Disclosure of Invention
In order to overcome the defects in the prior art, the embodiment of the invention provides an epitaxial layer of a gallium nitride HEMT device on a substrate and a manufacturing method thereof, which are used for solving one or more of the problems.
The embodiment of the application discloses an epitaxial layer of a gallium nitride HEMT device on a substrate, which comprises the substrate, and a SiO2 discontinuous layer, an AlN nucleation layer, an AlGaN layer, a buffer layer, a high-carbon GaN layer, a low-carbon GaN channel layer, an AlGaN barrier layer and a cap layer which are sequentially laminated on the surface of the substrate along the longitudinal direction, wherein random irregular triangles are distributed on the surface of the SiO2 discontinuous layer, so that part of the substrate can be exposed out of the surface of the substrate.
Further, the substrate is a silicon substrate or a monocrystalline silicon thin film on an insulator.
Further, the buffer layer is a superlattice buffer layer formed periodically by alternating AlN and AlGaN.
Further, the thickness of the buffer layer is 0.3-15 μm, the thickness of the AlN nucleation layer is 30-1500 nm, and the thickness of the AlGaN layer is 25-400 nm.
The embodiment of the application also discloses a manufacturing method of the gallium nitride HEMT device on the substrate, which comprises the following steps of preparing the substrate, forming a SiO2 continuous layer on the surface of the substrate, removing part of the SiO2 continuous layer to form a SiO2 discontinuous layer, epitaxially growing an AlN nucleation layer on the SiO2 discontinuous layer, and sequentially epitaxially growing an AlGaN layer, a buffer layer, a high-carbon GaN layer, a low-carbon GaN channel layer, an AlGaN barrier layer and a cap layer on the surface of the AlN nucleation layer along the longitudinal direction.
Further, in the epitaxial growth process, a metal organic chemical vapor deposition or molecular beam epitaxy method is adopted.
Further, in the step of "preparing a substrate", the thickness of the substrate is 300 μm to 3000 μm, and the resistivity is 0.001 Ω·cm to 5000 Ω·cm.
Further, in the step of forming a continuous layer of SiO2 on the substrate surface, the continuous layer of SiO2 completely covers the substrate surface, and the continuous layer of SiO2 has a thickness of 0.5nm to 5nm.
Further, in the step of removing a portion of the continuous SiO2 layer to form a discontinuous SiO2 layer, the method comprises the steps of treating the continuous SiO2 layer in a Metal Organic Chemical Vapor Deposition (MOCVD) furnace or etching a portion of the continuous SiO2 layer with hydrofluoric acid to remove a portion of the continuous SiO2 layer and expose a substrate thereunder, wherein the surface of the discontinuous SiO2 layer is distributed with random irregular triangles.
Further, in the step of epitaxially growing an AlN nucleation layer on the discontinuous SiO2 layer, the method comprises the steps of firstly depositing AlN only on the exposed surface of the substrate to form a plurality of mutually-spaced AlN islands, and continuing epitaxial growth of AlN to gradually combine the AlN islands to form a continuous AlN nucleation layer, wherein the thickness of the AlN nucleation layer is 30-1500 nm.
The beneficial effects of the invention are as follows:
the substrate is discontinuously covered by the random irregular SiO2 thin layer, only part of the substrate is exposed, the high-carbon GaN layer and the GaN threading dislocation density in the low-carbon GaN channel layer are reduced by growing the HEMT structure on the substrate, and the performance and the reliability of the HEMT power device prepared by using the low-dislocation density epitaxial structure are improved. In addition, the SiO2 discontinuous layer is directly formed on the substrate, no extra deposition-photoetching-etching steps are needed, the cost is effectively reduced, meanwhile, the thickness of the SiO2 discontinuous layer can be made to be very thin, the influence on the subsequent epitaxial AlN nucleation layer and the whole HEMT structure is small, the epitaxial window is larger, and the epitaxial mass production yield is high.
The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments, as illustrated in the accompanying drawings.
Drawings
In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a schematic diagram of an epitaxial layer of a gallium nitride HEMT device on a substrate in one embodiment of the prior art;
Fig. 2 is a schematic diagram of an epitaxial layer of a gallium nitride HEMT device on a substrate according to the prior art in another embodiment;
Fig. 3 is a schematic structural diagram of an epitaxial layer of a gallium nitride HEMT device on a substrate according to an embodiment of the invention;
Fig. 4 is a flowchart of a method for manufacturing a gallium nitride HEMT device on a substrate according to an embodiment of the invention;
Fig. 5 is a schematic diagram of a process for preparing a discontinuous SiO2 layer in a method for manufacturing a gallium nitride HEMT device on a substrate according to an embodiment of the present invention;
fig. 6 shows the surface topography shown by Atomic Force Microscopy (AFM).
The reference numerals of the drawings comprise 1, a substrate, 2, an AlN nucleation layer, 3, an AlGaN layer, 4, a buffer layer, 5, a high-carbon GaN layer, 6, a low-carbon GaN channel layer, 7, an AlGaN barrier layer, 8, a cap layer, 9, a SiO2 mask, 10, a SiO2 continuous layer and 11, a SiO2 discontinuous layer.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The epitaxial layer structure commonly used in the prior art is shown in fig. 1, and comprises a substrate 1 (such as a silicon substrate 1), an aluminum nitride (AlN) nucleation layer and an AlGaN layer 3 sequentially from bottom to top, wherein the AlGaN layer 3 is formed by one or more layers of AlGaN with different aluminum contents, a Buffer layer 4 (Buffer layer), wherein the Buffer layer 4 is formed by superlattice Buffer layers 4 formed by alternately and periodically forming AlN and AlGaN, the Buffer layer 4 is sequentially a high-carbon GaN layer 5, a low-carbon GaN channel layer 6, an AlGaN barrier layer 7 and a cap layer 8, in the structure, due to the larger lattice mismatch of GaN/AlN and silicon in the substrate 1, high-density dislocation is generated in the epitaxial growth process, and the dislocation penetrates to the surface of the epitaxial layer along with the epitaxial growth, so that the dislocation with high-density penetration dislocation exists when the low-carbon GaN channel layer 6 and the following AlGaN barrier layer 7 and the cap layer 8 are both critical to the performance of the gallium nitride high-electron mobility transistor device, and the dislocation reduces the device performance and reliability.
The optimized epitaxial layer structure in the prior art is shown in fig. 2, and is different from the first one in that a GaN layer is grown above the buffer layer 4, then a periodic and regular silicon dioxide SiO2 mask 9 is formed on this layer by deposition-lithography-etching technique, and then a low-carbon GaN channel layer 6 and a subsequent AlGaN barrier layer 7 and cap layer 8 are grown on the patterned epitaxial structure. Before the low-carbon GaN channel layer 6 is grown, the periodical SiO2 mask 9 is formed on the GaN layer to prevent the threading dislocation from continuously extending upwards, so that the dislocation density of the subsequent low-carbon GaN channel layer 6 and the upper layer can be greatly reduced, however, the second epitaxial structure has the following 2 major defects that 1, an additional deposition-photoetching-etching step is needed to form the periodical SiO2 mask 9, the cost is increased, 2, the introduction of the SiO2 mask 9 brings about epitaxial growth interruption, interface problems are caused, meanwhile, the difficulty of secondary epitaxial growth of GaN on the SiO2 mask 9 is high, and a series of problems such as incapability of smoothly merging epitaxial layers, occurrence of holes in epitaxy and the like are caused.
In order to solve the above-mentioned problems, as shown in fig. 3, an epitaxial layer of a gallium nitride HEMT device on a substrate of the present embodiment includes a substrate 1, and a SiO2 discontinuous layer 11, an AlN nucleation layer 2, an AlGaN layer 3, a buffer layer 4, a high-carbon GaN layer 5, a low-carbon GaN channel layer 6, an AlGaN barrier layer 7 and a cap layer 8 which are sequentially stacked on the surface of the substrate 1 in the longitudinal direction, wherein the surface of the SiO2 discontinuous layer 11 is distributed with random irregular triangles, so that part of the substrate 1 can be exposed to the surface of the substrate 1, so that the AlN nucleation layer 2 can be partially contacted with the substrate 1 exposed to the surface of the SiO2 discontinuous layer 11, and the rest of the AlN nucleation layer 2 is continuous, that is, the bottom end of the SiO2 discontinuous layer 11 is communicated with the substrate 1, so that the surface of the substrate 1 is exposed, and the surface of the SiO2 discontinuous layer 11 is randomly spliced by triangles different in size and dimension, so that the surface of the SiO2 discontinuous layer 11 is formed. Preferably, the substrate 1 is a silicon substrate 1, and of course, in other alternative embodiments, the substrate 1 may be a substrate 1 formed by compounding several materials such as a monocrystalline silicon thin film on an insulator. Preferably, the thickness of the buffer layer 4 is 0.3 μm to 15 μm, the thickness of the AlN nucleation layer 2 is 30nm to 1500nm, and the thickness of the AlGaN layer 3 is 25nm to 400nm.
In this embodiment, taking the substrate 1 as the silicon substrate 1 as an example, before epitaxial growth from the AlN nucleation layer 2, several randomly distributed SiO2 discontinuous layers 11 (SiO2 discontinuous layer) with thicknesses around nanometers are first formed on the silicon substrate 1, that is, the silicon substrate 1 is discontinuously covered by a SiO2 thin layer, only part of the surface of the silicon substrate 1 is exposed, so that when epitaxial growth is started, alN is firstly deposited only on the exposed surface of the silicon substrate 1 to form a plurality of mutually spaced AlN islands, and subsequent AlN continues epitaxial growth, so that the AlN islands gradually merge to form a continuous AlN nucleation layer 2, so that the growth mode reduces the density of threading dislocation generated between AlN and Si on the silicon substrate 1 due to larger lattice mismatch, simultaneously accelerates turning and annihilation of threading dislocation in the subsequent epitaxial growth process, effectively reduces the subsequent low-carbon GaN channel layer 6 and other upper layers, and does not require an additional deposition-photolithography-etching step, thereby greatly reducing the cost of dislocation. By means of the above process, a random irregular distribution of the discontinuous layer 11 of SiO2 can be produced, i.e. the above process is able to obtain such random results, instead of the regular periodic shape of the prior art.
By means of the structure, the substrate 1 is discontinuously covered by the random irregular SiO2 thin layer, only part of the substrate 1 is exposed on the surface, the density of GaN threading dislocation in the high-carbon GaN layer 5 and the low-carbon GaN channel layer 6 is reduced by growing the HEMT structure on the substrate 1, and the performance and the reliability of the HEMT power device manufactured by using the low-dislocation density epitaxial structure are improved. In addition, the SiO2 discontinuous layer 11 is directly formed on the substrate 1, no extra deposition-photoetching-etching steps are needed, the cost is effectively reduced, meanwhile, the thickness of the SiO2 discontinuous layer 11 can be made to be very thin, the influence on the subsequent epitaxial AlN nucleation layer 2 and the whole HEMT structure is small, the epitaxial window is larger, and the epitaxial mass production yield is high.
As shown in fig. 4 to 5, the present embodiment further provides a method for manufacturing a gallium nitride HEMT device on a substrate, including the following steps:
The substrate 1 is prepared, the substrate 1 may be a silicon (Si) substrate 1, or a substrate 1 formed by compounding several materials such as a monocrystalline silicon thin film (Silicon On Insulator, SOI for short) on an insulator, wherein the thickness of the substrate 1 is 300-3000 μm, and the resistivity of the silicon substrate 1 is 0.001-5000 Ω cm when the silicon substrate 1 is used.
The continuous layer 10 of SiO2 is formed on the surface of the substrate 1, preferably, the thickness thereof is in the range of 0.5nm to 5nm, and the formation mode can be natural oxidation of the surface of the silicon substrate 1 exposed to air, thermal oxidation and other modes, and the continuous layer 10 of SiO2 completely covers the surface of the silicon substrate 1.
Removing part of the continuous SiO2 layer 10 to form a SiO2 discontinuous layer 11, treating the continuous SiO2 layer 10 in a Metal Organic Chemical Vapor Deposition (MOCVD) furnace, or etching part of the continuous SiO2 layer 10 with hydrofluoric acid to remove part of the continuous SiO2 layer 10 on the surface and expose the underlying substrate 1, while the rest of the SiO2 remains, exhibiting a surface morphology as shown in an Atomic Force Microscope (AFM) of fig. 6, wherein the rough areas with higher heights are shown in fig. 6 as a SiO2 discontinuous layer 11, the remaining flatter areas with lower heights are shown in the exposed silicon substrate 1, the surface of the rest of the discontinuous SiO2 layer 11 exhibits a random irregular, triangle-like shape with a thickness of 0.5nm-5nm, and a coverage of 5% -90% of the surface of the covering silicon substrate 1. That is, the bottom end of the SiO2 discontinuous layer 11 communicates with the substrate 1, so that the surface of the substrate 1 is exposed, and the surface of the SiO2 discontinuous layer 11 is formed by splicing triangles of a size and dimension, so that the surface shape of the SiO2 discontinuous layer 11 is irregular. Thereby distinguishing periodic, regularly shaped surfaces formed by conventional etching or the like.
In the epitaxial growth of the discontinuous SiO2 layer 11, alN is firstly deposited on the exposed surface of the silicon substrate 1 to form a plurality of mutually-spaced AlN islands, the subsequent AlN continues to be epitaxially grown so that the AlN islands gradually merge to form a continuous AlN nucleation layer 2, and the epitaxial growth can be completed by using a Metal Organic Chemical Vapor Deposition (MOCVD) device, and the thickness of the AlN islands is 30-1500 nm.
An AlGaN layer 3, a buffer layer 4, a high-carbon GaN layer 5, a low-carbon GaN channel layer 6, an AlGaN barrier layer 7 and a cap layer 8 are sequentially epitaxially grown on the surface of the AlN nucleation layer 2 in the longitudinal direction. The buffer layer 4 is formed by periodically forming superlattice buffer layers 4 of AlN and AlGaN alternately, and according to the specific situation, the superlattice buffer layers 4 can be directly replaced by AlGaN buffer layers 4 without the periodic superlattice buffer layers 4, the resistivity of the superlattice buffer layers 4 can be increased by doping elements such as carbon, iron and the like, the doping concentration of the doping elements is between 5 multiplied by 1017cm-3 and 5 multiplied by 1019cm-3, and the thickness of the superlattice buffer layers 4 is in the range of 0.3 mu m-15 mu m. Above the buffer layer 4 are a high-carbon GaN layer 5 (carbon concentration is greater than 1018cm-3), a low-carbon GaN channel layer 6 (carbon concentration is less than 1018cm-3), an AlGaN barrier layer 7, and a cap layer 8 in this order, the material of the cap layer 8 is different according to whether the device is enhancement type or depletion type, the cap layer 8 of the enhancement type HEMT is usually magnesium doped gallium nitride, and the cap layer 8 of the depletion type HEMT may be silicon nitride or intentionally doped gallium nitride.
It is noted that metal organic chemical vapor deposition or molecular beam epitaxy methods may be employed in the above-mentioned epitaxial growth processes.
In this embodiment, taking the substrate 1 as the silicon substrate 1 as an example, before epitaxial growth from the AlN nucleation layer 2, several randomly distributed SiO2 discontinuous layers 11 (SiO2 discontinuous layer) with thicknesses around nanometers are first formed on the silicon substrate 1, that is, the silicon substrate 1 is discontinuously covered by a SiO2 thin layer, only part of the surface of the silicon substrate 1 is exposed, so that when epitaxial growth is started, alN is firstly deposited only on the exposed surface of the silicon substrate 1 to form a plurality of mutually spaced AlN islands, and subsequent AlN continues epitaxial growth, so that the AlN islands gradually merge to form a continuous AlN nucleation layer 2, so that the growth mode reduces the density of threading dislocation generated between AlN and Si on the silicon substrate 1 due to larger lattice mismatch, simultaneously accelerates turning and annihilation of threading dislocation in the subsequent epitaxial growth process, effectively reduces the subsequent low-carbon GaN channel layer 6 and other upper layers, and does not require an additional deposition-photolithography-etching step, thereby greatly reducing the cost of dislocation.
By means of the structure, the substrate 1 is discontinuously covered by the random irregular SiO2 thin layer, only part of the substrate 1 is exposed on the surface, the density of GaN threading dislocation in the high-carbon GaN layer 5 and the low-carbon GaN channel layer 6 is reduced by growing the HEMT structure on the substrate 1, and the performance and the reliability of the HEMT power device manufactured by using the low-dislocation density epitaxial structure are improved. In addition, the SiO2 discontinuous layer 11 is directly formed on the substrate 1, no extra deposition-photoetching-etching steps are needed, the cost is effectively reduced, meanwhile, the thickness of the SiO2 discontinuous layer 11 can be made to be very thin, the influence on the subsequent epitaxial AlN nucleation layer 2 and the whole HEMT structure is small, the epitaxial window is larger, and the epitaxial mass production yield is high.
While the principles and embodiments of the present invention have been described in detail in the foregoing application of the principles and embodiments of the present invention, the above examples are provided for the purpose of aiding in the understanding of the principles and concepts of the present invention and may be varied in many ways by those of ordinary skill in the art in light of the teachings of the present invention, and the above descriptions should not be construed as limiting the invention.