阅读说明：本技术 基于氮化镓衬底的渐变铝组分铝镓氮mosfet及制备方法 (Gallium nitride substrate-based gradient aluminum component aluminum gallium nitride MOSFET and preparation method thereof ) 是由 周弘 王捷英 张进成 刘志宏 许晟瑞 郝跃 于 2021-07-26 设计创作，主要内容包括：本发明公开了一种基于氮化镓衬底的渐变铝组分铝镓氮金属氧化物半导体场效应晶体管,主要解决现有技术衬底位错密度高、器件击穿电压低的问题。其自下而上依次为漏极、掺杂浓度为10～(16)-10～(20)cm～(-3)的氮化镓衬底、掺杂浓度为10～(15)-10～(20)cm～(-3)的氮化镓外延层、掺杂浓度为10～(15)-10～(20)cm～(-3)的铝镓氮漂移区和栅介质,该栅介质的两侧和上方分别为源极和栅极；该铝镓氮漂移区的铝组分从靠近氮化镓外延到远离氮化镓外延逐渐增加,铝组分的变化范围为0％-100％。本发明减小了衬底本身的穿透位错和外延层与衬底之间的晶格失配,改善了外延层的生长质量,提高了击穿电压,可用作高压、高功率的电力电子器件。(The invention discloses a gallium nitride substrate-based gradient aluminum component aluminum gallium nitride metal oxide semiconductor field effect transistor, which mainly solves the problems of high substrate dislocation density and low device breakdown voltage in the prior art. The drain electrode and the doping concentration are 10 from bottom to top 16 ‑10 20 cm ‑3 Has a doping concentration of 10 15 ‑10 20 cm ‑3 Has a doping concentration of 10 15 ‑10 20 cm ‑3 The two sides and the upper part of the gate medium are respectively provided with a source electrode and a gate electrode; the Al component of the AlGaN drift region is extended from near to GaN to far from GaNThe gallium epitaxy is gradually increased, and the variation range of the aluminum component is 0-100%. The invention reduces the threading dislocation of the substrate and the lattice mismatch between the epitaxial layer and the substrate, improves the growth quality of the epitaxial layer, improves the breakdown voltage, and can be used as a high-voltage and high-power electronic device.)

1. A graded aluminum component AlGaN MOSFET based on a gallium nitride substrate comprises from bottom to top: drain electrode (1), gallium nitride substrate (2), gallium nitride epitaxial layer (3), aluminium gallium nitrogen drift region (4), the intermediate position of aluminium gallium nitrogen drift region (4) top is source (5), and both sides are grid dielectric layer (6), and the top of grid dielectric layer (6) is grid (7), its characterized in that:

the substrate (2) adopts n-type gallium nitride with the doping concentration of 10¹⁶-10²⁰cm^-3To reduceThe threading dislocation of the small substrate and the lattice mismatch and electric leakage between the epitaxial layer and the substrate improve the growth thickness and quality of the aluminum gallium nitrogen drift region.

The gallium nitride epitaxial layer (3) has a doping concentration of 10¹⁵-10²⁰cm^-3The transition layer is used between the substrate and the AlGaN epitaxy to reduce lattice mismatch between the substrate and the AlGaN epitaxy layer and improve the quality of the AlGaN epitaxy.

The AlGaN drift region (4) is made of an AlGaN material with gradually changed aluminum components, the AlGaN is doped in an n type mode, the aluminum components are gradually increased from one side close to the gallium nitride epitaxy (3) to one side far away from the gallium nitride epitaxy (3), the variation range of the aluminum components is 0-100%, and the doping concentration is 10¹⁵-10²⁰cm^-3The mismatch and dislocation density between the low-aluminum component aluminum gallium nitrogen close to the gallium nitride epitaxy (3) and the gallium nitride epitaxy are reduced, and the high-aluminum component aluminum gallium nitrogen material far away from the substrate has the characteristics of high critical breakdown electric field and high Baynaud figure of merit.

2. The device of claim 1, wherein: the metal deposited on the drain electrode (1) and the source electrode (5) is any one or combination of any several of Ni, Ti, Al, Au, W, Cr, Ta, Mo, TiC, TiN and TiW.

3. The device of claim 1, wherein: the grid dielectric layer (6) is made of insulating material Al₂O₃、SiO₂、SiN_x、HfO₂、MgO、CaO、MgCaO、ScO_xAny one or a combination of two or more of them.

4. The device of claim 1, wherein: the grid metal (7) is any one or combination of any several of Ni, Ti, Al, Au, W, Cr, Ta, Mo, Pt, TiC, TiN and TiW.

5. A preparation method of a gradient aluminum component aluminum gallium nitride MOSFET of a gallium nitride substrate is characterized by comprising the following steps:

1) the doping concentration is 10¹⁶-10²⁰cm^-3The n-type gallium nitride substrate (2) adopts a molecular beam epitaxial growth method or a metal organic compound chemical vapor deposition method to grow a gallium nitride epitaxial layer (3) and a gradient aluminum component aluminum gallium nitrogen drift region (4) from bottom to top, wherein the doping concentration of the gallium nitride epitaxial layer is 10¹⁵-10²⁰cm^-3The aluminum component of the aluminum gallium nitrogen drift region with gradually changed aluminum component gradually increases from one side close to the gallium nitride epitaxial layer (3) to one side far away from the gallium nitride epitaxial layer (3), the range of the aluminum component is 0-100%, and the doping concentration is 10¹⁵-10²⁰cm^-3；

2) Carrying out organic cleaning and inorganic cleaning on the epitaxial wafer on which the gallium nitride epitaxial layer (3) and the gradient aluminum component AlGaN drift region (4) grow;

3) depositing drain metal below an n-type gallium nitride substrate (2) of the epitaxial wafer to form a drain (1), and forming ohmic contact on the drain through a high-temperature annealing process;

4) photoetching source electrode regions in two side regions above a gradient aluminum component AlGaN drift region (4) of an epitaxial wafer, depositing metal in the source electrode regions by using photoresist as a mask to form a source electrode (5), and forming source electrode ohmic contact through a high-temperature annealing process;

5) placing the epitaxial wafer with the ohmic contact of the drain electrode and the source electrode into an insulating medium growth system, depositing a grid electrode medium (6) above the aluminum gallium nitrogen drift region (4), and annealing the grid electrode medium by adopting an annealing process;

6) and photoetching a grid electrode region above the grid electrode dielectric (6), and depositing metal in the grid electrode region to form a grid electrode (7), thereby completing the manufacture of the device.

6. The method of claim 5, wherein: the method comprises the following steps of 1) growing a gallium nitride epitaxial layer (3) and a gradient aluminum component aluminum gallium nitrogen drift region (4) on a gallium nitride substrate by using a molecular beam epitaxial growth method or a metal organic compound chemical vapor deposition method after obtaining an n-type gallium nitride substrate (2), and realizing the following processes:

putting an n-type gallium nitride substrate into a material growth system, introducing a gallium source and a nitrogen source into the material growth system, controlling the proportion of doped impurities and the gallium source, and forming a gallium nitride epitaxial layer (3) on the gallium nitride substrate (2);

and introducing an aluminum source, a gallium source and a nitrogen source into the material growth system, gradually increasing the flow of the aluminum source or gradually reducing the flow of the gallium source, controlling the proportion of the doped impurities to the gallium source aluminum source, and forming a gradually-changed aluminum component aluminum gallium nitrogen drift region (4) on the gallium nitride epitaxial layer (3).

7. The method of claim 5, wherein: the metals of the drain electrode (1) and the source electrode (5) deposited in the steps 3) and 4) adopt an electron beam evaporation or sputtering process, and the types of the deposited metals are any one or the combination of any more of Ni, Ti, Al, Au, W, Cr, Ta, Mo, TiC, TiN and TiW.

8. The method of claim 5, wherein: and 3) annealing for the medium-high temperature annealing process in the step 3) and the step 4) for 10s-10min at the temperature of 400-1200 ℃ according to the selection of the deposited metal species, so that ohmic contact is formed between the metal and the gallium nitride substrate or the aluminum gallium nitrogen epitaxy.

9. The method of claim 5, wherein:

the gate dielectric (6) deposited in the step 5) adopts an insulating material Al₂O₃、SiO₂、SiN_x、HfO₂、MgO、CaO、MgCaO、ScO_xOr a combination of two or more thereof, and the process used for depositing the insulating material is an atomic layer deposition method or a chemical vapor deposition method.

And 6) depositing a grid metal (7) by adopting an electron beam evaporation or sputtering process, wherein the grid metal is any one or combination of any more of Ni, Ti, Al, Au, W, Cr, Ta, Mo, Pt, TiC, TiN and TiW.

10. The method of claim 5, wherein: the annealing process after deposition in the step 5) is annealing treatment for 10s-30min under the environment of 400-1000 ℃ so as to improve the quality of the interface between the medium and the semiconductor.

Technical Field

The invention belongs to the technical field of semiconductor devices, and particularly relates to a vertical-structure gradient aluminum component aluminum gallium nitride metal oxide semiconductor field effect transistor MOSFET which can be used as a high-voltage and high-power electronic device.

Background

The AlGaN belongs to a super-wide bandgap semiconductor material, and the forbidden band width of the AlGaN is 4-6eV according to the difference of aluminum components in the AlGaN, so that the critical breakdown electric field strength of 8-12MV/cm is obtained, and the Baligy value reaches 10⁴The above characteristics show that the AlGaN has great development potential in the field of power electronics. Meanwhile, the AlGaN material also has higher thermal conductivity, so that the AlGaN device can stably work in a high-temperature environment. In addition, the AlGaN material can be doped in an n-type and a p-type manner, so that the AlGaN material has the possibility of preparing devices with complex structures and excellent performance.

At present, most of AlGaN MOSFETs use sapphire as substrate materials, although the technology for growing AlGaN on the sapphire substrate is mature, the growth thickness of the AlGaN materials on the sapphire is limited by huge lattice mismatch between the sapphire and the AlGaN, and the AlGaN materials are easy to crack in the growth process, so that the AlGaN MOSFETs of the sapphire substrate have single structures and are all horizontal structures. Sanyam Bajaj and hirori Okumura have published papers on aluminum gallium nitride field effect transistors on sapphire substrates in 2018, respectively. The thickness of the AlGaN wafer channel layer selected by the AlGaN wafer is 100-250nm, and the thickness of the field effect transistor channel is thin, so that the application of a complex terminal structure in a device is limited, and the breakdown voltage of the device cannot be further improved by depending on the terminal structure. In addition, the horizontal structure MOSFET only can increase the breakdown voltage by increasing the distance between the grid and the drain, and the power device wastes a larger area and is difficult to apply to a large-scale circuit.

Compared with a sapphire substrate, the lattice mismatch between the aluminum nitride substrate and the aluminum gallium nitrogen epitaxy is small, the thermal expansion coefficients are basically the same, the vertical MOSFET can be prepared by adopting the aluminum nitride as the substrate of the aluminum gallium nitrogen MOSFET device, and the performance of the device is greatly improved. Yoshihiro Irokawa published a paper about an aluminum nitride substrate in 2012, which prepared the aluminum nitride substrate using a physical vapor transport method and prepared a schottky diode on the aluminum nitride substrate. The threading dislocation of the aluminum nitride substrate provides a leakage path for the device, so that the prepared Schottky diode has high leakage current and cannot be practically applied. In addition, the aluminum nitride single crystal substrate which is available at present is expensive in sale price, the price of the aluminum nitride single crystal substrate with the diameter of 5 cm is as high as 5 ten thousand yuan RMB, and the high price limits research on related devices by research institutions.

Disclosure of Invention

The invention aims to provide a gallium nitride substrate-based gradient aluminum component aluminum gallium nitride MOSFET and a preparation method thereof aiming at the defects of the prior art, so as to improve the breakdown voltage of a device, reduce the cost and reduce the electric leakage of the device.

The technical scheme of the invention is as follows:

1. a graded aluminum component AlGaN MOSFET based on a gallium nitride substrate comprises from bottom to top: drain electrode, gallium nitride substrate, gallium nitride epitaxial layer, aluminium gallium nitrogen drift region, the intermediate position of aluminium gallium nitrogen drift region top is source metal, and both sides are the grid dielectric layer, and the top of grid dielectric layer is grid metal, its characterized in that:

the gallium nitride substrate adopts n-type gallium nitride with the doping concentration of 10¹⁶-10²⁰cm^-3The threading dislocation of the substrate and the lattice mismatch and electric leakage between the epitaxial layer and the substrate are reduced, and the growth thickness and quality of the aluminum gallium nitrogen drift region are improved.

The gallium nitride epitaxial layer has a doping concentration of 10¹⁵-10²⁰cm^-3Used as a transition layer between the substrate and the AlGaN epitaxy to reduce lattice mismatch between the substrate and the AlGaN drift region and improve AlGaNAnd (4) quality of the epitaxial wafer.

The AlGaN drift region is made of an AlGaN material with gradually changed aluminum components, the AlGaN is doped in an n type mode, the aluminum components are gradually increased from one side close to the gallium nitride epitaxy to one side far away from the gallium nitride epitaxy, the variation range of the aluminum components is 0-100%, and the doping concentration is 10¹⁵-10²⁰cm^-3The mismatch and dislocation density between the low-aluminum component AlGaN close to the GaN epitaxy and the GaN epitaxy are reduced, and the high-aluminum component AlGaN material far away from the substrate has the characteristics of high critical breakdown electric field and high Baglia optimum value.

Furthermore, the metal deposited on the drain electrode and the source electrode is any one or the combination of any several of Ni, Ti, Al, Au, W, Cr, Ta, Mo, TiC, TiN and TiW.

Further, the grid dielectric layer is made of insulating material Al₂O₃、SiO₂、SiN_x、HfO₂、MgO、CaO、MgCaO、ScO_xAny one or a combination of two or more of them.

Further, the grid metal is any one or combination of any several of Ni, Ti, Al, Au, W, Cr, Ta, Mo, Pt, TiC, TiN and TiW.

2. A preparation method of a gradient aluminum component AlGaN MOSFET of a gallium nitride substrate is characterized by comprising the following steps:

1) the doping concentration is 10¹⁶-10²⁰cm^-3The n-type gallium nitride substrate adopts a molecular beam epitaxy growth method or a metal organic compound chemical vapor deposition method to grow a gallium nitride epitaxial layer and an aluminum gallium nitrogen drift region with gradually changed aluminum components from bottom to top, wherein the doping concentration of the gallium nitride epitaxial layer is 10¹⁵-10²⁰cm^-3The aluminum component of the aluminum gallium nitrogen drift region with gradually changed aluminum component gradually increases from one side close to the gallium nitride epitaxial layer to one side far away from the gallium nitride epitaxial layer, the range of the aluminum component is 0-100%, and the doping concentration is 10¹⁵-10²⁰cm^-3；

2) Carrying out organic cleaning and inorganic cleaning on the epitaxial wafer on which the gallium nitride epitaxial layer and the gradient aluminum component AlGaN drift region grow;

3) depositing drain metal below the n-type gallium nitride substrate of the epitaxial wafer to form a drain, and forming ohmic contact on the drain through a high-temperature annealing process;

4) photoetching source electrode regions in regions on two sides above an aluminum gallium nitrogen drift region with a gradually-changed aluminum component of an epitaxial wafer, depositing metal in the source electrode regions by using photoresist as a mask to form source electrodes, and forming source electrode ohmic contact through a high-temperature annealing process;

5) placing the epitaxial wafer with the ohmic contact of the drain electrode and the source electrode into an insulating medium growth system, depositing a grid medium above the AlGaN drift region, and annealing the grid medium by adopting an annealing process;

6) and photoetching a grid electrode region above the grid electrode medium, and depositing metal in the grid electrode region to form a grid electrode, thereby finishing the manufacture of the device.

Compared with the prior art, the invention has the following advantages:

1. the invention adopts the doping concentration of 10¹⁶-10²⁰cm^-3The n-type gallium nitride substrate reduces the threading dislocation of the substrate and the lattice mismatch and electric leakage between the epitaxial layer and the substrate, improves the growth thickness and quality of the aluminum gallium nitrogen drift region, and reduces the preparation cost of the device.

2. The invention adopts the gradient aluminum component aluminum gallium nitrogen material as the drift region, the aluminum component of the aluminum gallium nitrogen material close to the substrate is low, the lattice constant of the low aluminum component aluminum gallium nitrogen is similar to that of the gallium nitride, not only can the lattice mismatch and the dislocation density be effectively reduced, but also the gradient aluminum component can avoid the cracking caused by the lattice mismatch in the wafer growth process, the growth thickness of the epitaxial layer is increased, and the breakdown voltage of the MOSFET is improved.

3. The invention adopts the gradient aluminum component aluminum gallium nitrogen material as the drift region, so that the aluminum component of the aluminum gallium nitrogen material near the grid electrode is high, the forbidden band width of the high-aluminum component aluminum gallium nitrogen material is large, the critical breakdown electric field intensity is high, and the breakdown voltage of the MOSFET can be further improved.

Drawings

FIG. 1 is a diagram of the structure of a device of the present invention;

fig. 2 is a flow chart of an implementation of the present invention to fabricate the device of fig. 1.

Detailed Description

The invention is described in further detail below with reference to the figures and examples.

Referring to fig. 1, the gradually-changed aluminum component aluminum gallium nitride metal oxide semiconductor field effect transistor MOSFET based on a gallium nitride substrate of the invention comprises a drain 1, a gallium nitride substrate 2, a gallium nitride epitaxial layer 3, a gradually-changed aluminum component aluminum gallium nitride drift region 4, a source 5, a gate dielectric layer 6 and a gate 7, wherein the drain 1, the gallium nitride substrate 2, the gallium nitride epitaxial layer 3 and the gradually-changed aluminum component aluminum gallium nitride drift region 4 are distributed from bottom to top, the source 5 is located in two side regions above the gradually-changed aluminum component aluminum gallium nitride drift region 4, the gate dielectric layer 6 is located in the middle position above the gradually-changed aluminum component aluminum gallium nitride drift region 4, and the gate 7 is located above the gate dielectric layer 6.

The doping concentration of the gallium nitride substrate 2 is 10¹⁶-10²⁰cm^-3；

The growth method of the gallium nitride epitaxial layer 3 and the gradient aluminum component AlGaN drift region 4 is a molecular beam epitaxy growth method or a metal organic compound chemical vapor deposition method, and the doping concentration is 10¹⁵-10²⁰cm^-3The content of aluminum in the aluminum gallium nitrogen drift region with gradually changed aluminum components is gradually increased from the position close to the gallium nitride epitaxial layer 3 to the position far away from the gallium nitride epitaxial layer 3, and the aluminum components are 0-100%;

the drain electrode 1 and the source electrode 5 are made of any one or a combination of any several of Ni, Ti, Al, Au, W, Cr, Ta, Mo, TiC, TiN and TiW, and the deposition process of the metal is electron beam evaporation or sputtering;

the grid dielectric layer 6 is made of insulating material Al₂O₃、SiO₂、SiN_x、HfO₂、MgO、CaO、MgCaO、ScO_xAny one or the combination of two or more, the deposited insulating material adopts an atomic layer deposition method or a chemical vapor deposition method;

the grid 7 is made of any one or combination of any several of Ni, Ti, Al, Au, W, Cr, Ta, Mo, Pt, TiC, TiN and TiW, and the deposition process of the metal is electron beam evaporation or sputtering.

Referring to fig. 2, the invention produces a graded aluminum composition aluminum gallium nitride MOSFET based on a gallium nitride substrate, and provides the following three embodiments:

example 1: at a doping concentration of 5X 10¹⁹cm^-3The doping concentration of the epitaxial layer of the gallium nitride prepared on the n-type gallium nitride substrate is 5 multiplied by 10¹⁶cm^-3The doping concentration of the Al-Ga-N drift region with gradually changed Al component is 1 multiplied by 10¹⁷cm^-3And the aluminum component of the aluminum gallium nitride near one side of the gallium nitride epitaxial layer is 10 percent, and the aluminum component of the aluminum gallium nitride far away from the gallium nitride epitaxial layer is 70 percent of the gradient aluminum component aluminum gallium nitride MOSFET.

Step 1: and growing a gallium nitride epitaxial layer and a gradient aluminum component aluminum gallium nitrogen drift region on the n-type gallium nitride substrate in sequence, and cleaning.

1.1) selecting a doping concentration of 5X 10¹⁹cm^-3An n-type gallium nitride substrate of (1);

1.2) putting the gallium nitride substrate into a molecular beam epitaxy growth instrument, keeping the temperature of the substrate sheet at 730 ℃, introducing gallium metal molecular beams and nitrogen into the molecular beam epitaxy growth instrument, and setting the equivalent pressure of the gallium metal molecular beams to be 2 multiplied by 10^-7Torr, plasma generating power of nitrogen gas is 200W, flow is 1.85sccm, SiH is doped in the growth process₄SiH control as n-type impurity₄The ratio of the flux to the gallium metal molecular beam is 5 multiplied by 10^-4The doping concentration of the gallium nitride epitaxial layer is 1 × 10¹⁷cm^-3Growing a gallium nitride epitaxial layer with the thickness of 200nm on a gallium nitride substrate;

1.3) keeping the temperature of the epitaxial wafer at 850 ℃, introducing aluminum metal molecular beams, gallium metal molecular beams and nitrogen into a molecular beam epitaxial growth instrument, wherein the plasma generation power of the nitrogen is 200W, the flow rate is 1.85sccm, and an aluminum gallium nitrogen drift region grows on a gallium nitride epitaxial layer:

SiH incorporation during growth₄SiH control as n-type impurity₄The ratio of the flux of the gallium metal molecular beam to the flux of the gallium metal molecular beam is 3 multiplied by 10^-4The doping concentration of the AlGaN drift region is 510¹⁶cm^-3And the ratio of the aluminum molecular beam flow rate is 10% and the ratio of the gallium molecular beam flow rate is 90% at the beginning of growth;

then, controlling the flow ratio of the aluminum and gallium molecular beams by adjusting the temperature of an aluminum source and a gallium source, so that the flow ratio of the aluminum source is gradually increased until the flow ratio of the aluminum molecular beam is 70 percent and the flow ratio of the gallium molecular beam is 30 percent, and obtaining an n-type gradually-changed aluminum component aluminum gallium nitrogen drift region with the thickness of 8 mu m;

1.4) putting the epitaxial wafer into acetone, isopropanol and deionized water in sequence, respectively carrying out ultrasonic cleaning for 5min for organic cleaning, and then carrying out organic cleaning by using H₂SO₄:H₂O₂Soaking the epitaxial wafer in piranha solution with the ratio of 3:1 for 2min for inorganic cleaning, and finally drying the epitaxial wafer by using a nitrogen gun.

Step 2: and preparing a drain electrode.

2.1) putting the cleaned epitaxial wafer into an electron beam evaporation table, and depositing Ti/Al/Ni/Au with the thickness of 22/140/55/45nm below the n-type high-nitrogen-doped gallium substrate to be used as drain metal of the MOSFET;

2.2) putting the epitaxial wafer into a rapid thermal annealing furnace, and annealing the epitaxial wafer deposited with the drain metal for 30s in the atmosphere of nitrogen at 800 ℃ to ensure that the drain metal and the gallium nitride substrate form ohmic contact.

And step 3: and preparing a source electrode.

3.1) photoetching the epitaxial wafer which finishes the step 2 on the gradient aluminum component AlGaN drift region to determine the position of a source electrode;

3.2) putting the epitaxial wafer into an electron beam evaporation table, and performing Ti/Al/Au source electrode metal deposition with the thickness of 15/60/50nm on the aluminum gallium nitrogen drift region with the gradually-changed aluminum component;

3.3) placing the epitaxial wafer with the deposited source metal into a rapid thermal annealing furnace, and annealing for 30s in the atmosphere of nitrogen at 900 ℃ to form ohmic contact between the source metal and the AlGaN drift region.

And 4, step 4: and growing a gate dielectric.

4.1) sequentially putting the slices which are subjected to the step 3 into acetone, isopropanol and deionized water, and respectively carrying out ultrasonic cleaning for 5 min;

4.2) putting the cleaned epitaxial wafer into an atomic layer deposition device, using magnesium dicocene as a precursor of magnesium, keeping the temperature of a magnesium source at 110 ℃, keeping the temperature of a reaction cavity at 320 ℃, sequentially introducing the magnesium dicocene and water into the reaction cavity for cyclic growth according to the duration of 0.15s/0.3s, and growing 20nm of MgO above an AlGaN drift region of the epitaxial wafer as a gate medium by controlling the cycle times;

4.3) putting the epitaxial wafer on which the gate dielectric is deposited into a rapid annealing furnace, and annealing for 5min in the atmosphere of nitrogen at 400 ℃ to reduce the interface state density between the gate dielectric and the AlGaN drift region.

And 5: and preparing a grid electrode.

5.1) photoetching the epitaxial wafer which is subjected to the step 4 above a grid medium to determine the position of a grid;

and 5.2) putting the epitaxial wafer into an electron beam evaporation table, performing Ni/Au deposition with the thickness of 50/150nm on a gate medium, and performing gate metal deposition to finish the manufacture of the device.

Example 2: at a doping concentration of 8 × 10¹⁶cm^-3The doping concentration of the epitaxial layer of the gallium nitride prepared on the n-type gallium nitride substrate is 1 multiplied by 10¹⁶cm^-3The doping concentration of the aluminum gallium nitrogen drift region with gradually changed aluminum components is 3 multiplied by 10¹⁵cm^-3And the aluminum component of the aluminum gallium nitride near one side of the gallium nitride epitaxial layer is 5 percent, and the aluminum component of the aluminum gallium nitride far away from the gallium nitride epitaxial layer is 60 percent of the gradual change aluminum component aluminum gallium nitride MOSFET.

Step A: and growing a gallium nitride epitaxial layer and a gradient aluminum component aluminum gallium nitrogen drift region on the n-type gallium nitride substrate in sequence, and cleaning.

A1) The doping concentration is selected to be 8 multiplied by 10¹⁶cm^-3An n-type gallium nitride substrate of (1);

A2) putting a gallium nitride substrate into a metal organic compound chemical vapor deposition system, keeping the temperature of a cavity at 1050 ℃ and the pressure at 400mbar, growing a gallium nitride epitaxial layer by using trimethyl gallium and ammonia as precursors of aluminum, gallium and nitrogen elements, wherein the flow rates of the trimethyl gallium and the ammonia are 440ml/min and 28000ml/min respectively, and SiH is doped in the growth process₄SiH control as n-type impurity₄The ratio of the flow rate of trimethyl gallium to the flow rate of trimethyl gallium is 6 x 10^-5The doping concentration of the gallium nitride epitaxial layer is 1 x 10¹⁶cm^-3Growing a gallium nitride epitaxial layer with the thickness of 1 mu m on a gallium nitride substrate;

A3) after growing the gallium nitride epitaxial layer, keeping the temperature of the cavity at 1200 ℃ and the pressure at 400mbar in the nitrogen atmosphere, and growing an aluminum gallium nitrogen drift region by using trimethylaluminum, trimethylgallium and ammonia as precursors of aluminum, gallium and nitrogen elements respectively:

SiH incorporation during growth₄SiH control as n-type impurity₄The ratio of the flow rate to the sum of the flow rates of the aluminum source and the gallium source is 2 x 10^-5The doping concentration of the AlGaN drift region is 3 multiplied by 10¹⁵cm^-3And keeping the flow rate of ammonia at 30000ml/min, and enabling the flow rates of an aluminum source and a gallium source to be 20ml/min and 400ml/min respectively when the growth is started so that the aluminum component in the aluminum gallium nitrogen is 5 percent;

then gradually increasing the flow rate of an aluminum source and reducing the flow rate of a gallium source to ensure that the flow rates of the aluminum source and the gallium source are 270ml/min and 180ml/min respectively, and the aluminum component in the aluminum-gallium-nitrogen is 60 percent to obtain an n-type gradually-changed aluminum component aluminum-gallium-nitrogen drift region with the thickness of 10 mu m;

A4) sequentially placing the epitaxial wafer into acetone, isopropanol and deionized water, respectively ultrasonically cleaning for 10min for organic cleaning, and then cleaning with HCl H₂Soaking the epitaxial wafer in a hydrochloric acid diluent with the ratio of O to 10 for 5min for inorganic cleaning, and finally blowing the epitaxial wafer by using a nitrogen gun.

And B: and preparing a drain electrode.

B1) Putting the cleaned epitaxial wafer into a magnetron sputtering system, and sputtering Ti/Al with the thickness of 40/200nm below the n-type gallium nitride substrate to be used as drain metal of the MOSFET;

B2) putting the epitaxial wafer into a rapid thermal annealing furnace, and annealing the epitaxial wafer deposited with the drain metal for 30s in the atmosphere of nitrogen at 750 ℃ so as to form ohmic contact between the drain metal and the gallium nitride substrate;

and C: and preparing a source electrode.

C1) B, photoetching the epitaxial wafer which is subjected to the step B above the gradient aluminum component AlGaN drift region to determine the position of the source electrode;

C2) placing the epitaxial wafer into a magnetron sputtering system, and depositing Ti/Al/Au with the thickness of 15/60/50nm on the gradient aluminum component AlGaN drift region to serve as source metal;

C3) placing the epitaxial wafer on which the source metal is deposited into a rapid thermal annealing furnace, and annealing for 30s in a nitrogen atmosphere at 950 ℃ to form ohmic contact between the source metal and the AlGaN drift region;

step D: and growing a gate dielectric.

D1) C, sequentially putting the chips subjected to the step C into acetone, isopropanol and deionized water, and respectively ultrasonically cleaning for 5 min;

D2) putting the cleaned epitaxial wafer into atomic layer deposition equipment, and depositing Al with the thickness of 5/15nm above an AlGaN drift region by using trimethylaluminum as a precursor of an aluminum element₂O₃/HfO₂As a grid medium, keeping the temperature of an aluminum source at 200 ℃, simultaneously keeping the temperature of a reaction cavity at 250 ℃, sequentially introducing trimethylaluminum and water into the reaction cavity for cyclic growth according to the time length of 0.2s/0.3s, and growing 5nm of Al on one side of a source electrode by controlling the cycle times₂O₃；

D3) Keeping an epitaxial wafer in atomic layer deposition equipment, using tetra (dimethylamino) hafnium as a precursor of a hafnium element, enabling the temperature of a hafnium source to be 120 ℃, simultaneously keeping the temperature of a reaction cavity to be 300 ℃, sequentially introducing the tetra (dimethylamino) hafnium and water into the reaction cavity for cyclic growth according to the duration of 0.2s/0.4s, and controlling the cycle number to perform cyclic growth on Al₂O₃Overgrowth of HfO of 15nm₂To obtain 5/15nm thick Al₂O₃/HfO₂Depositing a grid dielectric;

D4) and (3) placing the epitaxial wafer on which the gate dielectric is deposited into a rapid annealing furnace, and annealing for 5min in a nitrogen atmosphere at 500 ℃ to reduce the interface state density between the gate dielectric and the AlGaN drift region.

Step E: and preparing a grid electrode.

E1) D, photoetching is carried out on the epitaxial wafer which is subjected to the step D at one side of the grid dielectric, and the position of the grid is determined;

E2) and (3) putting the epitaxial wafer into an electron beam evaporation table, and depositing Ni/Au/Ni with the thickness of 50/100/50nm above the gate dielectric to be used as gate metal to finish the manufacture of the device.

Example 3: at a doping concentration of 1X 10²⁰cm^-3The doping concentration of the epitaxial layer of the gallium nitride prepared on the n-type gallium nitride substrate is 1 multiplied by 10²⁰cm^-3The doping concentration of the Al-Ga-N drift region with gradually changed Al component is 1 multiplied by 10¹⁹cm^-3And the aluminum component of the aluminum gallium nitride near one side of the gallium nitride epitaxial layer is 15%, and the aluminum component of the aluminum gallium nitride far away from the gallium nitride epitaxial layer is 85% of the gradient aluminum component aluminum gallium nitride MOSFET.

The method comprises the following steps: an n-type gallium nitride substrate is selected, a gallium nitride epitaxial layer and a gradient aluminum component aluminum gallium nitrogen drift region are sequentially grown on the substrate, and cleaning operation is carried out.

Firstly, the doping concentration is selected to be 1 × 10²⁰cm^-3An n-type gallium nitride substrate of (1);

secondly, putting the gallium nitride substrate into a metal organic compound chemical vapor deposition system, keeping the temperature of a cavity at 1050 ℃ and the pressure at 400mbar, growing a gallium nitride epitaxial layer by using trimethyl gallium and ammonia as precursors of aluminum, gallium and nitrogen elements, wherein the flow rates of the trimethyl gallium and the ammonia during growth are 440ml/min and 28000ml/min respectively, and doping SiH during growth₄SiH control as n-type impurity₄The ratio of the flow rate of trimethyl gallium to the flow rate of trimethyl gallium is 8 x 10^-2The doping concentration of the gallium nitride epitaxial layer is 1 x 10²⁰cm^-3Growing a gallium nitride epitaxial layer with the thickness of 2 mu m on the gallium nitride substrate;

thirdly, after growing the gallium nitride epitaxial layer, keeping the temperature of the cavity at 1200 ℃ and the pressure at 400mbar in the nitrogen atmosphere, growing an aluminum gallium nitrogen drift region by using trimethylaluminum, trimethylgallium and ammonia as precursors of aluminum, gallium and nitrogen elements respectively, and keeping the flow rate of ammonia at 30000ml/min during growth, and doping SiH₄SiH control as n-type impurity₄The ratio of the flow rate to the sum of the flow rates of the aluminum source and the gallium source is 1 x 10^-2The doping concentration of the AlGaN drift region is 1 multiplied by 10¹⁹cm^-3；

When the growth is started, setting the flow rates of an aluminum source and a gallium source to be 60ml/min and 360ml/min respectively to ensure that the aluminum component in aluminum gallium nitrogen is 15 percent, gradually increasing the flow rate of the aluminum source and reducing the flow rate of the gallium source in the growth process to ensure that the flow rates of the aluminum source and the gallium source are 380ml/min and 70ml/min respectively, and the aluminum component in the aluminum gallium nitrogen is 85 percent to obtain an n-type gradual change aluminum component aluminum gallium nitrogen drift region with the thickness of 15 mu m;

finally, the epitaxial wafer after the epitaxial growth is sequentially placed into acetone, isopropanol and deionized water to be ultrasonically cleaned for 5min respectively for organic cleaning, and then H is used for cleaning₂SO₄:H₂O₂Soaking the epitaxial wafer in piranha solution with the ratio of 3:1 for 2min for inorganic cleaning, and finally drying the epitaxial wafer by using a nitrogen gun.

Step two: and preparing a drain electrode.

Placing the cleaned epitaxial wafer into an electron beam evaporation table, and depositing Ti/Al/Ni/Au below the n-type gallium nitride substrate to be used as drain metal of the MOSFET, wherein the thickness of the drain metal is 22/140/55/45 nm; and then putting the epitaxial wafer into a rapid thermal annealing furnace, and annealing the epitaxial wafer deposited with the drain metal for 30s in the atmosphere of nitrogen at 1000 ℃ to form ohmic contact between the drain metal and the gallium nitride substrate.

Step three: and preparing a source electrode.

Photoetching the epitaxial wafer which is subjected to the second step above the gradient aluminum component AlGaN drift region to determine the position of the source electrode; then placing the silicon substrate in an electron beam evaporation table, and depositing Ti with the thickness of 100nm on the aluminum gallium nitrogen drift region of the gradual change aluminum component to serve as source metal; and (3) placing the epitaxial wafer on which the source metal is deposited into a rapid thermal annealing furnace, and annealing for 30s in the atmosphere of nitrogen at 800 ℃ to enable the source metal and the AlGaN drift region to form ohmic contact.

Step four: and growing a gate dielectric.

Sequentially putting the slices subjected to the third step into acetone, isopropanol and deionized water, and respectively ultrasonically cleaning for 5 min; placing the cleaned epitaxial wafer into a chemical vapor deposition device, setting the pressure of a reaction chamber to be 0.5Pa and the temperature to be 200 ℃, and simultaneously introducing SiH with the flow of 20sccm into the reaction chamber₄And 15sccm of N₂O, in AlGaN bleachingDepositing 50nm SiO on the moving region₂As a gate dielectric; and (3) placing the epitaxial wafer on which the gate dielectric is deposited into a rapid annealing furnace, and annealing for 5min in a nitrogen atmosphere at 500 ℃ to reduce the interface state density between the gate dielectric and the AlGaN drift region.

Step five: and preparing a grid electrode.

Photoetching the epitaxial wafer which is subjected to the fourth step at one side of the grid dielectric of the epitaxial wafer to determine the position of the grid; and then putting the silicon wafer into a magnetron sputtering device, and depositing 100nm W above the gate dielectric to be used as gate metal to finish the manufacture of the device.

While the foregoing is directed to three specific examples of the present invention and is not intended to limit the invention thereto, it will be apparent to those skilled in the art that various changes and modifications in form and detail may be made therein without departing from the principles and structures of the present invention, such as adding termination structures to the MOSFET devices; the source and drain metals may be any one or a combination of any several of W, Cr, Ta, Mo, TiC, TiN and TiW in addition to the metals used in the above embodiments, the gate metal may be any one or a combination of any several of Cr, Ta, Mo, Pt, TiC, TiN and TiW in addition to the metals used in the above embodiments, and the gate dielectric may be SiN in addition to the insulating material used in the above embodiments_x、CaO、MgCaO、ScO_xAny one or any combination of several. Such modifications and variations are within the spirit of the invention and the scope of the following claims.