WO2021093127A1 - AlGaN/GaN欧姆接触电极及其制备方法和降低欧姆接触的方法 - Google Patents

AlGaN/GaN欧姆接触电极及其制备方法和降低欧姆接触的方法 Download PDF

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WO2021093127A1
WO2021093127A1 PCT/CN2019/130351 CN2019130351W WO2021093127A1 WO 2021093127 A1 WO2021093127 A1 WO 2021093127A1 CN 2019130351 W CN2019130351 W CN 2019130351W WO 2021093127 A1 WO2021093127 A1 WO 2021093127A1
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algan
layer
ohmic contact
gan
alloy layer
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PCT/CN2019/130351
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French (fr)
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于洪宇
蒋玉龙
范梦雅
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南方科技大学
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
    • H01L29/40—Electrodes ; Multistep manufacturing processes therefor
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
    • H01L29/40—Electrodes ; Multistep manufacturing processes therefor
    • H01L29/401—Multistep manufacturing processes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
    • H01L29/40—Electrodes ; Multistep manufacturing processes therefor
    • H01L29/43—Electrodes ; Multistep manufacturing processes therefor characterised by the materials of which they are formed
    • H01L29/45—Ohmic electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
    • H01L29/40—Electrodes ; Multistep manufacturing processes therefor
    • H01L29/43—Electrodes ; Multistep manufacturing processes therefor characterised by the materials of which they are formed
    • H01L29/45—Ohmic electrodes
    • H01L29/452—Ohmic electrodes on AIII-BV compounds
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
    • H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
    • H01L29/68—Types of semiconductor device ; Multistep manufacturing processes therefor controllable by only the electric current supplied, or only the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched
    • H01L29/76—Unipolar devices, e.g. field effect transistors
    • H01L29/772—Field effect transistors
    • H01L29/778—Field effect transistors with two-dimensional charge carrier gas channel, e.g. HEMT ; with two-dimensional charge-carrier layer formed at a heterojunction interface

Definitions

  • This application relates to the technical field of electronic semiconductor devices, for example, to a gallium aluminum nitride/gallium nitride AlGaN/GaN ohmic contact electrode, a preparation method thereof, and a method for reducing ohmic contact.
  • the third-generation semiconductor material gallium nitride has a wide band gap, high breakdown electric field, high thermal conductivity, high electron saturation rate and higher radiation resistance. It is resistant to radiation and high power at high temperatures, high frequencies, and There are broad application prospects in semiconductor devices.
  • AlGaN/GaN High Electron Mobility Transistors AlGaN/GaN High Electron Mobility Transistors
  • AlGaN/GaN High Electron Mobility Transistors AlGaN/GaN High Electron Mobility Transistors
  • Two-Dimensional Electron Gas, 2DEG has great application prospects in radio frequency and power switching devices.
  • the ohmic contact quality of AlGaN/GaN HEMTs is an important indicator that affects the final output parameters of the device, which directly affects the source and drain output current, on-resistance, and breakdown voltage of the device.
  • High-quality ohmic contacts are more important in GaN high-frequency devices.
  • gold-free ohmic contact technology plays a vital role in silicon-complementary metal oxide semiconductor Si-CMOS mass production baseline and cost reduction.
  • Gold process Ti/Al/Ni/Au, Ti/Al/Ti/Au, Ti/Al /Molybdenum/Mo/Au and other metal stacked structures are often used in AlGaN/GaN HEMTs.
  • Au is more conducive to the formation of titanium nitride TiN pillars, which can form direct TiN conduction between the metal and the two-dimensional electron gas.
  • Gold-free process The gold-free ohmic contact process of GaN HEMTs devices is more compatible with the development of Si-CMOS, and can greatly reduce production costs, which is the key to achieving large-scale Si-CMOS manufacturing process lines.
  • Commonly used metals are Ti and Al.
  • Ti has a low work function, which can reduce the barrier height with AlGaN materials. At the same time, it can extract N in AlGaN to form TiN during the annealing process, and leave N vacancies in AlGaN at the same time.
  • the addition of Al can inhibit a large amount of out-diffusion of Al in AlGaN, thereby maintaining a relatively high concentration of two-dimensional electron gas, which is conducive to achieving low ohmic contact values.
  • the thicker Al layer will melt and form alloys with other metals, which has a bad influence on the surface roughness. Not only that, but different Ti/Al thickness ratios and different annealing temperatures also have a greater impact on the formation of ohmic contacts.
  • the commonly used methods to reduce the ohmic contact are: 1) Adjust the Ti/Al thickness ratio and overall thickness: On the one hand, TiN is formed by the reaction of Ti and AlGaN, and The electron concentration is increased through the N vacancy. On the other hand, the metal Al is beneficial to suppress the out-diffusion of Al in AlGaN, so as to facilitate the assurance of the Al content in AlGaN and maintain the concentration of the two-dimensional electron gas.
  • a suitable Ti/Al ratio has an important effect on the final ohmic contact; 2) recess etching process: due to the wide band gap of AlGaN, the barrier height between the metal and the semiconductor will be increased, so AlGaN is formed by the etching process The trench reduces the barrier width and promotes the formation of ohmic contacts. Among them, different etching depths have different effects on the quality of the ohmic contact.
  • the ohmic contact value can be adjusted by adjusting the etching depth; 3) the addition of a silicon Si layer or a tantalum Ta layer: the self-restraint is achieved through a thin layer of Si during the annealing process.
  • Doping increases the electron concentration in the semiconductor and promotes the formation of ohmic contacts.
  • the addition of the Ta layer helps to form a smoother ohmic contact interface, and has a certain improvement in the quality and reliability of the ohmic contact.
  • the lowest ohmic contact value achieved by the recess process is 0.21 ⁇ mm, which is far from enough for radio frequency devices, and the deposition of multiple metal layers greatly increases the complexity of the process and reduces the process The stability.
  • the addition of the additional film layer of the Ta layer or the Si layer will also increase the complexity of the film layer, and it is necessary to provide a variety of different metal targets and target positions in the process of preparing the film, and it is not conducive to the stability of the coating chamber.
  • the increased difficulty of multi-layer metal deposition directly reduces the yield rate, which is not conducive to industrialization.
  • the process stability and reliability of gold-free ohmic contacts are critical to the preparation of GaN HEMTs.
  • This application provides an AlGaN/GaN ohmic contact electrode, a preparation method thereof, and a method for reducing ohmic contact.
  • the electrode uses a Ti x Al y alloy layer as a direct contact layer, replacing the Ti/Al multilayer film as the direct contact layer. Structure, the full and uniform mixing of Ti and Al can avoid the roughness problem caused by excessive alloying in the heat treatment stage, can maintain a good contact surface, greatly reduce the roughness of the electrode surface, improve the stability and reliability of the device, and improve industrialization effectiveness.
  • the present application provides an AlGaN/GaN ohmic contact electrode, the electrode includes an AlGaN/GaN substrate, a cap layer metal layer, and a Ti x Al y alloy layer from bottom to top, wherein x>0, y>0.
  • the present application provides a method for preparing the AlGaN/GaN ohmic contact electrode as described above, and the method includes the following steps:
  • the present application also provides a method for reducing the ohmic contact between the AlGaN/GaN substrate and the electrode.
  • the method includes: depositing a Ti x Al y alloy layer on the surface of the AlGaN/GaN substrate as the electrode.
  • FIG. 1 is a schematic diagram of the structure of the AlGaN/GaN substrate used in this application.
  • FIG. 2 is a schematic diagram of the structure of the drain and/or source patterns formed on the AlGaN/GaN substrate provided by the present application after photolithography and development.
  • Example 3 is a schematic diagram of the structure of the Ti 5 Al 1 /TiN double-layer metal structure after sputtering provided in Example 2 of the present application.
  • FIG. 4 is a schematic diagram of the structure of the metal source and drain ohmic patterns formed after removing the photoresist provided in Embodiment 2 of the present application.
  • a 1-Si substrate layer a 2-GaN buffer layer, a 3-GaN layer, a 4-AlGaN layer, a 5-photoresist layer, a 6-Ti 5 Al 1 alloy layer, and a 7-TiN cap layer metal layer.
  • the present application provides an AlGaN/GaN ohmic contact electrode, the electrode includes an AlGaN/GaN substrate, a cap layer metal layer, and a Ti x Al y alloy layer from bottom to top, wherein x>0, y>0.
  • the AlGaN/GaN ohmic contact electrode replaces the Ti/Al laminated structure with a Ti x Al y alloy layer.
  • the fully uniform mixing of Ti and Al avoids the uniformity problem caused by the excessive alloying of the metal during the high temperature annealing process , Can achieve lower electrode surface roughness; Ti x Al y alloy layer is in direct contact with the AlGaN layer, and low ohmic contact value can be obtained, which meets the preparation standard of radio frequency devices.
  • x>0, y>0 in the Ti x Al y alloy layer for example, x can be 0.1, 0.5, 1, 2, 5, 8, 10, 15 or 20, etc., and y can be 0.1, 0.4, 1 , 3, 5, 8, 10, 14, or 20, etc.
  • x may be 0.1, 0.2, 0.5, 0.8, 1, 2, 3, 5, 8, 9 or 10 etc.
  • y can be 0.1, 0.3, 0.5, 1, 2, 3, 5, 7, 9, or 10, etc.
  • the ratio of x to y in the Ti x Al y alloy layer is 1:10-10:1, and the ratio of x to y is the atomic ratio of Ti to Al, for example, it may be 1:10, 1: 5. 1:1, 2:1, 5:1, 8:1 or 10:1, etc. If the x:y is less than 1:10, the Al composition in the alloy is too high, which will cause the metal surface during the high temperature annealing process Roughness increases; x:y is greater than 10:1, and the Al composition is too low, which will cause Al to fail to function substantially, thereby failing to suppress the out-diffusion of Al in AlGaN to maintain a high two-dimensional electron gas concentration.
  • the thickness of the Ti x Al y alloy layer is 20-100 nm, for example, 20 nm, 25 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 95 nm or 100 nm, etc., if the thickness is less than 20nm, the parasitic resistance of the metal itself will be relatively large, and a thick metal layer is more conducive to the reduction of the parasitic resistance of the metal itself; a thickness greater than 100nm will cause the thicker metal layer to become the edge due to the high temperature after high temperature annealing. Roughness affects the stability and reliability of the final device.
  • the cap metal layer includes any one of TiN, W, or TiW.
  • the thickness of the cap layer metal layer is 20-200nm, for example 20nm, 25nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 120nm, 150nm, 180nm or 200nm, etc., if If the thickness is less than 20nm, the parasitic resistance of the metal itself will be relatively large, a thick metal layer is more conducive to the reduction of the parasitic resistance of the metal itself, while a thicker cap layer metal layer is more conducive to blocking oxygen pollution; thickness greater than 100nm, it will As a result, after high temperature annealing, the thicker metal layer will roughen the edges due to the effect of high temperature, which affects the stability and reliability of the device.
  • the AlGaN/GaN substrate is not specifically limited.
  • the present application provides a method for preparing the AlGaN/GaN ohmic contact electrode as described above, and the method includes the following steps:
  • the preparation method of the AlGaN/GaN ohmic contact electrode provided in this application accurately controls the position and size of the drain and/or source by using photolithography technology, and after the photoetched substrate is subjected to hydrochloric acid surface treatment to remove the natural oxide layer, The Ti x Al y alloy is deposited on the AlGaN surface to closely combine the two.
  • Ti x Al y alloy can reduce the complexity of the process, and by fixing the atomic ratio of Ti x Al y , only by changing the total thickness of the deposition It can adjust the optimal value of the heat treatment temperature, avoiding the mutual interference of various influencing factors (Ti/Al thickness ratio, total thickness, annealing temperature); on the other hand, Ti and Al can directly contact the AlGaN surface during the heat treatment. At the same time, the role of Ti and Al is fully displayed at the beginning of heat treatment. Ti metal has a low work function and can reduce the barrier height with AlGaN materials. At the same time, it can extract N in AlGaN to form TiN during the heat treatment process.
  • N vacancies are left in AlGaN, and the increase in electron concentration is conducive to the formation of ohmic contacts; the direct contact of Al can inhibit the out-diffusion of Al in AlGaN and maintain the two-dimensional electron gas concentration; and the full and uniform mixing of Ti and Al is also conducive to the formation of ohmic contacts.
  • the problem of roughness caused by over-alloying can be avoided, a good contact surface can be maintained, the roughness of the electrode surface can be greatly reduced, the stability and reliability of the device can be improved, and the industrialization efficiency can be improved.
  • the process of the photolithography technology is not limited, and the patterns of the drain and/or source can be defined, which are all applicable to this application.
  • the solvent and process used for removing the photoresist and performing the stripping process are not limited.
  • the Ti x Al y alloy layer deposited in step (1) adopts Ti x Al y alloy target and/or two metal targets of Ti and Al, optionally Ti x Al y alloy, where x >0, y>0, the ratio of x to y is the atomic ratio of Ti to Al.
  • the deposition of Ti x Al y alloy layer can be completed by occupying only one target position, which improves the stability of the deposition chamber and avoids cross-contamination.
  • x>0, y>0 for example, x can be 0.1, 0.5, 1, 2, 5, 8, 10, 15 or 20, etc., and y can be 0.1, 0.4, 1, 3, 5, 8, 10, 14, or 20, etc.
  • x can be 0.1, 0.2, 0.5, 0.8, 1, 2, 3, 5, 8, 9 Or 10, etc.
  • y can be 0.1, 0.3, 0.5, 1, 2, 3, 5, 7, 9, or 10, etc.
  • the ratio of x to y in the Ti x Al y alloy target is 1:10-10:1, and the ratio of x to y is the atomic ratio of Ti to Al, for example, it can be 1:10, 1. :5, 1:1, 2:1, 5:1, 8:1 or 10:1, etc. If the x:y is less than 1:10, the Al composition in the alloy is too high, which will cause the metal during the high temperature annealing process The surface roughness increases; if x:y is greater than 10:1, the Al composition is too low, which will cause the Al to not function substantially, and thus it is impossible to suppress the out-diffusion of Al in AlGaN to maintain a high two-dimensional electron gas concentration.
  • the thickness of the deposited Ti x Al y alloy layer is 20-100 nm, for example, 20 nm, 25 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 95 nm or 100 nm, etc., if the thickness If it is less than 20nm, the parasitic resistance of the metal itself will be relatively large. A thick metal layer is more conducive to the reduction of the parasitic resistance of the metal itself; a thickness greater than 100nm will cause the thicker metal layer to change the edge due to the effect of high temperature after high temperature annealing. It is rough, which affects the stability and reliability of the device.
  • the cap metal layer includes any one of TiN, W, or TiW.
  • the thickness of the cap layer metal layer is 20-200nm, for example 20nm, 25nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 120nm, 150nm, 180nm or 200nm, etc., if If the thickness is less than 20nm, the parasitic resistance of the metal itself will be relatively large, a thick metal layer is more conducive to the reduction of the parasitic resistance of the metal itself, while a thicker cap layer metal layer is more conducive to blocking oxygen pollution; thickness greater than 100nm, it will As a result, after high temperature annealing, the thicker metal layer will roughen the edges due to the effect of high temperature, which affects the stability and reliability of the device.
  • the step of defining an electrode pattern on the AlGaN layer by using a photolithography technique is obtained by sequentially performing the process steps of homogenization, pre-baking, photolithography, development, and post-baking.
  • the method of deposition in step (1) includes magnetron sputtering and/or ion sputtering, and may be magnetron sputtering.
  • the gas for depositing the Ti x Al y alloy layer is argon (Ar).
  • the gas for depositing the metal layer of the cap layer is Ar or nitrogen N 2 .
  • the heat-treated gas is any one or a combination of at least two of N 2 , ammonia NH 3 , hydrogen H 2 or Ar, wherein the optional combination is: N 2 and H 2 , H 2 And Ar.
  • the temperature of the heat treatment is 700-1000°C, for example, 700°C, 750°C, 780°C, 800°C, 850°C, 900°C, 950°C, 980°C or 1000°C, etc., if the temperature Below 700°C, it is difficult for the metal and semiconductor AlGaN to react in a solid phase, and it is difficult to form ohmic contacts on the planar AlGaN material. Temperatures higher than 1000°C will affect the material properties of the semiconductor AlGaN itself, resulting in a decrease in the concentration of two-dimensional electron gas. , Increase the sheet resistance of semiconductor materials.
  • the heat treatment time is 20-80s, for example, it can be 20s, 25s, 30s, 40s, 50s, 60s, 70s, 75s, or 80s, etc. If the time is less than 20s, the solidification of metal and semiconductor AlGaN On the contrary, it should be less favorable and not conducive to the formation of ohmic contacts; the time is longer than 100s, which will affect the material properties of the semiconductor AlGaN itself, causing the two-dimensional electron gas concentration to decrease and increasing the sheet resistance of the semiconductor material.
  • the preparation method includes the following steps:
  • step (3) Deposit a 20-100 nm Ti x Al y alloy layer and a 20-200 nm cap metal layer on the sample surface processed in step (2) in sequence, remove the photoresist, and perform a stripping treatment.
  • the gas of the atmosphere contains any one or a combination of at least two of N 2 , NH 3 , H 2 or Ar.
  • the concentration of dilute hydrochloric acid is not limited, as long as it can remove oxides and other substances on the surface of the substrate.
  • the present application also provides a method for reducing the ohmic contact between the AlGaN/GaN substrate and the electrode.
  • the method includes: depositing a Ti x Al y alloy layer on the surface of the AlGaN/GaN substrate as the electrode.
  • the method provided in this application uses a Ti x Al y alloy layer as a direct contact electrode.
  • Ti and Al are fully and uniformly mixed to avoid excessive alloying of the metal during high-temperature annealing, thereby reducing the surface roughness.
  • both Ti and Al metals are at the same time
  • Direct contact with the AlGaN/GaN substrate makes Al play a direct role in the initial stage of annealing, effectively inhibits the out-diffusion of Al in AlGaN, maintains the two-dimensional electron gas concentration, reduces the ohmic contact between the electrode and the AlGaN/GaN substrate, and forms low resistance Ohmic contact.
  • the ratio of x to y in the Ti x Al y alloy layer is 1:10-10:1, for example, it may be 1:10, 1:5, 1:1, 2:1, 5:1, 8:1 or 10:1 etc.
  • the thickness of the deposited Ti x Al y alloy layer is 20-100 nm, for example, it may be 20 nm, 25 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 95 nm or 100 nm.
  • the deposition method includes magnetron sputtering and/or ion sputtering, and may be magnetron sputtering.
  • the AlGaN/GaN ohmic contact electrode uses a Ti x Al y alloy layer to replace the Ti/Al laminated structure, and the fully uniform mixing of Ti and Al and the adjustable ratio make the surface roughness of the electrode lower; Ti The x Al y 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 ⁇ mm, which meets the preparation standard of radio frequency devices ( ⁇ 0.1 ⁇ mm).
  • the preparation method of the AlGaN/GaN ohmic contact electrode provided by this application by fixing the atomic ratio of Ti x Al y , can adjust the optimal value of annealing temperature only by changing the total thickness of the deposition, avoiding various influences Factors interfere at the same time; Al directly contacts the AlGaN surface in the initial stage of heat treatment, inhibits the out-diffusion of Al in AlGaN, maintains the two-dimensional electron gas concentration, and is more conducive to achieving low ohmic contact values, and the full and uniform mixing of Ti and Al also avoids
  • the roughness problem caused by heat treatment alloying can maintain a good contact surface, improve the stability and reliability of the device, and the process steps are simple and reliable, which is more conducive to improving the industrialization efficiency.
  • This application provides a method for reducing the ohmic contact between the AlGaN/GaN substrate and the electrode.
  • a Ti x Al y alloy layer on the surface of the AlGaN/GaN substrate as the electrode, the surface roughness of the AlGaN/GaN substrate is relatively low.
  • Ti and Al are fully and uniformly mixed and tightly combined with the AlGaN/GaN substrate, effectively suppressing the out-diffusion of Al in AlGaN, maintaining the two-dimensional electron gas concentration, and effectively reducing the ohmic contact between the electrode and the AlGaN/GaN substrate.
  • FIG. 1 The schematic diagram of the AlGaN/GaN substrate structure used in this application is shown in FIG. 1, which shows that the AlGaN/GaN substrate is composed of a Si substrate layer, a GaN buffer layer, a GaN layer, and an AlGaN layer in order from bottom to top.
  • FIG. 2 The schematic diagram of the structure of the drain and/or source pattern formed on the AlGaN/GaN substrate after photolithography development provided in this application is shown in Figure 2, which shows that the surface of the AlGaN layer is not covered by photolithography after development through photolithography.
  • the glued part is the pattern of the drain and/or source.
  • This embodiment provides a method for preparing an AlGaN/GaN ohmic contact electrode, which includes the following steps:
  • the AlGaN/GaN substrate was ultrasonically cleaned with acetone for 5 minutes, isopropanol for 15 minutes, deionized water for 10 minutes, and nitrogen blown dry.
  • step (3) Put the processed sample in step (2) into the vacuum transmission chamber of the magnetron sputtering equipment immediately for the coating process.
  • the Ti 10 Al 1 alloy layer was deposited by magnetron sputtering for 60 nm, and the metal layer of the TiN cap layer was sputtered for 60 nm by reactive magnetron sputtering with a Ti target in N 2 atmosphere, and then at 60 °C in dimethyl sulfoxide.
  • the photoresist and the metal on the glue are removed by immersion in a water bath.
  • This embodiment provides a method for preparing an AlGaN/GaN ohmic contact electrode, which includes the following steps:
  • the AlGaN/GaN substrate was ultrasonically cleaned with acetone for 5 minutes, isopropanol for 15 minutes, deionized water for 10 minutes, and nitrogen blown dry.
  • step (3) Put the processed sample in step (2) into the vacuum transmission chamber of the magnetron sputtering equipment immediately for the coating process.
  • the Ti 5 Al 1 alloy layer was deposited by magnetron sputtering for 20 nm, and the metal layer of the TiN cap layer was sputtered for 80 nm by reactive magnetron sputtering with a Ti target in N 2 atmosphere, and then at 60 °C in dimethyl sulfoxide.
  • the photoresist and the metal on the glue are removed by immersion in a water bath.
  • the stripped sample is heated to 900° C. in an H 2 /Ar mixture with a volume fraction of H 2 of 3% for 30 seconds to obtain the AlGaN/GaN ohmic contact electrode.
  • step (3) the structure diagram of the Ti 5 Al 1 /TiN double-layer metal structure after sputtering is shown in FIG. 3, which shows the deposition of Ti 5 on the pattern defining the drain and source on the AlGaN layer.
  • the Al 1 alloy layer and the TiN cap metal layer, and the photoresist is also covered with the Ti 5 Al 1 alloy layer and the TiN cap metal layer.
  • step (3) the structure diagram of the metal drain and source ohmic patterns formed after the photoresist is removed is shown in FIG. 4, which shows that the drain is formed on the AlGaN/GaN substrate after the photoresist is removed.
  • the electrode and the source electrode are in direct contact with the AlGaN layer.
  • This embodiment provides a method for preparing an AlGaN/GaN ohmic contact electrode, which includes the following steps:
  • the AlGaN/GaN substrate was ultrasonically cleaned with acetone for 10 minutes, isopropanol for 5 minutes, deionized water for 15 minutes, and nitrogen blown dry.
  • step (3) Put the processed sample in step (2) into the vacuum transmission chamber of the ion sputtering equipment immediately for the coating process.
  • the Ti 1 Al 1 alloy layer was deposited by ion sputtering for 40 nm, and the metal layer of the TiN cap layer was sputtered for 200 nm by reactive ion sputtering using a Ti target in a N 2 atmosphere, and then in a 60 °C water bath of dimethyl sulfoxide In the process, the photoresist and the metal on the glue are removed by immersion.
  • This embodiment provides a method for preparing an AlGaN/GaN ohmic contact electrode, which includes the following steps:
  • the AlGaN/GaN substrate was ultrasonically cleaned with acetone for 8 min, isopropanol for 10 min, rinsed with deionized water for 5 min, and dried with nitrogen.
  • step (3) Put the processed sample in step (2) into the vacuum transmission chamber of the ion sputtering equipment immediately for the coating process.
  • the Ti 1 Al 5 alloy layer was deposited by ion sputtering for 80 nm, and the W cap layer metal layer was sputtered for 100 nm by ion sputtering with a W target in an argon atmosphere, and then in a 60 °C water bath of dimethyl sulfoxide The method of immersion removes the photoresist and the metal on the glue.
  • This embodiment provides a method for preparing an AlGaN/GaN ohmic contact electrode, which includes the following steps:
  • the AlGaN/GaN substrate was ultrasonically cleaned with acetone for 5 minutes, isopropanol for 10 minutes, deionized water for 8 minutes, and nitrogen blown dry.
  • step (3) Put the processed sample in step (2) into the vacuum transmission chamber of the magnetron sputtering equipment immediately for the coating process.
  • the Ti 1 Al 10 alloy layer was deposited by magnetron sputtering for 100 nm, and the TiW cap metal layer was sputtered with a TiW target in an argon atmosphere by magnetron sputtering for 150 nm, and then in dimethyl sulfoxide in a 60 °C water bath The method of immersion removes the photoresist and the metal on the glue.
  • Example 1 Compared with Example 1, the only difference is that the Ti 10 Al 1 alloy in step (3) is replaced with Ti 3 Al 7 alloy.
  • Example 1 Compared with Example 1, the only difference is that the Ti 10 Al 1 alloy in step (3) is replaced with Ti 7 Al 3 alloy.
  • Example 1 Compared with Example 1, the only difference is that the Ti 10 Al 1 alloy in step (3) is replaced by Ti and Al co-sputtering, and the Ti:Al atomic ratio is controlled to be 10:1.
  • Example 1 Compared with Example 1, the only difference is that this comparative example provides an AlGaN/GaN ohmic contact electrode, the electrode adopts a Ti/Al laminated structure, and the Ti:Al atomic ratio is controlled to be 10:1.
  • the ohmic contact electrodes prepared in the foregoing Examples 1-8 and Comparative Example 1 were tested for the structure of the ohmic circular transmission line model (Circular Transmission Line Model, CTLM).
  • CTLM Circular Transmission Line Model
  • the test method is as follows: resistance measurement by four probes Test the resistance and get R c by fitting. The four-probe measurement is performed on the resistance on the metal ring of different sizes in the CTLM structure to obtain different resistance values, and linear fitting is performed on the resistance values under different sizes to obtain R c .
  • Performance evaluation standard The final ohmic contact resistance R c is used as the final evaluation standard. The smaller the R c, the smaller the parasitic resistance in the device, which is more conducive to the output characteristics of the final AlGaN/GaN HEMTs device.
  • R c ⁇ 0.1 ⁇ mm is more conducive to the radio frequency characteristics of the device.
  • the ohmic contact resistance value obtained by using the Ti/Al multilayer film method is generally >0.5 ⁇ mm.
  • the Ti x Al y alloy used in this application as the ohmic contact layer can achieve an ohmic contact resistance R c of ⁇ 0.2 ⁇ mm, which is the lowest It can achieve R c ⁇ 0.1 ⁇ mm, greatly reducing the ohmic contact resistance value, which is beneficial to the development of radio frequency devices.
  • the ohmic contact resistance of the electrodes prepared in Examples 1-8 is 0.08-0.2 ⁇ mm, which meets the preparation standard of radio frequency devices ( ⁇ 0.1 ⁇ mm).
  • the ohmic contact resistance of Example 6 is 0.08 ⁇ mm, which is much lower than that of other embodiments, which shows that by controlling the ratio of Ti and Al atoms in the Ti x Al y alloy layer, a lower ohmic contact resistance can be obtained. value;
  • Example 1 deposits a Ti 10 Al 1 alloy layer on the AlGaN layer, and the ohmic contact resistance of the corresponding electrode is 0.2 ⁇ mm, while Comparative Example 1 is on the AlGaN layer
  • the Ti/Al laminated structure is set, and the corresponding ohmic contact resistance is 0.6 ⁇ mm, which shows that the resistance value of the ohmic contact electrode prepared in Example 1 is lower than that of Comparative Example 1, and it is further explained that the Ti x Al y alloy layer is used
  • the ohmic contact resistance in direct contact with the AlGaN layer is lower than the ohmic contact resistance of the Ti/Al laminated structure on the AlGaN layer in the conventional method.
  • the AlGaN/GaN ohmic contact electrode uses the Ti x Al y alloy layer to directly contact the AlGaN layer, thereby reducing the ohmic contact resistance of the electrode and meeting the preparation standard of radio frequency devices ( ⁇ 0.1 ⁇ mm ); while maintaining a good contact surface, improving the stability and reliability of the device, the process steps are simple and reliable, and it is more conducive to improving the efficiency of industrialization.

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Abstract

一种铝镓氮/氮化镓AlGaN/GaN欧姆接触电极及其制备方法和降低欧姆接触的方法，所述电极由下而上依次包括AlGaN/GaN基底、帽层金属层（7）和TixAly合金层（6），其中，x＞0，y＞0。所述方法采用光刻技术在AlGaN层（4）上定义漏极和/或源极图形，在AlGaN（4）表面依次沉积TixAly合金（6）和帽层金属层（7），去除光刻胶（5），进行剥离处理，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。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TixAly合金层（6）作为电极而实现。

Description

AlGaN/GaN欧姆接触电极及其制备方法和降低欧姆接触的方法
本申请要求在2019年11月12日提交中国专利局、申请号为201911100606.1的中国专利申请的优先权，该申请的全部内容通过引用结合在本申请中。
技术领域
本申请涉及电子半导体器件技术领域，例如涉及一种氮化镓铝/氮化镓AlGaN/GaN欧姆接触电极及其制备方法和降低欧姆接触的方法。
背景技术
第三代半导体材料氮化镓(GaN)具有宽的禁带宽度，高击穿电场，高热导率，高电子饱和速率以及更高的抗辐射能力，在高温、高频、抗辐射以及大功率半导体器件中有广泛的应用前景。其中，铝镓氮/氮化镓高电子迁移率晶体管(AlGaN/GaN High Electron Mobility Transistors，AlGaN/GaN HEMTs)是(AlGaN/GaN高电子迁移率晶体管)具有高电子迁移率的二维电子气(Two-Dimensional Electron Gas，2DEG)，在射频和功率开关器件中具有极大的应用前景。
AlGaN/GaN HEMTs器件的欧姆接触质量是影响器件最终输出参数的重要指标，直接影响到器件的源漏输出电流、导通电阻、击穿电压等。高质量的欧姆接触在GaN高频器件中更为重要，其中无金欧姆接触技术工艺对硅-互补金属氧化物半导体Si-CMOS大规模生产基线以及降低成本上有至关重要的作用。在GaN HEMTs欧姆接触的研究问题上，基本分为有金工艺与无金工艺：1)有金工艺：钛Ti/铝Al/镍Ni/金Au、Ti/Al/Ti/Au、Ti/Al/钼Mo/Au等金属叠层结构常用于AlGaN/GaN HEMTs，有研究表明Au的加入更有利于促进氮化钛TiN柱的形成，可以在金属以及二维电子气之间形成直接的TiN导电通道；2)无金工艺：GaN HEMTs器件的无金欧姆接触工艺与Si-CMOS的发展更加兼容，同时可以大大降低生产成本，是实现Si-CMOS大规模制造工艺线的关键。常用的金属是Ti和Al，Ti金属功函数低，可以降低与AlGaN材料的势垒高度，同时在退火过程中可以萃取AlGaN中的N形成TiN，同时在AlGaN中留下N空位，电子浓度的增高有利于欧姆接触的形成；Al的加入可以抑制AlGaN中Al的大量外扩散，从而维持比较高浓度的二维电子气，有利于实现低欧姆接触值。但由于Al的熔点较低(660℃)，在高温退火下，较厚的Al层会融化并与其他金属形成合金，对表面粗糙度有不好的影响。不仅如此，不同的Ti/Al厚度比以及不同的退火温度对欧姆接触的形成也有较大的影响。同时鉴于AlGaN的宽禁带宽度， 无金欧姆工艺对实现高质量欧姆接触具有一定挑战性。因此，有研究通过刻蚀recess工艺使AlGaN形成凹槽结构，减薄势垒层的厚度降低欧姆接触值，但这些在工业生产中会大大增加工艺的复杂性，降低生产效率。
基于无金多层金属结构AlGaN/GaN HEMTs的欧姆接触的形成机制，常用降低欧姆接触的方法有：1)调节Ti/Al厚度比以及整体厚度：一方面通过Ti与AlGaN发生反应形成TiN，并通过N空位提高电子浓度，另一方面金属Al有利于抑制AlGaN中Al的外扩散，以方便保证AlGaN中的Al含量，维持二维电子气的浓度。合适的Ti/Al比对最终欧姆接触有重要的影响；2)recess刻蚀工艺：由于AlGaN的宽禁带宽度，会加大金属与半导体之间的势垒高度，因此通过刻蚀工艺形成AlGaN沟槽，减小势垒宽度，促进欧姆接触的形成。其中不同的刻蚀深度对欧姆接触的质量也有不同的影响，通过调节刻蚀深度调节欧姆接触值的大小；3)硅Si层或钽Ta层的加入：通过薄层Si在退火过程中实现自掺杂，增大半导体中的电子浓度，促进欧姆接触的形成。Ta层的加入有助于形成较平滑的欧姆接触界面，对欧姆接触的质量以及可靠性上有一定改善。有关无金欧姆接触，通过recess工艺所实现的最低欧姆接触值为0.21Ω·mm，这对射频器件来说是远远不够的，且多层金属层的沉积大大增加工艺的复杂性，降低工艺的稳定性。Ta层或者Si层的额外膜层的加入也会增加膜层的复杂度，且在制备薄膜的过程中需要提供多种不同的金属靶材及靶位，且不利于镀膜腔室的稳定性，多层金属沉积的难度增加直接降低良率，不利于产业化。无金欧姆接触的工艺稳定性以及可靠性对GaN HEMTs器件制备来说至关重要。
基于相关技术存在的问题，如何保证GaN HEMTs无金欧姆接触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，成为亟需解决的问题。
发明内容
本申请提供一种AlGaN/GaN欧姆接触电极及其制备方法和降低欧姆接触的方法，所述电极采用Ti xAl y合金层作为直接接触层，替换掉Ti/Al多层膜作为直接接触层的结构，Ti、Al的充分均匀混合可避免热处理阶段过度合金化而导致的粗糙度问题，可以保持良好的接触表面，大大降低电极表面的粗糙度，提高器件的稳定性以及可靠性，提高产业化效率。
在一实施例中，本申请提供一种AlGaN/GaN欧姆接触电极，所述电极由下而上依次包括AlGaN/GaN基底、帽层金属层和Ti xAl y合金层，其中，x＞0，y＞0。
在一实施例中，本申请提供一种如上述的AlGaN/GaN欧姆接触电极的制备 方法，所述方法包括以下步骤：
(1)采用光刻技术在AlGaN/GaN基底上定义漏极和/或源极的图形，在AlGaN层表面依次沉积Ti xAl y合金层和帽层金属层，去除光刻胶，进行剥离处理得到剥离后的样品。
(2)对剥离后的样品进行热处理，得到所述AlGaN/GaN欧姆接触电极。
在一实施例中，本申请还提供了一种降低AlGaN/GaN基底与电极之间欧姆接触的方法，所述方法包括：在AlGaN/GaN基底表面沉积Ti xAl y合金层作为电极。
附图说明
图1是本申请采用的AlGaN/GaN基底的结构示意图。
图2是本申请提供的AlGaN/GaN基底上经过光刻显影后形成的漏极和/或源极图形的结构示意图。
图3是本申请实施例2提供的溅射Ti 5Al 1/TiN双层金属结构后的结构示意图。
图4是本申请实施例2提供的去除光刻胶后形成的金属源极和漏极欧姆图形的结构示意图。
图中，1-Si衬底层，2-GaN缓冲层，3-GaN层，4-AlGaN层，5-光刻胶层，6-Ti 5Al 1合金层，7-TiN帽层金属层。
具体实施方式
下面结合附图并通过实施方式进行说明，对本申请的实施方式说明如下。
在一实施例中，本申请提供一种AlGaN/GaN欧姆接触电极，所述电极由下而上依次包括AlGaN/GaN基底、帽层金属层和Ti xAl y合金层，其中，x＞0，y＞0。
本申请提供的AlGaN/GaN欧姆接触电极，通过采用Ti xAl y合金层替换Ti/Al叠层结构，Ti、Al的充分均匀混合避免了在高温退火过程中金属过度合金化造成的均匀性问题，可达到较低的电极表面粗糙度；Ti xAl y合金层与AlGaN层直接接触，可获得低的欧姆接触值，达到射频器件的制备标准。
本申请中，Ti xAl y合金层中x＞0，y＞0，例如x可以是0.1、0.5、1、2、5、8、10、15或20等，y可以是0.1、0.4、1、3、5、8、10、14或20等。
可选地，所述Ti xAl y合金层中，0＜x≤10，0＜y≤10，例如x可以是0.1、 0.2、0.5、0.8、1、2、3、5、8、9或10等，y可以是0.1、0.3、0.5、1、2、3、5、7、9或10等。
可选地，所述Ti xAl y合金层中x与y的比为1:10-10:1，x与y的比即为Ti与Al的原子比，例如可以是1:10、1:5、1:1、2:1、5:1、8:1或10:1等，若所述x:y小于1:10，合金中Al的成分偏高，会造成高温退火过程中金属表面粗糙度的上升；x:y大于10:1，Al的成分过低，会造成Al无法实质性的发挥作用，从而无法抑制AlGaN中Al的外扩散，以维持较高的二维电子气浓度。
可选地，所述Ti xAl y合金层的厚度为20-100nm，例如可以是20nm、25nm、30nm、40nm、50nm、60nm、70nm、80nm、90nm、95nm或100nm等，若所述厚度小于20nm，金属本身的寄生电阻会比较大，厚的金属层更有利于金属本身寄生电阻的下降；厚度大于100nm，会导致在高温退火后，较厚的金属层会由于高温的作用使得边缘变得粗糙，影响最终器件的稳定性及可靠性。
可选地，所述帽层金属层包含TiN、W或TiW中的任意一种。
可选地，所述帽层金属层的厚度为20-200nm，例如可以是20nm、25nm、30nm、40nm、50nm、60nm、70nm、80nm、90nm、100nm、120nm、150nm、180nm或200nm等，若所述厚度小于20nm，金属本身的寄生电阻会比较大，厚的金属层更有利于金属本身寄生电阻的下降，同时较厚的帽层金属层更有利于阻隔氧的污染；厚度大于100nm，会导致在高温退火后，较厚的金属层会由于高温的作用使得边缘变得粗糙，影响器件的稳定性及可靠性。
本申请中，对AlGaN/GaN基底不做特殊的限定。
在一实施例中，本申请提供一种如上述的AlGaN/GaN欧姆接触电极的制备方法，所述方法包括以下步骤：
(1)采用光刻技术在AlGaN/GaN基底上定义漏极和/或源极的图形，在AlGaN表面依次沉积Ti xAl y合金层和帽层金属层，去除光刻胶，进行剥离处理得到剥离后的样品。
(2)对剥离后的样品进行热处理，得到所述AlGaN/GaN欧姆接触电极。
本申请提供的AlGaN/GaN欧姆接触电极的制备方法，通过采用光刻技术，精确控制漏极和/或源极的位置和尺寸，将光刻后的基底进行盐酸表面处理去除天然氧化层后，将Ti xAl y合金沉积在AlGaN表面，使二者紧密结合，Ti xAl y合金的使用可以减小工艺的复杂性，而且通过固定Ti xAl y的原子比例，仅通过改变沉积的总厚度即可调节与热处理温度的最优值，避免了多种影响因子(Ti/Al厚度比，总厚度，退火温度)的共同干扰；另一方面可以在热处理过程中Ti、Al直接接触到AlGaN表面同时发挥作用，使得Ti和Al的作用在热处理开始阶段 就充分显示出来，Ti金属功函数低，可以降低与AlGaN材料的势垒高度，同时在热处理过程中可以萃取AlGaN中的N形成TiN，同时在AlGaN中留下N空位，电子浓度的增高有利于欧姆接触的形成；Al的直接接触来抑制AlGaN中Al的外扩散，维持二维电子气浓度；且Ti、Al的充分均匀混合也有利于在热处理过程中避免过度合金化而导致的粗糙度问题，可以保持良好的接触表面，大大降低电极表面的粗糙度，提高器件的稳定性以及可靠性，提高产业化效率。
本申请中，对光刻技术的工艺不做限定，能够定义漏极和/或源极的图形，均适用于本申请。
本申请中，对去除光刻胶，进行剥离处理使用的溶剂和工艺不做的限定。
可选地，步骤(1)中所述沉积Ti xAl y合金层采用Ti xAl y合金靶材和/或Ti与Al两种金属靶材，可选为Ti xAl y合金，其中，x＞0，y＞0，x与y的比即为Ti与Al的原子比。使用Ti xAl y合金，仅需占用一个靶位即可完成Ti xAl y合金层的沉积，提高沉积腔室的稳定性，避免交叉污染。
本申请中，Ti xAl y合金靶材中，x＞0，y＞0，例如，x可以是0.1、0.5、1、2、5、8、10、15或20等，y可以是0.1、0.4、1、3、5、8、10、14或20等。
可选地，所述Ti xAl y合金靶材中，0＜x≤10，0＜y≤10，例如x可以是0.1、0.2、0.5、0.8、1、2、3、5、8、9或10等，y可以是0.1、0.3、0.5、1、2、3、5、7、9或10等。
可选地，所述Ti xAl y合金靶材中x与y的比为1:10-10:1，x与y的比即为Ti与Al的原子比，例如可以是1:10、1:5、1:1、2:1、5:1、8:1或10:1等，若所述x:y小于1:10，合金中Al的成分偏高，会造成高温退火过程中金属表面粗糙度的上升；若x:y大于10:1，Al的成分过低，会造成Al无法实质性的发挥作用，从而无法抑制AlGaN中Al的外扩散，以维持较高的二维电子气浓度。
可选地，所述沉积Ti xAl y合金层的厚度为20-100nm，例如可以是20nm、25nm、30nm、40nm、50nm、60nm、70nm、80nm、90nm、95nm或100nm等，若所述厚度小于20nm，金属本身的寄生电阻会比较大，厚的金属层更有利于金属本身寄生电阻的下降；厚度大于100nm，会导致在高温退火后，较厚的金属层会由于高温的作用使得边缘变得粗糙，影响器件的稳定性及可靠性。
可选地，所述帽层金属层包含TiN、W或TiW中的任意一种。
可选地，所述帽层金属层的厚度为20-200nm，例如可以是20nm、25nm、30nm、40nm、50nm、60nm、70nm、80nm、90nm、100nm、120nm、150nm、180nm或200nm等，若所述厚度小于20nm，金属本身的寄生电阻会比较大，厚的金属层更有利于金属本身寄生电阻的下降，同时较厚的帽层金属层更有利于 阻隔氧的污染；厚度大于100nm，会导致在高温退火后，较厚的金属层会由于高温的作用使得边缘变得粗糙，影响器件的稳定性及可靠性。
可选地，所述采用光刻技术在AlGaN层上定义电极图形的步骤为：依次进行匀胶、前烘、光刻、显影、后烘的工艺步骤得到。可选地，步骤(1)中所述沉积的方式包含磁控溅射和/或离子溅射，可选为磁控溅射。
可选地，所述沉积Ti xAl y合金层的气体为氩气Ar。
可选地，所述沉积帽层金属层的气体为Ar或氮气N 2。
可选地，所述热处理的气体为N 2、氨气NH 3、氢气H 2或Ar中的任意一种或至少两种的组合，其中可选的组合为：N 2和H 2，H 2和Ar。
可选地，所述热处理的温度为700-1000℃，例如可以是700℃、750℃、780℃、800℃、850℃、900℃、950℃、980℃或1000℃等，若所述温度低于700℃，金属与半导体AlGaN很难发生固相反应，很难在平面AlGaN材料上形成欧姆接触；温度高于1000℃，会对半导体AlGaN本身材料特性产生影响，使得二维电子气浓度下降，增加半导体材料的方块电阻。
可选地，所述热处理的时间为20-80s，例如可以是20s、25s、30s、40s、50s、60s、70s、75s或80s等，若所述时间小于20s，对金属与半导体AlGaN的固相反应不太有利，不利于欧姆接触的形成；时间大于100s，对半导体AlGaN本身材料特性产生影响，使得二维电子气浓度下降，增加半导体材料的方块电阻。
可选地，所述制备方法，包括以下步骤：
(1)对AlGaN/GaN基底进行洗涤，氮气吹干。
(2)在AlGaN层上依次进行匀胶、前烘、光刻、显影、后烘的工艺步骤，定义出漏极和/或源极图形，浸入稀盐酸中表面处理后，用去离子水冲洗，氮气吹干。
(3)向步骤(2)处理后的样品表面依次沉积20-100nm的Ti xAl y合金层和20-200nm帽层金属层，去除光刻胶，进行剥离处理。
(4)对剥离后的样品在气氛中加热到700-1000℃，保持20-80s，得到所述AlGaN/GaN欧姆接触电极。
所述气氛的气体包含N 2、NH 3、H 2或Ar中的任意一种或至少两种的组合。
本申请中，对稀盐酸的浓度不做限定，只要能除去基底表面的氧化物等物质即可。
在一实施例中，本申请还提供了一种降低AlGaN/GaN基底与电极之间欧姆接触的方法，所述方法包括：在AlGaN/GaN基底表面沉积Ti xAl y合金层作为电 极。
本申请提供的方法，采用Ti xAl y合金层作为直接接触电极，Ti和Al充分均匀混合避免了高温退火中金属的过度合金化，从而降低表面的粗糙度，同时Ti、Al两种金属同时与AlGaN/GaN基底直接接触，使得Al在退火初级阶段直接发挥作用，有效抑制AlGaN中Al的外扩散，维持二维电子气浓度，降低电极与AlGaN/GaN基底之间的欧姆接触，形成低阻欧姆接触。
可选地，所述Ti xAl y合金层中x与y的比为1:10-10:1，例如可以是1:10、1:5、1:1、2:1、5:1、8:1或10:1等。
可选地，所述沉积Ti xAl y合金层的厚度为20-100nm，例如可以是20nm、25nm、30nm、40nm、50nm、60nm、70nm、80nm、90nm、95nm或100nm等。
可选地，所述沉积的方式包含磁控溅射和/或离子溅射，可选为磁控溅射。
(1)本申请提供的AlGaN/GaN欧姆接触电极，采用Ti xAl y合金层替换Ti/Al叠层结构，Ti、Al的充分均匀混合且比例可调，使得电极表面粗糙度较低；Ti xAl y合金层与AlGaN层直接接触，使得所述电极的欧姆接触≤0.2Ω·mm，达到射频器件的制备标准(～0.1Ω·mm)。
(2)本申请提供的AlGaN/GaN欧姆接触电极的制备方法，通过固定Ti xAl y的原子比例，仅通过改变沉积的总厚度即可调节与退火温度的最优值，避免了多种影响因子同时干扰；Al在热处理初始阶段就直接接触AlGaN表面，抑制AlGaN中Al的外扩散，维持二维电子气浓度，更有利于实现低欧姆接触值，且Ti、Al的充分均匀混合也避免由于热处理合金化而导致的粗糙度问题，保持良好的接触表面，提高器件的稳定性以及可靠性，工艺步骤简单可靠，更有利于提高产业化效率。
(3)本申请提供的一种降低AlGaN/GaN基底与电极之间欧姆接触的方法，通过在AlGaN/GaN基底表面沉积Ti xAl y合金层作为电极，AlGaN/GaN基底表面的粗糙度较低，Ti和Al充分均匀混合，与AlGaN/GaN基底紧密结合，有效抑制AlGaN中Al的外扩散，维持二维电子气浓度，有效降低电极与AlGaN/GaN基底之间的欧姆接触。
本申请采用的AlGaN/GaN基底结构示意图如图1所示，图1显示AlGaN/GaN基底由下而上依次为Si衬底层、GaN缓冲层、GaN层和AlGaN层。
本申请提供的AlGaN/GaN基底上经过光刻显影后形成的漏极和/或源极图形的结构示意图如图2所示，图2显示通过光刻显影后，在AlGaN层表面未覆盖光刻胶的部分，即为漏极和/或源极的图形。
实施例1
本实施例提供一种AlGaN/GaN欧姆接触电极的制备方法，包括以下步骤：
(1)将AlGaN/GaN基底依次使用丙酮超声清洗5min，异丙醇清洗15min，去离子水冲洗10min，氮气吹干。
(2)在AlGaN层上依次进行匀胶、前烘、光刻、显影、后烘的工艺步骤，定义出漏极和源极图形，浸没于盐酸：水HCl:H 2O＝1:4的盐酸溶液中3min以去除基底表面的氧化物，然后用去离子水冲洗15min，最后氮气吹干。
(3)向步骤(2)处理后的样品立即放入磁控溅射设备真空传输室内，进行镀膜工艺。Ti 10Al 1合金层采用磁控溅射方式沉积60nm，TiN帽层金属层采用Ti靶在N 2氛围中通过反应磁控溅射的方式溅射60nm，然后在二甲基亚砜的60℃水浴中以浸没的方式去除光刻胶及胶上金属。
(4)对剥离后的样品在H 2体积分数为3％的H 2/Ar混合气中加热到950℃，保持60s，得到所述的AlGaN/GaN欧姆接触电极。
实施例2
本实施例提供一种AlGaN/GaN欧姆接触电极的制备方法，包括以下步骤：
(1)将AlGaN/GaN基底依次使用丙酮超声清洗5min，异丙醇清洗15min，去离子水冲洗10min，氮气吹干。
(2)在AlGaN层上依次进行匀胶、前烘、光刻、显影、后烘的工艺步骤，定义出漏极和源极图形，浸没于HCl:H 2O＝1:4的盐酸溶液中5min以去除基底表面的氧化物，然后用去离子水冲洗15min，最后氮气吹干。
(3)向步骤(2)处理后的样品立即放入磁控溅射设备真空传输室内，进行镀膜工艺。Ti 5Al 1合金层采用磁控溅射方式沉积20nm，TiN帽层金属层采用Ti靶在N 2氛围中通过反应磁控溅射的方式溅射80nm，然后在二甲基亚砜的60℃水浴中以浸没的方式去除光刻胶及胶上金属。
(4)对剥离后的样品在H 2体积分数为3％的H 2/Ar混合气中加热到900℃，保持30s，得到所述的AlGaN/GaN欧姆接触电极。
本实施例经过步骤(3)，溅射Ti 5Al 1/TiN双层金属结构后的结构示意图如图3所示，图3显示在AlGaN层上定义漏极和源极的图形上沉积Ti 5Al 1合金层和TiN帽层金属层，光刻胶上也覆盖有Ti 5Al 1合金层和TiN帽层金属层。
本实施例经过步骤(3)，去除光刻胶后形成的金属漏极和源极欧姆图形的结构示意图如图4所示，图4显示除去光刻胶后，在AlGaN/GaN基底上形成漏极和源极，与AlGaN层直接接触。
实施例3
本实施例提供一种AlGaN/GaN欧姆接触电极的制备方法，包括以下步骤：
(1)将AlGaN/GaN基底依次使用丙酮超声清洗10min，异丙醇清洗5min，去离子水冲洗15min，氮气吹干。
(2)在AlGaN层上依次进行匀胶、前烘、光刻、显影、后烘的工艺步骤，定义出漏极和源极图形，浸没于HCl:H 2O＝1:4的盐酸溶液中2min以去除基底表面的氧化物，然后用去离子水冲洗5min，最后氮气吹干。
(3)向步骤(2)处理后的样品立即放入离子溅射设备真空传输室内，进行镀膜工艺。Ti 1Al 1合金层采用离子溅射的方式沉积40nm，TiN帽层金属层采用Ti靶在N 2氛围中通过反应离子溅射的方式溅射200nm，然后在二甲基亚砜的60℃水浴中以浸没的方式去除光刻胶及胶上金属。
(4)对剥离后的样品在N 2中加热到850℃，保持60s，得到所述的AlGaN/GaN欧姆接触电极。
实施例4
本实施例提供一种AlGaN/GaN欧姆接触电极的制备方法，包括以下步骤：
(1)将AlGaN/GaN基底依次使用丙酮超声清洗8min，异丙醇清洗10min，去离子水冲洗5min，氮气吹干。
(2)在AlGaN层上依次进行匀胶、前烘、光刻、显影、后烘的工艺步骤，定义出漏极和源极图形，浸没于HCl:H 2O＝1:4的盐酸溶液中3min以去除基底表面的氧化物，然后用去离子水冲洗12min，最后氮气吹干。
(3)向步骤(2)处理后的样品立即放入离子溅射设备真空传输室内，进行镀膜工艺。Ti 1Al 5合金层采用离子溅射方式沉积80nm，W帽层金属层采用W靶在氩气氛围中采用离子溅射的方式溅射100nm，然后在二甲基亚砜的60℃水浴中以浸没的方式去除光刻胶及胶上金属。
(4)对剥离后的样品在NH 3中加热到700℃，保持70s，得到所述的AlGaN/GaN欧姆接触电极。
实施例5
本实施例提供一种AlGaN/GaN欧姆接触电极的制备方法，包括以下步骤：
(1)将AlGaN/GaN基底依次使用丙酮超声清洗5min，异丙醇清洗10min，去离子水冲洗8min，氮气吹干。
(2)在AlGaN层上依次进行匀胶、前烘、光刻、显影、后烘的工艺步骤， 定义出漏极和源极图形，浸没于HCl:H 2O＝1:4的盐酸溶液中4min以去除基底表面的氧化物，然后用去离子水冲洗10min，最后氮气吹干。
(3)向步骤(2)处理后的样品立即放入磁控溅射设备真空传输室内，进行镀膜工艺。Ti 1Al 10合金层采用磁控溅射方式沉积100nm，TiW帽层金属层采用TiW靶在氩气氛围中采用磁控溅射的方式溅射150nm，然后在二甲基亚砜中60℃水浴浸没的方式去除光刻胶及胶上金属。
(4)对剥离后的样品在H 2中加热到1000℃，保持80s，得到所述的AlGaN/GaN欧姆接触电极。
实施例6
与实施例1相比，区别仅在于，将步骤(3)中的Ti 10Al 1合金替换为Ti 3Al 7合金。
实施例7
与实施例1相比，区别仅在于，将步骤(3)中的Ti 10Al 1合金替换为Ti 7Al 3合金。
实施例8
与实施例1相比，区别仅在于，将步骤(3)中Ti 10Al 1合金替换为Ti和Al共溅射，控制Ti:Al原子比为10:1。
对比例1
与实施例1相比，区别仅在于，本对比例提供一种AlGaN/GaN欧姆接触电极，所述电极中采用Ti/Al叠层结构，控制Ti:Al原子比为10:1。
AlGaN/GaN欧姆接触电极性能的评价：
将上述实施例1-8和对比例1制备的欧姆接触电极，进行欧姆圆形传输线模型圆形传输线模型(Circular Transmission Line Model，CTLM)结构测试，测试方法如下：通过四探针测电阻的方式测试电阻并通过拟合得到R c。对CTLM结构中不同尺寸金属环上的电阻进行四探针测量，得到不同的电阻值，对不同尺寸下的电阻值进行线性拟合，得到R c。性能评价标准：将最终的欧姆接触电阻R c作为最终的评价标准。R c越小，在器件中的寄生电阻越小，越有利于最终AlGaN/GaN HEMTs器件的输出特性。其中对于射频器件，R c～0.1Ω·mm更有利于器件的射频特性。使用Ti/Al多层膜方式所得的欧姆接触电阻值一般>0.5Ω·mm，本申请所采用的Ti xAl y合金作为欧姆接触层可实现≤0.2Ω·mm的欧姆接触电阻R c，最低可实现R c～0.1Ω·mm，大大降低欧姆接触电阻值，有利于射频器件的发展。
测试结果如表1所示。
表1
Figure PCTCN2019130351-appb-000001
通过表1可以看出以下几点：
(1)综合实施例1-8可以看出，实施例1-8制备的电极的欧姆接触电阻为0.08-0.2Ω·mm，符合射频器件的制备标准(～0.1Ω·mm)。其中，实施例6的欧姆接触电阻为0.08Ω·mm，远低于其它实施例，由此说明，通过控制Ti xAl y合金层中Ti和Al原子的比例，可以得到更低的欧姆接触电阻值；
(2)综合实施例1和对比例1可以看出，实施例1在AlGaN层上沉积Ti 10Al 1合金层，对应电极的欧姆接触电阻为0.2Ω·mm，而对比例1在AlGaN层上设置Ti/Al叠层结构，对应的欧姆接触电阻为0.6Ω·mm，由此说明，实施例1制备的欧姆接触电极的电阻值低于对比例1，进而说明，采用Ti xAl y合金层直接与AlGaN层接触的欧姆接触电阻，低于常规方法在AlGaN层上设置Ti/Al叠层结构的欧姆接触电阻。
综上，本申请提供的AlGaN/GaN欧姆接触电极，通过采用Ti xAl y合金层与AlGaN层直接接触，降低了所述电极的欧姆接触电阻，符合射频器件的制备标准(～0.1Ω·mm)；同时保持良好的接触表面，提高器件的稳定性以及可靠性，工艺步骤简单可靠，更有利于提高产业化效率。

Claims (18)

  1. 一种铝镓氮/氮化镓AlGaN/GaN欧姆接触电极，所述电极由下而上依次包括AlGaN/GaN基底、帽层金属层和钛铝合金Ti xAl y合金层，其中，x大于0，y大于0。
  2. 根据权利要求1所述的AlGaN/GaN欧姆接触电极，其中，所述Ti xAl y合金层中，x大于0且x小于或等于10，y大于0且y小于或等于10。
  3. 根据权利要求2所述的AlGaN/GaN欧姆接触电极，其中，所述Ti xAl y合金层包括以下至少之一：
    所述Ti xAl y合金层中所述x与所述y的比为1:10-10:1；
    所述Ti xAl y合金层的厚度为20nm-100nm。
  4. 根据权利要求1-3任一项所述的AlGaN/GaN欧姆接触电极，其中，所述帽层金属层包含氮化钛TiN、钨W或钛钨TiW中的任意一种。
  5. 根据权利要求4所述的AlGaN/GaN欧姆接触电极，其中，所述帽层金属层的厚度为20nm-200nm。
  6. 一种铝镓氮/氮化镓AlGaN/GaN欧姆接触电极的制备方法，应用于权利要求1-5任一项所述的AlGaN/GaN欧姆接触电极，所述方法包括：
    采用光刻技术在AlGaN/GaN基底上定义漏极和源极的至少一种图形，在AlGaN层表面依次沉积Ti xAl y合金层和帽层金属层，去除光刻胶，进行剥离处理得到剥离后的样品；
    对剥离后的样品进行热处理，得到所述AlGaN/GaN欧姆接触电极。
  7. 根据权利要求6所述的制备方法，其中，所述沉积Ti xAl y合金层采用以下至少之一：Ti xAl y合金靶材和Ti与Al两种金属靶材。
  8. 根据权利要求7所述的制备方法，其中，所述Ti xAl y合金层为Ti xAl y合金靶材所制备，其中，x＞0，y＞0。
  9. 根据权利要求6所述的制备方法，其中，
    所述Ti xAl y合金层中，0＜x≤10，0＜y≤10。
  10. 根据权利要求8所述的制备方法，其中，所述方法包括以下至少之一：
    所述Ti xAl y合金靶材中x与y的比为1:10-10:1；
    所述Ti xAl y合金层的厚度为20-100nm；
    所述帽层金属层包含氮化钛TiN、钨W或钛钨TiW中的任意一种；
    所述帽层金属层的厚度为20-200nm。
  11. 根据权利要求6所述的制备方法，其中，所述采用光刻技术在AlGaN/GaN基底上定义漏极和源极的至少一种图形，包括：依次进行匀胶、前烘、光刻、显影、后烘的工艺步骤得到。
  12. 根据权利要求6-10任一项所述的制备方法，其中，所述沉积的方式包含磁控溅射和离子溅射中的至少一种。
  13. 根据权利要求12所述的制备方法，其中，所述方法包括以下至少之一：
    所述沉积的方式为磁控溅射；
    所述沉积Ti xAl y合金层的气体为氩气Ar；
    所述沉积帽层金属层的气体为Ar或氮气N 2。
  14. 根据权利要求6所述的制备方法，其中，所述热处理的气体为N 2、氨气NH 3、氢气H 2或Ar中的任意一种或至少两种的组合。
  15. 根据权利要求14所述的制备方法，所述热处理包括以下至少之一：
    所述热处理的温度为700-1000℃；
    所述热处理的时间为20-80s。
  16. 根据权利要求6-15任一项所述的制备方法，包括以下步骤：
    对AlGaN/GaN基底进行洗涤，氮气吹干；
    在AlGaN层上依次进行匀胶、前烘、光刻、显影、后烘的工艺步骤，定义出漏极和源极的至少一种图形，浸入稀盐酸中清洗，用去离子水冲洗，氮气吹干得到处理后的样品；
    向处理后的样品表面依次沉积20nm-100nm的Ti xAl y合金层和20-200nm的帽层金属层，去除光刻胶，进行剥离处理得到剥离后的样品；
    对剥离后的样品在气氛中加热到700℃-1000℃，保持20s-80s，得到所述AlGaN/GaN欧姆接触电极；
    其中，所述气氛的气体包含N 2、NH 3、H 2或Ar中的任意一种或至少两种的组合。
  17. 一种降低铝镓氮/氮化镓AlGaN/GaN基底与电极之间欧姆接触的方法，所述方法包括：在AlGaN/GaN基底表面沉积Ti xAl y合金层作为电极。
  18. 根据权利要求17所述的方法，所述方法包括以下至少之一：
    所述Ti xAl y合金层中x与y的比为1:10-10:1；
    所述Ti xAl y合金层的厚度为20-100nm；
    所述沉积的方式包含如下至少之一：磁控溅射和离子溅射。
PCT/CN2019/130351 2019-11-12 2019-12-31 AlGaN/GaN欧姆接触电极及其制备方法和降低欧姆接触的方法 WO2021093127A1 (zh)

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CN111710650B (zh) * 2020-08-20 2020-11-20 浙江集迈科微电子有限公司 基于双沟道栅的GaN器件及其制备方法
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