Radio frequency HEMT device structure and method of making the same

Abstract

The present application discloses a radio frequency HEMT device structure and a method for preparing the same. The method comprises: forming a GaN sacrificial layer, an AlN back barrier layer, an AlN back barrier layer, and a GaN sacrificial layer on a first substrate. x1 Ga 1‑x1 N channel layer, Al x2 Ga 1‑x2 The invention relates to a method for forming an epitaxial structure by forming an AlN back barrier layer, wherein 0≤x1≤1, 0<x2<0.4; irradiating the GaN sacrificial layer with a laser to at least partially decompose the GaN sacrificial layer, thereby separating the epitaxial structure from the first substrate; and then bonding the epitaxial structure to the second substrate via a thermally conductive connection structure, with the AlN back barrier layer positioned relative to the second substrate. The RF HEMT device structure of the present application has low dissipation and excellent heat dissipation performance under high-frequency operation, which can effectively meet the high voltage and high power application requirements of high-power RF devices, and has a simple manufacturing process.

Description

Technical Field

[0001] The present application specifically relates to a radio frequency HEMT device structure and a preparation method thereof, belonging to the field of semiconductor technology. Background Art

[0002] GaN RF devices have attracted widespread attention due to their higher integration, smaller size, lower weight, and lower power consumption. They can replace traditional silicon-based and GaAs-based devices on a large scale and be used in radar, electronic countermeasures, and communication systems. Generally speaking, if you want to increase the power density of GaN microwave power devices, you need to meet the following two prerequisites:

[0003] 1)Higher crystal quality and better heat dissipation characteristics;

[0004] 2) Lower trapping effect to avoid current collapse at high frequencies.

[0005] Existing HEMT devices use a GaN buffer layer, which requires GaN to be doped with C or Fe, thus introducing a large number of deep energy level defects.

[0006] Secondly, to ensure the high breakdown voltage and frequency characteristics of GaN HEMTs, high-quality epitaxial films are crucial. Due to their low lattice mismatch, HEMTs are currently primarily grown epitaxially on sapphire or silicon carbide substrates. However, sapphire and silicon carbide have poor thermal conductivity, which affects the heat dissipation characteristics of HEMT devices under high-power operating conditions.

[0007] To address this issue, researchers have proposed a HEMT epitaxial structure based on AlN single crystals, which involves epitaxially growing an AlN / GaN / AlN quantum well HEMT structure on an AlN single crystal substrate, with the GaN channel layer having a thickness between 15 and 22 nm. AlN single crystal substrates have good thermal conductivity, and homoepitaxial AlN buffer layers grown on them can minimize the dislocation density of the thin film and improve crystal quality. Researchers have proposed a HEMT device structure based on a diamond substrate, which utilizes the high thermal conductivity of the diamond substrate. By using a single crystal AlN layer as an intermediate insertion layer, the interfacial thermal resistance between the GaN layer and the diamond substrate and the insertion layer thermal resistance can be significantly reduced, thereby improving the heat dissipation capacity of the wafer. Researchers have also proposed a method for transferring flip-chip HEMT devices. By adopting a specific electrochemical stripping method, the bonding of flip-chip GaN HEMT array devices to the target substrate is achieved, enabling lossless and efficient device stripping and device array transfer.

[0008] However, all of the above existing solutions have some shortcomings. For example, although the use of AlN single crystal substrates to prepare HEMT RF devices can improve their heat dissipation characteristics, AlN single crystals are small in size and expensive, making them unsuitable for large-scale mass production. For another example, diamond substrates offer the best heat dissipation performance, but single crystal diamonds are small in size. Direct epitaxial HEMT structures on polycrystalline diamond introduce a large number of threading dislocations and degrade device performance due to the lattice mismatch between nitride and diamond. For another example, the bonding of HEMTs to high thermal conductivity substrates based on electrochemical etching of sacrificial layers suffers from uneven etching, low yield, and complex processes. Summary of the Invention

[0009] The purpose of this application is to provide a radio frequency HEMT device structure and a preparation method thereof to overcome the shortcomings of the prior art.

[0010] To achieve the aforementioned invention objectives, the technical solutions adopted in this application include:

[0011] A first aspect of the present application provides a method for preparing a radio frequency HEMT device structure, comprising:

[0012] A GaN sacrificial layer, an AlN back barrier layer, an AlN back barrier layer, and a GaN layer are sequentially formed on the first substrate. x1 Ga 1-x1 N channel layer, Al x2 Ga 1-x2 N barrier layer, where 0≤x1≤1, 0<x2<0.4, forming an epitaxial structure;

[0013] The GaN sacrificial layer is irradiated with a laser to at least partially decompose the GaN sacrificial layer, thereby separating the epitaxial structure from the first substrate. The epitaxial structure and the second substrate are then bonded to each other via a thermally conductive connection structure, and the AlN back barrier layer is arranged opposite to the second substrate, wherein the thermal conductivity of the second substrate is greater than the thermal conductivity of the first substrate.

[0014] In one embodiment, the preparation method specifically includes: forming an AlN seed layer with a thickness of 50-500 nm on a GaN sacrificial layer using a polycrystalline magnetron sputtering process, wherein the magnetron sputtering temperature used is 300-500°C, the gas pressure is 0.1-1 Pa, the Ar and N2 flow ratio is 0-1, and the power supply power is 100W-800W, and then continuing to grow an AlN film on the AlN seed layer by at least MOCVD or MBE process to form the AlN back barrier layer.

[0015] Among them, by depositing a polycrystalline magnetron sputtered AlN seed layer on the GaN sacrificial layer, on the one hand, the magnetron sputtering temperature is low, so it covers the GaN sacrificial layer and avoids the decomposition of GaN therein; on the other hand, the magnetron sputtered AlN serves as the seed layer for growing a high-temperature AlN buffer layer (back barrier layer), effectively improving the crystal quality of AlN and avoiding problems such as surface cracking caused by lattice mismatch between GaN and AlN.

[0016] Furthermore, the preparation method specifically includes: continuing to grow an AlN film on the AlN seed layer using an MOCVD process, and controlling the growth temperature to 1100-1300° C., the gas pressure to 20-200 mbar, and the V / III ratio to 20-500, thereby forming the AlN back barrier layer.

[0017] In one embodiment, the preparation method specifically includes: forming the AlN back barrier layer on the GaN sacrificial layer by at least an MOCVD or MBE process, and controlling the growth temperature to gradually increase from the growth temperature of the GaN sacrificial layer to 1100-1300°C at a heating rate of 5-80°C / min during the growth process. This gradual growth temperature gradient, i.e., first depositing at a low temperature and then gradually increasing the temperature, can avoid GaN decomposition during the AlN growth process, while alleviating the thermal stress mismatch between GaN and AlN, thereby reducing thermal stress and improving film morphology.

[0018] In one embodiment, the preparation method specifically includes: after separating the epitaxial structure from the first substrate, combining the epitaxial structure with a transfer substrate, and placing the AlN back barrier layer away from the transfer substrate, and then combining the epitaxial structure with the second substrate through a thermally conductive connection structure, and then removing the transfer substrate.

[0019] Furthermore, the first substrate includes a sapphire substrate, etc., but is not limited thereto.

[0020] Furthermore, the second substrate includes one or more combinations of diamond, AlN ceramics, or metal plates, but may also be other substrates with high thermal conductivity.

[0021] Furthermore, the transfer substrate includes one or more of PET, PDMS or single crystal silicon, but is not limited thereto.

[0022] In one embodiment, the thickness of the GaN sacrificial layer is 10-300 nm.

[0023] In one embodiment, the Al x1 Ga 1-x1 The thickness of the N-channel layer is 50-500 nm.

[0024] In one embodiment, the thickness of the AlN back barrier layer is 1-4 μm.

[0025] In one embodiment, the Al x2 Ga 1-x2 The thickness of the N barrier layer is 10-30 nm.

[0026] Furthermore, the thermally conductive connection structure may be formed of metal bonding materials, thermally conductive adhesive, etc.

[0027] In one embodiment, the preparation method further comprises: x2 Ga 1-x2 A cap layer is formed on the N barrier layer. Further, the material of the cap layer may include but is not limited to GaN.

[0028] In one embodiment, the preparation method further comprises: x1 Ga 1-x1 N channel layer and Al x2 Ga 1-x2 A space layer is formed between the N barrier layers. Furthermore, the material of the space layer, also called the insertion layer, may include but is not limited to AlN.

[0029] In one embodiment, the preparation method further comprises: forming a source, a drain and a gate on the epitaxial structure.

[0030] A second aspect of the present application provides an intermediate structure for preparing a radio frequency HEMT device structure, comprising:

[0031] first substrate,

[0032] The epitaxial structure comprises a GaN sacrificial layer, an AlN back barrier layer, an AlN layer and a GaN layer formed in sequence on the first substrate. x 1Ga 1- x1 N channel layer, Al x2 Ga 1-x2 N barrier layers, wherein 0≤x1≤1, 0<x2<0.4.

[0033] In one embodiment, the thickness of the GaN sacrificial layer is 10-300 nm.

[0034] In one embodiment, the GaN sacrificial layer can be at least partially decomposed by laser irradiation of a predetermined wavelength and power. Furthermore, the AlN back barrier layer can exist stably under the laser irradiation of the predetermined wavelength and power.

[0035] In one embodiment, the first substrate includes a sapphire substrate, etc., but is not limited thereto.

[0036] In this application, considering the high-frequency application requirements of RF HEMT devices in the C, X, and Ku bands, AlN is used to form a back barrier layer to avoid problems such as the trap effect caused by the doping of the buffer layer of existing GaN HEMTs. However, using AlN as a buffer layer makes it difficult to achieve the peeling and transfer of the epitaxial structure growth substrate. To this end, this application adopts the method of growing AlN, which serves as both a buffer layer and a back barrier layer, on a GaN sacrificial layer. By taking advantage of the fact that GaN is easily decomposed by laser irradiation, while AlN is basically not decomposed by laser, the laser peeling of the growth substrate is conveniently achieved, and the AlN back barrier layer is well protected. On the other hand, although laser lift-off of the GaN sacrificial layer has the advantages of large area and high yield, depositing high-quality AlN on the GaN sacrificial layer requires overcoming at least the following difficulties: 1) The lattice constant of AlN is smaller than that of GaN, so directly growing an AlN buffer layer on the GaN sacrificial layer using methods such as MOCVD will result in large tensile stress, causing cracking of the AlN film; 2) The deposition temperature of AlN is relatively high (>1100°C), so directly depositing AlN on the GaN sacrificial layer will cause GaN decomposition. The present application effectively solves the above problems and obtains a high-quality AlN buffer layer by growing an AlN buffer layer on the GaN sacrificial layer using the above-mentioned polycrystalline magnetron sputtering or temperature gradient growth method.

[0037] A third aspect of the present application provides a radio frequency HEMT device structure, comprising:

[0038] The second substrate,

[0039] The epitaxial structure is combined with the second substrate through a heat-conducting connection structure, and includes an AlN back barrier layer, an AlN back barrier layer, and an AlN back barrier layer. x1 Ga 1-x1 N channel layer, Al x 2Ga 1-x2 N barrier layers, wherein 0≤x1≤1, 0<x2<0.4.

[0040] In one embodiment, the AlN back barrier layer is deposited on the GaN sacrificial layer by a polycrystalline magnetron sputtering process, wherein the magnetron sputtering temperature used is 300-500°C, the gas pressure is 0.1-1 Pa, the Ar and N2 flow ratio is 0-1, and the power supply power is 100W-800W.

[0041] In one embodiment, the AlN back barrier layer is grown on the GaN sacrificial layer at least by MOCVD or MBE process, and during the growth process, the growth temperature is gradually increased to 1100-1300° C. at a heating rate of 5-80° C. / min.

[0042] In one embodiment, the second substrate includes one or more of diamond, AlN ceramic, or a metal plate, but is not limited thereto.

[0043] In one embodiment, the thickness of the GaN sacrificial layer is 10-300 nm.

[0044] In one embodiment, the Al x1 Ga 1-x1 The thickness of the N-channel layer is 50-500 nm.

[0045] In one embodiment, the thickness of the AlN back barrier layer is 1-4 μm.

[0046] In one embodiment, the Al x2 Ga 1-x2 The thickness of the N barrier layer is 10-30 nm.

[0047] See also Figure 1 The figure shows a schematic diagram of a radio frequency HEMT device structure in a typical embodiment of the present application, which includes a second substrate 1 as a high thermal conductivity base and an epitaxial structure arranged on the second substrate 1, the epitaxial structure including an AlN back barrier layer 3, a GaN or AlGaN channel layer 4 and an AlN back barrier layer 5 arranged in sequence in a direction away from the second substrate. x 2Ga 1-x2 N barrier layer 6, where 0<x2<0.4. In some cases, it is also possible to x2 Ga 1-x2 AlN insertion layer 5 is provided between N barrier layer 6. In some cases, AlN can also be inserted between x2 Ga 1-x2 A cap layer 7 and the like are provided on the N barrier layer 6 .

[0048] Furthermore, a source electrode 8 , a drain electrode 9 , and a gate electrode 10 may be provided on the epitaxial structure.

[0049] The high thermal conductivity substrate may be diamond, AlN ceramic or metal composite substrate, etc. The thickness of the GaN or AlGaN channel layer 4 may be 50-500 nm.

[0050] See also Figure 2 A process schematic diagram for preparing the RF HEMT device structure is shown, which includes the following steps:

[0051] S1, a GaN sacrificial layer 2, an AlN back barrier layer 3, a GaN or AlGaN channel layer 4 and an AlN back barrier layer 5 are sequentially grown on a large-size sapphire substrate 1' as a first substrate. x 2Ga 1-x2 The N barrier layer 6 and the like form an epitaxial structure.

[0052] The thickness of the GaN sacrificial layer 2 may be 10-300 nm.

[0053] Optionally, the source electrode 8, the drain electrode 9, and the gate electrode 10 may be manufactured on the epitaxial structure by metal sputtering or the like.

[0054] S2. If the end of the epitaxial structure combined with the substrate 1 is set as the bottom end and the other end away from the substrate 1' is set as the top end, then the transfer base 11 is combined with the top end of the epitaxial structure, and then the bottom end of the epitaxial structure is irradiated with laser to at least partially decompose the GaN sacrificial layer therein, thereby separating the substrate 1' from the epitaxial structure, thereby realizing laser peeling of the substrate 1'.

[0055] The material of the transfer substrate may be PET, PDMS, single crystal silicon, etc., but is not limited thereto.

[0056] Optionally, after the laser lift-off operation is completed, a wet cleaning process may be used to remove the Ga metal particles and defects after lift-off.

[0057] S3, transferring the epitaxial structure onto a second substrate 1, and reducing the thermal resistance between the second substrate 1 and the AlN back barrier layer 3 based on interface treatment, and finally removing the transfer base 11 on the top of the epitaxial structure.

[0058] The epitaxial structure can be fixedly combined with the second substrate 1 by metal bonding or heat-conducting adhesive bonding.

[0059] Furthermore, in the aforementioned step S1, considering the problems of high growth difficulty and low quality of AlN film when growing AlN back barrier layer 3 directly on GaN sacrificial layer 2, refer to Figure 3 and Figure 4 , the following two schemes can be used to grow the AlN back barrier layer 3, namely:

[0060] Option 1: See Figure 3, first grow a GaN sacrificial layer 2 on the first substrate 1' by MOCVD or other methods, then deposit an AlN seed layer 31 on the GaN sacrificial layer 2 by a polycrystalline magnetron sputtering process, wherein the magnetron sputtering temperature used is 300-500℃, the gas pressure is 0.1-1pa, the Ar and N2 flow ratio is 0-1, and the power supply is 100W-800W, and then continue to deposit the AlN film by MOCVD or other methods to form an AlN back barrier layer 3. Exemplarily, the MOCVD process can be used to continue to grow the AlN film on the AlN seed layer, and during the growth process, the temperature in the growth environment is controlled to be 1100-1300℃, the gas pressure is 20mbar-200mbar, and the V / III ratio is 20-500, until the AlN back barrier layer is obtained. Then continue to use MOCVD or other methods to sequentially grow the GaN or AlGaN channel layer 4 and Al on the AlN back barrier layer 3. x2 Ga 1-x2 The N barrier layer 6 and the like form an epitaxial structure.

[0061] Option 2: See Figure 4 First, a GaN sacrificial layer 2 is grown on the first substrate 1 by MOCVD or other methods, and then a temperature gradient AlN layer 31' is grown on the GaN sacrificial layer by MOCVD or MBE process. During the growth process, the growth temperature is gradually increased to 1100-1300℃ at a heating rate of 5-80℃ / min (preferably 20-60℃ / min), and then AlN is continued to grow at a growth temperature of 1100-1300℃ until an AlN back barrier layer 3' is formed. Then, a GaN or AlGaN channel layer 4 and an AlN back barrier layer 3 are sequentially grown on the AlN back barrier layer 3 by MOCVD or other methods. x 2Ga 1-x2 The N barrier layer 6 and the like form an epitaxial structure.

[0062] By adopting the above two solutions, the lattice mismatch and thermal stress mismatch between the GaN sacrificial layer and the AlN back barrier layer can be improved, thereby avoiding the decomposition of GaN during the AlN epitaxial growth process and the deterioration of the AlN epitaxial quality and morphology.

[0063] Furthermore, in the aforementioned step S3, the "interface treatment" includes: using dilute hydrochloric acid treatment to remove Ga particles on the laser-stripped surface, or removing metal residues and damage on the laser-stripped surface by mechanical-chemical polishing (CMP).

[0064] Compared with the prior art, the advantages of this application include:

[0065] (1) The RF HEMT device structure provided by using an AlN single crystal thin film based on a sapphire substrate as a buffer layer can achieve high crystal quality, low cost, good size, and no need for doping, thereby significantly reducing the impact of deep energy level defects on the material, reducing the dissipation of the device under high-frequency operation, and improving the power of the HEMT device, so that it can meet the application requirements of high voltage resistance and high power for high-power RF devices.

[0066] (2) The provided method for preparing the RF HEMT device structure adopts substrate transfer technology to transfer the HEMT device to a high thermal conductivity substrate such as diamond, so that the RF HEMT device has excellent heat dissipation properties and can effectively avoid failure at high junction temperatures.

[0067] (3) The provided method for preparing the structure of the RF HEMT device grows an AlN film on a GaN sacrificial layer by adopting methods such as polycrystalline magnetron sputtering or gradual temperature gradient growth, thereby obtaining a high-quality AlN buffer layer and enabling the growth substrate to be removed by laser stripping, thereby ensuring and improving the performance of the RF HEMT device and reducing the difficulty of its manufacturing process. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Figure 1 is a schematic diagram of a radio frequency HEMT device structure in a typical embodiment of the present application;

[0069] Figure 2 This is a schematic diagram of a manufacturing process of a radio frequency HEMT device structure in a typical embodiment of the present application;

[0070] Figure 3 Schematic diagram of forming an AlN back barrier layer based on a polycrystalline magnetron sputtering process in a typical embodiment of the present application;

[0071] Figure 4 This is a schematic diagram of forming an AlN back barrier layer based on a gradual change of growth temperature gradient in a typical embodiment of the present application. DETAILED DESCRIPTION

[0072] In view of the shortcomings of the existing technology, the inventors of this case, after long-term research and extensive practice, have proposed the technical solution of this application. The following will further explain this technical solution, its implementation process and principles.

[0073] Example 1

[0074] The structure of the RF HEMT device provided in this embodiment can be referred to Figure 1The epitaxial structure is arranged on a diamond substrate and includes an AlN ultra-wide bandgap back barrier layer with a thickness of about 2.2 μm, a GaN channel layer with a thickness of about 50 nm, an AlN insertion layer with a thickness of about 1 nm, an AlN layer with a thickness of about 25 nm, and an AlN layer with a thickness of about 10 nm. 0.22 GaN barrier layer and GaN cap layer with thickness of about 1nm. 0.22 A source electrode and a drain electrode are provided on the GaN barrier layer, and a gate electrode is provided on the GaN cap layer.

[0075] A method for preparing the radio frequency HEMT device comprises the following steps:

[0076] S1. First, a GaN sacrificial layer with a thickness of about 200nm is epitaxially grown on a sapphire substrate by an MOCVD process. Then, an AlN seed layer is deposited on the GaN sacrificial layer by a polycrystalline magnetron sputtering process, wherein the magnetron sputtering temperature is about 300°C, the gas pressure is about 0.1pa, the Ar and N2 flow ratio is about 0.5, and the power supply power is 100W. Then, an AlN film is continued to grow on the AlN seed layer by an MOCVD process, and during the growth process, the temperature in the growth environment is controlled to be about 1150°C, the gas pressure is about 100mbar, and the V / III ratio is about 150, until an AlN back barrier layer is formed to improve the lattice mismatch and thermal stress mismatch between the GaN sacrificial layer and the AlN back barrier layer, and to avoid the decomposition of GaN during the AlN epitaxial growth process and the deterioration of the AlN epitaxial quality and morphology. Subsequently, a GaN channel layer, an AlN insertion layer, an AlN back barrier layer are continued to be epitaxially grown on the AlN back barrier layer by an MOCVD process. 0.22 GaN barrier layer and GaN cap layer to obtain epitaxial wafer.

[0077] S2. Processing the epitaxial wafer to form a radio frequency HEMT device, which includes the following steps:

[0078] Step 1: Cleaning the surface of the epitaxial wafer.

[0079] 1a) Organic cleaning:

[0080] 1b) Inorganic cleaning:

[0081] Place the epitaxial wafer in a solution of H2SO4:H2O2 at a volume ratio of about 3:1 heated on a hot plate at about 100°C for about 10 minutes;

[0082] After taking it out, put it into a solution of HCl:H2O2:H2O (volume ratio) of about 1:1:5 heated on a hot plate at about 80°C for about 10 minutes;

[0083] After taking it out, rinse it in deionized water and blow it dry with nitrogen.

[0084] Step 2: Prepare source and drain electrodes on the surface of the GaN cap layer.

[0085] 2a) Photolithography of source and drain electrodes on the surface of the GaN cap layer:

[0086] Place the cleaned epitaxial wafer on a hot plate at about 95°C for pre-baking, coating, and leveling;

[0087] The cooled sample is placed in the photolithography machine, and the pattern on the mask is exposed to the sample using the alignment exposure method, which takes about 8 seconds.

[0088] The exposed sample is placed in a developer for development, cleaning and nitrogen drying;

[0089] The photolithographically processed samples were placed in an oxygen plasma cleaner to remove residual glue, and a dilute hydrochloric acid solution was used to remove oxides.

[0090] 2b) Electron beam evaporation of metal electrodes:

[0091] The sample was placed in an electron beam chamber and evaporated with Ti of about 30 nm in thickness, Al of about 120 nm in thickness, Ni of about 30 nm in thickness, and Au of about 50 nm in thickness.

[0092] The resin was removed by NMP, and the mixture was rinsed with deionized water and dried with nitrogen.

[0093] 2c) Rapidly anneal the sample to form ohmic contacts between the source and drain electrodes

[0094] Step 3: Photolithography the pattern of the device isolation region on the GaN cap layer, and isolation of the device active region is achieved by ion implantation.

[0095] 3c) Organic cleaning to remove photoresist:

[0096] Step 4: Prepare a gate electrode on the surface of the GaN cap layer.

[0097] Step 5: Separate the sapphire substrate and the HEMT epitaxial structure.

[0098] 9a) Fixing a PET transfer substrate on top of the HEMT epitaxial structure using a wafer bonder;

[0099] 9b) using a 248 nm KrF excimer laser with a pulse energy of 800 mJ to decompose the GaN sacrificial layer by laser lift-off, and removing the Ga metal particles and defects after lift-off with a diluted hydrochloric acid solution;

[0100] 9c) Transfer the epitaxial structure to a diamond substrate using a wafer bonder and remove the top PET transfer substrate.

[0101] Example 2

[0102] The structure and preparation method of a radio frequency HEMT device provided in this embodiment are substantially the same as those in Example 1, differing only in that the AlN back barrier layer is grown using a gradual temperature gradient. Specifically, the AlN back barrier layer is grown on a GaN sacrificial layer using an MOCVD process. During the growth process, the initial growth temperature is set at approximately 900°C, and the growth temperature is gradually increased to approximately 1100°C at a rate of approximately 20°C / min. Growth is then maintained at approximately 1100°C until an AlN ultra-wide bandgap back barrier layer with a thickness of approximately 2.2μm is formed.

[0103] Comparative Example 1

[0104] The preparation method of a radio frequency HEMT device provided in this comparative example is basically the same as that of Example 1, with the only difference being that the AlN back barrier layer is directly grown on the GaN sacrificial layer by an MOCVD process.

[0105] During the preparation of the devices of Examples 1-2 and Comparative Example 1, after the preparation of the AlN back barrier layer, each AlN back barrier layer was observed by scanning electron microscopy. It can be seen that the surface of the AlN back barrier layer in Examples 1-2 is smooth, with a roughness of less than 0.2 nm, and a defect density such as dislocation within 1×10 8 / cm 2 However, in Comparative Example 1, many cracks exist on the surface of the AlN back barrier layer.

[0106] Furthermore, the RF HEMT device of Example 1 achieved an output power of 9.1 W / mm at 10 GHz, a power added efficiency (PAE) of approximately 50%, and a power dissipation of approximately 6.9 W / mm. The RF HEMT device of Example 2 achieved an output power of 8 W / mm at 10 GHz, with a power added efficiency (PAE) of approximately 64%. Compared to these devices, the RF HEMT device of Comparative Example 1 achieved a maximum output power of approximately 6.5 W / mm at 10 GHz, a power added efficiency (PAE) of approximately 48%, and a power dissipation of approximately 6 W / mm.

[0107] Example 3

[0108] The structure of the RF HEMT device provided in this embodiment is basically the same as that of Example 1, with the only difference being that the thickness of the AlN back barrier layer is about 4 μm, the thickness of the GaN channel layer is about 500 nm, the thickness of the AlN insertion layer is about 2 nm, and the thickness of the GaN cap layer is about 2 nm.

[0109] The method for preparing a radio frequency HEMT device provided in this embodiment is also substantially the same as that in embodiment 1, and includes the following steps:

[0110] S1. First, a GaN sacrificial layer with a thickness of about 200nm is epitaxially grown on a sapphire substrate by an MOCVD process. Then, an AlN back barrier layer is grown on the GaN sacrificial layer by a gradual temperature gradient. Specifically, an MOCVD process is used, and the starting growth temperature is controlled to be about 950°C, and the growth temperature is controlled to gradually increase to about 1300°C at a heating rate of about 60°C / min, and then the growth temperature is maintained at 1300°C to continue growing AlN until an AlN back barrier layer with a thickness of about 4μm is formed. Thereafter, a GaN channel layer, an AlN insertion layer, an AlN back barrier layer, and an AlN back barrier layer are epitaxially grown on the AlN back barrier layer in sequence by an MOCVD process. 0.22 GaN barrier layer and GaN cap layer to obtain epitaxial wafer.

[0111] S2. Processing the epitaxial wafer to form a radio frequency HEMT device, which includes the following steps:

[0112] Step 1, cleaning the surface of the epitaxial wafer, is the same as step 1 of embodiment 1.

[0113] Step 2: Prepare source and drain electrodes on the surface of the GaN cap layer. This is the same as Step 2 in Example 1.

[0114] Step 3: Photolithography a pattern of the device isolation region on the GaN cap layer, and isolation of the device active region is achieved by ion implantation. This is the same as step 3 of embodiment 1.

[0115] Step 4: Prepare a gate electrode on the surface of the GaN cap layer, which is the same as Step 4 in Example 1.

[0116] 8a) Fabricating a 10-gate electrode pattern on the surface of the 7-GaN cap layer:

[0117] The sample was placed on a hot plate at 100 °C and pre-baked for 10 min;

[0118] The cooled sample was placed on a glue spreader for glue coating and glue spreading at 600 r / min for 6 seconds and 4000 r / min for 30 seconds. After that, the sample was placed on a hot plate at 100°C for soft drying for 2 minutes.

[0119] The cooled sample was placed in a photolithography machine for alignment of the gate electrode pattern and mask exposure for 3 seconds;

[0120] The sample after mask exposure was placed on a hot plate at 100°C and reverse baked for 100 seconds;

[0121] After the sample has cooled, it is placed in the photolithography machine for 40 seconds of flood exposure;

[0122] After developing in the developer for 55 seconds, the film was rinsed in deionized water and blown dry with nitrogen.

[0123] 8b) Forming a gate electrode by electron beam evaporation:

[0124] The sample was placed in an electron beam chamber. After the vacuum in the chamber reached below 4E-4 Pa, 30 nm of Ni and 100 nm of Au were evaporated on the sample.

[0125] The sample was placed in NMP stripping solution heated to 80°C on a hot plate and soaked for 20 minutes to peel off the photoresist and the metal on the photoresist, and then washed with deionized water and blown dry with nitrogen.

[0126] Step 5: Separate the sapphire substrate and the HEMT epitaxial structure.

[0127] 9a) Bonding a PDMS transfer substrate on top of the HEMT epitaxial structure using a wafer bonder and performing a post-heating treatment to stabilize the interface;

[0128] 9b) using a 355 nm Nd:YAG laser with a pulse energy of approximately 300 mJ to decompose the GaN sacrificial layer using laser lift-off technology, and treating the lift-off surface using CMP (chemical mechanical polishing);

[0129] 9c) Transfer the epitaxial structure to AlN ceramic using a wafer bonder and remove the top PDMS transfer substrate.

[0130] The RF HEMT device of this embodiment has an output power of approximately 7.7 W / mm, a power added efficiency (PAE) of approximately 56%, and a dissipated power of approximately 7.1 W / mm.

[0131] It should be understood that the above embodiments are merely illustrative of the technical concepts and features of this application. Their purpose is to enable those familiar with the art to understand the content of this application and implement it accordingly. They are not intended to limit the scope of protection of this application. Any equivalent changes or modifications made in accordance with the spirit and substance of this application shall be included within the scope of protection of this application.

Claims

1. A method for preparing a radio frequency HEMT device structure, characterized in that: include: forming a GaN sacrificial layer on the first substrate; forming an AlN seed layer with a thickness of 50-500 nm on the GaN sacrificial layer by a polycrystalline magnetron sputtering process, wherein the magnetron sputtering temperature is 300-500° C., the gas pressure is 0.1-1 Pa, the Ar and N2 flow ratio is 0-1, and the power supply is 100 W-800 W, and then continuing to grow an AlN film on the AlN seed layer by at least MOCVD or MBE process to form an AlN back barrier layer; Alternatively, an AlN back barrier layer is grown on the GaN sacrificial layer by at least one MOCVD or MBE process, and during the growth process, the growth temperature is controlled to start from the growth temperature of the GaN sacrificial layer and gradually increase to 1100-1300° C. at a heating rate of 5-80° C. / min; An Al is sequentially grown on the AlN back barrier layer x1 Ga 1-x1 N channel layer and an Al x2 Ga 1-x2 N barrier layer, where 0 ≤ x1 ≤ 1 and 0 < x2 < 0.4, to form an epitaxial structure; The GaN sacrificial layer is irradiated with a laser to at least partially decompose the GaN sacrificial layer, thereby separating the epitaxial structure from the first substrate. The epitaxial structure and the second substrate are then bonded to each other via a thermally conductive connection structure, and the AlN back barrier layer is arranged opposite to the second substrate, wherein the thermal conductivity of the second substrate is greater than the thermal conductivity of the first substrate.

2. The preparation method according to claim 1, characterized in that Specifically include: The AlN film is continued to grow on the AlN seed layer using an MOCVD process, and the growth temperature is controlled to be 1100-1300° C., the gas pressure is controlled to be 20 mbar-200 mbar, and the V / III ratio is controlled to be 20-500, thereby forming the AlN back barrier layer.

3. The preparation method according to claim 1, characterized in that Specifically include: After separating the epitaxial structure from the first substrate, the epitaxial structure is combined with a transfer substrate, and the AlN back barrier layer is arranged away from the transfer substrate. Thereafter, the epitaxial structure is combined with a second substrate via a thermally conductive connection structure, and then the transfer substrate is removed.

4. The preparation method according to claim 3, wherein: The transfer substrate includes one or more of PET, PDMS or single crystal silicon.

5. The preparation method according to claim 1, characterized in that Also includes: In the Al x2 Ga 1-x2 A cap layer is formed on the N barrier layer.

6. The preparation method according to claim 1, characterized in that Also includes: In the Al x1 Ga 1-x1 N channel layer and Al x2 Ga 1-x2 A space layer is formed between the N barrier layers.

7. The preparation method according to claim 1, characterized in that Also includes: A source, a drain and a gate are fabricated on the epitaxial structure.

8. The preparation method according to claim 1, wherein: The first substrate includes a sapphire substrate.

9. The preparation method according to claim 1, wherein: The second substrate includes one or more of diamond, AlN ceramics, or a metal plate.

10. The preparation method according to claim 1, characterized in that: The thickness of the GaN sacrificial layer is 10-300 nm.

11. The preparation method according to claim 1, characterized in that: The Al x1 Ga 1-x1 The thickness of the N-channel layer is 50-500 nm.

12. The preparation method according to claim 1, characterized in that: The thickness of the AlN back barrier layer is 1-4 μm.

13. The preparation method according to claim 1, characterized in that: The Al x2 Ga 1-x2 The thickness of the N barrier layer is 10-30 nm.

14. An intermediate structure for preparing a radio frequency HEMT device structure, characterized in that: include: first substrate, The epitaxial structure comprises a GaN sacrificial layer, an AlN back barrier layer, an AlN layer and a GaN layer formed in sequence on the first substrate. x1 Ga 1-x1 N channel layer, Al x2 Ga 1-x2 N barrier layers, where 0≤x1≤1, 0 <x2<0.4; The method for preparing the AlN back barrier layer includes: forming an AlN seed layer with a thickness of 50-500 nm on the GaN sacrificial layer by a polycrystalline magnetron sputtering process, wherein the magnetron sputtering temperature is 300-500° C., the gas pressure is 0.1-1 Pa, the Ar and N2 flow ratio is 0-1, and the power supply is 100 W-800 W, and then continuing to grow an AlN film on the AlN seed layer by at least MOCVD or MBE process to form the AlN back barrier layer; Alternatively, the AlN back barrier layer is formed on the GaN sacrificial layer by at least MOCVD or MBE process, and during the growth process, the growth temperature is controlled to start from the growth temperature of the GaN sacrificial layer and gradually increase to 1100-1300° C. at a heating rate of 5-80° C. / min.

15. The intermediate structure for preparing a radio frequency HEMT device structure according to claim 14, characterized in that: The thickness of the GaN sacrificial layer is 10-300 nm.

16. The intermediate structure for preparing a radio frequency HEMT device structure according to claim 14, characterized in that: The GaN sacrificial layer can be at least partially decomposed by irradiation with laser light of a predetermined wavelength and power.

17. The intermediate structure for preparing a radio frequency HEMT device structure according to claim 14, characterized in that: The first substrate includes a sapphire substrate.

18. A radio frequency HEMT device structure, characterized in that: include: The second substrate, The epitaxial structure is combined with the second substrate through a heat-conducting connection structure, and includes an AlN back barrier layer, an AlN back barrier layer, and an AlN back barrier layer. x1 Ga 1-x1 N channel layer, Al x2 Ga 1-x2 N barrier layers, where 0≤x1≤1, 0 <x2<0.4; The method for preparing the AlN back barrier layer includes: forming an AlN seed layer with a thickness of 50-500 nm on the GaN sacrificial layer by a polycrystalline magnetron sputtering process, wherein the magnetron sputtering temperature is 300-500° C., the gas pressure is 0.1-1 Pa, the Ar and N2 flow ratio is 0-1, and the power supply is 100W-800W, and then continuing to grow an AlN film on the AlN seed layer by at least MOCVD or MBE process to form the AlN back barrier layer; Alternatively, the AlN back barrier layer is formed on the GaN sacrificial layer by at least MOCVD or MBE process, and during the growth process, the growth temperature is controlled to start from the growth temperature of the GaN sacrificial layer and gradually increase to 1100-1300° C. at a heating rate of 5-80° C. / min.

19. The radio frequency HEMT device structure according to claim 18, characterized in that: The second substrate includes one or more of diamond, AlN ceramics, or a metal plate.

20. The radio frequency HEMT device structure according to claim 18, wherein: The thickness of the GaN sacrificial layer is 10-300 nm.

21. The radio frequency HEMT device structure according to claim 18, wherein: The thickness of the AlN back barrier layer is 1-4 μm.

22. The radio frequency HEMT device structure according to claim 18, wherein: The Al x1 Ga 1-x1 The thickness of the N-channel layer is 50-500 nm.

23. The radio frequency HEMT device structure according to claim 18, wherein: The Al x2 Ga 1-x2 The thickness of the N barrier layer is 10-30 nm.

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