Nitride epitaxial structure

Abstract

The invention discloses a nitride epitaxial structure, which comprises a substrate, a nucleation layer and a buffer layer on the nucleation layer, and is characterized in that the buffer layer structurally comprises a nitride superlattice structure, the nitride superlattice structure is provided with an insertion layer, and the insertion layer comprises at least one of AlN and AlGaN so as to increase the pressure stress in the superlattice structure above the insertion layer. And the tensile stress generated in the growth process of the high Al component is counteracted, so that a superlattice structure with higher average Al component can be grown, and the voltage endurance capability of the epitaxial layer is improved.

Description

Technical Field

[0001] The present invention belongs to the field of semiconductor technology, and particularly relates to a nitride epitaxial structure. Background Art

[0002] Nitride semiconductors, as a new type of wide-bandgap semiconductors, nitride power devices have higher breakdown electric fields compared with traditional silicon-based devices, are more energy-efficient, have more stable physical and chemical properties, can operate at higher ambient temperatures, have higher switching speeds, and can reduce the volume and weight of application systems. They have various advantages and can be applied to a wide range of fields such as various household appliances, electric vehicles, new energy power generation such as solar and wind energy, electric vehicles, robots, intelligent manufacturing industries, and large data processing centers. However, nitride power devices are currently mainly applied to the medium- and low-voltage consumer electronics field. One of the reasons is that nitride epitaxial materials are grown by heteroepitaxy on large-sized silicon substrates to form nitride semiconductor thin film materials. Because a conductive channel will be formed at the interface between the silicon substrate and the nitride epitaxial layer, the device will tend to break down first in the vertical direction under high voltage, and the breakdown voltage of the gallium nitride power device is limited by the breakdown voltage of the epitaxial material in the vertical direction. Increasing the thickness of the epitaxial material can correspondingly increase the breakdown voltage of the material. However, due to the mismatch in lattice size and thermal expansion coefficient between the silicon substrate and the nitride epitaxial material, the thicker the grown epitaxial layer, the greater the stress inside the epitaxial wafer, making it difficult to control the stress and warping of the epitaxial wafer. Another method to increase the breakdown voltage of the epitaxial material is to increase the average Al composition in the nitride epitaxial layer. Because AlN has a wider bandgap width and breakdown electric field compared with GaN, it will have a higher breakdown voltage at the same epitaxial thickness. However, growing an epitaxial layer with a high Al composition will generate more tensile stress in the epitaxial layer. When growing a buffer layer with a high Al composition superlattice structure, cracks will be generated in the epitaxial layer when the thickness exceeds a certain value, limiting the application of the epitaxial layer with a high Al composition superlattice structure.

[0003] Research has confirmed that during the nitride epitaxial growth process, by using techniques such as low-temperature AlN or AlGaN insertion layers, or by growing buffer layers using methods such as AlN / GaN and AlGaN / AlGaN superlattice structures, compressive stress can be introduced into the epitaxial layer to offset the tensile stress introduced by the mismatch in thermal expansion coefficient between the substrate and the epitaxial material, effectively controlling the stress in the epitaxial layer and the warping of the epitaxial wafer, and obtaining a crack-free epitaxial wafer. For example, in the non-patent literature Journal of Crystal Growth 314(2011)85–91, H.P.D. Schenk et al. reported growing an epitaxial thick film by inserting a low-temperature AlN layer into the GaN epitaxial layer; Patent EP2434532A1 discloses a method of growing an epitaxial thick film by introducing compressive stress by inserting an AlGaN insertion layer into the GaN layer.

[0004] A nitride epitaxial structure is disclosed in the invention patent with the patent number 《CN114823853A》, which includes a substrate. A nucleation layer, a transition layer, a composite buffer layer, a top gallium nitride layer, and a coating layer are sequentially provided on the substrate. The composite buffer layer contains a superlattice structure. This epitaxial structure can effectively control warping, thereby improving the quality of gallium nitride, reducing defects, and increasing the product yield. In the growth method of the superlattice composite buffer structure, by adding different aluminum content growth methods, warping can be further effectively improved, and the product yield can be increased. However, although the aluminum component of the superlattice structure in this patent solution is variable, the superlattices are interconnected and do not involve AlN or high-Al component AlGaN insertion layers.

[0005] A nitride epitaxial structure is disclosed in the invention patent with the patent number 《CN108461591A》, which includes a silicon substrate, an aluminum-containing nucleation layer, a buffer layer, a channel layer, and a blocking layer. The buffer layer sequentially includes: a first superlattice stack structure, a first thick gallium nitride layer, a second superlattice stack structure, and a second thick gallium nitride layer. The total thickness of the first thick gallium nitride layer and the second thick gallium nitride layer is greater than two micrometers. This structure has a plurality of separated superlattice structures. However, this solution does not involve AlN or high-Al component AlGaN insertion layers that can introduce compressive stress. Summary of the Invention

[0006] The present invention provides a nitride epitaxial structure including a substrate, a nucleation layer, and a buffer layer on the nucleation layer, wherein the buffer layer structure contains a nitride superlattice structure.

[0007] An insertion layer is provided in the nitride superlattice structure, and the insertion layer includes at least one of the following: AlN, AlGaN. To increase the compressive stress in the superlattice structure above it and offset the tensile stress generated during the growth of the high-Al component, so that a superlattice structure with a higher average Al component can be grown, thereby improving the breakdown voltage of the epitaxial layer.

[0008] Furthermore, the substrate is a silicon substrate, a sapphire substrate, a silicon carbide substrate, a gallium nitride substrate, or a composite substrate containing the above substrate materials, and the composite substrate has one of the silicon substrate, the sapphire substrate, the silicon carbide substrate, and the gallium nitride substrate as the surface.

[0009] Furthermore, the nucleation layer includes gallium nitride, aluminum nitride, indium nitride, or their alloy materials, or a multi-layer stack structure of the above materials; or a layer of 3C-SiC or SiN material is first grown on the surface of the silicon substrate, and then the above gallium nitride, aluminum nitride, indium nitride, or their alloy materials, or a multi-layer stack structure of the above materials are continuously grown.

[0010] Further, the buffer layer is a nitride superlattice structure, which can be an AlN / GaN superlattice structure, an AlN / AlGaN superlattice structure, or an AlGaN / GaN superlattice structure, or a combined structure including the above structures.

[0011] Further, a transition layer is further included between the nucleation layer and the buffer layer, and the transition layer is a single-layer AlN structure, a single-layer AlGaN structure, or a multi-layer stacked structure of the above materials.

[0012] Further, the Al component in the AlN or AlGaN insertion layer is 40% - 100%, and the Al component content in the insertion layer is greater than the average Al component content of the superlattice structure grown above it.

[0013] Further, the thickness of the insertion layer is 8 - 100 nm, and the thickness of the insertion layer is greater than the thickness of the high-Al component single layer in a single period of the superlattice structure (the thickness of the high-Al component single layer in a single period of the superlattice structure is about 4 nm).

[0014] Further, the growth temperature of the AlN or AlGaN insertion layer is lower than the growth temperature of the superlattice structure.

[0015] Further, a GaN layer, or a single-layer or multi-layer structure of AlGaN with an Al component lower than that of the insertion layer, can be inserted between the insertion layer and the superlattice structure above or below it.

[0016] Further, a channel layer is continuously grown above the buffer layer, and a barrier layer above the channel layer is formed to form a nitride semiconductor transistor structure.

[0017] Compared with the prior art, the present invention provides a nitride epitaxial structure, which has the following beneficial effects: The present invention provides a nitride epitaxial structure. By inserting an AlN or high-Al component AlGaN insertion layer in the nitride superlattice buffer layer structure, the compressive stress in the superlattice structure above it is increased to offset the tensile stress generated during the growth of the high-Al component, so that a superlattice structure with a higher average Al component can be grown, improving the breakdown voltage capability of the epitaxial layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the epitaxial wafer structure of Embodiment 1 of the present invention.

[0019] Figure 2 It is a schematic diagram of the epitaxial wafer structure of Embodiment 2 of the present invention.

[0020] Figure 3 It is a schematic diagram of the epitaxial wafer structure of Embodiment 3 of the present invention.

[0021] Figure 4 It is a schematic diagram of the epitaxial wafer structure of Embodiment 4 of the present invention.

[0022] Figure 5 Schematic diagram of the epitaxial wafer structure of Embodiment 5 of the present invention.

[0023] Wherein: 10 - substrate; 11 - nucleation layer; 12 - first superlattice structure; 13 - insertion layer; 14 - second superlattice structure; 20 - substrate; 21 - nucleation layer; 22 - first superlattice structure; 23 - insertion layer; 24 - second superlattice structure; 25 - channel layer; 26 - barrier layer; 271 - source electrode; 272 - gate electrode; 273 - drain electrode; 30 - substrate; 31 - nucleation layer; 32 - first superlattice structure; 33 - insertion layer; 34 - second superlattice structure; 35 - capping layer; 40 - substrate; 41 - nucleation layer; 42 - first superlattice structure 43 - first insertion layer 43; 43' - second insertion layer, 44 - second superlattice structure; 45 - capping layer; 50 - substrate; 51 - nucleation layer; 52 - first superlattice structure; 53 - insertion layer; 54 - intermediate layer; 55 - second superlattice structure; 56 - capping layer. Detailed implementation manners

[0024] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention can be implemented in different forms, and the present invention should not be construed as being limited to the specific embodiments set forth herein. On the contrary, these embodiments are provided to explain the principles of the invention and its practical applications, so that other technicians in the art can understand the embodiments of the present invention and various other modifications based on the core technical content of the present invention.

[0025] Embodiment 1

[0026] Referring to Figure 1 , the nitride semiconductor epitaxial structure provided in this embodiment includes: a substrate 10, and a nucleation layer 11, a first superlattice structure 12, an insertion layer 13, and a second superlattice structure 14 formed in sequence on the substrate 10.

[0027] The substrate 10 of this embodiment is a silicon material substrate. The nucleation layer 11 is an AlN layer with a thickness of 150 nm. The first superlattice structure 12 and the second superlattice structure 14 are AlN / GaN, AlN / AlGaN, or AlGaN / GaN superlattice structures, or a combined structure including the above structures. In this embodiment, the first superlattice structure adopts an AlN / AlGaN superlattice structure, each period includes 4 nm of AlN, 20 nm of AlGaN, the Al component is 20%, the total thickness is about 1.5 μm, and the carbon doping concentration is about 1×10 19 / cm 3The second superlattice structure 14 adopts an AlN / AlGaN superlattice structure. Each period includes 4 nm of AlN, 20 nm of AlGaN, with an Al component of 15%, a total thickness of approximately 1.5 μm, and a carbon doping concentration of approximately 1×10 19 / cm 3 . The growth temperature of the superlattice structure is 990 °C. A single layer or multiple layers of AlGaN transition layers can also be inserted between the nucleation layer 11 and the first superlattice structure 12. The insertion layer 13 can be a structure of single-layer or multi-layer stacked AlN or AlGaN. In this embodiment, the insertion layer 13 is an AlN layer with a thickness of 10 nm and a growth temperature of 820 °C.

[0028] Embodiment 2

[0029] Referring to Figure 2 , the nitride semiconductor epitaxial structure provided in this embodiment includes: a substrate 20, and a nucleation layer 21, a first superlattice structure 22, an insertion layer 23, a second superlattice structure 24, which are sequentially formed on the substrate 20. On the basis of Embodiment 1, a channel layer 25 and a barrier layer 26 are further grown above the second superlattice structure 24. In this embodiment, the channel layer 25 adopts an 800-nm unintentionally doped GaN layer, and the electron concentration is approximately 4×10 16 / cm 3 . Between the second superlattice structure 24 and the channel layer 25, a carbon-doped GaN layer, an AlGaN back barrier layer, or other structures can also be inserted as needed to achieve functions such as improving the breakdown voltage of the epitaxial layer and enhancing the electron confinement of the channel layer. The barrier layer 26 adopts a 20-nm AlGaN layer with an Al component of 25%. Electrodes are fabricated above the barrier layer 26, including a source electrode 271 and a drain electrode 273, and a gate electrode 272 is fabricated above the gate dielectric to form a nitride semiconductor transistor structure.

[0030] Embodiment 3

[0031] Referring to Figure 3 , the nitride semiconductor epitaxial structure provided in this embodiment includes a substrate 30, and a nucleation layer 31, a first superlattice structure 32, an insertion layer 33, a second superlattice structure 34, which are sequentially formed on the substrate 30. A second-period insertion layer and a superlattice structure above the second superlattice structure, and a cap layer 35 above.

[0032] The substrate 30 of this embodiment is a silicon material substrate. The nucleation layer 31 is an AlN layer with a thickness of 150 nm. The first superlattice structure 32 and the second superlattice structure 34 are AlN / GaN, AlN / AlGaN, or AlGaN / GaN superlattice structures, or a combined structure including the above structures. In this embodiment, the first superlattice structure 32 adopts an AlN / AlGaN superlattice structure, each period includes 4 nm of AlN, 20 nm of AlGaN, the Al component is 20%, the total thickness is about 1.5 μm, and the carbon doping concentration is about 1×10 19 / cm 3 . The second superlattice structure 34 adopts an AlN / AlGaN superlattice structure, each period includes 4 nm of AlN, 20 nm of AlGaN, the Al component is 15%, the total thickness is about 1 μm, and the carbon doping concentration is about 1×10 19 / cm 3 , the growth temperature of the superlattice structure is 990 °C. The insertion layer 33 can be a structure of a single layer or multiple layers of AlN or AlGaN stacked. In this embodiment, the insertion layer 13 is an AlN layer with a thickness of 10 nm and a growth temperature of 820 °C. After growing the second superlattice structure 34, repeat the previous process parameters, continue to grow the second period of the insertion layer 33 and the second superlattice structure 34, and grow a cap layer 35 above it to further regulate the stress in the epitaxial layer. In this embodiment, a 0.8-μm GaN layer is used.

[0033] Embodiment 4

[0034] Referring to Figure 4 , the nitride semiconductor epitaxial structure provided in this embodiment includes a substrate 40, and a nucleation layer 41, a first superlattice structure 42, a first insertion layer 43 and a second insertion layer 43', a second superlattice structure 44, and a cap layer 45 formed in sequence on the substrate 40.

[0035] The substrate 40 of this embodiment is a silicon material substrate. The nucleation layer 41 is an AlN layer with a thickness of 150 nm. The first superlattice structure 42 and the second superlattice structure 44 are AlN / GaN, AlN / AlGaN, or AlGaN / GaN superlattice structures, or a combined structure including the above structures. In this embodiment, the first superlattice structure 42 adopts an AlN / AlGaN superlattice structure, each period includes 4 nm of AlN, 20 nm of AlGaN, the Al component is 20%, the total thickness is about 1.5 μm, and the carbon doping concentration is about 1×10 19 / cm 3 . The second superlattice structure 44 adopts an AlN / AlGaN superlattice structure, each period includes 4 nm of AlN, 20 nm of AlGaN, the Al component is 15%, the total thickness is about 1.5 μm, and the carbon doping concentration is about 1×1019 / cm 3 The growth temperature of the superlattice structure is 990 °C. The first insertion layer 43 can be a single layer or a multi-layer stack of AlN or AlGaN. In this embodiment, the first insertion layer and the second insertion layer form an AlN / AlGaN composite structure. The first insertion layer 43 is an AlN layer with a thickness of 8 nm. The second insertion layer 43' is an AlGaN layer with an Al component of 70% and a thickness of 10 nm, and the growth temperature is 820 °C. An 800-nm GaN cap layer 45 is grown above the second superlattice structure 44 to further regulate the stress in the epitaxial layer.

[0036] Embodiment 5

[0037] Referring to Figure 5 The nitride semiconductor epitaxial structure provided in this embodiment includes a substrate 50, and a nucleation layer 51, a first superlattice structure 52, an insertion layer 53, an intermediate layer 54, a second superlattice structure 55, and a cap layer 56 formed on the substrate 50 in sequence.

[0038] The substrate 50 in this embodiment is a silicon material substrate. The nucleation layer 51 is an AlN layer with a thickness of 150 nm. The first superlattice structure 52 and the second superlattice structure 55 are AlN / GaN, AlN / AlGaN, or AlGaN / GaN superlattice structures, or a combined structure including the above structures. In this embodiment, the first superlattice structure 52 adopts an AlN / AlGaN superlattice structure, each period includes 4 nm of AlN, 20 nm of AlGaN with an Al component of 20%, the total thickness is about 1.5 μm, and the carbon doping concentration is about 1×10 19 / cm 3 . The second superlattice structure 55 adopts an AlN / AlGaN superlattice structure, each period includes 4 nm of AlN, 20 nm of AlGaN with an Al component of 15%, the total thickness is about 1.5 μm, and the carbon doping concentration is about 1×10 19 / cm 3 The growth temperature of the superlattice structure is 990 °C. The insertion layer 53 can be a single layer or a multi-layer stack of AlN or AlGaN. In this embodiment, the insertion layer adopts an AlN layer with a thickness of 10 nm and a growth temperature of 820 °C. An intermediate layer 54 is grown above the insertion layer 53. In this embodiment, an Al 0.05 Ga 0.95 N layer of 200 nm is grown, and an 800-nm GaN cap layer 56 is grown above the second superlattice structure 55 to further regulate the stress in the epitaxial layer.

[0039] As described above, it is only the specific implementation manner of the embodiments of the present invention, but the protection scope of the embodiments of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the embodiments of the present invention can easily think of changes or substitutions, which should all be covered within the protection scope of the embodiments of the present invention. Therefore, the protection scope of the embodiments of the present invention shall be subject to the protection scope of the claims.

Claims

1. A nitride epitaxial structure, comprising a substrate, a nucleation layer, and a buffer layer on the nucleation layer, characterized in that: The buffer layer structure includes a nitride superlattice structure, and an insertion layer is provided in the nitride superlattice structure. The insertion layer includes at least one of the following: AlN, AlGaN.

2. The nitride epitaxial structure according to claim 1, wherein, The substrate is selected from: a silicon substrate, a sapphire substrate, a silicon carbide substrate, a gallium nitride substrate, or a composite substrate having any of the above substrates as a surface.

3. The nitride epitaxial structure according to claim 1, characterized in that, The nucleation layer is gallium nitride, aluminum nitride, indium nitride, or an alloy material thereof, or a multi-layer stacked structure of the above materials; or a layer of 3C-SiC or SiN material is first grown on the surface of the silicon substrate, and then the above gallium nitride, aluminum nitride, indium nitride, or an alloy material thereof, or a multi-layer stacked structure of the above materials is continuously grown.

4. The nitride epitaxial structure according to claim 1, characterized in that, The buffer layer is a nitride superlattice structure.

5. The nitride epitaxial structure according to claim 4, wherein, The buffer layer is an AlN / GaN superlattice structure, an AlN / AlGaN superlattice structure, or an AlGaN / GaN superlattice structure, or a combined structure including the above structures.

6. The nitride epitaxial structure according to claim 4, wherein, A transition layer is further included between the nucleation layer and the buffer layer. The transition layer is a single-layer AlN structure, a single-layer AlGaN structure, or a multi-layer stacked structure of the above materials.

7. The nitride epitaxial structure according to claim 1, wherein The Al component in the insertion layer is 40% to 100%. The Al component content in the insertion layer is greater than the average Al component content of the superlattice structure grown above it. The thickness of the insertion layer is 8 to 100 nm, and the thickness of the insertion layer is greater than the thickness of the high-Al component single layer in a single period of the superlattice structure.

8. The nitride epitaxial structure according to claim 7, characterized in that, The epitaxial layer includes one or more insertion layers.

9. The nitride epitaxial structure according to claim 7, characterized in that, A GaN layer, or a single layer or multi-layer structure of AlGaN with an Al component lower than that of the insertion layer, can also be inserted between the insertion layer and the superlattice structure above or below it.

10. A nitride epitaxial structure according to claim 1, wherein, A channel layer is grown above the buffer layer, and a barrier layer is grown above the channel layer to form a nitride semiconductor transistor structure.

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