阅读说明：本技术 一种GaN基肖特基二极管及其制备方法 (GaN-based Schottky diode and preparation method thereof ) 是由 王登贵 周建军 陈韬 孔岑 孔月婵 陈堂胜 于 2020-04-28 设计创作，主要内容包括：本发明涉及一种GaN基肖特基二极管及其制备方法,属于半导体器件技术领域。GaN基肖特基二极管包括衬底、缓冲层、沟道层、势垒层、p-GaN帽层、绝缘介质、电极以及钝化层。所述电极中阴极是在势垒层上沉积低功函数金属并退火而形成的欧姆接触,所述电极中阳极指金属-绝缘层-半导体(MIS)栅控结构中的高功函数金属与后沉积的低功函数金属共同组成的混合阳极结构。本发明基于高功函数金属/绝缘介质/p-GaN的MIS栅控结构与高功函数金属/低功函数金属的混合阳极结构,不仅能够有效减小并调控器件的正向开启电压,降低导通电阻,而且可进一步改善器件的反向漏电,提高反向击穿电压。(The invention relates to a GaN-based Schottky diode and a preparation method thereof, belonging to the technical field of semiconductor devices. The GaN-based Schottky diode comprises a substrate, a buffer layer, a channel layer, a barrier layer, a p-GaN cap layer, an insulating medium, an electrode and a passivation layer. The cathode in the electrode is ohmic contact formed by depositing low work function metal on the barrier layer and annealing, and the anode in the electrode refers to a mixed anode structure formed by high work function metal in a metal-insulating layer-semiconductor (MIS) gate control structure and low work function metal deposited later. The invention is based on the MIS gate control structure of high work function metal/insulating medium/p-GaN and the mixed anode structure of high work function metal/low work function metal, which not only can effectively reduce and regulate the forward starting voltage of the device and reduce the on-resistance, but also can further improve the reverse leakage of the device and improve the reverse breakdown voltage.)

1. A GaN-based schottky diode, characterized by: the device comprises a substrate (1), a buffer layer (2), a channel layer (3), a barrier layer (4), a p-GaN cap layer (5), an insulating medium (6), a first anode metal (7), a second anode metal (8), a cathode metal (9) and a passivation layer (10); the structure of the Schottky diode sequentially comprises a substrate (1), a buffer layer (2), a channel layer (3), a barrier layer (4) and a p-GaN cap layer (5) from bottom to top, a p-GaN-based MIS gate control structure, a mixed anode structure and a cathode structure are arranged above the barrier layer (4), the p-GaN-based MIS gate control structure comprises the p-GaN cap layer (5), an insulating medium (6) and first anode metal (7), the mixed anode structure comprises the first anode metal (7) and second anode metal (8), the first anode metal (7) is high-work-function metal and is positioned on the upper part of the insulating medium (6) to form the MIS gate control structure with the p-GaN cap layer (5), the second anode metal (8) is low-work-function metal, and one part of the second anode metal covers the first anode metal (7) to form a field plate structure, the other part of the cathode metal (9) covers the barrier layer (4) to form ohmic contact, the cathode metal is formed by depositing metal on the barrier layer (4) and annealing the metal, the passivation layer (10) covers the surface of the barrier layer (4), and a window is formed in the position corresponding to the electrode.

2. The GaN-based schottky diode of claim 1 wherein: the substrate (1) is any one of SiC, Si, sapphire, diamond and GaN self-supporting substrates; the buffer layer (2) is of a single-layer or multi-layer structure consisting of one or more of AlN, AlGaN and GaN materials; the channel layer (3) is one of GaN, AlN and AlGaN; the barrier layer (4) is one of AlGaN, AlInN, AlN and AlInGaN.

3. The GaN-based schottky diode of claim 1 wherein: the insulating medium (6) is HfO₂、ZrO₂、Si₃N₄、SiO₂、Al₂O₃And AlON, the total thickness is 1-100 nm.

4. The GaN-based schottky diode of claim 1 wherein: the low work function metal is one of Ti, Al and Ti-Au alloy; the high work function metal is one of W, Ni, Pt and TiN.

5. The GaN-based schottky diode of claim 1 wherein: the cathode metal (9) is one of Ti-Al alloy, Ti-Al-Ti-Au alloy, Ti-Al-Ni-Au alloy and Ti-Al-Mo-Au alloy.

6. The GaN-based schottky diode of claim 1 wherein: the passivation layer (10) is SiO₂、Si₃N₄、Al₂O₃One or more of the media.

7. A preparation method of a GaN-based Schottky diode is characterized by comprising the following steps: the method comprises the following specific steps:

1) sequentially growing a buffer layer (2), a channel layer (3), a barrier layer (4) and a p-GaN epitaxial layer above a substrate (1) by using an epitaxial growth method;

2) defining a mask of a p-GaN cap layer (5) above the p-GaN epitaxial layer, and then forming the p-GaN cap layer (5) by an etching method;

3) growing an insulating medium (6) above the barrier layer (4) and the p-GaN cap layer (5);

4) defining a mask of first anode metal (7) above the insulating medium (6), depositing high-work-function metal by an evaporation or sputtering mode, and forming the first anode metal (7) by a stripping process so as to form an MIS gate control structure of the first anode metal (7), the insulating medium (6) and the p-GaN cap layer (5);

5) defining an opening mask of a second anode metal (8) and a cathode metal (9) above the insulating medium (6), and etching the insulating medium (6) by an etching method to form an opening;

6) defining a mask of a second anode metal (8) above the barrier layer (4), depositing a low work function metal by an evaporation or sputtering mode, and forming the second anode metal (8) by a stripping process so as to form a mixed anode structure of the first anode metal (7) and the second anode metal (8);

7) defining a mask of cathode metal (9) above the barrier layer (4), depositing the cathode metal (9) by an evaporation or sputtering mode, forming the cathode metal (9) by a stripping process, and forming ohmic contact by an annealing process;

8) an active area mask is manufactured above the barrier layer (4), and then an active area is formed by adopting an etching or ion implantation mode for isolation;

9) depositing a passivation layer (10) over the barrier layer (4), the second anode metal (8) and the cathode metal (9);

10) and defining an interconnection opening area mask above the second anode metal (8) and the cathode metal (9), and etching the passivation layer (10) by a dry etching method and a wet etching method to form interconnection openings.

8. The method of claim 7, wherein the GaN-based Schottky diode comprises: the epitaxial growth method in the step 1) comprises metal organic chemical vapor deposition, molecular beam epitaxy and hydride vapor phase epitaxy.

9. The method of claim 7, wherein the GaN-based Schottky diode comprises: the mask in the step 2) is manufactured in an optical lithography or electron beam direct writing mode.

10. The method of claim 7, wherein the GaN-based Schottky diode comprises: the growth method of the insulating medium in the step 3) comprises low-pressure chemical vapor deposition, plasma enhanced chemical vapor deposition and atomic layer deposition.

Technical Field

The invention relates to a GaN-based Schottky diode and a preparation method thereof, belonging to the technical field of semiconductor devices.

Background

The third generation semiconductor GaN material has excellent characteristics of wide band gap, high breakdown field strength, high saturated electron drift velocity, high-concentration heterojunction two-dimensional electron gas and the like, is an optimal structure for preparing high-power, high-breakdown-voltage and high-frequency power electronic devices, and has important application prospects in the fields of wireless communication, power systems, detection and the like.

In recent years, diode devices based on GaN heterojunction have been greatly advanced, and are widely used in structures such as rectifier circuits, inverter bridges, and switching voltage regulator circuits. How to reduce the forward starting voltage of the diode without influencing the reverse leakage current is the key point of the application research of the high-power switch. A commonly used means of reducing the diode turn-on voltage is by lowering the schottky contact barrier by selecting a low work function metal. However, while the diode on-voltage is effectively reduced, the schottky barrier is lowered, so that the current blocking effect of the diode in the reverse state is deteriorated, and the reverse leakage is increased.

The Cheng university of Zhongshan L iu and the like combine a high-low work function metal layer with a groove structure to realize the reduction of the starting voltage and the relative increase of the reverse breakdown voltage, however, the fluorine ion injection technology can introduce fluorine ions into a barrier layer, thereby causing the device to have a serious working reliability problem, the groove technology corresponding to the thinning of the barrier layer not only has the problem of high etching depth and etching uniformity requirement, but also has the problem of low interface state medium preparation, and the technology is relatively complex.

Disclosure of Invention

In view of the above technical problems, the present invention provides a GaN-based schottky diode and a method for manufacturing the same, which has the characteristics of low turn-on voltage, low on-resistance and high reverse breakdown voltage.

The invention adopts the following technical scheme for solving the technical problems:

a GaN-based Schottky diode comprises a substrate 1, a buffer layer 2, a channel layer 3, a barrier layer 4, a p-GaN cap layer 5, an insulating medium 6, a first anode metal 7, a second anode metal 8, a cathode metal 9 and a passivation layer 10; the structure of the Schottky diode comprises a substrate 1, a buffer layer 2, a channel layer 3, a barrier layer 4 and a p-GaN cap layer 5 from bottom to top in sequence, wherein a p-GaN-based MIS gate control structure, a mixed anode structure and a cathode structure are arranged above the barrier layer 4, the p-GaN-based MIS gate control structure comprises the p-GaN cap layer 5, an insulating medium 6 and a first anode metal 7, the mixed anode structure comprises the first anode metal 7 and a second anode metal 8, the first anode metal 7 is a high work function metal and is positioned on the upper part of the insulating medium 6, the MIS gate control structure is formed among the p-GaN cap layer 5, the second anode metal 8 is a low work function metal, one part of a field plate covers the first anode metal 7 to form a field plate structure, the other part of the field plate covers the barrier layer 4 to form ohmic contact, the cathode metal 9 is formed by depositing metal on the barrier layer 4 and annealing, the passivation layer 10 covers the surface of the barrier layer 4 and is provided with a window at a position corresponding to the electrode.

The substrate 1 is any one of SiC, Si, sapphire, diamond and GaN self-supporting substrates; the buffer layer 2 is a single-layer or multi-layer structure composed of one or more of AlN, AlGaN and GaN materials; the channel layer (3) is one of GaN, AlN and AlGaN; the barrier layer 4 is one of AlGaN, AlInN, AlN, and AlInGaN.

The insulating medium 6 is HfO₂、ZrO₂、Si₃N₄、SiO₂、Al₂O₃And AlON, the total thickness is 1-100 nm.

The low work function metal is one of Ti, Al and Ti-Au alloy; the high work function metal is one of W, Ni, Pt and TiN.

The cathode metal 9 is one of Ti-Al alloy, Ti-Al-Ti-Au alloy, Ti-Al-Ni-Au alloy and Ti-Al-Mo-Au alloy.

The passivation layer 10 is SiO₂、Si₃N₄、Al₂O₃One or more of the media.

A preparation method of a GaN-based Schottky diode comprises the following specific steps:

1) sequentially growing a buffer layer 2, a channel layer 3, a barrier layer 4 and a p-GaN epitaxial layer above a substrate 1 by an epitaxial growth method;

2) defining a mask of a p-GaN cap layer 5 above the p-GaN epitaxial layer, and then forming the p-GaN cap layer 5 by an etching method;

3) growing an insulating medium 6 above the barrier layer 4 and the p-GaN cap layer 5;

4) defining a mask of a first anode metal 7 above the insulating medium 6, depositing a high-work-function metal by an evaporation or sputtering mode, and forming the first anode metal 7 by a stripping process so as to form an MIS gate control structure of the first anode metal 7, the insulating medium 6 and the p-GaN cap layer 5;

5) defining an opening mask of a second anode metal 8 and a cathode metal 9 above the insulating medium 6, and etching the insulating medium 6 by an etching method to form an opening;

6) defining a mask of a second anode metal 8 above the barrier layer 4, depositing a low work function metal by an evaporation or sputtering mode, and forming the second anode metal 8 by a stripping process, thereby forming a mixed anode structure of the first anode metal 7 and the second anode metal 8;

7) defining a mask of cathode metal 9 above the barrier layer 4, depositing the cathode metal 9 by an evaporation or sputtering mode, forming the cathode metal 9 by a stripping process, and forming ohmic contact by an annealing process;

8) an active area mask is manufactured above the barrier layer 4, and then, an etching or ion implantation mode is adopted for isolation to form an active area;

9) depositing a passivation layer 10 over the barrier layer 4, the second anode metal 8 and the cathode metal 9;

10) and defining an interconnection opening area mask above the second anode metal 8 and the cathode metal 9, and etching the passivation layer 10 by a dry etching method and a wet etching method to form interconnection openings.

The epitaxial growth method in the step 1) comprises metal organic chemical vapor deposition, molecular beam epitaxy and hydride vapor phase epitaxy.

The mask in the step 2) is manufactured in an optical lithography or electron beam direct writing mode.

The growth method of the insulating medium in the step 3) comprises low-pressure chemical vapor deposition, plasma enhanced chemical vapor deposition and atomic layer deposition.

The invention has the following beneficial effects:

(1) under forward bias, the MIS (metal-insulator-semiconductor) grid control structure formed by the first anode metal, the insulating medium and the p-GaN can realize the opening of two-dimensional electron gas in the channel layer, and the reduction and regulation of forward opening voltage can be realized by adjusting the doping concentration of the p-GaN; meanwhile, after the two-dimensional electron gas channel in the device is opened, the mixed anode structure can realize that the current flows into the channel layer through the low-work-function metal electrode, and the on-resistance is reduced.

(2) Under reverse bias, the MIS gate control structure formed by the first anode metal, the insulating medium and the p-GaN can effectively reduce the reverse leakage current of the diode; meanwhile, the field plate structure formed by the second anode metal can improve the electric field distribution at the p-GaN region, and the reverse breakdown voltage characteristic of the device is remarkably improved.

(3) The p-GaN structure is utilized to realize the opening and closing of the two-dimensional electron gas in the channel layer, compared with the reported fluorine ion injection technology and groove technology, the method has higher process controllability, effectively reduces the crystal lattice damage or interface state introduction of the barrier layer, and improves the working reliability of the device.

Drawings

Fig. 1 is a schematic structural diagram of a GaN-based schottky diode according to the present invention.

FIG. 2(a) is a step of epitaxial growth of a GaN-based Schottky diode according to the present invention; FIG. 2(b) is a step of fabricating a p-GaN gate cap of a GaN-based Schottky diode according to the present invention; FIG. 2(c) is a MIS gate control fabrication step of a GaN-based Schottky diode according to the present invention; FIG. 2(d) is a step of fabricating a hybrid anode of a GaN-based Schottky diode according to the present invention; FIG. 2(e) is a step of fabricating a cathode of a GaN-based Schottky diode according to the present invention; fig. 2(f) shows a step of fabricating a passivation layer of a GaN-based schottky diode according to the present invention.

Wherein: 1. a substrate; 2. a buffer layer; 3. a channel layer; 4. a barrier layer; 5. a p-GaN cap layer; 6. an insulating medium; 7. a first anode metal; 8. a second anode metal; 9. a cathode metal; 10. and a passivation layer.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention are further described below with reference to the accompanying drawings and examples.

Fig. 1 is a schematic structural diagram of a GaN-based schottky diode according to the present invention, which includes a substrate 1, a buffer layer 2, a channel layer 3, a barrier layer 4, a p-GaN cap layer 5, an insulating medium 6, a first anode metal 7, a second anode metal 8, a cathode metal 9, and a passivation layer 10; the diode structure sequentially comprises a substrate 1, a buffer layer 2, a channel layer 3, a barrier layer 4 and a p-GaN cap layer 5 from bottom to top, a p-GaN-based MIS gate control structure, a mixed anode structure and a cathode structure are arranged above the barrier layer 4, the p-GaN-based MIS gate control structure comprises the p-GaN cap layer 5, an insulating medium 6 and a first anode metal 7, the first anode metal 7 is a high work function metal and is positioned on the upper part of the insulating medium 6, the MIS gate control structure is formed among the first anode metal 7 and the insulating medium 6, the mixed anode structure comprises the first anode metal 7 and a second anode metal 8, the second anode metal 8 is a low work function metal, one part of the mixed anode metal covers the first anode metal 7 to form a field plate structure, the other part of the mixed anode metal covers the barrier layer 4 to form ohmic contact, the cathode metal 9 is ohmic contact formed by depositing metal on the barrier, the passivation layer 10 covers the surface of the barrier layer 4, and a window is opened at a position corresponding to the electrode so as to be electrically contacted with the outside.

Referring to fig. 2, the method for preparing the GaN-based schottky diode provided by the invention comprises the following specific steps:

1) sequentially growing a buffer layer 2, a channel layer 3, a barrier layer 4 and a p-GaN epitaxy 5 over a substrate 1 by an epitaxial growth method, as shown in FIG. 2 (a); wherein the substrate 1 is any one of SiC, Si, sapphire, diamond and GaN self-supporting substrate; the buffer layer 2 is a single-layer or multi-layer structure composed of one or more of AlN, AlGaN and GaN materials; the channel layer 3 is one of GaN, AlN and AlGaN; the barrier layer 4 is one of AlGaN, AlInN, AlN, and AlInGaN. Epitaxial growth methods include MOCVD (metal organic chemical vapor deposition), MBE (molecular beam epitaxy), and HVPE (hydride vapor phase epitaxy).

2) A mask of the p-GaN cap layer 5 is defined above the p-GaN epitaxial layer, and then the p-GaN cap layer 5 shown in fig. 2(b) is formed by an etching method including dry etching and wet etching.

3) Growing an insulating medium 6 above the barrier layer 4 and the p-GaN cap layer 5, defining a mask of a first anode metal 7, depositing a high work function metal by an evaporation or sputtering mode, and forming the first anode metal 7 by a stripping process, thereby forming an MIS gate control structure of the first anode metal 7, the insulating medium 6 and the p-GaN cap layer 5 as shown in figure 2(c), wherein the growing method of the insulating medium comprises L PCVD (low pressure chemical vapor deposition), PECVD (plasma enhanced chemical vapor deposition) and A L D (atomic layer epitaxy), the high work function metal is one of W, Ni, Pt and TiN, and the insulating medium is HfO₂、ZrO₂、Si₃N₄、SiO₂、Al₂O₃And AlON, the total thickness is 1-100 nm.

4) And defining an opening mask of the second anode metal 8 and the cathode metal 9 above the insulating medium 6, and etching the insulating medium by an etching method to form an opening.

5) Defining a mask of a second anode metal 8 above the barrier layer 4, depositing a low work function metal by evaporation or sputtering, and forming the second anode metal 8 by a stripping process, as shown in fig. 2 (d); the low work function metal is one of Ti, Al and Ti-Au alloy.

6) Defining a mask of cathode metal 9 above the barrier layer 4, depositing the cathode metal 9 by evaporation or sputtering, forming the cathode metal 9 by lift-off process, and forming ohmic contact by annealing process, as shown in fig. 2 (e); the cathode metal 9 is one of Ti-Al alloy, Ti-Al-Ti-Au alloy, Ti-Al-Ni-Au alloy and Ti-Al-Mo-Au alloy.

7) An active area mask is manufactured above the barrier layer 4, and then, an etching or ion implantation mode is adopted for isolation to form an active area;

8) depositing a passivation layer 10 above the barrier layer 4, the second anode metal 8 and the cathode metal 9, defining an interconnection opening area mask above the second anode metal 8 and the cathode metal 9, and etching the passivation layer 10 by an etching method to form an interconnection opening, as shown in fig. 2(f), thereby completing the preparation of the diode device; the passivation layer 10 is SiO₂、Si₃N₄、Al₂O₃One or more of the media.

Up to this point, the present embodiment has been described in detail with reference to the accompanying drawings. From the above description, those skilled in the art should clearly understand "a GaN-based schottky diode and a method for manufacturing the same" in the present invention. The invention combines the p-GaN-based MIS gate control structure and the mixed anode structure, not only can reduce the forward starting voltage and the on-resistance of the diode, but also can effectively reduce the reverse leakage of the device and improve the reverse breakdown voltage, and has simple preparation process and strong controllability.

It is to be noted that, in the attached drawings or in the description, the implementation modes not shown or described are all the modes known by the ordinary skilled person in the field of technology, and are not described in detail. Furthermore, the above definitions of the various elements and methods are not limited to the particular structures, shapes or arrangements of parts mentioned in the examples, which may be easily modified or substituted by one of ordinary skill in the art, for example:

(1) the p-GaN cap layer can be replaced by a p-AlGaN cap layer;

(2) the second anodic metal and the cathodic metal can be replaced by the same ohmic metal or alloy by simultaneous sputtering or evaporation.

It should also be noted that the present invention may provide exemplary for parameters that include particular values, but these parameters need not be exactly equal to the corresponding values, but may be approximated to the corresponding values within acceptable error tolerances or design constraints. Directional phrases used in the embodiments, such as "upper", "lower", "front", "rear", "left", "right", etc., refer only to the direction of the attached drawings and are not intended to limit the scope of the present invention. In addition, unless steps are specifically described or must occur in sequence, the order of the steps is not limited to that listed above and may be changed or rearranged as desired by the desired design. The embodiments described above may be mixed and matched with each other or with other embodiments based on design and reliability considerations, i.e., technical features in different embodiments may be freely combined to form further embodiments.

The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention, and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.