A GaN-based HEMT low-temperature gold-free ohmic contact electrode and a preparation method thereof

Abstract

The present invention discloses a low-temperature gold-free ohmic contact electrode for a GaN-based HEMT, comprising a GaN-based HEMT epitaxial layer, a GaN channel layer arranged in the GaN-based HEMT epitaxial layer, and the electrode comprising a first metal layer Ti, a second metal layer Al and a third metal layer TiW arranged in sequence from bottom to top on the upper surface of the GaN-based HEMT epitaxial layer, or a first metal layer Ti, a second metal layer Al, a third metal layer Ti and a fourth metal layer TiW arranged in sequence from bottom to top. A preparation method of the electrode is also disclosed accordingly. The present invention effectively reduces the annealing temperature of the GaN-based HEMT ohmic contact, improves the 2DEG leakage caused by the overall etching of the AlGaN barrier layer and the reduction of the current when the ohmic contact is formed, reduces the difficulty of forming the ohmic contact, and the surface morphology and edge of the ohmic contact after the low-temperature annealing alloy are smoother. At the same time, it helps to reduce the manufacturing cost of GaN-based HEMT devices.

Description

Technical Field

[0001] The invention relates to a semiconductor device, and in particular to a GaN-based HEMT low-temperature gold-free ohmic contact electrode and a preparation method thereof. Background Art

[0002] GaN-based high electron mobility transistors (HEMTs) have broad application prospects in high-voltage, high-frequency, high-power semiconductor laser devices, and high-performance ultraviolet detectors. However, the technology of compound semiconductor dedicated production lines is relatively backward, and the process update and operation and maintenance costs are high, which increases the production cost of GaN-based HEMT devices. The use of mature and advanced Si-CMOS process lines to produce HEMT devices can effectively reduce the difficulty of preparing HEMT devices and reduce manufacturing costs. The heavy metal Au used in the ohmic and Schottky contact processes of conventional HEMT devices will form deep energy level impurities in Si and pollute the CMOS process line. Therefore, HEMT gold-free ohmic contact technology is the key to improving the reliability of HEMT devices and realizing large-scale manufacturing of Si-CMOS process lines.

[0003] The ohmic contact performance of GaN-based HEMT devices directly affects key device performance such as saturated output current, on-resistance, and breakdown voltage. High-quality ohmic contacts mainly require the following: (1) low contact resistivity (2) good thermal stability (3) small electrode surface roughness (4) strong corrosion resistance.

[0004] The industry has two main annealing windows for forming ohmic contacts on GaN-based HEMTs: 1. Low-temperature annealing window, nitrogen atmosphere, annealing temperature is 500-650°C; 2. High-temperature annealing window, nitrogen atmosphere, annealing temperature is 800-1000°C.

[0005] During the low-temperature annealing process, a small number of methods only optimize the thickness of Ti, Al and the relative thickness of Ti / Al, that is, adopt a Ti / Al-based metal solution with thinner Ti (thicker Al). Since the AlGaN barrier layer under the ohmic contact area is not etched and thinned, the interface reaction of the low-temperature annealing is weak, and a thicker AlGaN barrier layer still remains after annealing. The probability of electron tunneling between metal and semiconductor is still low, and the yield of the low-temperature ohmic contact without etching is poor.

[0006] During the low-temperature annealing process, the solutions reported in the literature all use dry etching, and the best etching distance is 1 to 2 nm from the two-dimensional electron gas (2DEG) channel. Since the conventional dry etching precision is difficult to control and the etching rates of different epitaxy vary greatly, the repeatability of the etching process is poor, which is not conducive to large-scale industrial production. However, for the low-temperature ohmic contact with the overall etching of the AlGaN barrier layer, since the AlGaN barrier layer is etched as a whole, the 2DEG in the ohmic region is interrupted. On the one hand, the high-density free electrons in the 2DEG may even leak. On the other hand, the area of ​​the 2DEG that forms contact with the metal is greatly reduced, resulting in a decrease in the current for forming the ohmic contact [G. Greco, et al, Appl. Surf. Sci., 2016, 383].

[0007] During the high temperature annealing process, the conventional source-drain ohmic contact usually adopts a four-layer metal structure of Ti / Al / X / Au, which is formed by a high temperature annealing process above 800°C. This gold-containing ohmic contact after the high temperature annealing process has a rough electrode surface morphology and electrode edge [Y.-H.Hwang, et al, J.Vac.Sci.Technol.B, Nanotechnol.Microelectron.Mater.Process.Meas.Phenom., 2015, 33(3)]. The high temperature gold-free ohmic contact is formed by selecting a suitable gold-free cap layer metal, optimizing the thickness of Ti, Al and the relative thickness of Ti / Al, and after high temperature annealing, a gold-free ohmic contact with low contact resistance and good surface morphology can be quickly obtained. However, on the one hand, high-temperature annealing will introduce high-density deep energy levels / surface states on the AlGaN surface, thereby affecting the dynamic performance of the device. On the other hand, the high-temperature annealing process of the ohmic contact can easily cause degradation of the heterojunction, increasing the sheet resistance of the material. The high-temperature process also limits the use of the self-aligned "gate-first" process. Summary of the invention

[0008] In order to overcome the above-mentioned shortcomings and deficiencies of the prior art, the object of the present invention is to provide a GaN-based HEMT low-temperature gold-free ohmic contact electrode and a preparation method thereof, which can effectively reduce the annealing temperature of the GaN-based HEMT ohmic contact, improve the 2DEG leakage caused by the overall etching of the AlGaN barrier layer and the current reduction when the ohmic contact is formed, reduce the difficulty of forming the ohmic contact, and the surface morphology and edge of the ohmic contact after low-temperature annealing of the alloy are smoother.

[0009] The purpose of the present invention is achieved at least by the following technical solutions.

[0010] A GaN-based HEMT low-temperature gold-free ohmic contact electrode comprises a GaN-based HEMT epitaxial layer, a GaN channel layer is arranged in the GaN-based HEMT epitaxial layer, and the electrode comprises a first metal layer Ti, a second metal layer Al and a third metal layer TiW arranged in sequence from bottom to top on the upper surface of the GaN-based HEMT epitaxial layer, or a first metal layer Ti, a second metal layer Al, a third metal layer Ti and a fourth metal layer TiW arranged in sequence from bottom to top.

[0011] Preferably, when a first metal layer Ti, a second metal layer Al and a third metal layer TiW are arranged in sequence from bottom to top on the upper surface of the GaN-based HEMT epitaxial layer, the thickness of the first metal layer Ti is 5 to 20 nm, the thickness of the second metal layer Al is 100 to 300 nm, and the thickness of the third metal layer TiW is 20 to 50 nm.

[0012] Preferably, when a first metal layer Ti, a second metal layer Al, a third metal layer Ti and a fourth metal layer TiW are arranged in sequence from bottom to top on the upper surface of the GaN-based HEMT epitaxial layer, the thickness of the first metal layer Ti is 5 to 20 nm, the thickness of the second metal layer Al is 100 to 300 nm, the thickness of the third metal layer Ti is 5 to 10 nm, and the thickness of the fourth metal layer TiW is 20 to 50 nm.

[0013] The present invention also provides a method for preparing a low-temperature gold-free ohmic contact electrode of a GaN-based HEMT, comprising the following steps:

[0014] (1) Using photolithography technology to define source and drain etching pattern areas on the GaN-based epitaxial layer;

[0015] (2) Using ICP etching technology to completely remove the AlGaN barrier layer and etch to 10 to 50 nm below the GaN channel layer;

[0016] (3) while retaining the photoresist, the source and drain etched patterns obtained in step (2) are cleaned;

[0017] (4) removing the photoresist of step (3) and performing surface oxidation treatment on the obtained GaN-based HEMT epitaxial layer;

[0018] (5) using photolithography technology to define source and drain ohmic contact pattern regions on the GaN-based HEMT epitaxial layer obtained in step (4);

[0019] (6) depositing source and drain ohmic contact metals in sequence;

[0020] (7) Performing metal stripping on step (6) to form source-drain electrodes, and performing alloy annealing at 550-700° C. to form source-drain ohmic contact electrodes.

[0021] Preferably, the inclination angle during ICP etching in step (2) is 20 to 50°.

[0022] Preferably, the surface oxidation treatment in step (4) is oxygen plasma treatment or oxygen atmosphere annealing treatment.

[0023] Preferably, when the surface oxidation treatment is oxygen plasma treatment, the oxygen flow rate is 50-100 sccm, the power is 150-400 W, and the time is 100 s-5 min.

[0024] Preferably, when the surface oxidation treatment is an oxygen atmosphere annealing treatment, the annealing temperature is 300° C. to 400° C., and the annealing time is 10 min to 40 min.

[0025] Preferably, the source and drain etching pattern area in step (1) is smaller than the source and drain ohmic contact pattern area in step (5), and the margin between the two patterns on a single electrode is 2 to 8 μm.

[0026] Preferably, the annealing time of the alloy annealing treatment in step (7) is 30s to 10min, and the atmosphere is high-purity nitrogen.

[0027] Compared with the prior art, the present invention has at least the following beneficial effects:

[0028] (1) The gold-free source-drain ohmic contact electrode of the present invention adopts a Ti / Al / TiW or Ti / Al / Ti / TiW multilayer metal system, which is deposited in sequence by magnetron sputtering. Different from the traditional low-temperature ohmic contact, the present invention adopts an ICP etching method to completely etch the AlGaN barrier layer, so that the metal is in direct contact with the 2DEG of the AlGaN / GaN heterojunction side wall, which is conducive to the formation of ohmic contact. In addition, before metal deposition, the present invention uses a surface oxidation process to treat the exposed AlGaN / GaN heterojunction side wall and GaN channel layer after etching to form a layer of gallium oxide to promote the ohmic contact between the metal and the GaN channel. On the one hand, the formed gallium oxide layer can alleviate the electron leakage caused by the removal of the AlGaN barrier layer; on the other hand, due to the doping of oxygen atoms into the surface of the GaN channel layer, the free carrier concentration is increased, causing the Fermi level of GaN to shift toward the bottom of the conduction band.

[0029] (2) The GaN-based HEMT of the present invention forms an ohmic contact through rapid annealing at 550-700°C for 30s-10min. Compared with the traditional ohmic contact metal system, the present invention reduces the annealing temperature for forming the ohmic contact and reduces the process difficulty. The surface morphology and edge of the ohmic contact after low-temperature annealing of the alloy are smoother, and the low temperature improves the process compatibility.

[0030] (3) The present invention adopts a method for etching the entire AlGaN barrier layer, which reduces the requirements for etching accuracy, improves the repetition rate and yield rate of low-temperature ohmic contacts, and helps to reduce the manufacturing cost of GaN-based HEMT devices.

[0031] (4) After the AlGaN barrier layer is etched as a whole, the present invention adopts a surface oxidation treatment process to improve the 2DEG leakage problem caused by the overall etching of the AlGaN barrier layer, increase the current when forming the ohmic contact, and reduce the difficulty of forming the ohmic contact.

[0032] (5) The gold-free ohmic contact electrode can be used in fields such as power electronics and microwave communications, and has a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the epitaxial layer of a GaN-based HEMT when forming source and drain etching patterns in the embodiment.

[0034] Figure 2 Schematic diagram of the GaN-based HEMT epitaxial layer after ICP etching in the embodiment.

[0035] Figure 3 Schematic diagram of the GaN-based HEMT epitaxial layer after surface oxidation treatment in the embodiment.

[0036] Figure 4 Schematic diagram of a GaN-based HEMT epitaxial layer when forming a source-drain ohmic contact pattern in an embodiment.

[0037] Figure 5 It is a schematic diagram of the epitaxy of a GaN-based HEMT after sequentially depositing a first metal layer Ti, a second metal layer Al, and a third metal layer TiW on the source-drain ohmic contact pattern region and the photolithography mask in an embodiment.

[0038] Figure 6 It is a schematic diagram of the epitaxial layer structure of the GaN-based HEMT after the first metal layer Ti, the second metal layer Al, and the third metal layer TiW on the photolithography mask are stripped off in the embodiment.

[0039] Figure 7 , 8 , 9, 10, 11, and 12 are graphs of the TLM test results in Examples 1, 2, 3, 4, 5, and 6, respectively.

[0040] The figure shows: 1-GaN-based HEMT epitaxial layer, 2-first metal layer Ti, 3-second metal layer Al, 4-third metal layer TiW, 5-photolithography mask, 6-source and drain etching pattern area, 7-area after ICP etching, 8-area after surface oxidation treatment, 9-photolithography mask, 10-source and drain electrode pattern area. DETAILED DESCRIPTION

[0041] The present invention is further described below in conjunction with the accompanying drawings and embodiments, but the embodiments of the present invention are not limited thereto; it should be pointed out that if there are processes or process parameters that are not particularly described in detail below, they can be implemented by those skilled in the art with reference to the prior art.

[0042] Example 1

[0043] The method for preparing the low-temperature gold-free ohmic contact of the GaN-based HEMT of this embodiment comprises the following steps:

[0044] (1) Using photolithography technology, define the source and drain etching pattern area on the GaN-based epitaxial layer;

[0045] (2) Using ICP etching technology, the AlGaN barrier layer is completely etched away, and the etching is continued to 10 nm below the GaN channel layer (the dotted line in the figure refers to the 2DEG channel, and the GaN channel layer is below it), with an etching tilt angle of 50°;

[0046] (3) on the basis of retaining the photoresist, cleaning the source and drain etching patterns obtained in step (2) with an acid-base solution;

[0047] (4) removing the photoresist in step (3), cleaning it, and placing the obtained GaN-based epitaxial layer in a rapid thermal annealing system for surface oxidation treatment to treat the AlGaN / GaN heterojunction sidewalls and GaN channel layer exposed after etching, the annealing temperature is 400° C., the annealing time is 40 min, and the atmosphere is high-purity oxygen;

[0048] (5) using photolithography technology, defining a source-drain ohmic contact pattern region for the GaN-based epitaxial layer obtained in step (4), wherein the source-drain ohmic contact pattern region is larger than the source-drain etching pattern region, and the margin between the two patterns is 8 μm;

[0049] (6) Using a magnetron sputtering method, a first metal layer Ti2, a second metal layer Al3 and a third metal layer TiW4 are sequentially deposited in the source-drain ohmic contact region, wherein the thickness of the first metal layer Ti2 is 5 nm, the thickness of the second metal layer Al3 is 100 nm, and the thickness of the third metal layer TiW4 is 20 nm.

[0050] (7) The source and drain electrodes formed by the debonding in step (6) are subjected to rapid thermal annealing in a nitrogen atmosphere at a temperature of 550° C. for 10 min to form ohmic contacts.

[0051] The TLM test structure of the GaN-based HEMT low-temperature gold-free ohmic contact prepared in this embodiment was subjected to IV test, and the TLM electrode spacing L was 10 μm, 20 μm, 30 μm, 40 μm, and 50 μm respectively. The RL curve was obtained, as shown in FIG. Figure 7 As shown in the figure, it can be known through calculation that the low-temperature ohmic contact resistance prepared in this embodiment is 2.57Ω·mm, and the specific contact resistivity is 1.40×10 -4 Ω·cm 2 , indicating that good ohmic contact performance was obtained.

[0052] Example 2

[0053] The method for preparing the low-temperature gold-free ohmic contact of the GaN-based HEMT of this embodiment comprises the following steps:

[0054] (1) Using photolithography technology, define the source and drain etching pattern area on the GaN-based epitaxial layer;

[0055] (2) Using ICP etching technology, the AlGaN barrier layer is completely removed and etched to 20 nm below the GaN channel layer with an etching angle of 40°;

[0056] (3) cleaning the source and drain etched pattern obtained in step (2) using an acid or alkali solution;

[0057] (4) removing the photoresist in step (3), cleaning it, and placing the obtained GaN-based epitaxial layer in a rapid thermal annealing system for surface oxidation treatment to treat the AlGaN / GaN heterojunction sidewalls and GaN channel layer exposed after etching, the annealing temperature is 350° C., the annealing time is 20 min, and the atmosphere is high-purity oxygen;

[0058] (5) Using photolithography technology, define the source-drain ohmic contact pattern area for the GaN-based epitaxial layer obtained in step (4), the source-drain ohmic contact pattern area is larger than the source-drain etching pattern area, and the margin between the two patterns is 4 μm;

[0059] (6) Using a magnetron sputtering method, a first metal layer Ti, a second metal layer Al, a third metal layer Ti and a fourth metal layer TiW are sequentially deposited in the source-drain ohmic contact region, wherein the thickness of the first metal layer Ti is 15 nm, the thickness of the second metal layer Al is 250 nm, the thickness of the third metal layer Ti is 8 nm, and the thickness of the fourth metal layer TiW is 30 nm.

[0060] (7) The source and drain electrodes are formed by stripping the resist in step (6), and a rapid thermal annealing treatment is performed in a nitrogen atmosphere at a temperature of 600° C. for 5 minutes to form an ohmic contact.

[0061] The TLM test structure of the GaN-based HEMT low-temperature gold-free ohmic contact prepared in this embodiment was subjected to IV test, and the TLM electrode spacing L was 10 μm, 20 μm, 30 μm, 40 μm, and 50 μm respectively. The RL curve was obtained, as shown in FIG. Figure 8 As shown, it can be known through calculation that the low-temperature ohmic contact resistance prepared in this embodiment is 2.08Ω·mm, and the specific contact resistivity is 8.73×10 -5 Ω·cm 2 , indicating that good ohmic contact performance was obtained.

[0062] Example 3

[0063] The method for preparing the low-temperature gold-free ohmic contact of the GaN-based HEMT of this embodiment comprises the following steps:

[0064] (1) Using photolithography technology, define the source and drain etching pattern area on the GaN-based epitaxial layer;

[0065] (2) Using ICP etching technology, the AlGaN barrier layer is completely removed and etched to 50 nm below the GaN channel layer with an etching tilt angle of 20°;

[0066] (3) cleaning the source and drain etched pattern obtained in step (2) using an acid or alkali solution;

[0067] (4) removing the photoresist in step (3), cleaning, and subjecting the obtained GaN-based epitaxial layer to oxygen plasma treatment to treat the AlGaN / GaN heterojunction sidewalls and GaN channel layer exposed after etching, with an oxygen flow rate of 60 sccm, a power of 250 W, and a time of 200 s;

[0068] (5) using photolithography technology, defining a source-drain ohmic contact pattern region for the GaN-based epitaxial layer obtained in step (4), wherein the source-drain ohmic contact pattern region is larger than the source-drain etching pattern region, and the margin between the two patterns is 2 μm;

[0069] (6) Using a magnetron sputtering method, a first metal layer Ti 2, a second metal layer Al 3 and a third metal layer TiW 4 are sequentially deposited in the source-drain ohmic contact region, wherein the thickness of the first metal layer Ti 2 is 20 nm, the thickness of the second metal layer Al 3 is 300 nm, and the thickness of the third metal layer TiW 4 is 50 nm.

[0070] (7) The source and drain electrodes are formed by stripping the resist in step (6), and a rapid thermal annealing treatment is performed in a nitrogen atmosphere at a temperature of 700° C. for 30 seconds to form an ohmic contact.

[0071] The TLM test structure of the GaN-based HEMT low-temperature gold-free ohmic contact prepared in this embodiment was subjected to IV test, and the TLM electrode spacing L was 10 μm, 20 μm, 30 μm, 40 μm, and 50 μm respectively. The RL curve was obtained, as shown in FIG. Fig. 9 As shown, it can be known through calculation that the low-temperature ohmic contact resistance prepared in this embodiment is 2.23Ω·mm, and the specific contact resistivity is 9.76×10 -5 Ω·cm 2 , indicating that good ohmic contact performance was obtained.

[0072] Example 4

[0073] The method for preparing the low-temperature gold-free ohmic contact of the GaN-based HEMT of this embodiment comprises the following steps:

[0074] (1) Using photolithography technology, define the source and drain etching pattern area on the GaN-based epitaxial layer;

[0075] (2) Using ICP etching technology, the AlGaN barrier layer is completely removed and etched to 50 nm below the GaN channel layer with an etching tilt angle of 20°;

[0076] (3) cleaning the source and drain etched pattern obtained in step (2) using an acid or alkali solution;

[0077] (4) removing the photoresist in step (3), cleaning, and subjecting the obtained GaN-based epitaxial layer to oxygen plasma treatment to treat the AlGaN / GaN heterojunction sidewalls and GaN channel layer exposed after etching, with an oxygen flow rate of 60 sccm, a power of 250 W, and a time of 200 s;

[0078] (5) using photolithography technology, defining a source-drain ohmic contact pattern region for the GaN-based epitaxial layer obtained in step (4), wherein the source-drain ohmic contact pattern region is larger than the source-drain etching pattern region, and the margin between the two patterns is 2 μm;

[0079] (6) Using a magnetron sputtering method, a first metal layer Ti 2, a second metal layer Al 3 and a third metal layer TiW 4 are sequentially deposited in the source-drain ohmic contact region, wherein the thickness of the first metal layer Ti 2 is 12 nm, the thickness of the second metal layer Al 3 is 200 nm, and the thickness of the third metal layer TiW 4 is 35 nm.

[0080] (7) The source and drain electrodes are formed by stripping the resist in step (6), and a rapid thermal annealing treatment is performed in a nitrogen atmosphere at a temperature of 700° C. for 30 seconds to form an ohmic contact.

[0081] The TLM test structure of the GaN-based HEMT low-temperature gold-free ohmic contact prepared in this embodiment was subjected to IV test, and the TLM electrode spacing L was 10 μm, 20 μm, 30 μm, 40 μm, and 50 μm respectively. The RL curve was obtained, as shown in FIG. Fig.10 As shown, it can be known through calculation that the low-temperature ohmic contact resistance prepared in this embodiment is 1.9Ω·mm, and the specific contact resistivity is 7.13×10 -5 Ω·cm 2 , indicating that good ohmic contact performance was obtained.

[0082] Example 5

[0083] The method for preparing the low-temperature gold-free ohmic contact of the GaN-based HEMT of this embodiment comprises the following steps:

[0084] (1) Using photolithography technology, define the source and drain etching pattern area on the GaN-based epitaxial layer;

[0085] (2) Using ICP etching technology, the AlGaN barrier layer is completely removed and etched to 50 nm below the GaN channel layer with an etching tilt angle of 20°;

[0086] (3) cleaning the source and drain etched pattern obtained in step (2) using an acid or alkali solution;

[0087] (4) removing the photoresist in step (3), cleaning, and subjecting the obtained GaN-based epitaxial layer to oxygen plasma treatment to treat the AlGaN / GaN heterojunction sidewalls and GaN channel layer exposed after etching, with an oxygen flow rate of 60 sccm, a power of 250 W, and a time of 200 s;

[0088] (5) using photolithography technology, defining a source-drain ohmic contact pattern region for the GaN-based epitaxial layer obtained in step (4), wherein the source-drain ohmic contact pattern region is larger than the source-drain etching pattern region, and the margin between the two patterns is 2 μm;

[0089] (6) Using a magnetron sputtering method, a first metal layer Ti, a second metal layer Al, a third metal layer Ti and a fourth metal layer TiW are sequentially deposited in the source-drain ohmic contact region, wherein the thickness of the first metal layer Ti is 5 nm, the thickness of the second metal layer Al is 100 nm, the thickness of the third metal layer Ti is 5 nm, and the thickness of the fourth metal layer TiW is 20 nm.

[0090] (7) The source and drain electrodes are formed by stripping the resist in step (6), and a rapid thermal annealing treatment is performed in a nitrogen atmosphere at a temperature of 700° C. for 8 minutes to form an ohmic contact.

[0091] The TLM test structure of the GaN-based HEMT low-temperature gold-free ohmic contact prepared in this embodiment was subjected to IV test, and the TLM electrode spacing L was 10 μm, 20 μm, 30 μm, 40 μm, and 50 μm respectively. The RL curve was obtained, as shown in FIG. Fig.11 As shown, it can be known through calculation that the low-temperature ohmic contact resistance prepared in this embodiment is 2.14Ω·mm, and the specific contact resistivity is 9.12×10 -5 Ω·cm 2 , indicating that good ohmic contact performance was obtained.

[0092] Example 6

[0093] The method for preparing the low-temperature gold-free ohmic contact of the GaN-based HEMT of this embodiment comprises the following steps:

[0094] (1) Using photolithography technology, define the source and drain etching pattern area on the GaN-based epitaxial layer;

[0095] (2) Using ICP etching technology, the AlGaN barrier layer is completely removed and etched to 50 nm below the GaN channel layer with an etching tilt angle of 20°;

[0096] (3) cleaning the source and drain etched pattern obtained in step (2) using an acid or alkali solution;

[0097] (4) removing the photoresist in step (3), cleaning, and subjecting the obtained GaN-based epitaxial layer to oxygen plasma treatment to treat the AlGaN / GaN heterojunction sidewalls and GaN channel layer exposed after etching, with an oxygen flow rate of 60 sccm, a power of 250 W, and a time of 200 s;

[0098] (5) using photolithography technology, defining a source-drain ohmic contact pattern region for the GaN-based epitaxial layer obtained in step (4), wherein the source-drain ohmic contact pattern region is larger than the source-drain etching pattern region, and the margin between the two patterns is 2 μm;

[0099] (6) Using a magnetron sputtering method, a first metal layer Ti, a second metal layer Al, a third metal layer Ti and a fourth metal layer TiW are sequentially deposited in the source-drain ohmic contact region, wherein the thickness of the first metal layer Ti is 20 nm, the thickness of the second metal layer Al is 300 nm, the thickness of the third metal layer Ti is 10 nm, and the thickness of the fourth metal layer TiW is 50 nm.

[0100] (7) The source and drain electrodes are formed by stripping the resist in step (6), and a rapid thermal annealing treatment is performed in a nitrogen atmosphere at a temperature of 700° C. for 2 minutes to form an ohmic contact.

[0101] The TLM test structure of the GaN-based HEMT low-temperature gold-free ohmic contact prepared in this embodiment was subjected to IV test, and the TLM electrode spacing L was 10 μm, 20 μm, 30 μm, 40 μm, and 50 μm respectively. The RL curve was obtained, as shown in FIG. Fig.12 As shown in the figure, it can be known through calculation that the low-temperature ohmic contact resistance prepared in this embodiment is 2.18Ω·mm, and the specific contact resistivity is 9.33×10 -5 Ω·cm 2 , indicating that good ohmic contact performance was obtained.

[0102] This embodiment does not constitute any limitation to the present invention. It is obvious that for professionals in this field, after understanding the content and principles of the present invention, they can make various modifications and changes in form and details according to the method of the present invention without departing from the principles and scope of the present invention. However, these modifications and changes based on the present invention are still within the scope of protection of the claims of the present invention.

Claims

1. A GaN-based HEMT device, It is characterized in that The invention comprises a GaN-based HEMT epitaxial layer, wherein a GaN channel layer is arranged in the GaN-based HEMT epitaxial layer, and an electrode comprises a first metal layer Ti, a second metal layer Al and a third metal layer TiW arranged in sequence from bottom to top on the upper surface of the GaN-based HEMT epitaxial layer, or a first metal layer Ti, a second metal layer Al, a third metal layer Ti and a fourth metal layer TiW arranged in sequence from bottom to top; the preparation of the GaN-based HEMT device comprises the following steps: (1) defining a source-drain etching pattern area on the GaN-based epitaxial layer by using a photolithography technique; (2) Use ICP etching technology to completely etch away the AlGaN barrier layer and etch to 10~50nm below the GaN channel layer; (3) Cleaning the source and drain etched patterns obtained in step (2); (4) After the cleaning process is completed, the obtained GaN-based HEMT epitaxial layer is subjected to surface oxidation treatment; (5) using photolithography technology to define source and drain ohmic contact pattern regions on the GaN-based HEMT epitaxial layer obtained in step (4); (6) Depositing source and drain ohmic contact metals in sequence; (7) Performing metal stripping on step (6) to form source-drain electrodes, and performing alloy annealing at 550-700° C. to form source-drain ohmic contact electrodes.

2. A GaN-based HEMT device according to claim 1, It is characterized in that When the first metal layer Ti, the second metal layer Al and the third metal layer TiW are arranged in sequence from bottom to top on the upper surface of the GaN-based HEMT epitaxial layer, the thickness of the first metal layer Ti is 5~20nm, the thickness of the second metal layer Al is 100~300nm, and the thickness of the third metal layer TiW is 20~50nm.

3. A GaN-based HEMT device according to claim 1 or 2, It is characterized in that When the first metal layer Ti, the second metal layer Al, the third metal layer Ti and the fourth metal layer TiW are arranged in sequence from bottom to top on the upper surface of the GaN-based HEMT epitaxial layer, the thickness of the first metal layer Ti is 5~20nm, the thickness of the second metal layer Al is 100~300nm, the thickness of the third metal layer Ti is 5~10nm, and the thickness of the fourth metal layer TiW is 20~50nm.

4. A method for preparing a GaN-based HEMT device, It is characterized in that The GaN-based HEM device comprises a GaN-based HEMT epitaxial layer, a GaN channel layer is arranged in the GaN-based HEMT epitaxial layer, and the electrode comprises a first metal layer Ti, a second metal layer Al and a third metal layer TiW arranged in sequence from bottom to top on the upper surface of the GaN-based HEMT epitaxial layer, or a first metal layer Ti, a second metal layer Al, a third metal layer Ti and a fourth metal layer TiW arranged in sequence from bottom to top; the preparation method comprises the following steps: (1) Using photolithography technology to define the source and drain etching pattern area on the GaN-based epitaxial layer; (2) Use ICP etching technology to completely etch away the AlGaN barrier layer and etch to 10~50nm below the GaN channel layer; (3) Cleaning the source and drain etched patterns obtained in step (2); (4) After the cleaning process is completed, the obtained GaN-based HEMT epitaxial layer is subjected to surface oxidation treatment; (5) using photolithography technology to define source and drain ohmic contact pattern regions on the GaN-based HEMT epitaxial layer obtained in step (4); (6) Depositing source and drain ohmic contact metals in sequence; (7) Performing metal stripping on step (6) to form source-drain electrodes, and performing alloy annealing at 550-700° C. to form source-drain ohmic contact electrodes.

5. The method for preparing a GaN-based HEMT device according to claim 4, It is characterized in that The tilt angle during CP etching in step (2) is 20 to 50°.

6. The method for preparing a GaN-based HEMT device according to claim 4, It is characterized in that The surface oxidation treatment in step (4) is oxygen plasma treatment or oxygen atmosphere annealing treatment.

7. The method for preparing a GaN-based HEMT device according to claim 6, It is characterized in that When the surface oxidation treatment is oxygen plasma treatment, the oxygen flow rate is 50-100 sccm, the power is 150-400 W, and the time is 100 s-5 min.

8. The method for preparing a GaN-based HEMT device according to claim 6, It is characterized in that When the surface oxidation treatment is an oxygen atmosphere annealing treatment, the annealing temperature is 300° C. to 400° C., and the annealing time is 10 min to 40 min.

9. The method for preparing a GaN-based HEMT device according to claim 4, It is characterized in that The source and drain etching pattern area described in step (1) is smaller than the source and drain ohmic contact pattern area described in step (5), and the margin between the two patterns on a single electrode is 2-8 μm.

10. A method for preparing a GaN-based HEMT device according to any one of claims 4 to 9, It is characterized in that The annealing time of the alloy annealing treatment in step (7) is 30s~10min, and the atmosphere is high-purity nitrogen.

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