An enhanced HEMT device and a method for preparing the same

Abstract

The present invention discloses an enhanced HEMT device and a preparation method thereof, comprising a SiC substrate, an AlN buffer layer, a GaN channel layer, an AlN insertion layer, an AlGaN barrier layer with a gradient Al component, an AlGaN barrier layer with a gradient Al component doped with Mg, a SiC substrate, an AlN buffer layer, a GaN channel layer, an AlN insertion layer, an AlGaN barrier layer with a gradient Al component, and a SiC substrate. X The invention adopts an AlGaN barrier layer with a gradient Al component to replace the AlGaN barrier layer, thereby reducing the difficulty of Mg diffusion, avoiding mechanical damage caused by etching of the traditional P-type gate, and improving the gate control capability of the device, which is conducive to realizing a GaN enhanced power device with a high threshold voltage.

Description

Technical Field

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

[0002] Power semiconductor devices are the key to realizing the conversion and utilization of energy and electric energy. In order to meet the rapidly growing energy demand of our society in a green way, the development of intelligent and efficient power conversion systems is the trend of today's social development. Since the beginning of the 20th century, with the continuous development and improvement of material growth, device design and semiconductor manufacturing technology, the power density of semiconductor power devices based on Si materials has approached the limit and is insufficient to meet the needs of the current market. In order to meet the needs of the market, GaN-based power devices with high breakdown voltage, low on-resistance, high operating temperature, low switching loss and high switching speed have become a hot spot in global research.

[0003] For switching applications, GaN-based depletion-mode power devices will not only introduce safety hazards to the entire system, but also increase the complexity of the drive circuit design. Therefore, the preparation of GaN-based enhancement-mode power devices is of vital importance. At present, the main methods for realizing enhancement-mode devices include groove gate structure, F ion implantation technology, P-GaN gate cap layer structure, etc. Among the above methods, the method currently used for enhancement-mode power devices that can be applied to commercial purposes is the P-GaN gate cap layer structure. In order to realize an enhancement-mode device with a P-GaN gate cap layer structure, it is necessary to etch the P-GaN on the barrier layer, leaving only the P-GaN under the gate. During the entire etching process, it is not only difficult to control the etching accuracy and it is easy to cause mechanical damage caused by etching during the etching process, but also a large number of defects caused by etching are generated during the etching process, which will also affect the performance of the device. It is helpful to avoid the above problems by using Mg doping to assist diffusion into the AlGaN barrier layer to replace the traditional P-GaN gate cap layer, but with the increase of the Al component in AlGaN, the difficulty of Mg diffusion increases accordingly, further limiting the depth and concentration of Mg doping diffusion. Summary of the invention

[0004] In order to overcome the shortcomings and deficiencies of the prior art, the primary purpose of the present invention is to provide an enhanced HEMT device, specifically an enhanced HEMT device based on a SiC substrate with a magnesium-doped AlGaN barrier layer and a gradient Al composition.

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

[0006] The primary purpose of the present invention adopts the following technical solution:

[0007] An enhanced HEMT device comprises: a SiC substrate, an AlN buffer layer, a GaN channel layer, an AlN insertion layer, an AlGaN barrier layer with a gradient Al component, an AlGaN barrier layer with a gradient Al component doped with Mg, a SiN X A passivation layer, a drain metal electrode, a source metal electrode and a gate metal electrode, wherein:

[0008] The SiC substrate, the AlN buffer layer, the GaN channel layer, the AlN insertion layer, the AlGaN barrier layer with a gradient Al component, and the Mg-doped AlGaN barrier layer with a gradient Al component are stacked in sequence from bottom to top;

[0009] The SiN X The passivation layer covers the upper surface area of ​​the AlGaN barrier layer with a gradient Al composition except the source, drain and gate metal electrode areas;

[0010] The drain metal electrode and the source metal electrode are respectively located on the AlGaN barrier layer with a gradient Al composition and are not covered by SiN X In the two side regions covered by the passivation layer, an ohmic contact is formed between the drain metal electrode and the source metal electrode and the AlGaN barrier layer with a gradient Al composition;

[0011] The gate metal electrode is located on the AlGaN barrier layer with a gradient Al composition and is not covered by SiN X In the middle region covered by the passivation layer, a Schottky contact is formed between the gate metal electrode and the AlGaN barrier layer with a gradient Al composition doped with Mg.

[0012] Preferably, the thickness of the AlN buffer layer is 1-3 μm.

[0013] Preferably, the GaN channel layer has a thickness of 1-3 μm.

[0014] Preferably, the thickness of the AlN insertion layer is 1 nm.

[0015] Preferably, the thickness of the AlGaN barrier layer with a gradient Al composition is 5-50 nm, and the composition of aluminum varies from bottom to top by 50-0%.

[0016] Preferably, the thickness of the metal Mg is 50-200 nm.

[0017] Preferably, the SiN X The thickness of the passivation layer is 50 to 150 nm.

[0018] Preferably, the drain metal electrode and the source metal electrode are composed of four metal layers of Ti, Al, Ni and Au.

[0019] Preferably, the gate metal electrode is composed of two metal layers of Ni and Au.

[0020] The secondary purpose of the present invention is to adopt the following technical solution:

[0021] A method for preparing an enhanced HEMT device comprises the following steps:

[0022] S1 epitaxially grows AlN buffer layer on SiC substrate;

[0023] S2 epitaxially grows a GaN channel layer on the AlN buffer layer;

[0024] S3 epitaxially growing an AlN insertion layer on the GaN channel layer;

[0025] S4 epitaxially growing an AlGaN barrier layer with a gradient Al composition on the AlN insertion layer;

[0026] S5 performs photolithography on the epitaxial wafer obtained in S4 to expose the gate region, and performs Mg evaporation, stripping, and annealing to form a P-type AlGaN layer with a gradient Al composition in which Mg is diffused in the region under the gate;

[0027] S6 performs photolithography on the epitaxial wafer obtained in S5 to expose the source and drain metal electrode regions, and performs evaporation, stripping, and annealing to form drain and source metal electrodes;

[0028] S7 performs table isolation on the epitaxial wafer obtained in S6;

[0029] S8, performing photolithography on the epitaxial wafer obtained in S7 to expose the gate metal electrode region, and forming a gate metal electrode by evaporation and stripping;

[0030] S9, growing SiN on the epitaxial wafer obtained in S8 X Passivation layer;

[0031] S10, based on S9, remove the SiN under the source, drain and gate metal electrode areas through chemical etching X The passivation layer is deposited and stripped to produce source, drain and gate metal electrodes.

[0032] Preferably, the epitaxially grown AlN buffer layer described in S1 is grown and prepared by metal organic chemical vapor deposition (MOCVD) at a growth temperature of 850-950°C.

[0033] Preferably, the epitaxially grown GaN channel layer described in S2 is grown and prepared by metal organic chemical vapor deposition (MOCVD) at a growth temperature of 850-950°C.

[0034] Preferably, the epitaxially grown AlN insertion layer described in S3 is grown and prepared by metal organic chemical vapor deposition (MOCVD) at a growth temperature of 850-950°C.

[0035] Preferably, the epitaxially grown AlGaN barrier layer with a gradient Al component described in S4 is grown and prepared by metal organic chemical vapor deposition (MOCVD) at a growth temperature of 850-950°C, specifically: (trimethylaluminum)TMAl, TMGa and NH 3 On the substrate surface, TMAl and TMGa change at a constant molar amount, NH 3 The flow rate is 10-30 sccm, and TMAl, TMGa and NH 3 The time is 40 to 60 s, and the AlGaN growth rate is kept constant regardless of how the Al composition changes.

[0036] Preferably, the thickness of the evaporated Mg in S5 is 50-200 nm, the annealing temperature is 550-650° C., the annealing time is 0.3-1 h, and a barrier layer with a gradient of Mg-doped Al components is formed in the area below the gate;

[0037] Preferably, the rapid thermal annealing of the ohmic contact in S6 is specifically: the annealing atmosphere is N 2 The annealing temperature is 800-900°C, the holding time is 20-40s, and the heating rate is 15-20°C / s.

[0038] Preferably, in S7 , the mesa isolation is etched to the GaN channel layer.

[0039] Preferably, S8 performs photolithography on the obtained epitaxial wafer to expose the gate metal electrode region, and forms the gate metal electrode by evaporation and stripping;

[0040] Preferably, S9 said SiN X The passivation layer is prepared by plasma enhanced chemical vapor deposition (PECVD) growth at a growth temperature of 230-320°C;

[0041] Preferably, the chemical etching treatment in S10 is specifically: using a mass fraction ratio of HF:HN 4 The solution is immersed in a buffered oxide etchant (BOE) solution with F=1:7-1:5 for 50-100 seconds, and the source, drain and gate metal electrodes are drawn out by evaporation and stripping.

[0042] Beneficial effects of the present invention:

[0043] (1) The present invention adopts Al with gradual Al composition change x Ga 1-xThe N barrier layer (x = 50-0%) is used to replace the AlGaN barrier layer, mainly because as the Al component in AlGaN increases, the lattice constant of AlGaN gradually decreases, making it difficult for Mg to diffuse in AlGaN. By using Mg to diffuse into the AlGaN barrier layer with a gradient Al component, the difficulty of diffusion is effectively reduced and the concentration of Mg diffusion is increased.

[0044] (2) The P-type AlxGa1-xN barrier layer (x=0-40%) with a gradient Al composition of the device of the present invention further reduces the distance between the gate and the barrier layer, enhances the gate control capability, avoids damage caused by etching and other problems, and reduces surface defects.

[0045] (3) In the process of realizing the enhancement mode power device of the present invention, as the concentration and depth of Mg diffusion increase, it is beneficial to improve the electrical characteristics of the device such as the threshold voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 is a schematic structural diagram of Embodiment 1 of the present invention;

[0047] Figure 2 is a transfer characteristic curve diagram of Example 1 of the present invention (V D =6V, the threshold voltage is 1.6V).

[0048] Figure 3 is the output characteristic curve diagram of the first embodiment of the present invention (V G =1~5). DETAILED DESCRIPTION

[0049] The present invention will be further described in detail below in conjunction with embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0050] Example 1

[0051] An AlGaN barrier layer enhanced HEMT device based on SiC substrate with magnesium doping and Al composition gradient, the structural schematic diagram of which is shown in Figure 1 As shown. It includes: SiC substrate 1, AlN buffer layer 2, GaN channel layer 3, AlN insertion layer 4, AlGaN barrier layer with Al component gradient 5, Mg-doped AlGaN barrier layer with Al component gradient 6, SiN X Passivation layer 7, drain metal electrode 8, source metal electrode 9 and gate metal electrode 10, wherein:

[0052] The SiC substrate 1, the AlN buffer layer 2, the GaN channel layer 3, the AlN insertion layer 4, the AlGaN barrier layer 5 with a gradient Al composition, and the Mg-doped AlGaN barrier layer 6 with a gradient Al composition are stacked in sequence from bottom to top;

[0053] The SiN X The passivation layer 7 covers the upper surface area of ​​the AlGaN barrier layer 5 with a gradient Al composition except the source metal electrode 9, the drain metal electrode 8, and the gate metal electrode 10;

[0054] The drain metal electrode 8 and the source metal electrode 9 are respectively located on the AlGaN barrier layer 5 with a gradient Al composition and not covered by SiN. X In the areas on both sides covered by the passivation layer 7, an ohmic contact is formed between the drain metal electrode 8 and the source metal electrode 9 and the AlGaN barrier layer with a gradient Al composition;

[0055] The gate metal electrode 10 is located on the Mg-doped AlGaN barrier layer 6 with a gradient Al composition and is not covered by SiN X In the middle region covered by the passivation layer 7 , a Schottky contact is formed between the gate metal electrode 10 and the AlGaN barrier layer 6 with a Mg-doped Al composition gradient.

[0056] Example 2

[0057] The AlGaN barrier layer enhanced HEMT device with a graded Al composition and magnesium doped SiC substrate as described in Example 1 is prepared by the following method, including:

[0058] Step 1, epitaxially growing an AlN buffer layer on a SiC substrate by metal organic chemical vapor deposition (MOCVD) at a growth temperature of 850° C.

[0059] Step 2, then continue to epitaxially grow a GaN channel layer on the epitaxial wafer obtained in step 1 by metal organic chemical vapor deposition (MOCVD) at a growth temperature of 850° C.;

[0060] Step 3, based on step 2, epitaxially growing an AlN insertion layer by metal organic chemical vapor deposition (MOCVD) at a growth temperature of 850° C.;

[0061] Step 4: The epitaxial wafer obtained in step 3 is subjected to metal organic chemical vapor deposition (MOCVD) to perform epitaxial growth of an AlGaN barrier layer with a gradient Al component, and the growth temperature is 850°C. Specifically, (trimethylaluminum)TMAl, TMGa and NH 3 On the substrate surface, TMAl and TMGa change at a constant molar amount, NH 3 The flow rate is 10sccm, and TMAl, TMGa and NH 3 The time is 40s, and the AlGaN growth rate is kept constant regardless of the change of Al composition;

[0062] Step 5, performing photolithography and vapor deposition on the epitaxial wafer obtained in step 4, wherein the thickness of the metal magnesium is 50 nm, the annealing temperature is 550° C., the annealing time is 0.3 h, and a barrier layer with a gradient of Mg-doped Al components is formed in the area below the gate;

[0063] Step 6, photolithography, evaporation of source and drain contact electrodes, and then rapid thermal annealing of the epitaxial wafer obtained in step 5, specifically: the annealing atmosphere is N 2 , annealing temperature is 800℃, holding time is 20s, and heating rate is 15℃ / s.

[0064] Step 7, isolating the epitaxial wafer obtained in step 6 and etching to the GaN channel layer.

[0065] Step 8, performing photolithography on the epitaxial wafer obtained in step 7 to expose the gate metal electrode region, and forming a gate metal electrode by evaporation and stripping;

[0066] Step 9: the SiN X The passivation layer was grown by plasma enhanced chemical vapor deposition (PECVD) at a growth temperature of 230°C;

[0067] Step 10: chemically etch the epitaxial wafer obtained in step 9 to remove the SiN under the source, drain and gate metal electrode regions. X The passivation layer is specifically: the mass fraction ratio is HF:HN 4 The substrate is immersed in a buffered oxide etchant (BOE) solution with F=1:5 for 50 seconds, and then photolithography, evaporation and stripping of the metal electrode are performed to lead out the source, drain and gate metal electrodes.

[0068] Example 3

[0069] The AlGaN barrier layer enhanced HEMT device with a graded Al composition based on a SiC substrate doped with magnesium as described in Example 1 is prepared by the following method, including the following steps:

[0070] Step 1, epitaxially growing an AlN buffer layer on a Si substrate by metal organic chemical vapor deposition (MOCVD) at a growth temperature of 900° C.

[0071] Step 2, then continue to use metal organic chemical vapor deposition (MOCVD) to epitaxially grow a GaN channel layer on the epitaxial wafer obtained in step 1, and the growth temperature is 900° C.;

[0072] Step 3, based on step 2, epitaxially growing an AlN insertion layer by metal organic chemical vapor deposition (MOCVD) at a growth temperature of 900° C.;

[0073] Step 4: The epitaxial wafer obtained in step 3 is subjected to epitaxial growth of an AlGaN barrier layer with a gradient Al component by metal organic chemical vapor deposition (MOCVD) at a growth temperature of 900°C. Specifically, (trimethylaluminum)TMAl, TMGa and NH 3 On the substrate surface, TMAl and TMGa change at a constant molar amount, NH 3 The flow rate is 20sccm, and TMAl, TMGa and NH 3 The time is 50s, and the AlGaN growth rate is kept constant regardless of the change of Al composition;

[0074] Step 5, performing photolithography and vapor deposition on the epitaxial wafer obtained in step 4, wherein the thickness of the metal magnesium is 100 nm, the annealing temperature is 600° C., the annealing time is 0.65 h, and a barrier layer with a gradient of Mg-doped Al components is formed in the area below the gate;

[0075] Step 6, photolithography, evaporation of source and drain contact electrodes, and then rapid thermal annealing are performed on the epitaxial wafer obtained in step 5, specifically: the annealing atmosphere is N 2 , annealing temperature is 850℃, holding time is 30s, and heating rate is 17℃ / s.

[0076] Step 7, isolating the epitaxial wafer obtained in step 6 and etching to the GaN channel layer.

[0077] Step 8, performing photolithography on the epitaxial wafer obtained in step 7 to expose the gate metal electrode region, and forming a gate metal electrode by evaporation and stripping;

[0078] Step 9: the SiN X The passivation layer was grown by plasma enhanced chemical vapor deposition (PECVD) at a growth temperature of 275°C;

[0079] Step 10: chemically etch the epitaxial wafer obtained in step 9 to remove the SiN under the source, drain and gate metal electrode regions. X The passivation layer is specifically: the mass fraction ratio is HF:HN 4 The substrate is immersed in a buffered oxide etchant (BOE) solution with F=1:6 for 75 seconds, and then photolithography, evaporation and stripping of the metal electrode are performed to lead out the source, drain and gate electrodes.

[0080] Example 4

[0081] The method for preparing the AlGaN barrier layer enhanced HEMT device with a graded Al composition based on a SiC substrate doped with magnesium as described in Example 1 comprises the following steps:

[0082] Step 1, epitaxially growing an AlN buffer layer on a Si substrate by metal organic chemical vapor deposition (MOCVD) at a growth temperature of 950° C.

[0083] Step 2, then continue to use metal organic chemical vapor deposition (MOCVD) to epitaxially grow a GaN channel layer on the epitaxial wafer obtained in step 1, and the growth temperature is 950° C.;

[0084] Step 3, based on step 2, epitaxially growing an AlN insertion layer by metal organic chemical vapor deposition (MOCVD) at a growth temperature of 950° C.;

[0085] Step 4: The epitaxial wafer obtained in step 3 is subjected to metal organic chemical vapor deposition (MOCVD) to perform epitaxial growth of an AlGaN barrier layer with a gradient Al component, and the growth temperature is 950°C. Specifically, (trimethylaluminum)TMAl, TMGa and NH 3 The TMAl and TMGa change at a constant molar amount on the substrate surface. The NH3 flow rate is 30sccm. TMAl, TMGa and NH 3 The time is 60s, and the AlGaN growth rate is kept constant regardless of the change of Al composition;

[0086] Step 5, performing photolithography and vapor deposition on the epitaxial wafer obtained in step 4, wherein the thickness of the metal magnesium is 200 nm, the annealing temperature is 650° C., the annealing time is 1 h, and a barrier layer with a gradient of Mg-doped Al components is formed in the area below the gate;

[0087] Step 6, photolithography, evaporation of source and drain contact electrodes, and then rapid thermal annealing of the epitaxial wafer obtained in step 5, specifically: the annealing atmosphere is N 2 , annealing temperature is 900℃, holding time is 40s, and heating rate is 20℃ / s.

[0088] Step 7, isolating the epitaxial wafer obtained in step 6 and etching to the GaN channel layer.

[0089] Step 8, performing photolithography on the epitaxial wafer obtained in step 7 to expose the gate metal electrode region, and forming a gate metal electrode by evaporation and stripping;

[0090] Step 9: the SiN X The passivation layer was grown by plasma enhanced chemical vapor deposition (PECVD) at a growth temperature of 320°C;

[0091] Step 10: chemically etch the epitaxial wafer obtained in step 9 to remove the SiN under the source, drain and gate metal electrode regions. XThe passivation layer is specifically: the mass fraction ratio is HF:HN 4 The substrate is immersed in a buffered oxide etchant (BOE) solution with F=1:7 for 100 seconds, and then photolithography, evaporation and stripping of the metal electrode are performed to lead out the source, drain and gate electrodes.

[0092] Figure 2 It is shown that the threshold voltage of the HEMT device prepared by this method is 1.6V.

[0093] Figure 3 It is shown that the HEMT device prepared by this method has a maximum output current of 200mA / mm.

[0094] 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 equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. An enhanced HEMT device, characterized in that: It includes SiC substrate, AlN buffer layer, GaN channel layer, AlN insertion layer, AlGaN barrier layer with gradient Al composition, AlGaN barrier layer with gradient Al composition doped with Mg, SiN X Passivation layer, drain metal electrode, source metal electrode and gate metal electrode; The SiC substrate, the AlN buffer layer, the GaN channel layer, the AlN insertion layer, the AlGaN barrier layer with a gradient Al component, and the Mg-doped AlGaN barrier layer with a gradient Al component are stacked in sequence from bottom to top; The SiN X The passivation layer covers the upper surface area of ​​the AlGaN barrier layer with a gradient Al composition except the source, drain and gate metal electrode areas; The drain metal electrode and the source metal electrode are respectively located on the AlGaN barrier layer with a gradient Al composition and are not covered by SiN X In the two side regions covered by the passivation layer, an ohmic contact is formed between the drain metal electrode and the source metal electrode and the AlGaN barrier layer with a gradient Al composition; The gate metal electrode is located on the AlGaN barrier layer with a gradient Al composition and is not covered by SiN X In the middle area covered by the passivation layer, a Schottky contact is formed between the gate metal electrode and the AlGaN barrier layer with a gradient Al composition doped with Mg; The thickness of the AlGaN barrier layer with a gradient Al composition is 5-50 nm, and the Al composition changes from bottom to top by 50-0%. The AlGaN barrier layer with a gradient Al component is prepared by epitaxially growing the AlGaN barrier layer with a gradient Al component on the AlN insertion layer, then performing photolithography to expose the gate region, performing Mg evaporation, stripping, and annealing to form a P-type AlGaN layer with a gradient Al component in which Mg is diffused in the region below the gate.

2. The enhanced HEMT device according to claim 1, characterized in that: The thickness of the AlN buffer layer is 1-3 μm.

3. The enhanced HEMT device according to claim 1, characterized in that: The thickness of the GaN channel layer is 1-3 μm.

4. The enhanced HEMT device according to claim 1, characterized in that: The thickness of the AlN insertion layer is 1 nm.

5. The enhanced HEMT device according to claim 1, characterized in that: The thickness of the metallic Mg is 50-200 nm.

6. The enhanced HEMT device according to claim 1, characterized in that: The SiN X The thickness of the passivation layer is 50~150 nm.

7. A method for preparing the enhanced HEMT device according to any one of claims 1 to 6, characterized in that: The steps include: S1 epitaxially grows AlN buffer layer on SiC substrate; S2 epitaxially grows a GaN channel layer on the AlN buffer layer; S3 epitaxially growing an AlN insertion layer on the GaN channel layer; S4 epitaxially growing an AlGaN barrier layer with a gradient Al composition on the AlN insertion layer; S5 performs photolithography on the epitaxial wafer obtained in S4 to expose the gate region, and performs Mg evaporation, stripping, and annealing to form a P-type AlGaN layer with a gradient Al composition and Mg diffusion in the region below the gate; S6 performs photolithography on the epitaxial wafer obtained in S5 to expose the source and drain metal electrode regions, and performs evaporation, stripping, and annealing to form drain and source metal electrodes; S7 performs table isolation on the epitaxial wafer obtained in S6; S8 performs photolithography on the epitaxial wafer obtained in S7 to expose the gate metal electrode region, and forms a gate metal electrode by evaporation and stripping; S9: growing SiN on the epitaxial wafer obtained in S8 X Passivation layer; S10 is based on S9 and undergoes chemical etching to remove SiN under the source, drain and gate metal electrode areas. X The passivation layer is deposited and stripped to produce source, drain and gate metal electrodes.

8. The method according to claim 7, characterized in that In S4, the epitaxially grown AlGaN barrier layer with a gradient Al component is grown and prepared by metal organic chemical vapor deposition, and the growth temperature is 850~950°C. Specifically, when the substrate temperature is 900~1000 ºC, TMAl, TMGa and NH3 are introduced to act on the substrate surface, TMAl and TMGa change at a constant molar amount, the NH3 flow rate is 10~30 sccm, and the time for introducing TMAl, TMGa and NH3 is 40~60 s. Regardless of how the Al composition changes, the AlGaN growth rate is kept constant.

9. The method according to claim 7, characterized in that: In the S5, the thickness of the evaporated Mg is 5-100 nm, the annealing temperature is 550-650 ºC, and the annealing time is 0.3~1 h.

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