An enhanced GaN HEMT radio frequency device and its preparation method

Abstract

The present invention discloses an enhanced-mode GaN HEMT radio frequency device and a method for preparing the same. The device includes a substrate, a first AlN insertion layer, a GaN buffer layer, a GaN channel layer, a second AlN insertion layer, an AlGaN barrier layer, a p-AlGaN layer, a drain metal electrode, a source metal electrode, and a gate metal electrode. The present invention utilizes Mg metal doping to diffuse the AlGaN layer under extremely high vacuum conditions to form p-AlGaN, which forms a p-n junction with the undoped AlGaN layer, depleting the 2DEG under the gate. The device is then coated with a layer of HfO2 to prevent oxidation of the metal Mg, thereby achieving a high-frequency, low-loss enhanced radio frequency device. This simplifies gate drive circuit design, reduces radio frequency integrated circuit power consumption and radio frequency signal loss, and also serves as a safety circuit protection.

Description

Technical Field

[0001] The present invention belongs to the field of semiconductor devices, and in particular relates to an enhanced GaN HEMT radio frequency device and a preparation method thereof. Background Art

[0002] With the urgent need for high-performance RF front-ends in 5G communication base stations, high-frequency, low-loss GaN HEMT RF devices have attracted extensive research interest. However, traditional GaN HEMT RF devices are depletion-mode devices. Depletion-mode GaN HEMT RF devices require complex gate drive circuits, requiring the addition of more passive components in IC design. This results in significant signal loss in GaN HEMT RF devices, making it difficult to fabricate high-frequency, low-loss, and miniaturized RF chips. Furthermore, because the heterojunction channel in depletion-mode GaN HEMT RF devices is in the on state, negative gate drive control is required during testing and use to prevent short circuits and irreversible device damage. Therefore, considering the device itself, an enhanced RF device is designed to enhance circuit safety protection capabilities, simplify circuit design capabilities, and reduce device power consumption, thereby achieving high-safety, high-frequency, low-loss, and miniaturized RF chips.

[0003] At present, the main technologies for realizing enhanced RF devices include groove gate technology, etc., which uses dry etching to thin the barrier layer under the gate to weaken the polarization effect of the channel under the gate and deplete its 2DEG channel, thereby realizing enhanced RF devices. Among them, the groove gate has the advantages of simple process, high threshold voltage, and high gate drive voltage. However, its electron mobility in the channel under the gate is low, making it difficult to prepare high-frequency RF devices. At the same time, the surface damage caused by etching the grooves causes high-density defects. The high-density defects increase the loss of RF signals, which is not conducive to the realization of high-frequency and low-loss RF devices. Although the enhancement power device with p-GaN gate cap layer structure has been commercialized, and the p-GaN gate cap layer structure retains the complete 2DEG channel and does not require any gate dielectric, which is conducive to the realization of high-frequency and low-loss RF devices, there are currently no reports on RF devices with p-GaN gate cap layer structure. This is mainly because the traditional p-GaN gate cap layer structure is achieved by dry etching the p-GaN gate cap layer outside the gate, which places extremely high demands on the uniformity and precision of the etching equipment. Obviously, this technology is not suitable for the preparation of enhanced RF devices with a gate length of less than 0.25μm. Summary of the Invention

[0004] In order to overcome the shortcomings and deficiencies of the prior art, the present invention provides an enhanced-mode GaN HEMT radio frequency device.

[0005] Another object of the present invention is to provide a method for preparing an enhanced-mode GaN HEMT radio frequency device.

[0006] The present invention is achieved through the following technical solutions:

[0007] An enhancement-mode GaN HEMT radio frequency device comprises, from bottom to top, a substrate, a first AlN insertion layer, a GaN buffer layer, a GaN channel layer, a second AlN insertion layer, and an AlGaN barrier layer. The AlGaN barrier layer is a compositionally graded layer. A drain metal electrode and a source metal electrode are disposed on the AlGaN barrier layer. The drain metal electrode and the source metal electrode are respectively located on the AlGaN barrier layer, forming ohmic contacts between the drain metal electrode and the source metal electrode and the AlGaN barrier layer. A p-AlGaN layer is disposed below the gate metal electrode. The p-AlGaN layer is embedded in the AlGaN barrier layer, forming a Schottky contact between the gate metal electrode and the AlGaN barrier layer.

[0008] Furthermore, the thickness of the first AlN insertion layer is 100 nm.

[0009] Furthermore, the thickness of the GaN buffer layer is 2-4 μm.

[0010] Furthermore, the thickness of the GaN channel layer is 1-2 μm.

[0011] Furthermore, the thickness of the second AlN insertion layer is 0.5-2 nm.

[0012] Furthermore, the thickness of the AlGaN barrier layer is 5-50 nm.

[0013] Furthermore, the gate metal electrode is a T-shaped gate structure.

[0014] A method for preparing an enhanced-mode GaN HEMT radio frequency device, comprising:

[0015] Epitaxially growing a first AlN insertion layer, a GaN buffer layer, a GaN channel layer, a second AlN insertion layer and an AlGaN barrier layer on the substrate in sequence;

[0016] Photolithography is performed on the AlGaN barrier layer epitaxial wafer to expose the gate metal electrode area, and Mg metal and HfO2 layers are evaporated. After annealing, a p-AlGaN layer is formed. The Mg metal forms a pn junction with the undiffused AlGaN layer, effectively depleting the 2DEG under the gate. A layer of HfO2 is then applied to prevent oxidation of the metal Mg, realizing an enhancement-mode RF device with a gate length of less than 0.25μm.

[0017] A source electrode, a drain electrode and a T-type gate metal electrode are prepared to obtain an enhanced-mode GaN HEMT radio frequency device.

[0018] Furthermore, the p-AlGaN layer is formed by spin-coating a 10 μm negative photoresist on the AlGaN barrier layer epitaxial wafer, performing photolithography using electron beam exposure to expose the area below the gate metal electrode, evaporating Mg metal and HfO2 layers, and annealing to form the p-AlGaN layer.

[0019] Furthermore, the annealing temperature is 400-850° C., and the annealing time is 1-10 minutes.

[0020] Furthermore, the drain electrode and the source metal electrode are formed by rapid annealing, wherein the rapid annealing atmosphere is N2, the annealing temperature is 800-900°C, the holding time is 10-60s, and the heating rate is 10-20°C / s.

[0021] Furthermore, the first and second AlN buffer layers, the GaN channel layer and the AlGaN barrier layer are grown by metal organic chemical vapor deposition at a growth temperature of 850-950°C.

[0022] Beneficial effects of the present invention:

[0023] (1) The present invention proposes to form a p-AlGaN layer by doping Mg metal into the AlGaN under the gate under extremely high vacuum conditions. By forming a pn junction with the undiffused AlGaN layer, the 2DEG under the gate is effectively depleted and alloy scattering is avoided, thereby realizing an enhancement-mode GaN HEMT RF device with a gate length of less than 0.25μm.

[0024] (2) In the present invention, since the evaporated Mg metal is covered by the HfO2 layer in an extremely high vacuum environment, the metal Mg does not undergo oxidation, thereby improving the diffusion efficiency of the metal Mg and facilitating the realization of an enhanced GaN HEMT radio frequency device.

[0025] (3) The enhanced RF device of the present invention improves the safety of the device during use and plays a role in protecting the circuit; it is conducive to simplifying the gate drive circuit design; reducing the use of passive devices and lowering the power consumption of the device, thereby realizing a safe, low-loss, miniaturized GaN HEMT RF device. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic structural diagram of the enhanced GaN HEMT radio frequency device of the present invention. DETAILED DESCRIPTION

[0027] The present invention will be further described in detail below with reference to the embodiments and the accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0028] Example 1

[0029] like Figure 1 As shown, an enhanced GaN HEMT radio frequency device of this embodiment has a structural schematic diagram as shown in FIG. Figure 1 As shown. It includes: a substrate 1, a first AlN insertion layer 2, a GaN buffer layer 3, a GaN channel layer 4, a second AlN insertion layer 5, an AlGaN barrier layer 6, a p-AlGaN layer 7, a drain metal electrode 8, a gate metal electrode 9 and a source metal electrode 10, wherein:

[0030] The substrate 1, the first AlN insertion layer 2, the GaN buffer layer 3, the GaN channel layer 4, the second AlN insertion layer 5, and the AlGaN barrier layer 6 are stacked in sequence from bottom to top;

[0031] The p-AlGaN layer is below the gate metal electrode 7;

[0032] The drain metal electrode 8 and the source metal electrode 10 are respectively located on the AlGaN barrier layer 6 , and ohmic contacts are formed between the drain metal electrode 8 and the source metal electrode 10 and the AlGaN barrier layer 6 ;

[0033] The gate metal electrode 9 is located on the AlGaN barrier layer 6 , and a Schottky contact is formed between the gate metal electrode 9 and the AlGaN barrier layer 6 .

[0034] The enhanced-mode GaN HEMT radio frequency device of this embodiment is prepared by the following method:

[0035] Step 1: epitaxially grow a 100 nm first AlN insertion layer on a silicon substrate using metal organic chemical vapor deposition (MOCVD) at a growth temperature of 850° C.

[0036] Step 2, epitaxially growing a GaN buffer layer on the epitaxial wafer obtained in step 1 by metal organic chemical vapor deposition (MOCVD) at a growth temperature of 850° C.

[0037] Step 3, epitaxially growing a GaN channel layer on the epitaxial wafer obtained in step 2 by metal organic chemical vapor deposition (MOCVD) at a growth temperature of 850° C.

[0038] Step 4: epitaxially growing a second AlN insertion layer on the epitaxial wafer obtained in step 3 by metal organic chemical vapor deposition (MOCVD) at a growth temperature of 850° C.

[0039] Step 5, epitaxially growing an AlGaN barrier layer on the epitaxial wafer obtained in step 4 by metal organic chemical vapor deposition (MOCVD) at a growth temperature of 850° C.

[0040] Step 6: Photolithography is performed on the epitaxial wafer obtained in step 5 to expose the gate metal electrode area, and 100nm of metal Mg and 10nm of HfO2 are evaporated. At this time, the vacuum degree needs to reach the limit of the equipment, which is generally 10 -5 Pa, then anneal at 550 ° C for 2 minutes; then heat to 850 ° C and keep constant temperature for 30 seconds; when the temperature drops below 100, heat to 250 ° C and keep constant temperature for 1 minute;

[0041] Step 7: Photolithography is performed on the epitaxial wafer obtained in step 6 to expose the source and drain metal electrode regions, and Ti / Al / Ni / Au metal is evaporated, stripped, and annealed to form drain and source metal electrodes. The specific annealing process is as follows: annealing atmosphere is N2, annealing temperature is 800°C, holding time is 40s, and heating rate is 15°C / s;

[0042] In step 8, the epitaxial wafer obtained in step 7 is subjected to photolithography to expose the gate metal electrode area, and Ni / Au metal is evaporated and peeled off to form a gate metal electrode with a gate length of 50 nm, thereby obtaining the final enhanced RF device.

[0043] The device obtained in step 8 was tested for DC characteristics and RF performance using a semiconductor analyzer and a vector network analyzer, resulting in a threshold voltage of 1.5 V, an on-resistance of 300 mΩ, a breakdown voltage of 200 V, an operating frequency of 30 GHz, a power gain of 10 dB, and a power added efficiency of 54%.

[0044] The device with good test results obtained in step 8 is used for circuit design, which reduces the original negative voltage drive circuit, makes the entire circuit simpler, and reduces the power consumption of the device; during the entire system testing process, the test procedure is simplified, the safety of the device during use and testing is improved, and the circuit is protected.

[0045] Example 2

[0046] An enhanced GaN HEMT radio frequency device according to this embodiment has a structural diagram as shown in FIG. Figure 1 As shown. It includes: a substrate 1, a first AlN insertion layer 2, a GaN buffer layer 3, a GaN channel layer 4, a second AlN insertion layer 5, an AlGaN barrier layer 6, a p-AlGaN layer 7, a drain metal electrode 8, a gate metal electrode 9 and a source metal electrode 10, wherein:

[0047] The substrate 1, the first AlN insertion layer 2, the GaN buffer layer 3, the GaN channel layer 4, the second AlN insertion layer 5, and the AlGaN barrier layer 6 are stacked in sequence from bottom to top;

[0048] The p-AlGaN layer 7 is below the gate metal electrode 9;

[0049] The drain metal electrode 8 and the source metal electrode 10 are respectively located on the AlGaN barrier layer 6 , and ohmic contacts are formed between the drain metal electrode 8 and the source metal electrode 10 and the AlGaN barrier layer 6 ;

[0050] The gate metal electrode 9 is located on the AlGaN barrier layer 6 , and a Schottky contact is formed between the gate metal electrode 9 and the AlGaN barrier layer 6 .

[0051] The enhanced-mode GaN HEMT radio frequency device of this embodiment is prepared by the following method:

[0052] Step 1: epitaxially grow a 100 nm first AlN insertion layer on a silicon substrate using metal organic chemical vapor deposition (MOCVD) at a growth temperature of 850° C.

[0053] Step 2, epitaxially growing a GaN buffer layer on the epitaxial wafer obtained in step 1 by metal organic chemical vapor deposition (MOCVD) at a growth temperature of 850° C.

[0054] Step 3, epitaxially growing a GaN channel layer on the epitaxial wafer obtained in step 2 by metal organic chemical vapor deposition (MOCVD) at a growth temperature of 850° C.

[0055] Step 4: epitaxially growing a second AlN insertion layer on the epitaxial wafer obtained in step 3 by metal organic chemical vapor deposition (MOCVD) at a growth temperature of 850° C.

[0056] Step 5, epitaxially growing an AlGaN barrier layer on the epitaxial wafer obtained in step 4 by metal organic chemical vapor deposition (MOCVD) at a growth temperature of 850° C.

[0057] Step 6: Photolithography is performed on the epitaxial wafer obtained in step 5 to expose the gate metal electrode area, and 50nm of metal Mg and 30nm of HfO2 are evaporated. At this time, the vacuum degree needs to reach the limit of the equipment, which is generally 10 -5 Pa, then anneal at 600℃ for 5 minutes; then heat to 800℃ and keep constant for 1 minute; when the temperature drops below 150℃, heat to 300℃ and keep constant for 2 minutes;

[0058] Step 7: Photolithography is performed on the epitaxial wafer obtained in step 6 to expose the source and drain metal electrode regions, and Ti / Al / Ni / Au metal is evaporated, stripped, and annealed to form drain and source metal electrodes. The specific annealing process is as follows: annealing atmosphere is N2, annealing temperature is 850°C, holding time is 30s, and heating rate is 15°C / s;

[0059] In step 8, the epitaxial wafer obtained in step 7 is subjected to photolithography to expose the gate metal electrode region, and Ni / Au metal is evaporated and peeled off to form a gate metal electrode with a gate length of 150 nm, thereby obtaining an enhanced RF device.

[0060] The device obtained in step 8 was tested for DC characteristics and RF performance using a semiconductor analyzer and a vector network analyzer, resulting in a threshold voltage of 1.3 V, an on-resistance of 300 mΩ, a breakdown voltage of 200 V, an operating frequency of 25 GHz, a power gain of 12 dB, and a power added efficiency of 62%.

[0061] The devices that tested well in step 8 were used for circuit design, which reduced the original negative voltage drive circuit, making the entire circuit simpler and reducing the power consumption of the device. During the entire system testing process, the test procedure was simplified, the safety of the device during use and testing was improved, and the circuit was protected.

[0062] Example 3

[0063] An enhanced GaN HEMT radio frequency device according to this embodiment has a structural diagram as shown in FIG. Figure 1 As shown. It includes: a substrate 1, a first AlN insertion layer 2, a GaN buffer layer 3, a GaN channel layer 4, a second AlN insertion layer 5, an AlGaN barrier layer 6, a p-AlGaN layer 7, a drain metal electrode 8, a gate metal electrode 9 and a source metal electrode 10, wherein:

[0064] The substrate 1, the first AlN insertion layer 2, the GaN buffer layer 3, the GaN channel layer 4, the second AlN insertion layer 5, and the AlGaN barrier layer 6 are stacked in sequence from bottom to top;

[0065] The p-AlGaN layer is below the gate metal electrode 7;

[0066] The drain metal electrode 8 and the source metal electrode 10 are respectively located on the AlGaN barrier layer 6 , and ohmic contacts are formed between the drain metal electrode 6 and the source metal electrode 10 and the AlGaN barrier layer 6 ;

[0067] The gate metal electrode 9 is located on the AlGaN barrier layer 6 , and a Schottky contact is formed between the gate metal electrode 9 and the AlGaN barrier layer 6 .

[0068] The enhanced-mode GaN HEMT radio frequency device of this embodiment is prepared by the following method:

[0069] Step 1: epitaxially grow a 100 nm first AlN insertion layer on a silicon substrate using metal organic chemical vapor deposition (MOCVD) at a growth temperature of 850° C.

[0070] Step 2, epitaxially growing a GaN buffer layer on the epitaxial wafer obtained in step 1 by metal organic chemical vapor deposition (MOCVD) at a growth temperature of 850° C.

[0071] Step 3, epitaxially growing a GaN channel layer on the epitaxial wafer obtained in step 2 by metal organic chemical vapor deposition (MOCVD) at a growth temperature of 850° C.

[0072] Step 4: epitaxially growing a second AlN insertion layer on the epitaxial wafer obtained in step 3 by metal organic chemical vapor deposition (MOCVD) at a growth temperature of 850° C.

[0073] Step 5, epitaxially growing an AlGaN barrier layer on the epitaxial wafer obtained in step 4 by metal organic chemical vapor deposition (MOCVD) at a growth temperature of 850° C.

[0074] Step 6: Photolithography is performed on the epitaxial wafer obtained in step 5 to expose the gate metal electrode area, and 200nm of metal Mg and 100nm of HfO2 are evaporated. At this time, the vacuum degree needs to reach the limit of the equipment, which is generally 10 -5 Pa, then anneal at 650℃ for 10min; then heat to 900℃ and keep constant for 5min; when the temperature drops below 100℃, heat to 200℃ and keep constant for 30s;

[0075] Step 7: Photolithography is performed on the epitaxial wafer obtained in step 6 to expose the source and drain metal electrode regions, and Ti / Al / Ni / Au metal is evaporated, stripped, and annealed to form drain and source metal electrodes. The specific annealing process is: annealing atmosphere is N2, annealing temperature is 900°C, holding time is 20s, and heating rate is 15°C / s;

[0076] In step 8, the epitaxial wafer obtained in step 7 is subjected to photolithography to expose the gate metal electrode region, and Ni / Au metal is evaporated and peeled off to form a gate metal electrode with a gate length of 250 nm, thereby obtaining an enhanced RF device.

[0077] The device obtained in step 8 was tested for DC characteristics and RF performance using a semiconductor analyzer and a vector network analyzer, resulting in a threshold voltage of 1.7 V, an on-resistance of 300 mΩ, a breakdown voltage of 250 V, an operating frequency of 18 GHz, a power gain of 15 dB, and a power added efficiency of 71%.

[0078] The device with good test results obtained in step 8 is used for circuit design, which reduces the original negative voltage drive circuit, makes the entire circuit simpler, and reduces the power consumption of the device; during the entire system testing process, the test procedure is simplified, the safety of the device during use and testing is improved, and the circuit is protected.

[0079] This paper uses the technology of forming p-AlGaN by Mg-doped diffused gradient AlGaN barrier layer to prepare enhanced high-frequency, low-loss RF devices. The Al component content in the top of AlGaN is low, which is easy to dope with metal Mg, while the Al component in the bottom is high, which is conducive to inhibiting the diffusion of Mg into the 2DEG channel, causing serious alloy scattering and reducing the frequency characteristics of the device. In this process, since metal Mg with a gate length of less than 0.25μm is easily oxidized to MgO during the evaporation and stripping process, it is difficult to dope into the AlGaN barrier layer. Therefore, on the basis of the evaporated Mg, a layer of HfO2 is covered to prevent the oxidation of metal Mg during the stripping process. At the same time, HfO2 can also serve as a gate dielectric, which is crucial for suppressing the current collapse of the device.

[0080] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. An enhanced-mode GaN HEMT radio frequency device, characterized in that: The structure includes, from bottom to top, a substrate, a first AlN insertion layer, a GaN buffer layer, a GaN channel layer, a second AlN insertion layer, and an AlGaN barrier layer. A drain metal electrode and a source metal electrode are provided on the AlGaN barrier layer. The drain metal electrode and the source metal electrode are respectively located on the AlGaN barrier layer. Ohmic contacts are formed between the drain metal electrode and the source metal electrode and the AlGaN barrier layer. A p-AlGaN layer is provided below the gate metal electrode. The p-AlGaN layer is embedded in the AlGaN barrier layer, so that a Schottky contact is formed between the gate metal electrode and the AlGaN barrier layer. The gate metal electrode is a T-type gate structure; During the preparation process, photolithography is performed on the AlGaN barrier layer epitaxial wafer to expose the gate metal electrode area, and Mg metal and HfO2 layers are evaporated. After annealing, a p-AlGaN layer is formed. The p-AlGaN layer forms a pn junction with the undiffused AlGaN layer, effectively depleting the 2DEG under the gate, realizing an enhancement-mode RF device with a gate length of less than 0.25μm. On the basis of the evaporated Mg, a layer of HfO2 is covered to prevent the metal Mg from being oxidized during the evaporation and stripping process. At the same time, HfO2 also serves as a gate dielectric, which is crucial for suppressing the current collapse of the device.

2. The enhancement mode GaN HEMT radio frequency device according to claim 1, characterized in that: The thickness of the GaN channel layer is 1-2 μm.

3. The enhancement mode GaN HEMT radio frequency device according to claim 1, characterized in that: The thickness of the second AlN insertion layer is 0.5-2 nm.

4. The enhancement mode GaN HEMT radio frequency device according to claim 1, characterized in that: The thickness of the AlGaN barrier layer is 5-50 nm.

5. A method for preparing the enhancement mode GaN HEMT radio frequency device according to any one of claims 1 to 4, characterized in that: include: Epitaxially growing a first AlN insertion layer, a GaN buffer layer, a GaN channel layer, a second AlN insertion layer and an AlGaN barrier layer on the substrate in sequence; Photolithography is performed on the AlGaN barrier layer epitaxial wafer to expose the gate metal electrode area, and Mg metal and HfO2 layers are evaporated. After annealing, a p-AlGaN layer is formed. The p-AlGaN layer forms a pn junction with the undiffused AlGaN layer, effectively depleting the 2DEG under the gate, realizing an enhancement-mode RF device with a gate length of less than 0.25μm. Prepare source electrode, drain electrode and T-shaped gate metal electrode.

6. The method according to claim 5, characterized in that The p-AlGaN layer is formed by spin-coating a 10 μm thick negative photoresist on the AlGaN barrier layer epitaxial wafer, performing photolithography using electron beam exposure to expose the area below the gate metal electrode, evaporating Mg metal and HfO2 layers, and annealing to form the p-AlGaN layer.

7. The method according to claim 6, characterized in that The annealing temperature is 400~850 ºC and the annealing time is 1~10 minutes.

8. The method according to claim 5, characterized in that The drain electrode and the source electrode are formed by rapid annealing. The rapid annealing atmosphere is N2, the annealing temperature is 800-900°C, the holding time is 10-60 s, and the heating rate is 10-20°C / s.

9. The method according to claim 5, characterized in that The first and second AlN insertion layers, the GaN channel layer and the AlGaN barrier layer are grown by metal organic chemical vapor deposition at a growth temperature of 850-950°C.

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