Epitaxial layer of lattice transition type gallium nitride HEMT device and manufacturing method

Abstract

The invention discloses an epitaxial layer of a lattice transition type gallium nitride HEMT device and a manufacturing method of the epitaxial layer. The epitaxial layer comprises a substrate, and an AlN nucleating layer, an AlGaN buffer layer, a superlattice buffer layer, an AlGaN transition layer, a high-carbon GaN layer, a low-carbon GaN channel layer, an AlGaN barrier layer and a cap layer which are sequentially stacked on the surface of the substrate in the longitudinal direction. According to the invention, after the AlGaN transition layer is inserted between the superlattice buffer layer and the high-carbon GaN layer, the superlattice buffer layer with high aluminum content is firstly transited to the AlGaN transition layer with medium aluminum content and then transited to the high-carbon GaN layer without aluminum, so that lattice mismatch between layers is reduced, and deformation and warping of a wafer are reduced.

Description

Technical Field

[0001] The present invention relates to the field of semiconductors, and specifically to an epitaxial layer of a lattice-transition gallium nitride HEMT device and a manufacturing method thereof. Background Art

[0002] The epitaxial layer structure of existing gallium nitride high electron mobility transistors (HEMTs) is as Figure 1 shown. From bottom to top, it sequentially includes a substrate (such as Silicon), an AlN (aluminum nitride) nucleation layer, an AlGaN buffer layer, where the AlGaN buffer layer is composed of one or more AlGaN layers with different aluminum contents, a superlattice buffer layer (superlattice), where the superlattice buffer layer is periodically composed of alternating AlN and AlGaN, and above the superlattice buffer layer are sequentially a high-carbon GaN layer, a low-carbon GaN channel layer, an AlGaN barrier layer, and a capping layer. In the above structure, due to the relatively high aluminum content of the superlattice buffer layer, there is a large lattice mismatch with the high-carbon GaN layer above it. Actually, during the growth processes such as metalorganic chemical vapor deposition (abbreviated as MOCVD) or molecular beam epitaxy (abbreviated as MBE), the bottom superlattice buffer layer is first formed, and then the high-carbon GaN layer above it is formed. Due to the large lattice mismatch between the two layers, the stress accumulated in the wafer at this time is relatively large, and the wafer will undergo a large degree of deformation and warping, resulting in cracks at the edge of the wafer, and even the wafer being deformed too much to carry out the subsequent HEMT process development, causing the wafer to be scrapped. Summary of the Invention

[0003] In order to overcome the defects in the prior art, the embodiments of the present invention provide an epitaxial layer of a lattice-transition gallium nitride HEMT device and a manufacturing method thereof, which are used to solve one or more of the above problems.

[0004] The embodiments of the present application disclose: an epitaxial layer of a lattice-transition gallium nitride HEMT device, including a substrate, and an AlN nucleation layer, an AlGaN buffer layer, a superlattice buffer layer, an AlGaN transition layer, a high-carbon GaN layer, a low-carbon GaN channel layer, an AlGaN barrier layer, and a capping layer that are sequentially stacked along the longitudinal direction on the surface of the substrate.

[0005] Further, the AlGaN transition layer includes multiple layers of AlGaN layers, and among them, the aluminum content of each AlGaN layer is different.

[0006] Further, the aluminum content of different AlGaN layers gradually decreases in the direction from adjacent to the superlattice buffer layer to adjacent to the high-carbon GaN layer.

[0007] The embodiments of the present application also disclose: a manufacturing method of a lattice-transition type gallium nitride HEMT device, including the following steps: preparing a substrate; epitaxially growing an AlN nucleation layer, an AlGaN buffer layer, and a superlattice buffer layer on the surface of the substrate in sequence; epitaxially growing an AlGaN transition layer on the surface of the superlattice buffer layer; and epitaxially growing a high-carbon GaN layer, a low-carbon GaN channel layer, an AlGaN barrier layer, and a capping layer on the surface of the AlGaN transition layer in sequence.

[0008] Further, in the step of "preparing a substrate", the substrate is a silicon substrate or a composite substrate formed by at least two materials among sapphire, silicon carbide, gallium nitride, and single-crystalline silicon thin film on insulator, and the thickness of the substrate is 300 μm - 3000 μm.

[0009] Further, in the step of "epitaxially growing an AlN nucleation layer, an AlGaN buffer layer, and a superlattice buffer layer on the surface of the substrate in sequence", the thickness of the AlN nucleation layer is 30 nm - 1500 nm, the thickness of the AlGaN buffer layer is 25 nm - 400 nm, and the thickness of the superlattice buffer layer is 0.3 μm - 15 μm.

[0010] Further, in the step of "epitaxially growing multiple layers of AlGaN layers on the surface of the superlattice buffer layer, where the aluminum content of the AlGaN layers decreases in sequence from adjacent to the superlattice buffer layer to away from the superlattice buffer layer", the carbon doping concentration of the AlGaN transition layer is 5×10 17 cm -3 -5×10 19 cm -3 .

[0011] Further, in the step of "epitaxially growing an AlGaN transition layer on the surface of the superlattice buffer layer", it specifically includes the following steps: epitaxially growing multiple layers of AlGaN layers on the surface of the superlattice buffer layer, where the aluminum content of the AlGaN layers decreases in sequence from adjacent to the superlattice buffer layer to away from the superlattice buffer layer.

[0012] Further, in the step of "epitaxially growing multiple layers of AlGaN layers on the surface of the superlattice buffer layer, where the aluminum content of the AlGaN layers decreases in sequence from adjacent to the superlattice buffer layer to away from the superlattice buffer layer", the total thickness of the AlGaN transition layer is 0.06 μm - 5 μm, the number of layers of the AlGaN layer is not more than 5 layers, where the thickness range of each AlGaN layer is 0.02 μm - 1 μm, and the aluminum content of each AlGaN layer is 1% - 99%.

[0013] Further, in the step of "epitaxially growing a high-carbon GaN layer, a low-carbon GaN channel layer, an AlGaN barrier layer, and a cap layer in sequence on the surface of the AlGaN transition layer", the carbon concentration in the high-carbon GaN layer is greater than 10 18 cm -3 , and the carbon concentration in the low-carbon GaN channel layer is less than 10 18 cm -3 .

[0014] The beneficial effects of the present invention are as follows:

[0015] 1. After inserting the AlGaN transition layer between the superlattice buffer layer and the high-carbon GaN layer, it transitions from the superlattice buffer layer with a relatively high aluminum content to the AlGaN transition layer with a medium aluminum content, and then to the high-carbon GaN layer without aluminum, reducing the lattice mismatch between layers, thereby reducing the deformation and warping of the wafer.

[0016] 2. The aluminum content of each AlGaN layer is different and gradually decreases from the superlattice buffer layer towards the GaN layer. By adjusting the number of layers, thickness, and aluminum content of the AlGaN transition layer, the strain degree of the wafer can be flexibly controlled. Thus, when there are significant adjustments in the HEMT epitaxial structure, such as adjustments in the total thickness and the thickness of specific layers, there is more room to adjust the wafer strain by adjusting the relevant structural parameters of the AlGaN transition layer.

[0017] To make the above and other objects, features, and advantages of the present invention more obvious and understandable, the following specifically enumerates preferred embodiments and, in conjunction with the accompanying drawings, provides a detailed description as follows. Description of the Drawings

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0019] Figure 1 is a schematic structural diagram of the epitaxial layer of a gallium nitride HEMT device in the prior art;

[0020] Figure 2 is a schematic structural diagram of the epitaxial layer of a lattice-transition type gallium nitride HEMT device in an embodiment of the present invention;

[0021] Figure 3 is a schematic structural diagram of the epitaxial layer of a lattice-transition type gallium nitride HEMT device in another embodiment of the present invention;

[0022] Figure 4 It is a schematic structural diagram of an epitaxial layer of a lattice-transition gallium nitride HEMT device in another embodiment in the embodiments of the present invention;

[0023] Figure 5 It is a flow chart of a manufacturing method of a lattice-transition gallium nitride HEMT device in the embodiments of the present invention;

[0024] Reference numerals of the above drawings: 1, substrate; 2, AlN nucleation layer; 3, AlGaN buffer layer; 4, superlattice buffer layer; 5, AlGaN transition layer; 51, first AlGaN layer; 52, second AlGaN layer; 53, third AlGaN layer; 54, fourth AlGaN layer; 55, fifth AlGaN layer; 6, high-carbon GaN layer; 7, low-carbon GaN channel layer; 8, AlGaN barrier layer; 9, capping layer. Detailed implementation manners

[0025] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0026] Such as Figure 2 Figure 4 An epitaxial layer of a lattice-transition gallium nitride HEMT device includes a substrate 1, and an AlN nucleation layer 2, an AlGaN buffer layer 3, a superlattice buffer layer 4, an AlGaN transition layer 5, a high-carbon GaN layer 6, a low-carbon GaN channel layer 7, an AlGaN barrier layer 8, and a capping layer 9 that are sequentially stacked along the longitudinal direction on the surface of the substrate 1. In this embodiment, the substrate 1 is a silicon substrate 1. Of course, in other alternative implementation manners, the substrate 1 may also be a composite substrate 1 formed of at least two materials such as sapphire, silicon carbide, gallium nitride, and a single-crystalline silicon thin film on insulator. The AlGaN buffer layer 3 may be composed of one or more AlGaN layers with different aluminum contents. The superlattice buffer layer 4 may be alternately and periodically composed of AlN and AlGaN, or may be alternately and periodically composed of AlGaN with different aluminum contents.

[0027] In this embodiment, an intermediate AlGaN transition layer 5 is inserted between the superlattice buffer layer 4 and the high-carbon GaN layer 6. The AlGaN transition layer 5 may be composed of one or more AlGaN layers. In this way, it can first transition from the superlattice buffer layer 4 with a relatively high aluminum content to the AlGaN transition layer 5 with a medium aluminum content, and then to the high-carbon GaN layer 6 without aluminum, reducing the lattice mismatch between layers, thereby reducing the deformation and warping of the wafer.

[0028] With the above structure, after the AlGaN transition layer 5 is inserted between the superlattice buffer layer 4 and the high-carbon GaN layer 6, it transitions from the superlattice buffer layer 4 with a higher aluminum content to the AlGaN transition layer 5 with a medium aluminum content, and then to the high-carbon GaN layer 6 without aluminum, reducing the lattice mismatch between layers, thereby reducing the deformation and warping of the wafer. That is, it can be understood that the aluminum content of the superlattice buffer layer 4 is greater than the aluminum content of the AlGaN transition layer 5, and the aluminum content of the AlGaN transition layer 5 is greater than the aluminum content of the high-carbon GaN layer 6.

[0029] Specifically, the AlGaN transition layer 5 includes multiple layers of AlGaN layers, where the aluminum content of each layer of the AlGaN layer is different. Preferably, the aluminum content of different AlGaN layers gradually decreases in the direction from adjacent to the superlattice buffer layer 4 to adjacent to the high-carbon GaN layer 6. Thus, the aluminum content of each layer of the AlGaN layer is different and gradually decreases from the superlattice buffer layer 4 towards the GaN layer. By adjusting the number of layers, thickness, and aluminum content of the AlGaN transition layer 5, the strain degree of the wafer can be flexibly controlled. Therefore, when there are significant adjustments in the HEMT epitaxial structure, such as adjustments in the total thickness and the thickness of specific layers, by adjusting the relevant structural parameters of the AlGaN transition layer 5, there is more room to adjust the wafer strain.

[0030] According to the AlGaN transition layer 5 being composed of different numbers of AlGaN layers, a comparison table of preferred parameters for the example in Table 1 and the AlGaN transition layer 5 is formed.

[0031]

[0032] Table 1

[0033] In an alternative embodiment, as Figure 2 shown, the AlGaN transition layer 5 is composed of a single layer of AlGaN layer, that is, the first AlGaN layer 51 forms the AlGaN transition layer 5.

[0034] In another alternative embodiment, as Figure 3 shown, the AlGaN transition layer 5 is composed of two layers of AlGaN layers, that is, the first AlGaN layer 51 and the second AlGaN layer 52 together form the AlGaN transition layer 5. Among them, the aluminum content of the first AlGaN layer 51 is 30%-60%, and the aluminum content of the second AlGaN layer 52 is 10%-30%.

[0035] In yet another alternative embodiment, as Figure 4As shown, the AlGaN transition layer 5 is composed of five layers of AlGaN layers, that is, the first AlGaN layer 51, the second AlGaN layer 52, the third AlGaN layer 53, the fourth AlGaN layer 54, and the fifth AlGaN layer 55 together form the AlGaN transition layer 5.

[0036] As Figure 5 shown, this embodiment also provides a manufacturing method of a lattice-transition gallium nitride HEMT device, including the following steps:

[0037] Prepare a substrate 1, the substrate 1 can be a silicon substrate 1 or a composite substrate 1 formed by at least two materials among sapphire, silicon carbide, gallium nitride, and a single-crystalline silicon film on insulator (Silicon On Insulator, abbreviated as SOI), and the thickness of the substrate 1 is 300 μm - 3000 μm.

[0038] Epitaxially grow an AlN nucleation layer 2, an AlGaN buffer layer 3, and a superlattice buffer layer 4 on the surface of the substrate 1 in sequence. It should be noted that the method used for epitaxial growth can be metal-organic chemical vapor deposition (abbreviated as MOCVD), or molecular beam epitaxy (abbreviated as MBE), etc. In this step, epitaxial growth is carried out by MOCVD or MBE to grow the AlN nucleation layer 2, the AlGaN buffer layer 3, and the superlattice buffer layer 4. The thickness of the AlN nucleation layer 2 is 30 nm - 1500 nm, and the thickness of the AlGaN buffer layer 3 is 25 nm - 400 nm. The AlGaN buffer layer 3 can be composed of one or more AlGaN layers with different aluminum contents, and the superlattice buffer layer 4 can be alternately and periodically composed of AlN and AlGaN, and the thickness of the superlattice buffer layer 4 is 0.3 μm - 15 μm.

[0039] An AlGaN transition layer 5 is epitaxially grown on the surface of the superlattice buffer layer 4. The AlGaN transition layer 5 can be composed of one or more AlGaN layers. When the AlGaN layers are multiple layers, the aluminum content of each AlGaN layer is different. Among them, when the AlGaN layers are multiple layers, the aluminum content of each AlGaN layer decreases gradually in the direction from adjacent to the superlattice buffer layer 4 to adjacent to the high-carbon GaN layer 6. The AlGaN layer closest to the superlattice buffer layer 4 is named the first AlGaN layer 51, and the AlGaN buffer layers 3 in the direction of the high-carbon GaN layer 6 are sequentially named the second AlGaN layer 52, the third AlGaN layer 53, the fourth AlGaN layer 54, the fifth AlGaN layer 55, and so on. The adjustment of the aluminum content is achieved by changing the proportion of the MO source containing aluminum atoms in the total MO source during the epitaxial growth process. The carbon doping concentration of the AlGaN transition layer 5 is 5×10 17 cm -3 -5×10 19 cm -3 . The carbon doping concentration can be measured by methods such as SIMS. The carbon doping method can be to control the amount of carbon doping by adjusting epitaxial growth conditions such as temperature, gas pressure, and growth rate, or to control the amount of carbon doping by introducing a doping source such as ethylene (C2H4) and adjusting its flow rate. Preferably, multiple AlGaN layers are sequentially epitaxially grown on the surface of the superlattice buffer layer 4. Among them, the aluminum content of the AlGaN layers decreases sequentially from adjacent to the superlattice buffer layer 4 to away from the superlattice buffer layer 4. The total thickness range of the AlGaN transition layer 5 is 0.06 μm - 5 μm, and it can be composed of at most 5 AlGaN layers with different aluminum contents. The thickness range of a single AlGaN transition layer 5 is 0.02 μm - 1 μm, and the aluminum content range is 1% - 99%.

[0040] A high-carbon GaN layer 6, a low-carbon GaN channel layer 7, an AlGaN barrier layer 8, and a cap layer 9 are sequentially epitaxially grown on the surface of the AlGaN transition layer 5. The carbon concentration in the high-carbon GaN layer 6 is greater than 10 18 cm -3 , and the carbon concentration in the low-carbon GaN channel layer 7 is less than 10 18 cm -3 . The material of the cap layer 9 can be different depending on whether the device is enhancement-mode or depletion-mode. The cap layer 9 of an enhancement-mode HEMT is usually magnesium-doped gallium nitride, while the cap layer 9 of a depletion-mode HEMT may be silicon nitride or undoped gallium nitride.

[0041] In this embodiment, an intermediate AlGaN transition layer 5 is inserted between the superlattice buffer layer 4 and the high-carbon GaN layer 6. The AlGaN transition layer 5 can be composed of one or more AlGaN layers. In this way, the transition can be made from the superlattice buffer layer 4 with a relatively high aluminum content to the AlGaN transition layer 5 with a medium aluminum content, and then to the high-carbon GaN layer 6 without aluminum, reducing the lattice mismatch between layers, thereby reducing the deformation and warping of the wafer.

[0042] By the above method, after the AlGaN transition layer 5 is inserted between the superlattice buffer layer 4 and the high-carbon GaN layer 6, the transition is first made from the superlattice buffer layer 4 with a relatively high aluminum content to the AlGaN transition layer 5 with a medium aluminum content, and then to the high-carbon GaN layer 6 without aluminum, reducing the lattice mismatch between layers, thereby reducing the deformation and warping of the wafer.

[0043] Preferably, in the step of "epitaxially growing an AlGaN transition layer 5 on the surface of the superlattice buffer layer 4", the following steps are specifically included:

[0044] A plurality of AlGaN layers are sequentially epitaxially grown on the surface of the superlattice buffer layer 4. Among them, the aluminum content of the AlGaN layers from the one adjacent to the superlattice buffer layer 4 to the one far from the superlattice buffer layer 4 decreases in sequence. The total thickness of the AlGaN transition layer 5 ranges from 0.06 μm to 5 μm and can be composed of at most 5 AlGaN layers with different aluminum contents. The thickness of a single AlGaN transition layer 5 ranges from 0.02 μm to 1 μm, and the aluminum content ranges from 1% to 99%. Thus, the aluminum content of each AlGaN layer is different and gradually decreases from the superlattice buffer layer 4 towards the GaN layer. By adjusting the number of layers, thickness, and aluminum content of the AlGaN transition layer 5, the strain degree of the wafer can be flexibly controlled. Therefore, when there are significant adjustments in the HEMT epitaxial structure, such as adjustments in the total thickness and the thickness of specific layers, by adjusting the relevant structural parameters of the AlGaN transition layer 5, there is a greater space for adjusting the wafer strain.

[0045] In the present invention, specific embodiments are used to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. An epitaxial layer of a lattice transition gallium nitride HEMT device, characterized in that: The invention comprises a substrate, and an AlN nucleation layer, an AlGaN buffer layer, a superlattice buffer layer, an AlGaN transition layer, a high-carbon GaN layer, a low-carbon GaN channel layer, an AlGaN barrier layer and a cap layer which are sequentially stacked in the longitudinal direction on the surface of the substrate.

2. The epitaxial layer of a lattice transition gallium nitride HEMT device according to claim 1, characterized in that: The AlGaN transition layer includes multiple AlGaN layers, wherein the aluminum content of each AlGaN layer is different.

3. The epitaxial layer of a lattice transition gallium nitride HEMT device according to claim 1, characterized in that: The aluminum content of the different AlGaN layers gradually decreases in a direction from adjacent to the superlattice buffer layer to adjacent to the high-carbon GaN layer.

4. A method for manufacturing a lattice transition gallium nitride HEMT device, characterized in that: The following steps are involved: preparing a substrate; Epitaxially growing an AlN nucleation layer, an AlGaN buffer layer and a superlattice buffer layer in sequence on the surface of the substrate; Epitaxially growing an AlGaN transition layer on the surface of the superlattice buffer layer; A high-carbon GaN layer, a low-carbon GaN channel layer, an AlGaN barrier layer and a cap layer are sequentially epitaxially grown on the surface of the AlGaN transition layer.

5. The method for manufacturing a lattice transition gallium nitride HEMT device according to claim 4, characterized in that: In the step of “preparing a substrate”, the substrate is a silicon substrate or a composite substrate formed of at least two materials selected from sapphire, silicon carbide, gallium nitride and a single crystal silicon film on an insulator, and the thickness of the substrate is 300 μm-3000 μm.

6. The method for manufacturing a lattice transition gallium nitride HEMT device according to claim 4, characterized in that: In the step of "epitaxially growing an AlN nucleation layer, an AlGaN buffer layer and a superlattice buffer layer in sequence on the surface of the substrate", the thickness of the AlN nucleation layer is 30nm-1500nm, the thickness of the AlGaN buffer layer is 25nm-400nm, and the thickness of the superlattice buffer layer is 0.3μm-15μm.

7. The method for manufacturing a lattice transition gallium nitride HEMT device according to claim 4, characterized in that: In the step of "epitaxially growing multiple AlGaN layers on the surface of the superlattice buffer layer in sequence, wherein the aluminum content of the AlGaN layer from the vicinity of the superlattice buffer layer to the distance from the superlattice buffer layer decreases in sequence", the carbon doping concentration of the AlGaN transition layer is 5×10 17 cm -3 -5×10 19 cm -3 .

8. The method for manufacturing a lattice transition gallium nitride HEMT device according to claim 4, characterized in that: In the step of "epitaxially growing an AlGaN transition layer on the surface of the superlattice buffer layer", the following steps are specifically included: Multiple AlGaN layers are epitaxially grown in sequence on the surface of the superlattice buffer layer, wherein the aluminum content of the AlGaN layer decreases in sequence from the layer adjacent to the superlattice buffer layer to the layer far away from the superlattice buffer layer.

9. The method for manufacturing a lattice transition gallium nitride HEMT device according to claim 8, characterized in that: In the step of "epitaxially growing multiple layers of AlGaN layers on the surface of the superlattice buffer layer in sequence, wherein the aluminum content of the AlGaN layer decreases successively from the layer adjacent to the superlattice buffer layer to the layer away from the superlattice buffer layer", the total thickness of the AlGaN transition layer is 0.06μm-5μm, the number of the AlGaN layers is not more than 5 layers, wherein the thickness of each AlGaN layer ranges from 0.02μm to 1μm, and the aluminum content of each AlGaN layer is 1%-99%.

10. The method for manufacturing a lattice transition gallium nitride HEMT device according to claim 4, characterized in that: In the step of "sequentially epitaxially growing a high-carbon GaN layer, a low-carbon GaN channel layer, an AlGaN barrier layer and a cap layer on the surface of the AlGaN transition layer", the carbon concentration in the high-carbon GaN layer is greater than 10 18 cm -3 The carbon concentration in the low-carbon GaN channel layer is less than 10 18 cm -3 .

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