阅读说明：本技术 一种AlGaN/GaN欧姆接触电极及其制备方法和用途 (AlGaN/GaN ohmic contact electrode and preparation method and application thereof ) 是由 于洪宇 蒋玉龙 范梦雅 于 2019-11-12 设计创作，主要内容包括：本发明涉及一种AlGaN/GaN欧姆接触电极及其制备方法和用途,所述电极由下而上依次包括AlGaN/GaN基底、帽层金属层和Ti<Sub>x</Sub>Al<Sub>y</Sub>合金层,其中,x＞0,y＞0。所述方法采用光刻技术在AlGaN层上定义漏极和/或源极图形,然后在AlGaN表面依次沉积Ti<Sub>x</Sub>Al<Sub>y</Sub>合金和帽层金属层,去除光刻胶,进行剥离处理,再对剥离后的样品进行热处理,得到所述的AlGaN/GaN欧姆接触电极。本发明同时还提供一种降低AlGaN/GaN基底与电极之间欧姆接触的方法,通过AlGaN/GaN基底表面沉积Ti<Sub>x</Sub>Al<Sub>y</Sub>合金层作为电极而实现。本发明提供的欧姆接触电极,达到射频器件的制备标准,同时提高器件的稳定性和可靠性。(The invention relates to an AlGaN/GaN ohmic contact electrode and a preparation method and application thereof, wherein the electrode sequentially comprises an AlGaN/GaN substrate, a cap layer metal layer and Ti from bottom to top x Al y An alloy layer, wherein x > 0, y > 0. The method comprises the steps of defining a drain electrode pattern and/or a source electrode pattern on an AlGaN layer by adopting a photoetching technology, and then sequentially depositing Ti on the surface of AlGaN x Al y And removing the photoresist from the alloy and the metal layer of the cap layer, carrying out stripping treatment, and carrying out heat treatment on the stripped sample to obtain the AlGaN/GaN ohmic contact electrode. The invention also provides a method for reducing ohmic contact between the AlGaN/GaN substrate and the electrode, and Ti is deposited on the surface of the AlGaN/GaN substrate x Al y The alloy layer is realized as an electrode. The ohmic contact electrode provided by the invention can be used for radio frequency devicesThe preparation standard of the device is improved, and the stability and the reliability of the device are improved.)

1. The AlGaN/GaN ohmic contact electrode is characterized by sequentially comprising an AlGaN/GaN substrate, a cap layer metal layer and Ti from bottom to top_xAl_yAn alloy layer, wherein x > 0, y > 0.

2. The AlGaN/GaN ohmic contact electrode of claim 1, wherein the Ti is_xAl_yIn the alloy layer, x is more than 0 and less than or equal to 10, and y is more than 0 and less than or equal to 10;

preferably, the Ti_xAl_yThe ratio of x to y in the alloy layer is 1:10-10: 1;

preferably, the Ti_xAl_yThe thickness of the alloy layer is 20-100 nm.

3. The AlGaN/GaN ohmic contact electrode according to claim 1 or 2, wherein the capping metal layer comprises any one of TiN, W or TiW;

preferably, the thickness of the capping metal layer is 20-200 nm.

4. The method of fabricating an AlGaN/GaN ohmic contact electrode according to any of claims 1 to 3, comprising the steps of:

(1) defining a drain electrode and/or a source electrode pattern on the AlGaN/GaN substrate by adopting a photoetching technology, and sequentially depositing Ti on the surface of the AlGaN_xAl_yRemoving the photoresist and carrying out stripping treatment;

(2) and carrying out heat treatment on the stripped sample to obtain the AlGaN/GaN ohmic contact electrode.

5. The production method according to claim 4, wherein the Ti is deposited in the step (1)_xAl_yThe alloy layer adopts Ti_xAl_yAn alloy target and/or a metal target of Ti and Al, preferably Ti_xAl_yAn alloy, wherein x > 0, y > 0;

the Ti_xAl_yIn the alloy layer, x is more than 0 and less than or equal to 10, and y is more than 0 and less than or equal to 10;

preferably, the Ti_xAl_yThe ratio of x to y in the alloy target material is 1:10-10: 1;

preferably, the Ti is deposited_xAl_yThe thickness of the alloy layer is 20-100 nm;

preferably, the capping layer metal layer comprises any one of TiN, W or TiW;

preferably, the thickness of the capping metal layer is 20-200 nm.

6. The method according to claim 4, wherein the step of defining the electrode pattern on the AlGaN layer by using the photolithography technique in the step (1) is: the photoresist is prepared by sequentially carrying out the processes of photoresist homogenizing, prebaking, photoetching, developing and postbaking.

7. The method according to claim 4 or 5, wherein the deposition in step (1) comprises magnetron sputtering and/or ion sputtering, preferably magnetron sputtering;

preferably, the Ti is deposited_xAl_yThe gas of the alloy layer is Ar;

preferably, the gas for depositing the capping layer metal layer is Ar or N₂。

8. The production method according to claim 4, wherein the gas for the heat treatment in the step (2) is N₂、NH₃、H₂Or Ar, or a combination of at least two thereof;

preferably, the temperature of the heat treatment is 700-1000 ℃;

preferably, the time of the heat treatment is 20 to 80 s.

9. The method for preparing according to any one of claims 4 to 8, comprising the steps of:

(1) washing the AlGaN/GaN substrate, and drying the AlGaN/GaN substrate by nitrogen;

(2) sequentially carrying out the process steps of spin coating, prebaking, photoetching, developing and postbaking on the AlGaN layer, defining the pattern of the drain electrode and/or the source electrode, immersing the drain electrode and/or the source electrode in dilute hydrochloric acid for cleaning, washing the source electrode with deionized water, and then blowing the source electrode with nitrogen;

(3) sequentially depositing Ti with the thickness of 20-100nm on the surface of the sample treated in the step (2)_xAl_yRemoving the photoresist and carrying out stripping treatment on the alloy layer and the 20-200nm cap metal layer;

(4) heating the stripped sample to 700-1000 ℃ in the atmosphere, and keeping the temperature for 20-80s to obtain the AlGaN/GaN ohmic contact electrode;

the gas of the atmosphere contains N₂、NH₃、H₂Or Ar, or a combination of at least two thereof.

10. A method of reducing ohmic contact between an AlGaN/GaN substrate and an electrode, the method comprising: depositing Ti on the surface of AlGaN/GaN substrate_xAl_yThe alloy layer is used as an electrode;

preferably, the Ti_xAl_yThe ratio of x to y in the alloy layer is 1:10-10: 1;

preferably, the Ti_xAl_yThe thickness of the alloy layer is 20-100 nm;

preferably, the deposition means comprises magnetron sputtering and/or ion sputtering, preferably magnetron sputtering.

Technical Field

The invention relates to the technical field of electronic semiconductor devices, in particular to an AlGaN/GaN ohmic contact electrode and a preparation method and application thereof.

Background

The third generation semiconductor material gallium nitride (GaN) has wide forbidden band width, high breakdown electric field, high thermal conductivity, high electronic saturation rate and higher radiation resistance, and has wide application prospect in high-temperature, high-frequency, radiation-resistant and high-power semiconductor devices. The AlGaN/GaN HEMTs (AlGaN/GaN high electron mobility transistors) have two-dimensional electron gas (2DEG) with high electron mobility, and have great application prospects in radio frequency and power switching devices.

The ohmic contact quality of the AlGaN/GaN HEMTs is an important index influencing the final output parameters of the device, and directly influences the source-drain output current, the on-resistance, the breakdown voltage and the like of the device. High quality ohmic contacts are more important in GaN high frequency devices, wherein gold-free ohmic contact technology process plays a crucial role in Si-CMOS large-scale production baseline and cost reduction. At present, the research problems of GaN HEMTs ohmic contact are basically divided into a gold process and a non-gold process: 1) the gold process comprises the following steps: the metal laminated structures of Ti/Al/Ni/Au, Ti/Al/Ti/Au, Ti/Al/Mo/Au and the like are commonly used for AlGaN/GaNHEMTs, and researches show that the addition of Au is more favorable for promoting the formation of TiN columns and can form direct TiN conductive channels between metal and two-dimensional electron gas; 2) the gold-free process comprises the following steps: the gold-free ohmic contact process of the GaN HEMTs is more compatible with the development of the Si-CMOS, and meanwhile, the production cost can be greatly reduced, so that the method is the key for realizing the large-scale manufacturing process line of the Si-CMOS. The existing commonly used metals are Ti and Al, the Ti metal has low work function, can reduce the barrier height with the AlGaN material, can extract N in AlGaN to form TiN in the annealing process, and leaves N vacancy in AlGaN, and the increase of the electron concentration is beneficial to the formation of ohmic contact; the addition of Al can inhibit a large amount of Al from diffusing out of AlGaN, so that two-dimensional electron gas with higher concentration is maintained, and the realization of low ohmic contact value is facilitated. However, since Al has a low melting point (660 ℃), a thick Al layer melts and alloys with other metals during high temperature annealing, which adversely affects surface roughness. Moreover, different Ti/Al thickness ratios and different annealing temperatures have a greater impact on the formation of the final ohmic contact. Meanwhile, the gold-free ohmic process has certain challenge on realizing high-low ohmic contact in view of the wide forbidden bandwidth of AlGaN. Therefore, research is currently carried out to form a groove structure on AlGaN by an etching process, and the ohmic contact value is further reduced by reducing the thickness of the barrier layer, but the complexity of the process is greatly increased in industrial production, and the production efficiency is reduced.

Based on the forming mechanism of ohmic contact of gold-free multilayer metal structure AlGaN/GaN HEMTs, the common method for reducing the ohmic contact at present comprises the following steps: 1) adjusting the thickness ratio of Ti/Al and the overall thickness: on one hand, TiN is formed by the reaction of Ti and AlGaN, and the electron concentration is improved by N vacancies, and on the other hand, the metal Al is beneficial to inhibiting the outward diffusion of Al in the AlGaN, so that the Al content in the AlGaN is conveniently ensured, and the concentration of two-dimensional electron gas is maintained. The proper Ti/Al ratio has important influence on the final ohmic contact; 2) the recess etching process comprises the following steps: due to the wide forbidden bandwidth of AlGaN, the barrier height between metal and semiconductor can be increased, so that an AlGaN groove is formed by an etching process, the barrier width is reduced, and the formation of ohmic contact is promoted. Wherein, different etching depths also have different influences on the quality of ohmic contact, and the magnitude of the ohmic contact value is further adjusted by adjusting the etching depths; 3) addition of Si layer or Ta layer: self-doping is realized through the thin layer Si in the annealing process, the electron concentration in the semiconductor is increased, and the formation of ohmic contact is promoted. The Ta layer is added to help form a smoother ohmic contact interface, and certain improvement is brought to the quality and reliability of ohmic contact. At present, the minimum ohmic contact value realized by a contact process is 0.21 omega mm related to gold-free ohmic contact, which is far from enough for radio frequency devices, and the deposition of a plurality of metal layers greatly increases the complexity of the process and reduces the stability of the process. The complexity of the film layer can be further increased by adding the extra film layer of the Ta layer or the Si layer, multiple different metal target materials and target positions need to be provided in the process of preparing the film, the stability of a film coating cavity is not facilitated, the difficulty of multi-layer metal deposition is increased, the yield is directly reduced, and the industrialization is not facilitated. The process stability and reliability of gold-free ohmic contacts are critical to the fabrication of GaN HEMTs devices.

Based on the problems in the prior art, how to ensure that the gold-free ohmic contact of the GaN HEMTs reaches the preparation standard of the radio frequency device and improve the stability and reliability of the device becomes a problem which needs to be solved urgently at present.

Disclosure of Invention

In view of the problems in the prior art, the present invention provides an AlGaN/GaN ohmic contact electrode, which uses Ti, and a method for preparing the same and a use thereof_xAl_yThe alloy layer is used as a direct contact layer, the structure that the traditional Ti/Al multilayer film is used as the direct contact layer is replaced, the roughness problem caused by excessive alloying in the heat treatment stage can be avoided by fully and uniformly mixing Ti and Al, a good contact surface can be kept, the roughness of the surface of the electrode is greatly reduced, the stability and the reliability of a device are improved, and the industrialization efficiency is improved.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the invention provides an AlGaN/GaN ohmic contact electrode, which comprises an AlGaN/GaN substrate, a cap layer metal layer and Ti in sequence from bottom to top_xAl_yAn alloy layer, wherein x > 0, y > 0.

The AlGaN/GaN ohmic contact electrode provided by the invention adopts Ti_xAl_yThe alloy layer replaces the traditional Ti/Al laminated structure, the sufficient and uniform mixing of Ti and Al avoids the uniformity problem caused by excessive alloying of metal in the high annealing process, and the lower surface roughness of the electrode can be achieved; ti_xAl_yThe alloy layer is in direct contact with the AlGaN layer, so that a low ohmic contact value can be obtained, and the preparation standard of a radio frequency device is met.

In the present invention, Ti_xAl_yX > 0 and y > 0 in the alloy layer, for example x may be 0.1, 0.5, 1, 2, 5, 8, 10, 15 or 20, etc., and y may be 0.1, 0.4, 1, 3, 5, 8, 10, 14 or 20, etc.

Preferably, the Ti_xAl_yIn the alloy layer, 0 < x.ltoreq.10, 0 < y.ltoreq.10, for example, x may be 0.1, 0.2, 0.5, 0.8, 1, 2, 3, 5, 8, 9 or 10, etc., and y may be 0.1, 0.3, 0.5, 1, 2, 3, 5, 7, 9 or 10, etc.

Preferably, the Ti_xAl_yThe ratio of x to y in the alloy layer is 1:10-10:1, the ratio of x to y being the atomic ratio of Ti to Al, for exampleCan be 1:10, 1:5, 1:1, 2:1, 5:1, 8:1 or 10:1, and if x: y is less than 1:10, the Al component in the alloy is higher, which can cause the increase of the roughness of the metal surface in the high-temperature annealing process; when x: y is larger than 10:1, the Al component is too low, so that Al cannot substantially play a role, and the Al out-diffusion in AlGaN cannot be inhibited, so that a high two-dimensional electron gas concentration is maintained.

Preferably, the Ti_xAl_yThe thickness of the alloy layer is 20-100nm, for example, 20nm, 25nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 95nm or 100nm, etc., if the thickness is less than 20nm, the parasitic resistance of the metal itself is relatively large, and the thick metal layer is more beneficial to the reduction of the parasitic resistance of the metal itself; the thickness is larger than 100nm, which causes the edge of the thicker metal layer to be rough due to the high temperature after the high temperature annealing, and influences the stability and reliability of the final device.

Preferably, the capping layer metal layer comprises any one of TiN, W or TiW.

Preferably, the thickness of the capping metal layer is 20-200nm, for example, 20nm, 25nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 120nm, 150nm, 180nm, or 200nm, etc., if the thickness is less than 20nm, the parasitic resistance of the metal itself will be larger, the thick metal layer is more favorable for reducing the parasitic resistance of the metal itself, and the thicker capping metal layer is more favorable for blocking oxygen pollution; the thickness is larger than 100nm, which causes the edge of the thicker metal layer to be rough due to the high temperature after the high temperature annealing, and influences the stability and reliability of the final device.

In the present invention, the AlGaN/GaN substrate is not particularly limited, and the present invention is applicable as long as it is commonly used by those skilled in the art.

In a second aspect, the present invention provides a method for preparing an AlGaN/GaN ohmic contact electrode as described in the first aspect, the method comprising the steps of:

(1) defining the pattern of a drain electrode and/or a source electrode on an AlGaN/GaN substrate by adopting the photoetching technology, and sequentially depositing Ti on the surface of AlGaN_xAl_yAlloy layer and capping layer goldRemoving the photoresist of the metal layer, and carrying out stripping treatment;

(2) and carrying out heat treatment on the stripped sample to obtain the AlGaN/GaN ohmic contact electrode.

The preparation method of the AlGaN/GaN ohmic contact electrode provided by the invention accurately controls the position and the size of the drain electrode and/or the source electrode by adopting the photoetching technology, performs hydrochloric acid surface treatment on a photoetching substrate to remove a natural oxide layer, and then performs Ti_xAl_yAlloy is deposited on the AlGaN surface to make the two tightly combined, Ti_xAl_yThe use of alloys can reduce process complexity and by fixing Ti_xAl_yThe optimal value of the atomic ratio of (1) and the heat treatment temperature can be adjusted only by changing the total thickness of the deposition, and the mutual interference of various influencing factors (Ti/Al thickness ratio, total thickness and annealing temperature) is avoided; on the other hand, Ti and Al can directly contact the surface of AlGaN and play roles simultaneously in the heat treatment process, so that the roles of Ti and Al are fully displayed at the beginning of the heat treatment, the work function of Ti metal is low, the barrier height between the Ti metal and the AlGaN material can be reduced, N in AlGaN can be extracted to form TiN in the heat treatment process, N vacancies are left in AlGaN, and the increase of electron concentration is beneficial to the formation of ohmic contact; the Al is directly contacted to inhibit the Al in the AlGaN from diffusing outwards and maintain the concentration of two-dimensional electron gas; and the sufficient and uniform mixing of Ti and Al is also beneficial to avoiding the roughness problem caused by excessive alloying in the heat treatment process, so that a good contact surface can be maintained, the roughness of the electrode surface is greatly reduced, the stability and the reliability of a device are improved, and the industrialization efficiency is improved.

In the present invention, the specific process of the photolithography technique is not limited, and any process commonly used by those skilled in the art can define the pattern of the drain and/or the source, and is suitable for the present invention.

In the present invention, the solvent and process used for removing the photoresist and performing the stripping treatment are not particularly limited, and are applicable to the present invention as long as they are commonly used by those skilled in the art.

Preferably, the Ti is deposited in step (1)_xAl_yThe alloy layer adopts Ti_xAl_yAn alloy target and/or a metal target of Ti and Al, preferably Ti_xAl_yThe alloy, wherein x is more than 0, y is more than 0, and the ratio of x to y is the atomic ratio of Ti to Al. Using Ti_xAl_yAlloy, only needs to occupy one target position to complete Ti_xAl_yThe deposition of the alloy layer improves the stability of the deposition chamber and avoids cross contamination.

In the present invention, Ti_xAl_yX > 0 and y > 0 in the alloy target, for example, x may be 0.1, 0.5, 1, 2, 5, 8, 10, 15, or 20, etc., and y may be 0.1, 0.4, 1, 3, 5, 8, 10, 14, or 20, etc.

Preferably, the Ti_xAl_yIn the alloy target material, 0 < x.ltoreq.10, 0 < y.ltoreq.10, for example, x may be 0.1, 0.2, 0.5, 0.8, 1, 2, 3, 5, 8, 9 or 10, etc., and y may be 0.1, 0.3, 0.5, 1, 2, 3, 5, 7, 9 or 10, etc.

Preferably, the Ti_xAl_yThe ratio of x to y in the alloy target material is 1:10-10:1, the ratio of x to y is the atomic ratio of Ti to Al, and can be 1:10, 1:5, 1:1, 2:1, 5:1, 8:1 or 10:1, for example, if x: y is less than 1:10, the Al component in the alloy is higher, which may cause the increase of the roughness of the metal surface in the high-temperature annealing process; when x: y is larger than 10:1, the Al component is too low, so that Al cannot substantially play a role, and the Al out-diffusion in AlGaN cannot be inhibited, so that a high two-dimensional electron gas concentration is maintained.

Preferably, the Ti is deposited_xAl_yThe thickness of the alloy layer is 20-100nm, for example, 20nm, 25nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 95nm or 100nm, etc., if the thickness is less than 20nm, the parasitic resistance of the metal itself is relatively large, and the thick metal layer is more beneficial to the reduction of the parasitic resistance of the metal itself; the thickness is larger than 100nm, which causes the edge of the thicker metal layer to be rough due to the high temperature after the high temperature annealing, and influences the stability and reliability of the final device.

Preferably, the capping layer metal layer comprises any one of TiN, W or TiW.

Preferably, the thickness of the capping metal layer is 20-200nm, for example, 20nm, 25nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 120nm, 150nm, 180nm or 200nm, etc., if the thickness is less than 20nm, the parasitic resistance of the capping metal layer is relatively large, the thick metal layer is more favorable for reducing the parasitic resistance of the metal, and the thicker capping metal layer is more favorable for blocking oxygen pollution; the thickness is larger than 100nm, which causes the edge of the thicker metal layer to be rough due to the high temperature after the high temperature annealing, and influences the stability and reliability of the final device.

Preferably, the step of defining the electrode pattern on the AlGaN layer by using the photolithography technique includes: the photoresist is prepared by sequentially carrying out the processes of photoresist homogenizing, prebaking, photoetching, developing and postbaking. Preferably, the deposition in step (1) comprises magnetron sputtering and/or ion sputtering, preferably magnetron sputtering.

Preferably, the Ti is deposited_xAl_yThe gas of the alloy layer is Ar.

Preferably, the gas for depositing the capping layer metal layer is Ar or N₂。

Preferably, the heat treatment gas is N₂、NH₃、H₂Or Ar or a combination of at least two of these, typical but not limiting combinations: n is a radical of₂And H₂，H₂And Ar.

Preferably, the temperature of the heat treatment is 700-; when the temperature is higher than 1000 ℃, the material characteristics of the semiconductor AlGaN can be affected, so that the concentration of the two-dimensional electron gas is reduced, and the square resistance of the semiconductor material is increased.

Preferably, the time of the heat treatment is 20 to 80s, for example, 20s, 25s, 30s, 40s, 50s, 60s, 70s, 75s, or 80s, and if the time is less than 20s, the solid phase reaction between the metal and the semiconductor AlGaN is not favorable, and the ohmic contact is not formed; the time is more than 100s, the material characteristics of the semiconductor AlGaN are influenced, the concentration of the two-dimensional electron gas is reduced, and the square resistance of the semiconductor material is increased.

Preferably, the preparation method comprises the following steps:

(1) washing the AlGaN/GaN substrate, and drying the AlGaN/GaN substrate by nitrogen;

(2) sequentially carrying out the process steps of spin coating, prebaking, photoetching, developing and postbaking on the AlGaN layer, defining a drain electrode pattern and/or a source electrode pattern, immersing the drain electrode pattern and/or the source electrode pattern in dilute hydrochloric acid for surface treatment, then washing the source electrode pattern by deionized water, and then drying the source electrode pattern by nitrogen;

(3) sequentially depositing Ti with the thickness of 20-100nm on the surface of the sample treated in the step (2)_xAl_yRemoving the photoresist and carrying out stripping treatment on the alloy layer and the 20-200nm cap metal layer;

(4) heating the stripped sample to 700-1000 ℃ in the atmosphere, and keeping the temperature for 20-80s to obtain the AlGaN/GaN ohmic contact electrode.

The gas of the atmosphere contains N₂、NH₃、H₂Or Ar, or a combination of at least two thereof.

In the present invention, the concentration of the dilute hydrochloric acid is not particularly limited as long as it can remove substances such as oxides on the surface of the substrate, and any concentration commonly used by those skilled in the art can be applied to the present invention.

In a third aspect, the present invention also provides a method of reducing ohmic contact between an AlGaN/GaN substrate and an electrode, the method comprising: depositing Ti on the surface of AlGaN/GaN substrate_xAl_yThe alloy layer serves as an electrode.

The method provided by the invention adopts Ti_xAl_yThe alloy layer is used as a direct contact electrode, Ti and Al are fully and uniformly mixed to avoid excessive alloying of metals in high-temperature annealing, so that the roughness of the surface is reduced, meanwhile, the Ti and the Al are simultaneously in direct contact with the AlGaN/GaN substrate, so that the Al directly plays a role in the primary annealing stage, the Al in AlGaN is effectively inhibited from diffusing outwards, the concentration of two-dimensional electron gas is maintained, the ohmic contact between the electrode and the AlGaN/GaN substrate is reduced, and the shape of the electrode is changedForming low resistance ohmic contact.

Preferably, the Ti_xAl_yThe ratio of x to y in the alloy layer is 1:10-10:1, and may be, for example, 1:10, 1:5, 1:1, 2:1, 5:1, 8:1, or 10: 1.

Preferably, the Ti is deposited_xAl_yThe thickness of the alloy layer is 20 to 100nm, and may be, for example, 20nm, 25nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 95nm, or 100 nm.

Preferably, the deposition means comprises magnetron sputtering and/or ion sputtering, preferably magnetron sputtering.

Compared with the prior art, the invention has at least the following beneficial effects:

(1) the AlGaN/GaN ohmic contact electrode provided by the invention adopts Ti_xAl_yThe alloy layer replaces the traditional Ti/Al laminated structure, the Ti and the Al are fully and uniformly mixed, and the proportion is adjustable, so that the roughness of the surface of the electrode is lower; ti_xAl_yThe alloy layer is in direct contact with the AlGaN layer, so that the ohmic contact of the electrode is less than or equal to 0.2 omega mm, and the electrode reaches the preparation standard (about 0.1 omega mm) of a radio frequency device.

(2) The preparation method of the AlGaN/GaN ohmic contact electrode provided by the invention fixes Ti_xAl_yThe optimal quality of the annealing temperature can be adjusted only by changing the total thickness of the deposition, so that the simultaneous interference of various influence factors is avoided; the Al directly contacts the AlGaN surface at the initial stage of heat treatment, the outward diffusion of the Al in the AlGaN is inhibited, the concentration of two-dimensional electron gas is maintained, the low-ohmic contact value is more favorably realized, the roughness problem caused by heat treatment alloying is avoided due to the sufficient and uniform mixing of the Ti and the Al, the good contact surface is kept, the stability and the reliability of the device are improved, the process steps are simple and reliable, and the industrialization efficiency is more favorably improved.

(3) The invention provides a method for reducing ohmic contact between an AlGaN/GaN substrate and an electrode, which is characterized in that Ti is deposited on the surface of the AlGaN/GaN substrate_xAl_yThe alloy layer is used as an electrode, the roughness of the surface of the alloy layer is low, Ti and Al are fully and uniformly mixed and are tightly combined with the AlGaN/GaN substrate, and the Al in the AlGaN is effectively inhibitedAnd the two-dimensional electron gas concentration is maintained through external diffusion, and the ohmic contact between the electrode and the AlGaN/GaN substrate is effectively reduced.

Drawings

FIG. 1 is a schematic view of the structure of an AlGaN/GaN substrate used in the present invention.

Fig. 2 is a schematic structural diagram of a drain and/or source pattern formed on the AlGaN/GaN substrate according to the present invention after photolithography and development.

FIG. 3 shows a sputtered Ti film provided in example 2 of the present invention₅Al₁Schematic structure diagram behind/TiN bilayer metal structure.

Fig. 4 is a schematic structural diagram of a metal source and drain ohmic pattern formed after removing the photoresist according to embodiment 2 of the present invention.

In the figure, a 1-Si substrate layer, a 2-GaN buffer layer, a 3-GaN layer, a 4-AlGaN layer, a 5-photoresist layer, and 6-Ti₅Al₁Alloy layer, 7-TiN capping layer metal layer

Detailed Description

The following further describes the technical means of the present invention to achieve the predetermined technical effects by means of embodiments with reference to the accompanying drawings, and the embodiments of the present invention are described in detail as follows. The structural schematic diagram of the AlGaN/GaN substrate adopted by the invention is shown in FIG. 1, which shows that the AlGaN/GaN substrate sequentially comprises a Si substrate layer, a GaN buffer layer, a GaN layer and an AlGaN layer from bottom to top.

The structure schematic diagram of the drain electrode and/or source electrode pattern formed on the AlGaN/GaN substrate through photolithography and development provided by the present invention is shown in fig. 2, which shows that after photolithography and development, the portion of the surface of the AlGaN layer which is not covered with the photoresist is the pattern of the drain electrode and/or source electrode.