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

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

Technical Field

[0001] The present invention relates to a HEMT device, in particular to a HEMT device, a HEMT epitaxial structure based on a GaN substrate and a manufacturing method, belonging to the field of semiconductor technology. Background Art

[0002] Most of the current GaN-based HEMT devices are fabricated on heterogeneous substrates such as SiC / Si. Figure 1 As shown, a HEMT epitaxial structure based on a SiC heterojunction substrate requires the deposition of an AlN buffer layer during the fabrication process to reduce the lattice mismatch with GaN. After the buffer layer transition, a high-resistance GaN layer doped with iron or carbon is grown. The high-resistance GaN layer is sequentially stacked with a GaN channel layer, an AlN spacer layer, an AlGaN barrier layer, and a GaN thresher layer. A large potential well is formed at the interface between the GaN channel layer and the AlGaN barrier layer. Electrons are confined within this thin layer, forming a high-density two-dimensional electron gas (2DEG) in the channel layer. The AlN spacer layer is very thin, which can improve the interface quality, reduce scattering, and increase electron mobility. It can also increase the discontinuity of the conduction band and increase the density of the 2DEG. The purpose of the GaN thresher layer is to reduce the gate electric field, suppress the gate current, and reduce the formation of surface oxides. The entire GaN-based HEMT device has Ga-face polarity.

[0003] Although advances in epitaxial growth technology have improved crystal quality, the demand for device output efficiency has further increased with new applications in high-frequency fields such as microwave heating and 5G system communications. This is due to the high density of dislocations in the buffer layer on the heterogeneous substrate and the formation of leakage channels for electron loss at the interface between the GaN sintering layer and the passivation layer (usually SiN), which leads to current collapse and restricts the improvement of GaN-based HEMT performance. At the same time, a high-resistance GaN layer of about 2 to 4 microns needs to be grown above the buffer layer on the heterogeneous substrate. The high-resistance GaN layer usually needs to be doped with iron or carbon, which will increase the risk of doping memory effect in subsequent growth, also adversely affecting the quality of the device. Summary of the Invention

[0004] The main purpose of the present invention is to provide a HEMT device, a HEMT epitaxial structure based on a GaN substrate, and a manufacturing method to overcome the deficiencies in the prior art.

[0005] To achieve the aforementioned object of the invention, the technical solutions adopted by the present invention include:

[0006] An embodiment of the present invention provides a HEMT epitaxial structure based on a GaN substrate, which includes an interface treatment layer, a barrier layer, an isolation layer, and a channel layer sequentially formed on an N-face polarity semi-insulating GaN substrate.

[0007] An embodiment of the present invention further provides a method for manufacturing the HEMT epitaxial structure, which includes:

[0008] Providing an N-face polarity semi-insulating GaN substrate;

[0009] An interface treatment layer is grown on an N-face polarity semi-insulating GaN substrate, and the growth conditions of the interface treatment layer include: using 50-80% hydrogen and 20-50% ammonia as raw materials, reacting at 1050°C to 1100°C and 400-700 mbar for 5-10 minutes, and then introducing an Al source at a flow rate of 0-50 umol / min;

[0010] A barrier layer, an isolation layer and a channel layer are sequentially grown on the interface treatment layer.

[0011] An embodiment of the present invention further provides a HEMT device, comprising:

[0012] The HEMT epitaxial structure;

[0013] Also, a source, a drain and a gate matched with the HEMT epitaxial structure, wherein the gate is distributed between the source and the drain.

[0014] Compared with the prior art, the advantages of the present invention include:

[0015] 1) The GaN substrate and semi-insulating properties of the HEMT epitaxial structure based on the GaN substrate provided by the embodiments of the present invention can be achieved through early preparation, thus avoiding the adverse effects caused by the subsequent growth of the high-resistance epitaxial layer;

[0016] 2) In the GaN substrate-based HEMT epitaxial structure provided by the embodiments of the present invention, homoepitaxial growth does not suffer from the problem of a high-density dislocation buffer layer on a heterogeneous substrate. Appropriate interface treatment during epitaxial growth can completely block the generation of leakage channels.

[0017] 3) GaN is a polar material. The contact resistance of N-face polar GaN material is lower, which can improve the surface state density between the passivation layer and the surface of the passivation layer, thereby avoiding leakage problems.

[0018] 4) N-side polar GaN material has higher transconductance and can support higher operating frequencies. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic structural diagram of a HEMT epitaxial structure based on a SiC heterogeneous substrate in the prior art;

[0020] Figure 2 1 is a schematic structural diagram of a HEMT epitaxial structure based on a GaN substrate provided in a typical embodiment of the present invention;

[0021] Figure 3 This is a rendering of a HEMT epitaxial structure based on a SiC heterogeneous substrate in the prior art;

[0022] Figure 4 This is a rendering of a HEMT epitaxial structure based on a GaN substrate provided in a typical embodiment of the present invention;

[0023] Figure 5 These are IV test curves of the HEMT device based on a GaN substrate obtained in Example 1 of the present invention and the HEMT device based on a SiC heterogeneous substrate obtained in Comparative Example 1. DETAILED DESCRIPTION

[0024] In view of the shortcomings of the prior art, the inventors of this case, after long-term research and extensive practice, have proposed the technical solution of the present invention. The following will further explain this technical solution, its implementation process and principles.

[0025] HEMT (High Electron Mobility Transistor), a high electron mobility transistor, is a heterojunction field-effect transistor, also known as modulation doped field-effect transistor (MODFET), two-dimensional electron gas field-effect transistor (2-DEGFET), selective doped heterojunction transistor (SDHT), etc.

[0026] HEMT devices and their integrated circuits are capable of operating in ultra-high frequency (millimeter wave) and ultra-high speed fields. This is because they utilize the so-called two-dimensional electron gas with very high mobility. The basic structure of HEMT is a modulation-doped heterojunction. The high-mobility two-dimensional electron gas (2-DEG) exists in the modulation-doped heterojunction. This 2-DEG not only has high mobility but also does not "freeze" at extremely low temperatures. Therefore, HEMT has excellent low-temperature performance and can be used for low-temperature research work (such as the fractional quantum Hall effect).

[0027] HEMT devices are voltage-controlled devices. The gate voltage Vg can control the depth of the heterojunction potential well, which in turn can control the surface density of 2-DEG in the potential well, thereby controlling the operating current of the device. For GaAs system HEMTs, the n-Al x Ga 1-x The As control layer should be depleted (typically hundreds of nanometers thick and with a doping concentration of 10 7 ~10 8 / cm 3 ); if n-Al x Ga 1-xIf the As layer is thick and has a high doping concentration, 2-DEG will exist when Vg=0, which means it is a depletion-mode device. Otherwise, it is an enhancement-mode device (when Vg=0, the Schottky depletion layer extends into the i-GaAs layer). However, if the thickness of this layer is too large and the doping concentration is too high, it cannot be depleted during operation, and a leakage resistance in parallel with SD will appear.

[0028] Silicon carbide (SiC) is made by smelting quartz sand, petroleum coke (or coal coke), sawdust (salt is added when producing green SiC) and other raw materials through high-temperature resistance furnace smelting. Among contemporary non-oxide high-tech refractory raw materials such as C, N, and B, SiC is the most widely used and economical one. It can be called diamond grit or refractory sand. Currently produced SiC is divided into black SiC and green SiC. Both are hexagonal crystals with a specific gravity of 3.20-3.25 and a microhardness of 2840-3320 kg.

[0029] Silicon carbide has many other uses besides being an abrasive due to its stable chemical properties, high thermal conductivity, low thermal expansion coefficient, and good wear resistance. For example, a special process can be used to apply silicon carbide powder to the inner wall of a turbine impeller or cylinder block to improve its wear resistance and extend its service life by 1 to 2 times. The high-grade refractory material made from it is resistant to thermal shock, compact, lightweight, yet high in strength and energy-efficient. Low-grade silicon carbide (containing approximately 85% SiC) is an excellent deoxidizer that can speed up steelmaking, facilitate control of chemical composition, and improve steel quality. In addition, silicon carbide is also widely used in the production of silicon carbide rods for electric heating elements.

[0030] In addition, silicon carbide is very hard, with a Mohs hardness of 9.5, second only to the world's hardest diamond (level 10). It has excellent thermal conductivity, is a semiconductor, and is resistant to oxidation at high temperatures.

[0031] GaN is an extremely stable compound and a hard, high-melting-point material with a melting point of approximately 1700°C. It has a high degree of ionization, the highest among III-V compounds (0.5 or 0.43). Under atmospheric pressure, GaN crystals generally have a hexagonal wurtzite structure. It has four atoms in a unit cell, and its atomic volume is approximately half that of GaAs. The electrical properties of GaN are the main factors affecting devices. Unintentionally doped GaN is n-type in all cases, and the electron concentration of the best sample is approximately 4×10 16 / cm 3 ; Generally speaking, the P-type samples prepared are highly compensated. The GaN material series has a low heat generation rate and a high breakdown electric field, and is an important material for the development of high-temperature, high-power electronic devices and high-frequency microwave devices.

[0032] At present, with the progress of MBE technology in GaN material application and breakthroughs in key thin film growth technology, various GaN heterostructures have been successfully grown, and new devices such as metal field effect transistors (MESFETs), heterojunction field effect transistors (HFETs), and modulation doped field effect transistors (MODFETs) have been prepared using GaN materials. The modulation doped AlGaN / GaN structure has high electron mobility (2000cm 2 ·s), high saturation speed (1×10 7 cm / s) and a low dielectric constant, making it a preferred material for making microwave devices; GaN's wider bandgap (3.4eV) and sapphire and other materials as substrates have good heat dissipation performance, which is conducive to the device working under high-power conditions.

[0033] GaN has a large bandgap (3.4eV) and high thermal conductivity (1.3W / cm-K), resulting in high operating temperature, high breakdown voltage, and strong radiation resistance. The bottom of the conduction band of GaN is at the Γ point, and the energy difference between it and other energy valleys of the conduction band is large, which makes it difficult to produce valley-to-valley scattering, thereby achieving a very high strong field drift velocity (the electron drift velocity is not easy to saturate). GaN can easily form mixed crystals with AlN, InN, etc., and can be made into various heterostructures. A mobility of 10 at low temperature has been obtained. 5 cm 2 / Vs 2-DEG (because of the high surface density of 2-DEG, it effectively shields factors such as optical phonon scattering, ionized impurity scattering and piezoelectric scattering); GaN lattice symmetry is relatively low (hexagonal wurtzite structure or tetragonal metastable zinc blende structure), with strong piezoelectricity (due to non-centrosymmetry) and ferroelectricity (spontaneous polarization along the hexagonal c-axis): strong piezoelectric polarization (polarization electric field of 2MV / cm) and spontaneous polarization (polarization electric field of 3MV / cm) are generated near the heterojunction interface, inducing extremely high density of interface charges, strongly modulating the band structure of the heterojunction, strengthening the two-dimensional spatial confinement of 2-DEG, thereby increasing the surface density of 2-DEG (up to 10 in AlGaN / GaN heterojunction). 13 / cm 2 , which is an order of magnitude higher than that in AlGaAs / GaAs heterojunction), which is of great significance for device operation.

[0034] An embodiment of the present invention provides a HEMT epitaxial structure based on a GaN substrate, which includes an interface treatment layer, a barrier layer, an isolation layer, and a channel layer sequentially formed on an N-face polarity semi-insulating GaN substrate.

[0035] Furthermore, the growth conditions of the interface treatment layer include: using 50-80% hydrogen and 20-50% ammonia as raw materials, reacting at 1050°C to 1100°C and 400-700 mbar for 5 to 10 minutes, and then introducing an Al source at a flow rate of 0 to 50 umol / min; wherein the ratio of hydrogen to ammonia can be a volume ratio or a mass ratio.

[0036] Furthermore, the material of the interface treatment layer includes AlN.

[0037] Furthermore, the thickness of the interface treatment layer is 2-5 nm.

[0038] Furthermore, the barrier layer is made of AlGaN or InGaN, wherein the content of Al or In component is 15-100%, and the thickness of the barrier layer is 15-25 nm.

[0039] Furthermore, the isolation layer is made of AlN and has a thickness of 0.5-1 nm.

[0040] Furthermore, the channel layer is made of GaN, InN, InGaN or AlGaN, and has a thickness of 100-300 nm, wherein the Al component content of AlGaN is 0-15%, and the In component content of InGaN is 0-15%.

[0041] Furthermore, a contact layer is formed on the channel layer. The material of the contact layer includes InN and has a thickness of 1-3 nm.

[0042] An embodiment of the present invention further provides a method for manufacturing the HEMT epitaxial structure, which includes:

[0043] Providing an N-face polarity semi-insulating GaN substrate;

[0044] An interface treatment layer is grown on an N-face polarity semi-insulating GaN substrate, and the growth conditions of the interface treatment layer include: using 50-80% hydrogen and 20-50% ammonia as raw materials, reacting at 1050°C to 1100°C and 400-700 mbar for 5-10 minutes, and then introducing an Al source at a flow rate of 0-50 umol / min, wherein the ratio of hydrogen to ammonia can be a volume ratio or a mass ratio;

[0045] An insertion layer, a barrier layer and a channel layer are sequentially grown on the interface treatment layer.

[0046] It should be noted that, when manufacturing the HEMT epitaxial structure, only a small amount of Al source needs to be introduced. The specific amount of Al source introduced can be determined according to specific production needs and is not specifically limited here.

[0047] Furthermore, the manufacturing method further includes: growing a contact layer on the channel layer.

[0048] An embodiment of the present invention further provides a HEMT device, comprising:

[0049] The HEMT epitaxial structure; and a source, a drain and a gate matched with the HEMT epitaxial structure, wherein the gate is distributed between the source and the drain.

[0050] Furthermore, the source electrode and the drain electrode are both electrically coupled to the contact layer. For example, the source electrode and the drain electrode form ohmic contacts with the contact layer.

[0051] Furthermore, a gate dielectric layer is distributed between the gate and the contact layer. The material of the gate dielectric layer can be any material known to those skilled in the art, and the thickness is not specifically limited.

[0052] The technical solution, its implementation process and principles will be further explained below with reference to the accompanying drawings and specific embodiments.

[0053] Example 1

[0054] See also Figure 2 A HEMT epitaxial structure based on a GaN substrate 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-face polarity 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 present between the AlGaN barrier layer and the GaN channel layer; wherein the interface treatment layer is a 5nm thick AlN layer, the AlGaN barrier layer is 20nm thick, the Al component content is 25% (mass fraction, the same below), the AlN isolation layer is 1nm thick, the GaN channel layer is 300nm thick, and the InN contact layer is 2nm thick.

[0055] The method for manufacturing the HEMT epitaxial structure based on the GaN substrate specifically includes the following steps:

[0056] 1) Providing an N-face polarity semi-insulating GaN substrate;

[0057] 2) placing an N-face polar semi-insulating GaN substrate in a reaction vessel or reaction system, introducing 70% hydrogen and 30% ammonia into the reaction vessel or reaction system at 1100° C. and 600 mbar, and baking for 10 minutes (the purpose is to remove impurities such as O in the highly active N-face GaN on the surface of the semi-insulating GaN substrate while ensuring flatness);

[0058] 3) The temperature of the reaction vessel or reaction system is then cooled to 1000°C, and a small amount of Al is introduced at a pressure of 100 mbar to deposit a flat AlN layer of approximately 5 nm. Since Al fills holes, it can further improve the flatness of the epitaxial layer and serve as a foundation and transition for the growth of the Al-containing barrier layer, thereby improving the flatness and crystal quality of the subsequent AlGaN / GaN heterojunction.

[0059] 4) Maintaining the growth conditions of the AlN interface treatment layer, a 20nm AlGaN (25% Al content) barrier layer, a 1nm AlN spacer layer, and a 300nm GaN channel layer are sequentially grown on the AlN interface treatment layer. The order of fabrication of the AlGaN barrier layer and the GaN channel layer differs from that of conventional Ga-face HEMTs because the built-in electric field of N-face GaN is opposite, resulting in a different location of the generated two-dimensional electron gas (2DEG);

[0060] 5) The temperature of the reaction vessel or the reaction system is lowered to 700° C., and an InN contact layer is grown on the GaN channel layer under a pressure of 300 mbar.

[0061] Comparative Example 1

[0062] like Figure 1 As shown, a HEMT epitaxial structure based on a SiC heterogeneous substrate includes a SiC heterogeneous substrate and an AlN buffer layer (about 200nm), a high-resistance GaN layer (about 2um), a GaN channel layer (about 300nm), an AlN isolation layer (about 1nm), an AlGaN barrier layer (about 20nm) and a GaN (about 2nm) capping layer sequentially arranged on the SiC heterogeneous substrate.

[0063] IV tests were performed on the GaN substrate-based HEMT device obtained in Example 1 of the present invention (defined as HEMT-1) and the SiC heterogeneous substrate-based HEMT device obtained in Comparative Example 1 (defined as HEMT-2). The test results are shown in FIG. Figure 5 As shown by Figure 5 It can be seen 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.

[0064] For details, please refer to Figure 3 and Figure 4When the HEMT device is subjected to more stringent operating conditions, the HEMT epitaxial structure based on a GaN substrate provided in Example 1 of the present invention, compared to the HEMT epitaxial structure based on a SiC heterojunction substrate in Comparative Example 1, utilizes an N-face polarity semi-insulating GaN free-standing substrate. This can avoid defects caused by lattice mismatch and thermal mismatch due to heteroepitaxial growth, thereby causing leakage channels in the buffer layer. Furthermore, Example 1 of the present invention utilizes an N-face polarity semi-insulating GaN substrate to improve high-frequency response, and utilizes an InN contact layer to reduce the surface state density of the device, thereby suppressing leakage channels between the epitaxial layer and the passivation layer. By cutting off leakage channels from these two aspects, the current collapse effect is eliminated and reduced, thereby improving the high performance of GaN-based HEMT devices and broadening their applications in high-temperature, high-frequency, and high-power applications.

[0065] Specifically, an embodiment of the present invention provides a method for fabricating a HEMT epitaxial structure based on a GaN substrate. This method achieves low-resistance connection between the source and drain terminals by simply passing through a GaN channel layer with a relatively small bandgap width. This differs from existing HEMT epitaxial structures that require passing through an AlGaN barrier layer with a relatively large bandgap width. Therefore, the present invention can achieve lower surface state contact resistance.

[0066] The semi-insulating properties of the GaN substrate in the HEMT epitaxial structure based on the GaN substrate provided by the embodiments of the present invention can be achieved through early preparation, thereby avoiding the adverse effects caused by the subsequent growth of a high-resistance epitaxial layer. The semi-insulating properties of the GaN substrate can be achieved by, after preparation in an HVPE reactor, forming the GaN substrate through peeling, grinding, and polishing, and then growing the HEMT structure in an MOCVD reactor. The specific parameters and processes can be implemented using existing technologies known to those skilled in the art.

[0067] Specifically, homoepitaxial growth does not have the problem of high-density dislocation buffer layer on heterogeneous substrate. Appropriate interface treatment and growth during epitaxy can completely block the generation of leakage channels. Furthermore, GaN is a polar material, and the contact resistance of N-face polar GaN material is lower, which can improve the surface state density between the passivation layer and the passivation layer, thereby avoiding the occurrence of leakage problems. In addition, N-face polar GaN material also has higher transconductance and can operate at higher frequencies. In addition, compared with heterogeneous growth, high-quality single-polarity N-face polar GaN material can only be obtained in homoepitaxial growth.

[0068] It should be understood that the above embodiments are merely illustrative of the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent variations or modifications made in accordance with the spirit and substance of the present invention are intended to be encompassed within the scope of protection of the present invention.

Claims

1. A HEMT epitaxial structure based on a GaN substrate, characterized in that: The method comprises an interface processing layer, a barrier layer, an isolation layer and a channel layer sequentially formed on an N-face polarity semi-insulating GaN substrate; Among them, the material of the interface treatment layer is AlN, and the growth conditions of the interface treatment layer include: using 50~80% hydrogen and 20~50% ammonia as raw materials, reacting at 1050℃~1100℃ and 400~700mbar for 5~10 minutes to remove impurity elements on the surface of the semi-insulating GaN substrate; then introducing an Al source, and controlling the flow rate of the Al source to be greater than 0 and less than or equal to 50μmol / min.

2. The HEMT epitaxial structure according to 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 component is 15-100%, and the thickness of the barrier layer is 15-25 nm.

4. The HEMT epitaxial structure according to claim 1, wherein: The isolation layer is made of AlN and has a thickness of 0.5-1 nm.

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

6. The HEMT epitaxial structure according to claim 1, wherein: A contact layer is further formed on the channel layer. The material of the contact layer includes InN and has a thickness of 1-3 nm.

7. The method for manufacturing a HEMT epitaxial structure according to any one of claims 1 to 6, characterized in that include: Providing an N-face polarity semi-insulating GaN substrate; An interface treatment layer is grown on an N-face polarity semi-insulating GaN substrate, wherein the growth conditions of the interface treatment layer include: using 50-80% hydrogen and 20-50% ammonia as raw materials, reacting at 1050° C. to 1100° C. and 400-700 mbar for 5-10 minutes; then introducing an Al source, and controlling the Al source flow rate to be greater than 0 and less than or equal to 50 μmol / min; A barrier layer, an isolation layer and a channel layer are sequentially grown on the interface treatment layer.

8. The production method according to claim 7, characterized in that: Also includes: A contact layer is grown on the channel layer.

9. A HEMT device, characterized in that: include: The HEMT epitaxial structure according to any one of claims 1 to 6; Also, a source, a drain and a gate matched with the HEMT epitaxial structure, wherein the gate is distributed between the source and the drain.

10. The HEMT device according to claim 9, wherein The source electrode and the drain electrode are both electrically connected to the contact layer.

11. The HEMT device according to claim 9, wherein A gate dielectric layer is also distributed between the gate and the contact layer.

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