000 nm. y0 can be equal to x.

[0087] As a specific example, y0=0.3, y2=0; in other words, the gradual range of y in the first gradient buffer layer 131 is from 30% to 0%.

[0088] Then, please refer to Figure 6 A second gradient buffer layer 132 is epitaxially grown on the first gradient buffer layer 131. The second gradient buffer layer 132 corresponds to the portion where y increases from y2 to y1 or decreases from y3 to y1.

[0089] The second gradient buffer layer 132 can be grown directly on the first gradient buffer layer 131. The thickness of the second gradient buffer layer 132 can be 10 nm to 2500 nm. Optionally, y1 is approximately equal to 0.12, thereby achieving lattice matching.

[0090] As a specific example, y2=0, y1=0.12; in other words, the gradual range of y in the second gradient buffer layer 132 is from 0% to 12%.

[0091] It should be understood that, although the figure illustrates an example of a gradient buffer layer (first gradient buffer layer 131 and second gradient buffer layer 132) that varies in two directions, in this application, in B... x Al 1-x The N-nucleation layer 120 may include multiple pairs of first gradient buffer layers 131 and second gradient buffer layers 132; in other words, multiple B-nucleation layers can be epitaxially grown. y Al 1-y The N-gradient buffer layer 130 allows component B to undergo multiple adjustments between increasing and decreasing.

[0092] Next, please refer to Figure 7 In epitaxial growth M z Ga 1-z Before the N epitaxial layer, the method may further include: at B y Al 1- y A superlattice structure layer 140 is epitaxially grown on an N-gradient buffer layer 130, wherein the superlattice structure layer 140 includes periodically alternating B-type elements. y1 Al 1-y1N sublayer 140a and M z Ga 1-z N sublayer 140b.

[0093] It should be understood that B y1 Al 1-y1 N sublayer refers to the layer using B. y1 Al 1-y1 N forms the sublayer; M z Ga 1-z N sublayer refers to the use of M z Ga 1-z Sublayer formed of N material; B y1 Al 1-y1 N and M z Ga 1-z The lattice constants of N are equal, therefore B y1 Al 1-y1 N sublayer 140a and M z Ga 1-z The N sublayer 140b is all related to the M layer to be formed. z Ga 1-z N-layer epitaxial layer is a lattice-matched material layer.

[0094] The superlattice structure layer 140 can also be called the third buffer layer. In this embodiment, it is achieved through B... y Al 1-y A superlattice structure layer 140 is further disposed on the N-gradient buffer layer 130, thereby further preventing the upward extension of penetrating dislocations while fully releasing stress.

[0095] Alternatively, the superlattice structure layer 140 is grown directly on B y Al 1-y N gradient buffer layer 130.

[0096] Optionally, the thickness of each layer in the superlattice structure layer 140 is in the range of 10 nm to 500 nm.

[0097] Optionally, in superlattice structure layer 140, B y1 Al 1-y1 N sublayer 140a and M z Ga 1-z The arrangement period of the N sublayer 140b is 5 to 100.

[0098] Next, please refer to Figure 8 Epitaxial growth M z Ga 1-z N is an epitaxial layer 150, wherein 0 ≤ z < 1, and M includes at least one of B, Al, In, and Ti.

[0099] Through the preceding steps, this embodiment can obtain M crystals with better quality.z Ga 1-z N epitaxial layer 150.

[0100] Optionally, M z Ga 1-z The thickness of the N epitaxial layer 150 is in the range of 100nm to 1500nm.

[0101] Optionally, M z Ga 1-z The N-epitaxial layer 150 is grown directly on the superlattice structure layer 140.

[0102] Further, please refer to Figure 9 It can also include M z Ga 1-z The steps for epitaxially growing a barrier layer 160 on an N-epitaxy layer 150.

[0103] Understandably, barrier layer 160 and M z Ga 1-z A heterojunction is formed between the N epitaxial layers 150, and the band gap width of the barrier layer 160 is greater than that of M. z Ga 1-z With a bandgap width of 150 for the N epitaxial layer, in M z Ga 1-z Two-dimensional electron gas (2DEG) can be induced in at least a portion of the region of the N epitaxial layer 150 near the barrier layer 160. z Ga 1-z The N-epipolar layer 150 can also be called the channel layer.

[0104] The barrier layer 160 can be a GaN-based material layer. As a specific example, the barrier layer 160 is an AlGaN layer; wherein the Al content can be greater than or equal to 0.1 to less than 1; of course, this application is not limited thereto.

[0105] The thickness of the barrier layer 160 can be 10nm~50nm.

[0106] Although not shown in the figure, embodiments of this application may also include a p-GaN cap layer epitaxially grown on the barrier layer 160.

[0107] This application also provides an epitaxial structure, please refer to... Figure 9 The epitaxial structure includes: a substrate 100; and B located on the substrate 100. x Al 1-x N is a nucleation layer of 120, where 0 < x ≤ 1; located in B x Al 1-x B on N nucleation layer 120 y Al 1-yN-gradient buffer layer 130, wherein 0≤y≤1, and along the direction away from the substrate 100, y first decreases from y0 to y2 and then increases to y1 or first increases to y3 and then decreases to y1; located in B y Al 1-y M on N gradient buffer layer 130 z Ga 1-z N is an epitaxial layer 150, wherein 0 ≤ z < 1, M includes at least one of B, Al, In, and Ti, and B y1 Al 1-y1 N and M z Ga 1-z The difference in lattice constant of N is smaller than that of B. y2 Al 1-y2 N or B y3 Al 1- y3 N and M z Ga 1-z The difference in the lattice constant of N.

[0108] Thus, by introducing the B atom, B is set... x Al 1-x N nucleation layer 120 and B y Al 1-y The N-gradient buffer layer 130 effectively mitigates the effects of substrate 100 and M-gradient buffer layer 130. z Ga 1-z Stress difference between N epitaxial layers 150; B y Al 1-y In the N-gradient buffer layer 130, two opposite buffer adjustments are achieved through changes in y, allowing the internal stress to be fully released; ultimately, high-quality M can be obtained. z Ga 1-z The N epitaxial layer is 150, which effectively ensures the quality of GaN devices.

[0109] As an optional specific implementation, the material of the substrate 100 may include at least one of Si, SiC, and sapphire. Exemplarily, the substrate 100 is a Si substrate.

[0110] As an optional specific implementation, it also includes: located at substrate 100 and B x Al 1-x B between N nucleation layers 120 k Al 1-k N transition layer 110, where 0 < k ≤ 1, B k Al 1-k The N transition layer 110 is grown in a 3D island pattern.

[0111] As one optional specific implementation method, B k Al 1-kThe N-transition layer 110 is located directly on the substrate 100.

[0112] As one optional specific implementation method, B k Al 1-k The growth thickness of the N transition layer 110 is less than or equal to 10 nm.

[0113] As one optional specific implementation method, B x Al 1-x The thickness of the N nucleation layer 120 is greater than that of B. k Al 1-k The thickness of the N transition layer 110.

[0114] As one optional specific implementation method, B x Al 1-x The growth mode of N nucleation layer 120 is 2D.

[0115] As one optional specific implementation method, B x Al 1-x The composition of B in the N nucleation layer 120 is 0 < x ≤ 0.3.

[0116] As an optional specific implementation, k is equal to x, or the absolute value of x-y1 is less than the absolute value of k-y1.

[0117] As one optional specific implementation method, B x Al 1-x The thickness of the N nucleation layer 120 can range from 10 nm to 500 nm. B x Al 1-x The thickness of the N nucleation layer 120 can be B k Al 1-k The thickness of the N transition layer 110 is several times or even tens of times greater.

[0118] As one optional specific implementation method, B x Al 1-x The N nucleation layer 120 is directly located in B. k Al 1-k On the N transition layer 110.

[0119] As one optional specific implementation method, B y Al 1-y N gradient buffer layer 130 is directly located at B x Al 1-x On N nucleation layer 120.

[0120] As another optional specific implementation, B y Al 1-y N gradient buffer layer 130 and B x Al1-x The N nucleation layers 120 may also include one or more B layers. i Al 1-i N is a gradient buffer layer (not shown in the figure), where 0 ≤ i ≤ 1, and along the direction away from the substrate 100, i first decreases from i0 to i2 and then increases to i1 or first increases to i3 and then decreases to i1.

[0121] As one optional specific implementation method, B y1 Al 1-y1 N and M z Ga 1-z The lattice constants of N are equal; y2≤1 / 2y1 or y3≥2y1.

[0122] As an optional specific implementation, y0=0.3.

[0123] As an optional specific implementation, y2=0.

[0124] As an optional specific implementation, y1=0.12.

[0125] As an optional specific implementation, it also includes: located at B y Al 1-y N gradient buffer layer 130 and M z Ga 1-z The superlattice structure layer 140 between the N epitaxial layers 150, wherein the superlattice structure layer 140 includes periodically alternating B atoms y1 Al 1-y1 N sublayer 140a and M z Ga 1-z N sublayer 140b.

[0126] As one optional specific implementation, the superlattice structure layer 140 is directly located in B. y Al 1-y N gradient buffer layer 130.

[0127] As an optional specific implementation, the thickness of each layer in the superlattice structure layer 140 is in the range of 10 nm to 500 nm.

[0128] As one optional specific implementation, B in superlattice structure layer 140 y1 Al 1-y1 N sublayer 140a and M z Ga 1-z The arrangement period of the N sublayer 140b is 5 to 100.

[0129] As one optional specific implementation method, M z Ga 1-zThe thickness of the N epitaxial layer 150 is in the range of 100nm to 1500nm.

[0130] As one optional specific implementation method, M z Ga 1-z The N-epitaxial layer 150 is located directly on the superlattice structure layer 140.

[0131] As an optional specific implementation, it also includes: located in M z Ga 1-z Barrier layer 160 on N epitaxial layer 150.

[0132] Understandably, this application provides an epitaxial structure including a low-stress buffer layer and a method for preparing the same. In one specific embodiment, by introducing boron atoms, a BAlN transition layer is grown at low temperature, followed by high-temperature annealing to form a resistive oxide / nitride layer; a BAlN nucleation layer is grown on the transition layer; then the concentration of boron is controlled, transitioning from high to low concentration, and then gradually growing from low concentration to the target boron concentration; finally, through a superlattice structure, the GaN and the underlying BAlN layer achieve stress release, ultimately forming a high-quality GaN layer.

[0133] Based on this, the present application also provides a method for fabricating a HEMT device, which includes the steps in any of the aforementioned methods for fabricating epitaxial structures, or includes fabricating a HEMT device using the epitaxial structure in any of the aforementioned embodiments.

[0134] For details, please refer to Figure 10 This method includes the steps in the aforementioned method for preparing epitaxial structures, and further includes M... z Ga 1-z A source electrode 171, a drain electrode 172, and a gate electrode 173 are formed on a heterojunction stack consisting of an N-epitaxy layer 150 and a barrier layer 160. Alternatively, the method includes fabricating a HEMT device using the epitaxial structure of any of the foregoing embodiments.

[0135] Based on this, this application also provides a HEMT device, please refer to... Figure 10 It includes: an epitaxial structure in any of the foregoing embodiments; and a source electrode 171, a drain electrode 172 and a gate electrode 173 located on the epitaxial structure.

[0136] It should be noted that the epitaxial structure embodiments, HEMT device fabrication method embodiments, and HEMT device embodiments and epitaxial structure fabrication method 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.

[0137] 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, The method includes: Provide substrate; B is epitaxially grown on the substrate x Al 1-x N is a nucleation layer, where 0 < x ≤ 1; In the B x Al 1-x B epitaxial growth on N nucleation layer y Al 1-y N-gradient buffer layer, wherein 0≤y≤1, and along the direction away from the substrate, y first decreases from y0 to y2 and then increases to y1 or first increases to y3 and then decreases to y1; In the B y Al 1-y M epitaxial growth on N gradient buffer layer z Ga 1-z N is an epitaxial layer, where 0 ≤ z < 1, and M includes at least one of B, Al, In, and Ti, where B y1 Al 1-y1 N and M z Ga 1-z The difference in lattice constant of N is smaller than that of B. y2 Al 1-y2 N or B y3 Al 1-y3 N and M z Ga 1- z The difference in the lattice constant of N.

2. The method for preparing the epitaxial structure according to claim 1, characterized in that, B y1 Al 1-y1 N and M z Ga 1-z The lattice constants of N are equal; y2≤1 / 2y1 or y3≥2y1.

3. The method for preparing the epitaxial structure according to claim 1, characterized in that, In the epitaxial growth of M z Ga 1-z Before the N-epitaxy layer, the method further includes: In the B y Al 1-y A superlattice structure layer is epitaxially grown on an N-graded buffer layer, wherein the superlattice structure layer comprises periodically alternating B-type elements. y1 Al 1-y1 N sublayer and M z Ga 1-z N sublayer.

4. The method for preparing the epitaxial structure according to claim 1, characterized in that, In the epitaxial growth of B x Al 1-x Before the N nucleation layer, the method further includes: B is epitaxially grown on the substrate k Al 1-k N transition layers, where 0 < k ≤ 1, the B k Al 1-k The growth temperature of the N transition layer is 300℃~800℃ to achieve a 3D island-like growth pattern.

5. The method for preparing the epitaxial structure according to claim 4, characterized in that, In the epitaxial growth of B k Al 1-k Following the N transition layer, the method further includes: For the B k Al 1-k The N-transition layer is subjected to high-temperature annealing.

6. The method for preparing the epitaxial structure according to claim 4, characterized in that, The B x Al 1-x The thickness of the N nucleation layer is greater than that of B. k Al 1-k The thickness of the N transition layer.

7. The method for preparing the epitaxial structure according to claim 1 or 4, characterized in that, The B x Al 1-x The growth temperature of the N nucleation layer is 800℃~1300℃ to ensure that the growth mode is 2D.

8. An epitaxial structure, characterized in that, include: Substrate; B located on the substrate x Al 1-x N is a nucleation layer, where 0 < x ≤ 1; Located in B x Al 1-x B on the N nucleation layer y Al 1-y N-gradient buffer layer, wherein 0≤y≤1, and along the direction away from the substrate, y first decreases from y0 to y2 and then increases to y1 or first increases to y3 and then decreases to y1; Located in B y Al 1-y M on the N gradient buffer layer z Ga 1-z N is an epitaxial layer, where 0 ≤ z < 1, and M includes at least one of B, Al, In, and Ti, where B y1 Al 1-y1 N and M z Ga 1-z The difference in lattice constant of N is smaller than that of B. y2 Al 1-y2 N or B y3 Al 1-y3 N and M z Ga 1-z The difference in the lattice constant of N.

9. The epitaxial structure according to claim 8, characterized in that, B y1 Al 1-y1 N and M z Ga 1-z The lattice constants of N are equal; y2≤1 / 2y1 or y3≥2y1.

10. The epitaxial structure according to claim 8, characterized in that, Also includes: Located in B y Al 1-y N gradient buffer layer and the M z Ga 1-z A superlattice structure layer between N epitaxial layers, wherein the superlattice structure layer comprises periodically alternating B layers. y1 Al 1-y1 N sublayer and M z Ga 1-z N sublayer.

11. The epitaxial structure according to claim 8, characterized in that, Also includes: Located between the substrate and the B x Al 1-x B between N nucleation layers k Al 1-k N transition layers, where 0 < k ≤ 1, the B k Al 1- k The growth pattern of the N transition layer is a 3D island pattern.

12. The epitaxial structure according to claim 11, characterized in that, The B x Al 1-x The thickness of the N nucleation layer is greater than that of B. k Al 1-k The thickness of the N transition layer.

13. The epitaxial structure according to claim 8 or 11, characterized in that, The B x Al 1-x The growth pattern of the N nucleation layer is a 2D pattern.

14. A method for fabricating a HEMT device, characterized in that, The method includes the steps of the method for preparing an epitaxial structure as described in any one of claims 1 to 7, or includes preparing a HEMT device using the epitaxial structure as described in any one of claims 8 to 13.

15. A HEMT device, characterized in that, include: The epitaxial structure according to any one of claims 8 to 13; And the source electrode, drain electrode and gate electrode located on the epitaxial structure.

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