WO2021027903A1 - Gan-based hemt gold-free ohmic contact electrode and thermal nitridation forming method therefor - Google Patents

Abstract

A GaN-based HEMT gold-free ohmic contact electrode and a thermal nitridation forming method therefor. The electrode is made of a first metal layer Ti (2), a second metal layer Al (3), a third metal layer X (4), a fourth metal layer Ti (5) and a cap layer metal layer TiN (6) that are successively arranged from bottom to top at two sides of the upper surface of a GaN-based HEMT epitaxial layer (1), wherein X is one or more among Ni, Ni/Ti/Ni or Ni/Ti/Ni/Ti/Ni multi-layer metals. The described electrode and thermal nitridation forming method therefor avoid a process of preparing a cap layer metal layer TiN at a high temperature, reduces the processing temperature and processing difficulty, simplifies the processing procedure and, at the same time, enhances the processing capabilities at a low temperature, and is helpful in reducing the fabrication costs of a GaN-based HEMT device.

Description

GaN-based HEMT gold-free ohmic contact electrode and thermal nitridation forming method thereof Technical field

The invention relates to a semiconductor device, in particular to a GaN-based HEMT gold-free ohmic contact electrode and a thermal nitridation forming method thereof.

Background technique

GaN-based high electron mobility transistors (HEMT) have broad application prospects in high-voltage, high-frequency, high-power semiconductor laser devices and high-performance ultraviolet detectors. However, compound semiconductor dedicated production line technology is relatively backward, process update and operation and maintenance costs are relatively high, which increases the production cost of GaN-based HEMT devices. Using 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 Ohm and Schottky contact processes of conventional HEMT devices will form deep-level impurities in Si, contaminating 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.

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

The industry has two main annealing windows for forming ohmic contacts on GaN-based HEMTs: 1. Low temperature annealing window, nitrogen atmosphere, annealing temperature 500~650℃, annealing time 2-10min; 2. High temperature annealing window, nitrogen atmosphere, The annealing temperature is 800~1000℃, and the annealing time is 15~60sec.

In the low-temperature annealing process, the solution reported in the literature is to use dry etching. The best etching distance is 1~2nm from the two-dimensional electron gas channel. Because the precision of conventional dry etching is not easy to control, different epitaxial etching The large difference in etching rate results in poor repeatability of the etching process, which is not conducive to large-scale industrial production. In the high temperature annealing process, the conventional gold ohmic contact electrodes and the W, Mo, Cu and other non-gold ohmic contact electrodes reported in the literature, because the metal Al layer usually requires more than 100nm (the thickness of Al is much greater than the thickness of the underlying Ti), a lot of The unreacted Al is incompatible with the Ti-Al alloy that agglomerates to form an island structure, resulting in extremely poor surface morphology and edge morphology of the source and drain electrodes. In addition, in the gold ohmic contact electrode, the mutual diffusion of Al and Au to form an alloy is also one of the reasons for the poor surface morphology of the electrode, while the gold-free ohmic contact electrode has good chemical and thermal stability and no gold cap layer metal Poor adhesion to a large number of highly active Al layers is also one of the reasons for the poor surface morphology of the electrode.

Titanium nitride (TiN) is a transition metal nitride, which is a mixture of ionic bonds, metal bonds and covalent bonds. It has high strength, high hardness, high temperature resistance, acid and alkali corrosion resistance, abrasion resistance and good electrical conductivity It is an excellent material to replace Au as the ohmic contact cap layer metal. At present, high-performance TiN films are usually deposited by DC reactive magnetron sputtering at a higher substrate temperature (300~700℃). However, the deposition of ohmic metal in a high-temperature environment is incompatible with the traditional metal stripping process. The electrode pattern can only be formed by methods such as metal etching and special mask design. The electrode preparation process becomes more complicated and may cause adverse effects on the device, such as Etching damage, solid phase reaction between metal and semiconductor at high temperature, etc. In addition, high-temperature magnetron sputtering deposition of metal and its alloy films requires a long subsequent cooling time, increases production costs and decreases efficiency, which is not conducive to large-scale industrial production.

Technical solutions

In order to overcome the above shortcomings and shortcomings of the prior art, the purpose of the present invention is to provide a GaN-based HEMT gold-free ohmic contact electrode and a thermal nitridation forming method thereof. The solid phase reaction of the contact is combined, and a part of the surface of the fourth metal Ti layer undergoes a thermal nitridation reaction to form a cap layer metal TiN with good chemical stability, avoiding the direct high-temperature preparation of the cap layer metal TiN, and at the same time, the source and drain electrodes of the multilayer metal A solid-phase reaction occurs between them, and a good ohmic contact is formed with the GaN-based epitaxy, which reduces the difficulty of the source and drain electrode preparation process, simplifies the process flow, and solves the technical bottleneck of the compatibility of AlGaN/GaN heterojunction HEMT and Si-CMOS process, which is helpful To reduce the manufacturing cost of AlGaN/GaN heterojunction HEMT.

Using thermal nitridation to form the cap metal layer TiN can effectively solve the series of problems caused by direct high-temperature deposition of TiN films.

Using thermal nitridation to form GaN-based HEMT gold-free ohmic contact electrodes can effectively solve the problem of poor electrode surface morphology under high-temperature annealing.

The purpose of the present invention is achieved by at least one of the following technical solutions.

The present invention provides a GaN-based HEMT gold-free ohmic contact electrode. The electrode is a first metal layer Ti and a second metal layer Al which are arranged sequentially from bottom to top on both sides of the upper surface of the epitaxial layer of the GaN-based HEMT. , The third metal layer X, the fourth metal layer Ti and the cap layer metal layer TiN, where X is one or more of Ni, Ni/Ti/Ni or Ni/Ti/Ni/Ti/Ni multilayer metals.

Preferably, the thickness of the first metal layer Ti is 1 to 30 nm, the thickness of the second metal layer Al is 40 to 200 nm, the thickness of the third metal layer X is 5 to 30 nm, and the thickness of the fourth metal layer Ti is 60 to 120 nm. The thickness of the cap metal layer TiN is 10-40 nm.

The present invention also provides a method for forming the GaN-based HEMT gold-free ohmic contact electrode by thermal nitriding reaction, which includes the following steps:

(1) Define the source and drain electrode pattern area: Using photolithography technology, define the source and drain electrode pattern areas on both sides of the upper surface of the GaN-based HEMT epitaxial layer. The photolithography mask covers the GaN-based HEMT epitaxial layer except for the source and drain electrode patterns. Area;

(2) Surface treatment: use acid-base solution to clean the pattern area of source and drain electrodes;

(3) Electrode metal layer deposition: the first metal layer Ti, the second metal layer Al, the third metal layer X, and the fourth metal are sequentially deposited on the source and drain electrode pattern area and the photolithography mask on the GaN-based HEMT epitaxial layer Layer Ti; where the first metal layer Ti, the second metal layer Al, the third metal layer X, and the fourth metal layer Ti of the source and drain electrodes are prepared at a low temperature, and the temperature of the substrate is 25-50 ℃; the substrate is passed through Step (2) The processed GaN-based HEMT epitaxial layer;

(4) Stripping: For step (3), remove the photolithography mask and the first metal layer Ti, second metal layer Al, third metal layer X, and fourth metal layer Ti on the photolithography mask through the stripping process, leaving The first metal layer Ti, the second metal layer Al, the third metal layer X, and the fourth metal layer Ti at the lower source and drain electrode pattern area form source and drain electrodes;

(5) Annealing: Anneal the source and drain electrodes obtained in step (4) to combine the thermal nitridation reaction with the solid phase reaction of the ohmic contact, and the thermal nitridation reaction occurs on the Ti surface of the fourth metal layer to form chemical stability With a good cap metal layer TiN, a solid phase reaction occurs between the multilayer metals of the source and drain electrodes, and a good ohmic contact is formed with the GaN-based HEMT epitaxial layer.

Preferably, the method of electrode metal layer deposition in step (3) is electron beam evaporation or magnetron sputtering deposition.

Preferably, the fourth metal layer Ti is evaporated using an electron beam, and the evaporation rate is 0.4-0.8 nm/sec.

Preferably, the method of electrode metal layer deposition in step (3) is magnetron sputtering deposition, and the magnetron sputtering selects the DC magnetron sputtering mode.

Preferably, magnetron sputtering is used to deposit the fourth metal layer Ti in step (3), and the vacuum degree in the vacuum chamber is below 4E-04Pa before the deposition of the fourth metal layer Ti.

Preferably, the annealing temperature in step (5) is 500 to 900° C., the annealing time is 15 s to 10 min, and the atmosphere is high-purity nitrogen.

The gold-free source and drain electrodes of the present invention are the first metal layer Ti, the second metal layer Al, the third metal layer X, the fourth metal layer Ti, and the third metal layer X is Ni, Ni/Ti/Ni or Ni/ Ti/Ni/Ti/Ni multilayer metal, forming Ti/Al/Ni/Ti, Ti/Al/Ni/Ti/Ni/Ti, Ti/Al/Ni/Ti/Ni/Ti/Ni/Ti, etc. Layer source and drain electrode metal system. Through the annealing process in a high-purity nitrogen atmosphere, the thermal nitridation reaction is combined with the solid-phase reaction between the multilayer metals, and a thermal nitridation reaction occurs on a part of the surface of the fourth metal Ti layer, forming a cap layer metal TiN with good chemical stability , Make the multilayer source and drain electrode metal system form ohmic contact with the AlGaN or InAlN intrinsic barrier layer to form good contact ohmic contact electrodes Ti/Al/Ni/Ti/TiN, Ti/Al/Ni/Ti/Ni/Ti /TiN, Ti/Al/Ni/Ti/Ni/Ti/Ni/Ti/TiN.

Beneficial effect

Compared with the prior art, the present invention has the following advantages and beneficial effects:

(1) In the present invention, the fourth metal layer Ti is prepared at a low temperature. Through post-annealing treatment, a part of the surface of the fourth metal Ti layer undergoes a thermal nitridation reaction to form a stable cap layer metal TiN, which undergoes solid phase reaction with other electrode metals, and The GaN-based HEMT epitaxial layer forms a good ohmic contact; the cap metal layer TiN is formed by the thermal nitridation reaction of the fourth metal layer Ti, rather than directly deposited, thereby avoiding the direct preparation of TiN at high temperatures (100-700°C).

(2) The thermal nitridation reaction of the present invention forms a GaN-based HEMT gold-free ohmic contact electrode, which can effectively solve the problem of poor electrode surface morphology under high temperature annealing;

(3) The present invention avoids the process of preparing the cap layer metal layer TiN at high temperature, reduces the process temperature and process complexity, simplifies the process flow, and at the same time improves the compatibility of the process at low temperature, which helps reduce the manufacturing cost of GaN-based HEMT devices .

Description of the drawings

1 is a schematic diagram of the GaN-based HEMT epitaxial layer when the source and drain electrode patterns are formed in Embodiments 1 to 3;

2 is a GaN-based HEMT after sequentially depositing the first metal layer Ti, the second metal layer Al, the third metal layer X, and the fourth metal layer Ti on the source and drain electrode pattern areas and the photolithography mask in Embodiments 1 to 3 Schematic diagram on the epitaxial layer;

3 is a schematic diagram of the structure of the GaN-based HEMT epitaxial layer after stripping off the first metal layer Ti, the second metal layer Al, the third metal layer X, and the fourth metal layer Ti on the photolithography mask in Embodiments 1 to 3;

4 is a schematic diagram of the structure of the GaN-based HEMT gold-free ohmic contact electrode formed by thermal nitridation in Examples 1 to 3;

FIG. 5 is an I-V curve of the test of forming a GaN-based HEMT gold-free ohmic contact electrode by the thermal nitridation reaction in Example 1;

The figure shows: 1-GaN-based HEMT epitaxial layer; 2-first metal layer Ti; 3-second metal layer Al; 4-third metal layer X; 5-fourth metal layer Ti; 6-cap layer metal Layer TiN; 7-source and drain electrode pattern area; 8-photolithography mask.

Embodiments of the invention

The present invention will be further described below in conjunction with the drawings and examples, but the implementation of the present invention is not limited to this; it should be pointed out that if there are processes or process parameters that are not specifically described in detail below, those skilled in the art can refer to Realized by existing technology.

Example 1

This embodiment provides a GaN-based HEMT gold-free ohmic contact electrode. As shown in FIG. 4, the electrode is a first metal arranged sequentially from bottom to top on both sides of the upper surface of the epitaxial layer 1 of the GaN-based HEMT. Ti 2, the second metal layer Al 3, the third metal layer X 4, the fourth metal layer Ti 5 and the cap metal layer TiN 6, where X is Ni. The thickness of the first metal layer Ti is 20 nm, the thickness of the second metal layer Al is 60 nm, the thickness of the third metal layer X is 10 nm, the thickness of the fourth metal layer Ti is 80 nm, and the thickness of the cap metal layer TiN is The thickness is 20nm.

This embodiment also provides a method for forming the GaN-based HEMT gold-free ohmic contact electrode by thermal nitriding reaction, which includes the following steps:

(1) Define the source and drain electrode pattern area: Using photolithography technology, define the source and drain electrode pattern area 7 on both sides of the upper surface of the GaN-based HEMT epitaxial layer 1, and the photolithography mask 8 covers the GaN-based HEMT epitaxial layer except for source and drain. The area outside the polar figure, as shown in Figure 1;

(2) Surface treatment: Use acid-base solution to clean the source and drain electrode pattern area 7;

(3) Electrode metal layer deposition: the first metal layer Ti 2 and the second metal layer are sequentially deposited on the source and drain electrode pattern area 7 and the photolithography mask 8 on the GaN-based HEMT epitaxial layer 1 by magnetron sputtering Al 3, the third metal layer X 4, the fourth metal layer Ti 5, as shown in FIG. 2; wherein, the first metal layer Ti 2, the second metal layer Al 3, the third metal layer X 4, the source and drain electrodes The fourth metal layer Ti 5 is prepared at a low temperature, and the temperature of the substrate is 35°C; the substrate is the GaN-based HEMT epitaxial layer 1 processed in step (2);

The fourth metal layer Ti 5 of low temperature magnetron sputtering is deposited by conventional magnetron sputtering method. Before the deposition of the fourth metal layer Ti 5, the vacuum degree in the vacuum chamber is 3.2E-04Pa; the fourth metal layer Ti 5 is DC magnetic In the controlled sputtering mode, the sputtering gas is argon, the sputtering target is Ti target, the substrate temperature is 35°C, the sputtering power is 280W, and the working pressure is 0.6Pa.

(4) Stripping: For step (3), remove the photolithography mask and the first metal layer Ti 2, the second metal layer Al 3, the third metal layer X 4, and the fourth metal layer on the photolithography mask through a stripping process Ti 5, leaving the first metal layer Ti 2, the second metal layer Al 3, the third metal layer X 4, and the fourth metal layer Ti 5 at the pattern area of the source and drain electrodes to form the source and drain electrodes, as shown in FIG. 3 ；

(5) Annealing: Anneal the source and drain electrodes obtained in step (4) to combine the thermal nitridation reaction with the solid phase reaction of ohmic contact. The surface part of the fourth metal layer Ti 5 undergoes thermal nitridation reaction to form chemical stability The high-performance cap layer metal layer TiN 6, solid-phase reaction occurs between the multilayer metal of the source and drain electrodes, and forms a good ohmic contact with the GaN-based HEMT epitaxial layer. The annealing temperature is 900°C, the annealing time is 30s, and the atmosphere is high-purity nitrogen.

The IV test is performed on the GaN-based HEMT gold-free ohmic contact electrode prepared in this embodiment, and the IV characteristic curve of FIG. 5 is obtained. In Figure 5, the abscissa is the voltage, the unit is V, the ordinate is the current, the unit is A. The solid line is the current curve of the traditional high-temperature gold ohmic contact electrode, and the dashed line is the current curve of the gold-free ohmic contact electrode formed by the thermal nitridation reaction of this embodiment (GaN-based HEMT gold-free ohmic contact electrode). It can be seen from FIG. 5 that the GaN-based HEMT gold-free ohmic contact electrode of this embodiment exhibits a good ohmic contact, and the current curve is similar to the current curve with gold contact, and the magnitude of the current is the same, and the IV curve is straight near 0V. Under the same GaN-based HEMT epitaxial layer, the specific contact resistivity of the traditional gold ohmic contact electrode after high temperature annealing is 3.12E-05Ω•cm ² , the contact resistance is 1.04Ω•mm, and the surface roughness is 51.56nm. The specific contact resistivity of the gold-free ohmic contact electrode formed by the thermal nitriding reaction of the embodiment is 3.42E-05 Ω·cm ² , the contact resistance is 1.1 Ω·mm, and the surface roughness is 6.22 nm. The specific contact resistivity of the gold-free ohmic contact electrode of this embodiment is comparable to that of the gold-free ohmic contact electrode, and has a greater advantage in surface morphology or surface roughness.

Example 2

This embodiment provides a GaN-based HEMT gold-free ohmic contact electrode. As shown in FIG. 4, the electrode is a first metal arranged sequentially from bottom to top on both sides of the upper surface of the epitaxial layer 1 of the GaN-based HEMT. Ti 2, the second metal layer Al 3, the third metal layer X 4, the fourth metal layer Ti 5 and the cap metal layer TiN 6, where X is Ni. The thickness of the first metal layer Ti is 20 nm, the thickness of the second metal layer Al is 100 nm, the thickness of the third metal layer X is 10 nm, the thickness of the fourth metal layer Ti is 70 nm, and the thickness of the cap metal layer TiN is The thickness is 20nm.

This embodiment also provides a method for forming the GaN-based HEMT gold-free ohmic contact electrode by thermal nitriding reaction, which includes the following steps:

(1) Define the source and drain electrode pattern area: Using photolithography technology, define the source and drain electrode pattern area 7 on both sides of the upper surface of the GaN-based HEMT epitaxial layer 1, and the photolithography mask 8 covers the GaN-based HEMT epitaxial layer except for source and drain. The area outside the polar figure, as shown in Figure 1;

(2) Surface treatment: Use acid-base solution to clean the source and drain electrode pattern area 7;

(3) Electrode metal layer deposition: The first metal layer Ti 2 and the second metal layer Al are sequentially deposited on the source and drain electrode pattern area 7 and the photolithography mask 8 on the GaN-based HEMT epitaxial layer 1 by electron beam evaporation. 3. The third metal layer X4, the fourth metal layer Ti5, as shown in FIG. 2; among them, the first metal layer Ti2 of the source and drain electrodes, the second metal layer Al3, the third metal layer X4, the third metal layer The four-metal layer Ti 5 is prepared at a low temperature, and the temperature of the substrate is 25°C; the substrate is the GaN-based HEMT epitaxial layer 1 processed in step (2);

The fourth metal layer Ti 5 is evaporated by low-temperature electron beam, and the rate of electron beam evaporation and coating is 0.6 nm/sec.

(4) Stripping: For step (3), remove the photolithography mask and the first metal layer Ti 2, the second metal layer Al 3, the third metal layer X 4, and the fourth metal layer on the photolithography mask through a stripping process Ti 5, leaving the first metal layer Ti 2, the second metal layer Al 3, the third metal layer X 4, and the fourth metal layer Ti 5 at the pattern area of the source and drain electrodes to form the source and drain electrodes, as shown in FIG. 3 ；

(5) Annealing: Anneal the source and drain electrodes obtained in step (4) to combine the thermal nitridation reaction with the solid phase reaction of ohmic contact. The surface part of the fourth metal layer Ti 5 undergoes thermal nitridation reaction to form chemical stability The cap layer metal layer TiN 6 with good performance has a solid phase reaction between the multilayer metals of the source and drain electrodes, and forms a good ohmic contact with the GaN-based HEMT epitaxial layer 1. The annealing temperature is 900°C, the annealing time is 60s, and the atmosphere is high-purity nitrogen.

The ohmic contact test result of the GaN-based HEMT gold-free ohmic contact electrode obtained in this example is similar to that of Example 1, showing a good ohmic contact, the IV curve is a straight line near 0V, and the specific contact resistivity is 3.98E-05Ω•cm ² . The contact resistance is 1.04Ω•mm. Since the thickness of the second metal layer Al 3 of Example 2 is larger, the surface roughness is 12.2 nm.

Example 3

This embodiment provides a GaN-based HEMT gold-free ohmic contact electrode. As shown in FIG. 4, the electrode is a first metal arranged sequentially from bottom to top on both sides of the upper surface of the epitaxial layer 1 of the GaN-based HEMT. Ti 2, the second metal layer Al 3, the third metal layer X 4, the fourth metal layer Ti 5 and the cap metal layer TiN 6, where X is Ni. The thickness of the first metal layer Ti is 3 nm, the thickness of the second metal layer Al is 150 nm, the thickness of the third metal layer X is 10 nm, the thickness of the fourth metal layer Ti is 100 nm, and the thickness of the cap metal layer TiN is The thickness is 30nm.

This embodiment also provides a method for forming the GaN-based HEMT gold-free ohmic contact electrode by thermal nitriding reaction, which includes the following steps:

(1) Define the source and drain electrode pattern area: Using photolithography technology, define the source and drain electrode pattern area 7 on both sides of the upper surface of the GaN-based HEMT epitaxial layer 1, and the photolithography mask 8 covers the GaN-based HEMT epitaxial layer except for source and drain. The area outside the polar figure, as shown in Figure 1;

(2) Surface treatment: Use acid-base solution to clean the source and drain electrode pattern area 7;

(3) Electrode metal layer deposition: The first metal layer Ti 2 and the second metal layer Al are sequentially deposited on the source and drain electrode pattern area 7 and the photolithography mask 8 on the GaN-based HEMT epitaxial layer 1 by electron beam evaporation. 3. The third metal layer X 4, and then the fourth metal layer Ti 5 is deposited by magnetron sputtering, as shown in Fig. 2; among them, the first metal layer Ti of the source and drain electrodes 2, the second metal layer Al 3 The third metal layer X 4 and the fourth metal layer Ti 5 are prepared at a low temperature, and the temperature of the substrate is 35°C; the substrate is the GaN-based HEMT epitaxial layer 1 processed in step (2);

Low-temperature magnetron sputtering The fourth metal layer Ti is deposited by the conventional magnetron sputtering method. Before depositing the fourth metal layer Ti 5, the vacuum degree in the vacuum chamber is 3.2E-04Pa, and the fourth metal layer Ti 5 is DC magnetron. In the sputtering mode, the sputtering gas is argon, the sputtering target is Ti target, the sputtering power is 280W, and the working pressure is 0.6Pa.

(4) Stripping: For step (3), remove the photolithography mask and the first metal layer Ti 2, the second metal layer Al 3, the third metal layer X 4, and the fourth metal layer on the photolithography mask through a stripping process Ti 5, leaving the first metal layer Ti 2, the second metal layer Al 3, the third metal layer X 4, and the fourth metal layer Ti 5 at the pattern area of the source and drain electrodes to form the source and drain electrodes, as shown in FIG. 3 ；

(5) Annealing: Anneal the source and drain electrodes obtained in step (4) to combine the thermal nitridation reaction with the solid phase reaction of ohmic contact. The surface part of the fourth metal layer Ti 5 undergoes thermal nitridation reaction to form chemical stability The high-performance cap layer metal layer TiN 6, solid-phase reaction occurs between the multilayer metal of the source and drain electrodes, and forms a good ohmic contact with the GaN-based HEMT epitaxial layer. The annealing temperature is 600°C, the annealing time is 10 minutes, and the atmosphere is high-purity nitrogen.

In this embodiment, two methods of electron beam evaporation and magnetron sputtering are used to deposit the metal layer, and the preparation effect is equivalent to deposition only by the electron beam evaporation or magnetron sputtering method. Compared with the embodiment 1 and the embodiment 2, the thickness of the second metal layer Al 3 is much greater than the thickness of the first metal Ti layer 2, and the Al/Ti thickness ratio is as high as 50. The Al/Ti thickness of the embodiment 1 The ratio is only 3, and the Al/Ti thickness ratio of Example 2 is only 5. The specific contact resistivity of Example 3 is 1.12E-04Ω•cm ² , and the surface roughness is 3.48 nm.

The GaN-based HEMT gold-free ohmic contact electrode formed by the thermal nitridation reaction provided by the present invention deposits a Ti film by a low-temperature method, and combines the thermal nitridation reaction with the solid phase reaction between the multilayer metals forming the ohmic contact, through In the later suitable annealing process, a part of the surface of the Ti film is thermally nitridated to form stable TiN, and solid-phase reaction occurs with other electrode metals to form good ohmic contact with the GaN-based HEMT epitaxial layer. The invention avoids the process of preparing the TiN film at high temperature, reduces the process temperature and the complexity of the process, simplifies the process flow, and at the same time improves the compatibility of the process at low temperature, and helps reduce the manufacturing cost of the GaN-based HEMT device.

The embodiments do not constitute any limitation to the present invention. Obviously, for those skilled in the art, after understanding the content and principle of the present invention, they can perform according to the method of the present invention without departing from the principle and scope of the present invention. Various modifications and changes in form and details, but these modifications and changes based on the present invention are still within the protection scope of the claims of the present invention.

Claims (10)

1. The GaN-based HEMT gold-free ohmic contact electrode is characterized in that the electrode is a first metal layer Ti, a second metal layer Al, and a second metal layer Ti, the second metal layer Al, and the second metal layer arranged in sequence from bottom to top on both sides of the upper surface of the epitaxial layer of the GaN-based HEMT. The three metal layers X, the fourth metal layer Ti, and the cap layer metal layer TiN, where X is one or more of Ni, Ni/Ti/Ni or Ni/Ti/Ni/Ti/Ni multilayer metals.
2. The GaN-based HEMT gold-free ohmic contact electrode according to claim 1, wherein the thickness of the first metal layer Ti is 1-30 nm, and the thickness of the second metal layer Al is 40-200 nm.
3. The GaN-based HEMT gold-free ohmic contact electrode according to claim 1, wherein the thickness of the third metal layer X is 5-30 nm, and the thickness of the fourth metal layer Ti is 60-120 nm.
4. The GaN-based HEMT gold-free ohmic contact electrode according to claim 1, wherein the thickness of the cap metal layer TiN is 10-40 nm.
5. The method for forming the GaN-based HEMT gold-free ohmic contact electrode according to any one of claims 1 to 4 by thermal nitridation reaction, characterized in that it comprises the following steps:

   (1) Define the source and drain electrode pattern area: Using photolithography technology, define the source and drain electrode pattern areas on both sides of the upper surface of the GaN-based HEMT epitaxial layer. The photolithography mask covers the GaN-based HEMT epitaxial layer except for the source and drain electrode patterns. Area;

   (2) Surface treatment: use acid-base solution to clean the pattern area of source and drain electrodes;

   (3) Electrode metal layer deposition: the first metal layer Ti, the second metal layer Al, the third metal layer X, and the fourth metal are sequentially deposited on the source and drain electrode pattern area and the photolithography mask on the GaN-based HEMT epitaxial layer Layer Ti; where the first metal layer Ti, the second metal layer Al, the third metal layer X, and the fourth metal layer Ti of the source and drain electrodes are prepared at a low temperature, and the temperature of the substrate is 25-50 ℃; the substrate is passed through Step (2) The processed GaN-based HEMT epitaxial layer;

   (4) Stripping: For step (3), remove the photolithography mask and the first metal layer Ti, second metal layer Al, third metal layer X, and fourth metal layer Ti on the photolithography mask through the stripping process, leaving The first metal layer Ti, the second metal layer Al, the third metal layer X, and the fourth metal layer Ti at the lower source and drain electrode pattern area form source and drain electrodes;

   (5) Annealing: Anneal the source and drain electrodes obtained in step (4) to combine the thermal nitridation reaction with the solid phase reaction of the ohmic contact, and the thermal nitridation reaction occurs on the Ti surface of the fourth metal layer to form chemical stability With a good cap metal layer TiN, a solid phase reaction occurs between the multilayer metals of the source and drain electrodes, and a good ohmic contact is formed with the GaN-based HEMT epitaxial layer.
6. The method for forming a GaN-based HEMT gold-free ohmic contact electrode by thermal nitridation reaction according to claim 5, wherein the method of electrode metal layer deposition in step (3) is electron beam evaporation or magnetron sputtering deposition.
7. The method for forming a GaN-based HEMT gold-free ohmic contact electrode by thermal nitridation reaction according to claim 5, wherein the fourth metal layer Ti is evaporated by an electron beam at an evaporation rate of 0.4-0.8 nm/sec.
8. The method for forming a GaN-based HEMT gold-free ohmic contact electrode by thermal nitridation reaction according to claim 5, wherein the method of electrode metal layer deposition in step (3) is magnetron sputtering deposition, and magnetron sputtering is selected DC magnetron sputtering mode.
9. The method for forming a GaN-based HEMT gold-free ohmic contact electrode by thermal nitridation reaction according to claim 5, wherein the fourth metal layer Ti is deposited by magnetron sputtering in step (3) to deposit the fourth metal layer Ti Previously, the vacuum degree in the vacuum chamber was below 4E-04Pa.
10. The method for forming a GaN-based HEMT gold-free ohmic contact electrode by thermal nitridation reaction according to claim 5, wherein the annealing temperature in step (5) is 500~900℃, the annealing time is 15s~10min, and the atmosphere is High purity nitrogen.