Semiconductor epitaxial structure and method of making the same

Abstract

The present disclosure relates to a semiconductor epitaxial structure and a preparation method thereof, the semiconductor epitaxial structure comprising: a substrate; a thin layer containing aluminum-nitrogen-silicon atomic bonds arranged on the substrate; an aluminum layer arranged on the thin layer; and a first buffer layer arranged on the aluminum layer. The semiconductor epitaxial structure effectively reduces the mismatch between the substrate and the epitaxial interface and the defect problem, reduces the device current collapse caused by the trap effect in the later HEMT device, reduces the static current leakage, and improves the device performance.

Description

Technical Field

[0001] This disclosure generally relates to the field of semiconductor technology. More specifically, this disclosure relates to a semiconductor epitaxial structure and a method for fabricating the semiconductor structure. Background Technology

[0002] Gallium nitride (GaN) is one of the main representative materials of third-generation semiconductors. It has the advantages of high frequency, high reliability and low cost. However, in the fabrication process of GaN-based HEMT epitaxial materials, problems such as lattice mismatch and thermal mismatch between Si substrate and GaN epitaxial layer are easy to occur. In order to reduce the residual stress caused by lattice mismatch between Si substrate and GaN epitaxial layer and reduce the dislocation density of GaN epitaxial layer, an aluminum layer is usually grown on the substrate. However, due to the low mobility of Al, the quality of GaN epitaxial layer containing aluminum layer is poor. Summary of the Invention

[0003] To address some or all of the aforementioned problems, this disclosure provides a semiconductor epitaxial structure and its fabrication method. This semiconductor epitaxial structure overcomes a series of issues, such as the formation of back-dissolution pits on the surface caused by uneven Al pre-passing in Si-based GaN epitaxy, and the accumulation of localized excessive Al in subsequent epitaxial layers due to low Al atom mobility, resulting in high-density spiral dislocations. It effectively reduces the mismatch and defect problems between the substrate and the epitaxial interface, reduces the device current collapse caused by trap effects in GaN HEMT devices fabricated from the Si-based GaN epitaxial buffer layer, reduces static current leakage, and improves the performance of Si-based GaN HEMT devices from the bottom layer of the epitaxial layer.

[0004] According to a first aspect of this disclosure, a semiconductor epitaxial structure is provided, comprising: a substrate; a thin layer containing aluminum-nitrogen-silicon atomic bonds disposed on the substrate; a uniform aluminum layer disposed on the thin layer; and a first buffer layer disposed on the aluminum layer.

[0005] According to a second aspect of this disclosure, a HEMT device is provided, including a substrate; a compound semiconductor composite structure disposed on the substrate and generating a two-dimensional electron gas; wherein the semiconductor composite includes a thin layer containing aluminum nitride silicon atomic bonds disposed on the substrate, a uniform aluminum layer disposed on the thin layer, and a first buffer layer disposed on the aluminum layer; and an electrode layer disposed on the compound semiconductor composite structure.

[0006] According to a third aspect of this disclosure, a method for preparing a semiconductor epitaxial structure is provided, comprising: providing a substrate; forming a thin layer containing aluminum-nitrogen-silicon atomic bonds on the substrate and forming a uniform aluminum layer on the thin layer; and forming a first buffer layer on the aluminum layer.

[0007] The HEMT device, semiconductor epitaxial structure, and fabrication method provided in this disclosure embodiment grow a uniform aluminum layer by forming aluminum-nitrogen-silicon atomic bonds on the substrate, which effectively reduces the mismatch and defect problems between the Si substrate and the epitaxial layer, improves the quality of the epitaxial layer, and ensures the reliability of the device. Attached Figure Description

[0008] The preferred embodiments of this disclosure will now be described in detail with reference to the accompanying drawings. In the drawings:

[0009] Figure 1 This is a schematic diagram of a semiconductor epitaxial structure provided in some embodiments of the present disclosure;

[0010] Figure 2 This is a schematic diagram of the detection results provided in some embodiments of this disclosure;

[0011] Figure 3 This is a schematic diagram of a semiconductor epitaxial structure provided in some embodiments of the present disclosure;

[0012] Figure 4 This is a schematic diagram of the HEMT device disclosed herein;

[0013] Figure 5 This is a flowchart illustrating a method for fabricating a semiconductor epitaxial structure according to some embodiments of the present disclosure;

[0014] Figure 6 This is a schematic diagram of a semiconductor epitaxial structure formed on a substrate according to the present disclosure. Detailed Implementation

[0015] The present disclosure will now be further explained in conjunction with the accompanying drawings.

[0016] In the description of this application, "growth" refers to "epitaxygrowth," that is, growing a layer structure with certain requirements on a material to be treated. Techniques involving "growth" may include metal-organic chemical vapor deposition (MOCVD), liquid phase epitaxy (LPE), vapor phase epitaxy (VPE), molecular beam epitaxy (MBE), atomic layer deposition (ALD), etc. Those skilled in the art can select an appropriate epitaxial growth technique based on the specific circumstances.

[0017] In the description of this application, "etching" should be understood in a broad sense, that is, growing a layer of photoresist on the surface of the material to be processed, selectively exposing and developing the photoresist through a mask to leave a photoresist layer on the surface of the material to be processed that is the same as the mask pattern, then selectively etching the material to be processed by chemical or physical methods, and finally peeling off the photoresist layer to form a structure on the material to be processed that corresponds to the mask pattern.

[0018] In the description of this application, the orientation or positional relationship indicated by terms such as "upper" or "lower" is based on the orientation or positional relationship shown in the accompanying drawings and is only for the convenience of describing this disclosure and simplifying the description, and is not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this disclosure.

[0019] In the description of this application, except for Embodiment 1, the other embodiments are written in a manner that avoids repetition as much as possible, that is, focusing on the differences between each embodiment and other embodiments. In these embodiments, any technical features that are not explicitly described can be referred to the corresponding description in Embodiment 1.

[0020] The specific embodiments of this disclosure will now be described in detail with reference to the accompanying drawings.

[0021] For example, such as Figure 1 As shown, the semiconductor epitaxial structure 100 includes: a substrate 110; a thin layer 121 containing aluminum nitride silicon atomic bonds disposed on the substrate 110; an aluminum layer 122 disposed on the thin layer 121; and a first buffer layer 123 disposed on the aluminum layer 122.

[0022] Substrate 110 is a silicon (Si) substrate. The thin layer containing aluminum-nitrogen-silicon atomic bonds disposed on the Si substrate can provide sufficient migration time for aluminum atoms on the substrate surface, effectively reducing the accumulation of high-density spiral dislocations in subsequent epitaxial layers, and making the aluminum layer disposed on the thin layer more uniform. This avoids the reaction between silicon and gallium in the uneven aluminum layer during subsequent epitaxial growth, which can lead to the formation of silicon and gallium remelting effects and surface remelting pits.

[0023] Figure 2 This is a schematic diagram of the detection results provided in some embodiments of this disclosure. It should be noted that the detection results were measured using a scanning electron microscope (SEM). Figure 2 a is a schematic diagram without the aluminum layer. Figure 2 b is a schematic diagram showing the unevenness of the aluminum layer. Figure 2 c is a schematic diagram of the uniform aluminum layer obtained in this disclosure. For those skilled in the art, the uniformity of the film can be determined by the SEM scan image.

[0024] In some embodiments, the thickness of the aluminum-nitrogen-silicon atomic bond layer is 1-10 angstroms. This thickness design allows the aluminum layer to achieve a more uniform effect. It should be noted that the thin layer can be observed to have a uniformly distributed atomic layer structure through transmission electron microscopy (TEM) interface testing.

[0025] In some embodiments, a first buffer layer is grown on the aluminum layer. The first buffer layer is an aluminum nitride (AlN) buffer layer with a thickness between 100 nm and 300 nm. The surface roughness of the AlN is less than 1 nm as measured by atomic force microscopy (AFM).

[0026] In some embodiments, in order to better reduce the interfacial tension caused by lattice mismatch between the Si substrate and the GaN epitaxial layer, reduce the dislocation density of the GaN epitaxial layer, and improve the crystal quality of the epitaxial wafer, the thickness of the AlN buffer layer is 200 nm.

[0027] For example, such as Figure 3 As shown, an AlxGa1-xN composition-gradient high-resistivity stress transfer layer 124 is grown on the first buffer layer 123. The high-resistivity stress transfer layer 124 comprises a multilayer AlGaN monolayer structure with a graded Al composition.

[0028] In some embodiments, in order to better adjust the stress distribution in the epitaxial layer and avoid defects and cracks in the epitaxial layer, the high-resistivity stress transfer layer is a six-layer AlGaN monolayer structure with graded Al composition, wherein the Al composition of the six AlGaN monolayers from the substrate to the high-resistivity stress transfer layer is 86%, 75%, 50%, 38%, 25%, and 15%, respectively.

[0029] It should be noted that the preparation methods for AlGaN monolayers with different Al compositions via MOCVD epitaxial growth are as follows:

[0030] (1) The growth conditions for 86% AlGaN monolayer were as follows: growth temperature of 1050~1080℃, growth pressure of 50~75mbar, trimethylgallium (TMGa) flow rate of 18 sccm, TMAl flow rate of 580 sccm, and NH3 flow rate of 1400 sccm; growth time of 10 min and thickness of about 150 nm.

[0031] (2) The growth conditions for 75% AlGaN monolayer are as follows: growth temperature is 1050~1080℃, growth pressure is 50~75mbar, TMGa is introduced at a flow rate of 30 sccm, TMAl is introduced at a flow rate of 500 sccm, and NH3 is introduced at a flow rate of 1400 sccm; growth time is 15min and thickness is about 250 nm.

[0032] 3) The growth conditions for 50% AlGaN monolayer are as follows: growth temperature is 1050~1080℃, growth pressure is 50~75mbar, TMGa is introduced at a flow rate of 58 sccm, TMAl at a flow rate of 450 sccm, and NH3 is introduced at a flow rate of 1600 sccm; growth time is 35min and the thickness is about 600 nm.

[0033] (4) The growth conditions for 38% AlGaN monolayer are as follows: growth temperature is 1050~1080℃, growth pressure is 50~75mbar, TMGa is introduced at a flow rate of 76 sccm, TMAl is introduced at a flow rate of 400 sccm, and NH3 is introduced at a flow rate of 1600 sccm; growth time is 30 min and thickness is about 500 nm.

[0034] (5) The growth conditions for 25% AlGaN monolayer are as follows: growth temperature is 1050~1080℃, growth pressure is 50~75mbar, TMGa is introduced at a flow rate of 150 sccm, TMAl is introduced at a flow rate of 300 sccm, and NH3 is introduced at a flow rate of 2000 sccm; growth time is 20 min and thickness is about 500 nm.

[0035] (6) An AlGaN monolayer with 15% Al content was grown at a temperature of 1050~1080℃ and a growth pressure of 50~75mbar. TMGa was introduced at a flow rate of 280 sccm and TMAl at a flow rate of 300 sccm, and NH3 was introduced at a flow rate of 2000 sccm. The growth time was 45min and the thickness was about 900 nm.

[0036] In some embodiments, a high-resistivity buffer layer 125 is grown on the high-resistivity stress transfer layer 124. To reduce leakage current in the high-resistivity buffer layer, the high-resistivity buffer layer is an unintentionally carbon (C)-doped high-resistivity GaN layer. To obtain an excellent high-resistivity GaN layer and improve device performance, the high-resistivity GaN layer is grown in MOCVD using a low-pressure, low-temperature growth method to obtain the undoped GaN layer. Under the conditions of a growth surface temperature of 950~980℃, a reaction chamber gas pressure of 50mbar, a flow rate of 300 sccm of TMGa is introduced, and 11000 sccm of NH3 is introduced simultaneously. The growth rate is approximately 2.8 μm / h, the growth time is 42 min, and the thickness is approximately 2000 nm.

[0037] In some embodiments, a channel layer 126 is grown on a high-resistivity buffer layer 125, and an AlGaN barrier layer 127 is grown on the channel layer 126. To improve the film quality at the interface between the channel layer and the AlGaN barrier layer, thereby enhancing the mobility of the two-dimensional electron gas and forming a device with superior performance in all aspects, the following method was used to grow the channel layer and AlGaN barrier layer using MOCVD: Under the conditions of a surface temperature of 1070–1090 °C and a reaction chamber pressure of 200 mbar, TMGa was introduced at a flow rate of 220 sccm, and NH3 was introduced simultaneously at a flow rate of 32000 sccm. The growth rate was approximately 1.8–2 μm / h, the growth time was 7 min, and the thickness was approximately 200–250 nm, thus obtaining the channel layer. The method for further growing the AlGaN barrier layer on the channel layer was as follows: Under the conditions of a surface temperature of 1060–1075 °C, a reaction chamber pressure of 75–150 mbar, and an NH3 flow rate of 12000 sccm, only TMAl was introduced at a flow rate of 380 sccm, and the growth time lasted 12 s, resulting in an epitaxial layer with a thickness of 1 nm. An AlN intercalation was performed; subsequently, a flow rate of 160 sccm for TMGa and 380 sccm for TMAl was simultaneously introduced onto the AlN intercalation to generate an AlGaN barrier layer with a solid composition of 25%. The growth time was approximately 90 s, and an AlGaN barrier layer with a thickness of 20 nm and a composition of approximately 25% was finally obtained.

[0038] In some embodiments, to prevent oxidation of the AlGaN barrier layer surface and to improve device stability, a capping layer 128 is provided on the AlGaN barrier layer. The capping layer can be a P-GaN capping layer, a GaN capping layer, or a SiNx capping layer, depending on the product type. For example, a GaN capping layer or a SiNx capping layer can be selected for a D-mode HEMT (depletion-mode HEMT); a P-GaN layer can be selected for an E-mode HEMT (enhancement-mode HEMT). Those skilled in the art can configure the capping layer according to the specific circumstances.

[0039] The GaN capping layer growth conditions are as follows: the growth surface temperature is 1060~1075℃, the reaction chamber pressure and NH3 flow rate are as follows, the flow rate of TMGa is 160 sccm, the growth time is 15s, and a GaN capping layer with a thickness of 2 nm is obtained.

[0040] The growth conditions for the P-GaN capping layer are as follows: on the AlGaN barrier layer, the surface temperature is reduced to 940~990℃, the reaction chamber pressure is 250~300mbar, and the NH3 flow rate is 35000~40000sccm. At the same time, TMGa is introduced at a flow rate of 300 sccm and magnesia (Cp2Mg) at a flow rate of 380 sccm. The growth time is 15 min, and a P-GaN capping layer with a thickness of 80~120nm is obtained.

[0041] The growth conditions for the SiNx capping layer are as follows: on the AlGaN barrier layer, the surface temperature is reduced to 1000~1020℃, the reaction chamber pressure is 120~150 mbar, and the NH3 flow rate is 40000~45000 sccm. Then, 290 sccm of SiH4 is introduced, and the growth time is 40 min to obtain a SiNx capping layer with a thickness of 5~20 nm.

[0042] For example, such as Figure 4 As shown, the HEMT device 200 includes: a substrate 110; a compound semiconductor composite structure 120 disposed on the substrate 110 and generating a two-dimensional electron gas (2DEG); wherein the semiconductor composite structure 120 includes a thin layer 121 containing aluminum nitride silicon atomic bonds disposed on the substrate 110, an aluminum layer 122 disposed on the thin layer, and a first buffer layer 123 disposed on the aluminum layer 122; and an electrode layer 140 disposed on the compound semiconductor composite structure 120.

[0043] A thin layer of aluminum-nitrogen-silicon atoms bonded to the substrate provides sufficient migration time for aluminum atoms on the substrate surface, effectively reducing the accumulation of high-density spiral dislocations in subsequent epitaxial layers. It also makes the aluminum layer more uniform, preventing silicon-gallium reactions and subsequent melting-back effects at uneven aluminum layers during epitaxial growth, thus avoiding the formation of melting-back pits on the surface. This effectively reduces mismatch and defects at the substrate-epitaxy interface, minimizing current collapse caused by trap effects in later GaNHEMT devices, reducing static current leakage, and improving the performance of HEMT devices from the epitaxial layer level.

[0044] In some embodiments, in order to obtain a device with stable performance, the HEMT device 200 further includes a dielectric layer 130 disposed on the semiconductor composite layer 120. The positions of the electrode layer 140 are etched on the dielectric layer 130. The electrode layer 140 includes a drain electrode 141, a gate electrode 142, and a source electrode 143. The drain electrode 141 and the source electrode 142 are disposed on both sides of the gate electrode 143. The compound semiconductor layer 120 further includes, in sequence, a first buffer layer 123, a high-resistivity stress transfer layer 124, a high-resistivity buffer layer 125, a channel layer 126, and an AlGaN barrier layer 127 along the direction from the electrode layer 140 on the substrate 110. A two-dimensional electron gas (2DEG) exists between the channel layer 126 and the AlGaN barrier layer 127.

[0045] It should be noted that the structure of HEMT devices is not strictly limited. In practical applications, as long as a uniform aluminum layer can be achieved through a thin layer containing aluminum-nitrogen-silicon atomic bonds, the performance of the HEMT device can be improved from the epitaxial layer perspective. No restrictions are placed on the structure of the HEMT device here. (The fabrication of HEMT devices can be obtained by those skilled in the art using the above-described epitaxial layer fabrication methods).

[0046] Another aspect of this application provides a method for fabricating a semiconductor epitaxial structure, used to prepare the aforementioned epitaxial structure 100, such as... Figure 5 As shown, it includes:

[0047] S10: Provide a substrate 110, which is a silicon substrate. It should be noted that the silicon substrate is not limited to high or low resistance, or N-type or P-type.

[0048] S20: As Figure 6 As shown, a thin layer 121 containing aluminum nitrogen silicon atomic bonds is formed on a substrate 110, and an aluminum layer 122 is formed on the thin layer 121;

[0049] In some embodiments, the thin layer is formed from several layers of aluminum nitride silicon atoms, with a thickness of about 1-10 angstroms.

[0050] The thin layer provides sufficient migration time for aluminum atoms on the substrate surface, effectively reducing the accumulation of high-density spiral dislocations in subsequent epitaxial layers. It also ensures a more uniform aluminum layer on the thin layer, preventing the formation of silicon and gallium remelting effects and surface melting pits caused by silicon-gallium reactions at uneven aluminum layer locations during subsequent epitaxial growth. It should be noted that those skilled in the art can observe the uniformly distributed atomic layer structure of the thin layer through TEM interface testing.

[0051] In some embodiments, the step of forming a thin layer containing aluminum-nitrogen-silicon atomic bonds on a substrate and forming an aluminum layer on the thin layer includes:

[0052] A nitrogen source and an aluminum source are alternately supplied on the substrate multiple times, wherein the nitrogen source is supplied first and then the aluminum source is supplied, and the supply of the aluminum source is turned off when the supply of the nitrogen source is turned on, and the supply of the nitrogen source is turned off when the supply of the aluminum source is turned on.

[0053] Specifically, this embodiment uses MOCVD for deposition, wherein the nitrogen source is trimethylaluminum (TMAl) and the nitrogen source is ammonia (NH3). Those skilled in the art can choose the epitaxial growth method and source material according to the actual situation, and there are no limitations here.

[0054] It should be noted that the alternating supply of nitrogen and aluminum sources refers to the following process in MOCVD: first, NH3 is introduced, then the NH3 source is cut off, then TMAl is introduced, then the TMAl source is cut off, then NH3 is introduced again, then the NH3 source is cut off again, and so on, until a thin layer containing aluminum-nitrogen-silicon atomic bonds is formed on the substrate, and an aluminum layer is formed on the thin layer.

[0055] In some embodiments, the nitrogen and aluminum sources are provided by a dual-pulse growth method (alternating introduction of NH3 and TMAl). This method can not only form a uniform aluminum layer, but also avoid the problem that NH3 easily reacts with the substrate Si under high temperature conditions to form amorphous SiNx, which affects the crystal quality of subsequent GaN growth.

[0056] In some embodiments, the step of alternately providing a nitrogen source and an aluminum source on a substrate multiple times includes:

[0057] A first step of providing a nitrogen source on a substrate for a first predetermined duration; a second step of alternately providing an aluminum source and a nitrogen source for a second predetermined duration after the first step; and a third step of providing an aluminum source for a third predetermined duration after the second step.

[0058] To ensure a more uniform aluminum layer, the supply of nitrogen and aluminum sources can be divided into three steps: NH3 is introduced in the first step, TMAl and NH3 are introduced alternately multiple times in the second step, and TMAl is introduced in the third step. Those skilled in the art can adjust the first predetermined duration, the second predetermined duration, the third predetermined duration, and the flow rates of the nitrogen and aluminum sources according to actual needs, such as the thickness of the aluminum layer to be grown and the stress matching with the selected substrate or subsequent epitaxial layer growth.

[0059] In some embodiments, the second step of alternately providing an aluminum source and a nitrogen source over a second predetermined duration includes: periodically and alternately providing an aluminum source and a nitrogen source over a second predetermined duration, wherein the duration for providing the aluminum source is t1 and the duration for providing the nitrogen source is t2.

[0060] It should be noted that periodically alternating the supply of aluminum and nitrogen sources means first introducing the aluminum source, then cutting it off, then introducing the nitrogen source, and then cutting it off again, which constitutes one cycle. Furthermore, the quality of the aluminum-nitrogen-silicon atomically bonded thin layer formed can be adjusted by changing the TMA1 introduction time t1 and the NH3 introduction time t2, combined with other process parameters such as chamber pressure, temperature, and flow rate.

[0061] In some embodiments, in two adjacent cycles, the amount of aluminum source provided in the previous cycle is lower than the amount of aluminum source provided in the next cycle.

[0062] By gradually increasing the amount of aluminum in different cycles, it is ensured that after the introduction of NH3 in the first step, the N atoms can further effectively bond with Al-Si to form Al-N-Si bonds. This also gives the Al atoms sufficient migration time on the substrate surface, solving the problem of uneven Al pre-passing caused by the low mobility of Al atoms. It also avoids the problem that NH3 under high temperature conditions can easily react with Si to form amorphous SiNx, which would affect the crystal quality of subsequent GaN growth.

[0063] In some embodiments, to better form Al-N-Si bonds and thus a uniform aluminum layer, the following epitaxial growth conditions are used: TMAl is introduced in a pulsed manner at a flow rate of 5 sccm within a reaction chamber at 50–100 mbar and 700–800°C for a duration t1 of 15 s. The flow rate of TMAl is increased by 5 sccm per pulse with each additional pulse. Specifically, in the first cycle t1, a flow rate of 5 sccm of TMAl is introduced; in the second cycle t1, a flow rate of 10 sccm of TMAl is introduced; in the third cycle t1, a flow rate of 15 sccm of TMAl is introduced, and so on.

[0064] In some embodiments, in two adjacent cycles, the amount of nitrogen source provided in the previous cycle is higher than the amount of nitrogen source provided in the next cycle.

[0065] By gradually reducing the amount of nitrogen in different cycles, it is ensured that after the introduction of NH3 in the first step, N atoms can further effectively bond with Al-Si to form Al-N-Si bonds. This also gives Al atoms sufficient migration time on the substrate surface, solving the problem of uneven Al pre-passing caused by the low mobility of Al atoms. It also avoids the problem that NH3 under high temperature conditions can easily react with Si to form amorphous SiNx, which would affect the crystal quality of subsequent GaN growth.

[0066] In some embodiments, to better form Al-N-Si bonds and thus a uniform aluminum layer, the following epitaxial growth conditions are used: NH3 is introduced in a pulsed manner at a flow rate of 1000-50 smol in the reaction chamber at 50-100 mbar and 700-800°C, with an NH3 introduction time t2 of 5 s. The NH3 flow rate is decreased by 200 sccm per single pulse as the cycle increases.

[0067] In some embodiments, the number of cycles within the second predetermined duration is 1-20 times.

[0068] The periodic pulse provides Al atoms with sufficient migration time on the substrate surface, solving the problem of uneven Al pre-passing caused by the low mobility of Al atoms. It also avoids the problem that NH3 under high temperature NH3 conditions can easily react with Si to form amorphous SiNx, which affects the crystal quality of subsequent GaN growth.

[0069] In some embodiments, the number of cycles within the second predetermined duration is 6. This number of cycles, combined with the growth conditions of pulsed aluminum and nitrogen sources described above, can form a more uniform aluminum layer.

[0070] In some embodiments, the first step of providing a nitrogen source on the substrate for a first predetermined duration includes: providing NH3 at a flow rate of 1200 sccm on the substrate for a duration of 5 s.

[0071] After nitriding the substrate by introducing NH3 in a pulsed manner, the second step is performed. This ensures that the N atoms in the pulsed nitriding process can further effectively enhance Al-Si bonding and form Al-N-Si bonds. Specifically, the growth method is as follows: maintaining the reaction chamber at 50~100 mbar and 700~800℃, NH3 is introduced at 1200 sccm for 5 s.

[0072] In some embodiments, the substrate is desorbed at high temperature before the first step. Specifically, the growth method is as follows: under a hydrogen (H2) atmosphere at 50~100 mbar and 1070~1105℃ in the reaction chamber, the SiO2 on the surface of the Si substrate is desorbed at high temperature for 3~10 minutes to form a step flow with clear stripes of consistent size and spacing, thereby achieving the effect of removing oxygen atoms and other impurities from the surface of the Si substrate.

[0073] In some embodiments, the third step of providing the aluminum source for a third predetermined duration includes:

[0074] Provide an aluminum source with a flow rate of 30 sccm for 2-4 minutes.

[0075] In order to form an aluminum layer, those skilled in the art can adjust the process parameters of the third step, such as the flow rate, inlet time, cavity pressure, and temperature of TMA1, according to the desired properties of the aluminum layer, such as thickness.

[0076] S30: As Figure 1 As shown, a first buffer layer 123 is formed on the aluminum layer 122.

[0077] The first buffer layer is an aluminum nitride (AlN) buffer layer with a thickness between 100 nm and 300 nm. The surface roughness of AlN measured by atomic force microscopy (AFM) is less than 1 nm. This is to better reduce the interfacial tension caused by lattice mismatch between the Si substrate and the GaN epitaxial layer, reduce the dislocation density of the GaN epitaxial layer, and improve the crystal quality of the epitaxial wafer.

[0078] In some embodiments, the AlN buffer layer comprises a growth thickness of approximately 200 nm. It includes a low-temperature AlN layer with a growth thickness of 15–30 nm and a high-temperature AlN layer with a growth thickness of approximately 200 nm. Specifically, the low-temperature AlN layer is grown at 900–950 °C, with 200 sccm of TMAl and 3000–3500 sccm of NH3 introduced, for a growth time of 5 min; subsequently, the temperature is increased to 1100–1150 °C, the reaction chamber pressure is 70 mbar, 250–300 sccm of TMAl and 3000–10000 sccm of NH3 are introduced, the growth rate is approximately 0.3 μm / h, the growth time is 40 min, and a high-temperature AlN layer with a growth thickness of approximately 200 nm is formed.

[0079] The above description is merely a preferred embodiment of this disclosure, but the scope of protection of this disclosure is not limited thereto. Any person skilled in the art can easily make changes or variations within the technical scope disclosed in this disclosure, and such changes or variations should be included within the scope of protection of this disclosure. Therefore, the scope of protection of this disclosure should be determined by the scope of the claims. As long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. This disclosure is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for preparing a semiconductor epitaxial structure, characterized in that, include: Provide a substrate; A thin layer containing aluminum-nitrogen-silicon atomic bonds is formed on a substrate, and a uniform aluminum layer is formed on the thin layer; A first buffer layer is formed on the aluminum layer; The steps of forming a thin layer containing aluminum-nitrogen-silicon atomic bonds on a substrate and forming an aluminum layer on the thin layer include: A nitrogen source and an aluminum source are alternately supplied on the substrate multiple times, wherein the nitrogen source is supplied first and then the aluminum source is supplied, the supply of the aluminum source is turned off when the supply of the nitrogen source is turned on, and the supply of the nitrogen source is turned off when the supply of the aluminum source is turned on. The step of alternately providing a nitrogen source and an aluminum source on the substrate multiple times includes: The first step of providing a nitrogen source on the substrate for a first predetermined duration; Following the first step, a second step involves alternately providing aluminum and nitrogen sources for a second predetermined duration. Following the second step, a third step is performed to provide the aluminum source for a predetermined duration. The second step, which involves alternately providing the aluminum source and the nitrogen source over a second predetermined period of time, includes: An aluminum source and a nitrogen source are provided alternately and periodically over a second predetermined period of time, wherein the duration of providing the aluminum source is t1 and the duration of providing the nitrogen source is t2; in two adjacent periods, the amount of aluminum source provided in the previous period is less than the amount of aluminum source provided in the next period; in two adjacent periods, the amount of nitrogen source provided in the previous period is greater than the amount of nitrogen source provided in the next period.

2. The method for preparing a semiconductor epitaxial structure according to claim 1, characterized in that... The number of cycles within the second predetermined duration is 1-20.

3. The method for preparing a semiconductor epitaxial structure according to claim 1, characterized in that, The first step of providing a nitrogen source on the substrate for a first predetermined duration includes: NH3 is supplied to the substrate at a flow rate of 1200 sccm for a duration of 5 seconds.

4. The method for preparing a semiconductor epitaxial structure according to claim 1, characterized in that, The third step of providing the aluminum source for a third predetermined duration includes: Provide an aluminum source with a flow rate of 30 sccm for 2-4 minutes.

5. A semiconductor epitaxial structure, characterized in that, Prepared by the method according to any one of claims 1-4, comprising: Substrate; A thin layer containing aluminum-nitrogen-silicon atomic bonds is disposed on the substrate; A uniform aluminum layer is disposed on the thin layer; A first buffer layer is disposed on the aluminum layer.

6. The semiconductor epitaxial structure according to claim 5, characterized in that, The thickness of the thin layer is 1-10 angstroms.

7. A HEMT device, characterized in that, include: Substrate; A compound semiconductor composite structure disposed on the substrate and generating a two-dimensional electron gas; wherein the semiconductor composite structure comprises a thin layer containing aluminum-nitrogen-silicon atomic bonds disposed on the substrate, a uniform aluminum layer disposed on the thin layer, and a first buffer layer disposed on the aluminum layer; the substrate and the semiconductor composite structure are prepared by the method according to any one of claims 1-4; An electrode layer is disposed on the compound semiconductor composite structure.

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