Radio frequency HEMT device structure and preparation method thereof

Abstract

The invention discloses a radio frequency HEMT device structure and a preparation method thereof. The preparation method comprises the steps that a GaN sacrificial layer, an AlN back barrier layer, an Alx1Ga1-x1N channel layer and an Alx2Ga1-x2N barrier layer are sequentially formed on a first substrate, x1 is larger than or equal to 0 and smaller than or equal to 1, x2 is larger than 0 and smaller than 0.4, and an epitaxial structure is formed; the GaN sacrificial layer is irradiated by laser, so that at least part of the GaN sacrificial layer is decomposed, the epitaxial structure is separated from the first substrate, then the epitaxial structure and the second substrate are mutually combined through a heat conduction connection structure, and the AlN back barrier layer and the second substrate are oppositely arranged. The radio frequency HEMT device structure disclosed by the invention is low in dissipation and good in heat dissipation performance under high-frequency work, can better meet the application requirements of high voltage resistance and high power of a high-power radio frequency device, and is simple and convenient in manufacturing process.

Description

Technical Field

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

[0002] GaN RF devices have attracted widespread attention due to their higher integration, small size, weight and 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 improve the power density of GaN microwave power devices, you need to meet the following two prerequisites, namely:

[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 more deep energy level defects.

[0006] Secondly, in order to ensure the high breakdown voltage and frequency characteristics of GaN HEMT, high-quality epitaxial film is an important guarantee. Due to the low lattice mismatch, HEMT in the field is currently mainly based on sapphire or silicon carbide substrates for epitaxial growth. However, sapphire and silicon carbide have poor thermal conductivity, which affects the heat dissipation characteristics of HEMT devices under high-power working conditions.

[0007] In order to solve this problem, researchers have proposed a HEMT epitaxial structure based on AlN single crystal, which is an AlN / GaN / AlN quantum well HEMT structure epitaxially grown on an AlN single crystal substrate, in which the GaN channel layer thickness is between 15-22nm. AlN single crystal substrate has good thermal conductivity, and the homoepitaxial AlN buffer layer thereon can minimize the film dislocation density and improve the crystal quality. Researchers have proposed a HEMT device structure based on a diamond substrate, in which the high thermal conductivity of the diamond substrate is utilized. By using a single crystal AlN layer as an intermediate insertion layer, the interface 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. Other researchers have proposed a method for transferring flip-chip HEMT devices. By adopting a specific electrochemical stripping method, the bonding of the flip-chip GaN HEMT array device to the target substrate is achieved, and the lossless and efficient stripping of the device and the array transfer of the device are achieved.

[0008] However, the above existing solutions all have some shortcomings to a greater or lesser extent. For example, although the use of AlN single crystal substrates to prepare HEMT RF devices can improve their heat dissipation characteristics, the AlN single crystal is small in size and expensive, and is not suitable for large-scale mass production. For another example, the diamond substrate has the best heat dissipation performance, but the size of single crystal diamond is small, and the direct epitaxial HEMT structure on polycrystalline diamond will introduce a large number of threading dislocations and deteriorate device performance due to the lattice mismatch between nitride and diamond. For another example, the bonding of HEMT to a high thermal conductivity substrate based on the electrochemical corrosion of the sacrificial layer has problems such as uneven corrosion, low yield, and complex process. 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 deficiencies of the prior art.

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

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

[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 laser to at least partially decompose the GaN sacrificial layer, thereby separating the epitaxial structure from the first substrate, and then the epitaxial structure and the second substrate are combined with each other through 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 50-500nm 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 0.1-1pa, 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 is used as a seed layer for growing a high-temperature AlN buffer layer (back barrier layer), which effectively improves the crystal quality of AlN and avoids 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 a 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: growing the AlN back barrier layer on the GaN sacrificial layer by at least 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. By adopting this growth method with a gradual change in the growth temperature gradient, that is, first depositing a low temperature and then gradually heating up, the decomposition of GaN can be avoided during the growth of AlN, and the thermal stress mismatch between GaN and AlN can be alleviated, thereby reducing thermal stress and improving the 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 arranging 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] Further, the transfer substrate includes one or more combinations 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 50-500nm.

[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 by 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 and the like.

[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. Further, 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: manufacturing a source, a drain and a gate on the epitaxial structure.

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

[0031] The first substrate,

[0032] The epitaxial structure comprises a GaN sacrificial layer, an AlN back barrier layer, an Al 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 set wavelength and power. Further, the AlN back barrier layer can stably exist under the laser irradiation of the set wavelength and power.

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

[0036] In the present application, on the one hand, considering the high-frequency application requirements of RF HEMT devices in C, X and Ku bands, AlN is used to form a back barrier layer to avoid the trap effect and other problems caused by the buffer layer doping of the existing GaN HEMT. However, using AlN as a buffer layer makes it difficult to realize the stripping and transfer of the epitaxial structure growth substrate. To this end, the present application adopts the method of growing AlN, which is both a buffer layer and a back barrier layer, on a GaN sacrificial layer, and utilizing the characteristics that GaN is easily decomposed by laser irradiation, while AlN is basically not decomposed by laser, to conveniently realize the laser stripping of the growth substrate and to provide good protection for the AlN back barrier layer. On the other hand, although the laser stripping method of the GaN sacrificial layer has the characteristics of large area and high yield, the deposition of high-quality AlN on the GaN sacrificial layer requires at least overcoming 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 and cause 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 to decompose. The present application can effectively solve the above problems and obtain 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 a gradual change in the growth temperature gradient.

[0037] The third aspect of the present application provides a radio frequency HEMT device structure, which includes:

[0038] The second substrate,

[0039] The epitaxial structure is combined with the second substrate through a thermal conductive 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 0.1-1pa, 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 50-500nm.

[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 FIG. 1 is 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 substrate and an epitaxial structure arranged on the second substrate 1, wherein the epitaxial structure includes 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, GaN or AlGaN channel layer 4 and Al x2 Ga 1-x2 An AlN insertion layer 5 is provided between the N barrier layers 6. In some cases, an AlN insertion layer 5 can also be provided between the Al 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 disposed 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] Please see again Figure 2 A process schematic diagram for preparing the RF HEMT device structure is shown, which includes the following steps:

[0051] S1, sequentially growing 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 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 substrate 11 is combined on the top of the epitaxial structure, and then the bottom 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 Ga metal particles and defects after lift-off.

[0057] S3, transferring the epitaxial structure onto the 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 difficulty in growing the AlN back barrier layer 3 directly on the GaN sacrificial layer 2 and low quality of the AlN film, 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 the like, 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°C, 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 the like, thereby forming 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°C, 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 the like to sequentially grow the GaN or AlGaN channel layer 4 and 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, and during the growth process, the growth temperature is controlled to gradually increase to 1100-1300°C at a heating rate of 5-80°C / min (preferably 20-60°C / min), and then the AlN is continued to grow at a growth temperature of 1100-1300°C 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, and the decomposition of GaN during the AlN epitaxial growth process and the deterioration of the AlN epitaxial quality and morphology can be avoided.

[0063] Furthermore, in the aforementioned step S3, the "interface treatment" includes: using dilute hydrochloric acid treatment to remove Ga particles on the laser peeling surface, or removing metal residues and damage on the laser peeling 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 can achieve high crystal quality, low cost, good size, and no need for doping by using an AlN single crystal film based on a sapphire substrate as a buffer layer, 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 withstand voltage and high power for high-power RF devices.

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

[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 temperature gradient growth, so that a high-quality AlN buffer layer can be obtained and the growth substrate can 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 implementation scheme of the present application;

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

[0070] Figure 3 It is a schematic diagram of forming an AlN back barrier layer based on a polycrystalline magnetron sputtering process in a typical implementation scheme of the present application;

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

[0072] In view of the deficiencies in the prior art, the inventor of this case has proposed the technical solution of this application after long-term research and extensive practice. The technical solution, its implementation process and principle will be further explained as follows.

[0073] Example 1

[0074] The structure of a radio frequency 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, and an AlN layer with a thickness of about 25 nm. 0.22 GaN barrier layer and GaN cap layer with a thickness of about 1nm. 0.22 A source electrode and a drain electrode are disposed on the GaN barrier layer, and a gate electrode is disposed 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 a 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 is 100W. Then, an AlN film is continued to grow on the AlN seed layer by a 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. Afterwards, a GaN channel layer, an AlN insertion layer, and an AlN back barrier layer are successively epitaxially grown on the AlN back barrier layer by a MOCVD process. 0.22 GaN barrier layer and GaN cap layer are formed to obtain an 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] The epitaxial wafer was placed in a solution of H2SO4:H2O2 of about 3:1 (volume ratio) 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 of about 1:1:5 (volume ratio) 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 electrode patterns 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 of the adhesive;

[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 Ti with a thickness of about 30 nm, Al with a thickness of about 120 nm, Ni with a thickness of about 30 nm, and Au with a thickness of about 50 nm were evaporated respectively;

[0092] NMP degumming, and then rinse with deionized water and blow dry 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, separating the sapphire substrate and the HEMT epitaxial structure.

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

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

[0100] 9c) Transferring the epitaxial structure to a diamond substrate through a wafer bonder and removing the top PET transfer substrate.

[0101] Example 2

[0102] The structure of a radio frequency HEMT device provided in this embodiment and its preparation method are basically the same as those in embodiment 1, except that the AlN back barrier layer is grown by a gradual change of the growth temperature gradient. Specifically, the AlN back barrier layer is grown on a GaN sacrificial layer by an MOCVD process. During the growth process, the initial growth temperature is set to about 900°C, and the growth temperature is controlled to gradually increase to about 1100°C at a heating rate of about 20°C / min, and then the temperature is maintained at about 1100°C to continue growing until an AlN ultra-wide bandgap back barrier layer with a thickness of about 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, except that the AlN back barrier layer is directly grown on the GaN sacrificial layer by the MOCVD process.

[0105] In the preparation process 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, etc. It can be seen that the surface of the AlN back barrier layer in Examples 1-2 is flat, the roughness is less than 0.2 nm, and the defect density such as dislocation is less than 1×10 8 / cm 2 However, in Comparative Example 1, there are many cracks on the surface of the AlN back barrier layer.

[0106] In addition, the RF HEMT device of Example 1 can achieve an output power of 9.1 W / mm at 10 GHz, a power added efficiency (PAE) of about 50%, and a dissipated power of about 6.9 W / mm. The RF HEMT device of Example 2 can achieve an output power of 8 W / mm at 10 GHz, and a power added efficiency (PAE) of about 64%. Compared with these devices, the RF HEMT device of Comparative Example 1 has a maximum output power of about 6.5 W / mm at 10 GHz, a power added efficiency (PAE) of about 48%, and a dissipated power of about 6 W / mm.

[0107] Example 3

[0108] The structure of a radio frequency HEMT device provided in this embodiment is basically the same as that of Embodiment 1, except 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 basically 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 growth 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 to grow AlN until an AlN back barrier layer with a thickness of about 4μm is formed. Thereafter, a GaN channel layer, an AlN insertion layer, and an AlN back barrier layer are epitaxially grown in sequence on the AlN back barrier layer by an MOCVD process. 0.22 GaN barrier layer and GaN cap layer are formed to obtain an 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, which is the same as step 1 of embodiment 1.

[0113] Step 2, preparing source and drain electrodes on the surface of the GaN cap layer, which is the same as step 2 of embodiment 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 embodiment 1.

[0116] 8a) Preparing 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 samples were placed on a glue spreader for glue coating and glue spreading at 600r / min for 6s and 4000r / min for 30s. Afterwards, the samples were placed on a hot plate at 100°C for soft drying for 2min.

[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 mask-exposed sample was placed on a hot plate at 100°C for 100 s for reverse baking;

[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 dried with nitrogen.

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

[0124] The sample was placed in an electron beam chamber, and 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 respectively;

[0125] The sample was taken out and immersed in NMP degumming solution heated to 80°C on a hot plate for 20 minutes to peel off the photoresist and the metal on the photoresist, and then washed with deionized water and dried with nitrogen.

[0126] Step 5, separating the sapphire substrate and the HEMT epitaxial structure.

[0127] 9a) pasting a PDMS transfer substrate on top of the HEMT epitaxial structure by a wafer bonder, and stabilizing the interface by post-heating treatment;

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

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

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

[0131] It should be understood that the above embodiments are only for illustrating the technical concept and features of the present application, and their purpose is to enable people familiar with the technology to understand the content of the present application and implement it accordingly, and they cannot be used to limit the protection scope of the present application. Any equivalent changes or modifications made according to the spirit of the present application should be included in the protection scope of the present application.

Claims

1. A method for preparing a radio frequency HEMT device structure, characterized in that: include: A GaN sacrificial layer, an AlN back barrier layer, and Al are sequentially formed on a first substrate. x1 Ga 1-x1 an N-channel layer, and Al x2 Ga 1-x2 an N barrier layer, where 0 ≤ x1 ≤ 1 and 0 < x2 < 0.4, to form an epitaxial structure. The GaN sacrificial layer is irradiated with laser to at least partially decompose the GaN sacrificial layer, thereby separating the epitaxial structure from the first substrate, and then the epitaxial structure and the second substrate are combined with each other through 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: A polycrystalline magnetron sputtering process is used to form an AlN seed layer with a thickness of 50-500 nm on the GaN sacrificial layer, wherein the magnetron sputtering temperature used is 300-500° C., the gas pressure is 0.1-1 Pa, the flow ratio of Ar to N2 is 0-1, and the power supply is 100 W-800 W, and then an AlN film is continued to grow on the AlN seed layer by at least MOCVD or MBE process, thereby forming the AlN back barrier layer; Alternatively, the AlN back barrier layer is formed by at least growing the AlN sacrificial layer on the GaN sacrificial layer by 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.

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

4. The preparation method according to claim 1, characterized in that: Specifically include: After separating the epitaxial structure from the first substrate, combining the epitaxial structure with a transfer substrate, and disposing the AlN back barrier layer away from the transfer substrate, and then combining the epitaxial structure with the second substrate via a thermally conductive connection structure, and then removing the transfer substrate; Preferably, the transfer substrate comprises 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 forming a cap layer on the N barrier layer; and / or, 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; And / or, a source, a drain and a gate are fabricated on the epitaxial structure.

6. The preparation method according to claim 1, characterized in that: The first substrate comprises a sapphire substrate; and / or the second substrate comprises a combination of one or more of diamond, AlN ceramic or metal plate; and / or the thickness of the GaN sacrificial layer is 10-300 nm; and / or the Al x1 Ga 1-x1 The thickness of the N channel layer is 50-500 nm; and / or the thickness of the AlN back barrier layer is 1-4 μm; and / or the Al x2 Ga 1-x2 The thickness of the N barrier layer is 10-30 nm.

7. An intermediate structure for preparing a radio frequency HEMT device structure, characterized in that: include: The first substrate, The epitaxial structure comprises a GaN sacrificial layer, an AlN back barrier layer, an Al x1 Ga 1-x1 N channel layer, Al x2 Ga 1-x2 N barrier layers, where 0≤x1≤1, 0 <x2<0.4; Preferably, the thickness of the GaN sacrificial layer is 10-300 nm; Preferably, the GaN sacrificial layer can be at least partially decomposed by laser irradiation of a set wavelength and power. Preferably, the first substrate includes a sapphire substrate.

8. A radio frequency HEMT device structure, characterized in that: include: The second substrate, The epitaxial structure is combined with the second substrate through a thermal conductive 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。 9. The RF HEMT device structure according to claim 8, characterized in that: The AlN back barrier layer is formed by depositing on the GaN sacrificial layer through a polycrystalline magnetron sputtering process, wherein the magnetron sputtering temperature used is 300-500°C, the gas pressure is 0.1-1pa, the flow ratio of Ar to N2 is 0-1, and the power supply power is 100W-800W; Alternatively, the AlN back barrier layer is at least grown on the GaN sacrificial layer 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.

10. The RF HEMT device structure according to claim 8, characterized in that: The second substrate comprises a combination of one or more of diamond, AlN ceramic or metal plate; and / or the thickness of the GaN sacrificial layer is 10-300 nm; and / or the Alx1Ga 1-x1 The thickness of the N channel layer is 50-500 nm; and / or the thickness of the AlN back barrier layer is 1-4 μm; and / or the Al x2 Ga 1-x2 The thickness of the N barrier layer is 10-30 nm.

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