Semiconductor structure containing composite buffer layer and manufacturing method thereof

Abstract

The invention relates to an aluminum oxynitride (AlNO) thin film or a composite multilayer thin film structure which comprises aluminum oxynitride (AlNO) and aluminum nitride (AlN), gallium nitride (GaN) and / or aluminum gallium nitride (AlxGa1-xN) on the aluminum oxynitride (AlNO), wherein the aluminum oxynitride (AlNO) and the aluminum nitride (AlN), gallium nitride (GaN) and / or aluminum gallium nitride (AlxGa1-xN) are formed on a substrate made of a sapphire material, a silicon material or a silicon carbide (SiC) in a mode of introducing a proper amount of oxygen (O2) in a deposition (MOCVD (Metal Organic Chemical Vapor Deposition), PVD (Physical Vapor Deposition) or PECVD (Plasma Enhanced Chemical Vapor Deposition) process or an epitaxial (MBE) process. And the composite buffer layer structure can be used as a composite buffer layer structure on which a gallium nitride semiconductor element (GaN device) is subsequently manufactured. The technology provided by the invention can obtain better crystal quality, excellent surface smoothness, low roughness and homogeneous substrate materials which are not limited by manufacturers, a uniform and high-stability surface treatment layer is manufactured on the surface layer of the substrate, the problem of dislocation caused by mismatching of lattice constants of the substrate is reduced, the process of treating penetrating dislocation is shortened, and the production efficiency is improved. And the gallium nitride semiconductor element can obtain epitaxial quality with good stability and the like.

Description

Technical Field

[0001] The present invention relates to a semiconductor structure and manufacturing method containing a composite buffer layer, and more particularly to a semiconductor structure and manufacturing method containing a composite buffer layer formed on a silicon or sapphire substrate to manufacture a gallium nitride semiconductor device. Background Art

[0002] Gallium nitride (GaN) is a wide-bandgap semiconductor used in high-efficiency power transistors and integrated circuits. GaN materials can be used to manufacture semiconductor power devices, as well as radio frequency components and light-emitting diodes (LEDs). GaN technology has demonstrated its potential to replace silicon-based semiconductor technology in power conversion, radio frequency, and analog applications.

[0003] Current technology primarily uses sapphire (Al2O3) or silicon (Si) substrates to fabricate GaN devices. Due to the mismatch in lattice and thermal expansion coefficients between GaN and sapphire, heteroepitaxial growth leads to numerous defects and substrate bowing, reducing device performance and lifespan and complicating subsequent fabrication processes. Therefore, existing technology deposits an aluminum nitride (AlN) thin film on the substrate as a buffer layer between the substrate and the GaN device. However, the crystal quality, surface flatness, and lattice matching of AlN thin films still require further improvement.

[0004] To improve the above-mentioned shortcomings of the prior art, the present invention aims to provide a semiconductor structure and method containing a composite buffer layer, wherein a composite buffer layer including an aluminum oxynitride layer is formed on a silicon, silicon carbide or sapphire substrate to manufacture a gallium nitride semiconductor device. Summary of the Invention

[0005] The present invention aims to provide a semiconductor structure and method containing a composite buffer layer, wherein a composite buffer layer including an aluminum oxynitride layer is formed on a silicon, silicon carbide, or sapphire substrate to manufacture a gallium nitride semiconductor device. The structure can obtain a buffer layer with good crystal quality, excellent surface flatness, and low roughness, thereby improving the yield of the subsequent gallium nitride semiconductor device manufacturing process.

[0006] To achieve the above-mentioned object, the present invention provides a semiconductor structure containing a composite buffer layer, which mainly forms an aluminum oxynitride (AlNO) thin film or a thin film containing aluminum oxynitride (AlNO) and aluminum nitride (AlN), gallium nitride (GaN), and / or aluminum gallium nitride (AlN) thereon on a substrate made of sapphire, silicon (Si) or silicon carbide (SiC) by introducing an appropriate amount of oxygen (O2) during a deposition (MOCVD, PVD, ALD, PECVD) or epitaxial (MBE) process. x Ga 1-x N) composite multilayer thin film structure, serving as a composite buffer layer structure for subsequent fabrication of gallium nitride semiconductor devices. The technology of this invention achieves superior crystal quality, excellent surface flatness, low roughness, homogeneous substrate materials regardless of manufacturer, and produces a uniform and highly stable surface treatment layer on the substrate surface. This reduces the mismatching of substrate lattice constants and misalignment issues, shortens the dislocation process, and achieves excellent and stable epitaxial quality for gallium nitride semiconductor devices.

[0007] In one embodiment, the semiconductor structure containing a composite buffer layer includes: a substrate; a composite buffer layer formed on the substrate, wherein the composite buffer layer includes at least an aluminum oxynitride (AlNO) layer; and a semiconductor element formed on the composite buffer layer; characterized in that the aluminum oxynitride layer has an oxygen concentration between 3% and 3.5% and a thickness between 20 and 50 nm.

[0008] In one embodiment, the substrate is made of one of the following materials: sapphire (Al 2 O 3 ), silicon (Si), or silicon carbide (SiC); and the semiconductor device is a gallium nitride semiconductor device (GaNDevice).

[0009] In one embodiment, the composite buffer layer includes: the aluminum oxynitride layer directly formed on the substrate; and a gallium nitride (GaN) layer directly formed on the aluminum oxynitride layer; and the semiconductor device is directly formed on the GaN layer.

[0010] In one embodiment, the composite buffer layer includes: the aluminum oxynitride layer directly formed on the substrate, and an aluminum nitride (AlN) layer directly formed on the aluminum oxynitride layer; the semiconductor device is directly formed on the aluminum nitride layer.

[0011] In one embodiment, the composite buffer layer includes: the aluminum oxynitride layer directly formed on the substrate, an aluminum nitride layer directly formed on the aluminum oxynitride layer, and a gallium nitride layer directly formed on the aluminum nitride layer; the semiconductor device is directly formed on the gallium nitride layer.

[0012] In one embodiment, the composite buffer layer includes: an aluminum oxynitride layer directly formed on the substrate, an aluminum nitride layer directly formed on the aluminum oxynitride layer, an aluminum gallium nitride (Al x Ga 1-x N; where 0 < x < 1) layer directly formed on the aluminum gallium nitride layer, and a gallium nitride layer directly formed on the aluminum gallium nitride layer; the semiconductor element is directly formed on the gallium nitride layer.

[0013] In one embodiment, the aluminum oxynitride layer is formed by physical vapor deposition (PVD) process. During the process, oxygen with a flow rate of about 0.5% - 0.6% is introduced at a process temperature of 600 - 700 °C to form an aluminum oxynitride layer with a thickness ranging from 20 - 50 nm and an oxygen concentration of 3% - 3.5% on the substrate; the full width at half maximum (FWHM) crystallinity measurement value of the surface of the aluminum oxynitride layer ranges from 50 - 300 arcsec, and the roughness Ra / Rq value is less than 1 nm; the thickness of the aluminum nitride layer ranges from 10 - 200 nm; the thickness of the aluminum gallium nitride layer ranges from 10 - 800 nm; the aluminum gallium nitride layer is one of a single-layer or multi-layer structure; when the aluminum gallium nitride layer is a multi-layer structure, the aluminum composition ratio of the bottom layer is higher than that of the top layer; when the aluminum gallium nitride layer is a single-layer structure, it has a single aluminum composition or a gradient aluminum composition structure, and the aluminum composition at the bottom is higher than that at the top; wherein, the preferred implementation range of the aluminum composition content in the aluminum gallium nitride layer is between 5% - 80%; the thickness of the gallium nitride layer ranges from 50 - 500 nm.

[0014] To achieve the above object, the present invention provides a method for manufacturing a semiconductor structure with a composite buffer layer, including: providing a substrate; forming an aluminum oxynitride layer on the substrate by a first semiconductor thin film process; forming an aluminum nitride layer on the aluminum oxynitride layer by a second semiconductor thin film process; forming an aluminum gallium nitride layer on the aluminum nitride layer by a third semiconductor thin film process; forming a gallium nitride layer on the aluminum gallium nitride layer by a fourth semiconductor thin film process; wherein, a semiconductor element can be provided on the gallium nitride layer by a semiconductor epitaxial process; it is characterized in that the oxygen concentration of the aluminum oxynitride layer is between 3% - 3.5% and the thickness is between 20 - 50 nm. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 FIG. 1 is a schematic structural diagram of the first embodiment of the semiconductor structure with a composite buffer layer according to the present invention.

[0016] Figure 2 FIG. 2 is a schematic structural diagram of the second embodiment of the semiconductor structure with a composite buffer layer according to the present invention.

[0017] Figure 3FIG. 4 is a schematic structural diagram of a third embodiment of a semiconductor structure including a composite buffer layer according to the present invention.

[0018] Figure 4 FIG. 4 is a schematic structural diagram of a fourth embodiment of a semiconductor structure including a composite buffer layer according to the present invention.

[0019] Figure 5 FIG. 4 is a schematic structural diagram of a fifth embodiment of a semiconductor structure including a composite buffer layer according to the present invention.

[0020] Explanation of the accompanying drawings: 1-composite buffer layer semiconductor structure; 10-substrate; 20-composite buffer layer; 21-aluminum oxynitride layer; 22-gallium nitride layer; 23-aluminum nitride layer; 24-aluminum gallium nitride layer; 30-semiconductor element. DETAILED DESCRIPTION

[0021] In order to more clearly describe the specific structure, manufacturing method and effect of the semiconductor structure and manufacturing method containing a composite buffer layer proposed in the present invention, the same will be described in detail below with reference to the accompanying drawings.

[0022] The present invention provides a structure and method for manufacturing a composite buffer layer comprising aluminum oxynitride (AlNO) on a substrate. The substrate may be a sapphire (Al2O3, English name Sapphire), silicon (Si) or silicon carbide (SiC) substrate. By introducing an appropriate amount of oxygen (O2) during a deposition (MOCVD, PVD, ALD, PECVD) or epitaxial (MBE) process, an aluminum oxynitride (AlNO) film or a composite buffer layer comprising aluminum oxynitride (AlNO) and aluminum nitride (AlN), gallium nitride (GaN), and / or aluminum gallium nitride (AlN) thereon is formed. x Ga 1-x N) composite multilayer thin film structure, serving as a composite buffer layer structure for subsequent fabrication of gallium nitride semiconductor devices. The technology of this invention achieves superior crystal quality, excellent surface flatness, low roughness, homogeneous substrate materials regardless of manufacturer, and the production of a highly uniform and stable surface treatment layer on the substrate surface. This reduces the misalignment caused by substrate lattice constant mismatch, shortens the dislocation process, and achieves excellent and stable epitaxial quality for gallium nitride semiconductor devices.

[0023] See also Figure 1, is a structural schematic diagram of the first embodiment of the semiconductor structure containing a composite buffer layer of the present invention. The semiconductor structure containing a composite buffer layer of the present invention comprises, from bottom to top: a substrate 10, a composite buffer layer 20 formed on the substrate 10, and a semiconductor device 30 formed on the composite buffer layer 20. The composite buffer layer 20 is formed on the substrate 10 by a semiconductor thin film process, and at least includes an aluminum oxynitride (AlNO) layer. The material of the substrate is one of the following: sapphire (Al2O3, English name Sapphire), silicon (Si) or silicon carbide (SiC), but sapphire is a preferred embodiment. The semiconductor device is a gallium nitride semiconductor device (GaN Device).

[0024] In other embodiments of the present invention described below, since the structures, materials and functions of most elements are the same as those of the aforementioned embodiments, the same elements will be given the same names and numbers, and their details will not be repeated.

[0025] See also Figure 2 , is a schematic structural diagram of a second embodiment of a semiconductor structure containing a composite buffer layer according to the present invention. In the second embodiment, the semiconductor structure containing a composite buffer layer also comprises, from bottom to top, a substrate 10, a composite buffer layer 20 formed on the substrate 10, and a semiconductor device 30 formed on the composite buffer layer 20. The composite buffer layer 20 comprises an aluminum oxynitride layer 21 formed directly on the upper surface of the substrate 10 by a semiconductor thin film process, and a gallium nitride (GaN) layer 22 formed directly on the upper surface of the aluminum oxynitride layer 21 by a semiconductor thin film process. The semiconductor device 30 is formed directly on the upper surface of the GaN layer 22 by a semiconductor process.

[0026] See also Figure 3 , is a schematic structural diagram of a third embodiment of a semiconductor structure containing a composite buffer layer according to the present invention. In the third embodiment, the semiconductor structure containing a composite buffer layer also comprises, from bottom to top, a substrate 10, a composite buffer layer 20 formed on the substrate 10, and a semiconductor device 30 formed on the composite buffer layer 20. The composite buffer layer 20 comprises an aluminum oxynitride layer 21 formed directly on the upper surface of the substrate 10 by a semiconductor thin film process, and an aluminum nitride (AlN) layer 23 formed directly on the upper surface of the aluminum oxynitride layer 21 by a semiconductor thin film process. The semiconductor device 30 is formed directly on the upper surface of the aluminum nitride layer 23 by a semiconductor process.

[0027] See also Figure 4, is a schematic structural diagram of the fourth embodiment of the semiconductor structure with a composite buffer layer according to the present invention. In the fourth embodiment, the semiconductor structure with a composite buffer layer also includes, from bottom to top: a substrate 10, a composite buffer layer 20 formed on the substrate 10, and a semiconductor element 30 formed on the composite buffer layer 20. Among them, the composite buffer layer 20 includes: an aluminum oxynitride layer 21 directly formed on the upper surface of the substrate 10 by a semiconductor thin film process, a layer of aluminum nitride 23 directly formed on the upper surface of the aluminum oxynitride layer 21, and a layer of gallium nitride 22 directly formed on the upper surface of the aluminum nitride layer 23 by a semiconductor thin film process. The semiconductor element 30 is directly formed on the upper surface of the gallium nitride layer 22 by a semiconductor process.

[0028] Please refer to Figure 5 , is a schematic structural diagram of the fifth embodiment of the semiconductor structure with a composite buffer layer according to the present invention. Figure 5 The fifth embodiment shown is the best embodiment of the semiconductor structure with a composite buffer layer according to the present invention. In the fifth embodiment, the semiconductor structure with a composite buffer layer also includes, from bottom to top: a substrate 10, a composite buffer layer 20 formed on the substrate 10, and a semiconductor element 30 formed on the composite buffer layer 20. Among them, the composite buffer layer 20 includes: an aluminum oxynitride layer 21 directly formed on the upper surface of the substrate 10 by a first semiconductor thin film process, a layer of aluminum nitride 23 directly formed on the upper surface of the aluminum oxynitride layer 21 by a second semiconductor thin film process, a layer of aluminum gallium nitride (Al x Ga 1-x N; where 0 < x < 1) layer 24, and a layer of gallium nitride 22 directly formed on the upper surface of the aluminum gallium nitride layer 24 by a fourth semiconductor thin film process. The semiconductor element 30 is directly formed on the upper surface of the gallium nitride layer 22 by a semiconductor process. Among them, the lattice constant of the aluminum oxynitride layer (AlNO) 21 buffer layer is between the sapphire (Al2O3) substrate 10 and the aluminum nitride (AlN) layer 23 buffer layer, which can reduce the defects caused by lattice mismatch and improve the crystallization quality and roughness of the aluminum nitride (AlN) layer 23 buffer layer. The gallium nitride (GaN) layer 22 buffer layer can further increase the freedom of adjusting the epitaxial quality of the gallium nitride (GaN) layer 22 buffer layer under the condition that the aluminum nitride (AlN) layer 23 buffer layer has good crystallization quality. In this embodiment, the aluminum gallium nitride (Al x Ga 1-xN; where 0 < x < 1) layer 24 to solve the stress problem. The composite buffer layer 20 of the present invention formed by sequentially stacking an aluminum oxynitride layer 21, an aluminum nitride layer 23, an aluminum gallium nitride layer 24, and a gallium nitride layer 22 through a semiconductor thin film process can obtain a substrate buffer layer surface with good surface flatness, roughness, and crystal quality, further improving and enhancing the quality of the gallium nitride semiconductor device (GaN device) 30 fabricated on the surface of the composite buffer layer 20 of this substrate 10. In particular, the aluminum oxynitride layer 21 (AlNO) is a necessary condition for constituting the composite buffer layer 20 of the present invention, and the aluminum nitride layer 23, aluminum gallium nitride layer 24, and gallium nitride layer 22 sequentially stacked above the aluminum oxynitride layer 21 further improve the flatness, roughness, and crystal quality of the substrate buffer layer surface, and more effectively reduce the stress problem.

[0029] In a preferred embodiment of the present invention, in the manufacturing method of the semiconductor structure with a composite buffer layer, a semiconductor thin film process such as physical vapor deposition (PVD) process can be used to form thin films of an aluminum oxynitride (AlNO) layer 21, an aluminum nitride layer 23, an aluminum gallium nitride layer 24, and a gallium nitride layer 22 on the substrate 10. Although this embodiment is described with physical vapor deposition (PVD) as the preferred embodiment, other known semiconductor thin film manufacturing processes such as: metalorganic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), atomic layer deposition (ALD), plasma enhanced chemical vapor deposition (PECVD), physical vapor deposition (PVD), etc. can also be used to fabricate the aluminum oxynitride (AlNO) layer (thin film) described in the present invention. Although the process technologies and conditions of different processes are different, which will cause the oxygen flow rate conditions required in the process to change; however, the oxygen concentration required in the process and the "film thickness" and "oxygen content" of the formed aluminum oxynitride layer 21 are the necessary conditions and main technical features required to be achieved in the present invention.

[0030] The reason for choosing the physical vapor deposition (PVD) process as the best embodiment for fabricating the composite buffer layer 20 on the substrate 10 in the present invention is mainly because, compared with other processes, the physical vapor deposition process has the following advantages: good uniformity and density of the deposited thin film, few impurities in the thin film, extremely fast deposition rate, relatively low deposition process temperature, relatively low energy power consumption of the process machine, relatively easy internal cleaning and maintenance of the machine, relatively low machine maintenance cost, relatively low production cost, and relatively high batch production capacity.

[0031] The lattice constant of the aluminum oxynitride layer 21 is between the substrate 10 (sapphire Al2O3) and the aluminum nitride layer 23, which can reduce the defects caused by lattice mismatch and improve the crystal quality and roughness of the aluminum nitride layer 23. In the present invention Figure 5In the preferred embodiment shown, the method for fabricating a semiconductor structure including a composite buffer layer of the present invention utilizes a physical vapor deposition (PVD) process to directly form an aluminum oxynitride (AlNO) layer 21 thin film on the upper surface of a substrate 10. By introducing an oxygen flow rate of approximately 0.5% to 1% (optimally, an oxygen flow rate of 0.5% to 0.6% is optimal, which is the ultimate optimized value for uniformity of the aluminum oxynitride layer 21 coating) during the PVD process for depositing the aluminum nitride layer 21 on the substrate 10, the aluminum oxynitride (AlNO) layer 21 has an oxygen concentration of 3% to 5% (optimally, an oxygen concentration of 3% to 3.5%, but most preferably, 3.2 ± 0.1%). Consequently, an aluminum oxynitride (AlNO) layer 21 having a thickness of 25 to 45 nm ± 5 nm (i.e., preferably, a thickness in the range of 20 to 50 nm, but most preferably, 35 to 45 nm) can be formed on the substrate. The oxygen flow rate mentioned in this invention refers to the weight percentage of oxygen injected into the reaction chamber during the PVD process. In this embodiment, the PVD tool parameters include: (a) process temperature: 600-700°C; (b) gas flow rates: nitrogen (N2) 150-1000 sccm / argon (Ar) 20-200 sccm / oxygen (O2) 0.5-5 sccm; (c) converted oxygen (O2) flow rate: 0.5%-0.6%. Experimental results show that surface flatness deteriorates with increasing process temperature. For example, when the process temperature reaches above 700°C, surface flatness tends to deteriorate, with 650-680°C being the optimal process temperature. According to these process conditions, the aluminum oxynitride layer 21 (thickness range of 20-50 nm is preferred, but 35-45 nm is preferred) formed by introducing a small amount of oxygen (oxygen flow rate of 0.5% to 0.6%) during the PVD process of manufacturing aluminum oxynitride thin film (oxygen concentration of 3% to 3.5% is preferred, but 3.2+ / -0.1% is optimal) has a good crystalline quality, and its XRD AlNO(002) half-maximum width (FWHM) is between 50 and 300 arcsec (i.e., <300 arcsec); more preferably, it can reach 50 to 150 arcsec. The half-maximum width (FWHM) is a measurement of the quality of the crystalline product, and the smaller the value, the better the crystalline quality. In this embodiment, the surface flatness of the aluminum oxynitride layer 21 is good, and its roughness is low; the roughness Ra / Rq can be less than 1 nm, and more preferably, it can be less than 0.5 nm. Ra / Rq are both roughness measurements, calculated differently. Smaller values ​​indicate a smoother surface. Ra is the arithmetic mean deviation, representing the peaks and valleys in the height direction. Rq is the root mean square deviation, representing the average amplitude in the height direction.The “oxygen concentration” mentioned in the present invention refers to the “weight percentage (or atomic percentage)” of oxygen atoms contained in the aluminum oxynitride layer.

[0032] The present invention controls the oxygen concentration introduced in the deposition process between 3% and 5%, thereby obtaining an aluminum oxynitride (AlNO) layer with better crystal quality, good surface flatness, and low roughness. If the oxygen concentration is higher than 5% during the deposition process, the oxygen concentration in the formed aluminum oxynitride layer will exceed 10 atomic %, and the oxygen in the aluminum oxynitride layer will become excessive, the lattice constant matching between the substrate and the buffer layer will be reduced, and the surface roughness will become worse, resulting in a reduction in the function of the buffer layer. The oxygen content in the buffer layer is unstable, that is, the crystallinity of the buffer layer lacks reproducibility. When the crystallinity of the buffer layer lacks reproducibility, the crystallinity of the nitride semiconductor layer formed on the buffer layer also becomes unreproducible.

[0033] Although the oxygen flow conditions required for the process vary depending on the process technology (MOCVD, MBE, ALD, PECVD, PVD) or the tool used, the technical focus of the present invention is that when the aluminum oxynitride (AlNO) layer 21 formed on the substrate 10 has an oxygen concentration preferably between 3% and 3.5% (optimally 3.2 ± 0.1%) and a thickness between 25 nm and 45 nm (i.e., preferably 20 nm to 50 nm, but optimally 35 nm to 45 nm), the AlNO layer 21 can provide optimal crystal quality, surface flatness, low roughness, and avoid lattice mismatch between GaN and the substrate heterogeneous material. If the oxygen concentration in the AlNO layer 21 is too high (e.g., greater than 5%), the AlNO crystal quality and surface roughness will deteriorate. It is speculated that if the oxygen content in the buffer layer of the oxynitride aluminum film is greater than 5%, the oxygen in the oxynitride aluminum film becomes excessive, the lattice constant matching between the substrate and the oxynitride aluminum film is reduced, and the function as a buffer layer is reduced. The oxygen content in the buffer layer of the oxynitride aluminum film is unstable, that is, the crystallinity of the buffer layer lacks reproducibility. When the crystallinity of the buffer layer of the oxynitride aluminum film lacks reproducibility, the crystallinity of the nitride semiconductor layer formed on the buffer layer also becomes unreproducible. If the oxygen concentration is too low (less than 3%), it is difficult to form a uniform, low-roughness and high-quality oxynitride aluminum layer 21, that is, the overall uniformity and quality of the oxynitride aluminum layer 21 will deteriorate. Furthermore, the preferred thickness of the aluminum oxynitride layer 21 of the present invention is between 25 and 45 nm + / - 5 nm (i.e., a thickness range of 20 to 50 nm). The lattice constant of AlNO is between that of a sapphire Al2O3 substrate and AlN. Within this thickness range, the aluminum oxynitride layer 21 can provide the best effect of reducing defects caused by lattice mismatch and improving the crystal quality and roughness of AlN. If the thickness of the aluminum oxynitride layer 21 is too thin (e.g., less than 20 nm), it cannot effectively reduce defects caused by lattice mismatch, affecting the quality of the GaN material grown on top. Conversely, if the thickness of the aluminum oxynitride layer 21 is too thick (e.g., greater than 50 nm), production efficiency will be reduced, and the effects it can provide (reducing defects caused by lattice mismatch and improving the crystal quality and roughness of AlN) cannot be further effectively improved.

[0034] At Figure 5 In the illustrated embodiment, the aluminum nitride layer 23 is deposited directly on the top surface of the aluminum oxynitride layer 21 via PVD, MOCVD, or MBE processes. Its function is to adjust structural stress and epitaxial quality. The aluminum nitride layer 23 can also be doped with impurities such as carbon (C) and iron (Fe) to increase the buffer layer resistance and thus improve the structural withstand voltage. Its thickness is preferably in the range of 10 to 200 nm.

[0035] When the aluminum gallium nitride layer 24 has good crystallization quality on the aluminum nitride layer 23, it can increase the freedom to adjust the epitaxial quality of the gallium nitride layer 22 and solve the stress problem through the composite buffer layer 20. In Figure 5 the illustrated embodiment, the aluminum gallium nitride (Al x Ga 1-x N; where 0 < x < 1) layer 24 is directly stacked on the upper surface of the aluminum nitride layer 23 by PVD, MOCVD, or MBE process. Its function is to reduce structural stress and improve epitaxial quality, and can also拉升 the electron energy gap at the bottom of the electron channel layer, so as to better confine electrons in the channel. The aluminum gallium nitride layer 24 can be a single-layer or multi-layer structure; when it is a multi-layer aluminum gallium nitride layer 24 structure, the aluminum composition ratio of the bottom layer is higher than that of the top layer, that is, the aluminum composition content of the lower layer in two adjacent aluminum gallium nitride layers 24 is higher than that of the upper layer; when it is a single-layer aluminum gallium nitride layer 24 structure, it can be a single aluminum composition or a gradually changing aluminum composition. If it is a gradually changing aluminum composition, the aluminum composition ratio of the bottom is higher than that of the top, that is, the aluminum composition content of the single-layer gradually changing aluminum composition aluminum gallium nitride layer 24 gradually decreases from the bottom to the top. In other words, the closer to the aluminum nitride (AlN) layer 23, the larger the x value in the aluminum gallium nitride (Al x Ga 1-x N) layer 24; the closer to the gallium nitride (GaN) layer 22, the smaller the x value in the aluminum gallium nitride (Al x Ga 1-x N) layer 24. In this embodiment, the thickness of the aluminum gallium nitride layer 24 preferably ranges from 10 to 800 nm, and the aluminum composition content preferably ranges from 5 to 80%. The "aluminum composition content" mentioned in the present invention refers to the "weight percentage (or atomic percentage)" of aluminum atoms contained in the aluminum gallium nitride layer.

[0036] In Figure 5 the illustrated embodiment, the gallium nitride layer 22 is directly stacked on the upper surface of the aluminum gallium nitride layer 24 by PVD, MOCVD, or MBE process. Its function is the electron channel with as few impurities as possible. The thickness of the gallium nitride layer 22 preferably ranges from 50 to 500 nm. The gallium nitride semiconductor element 30 is directly stacked on the upper surface of the gallium nitride layer 22.

[0037] The present invention's semiconductor structure with a composite buffer layer utilizes an aluminum oxynitride layer 21 with an oxygen concentration between 3% and 3.5% and a thickness between 20 and 50 nm on the surface of a substrate 10 to achieve optimal crystal quality, surface flatness, low roughness, and avoid lattice constant mismatch between gallium nitride and the substrate's heterogeneous material. Next, an aluminum nitride layer 23 with a thickness between 10 and 200 nm is formed on the surface of the aluminum oxynitride layer 21 to increase the buffer layer's resistance and improve the structure's withstand voltage. Because the aluminum nitride layer 23 and the aluminum oxynitride layer 21 have similar material compositions, crystal quality is easily maintained and stress concentration is minimized. Next, an aluminum gallium nitride layer 24 with a thickness between 10 and 800 nm is formed on the surface of the aluminum nitride layer 23 to enhance epitaxial quality and mitigate stress. Because the aluminum content of the aluminum gallium nitride layer 24 gradually decreases from bottom to top, the bottom of the aluminum gallium nitride layer 24 has a similar material composition to the aluminum nitride layer 23, maintaining crystal quality and minimizing stress concentration. Next, a gallium nitride layer 22 with a thickness of 50-500 nm is deposited on the surface of the aluminum gallium nitride layer 24 to provide an electron channel. Because the aluminum content of the aluminum gallium nitride layer 24 gradually decreases from the bottom to the top, the material composition of the gallium nitride layer 22 and the top of the aluminum gallium nitride layer 24 is very similar, thus maintaining crystal quality and reducing stress concentration. Furthermore, because the gallium nitride layer 22 is made of the same substrate as the gallium nitride semiconductor device that will be subsequently deposited on it, crystal quality is significantly improved and stress concentration is reduced. Accordingly, the composite buffer layer 20 of the present invention, comprising an aluminum oxynitride layer 21, an aluminum nitride layer 23, an aluminum gallium nitride layer 24, and a gallium nitride layer 22, sequentially stacked from bottom to top via PVD, MOCVD, or MBE processes, not only ensures excellent surface flatness, low roughness, and superior crystalline quality on the substrate 10 surface, but also maintains crystalline quality and reduces stress concentration due to the proximity of the materials between adjacent layers. Furthermore, each layer provides distinct functions, further enhancing the crystalline quality and stress reduction effects, thereby further improving the quality of the gallium nitride semiconductor device 30 subsequently disposed thereon. The "thickness range" and "oxygen content range" of the aluminum oxynitride layer 21 are essential requirements and key technical features required by the present invention.

[0038] Through the above-mentioned process, the aluminum oxynitride (AlNO) layer in the semiconductor structure containing a composite buffer layer of the present invention has an XRD AlNO(002) FWHM of: <300 arcsec as an embodiment, and 50 to 200 arcsec as a preferred embodiment; the roughness rq of the surface of the aluminum oxynitride (AlNO) layer is less than 1 nm as an embodiment, and less than 0.5 nm as a preferred embodiment.

[0039] The present invention controls the oxygen concentration introduced in the deposition process between 3% and 5%, thereby obtaining an aluminum oxynitride (AlNO) layer with better crystal quality, good surface flatness, and low roughness. If the oxygen concentration is higher than 5% during the deposition process, the oxygen concentration in the formed aluminum oxynitride layer will exceed 10 atomic %, and the oxygen in the aluminum oxynitride layer will become excessive, the lattice constant matching between the substrate and the buffer layer will decrease, and the surface roughness will deteriorate, resulting in a reduction in the function of the buffer layer. The oxygen content in the buffer layer is unstable, that is, the crystallinity of the buffer layer lacks reproducibility. When the crystallinity of the buffer layer lacks reproducibility, the crystallinity of the nitride semiconductor layer formed on the buffer layer also becomes unreproducible.

[0040] The above-described embodiments should not be used to limit the scope of application of the present invention. The scope of protection of the present invention should be based primarily on the technical spirit defined in the claims and their equivalents. In other words, any equivalent variations and modifications made in accordance with the claims will not lose the essence of the present invention and will not depart from the spirit and scope of the present invention. Therefore, they should be considered as further implementations of the present invention.

Claims

1. A semiconductor structure containing a composite buffer layer, comprising: a substrate; A composite buffer layer is formed on the substrate; wherein the composite buffer layer at least comprises an aluminum oxynitride (AlNO) layer; a semiconductor element formed on the composite buffer layer; The invention is characterized in that the oxygen concentration of the aluminum oxynitride layer is between 3% and 3.5%, and the thickness is between 20 and 50 nm.

2. The semiconductor structure containing a composite buffer layer according to claim 1, wherein: The substrate is made of one of the following materials: sapphire, silicon, or silicon carbide; and the semiconductor element is a gallium nitride semiconductor element.

3. The semiconductor structure containing a composite buffer layer according to claim 2, wherein: The composite buffer layer includes: the aluminum oxynitride layer directly formed on the substrate, and a gallium nitride layer directly formed on the aluminum oxynitride layer; the semiconductor element is directly formed on the gallium nitride layer.

4. The semiconductor structure containing a composite buffer layer according to claim 2, wherein: The composite buffer layer includes: the aluminum oxynitride layer directly formed on the substrate, and an aluminum nitride layer directly formed on the aluminum oxynitride layer; the semiconductor element is directly formed on the aluminum nitride layer.

5. The semiconductor structure containing a composite buffer layer according to claim 2, wherein: The composite buffer layer includes: the aluminum oxynitride layer directly formed on the substrate, an aluminum nitride layer directly formed on the aluminum oxynitride layer, and a gallium nitride layer directly formed on the aluminum nitride layer; the semiconductor element is directly formed on the gallium nitride layer.

6. The semiconductor structure containing a composite buffer layer according to claim 2, wherein: The composite buffer layer includes: the aluminum oxynitride layer directly formed on the substrate, an aluminum nitride layer directly formed on the aluminum oxynitride layer, an aluminum gallium nitride layer directly formed on the aluminum nitride layer, and a gallium nitride layer directly formed on the aluminum gallium nitride layer; the semiconductor element is directly formed on the gallium nitride layer.

7. The semiconductor structure containing a composite buffer layer according to claim 6, wherein: The aluminum oxynitride layer is formed on the substrate by introducing oxygen flow rate of about 0.5% to 0.6% at a process temperature of 600 to 700° C. in a physical vapor deposition process, so as to form the aluminum oxynitride layer with a thickness ranging from 20 to 50 nm and an oxygen concentration of 3% to 3.5%; the half-height width of the surface of the aluminum oxynitride layer is measured to be between 50 and 300 arcsec, and the roughness Ra / Rq value is less than 1 nm; The aluminum nitride layer has a thickness ranging from 10 to 200 nm, and the aluminum nitride layer is doped with one of the following impurities: carbon, iron; The thickness of the aluminum gallium nitride layer ranges from 10 to 800 nm; the aluminum gallium nitride layer is one of a single layer or a multilayer structure; when the aluminum gallium nitride layer is a multilayer structure, the aluminum composition of the bottom layer is higher than that of the top layer; when the aluminum gallium nitride layer is a single layer structure, it is a gradient aluminum composition structure, and the aluminum composition of the bottom layer is higher than that of the top layer; wherein the aluminum composition content in the aluminum gallium nitride layer is preferably in the range of 5 to 80%; The thickness of the gallium nitride layer ranges from 50 to 500 nm.

8. A method for preparing a semiconductor structure containing a composite buffer layer, comprising: providing a substrate; Forming an aluminum oxynitride layer on the substrate by a first semiconductor thin film process; forming an aluminum gallium nitride layer on the aluminum nitride layer by a third semiconductor thin film process; forming a gallium nitride layer on the aluminum gallium nitride layer by a fourth semiconductor thin film process; Wherein, a gallium nitride semiconductor element can be disposed on the gallium nitride layer; The invention is characterized in that the oxygen concentration of the aluminum oxynitride layer is between 3% and 3.5%, and the thickness is between 20 and 45 nm.

9. The method for manufacturing a semiconductor structure containing a composite buffer layer according to claim 8, wherein: The substrate is a sapphire substrate; The aluminum oxynitride layer is formed on the substrate by introducing oxygen flow rate of about 0.5% to 0.6% at a process temperature of 600 to 700° C. in a physical vapor deposition process, so as to form the aluminum oxynitride layer with a thickness ranging from 20 to 50 nm and an oxygen concentration of 3% to 3.5%; the half-height width of the surface of the aluminum oxynitride layer is measured to be between 50 and 300 arcsec, and the roughness Ra / Rq value is less than 1 nm; The aluminum nitride layer has a thickness ranging from 10 to 200 nm, and the aluminum nitride layer is doped with one of the following impurities: carbon, iron; The thickness of the aluminum gallium nitride layer ranges from 10 to 800 nm; the aluminum gallium nitride layer is a single layer or a multilayer structure; when the aluminum gallium nitride layer is a multilayer structure, the aluminum composition of the bottom layer is higher than that of the top layer; when the aluminum gallium nitride layer is a single layer structure, it is a gradient aluminum composition structure, and the aluminum composition of the bottom layer is higher than that of the top layer; wherein the aluminum composition content in the aluminum gallium nitride layer is preferably in the range of 5 to 80%; The thickness of the gallium nitride layer ranges from 50 to 500 nm.

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