CN114420753B - HEMT device, HEMT epitaxial structure based on GaN substrate and manufacturing method - Google Patents

Abstract

The present invention discloses a HEMT device, a HEMT epitaxial structure based on a GaN substrate, and a manufacturing method. The HEMT epitaxial structure based on a GaN substrate includes an interface treatment layer, a barrier layer, an isolation layer, a channel layer, and a contact layer sequentially formed on an N-face polarity semi-insulating GaN substrate. Based on the characteristics of the N-face GaN substrate, the present invention proposes a HEMT device with a new epitaxial structure, which has higher frequency characteristics compared to traditional structures. In addition, the GaN substrate and the semi-insulating characteristics can be achieved through early preparation, which can avoid the adverse effects of the subsequent growth of a high-resistance epitaxial layer. In addition, homogeneous epitaxy does not have the problem of a high-density dislocation buffer layer on a heterogeneous substrate. Proper interface treatment before epitaxy can completely block the generation of leakage channels.

Description

HEMT device, HEMT epitaxial structure based on GaN substrate and manufacturing method

Technical Field

The invention relates to an HEMT device, in particular to an HEMT device, an HEMT epitaxial structure based on a GaN substrate and a manufacturing method, and belongs to the technical field of semiconductors.

Background

The prior GaN-based HEMT device is mainly prepared on a heterogeneous substrate such as SiC/Si, as shown in fig. 1, in the preparation process, an AlN buffer layer needs to be deposited firstly, so as to reduce lattice mismatch with GaN, after transition of the buffer layer, an iron-doped or carbon high-resistance GaN layer continues to grow, and a GaN channel layer, an AlN isolation layer, an AlGaN barrier layer and a GaN cap layer structure are sequentially stacked on the high-resistance GaN layer, wherein a very large potential well is formed at the interface of the GaN channel layer and the AlGaN barrier layer, electrons are limited in the thin layer, high-density two-dimensional electron gas (2 DEG) is formed in the channel layer, the AlN isolation layer is very thin, interface quality can be improved, scattering is reduced, electron mobility is improved, meanwhile discontinuity of a conduction band is also improved, density of the 2DEG is increased, the GaN layer aims at reducing a gate electric field, inhibiting gate current, and generating of surface oxides is reduced, and the whole GaN-based HEMT device is a Ga surface.

Although the improvement of the epitaxial technology improves the crystal quality, with the new application of the high-frequency field, such as microwave heating, 5G system communication and the like, the requirement on the output efficiency of the device is further improved, because the buffer layer on the heterogeneous substrate has high-density dislocation, and a leakage channel with electron loss is formed at the interface between the GaN cap layer and the passivation layer (usually SiN), so that current collapse is caused, the improvement of the performance of the GaN-based HEMT is restricted, meanwhile, the heterogeneous substrate needs to grow a high-resistance GaN layer with the thickness of about 2-4 microns above the buffer layer, and the high-resistance GaN layer generally needs to be doped with iron or carbon, which causes the risk of doped memory effect to exist in the subsequent growth, and also has adverse effect on the quality of the device.

Disclosure of Invention

The invention mainly aims to provide a HEMT device, a HEMT epitaxial structure based on a GaN substrate and a manufacturing method thereof, so as to overcome the defects in the prior art.

In order to achieve the purpose of the invention, the technical scheme adopted by the invention comprises the following steps:

The embodiment of the invention provides a High Electron Mobility Transistor (HEMT) epitaxial structure based on a gallium nitride (GaN) substrate, which comprises an interface treatment layer, a barrier layer, an isolation layer and a channel layer which are sequentially formed on a semi-insulating GaN substrate with N-face polarity.

The embodiment of the invention also provides a manufacturing method of the HEMT epitaxial structure, which comprises the following steps:

providing a semi-insulating GaN substrate with N-face polarity;

Forming an interface treatment layer on the N-face polar semi-insulating GaN substrate, wherein the growth conditions of the interface treatment layer comprise that 50-80% of hydrogen and 20-50% of ammonia are taken as raw materials, the raw materials react for 5-10 minutes under the conditions of 1050C-1100C and 400-700 mbar, and then an Al source is introduced at the flow rate of 0-50 umol/min;

and sequentially growing a barrier layer, an isolation layer and a channel layer on the interface treatment layer.

The embodiment of the invention also provides a HEMT device, which comprises:

the HEMT epitaxial structure;

And a source, a drain, and a gate cooperating with the HEMT epitaxial structure, the gate being distributed between the source and the drain.

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

1) The GaN substrate and the semi-insulating characteristic in the HEMT epitaxial structure based on the GaN substrate can be finished through early preparation, and adverse effects caused by the later growth of a high-resistance epitaxial layer can be avoided;

2) In the HEMT epitaxial structure based on the GaN substrate, the homoepitaxy does not have the problem of a high-density dislocation buffer layer on a heterogeneous substrate, and the generation of a leakage channel can be completely blocked by performing proper interface treatment in epitaxial growth;

3) GaN is a polar material, the contact resistance of the N-face polar GaN material is lower, and the surface state density between the N-face polar GaN material and the passivation layer can be improved, so that the occurrence of the problem of electric leakage is avoided;

4) The N-face polar GaN material has higher transconductance and can support higher working frequency.

Drawings

Fig. 1 is a schematic structural diagram of a HEMT epitaxial structure based on a SiC hetero-substrate in the prior art;

Fig. 2 is a schematic structural diagram of a GaN substrate-based HEMT epitaxial structure provided in an exemplary embodiment of the present invention;

FIG. 3 is an effect diagram of a prior art HEMT epitaxial structure based on a SiC hetero-substrate;

fig. 4 is an effect diagram of a GaN substrate-based HEMT epitaxial structure provided in an exemplary embodiment of the present invention;

Fig. 5 is an I-V test curve of the GaN substrate-based HEMT device obtained in example 1 of the present invention and the SiC hetero-substrate-based HEMT device obtained in comparative example 1.

Detailed Description

In view of the shortcomings in the prior art, the inventor of the present invention has long studied and practiced in a large number of ways to propose the technical scheme of the present invention. The technical scheme, the implementation process, the principle and the like are further explained as follows.

HEMT (High Electron Mobility Transistor), a high electron mobility transistor, is a heterojunction field effect transistor, also known as a modulation doped field effect transistor (MODFET), a two-dimensional electron gas field effect transistor (2-DEGFET), a Selectively Doped Heterojunction Transistor (SDHT), and the like.

The HEMT device and the integrated circuit thereof can work in the ultra-high frequency (millimeter wave) and ultra-high speed fields, because the HEMT device works by utilizing the so-called two-dimensional electron gas with very high mobility, the basic structure of the HEMT is a modulation doping heterojunction, the two-dimensional electron gas (2-DEG) with high mobility exists in the modulation doping heterojunction, the 2-DEG has very high mobility and is not frozen at very low temperature, and the HEMT has very good low-temperature performance and can be used in low-temperature research work (such as fractional quantum Hall effect).

The HEMT device is a voltage control device, and the gate voltage Vg can control the depth of a heterojunction potential well, so that the areal density of 2-DEG in the potential well can be controlled, and the working current of the device is controlled. For a GaAs system HEMT, the n-Al _xGa_1-x As control layer should be depleted (typically hundreds of nanometers in thickness and 10 ⁷～10⁸/cm³ in doping concentration), if the n-Al _xGa_1-x As layer is thicker and has a high doping concentration, then there is a 2-DEG at vg=0, and the depletion device is a depletion type device, otherwise an enhancement type device (the Schottky depletion layer extends into the i-GaAs layer at vg=0), but if the thickness is too great and the doping concentration is too high, the layer cannot be depleted during operation, and a leakage resistance in parallel with S-D will also occur.

Silicon carbide (SiC) is produced by high-temperature smelting of quartz sand, petroleum coke (or coal coke), wood dust (salt is needed to be added in the production of green silicon carbide) and other raw materials through a resistance furnace, and among the non-oxide high-technology refractory raw materials such as C, N, B in the current generation, silicon carbide is one of the most widely applied and economical raw materials, and can be called as diamond sand or refractory sand. The silicon carbide produced at present is divided into black silicon carbide and green silicon carbide, and the silicon carbide is hexagonal crystal, the specific gravity is 3.20-3.25, and the microhardness is 2840-3320 kg.

Silicon carbide has stable chemical performance, high heat conductivity, small heat expansion coefficient and good wear resistance, and besides being used as abrasive, the silicon carbide powder is coated on the inner wall of a turbine impeller or a cylinder body by a special process, for example, the wear resistance of the silicon carbide powder can be improved by 1-2 times, the service life of the silicon carbide powder can be prolonged, the silicon carbide powder is used for preparing high-grade refractory materials, and the silicon carbide powder has the advantages of heat shock resistance, small volume, light weight, high strength and good energy-saving effect, and low-grade silicon carbide (containing about 85 percent of SiC) is an excellent deoxidizer, so that the steelmaking speed can be accelerated, the chemical components can be conveniently controlled, and the quality of steel can be improved. In addition, silicon carbide is also used in large quantities for making electrical heating element silicon carbide rods.

In addition, silicon carbide has high hardness, mohs hardness of 9.5 grade, which is inferior to the hardest diamond (grade 10) in the world, has excellent heat conduction performance, is a semiconductor, and can resist oxidation at high temperature.

GaN is a very stable compound, a hard high melting point material, with a melting point of about 1700 ℃, and a high ionization degree, highest (0.5 or 0.43) in III-V compounds, and a crystal of GaN is typically a hexagonal wurtzite structure with 4 atoms in one cell and about half the atomic volume of GaAs at atmospheric pressure. The electrical characteristics of GaN are the main factors affecting the device, the undoped GaN is n-type in various cases, the electron concentration of the best sample is about 4 multiplied by 10 ¹⁶/cm³, the P-type samples prepared in general are high-compensation, the GaN material series has low heat generation rate and high breakdown electric field, and the GaN material series is an important material for developing high-temperature high-power electronic devices and high-frequency microwave devices.

At present, with the progress of MBE technology in GaN material application and the breakthrough of key film growth technology, a plurality of GaN heterostructures are successfully grown, and novel devices such as metal field effect transistors (MESFETs), heterojunction Field Effect Transistors (HFETs), modulation doped field effect transistors (MODFETs) and the like are prepared by using GaN materials. The modulated doped AlGaN/GaN structure has high electron mobility (2000 cm ² & s), high saturation speed (1 multiplied by 10 ⁷ cm/s) and lower dielectric constant, is a preferential material for manufacturing microwave devices, and has the advantages of good heat dissipation performance by taking materials such as GaN with wider forbidden band width (3.4 eV), sapphire and the like as a substrate, and is beneficial to the devices to work under high-power conditions.

GaN has large forbidden bandwidth (3.4 eV), high thermal conductivity (1.3W/cm-K), high working temperature, high breakdown voltage, strong radiation resistance, low GaN lattice symmetry (hexagonal wurtzite structure or tetragonal metastable sphalerite structure), strong piezoelectricity (caused by non-central symmetry) and ferroelectricity (spontaneous polarization along hexagonal c axis), strong piezoelectric polarization (polarization electric field reaching 2 MV/cm) and spontaneous polarization (spontaneous polarization) near a heterojunction interface, which can be made into various heterostructures, and has obtained 2-DEG with mobility reaching 10 ⁵cm²/Vs at low temperature (because the 2-DEG surface density is higher, effectively shielding factors such as optical phonon scattering, ionized impurity scattering and piezoelectric scattering), and extremely high piezoelectric polarization (spontaneous polarization along hexagonal c axis) near the heterojunction interface, thus achieving high-dimensional modulation effect of GaAs in the heterojunction (AlGaN) and having extremely high energy density of 5-62, and being more significant in the heterojunction space of the two-dimensional modulation of the heterojunction (GaAs) and having extremely high energy density of the heterojunction (AlGaN has been achieved.

The embodiment of the invention provides a High Electron Mobility Transistor (HEMT) epitaxial structure based on a gallium nitride (GaN) substrate, which comprises an interface treatment layer, a barrier layer, an isolation layer and a channel layer which are sequentially formed on a semi-insulating GaN substrate with N-face polarity.

Further, the growth conditions of the interface treatment layer comprise that 50-80% of hydrogen and 20-50% of ammonia are used as raw materials, the raw materials react for 5-10 minutes under the conditions of 1050deg.C-1100 ℃ and 400-700 mbar, and then an Al source is introduced at a flow rate of 0-50 umol/min, wherein the ratio of the hydrogen to the ammonia can be the volume ratio or the mass ratio.

Further, the interface treatment layer is made of AlN.

Further, the thickness of the interface treatment layer is 2-5nm.

Further, the material of the barrier layer comprises AlGaN or InGaN, wherein the content of Al or In components is 15-100%, and the thickness of the barrier layer is 15-25nm.

Further, the isolation layer is made of AlN, and the thickness of the isolation layer is 0.5-1nm.

Further, the channel layer is made of GaN, inN, in GaN or AlGaN, and has a thickness of 100-300 nm, wherein the AlGaN contains 0-15% of Al component and 0-15% of InGaN.

Further, a contact layer is formed on the channel layer, and the contact layer is made of InN and has a thickness of 1-3nm.

The embodiment of the invention also provides a manufacturing method of the HEMT epitaxial structure, which comprises the following steps:

providing a semi-insulating GaN substrate with N-face polarity;

forming an interface treatment layer on the N-face polar semi-insulating GaN substrate, wherein the growth conditions of the interface treatment layer comprise that 50-80% of hydrogen and 20-50% of ammonia are taken as raw materials, the raw materials react for 5-10 minutes under the conditions of 1050C-1100C and 400-700 mbar, and then an Al source is introduced at the flow rate of 0-50 umol/min, wherein the ratio of the hydrogen to the ammonia can be the volume ratio or the mass ratio;

and sequentially growing an insertion layer, a barrier layer and a channel layer on the interface treatment layer.

When the HEMT epitaxial structure is manufactured, only a small amount of Al source is required to be introduced, and the specific amount of Al source introduced can be determined according to specific production requirements, and is not particularly limited.

Further, the manufacturing method further comprises the step of growing a contact layer on the channel layer.

The embodiment of the invention also provides a HEMT device, which comprises:

And a source electrode, a drain electrode and a grid electrode matched with the HEMT epitaxial structure, wherein the grid electrode is distributed between the source electrode and the drain electrode.

Further, the source and the drain are electrically combined with the contact layer, for example, the source and the drain form ohmic contact with the contact layer.

Furthermore, a gate dielectric layer is further distributed between the gate and the contact layer, and the gate dielectric layer may be made of a material known to those skilled in the art, and the thickness is not specifically limited.

The technical scheme, implementation process and principle and the like will be further explained with reference to the attached drawings and specific embodiments.

Example 1

Referring to fig. 2, a GaN substrate-based HEMT epitaxial structure includes an interface treatment layer, an AlGaN barrier layer, an AlN isolation layer, a GaN channel layer and an InN contact layer sequentially formed on an N-side polar semi-insulating GaN substrate, wherein the AlGaN barrier layer and the GaN channel layer cooperate to form a heterojunction, and a two-dimensional electron gas is provided between the AlGaN barrier layer and the GaN channel layer, wherein the thickness of the interface treatment layer is an AlN layer with a thickness of 5nm, the thickness of the AlGaN barrier layer is 20nm, the content of al components is 25% (mass fraction, the same below), the thickness of the AlN isolation layer is 1nm, the thickness of the GaN channel layer is 300nm, and the thickness of the InN contact layer is 2nm.

The manufacturing method of the HEMT epitaxial structure based on the GaN substrate specifically comprises the following steps:

1) Providing a semi-insulating GaN substrate with N-face polarity;

2) Placing a semi-insulating GaN substrate with N-side polarity in a reaction container or a reaction system, introducing 70% of hydrogen and 30% of ammonia into the reaction container or the reaction system at 1100 ℃ and 600mbar, and baking for 10 minutes (the aim is to remove impurity elements such as O in high-activity N-side GaN on the surface of the semi-insulating GaN substrate under the premise of ensuring the flatness);

3) Then the temperature of the reaction vessel or the reaction system is reduced to 1000 ℃, and a small amount of Al is introduced under the condition of 100mbar of pressure, so that a flat AlN layer with the thickness of about 5nm is formed by deposition, and the flatness of the epitaxial layer can be improved again because of the effect of filling holes, and meanwhile, the barrier layer containing Al can be used for laying and overgrowing to improve the flatness and crystal quality of the subsequent AlGaN/GaN heterojunction;

4) Maintaining the growth condition of an AlN interface treatment layer, and sequentially growing a 20nm AlGaN (Al component of 25%) barrier layer, a 1nm AlN isolation layer and a 300nm GaN channel layer on the AlN interface treatment layer, wherein the arrangement and manufacturing sequence of the AlGaN barrier layer and the GaN channel layer are different from that of a traditional Ga-surface HEMT, and the reason is that the built-in electric field of N-surface GaN is opposite, and the generated two-dimensional electron gas (2 DEG) positions are different;

5) The reaction vessel or system was cooled to 700 ℃ and an InN contact layer was grown on the GaN channel layer under a pressure of 300 mbar.

Comparative example 1

As shown in fig. 1, a HEMT epitaxial structure based on a SiC hetero-substrate includes a SiC hetero-substrate and an AlN buffer layer (about 200 nm), a high-resistance GaN layer (about 2 um), a GaN channel layer (about 300 nm), an AlN isolation layer (about 1 nm), an AlGaN barrier layer (about 20 nm) and a GaN (about 2 nm) cap layer sequentially disposed on the SiC hetero-substrate.

The GaN substrate-based HEMT device (defined as HEMT-1) obtained in example 1 of the present invention and the SiC hetero-substrate-based HEMT device (defined as HEMT-2) obtained in comparative example 1 were subjected to I-V test (the test method may be performed using methods and apparatuses known to those skilled in the art), respectively, and the test results are shown in fig. 5, and it can be seen from fig. 5 that the GaN substrate-based HEMT device obtained in example 1 of the present invention has a higher breakdown voltage and a lower buffer leakage current.

Specifically, referring to fig. 3 and 4, when the HEMT device is under a harsher working condition, the HEMT epitaxial structure based on the GaN substrate provided by the embodiment 1 of the invention adopts the semi-insulating GaN self-supporting substrate with N-face polarity compared with the HEMT epitaxial structure based on the SiC heterogeneous substrate in the comparative example 1, so that defects caused by lattice mismatch and thermal mismatch caused by heteroepitaxy can be avoided, and a leakage channel is caused at a buffer layer, and meanwhile, the embodiment 1 adopts the semi-insulating GaN substrate with N-face polarity to improve high-frequency response, adopts an InN contact layer to reduce the surface state density of the device, inhibit the leakage channel between an epitaxial layer and a passivation layer, and cut off the leakage channel from the two aspects, eliminate and reduce the current collapse effect, improve the high performance of the GaN-based HEMT device, and widen the application of the GaN-based HEMT device in high-temperature, high-frequency and high-power occasions.

Specifically, according to the manufacturing method of the HEMT epitaxial structure based on the GaN substrate, low-resistance connection of source/drain ends can be achieved only by penetrating through the GaN channel layer with smaller forbidden band width, unlike the existing HEMT epitaxial structure which needs to penetrate through the AlGaN barrier layer with larger forbidden band width, and therefore contact resistance with lower surface state can be obtained.

The semi-insulating property of the GaN substrate in the HEMT epitaxial structure based on the GaN substrate can be finished through early preparation, adverse effects caused by later growth of a high-resistance epitaxial layer can be avoided, the semi-insulating property of the GaN substrate can be obtained through peeling, grinding and polishing after the preparation in an HVPE reactor is finished, the GaN substrate is formed, then the HEMT structure is grown in an MOCVD reactor, and specific parameters and processes can be achieved through the prior art known to a person skilled in the art.

The homoepitaxy has no problem of high-density dislocation buffer layer on heterogeneous substrate, and can completely block leakage channel, and the GaN is polar material, and has lower contact resistance, improved surface state density with passivation layer to avoid leakage problem, higher transconductance and higher frequency operation, and compared with heterogrowth, high quality single-polarity N-face polar GaN material can be obtained only in homoepitaxy.

It should be understood that the above embodiments are merely for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the present invention and implement the same according to the present invention without limiting the scope of the present invention. All equivalent changes or modifications made in accordance with the spirit of the present invention should be construed to be included in the scope of the present invention.

Claims (11)

1. The HEMT epitaxial structure based on the GaN substrate is characterized by comprising an interface treatment layer, a barrier layer, an isolation layer and a channel layer which are sequentially formed on the semi-insulating GaN substrate with N-face polarity;

The interface treatment layer is made of AlN, and the growth conditions of the interface treatment layer comprise the steps of taking 50-80% of hydrogen and 20-50% of ammonia as raw materials, reacting for 5-10 minutes at 1050-1100 ℃ and 400-700 mbar to remove impurity elements on the surface of the semi-insulating GaN substrate, introducing an Al source, and controlling the flow of the Al source to be more than 0 and less than or equal to 50 mu mol/min.

2. The HEMT epitaxial structure of claim 1, wherein the thickness of the interface treatment layer is 2-5 nm.

3. The HEMT epitaxial structure according to claim 1, wherein the barrier layer is made of AlGaN or InGaN, wherein the content of Al or In is 15-100%, and the thickness of the barrier layer is 15-25 nm.

4. The HEMT epitaxial structure of claim 1, wherein the spacer layer comprises AlN and has a thickness of 0.5-1 nm.

5. The HEMT epitaxial structure according to claim 1, wherein the channel layer comprises GaN, inN, inGaN or AlGaN with a thickness of 100-300 nm, wherein the Al component content of AlGaN is greater than 0 and less than or equal to 15%, and the In component content of InGaN is greater than 0 and less than or equal to 15%.

6. The HEMT epitaxial structure of claim 1, wherein a contact layer is further formed on the channel layer, and the contact layer comprises InN and has a thickness of 1-3 nm.

7. A method of fabricating a HEMT epitaxial structure according to any one of claims 1-6, comprising:

providing a semi-insulating GaN substrate with N-face polarity;

Forming an interface treatment layer on the N-face polar semi-insulating GaN substrate, wherein the growth conditions of the interface treatment layer comprise that 50-80% of hydrogen and 20-50% of ammonia are used as raw materials, and the raw materials react for 5-10 minutes at 1050-1100 ℃ and 400-700 mbar;

and sequentially growing a barrier layer, an isolation layer and a channel layer on the interface treatment layer.

8. The method of claim 7, further comprising growing a contact layer on the channel layer.

9. A HEMT device, comprising:

the HEMT epitaxial structure of any one of claims 1-6;

And a source, a drain, and a gate cooperating with the HEMT epitaxial structure, the gate being distributed between the source and the drain.

10. The HEMT device of claim 9, wherein the source and drain are both electrically coupled to a contact layer.

11. The HEMT device of claim 9, wherein a gate dielectric layer is further distributed between the gate and the contact layer.