阅读说明：本技术 低温无金欧姆接触GaN基HEMT器件及其制备方法 (Low-temperature gold-free ohmic contact GaN-based HEMT device and preparation method thereof ) 是由 王洪 熊年贺 高升 于 2021-07-21 设计创作，主要内容包括：本发明公开了一种低温无金欧姆接触GaN基HEMT器件及其制备方法。所述器件包括AlGaN/GaN外延层,AlGaN/GaN外延层上表面的两端刻蚀区域分别连接源电极和漏电极；AlGaN/GaN外延层包括从下往上依次层叠的衬底、GaN缓冲层、GaN沟道层和AlGaN势垒层。本发明制备的Ti/Al/Ta/W结构的器件的导通电阻(13.6Ω·mm)相较于传统的单独使用Ti做接触层的Ti/Al/W结构的器件(15.1Ω·mm)下降了9.9％,提高了器件的性能。(The invention discloses a low-temperature gold-free ohmic contact GaN-based HEMT device and a preparation method thereof. The device comprises an AlGaN/GaN epitaxial layer, wherein etching areas at two ends of the upper surface of the AlGaN/GaN epitaxial layer are respectively connected with a source electrode and a drain electrode; the AlGaN/GaN epitaxial layer comprises a substrate, a GaN buffer layer, a GaN channel layer and an AlGaN barrier layer which are sequentially stacked from bottom to top. Compared with the traditional device (15.1 omega mm) with a Ti/Al/Ta/W structure, the on-resistance (13.6 omega mm) of the device with the Ti/Al/Ta/W structure prepared by the invention is reduced by 9.9%, and the performance of the device is improved.)

1. The low-temperature gold-free ohmic contact GaN-based HEMT device is characterized by comprising an AlGaN/GaN epitaxial layer, wherein etching areas at two ends of the upper surface of the AlGaN/GaN epitaxial layer are respectively connected with a source electrode and a drain electrode;

the AlGaN/GaN epitaxial layer comprises a substrate (1), a GaN buffer layer (2), a GaN channel layer (3) and an AlGaN barrier layer (4) which are sequentially stacked from bottom to top.

2. The low-temperature gold-free ohmic contact GaN-based HEMT device according to claim 1, wherein the source electrode and the drain electrode each comprise a first layer of metal (5), a second layer of metal (6), a third layer of metal (7) and a fourth layer of metal (8);

the first layer of metal (5) is arranged in etching areas at two ends of the upper surface of the AlGaN/GaN epitaxial layer, the second layer of metal (6) is arranged on the first layer of metal (5), and the third layer of metal (7) wraps the top surfaces and the side surfaces of the first layer of metal (5) and the second layer of metal (6); the fourth layer of metal (8) wraps the top surface and the side surfaces of the third layer of metal (7).

3. The low-temperature gold-free ohmic contact GaN-based HEMT device as claimed in claim 2, characterized in that the first layer of metal (5) and the second layer of metal (6) are deposited by electron beam evaporation, and the third layer of metal (7) and the fourth layer of metal (8) are deposited by magnetron sputtering.

4. The low-temperature gold-free ohmic contact GaN-based HEMT device according to claim 2, wherein the contact layer of the multilayer metal structure formed after the source and drain electrodes are peeled off is the third layer metal (7)/the first layer metal (5)/the third layer metal (7) from one side to the other side.

5. The low-temperature gold-free ohmic contact GaN-based HEMT device according to claim 2, wherein the third layer of metal (7) wrapped on both sides of the first layer of metal (5) has a length of 0.5-1 μm.

6. The low-temperature gold-free ohmic contact GaN-based HEMT device of claim 2, wherein etched regions at both ends of the AlGaN barrier layer (4) on the upper surface of the AlGaN/GaN epitaxial layer remain 1-3nm thick.

7. The method for preparing the low-temperature gold-free ohmic contact GaN-based HEMT device of any one of claims 1-6 is characterized by comprising the following steps:

s1, defining an etching window on the AlGaN/GaN epitaxial layer, and after etching is completed, carrying out surface treatment on an etching area to remove etching residues and oxides;

s2, defining windows of a source electrode and a drain electrode on the AlGaN/GaN epitaxial layer, preparing a first layer of metal (5), a second layer of metal (6), a third layer of metal (7) and a fourth layer of metal (8) of the source electrode and the drain electrode, and annealing to form ohmic contact, so that the low-temperature gold-free ohmic contact GaN-based HEMT device is obtained.

8. The method for preparing a low-temperature gold-free ohmic contact GaN-based HEMT device according to claim 7, wherein in step S1, the etching window is designed to be 6-10 μm;

and the surface treatment is to clean oxide on the surface of the source electrode and drain electrode pattern area by using an acid-base solution, or to clean organic matter on the surface of the source electrode and drain electrode pattern area by using an organic solvent.

9. The method for manufacturing a low-temperature gold-free ohmic contact GaN-based HEMT device according to claim 7, wherein in step S2, the windows of the source electrode and the drain electrode are designed to be 5-8 μm;

in a first layer of metal (5), a second layer of metal (6), a third layer of metal (7) and a fourth layer of metal (8) of the source electrode and the drain electrode, the first layer of metal (5) is Ti or Ta, the second layer of metal (6) is Al, the third layer of metal (7) is Ta or Ti, and the fourth layer of metal (8) is W, Cu, TiN or TiW;

the thickness of the first layer metal (5) is 1-20nm, the thickness of the second layer metal (6) is 60-150nm, the thickness of the third layer metal (7) is 1-20nm, and the thickness of the fourth layer metal (8) is 60-200 nm.

10. The method for preparing a low-temperature gold-free ohmic contact GaN-based HEMT device according to claim 5, wherein in step S2, the annealing atmosphere is nitrogen or argon, and the annealing temperature and the annealing time are 450-650 ℃ and 30S-10 min, respectively.

Technical Field

The invention relates to the field of semiconductor devices, in particular to a low-temperature gold-free ohmic contact GaN-based HEMT device and a preparation method thereof.

Background

AlGaN/GaN High Electron Mobility Transistors (HEMTs) are receiving much attention due to their superior characteristics of high electron mobility, high breakdown field strength, and high electron saturation velocity. In the fabrication of HEMT devices, a multilayer metal structure with Au as a cap layer is often used, and ohmic contact with low contact resistance is obtained through high-temperature annealing. Au is used to cause fatal pollution to a Si-CMOS process line, and high-temperature annealing can not only form rough electrode surfaces and edges, thereby causing the appearance of a spike electric field and reducing the breakdown characteristic of a device; it also causes deterioration of dynamic performance of GaN-based HEMT devices (PIAZZAM, DUAC, OUALLI M, et al. degradation of TiAlN As ohmic contact metal for GaN HEMTs [ J ]. Microelectronics and reliability,2009,49(9): 1222-5). However, the low-temperature gold-free ohmic process uses metal compatible with a Si-CMOS process line as a cap layer on one hand, so that the pollution problem caused by Au is avoided, and on the other hand, the low-temperature annealing reduces the surface roughness of an electrode, thereby being beneficial to improving the breakdown voltage of a device. One of the common methods for achieving low temperature gold-free processes is to thin the barrier layer, then prepare the source and drain electrodes and anneal them to form ohmic contacts (FIRRINCIELI A, DE JAEGER B, YOU S, et al au-free low temperature ohmic contacts for AlGaN/GaN power devices on 200mm Si substrates [ J ]). The commonly used source and drain metal structure is Ti/Al/X or Ta/Al/X, wherein X is one or more of W, Ti, Ni, Ta, TiW and TiN.

The current equipment for depositing metals is generally magnetron sputtering or electron beam evaporation. Magnetron sputtering coating is a vacuum coating technique which utilizes charged ions to bombard the surface of a target material so that target material atoms obtain recoil kinetic energy to be separated from the surface of the target material and finally deposited on the surface of a wafer. The sputtered atoms collide with the sputtered gas atoms in front of the wafer surface in a series of collisions to change the moving direction of the sputtered atoms, and the incident angle of the sputtered atoms when they reach the wafer surface is large. In addition, for magnetron sputtering equipment, the sputtering distance is short, the energy of sputtered atoms is high, the atomic mobility of the surface of the wafer is increased, so that the lateral kinetic energy of the surface of the film is very large, and therefore, the area of the material sputtered on the surface of the wafer is larger than that of a defined photoetching window. The electron beam evaporation equipment mainly depends on electron beam heating to melt the material, and after reaching a boiling point, particles of the material are separated from the surface of the material and reach the surface of the wafer. The electron beam evaporation cavity is long, atoms evaporated by the electron beam contact the surface of the wafer, energy is lost quickly, and mobility is low, so that the atoms are difficult to rearrange on the surface, namely, a deposition area is a defined photoetching window.

In summary, when metal is deposited by using electron beams or magnetron sputtering alone, the metal serving as the protective layer cannot completely wrap the side wall of the lower layer metal, and the side wall of the lower layer metal is oxidized, so that the performance of the device is affected.

Disclosure of Invention

The invention provides a low-temperature gold-free ohmic contact GaN-based HEMT device and a preparation method thereof. After the metal is stripped, the metal of the lower layer is wrapped by the metal of the protective layer, the multi-layer metal structure is favorably stabilized, the surface appearance of the electrode is improved, and meanwhile, the oxidation of the metal of the lower layer is reduced or avoided, so that the performance of the device is improved.

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

The low-temperature gold-free ohmic contact GaN-based HEMT device comprises an AlGaN/GaN epitaxial layer, wherein two end etching areas on the upper surface of the AlGaN/GaN epitaxial layer are respectively connected with a source electrode and a drain electrode;

the AlGaN/GaN epitaxial layer comprises a substrate, a GaN buffer layer, a GaN channel layer and an AlGaN barrier layer which are sequentially stacked from bottom to top.

Further, the source electrode and the drain electrode both comprise a first layer of metal, a second layer of metal, a third layer of metal and a fourth layer of metal;

the first layer of metal is arranged in etching areas at two ends of the upper surface of the AlGaN/GaN epitaxial layer, the second layer of metal is arranged on the first layer of metal, and the third layer of metal wraps the top surfaces and the side surfaces of the first layer of metal and the second layer of metal; the fourth layer of metal wraps the top and side surfaces of the third layer of metal.

Further, the first layer of metal and the second layer of metal are deposited by an electron beam evaporation method, and the third layer of metal and the fourth layer of metal are deposited by a magnetron sputtering method.

Further, the contact layer of the multi-layer metal structure formed after the source electrode and the drain electrode are stripped is a third layer metal/a first layer metal/a third layer metal from one side to the other side.

Further, the length of the third layer of metal wrapped on both sides of the first layer of metal is 0.5-1 μm.

Furthermore, the etching areas at two ends of the AlGaN barrier layer on the upper surface of the AlGaN/GaN epitaxial layer are reserved with the thickness of 1-3 nm.

The preparation method for preparing the low-temperature gold-free ohmic contact GaN-based HEMT device comprises the following steps:

s1, defining an etching window on the AlGaN/GaN epitaxial layer, and after etching is completed, carrying out surface treatment on an etching area to remove etching residues and oxides;

s2, defining windows of a source electrode and a drain electrode on the AlGaN/GaN epitaxial layer, preparing a first layer of metal, a second layer of metal, a third layer of metal and a fourth layer of metal of the source electrode and the drain electrode, and annealing to form ohmic contact, so that the low-temperature gold-free ohmic contact GaN-based HEMT device is obtained.

Further, in step S1, the etching window is designed to be 6-10 μm;

and the surface treatment is to clean oxide on the surface of the source electrode and drain electrode pattern area by using an acid-base solution, or to clean organic matter on the surface of the source electrode and drain electrode pattern area by using an organic solvent.

Further, in step S2, the windows of the source and drain electrodes are designed to be 5 to 8 μm;

the first layer of metal is one of Ti and Ta, the second layer of metal is Al, the third layer of metal is one of Ta and Ti, and the fourth layer of metal is one of W, Cu, TiN and TiW;

the thickness of the first layer of metal is 1-20nm, the thickness of the second layer of metal is 60-150nm, the thickness of the third layer of metal is 1-20nm, and the thickness of the fourth layer of metal is 60-200 nm.

Further, in step S2, the annealing atmosphere is nitrogen or argon, and the annealing temperature and the annealing time are 450 to 650 ℃ and 30S to 10min, respectively.

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

the invention adopts a method of combining electron beams and magnetron sputtering, and the first layer metal and the second layer metal prepared by the electron beams are completely wrapped by the third layer metal and the fourth layer metal prepared by the magnetron sputtering. And an additional photoetching step is not needed, the contact layer of the multilayer metal structure formed after the source electrode and the drain electrode are stripped is a third layer of metal/a first layer of metal/a third layer of metal, and the ohmic contact electrode is formed by performing solid-phase reaction on multiple metals through low-temperature annealing. The metal of the protective layer wraps the metal of the lower layer, so that the multi-layer metal structure is stabilized, the surface appearance of the electrode is improved, and meanwhile, the oxidation of the metal of the lower layer is reduced or avoided, so that the performance of the device is improved. Through I-V characteristic tests, the on-resistance (13.6 omega mm) of the device with the Ti/Al/Ta/W structure prepared by the invention is reduced by 9.9 percent compared with that of the traditional device (15.1 omega mm) with the Ti/Al/W structure which only uses Ti as a contact layer, and the performance of the device is improved.

Drawings

Fig. 1 is a schematic view of an epitaxial layer of a GaN-based HEMT device of an embodiment before a source-drain contact electrode is prepared;

FIG. 2 is a schematic diagram of an embodiment of forming an etched region after etching and surface treatment;

FIG. 3 is a schematic structural diagram of a device after a source-drain contact electrode is manufactured according to an embodiment;

fig. 4 is a graph comparing I-V characteristics of devices according to example 1.

Detailed Description

The present invention is further described with reference to the following drawings and examples, but the embodiments of the present invention are not limited thereto; it is to be understood that the following processes and process parameters, if not specified in particular detail, are all within the skill of the art by reference to the prior art.

Example 1:

the low-temperature gold-free ohmic contact GaN-based HEMT device comprises an AlGaN/GaN epitaxial layer, wherein etching areas at two ends of the upper surface of the AlGaN/GaN epitaxial layer are respectively connected with a source electrode and a drain electrode;

as shown in fig. 1, the AlGaN/GaN epitaxial layer includes a substrate 1, a GaN buffer layer 2, a GaN channel layer 3, and an AlGaN barrier layer 4, which are sequentially stacked from bottom to top.

As shown in fig. 3, the source electrode and the drain electrode each include a first layer metal 5, a second layer metal 6, a third layer metal 7, and a fourth layer metal 8;

in this embodiment, the first layer metal 5, the second layer metal 6, the third layer metal 7, and the fourth layer metal 8 are Ti, Al, Ta, and W, respectively.

The first layer of metal 5 is arranged in etching areas at two ends of the upper surface of the AlGaN/GaN epitaxial layer, the second layer of metal 6 is arranged on the first layer of metal 5, and the third layer of metal 7 wraps the top surfaces and the side surfaces of the first layer of metal 5 and the second layer of metal 6; the fourth layer of metal 8 wraps the top and side surfaces of the third layer of metal 7.

In this embodiment, the first layer of metal 5 and the second layer of metal 6 are deposited by electron beam evaporation to form a third layer of metal 7 and a fourth layer of metal 8, and the third layer of metal and the fourth layer of metal are deposited by magnetron sputtering.

In this embodiment, the contact layer of the multilayer metal structure Ti/Al/Ta/W formed after peeling the source electrode and the drain electrode is Ta/Ti/Ta from one side to the other side.

In this embodiment, the length of the third layer of metal 7 wrapped on both sides of the first layer of metal 5 is 0.5 μm.

In this embodiment, the etched regions at both ends of the AlGaN barrier layer 4 on the upper surface of the AlGaN/GaN epitaxial layer have a thickness of 1 to 3 nm.

The preparation method for preparing the low-temperature gold-free ohmic contact GaN-based HEMT device comprises the following steps:

s1, as shown in figure 2, defining an etching window on the AlGaN/GaN epitaxial layer, and after etching, performing surface treatment on an etching area to remove etching residues and oxides;

in this embodiment, the etching window is designed to be 6 μm;

and the surface treatment is to clean oxide on the surface of the source electrode and drain electrode pattern area by using an acid-base solution, or to clean organic matter on the surface of the source electrode and drain electrode pattern area by using an organic solvent.

S2, as shown in fig. 3, defining windows of the source electrode and the drain electrode on the AlGaN/GaN epitaxial layer, preparing a first layer of metal 5, a second layer of metal 6, a third layer of metal 7, and a fourth layer of metal 8 of the source electrode and the drain electrode, and annealing to form ohmic contact, thereby obtaining the low-temperature gold-free ohmic contact GaN-based HEMT device.

In this example, the windows of the source and drain electrodes were designed to be 5 μm;

in this example, the thickness of the first metal layer 5 is 10nm, the thickness of the second metal layer 6 is 80nm, the thickness of the third metal layer 7 is 20nm, and the thickness of the fourth metal layer 8 is 150 nm.

In this embodiment, the annealing atmosphere is nitrogen or argon, and the annealing temperature and the annealing time are 550 ℃ and 10min, respectively.

Example 2:

in this embodiment, the first layer metal 5, the second layer metal 6, the third layer metal 7, and the fourth layer metal 8 are Ta, Al, Ti, and W, respectively.

In this embodiment, the method for manufacturing the low-temperature gold-free ohmic contact GaN-based HEMT device includes the following steps:

s1, defining an etching window on the AlGaN/GaN epitaxial layer, wherein the etching window is designed to be 8 microns, and after etching is completed, carrying out surface treatment on an etching area to remove etching residues and oxides, as shown in FIG. 2;

s2, defining windows of a source electrode and a drain electrode on the AlGaN/GaN epitaxial layer, wherein the windows of the source electrode and the drain electrode are designed to be 6 microns, depositing a first layer of metal 5 and a second layer of metal 6 of the source electrode and the drain electrode in an electron beam evaporation mode, and depositing a third layer of metal 7 and a fourth layer of metal 8 in a magnetron sputtering mode. The contact layer of the metal structure Ta/Al/Ti/W formed after the source electrode and the drain electrode are stripped is Ti/Ta/Ti. The length of the third layer metal 7 on both sides of the first layer metal 5 is 1 μm, the thickness of the first layer metal 5 is 10nm, the thickness of the second layer metal 6 is 80nm, the thickness of the third layer metal 7 is 20nm, and the thickness of the fourth layer metal 8 is 150nm, as shown in fig. 3;

and S3, placing the sample in a pure nitrogen atmosphere, annealing at 550 ℃, wherein the annealing time is 10min, promoting the electrode metal to generate solid phase reaction, and simultaneously enabling the source electrode and the drain electrode to form ohmic contact with the GaN-based epitaxy.

Fig. 4 is a comparison graph of I-V characteristics of the device corresponding to example 1, and it can be seen that the on-resistance (13.6 Ω · mm) of the device having the Ti/Al/Ta/W structure prepared in this example is reduced by 9.9% compared to the conventional device having the Ti/Al/W structure (15.1 Ω · mm) using Ti alone as the contact layer, and the performance of the device is improved.

The above examples are only preferred embodiments of the present invention, which are intended to be illustrative and not limiting, and those skilled in the art should understand that they can make various changes, substitutions and alterations without departing from the spirit and scope of the invention.