A high-power, low-loss AlN diode and its fabrication method

Abstract

This invention discloses a high-power, low-loss AlN diode and its fabrication method. The diode comprises a substrate layer (6), an AlN buffer layer (5), an n-AlN layer (4), and a p-type AlN layer (5). ‑ NiO x Layer (3), anode metal layer (1), cathode metal layer (2) and passivation layer (7), wherein p-NiO x Layer (3) and n-AlN layer (4) form p-NiO x An / n-AlN heterojunction is constructed, with a junction termination structure set in the anode edge region. AlN possesses extremely high critical breakdown field strength and high thermal conductivity. This invention utilizes p... ‑ NiO x The enhanced bandgap of the n-AlN heterojunction strongly blocks the reverse drift of electrons, suppressing the drift current of the AlN diode under reverse bias; simultaneously, the groove structure and p-NiO x The lateral extensions of the layers collectively form the junction termination structure, which smoothly expands the depletion region at the anode edge, suppresses electric field accumulation at the anode edge, reduces the electric field peak value, and thus improves the reverse breakdown voltage of the diode. The AlN diode of this invention simultaneously possesses low leakage current and high withstand voltage performance, making it suitable for high-voltage, low-loss power rectification applications.

Description

Technical Field

[0001] This invention relates to the field of semiconductor power device technology, specifically to a high-performance AlN diode and its fabrication method, which combines high breakdown voltage and low leakage current characteristics. Background Technology

[0002] As power electronics technology advances towards higher frequencies, higher power, and lower power consumption, higher demands are placed on the voltage withstand capability, leakage current control capability, and thermal stability of power rectifier devices. Aluminum nitride (AlN), as an ultra-wide bandgap semiconductor material, possesses a bandgap of approximately 6.2 eV, extremely high critical breakdown field strength, and good thermal conductivity, making it highly promising for applications under high voltage, low loss, and high-temperature operating conditions. Compared to traditional silicon-based materials and some wide bandgap semiconductor materials (such as GaN and SiC), AlN is expected to achieve lower intrinsic carrier concentration, higher reverse breakdown voltage, and superior heat dissipation performance, thus showing promising application prospects in the field of high-power diodes. AlN diodes are expected to achieve lower reverse leakage current, higher reverse blocking voltage, and better high-temperature stability in high-voltage rectification applications. However, the fabrication of p-type AlN material is extremely difficult, making it impossible to realize rectifier devices based on AlN pn junctions. Due to the high trap state density in AlN materials, AlN diodes exhibit a large reverse leakage current under reverse bias. Electrons may form leakage channels through depletion region defects, material defects, or surface states, increasing reverse losses and reducing rectification performance.

[0003] NiO X As an ultrawide bandgap semiconductor material with intrinsic p-type conductivity, it can be deposited on the surface of n-AlN using processes such as magnetron sputtering. p-NiO X / n-AlN can form a typical interleaved pn heterojunction, possessing moderate conduction and valence band steps at the interface, providing a feasible solution for realizing high-power, low-power AlN diodes. Through reasonable design of p-NiO... X / n-AlN heterojunctions can utilize interface band shift to weaken the drift current of reverse electrons in the junction region, thereby helping to reduce the reverse leakage current of the diode and improve rectification performance.

[0004] Furthermore, under reverse bias, based on p-NiO XThe AlN diode formed by the / n-AlN heterojunction still suffers from a severe electric field concentration effect at the anode edge, and this local peak electric field limits further improvement in the reverse breakdown voltage of the AlN diode. To address this issue, although a metal field plate can reduce the peak electric field by controlling the electric field distribution, this structure introduces additional parasitic capacitance, increasing the junction capacitance and affecting the high-frequency switching applications of the AlN diode. The junction termination structure can more efficiently modulate the electric field distribution at the anode edge without introducing additional parasitic capacitance, enabling the AlN junction-terminated diode to have a higher reverse breakdown voltage. Therefore, this patent is based on p-NiO... X A novel AlN junction terminating diode with high voltage withstand capability and low power consumption is proposed for the / n-AlN heterojunction. Summary of the Invention

[0005] This invention proposes a novel AlN junction-terminated diode and its fabrication method. This device is based on ultra-wide bandgap AlN and utilizes p-NiO. X The / n-AlN structure realizes an interleaved pn junction and has a junction termination structure. This device features low reverse leakage current, high reverse breakdown voltage, low parasitic capacitance, good high-frequency switching adaptability, and excellent thermal stability, making it suitable for high-voltage, high-frequency, and low-power power electronics applications.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] The core idea of ​​this invention is to construct grooves on the surface of the n-AlN layer and introduce p-NiO into the groove region. X The layer is formed to create a heterojunction with the n-AlN layer. Figures 3a to 3c show the p-NiO layer of the device under thermal equilibrium, forward bias, and reverse bias. X A schematic diagram of the band structure and carrier transport in an n-AlN heterojunction. This invention utilizes the band shift at the heterojunction interface under reverse bias to suppress the transport of reverse electrons, thereby reducing leakage current. Simultaneously, p-NiO extending laterally from the n-AlN layer surface towards the cathode is retained outside the groove. X The layers form a junction terminal structure, which together regulate the surface potential and electric field distribution near the anode edge, thereby alleviating the local electric field concentration at the anode edge and improving the reverse breakdown capability and stability of the diode.

[0008] Based on the above ideas, the present invention provides an AlN heterojunction diode structure, comprising, from bottom to top, a substrate layer (6), an AlN buffer layer (5), an n-AlN layer (4), and a p-NiO layer. X The n-AlN layer comprises a 3-layer anode metal layer (1), a 2-layer cathode metal layer (2), and a passivation layer (7); the upper surface of the n-AlN layer is provided with a groove, and p-NiO is disposed in the groove. X Layer. The p-NiOX The layer comprises a first portion located within a groove and a second portion located on the surface of the n-AlN layer, wherein the first portion forms p-NiO with the n-AlN layer. X The n-AlN heterojunction, the second portion extends laterally from the groove opening along the surface of the n-AlN layer towards the cathode to form a junction termination structure. The p-NiO X An anode metal layer is disposed above the n-AlN layer, and cathode metal layers are disposed on both sides of the surface of the n-AlN layer. A passivation layer covers the surface of the diode structure, and the passivation layer at least covers the anode edge region and the p-NiO layer. X The second part of the layer is located in the region to reduce the influence of surface states and improve the edge electric field distribution.

[0009] In some embodiments of the present invention, the substrate layer may be made of sapphire, silicon carbide, silicon, or aluminum nitride. The associated AlN buffer layer is used to improve the epitaxial quality of the upper layer and provide a growth base for the n-AlN layer. Preferably, the AlN buffer layer has a thickness of 300–500 nm, and the n-AlN layer has a thickness of 50–200 nm. The passivation layer may be formed using silicon nitride, silicon dioxide, or a high-dielectric-constant dielectric material, wherein the high-dielectric-constant dielectric may be hafnium oxide. Preferably, the passivation layer has a thickness of 20–500 nm.

[0010] The upper surface of the n-AlN layer has grooves formed therein, the depth of which is 0 to the full thickness of the n-AlN layer; the p-NiO X The layer includes a first portion located within the groove and a second portion located on the upper surface of the n-AlN layer. The second portion is located in the corresponding region of the anode metal layer, and its thickness is 0 to the height of the bottom of the anode metal layer. The second portion also extends from the opening of the groove along the upper surface of the n-AlN layer towards the cathode, with an extension length of 0 to the location of the cathode metal layer. The p-NiO X The second part of the layer constitutes the junction termination structure of the device. This is achieved by adjusting the groove depth and p-NiO... X The thickness and lateral extension length of the second part of the layer are matched and set to meet the requirements of p-NiO. X The / n-AlN heterostructure optimizes the potential and electric field distribution in the anode edge region while meeting the requirements, thereby alleviating the phenomenon of local electric field concentration and improving the reverse withstand voltage performance of the diode while reducing the reverse leakage current.

[0011] p-NiO located in the groove X The first part of the layer forms an interleaved Type-II p-NiO layer with the n-AlN layer. X / n-AlN heterojunction. Further, the p-NiO XThe layer can have a three-level acceptor concentration distribution along the vertical direction, consisting of light doping, heavy doping, and light doping, specifically including the first lightly doped p-NiO near the n-AlN layer. X The second doped p-NiO layer in the middle X The third lightly doped p-NiO layer and the layer near the anode metal layer X Layer. The light doping concentration can range from 10. 16 ~10 17 cm -3 The heavy doping concentration range can be 10. 17 ~10 18 cm -3 This doping distribution is beneficial for balancing the heterojunction interface barrier modulation and carrier transport characteristics.

[0012] The diode structure may further include a heat dissipation enhancement structure. The anode metal layer and cathode metal layer may be thickened, with a thickness of 1–5 μm, to assist in dissipating heat generated in the active region of the device. Furthermore, an auxiliary heat dissipation film layer may be provided above the passivation layer, with a thickness of 50–200 nm, preferably a diamond-like carbon film, to further improve the heat dissipation capability and thermal stability of the device.

[0013] The anode metal layer may be made of one or more materials selected from Ni, Ti, Al, Au, W, Cr, Ta, Mo, or TiN; the cathode metal layer may be made of one or more materials selected from Ni, Ti, Al, Au, TiN, W, Ta, Pt, or Pd. The p-NiO X The layer can be formed through processes such as magnetron sputtering to avoid the difficulty of p-type doping in AlN materials and to facilitate the realization of device structures.

[0014] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0015] This invention realizes a diode structure based on AlN ultrawide bandgap semiconductor material. AlN has a large bandgap, high critical breakdown field strength, and good thermal conductivity. Therefore, compared with existing power diodes, the AlN diode proposed in this invention has higher reverse breakdown voltage potential and better thermal stability, making it more suitable for high-voltage, high-temperature, and low-loss power electronics applications.

[0016] This invention proposes an AlN diode based on p-NiO X The p-n-AlN heterojunction was achieved, overcoming the difficulty in fabricating p-type AlN materials and realizing a high-quality interleaved pn junction with adjustable conduction and valence band orders. Under reverse bias, p-NiO XThe enhanced bandgap effect of the n-AlN heterojunction strongly blocks the reverse drift of electrons, suppressing the drift current of the AlN diode under reverse bias, reducing the reverse leakage current, and improving the rectification performance of the device. Figures 3a to 3c show the p-NiO diode under thermal equilibrium, forward bias, and reverse bias conditions. X Schematic diagram of the band structure and carrier transport in an n-AlN heterojunction.

[0017] The AlN diode proposed in this invention features a junction termination structure. This structure modulates the surface potential and electric field distribution near the anode edge, reducing local peak electric field and mitigating electric field concentration at the anode edge, thereby effectively improving the reverse breakdown voltage and operational stability of the device. Compared to structures using metal field plates, the junction termination structure employed in this invention eliminates the need for additional parasitic capacitance introduced by metal-dielectric coupling. Therefore, while improving withstand voltage, it is more advantageous for applications under high-frequency switching conditions.

[0018] This invention involves creating grooves on the surface of an n-AlN layer and forming p-NiO within the grooves. X The / n-AlN heterojunction utilizes the band difference at the heterojunction interface to enhance the blocking effect on reverse charge carriers. Figure 3 shows the p-NiO device of the present invention under thermal equilibrium, forward bias, and reverse bias. X A schematic diagram of the band structure and carrier transport in an n-AlN heterojunction. This invention utilizes the band shift at the heterojunction interface under reverse bias to suppress the transport of reverse electrons, thereby reducing leakage current. Simultaneously, this invention retains p-NiO extending laterally from the n-AlN layer surface towards the cathode outside the groove. X The second part of the layer forms a junction termination structure, which, together with the surface passivation layer, regulates the surface potential and electric field distribution near the anode edge. This helps reduce the local peak electric field and alleviate the electric field concentration phenomenon at the anode edge, thereby improving the reverse breakdown capability and operational stability of the device. Compared with AlN diodes with a metal field plate, this invention enables a smoother expansion of the depletion region at the diode edge, reducing the risk of premature breakdown at the anode edge, thus achieving both low leakage current and high withstand voltage performance. Figures 7a and 7b compare the breakdown characteristics of the device of this invention with, without, and with junction termination in three structures.

[0019] Furthermore, this invention is compatible with a variety of substrate materials such as sapphire, silicon carbide, silicon, and aluminum nitride, and p-NiO X The layer can be formed through processes such as magnetron sputtering, which is beneficial for expanding the fabrication conditions and application scenarios of the device, and provides a foundation for subsequent structural optimization and large-scale fabrication. Attached Figure Description

[0020] The accompanying drawings, which are included to provide a further understanding of the embodiments of the present invention and form part of this application, are not intended to limit the embodiments of the present invention.

[0021] Figure 1 This is a non-limiting structural schematic diagram of an AlN heterojunction diode with high breakdown voltage and low leakage current characteristics provided in Embodiment 1 of the present invention;

[0022] Figures 2(a) to 2(f) This is a schematic diagram of the process flow of an AlN heterojunction diode with high breakdown voltage and low leakage current characteristics provided in Embodiment 1 of the present invention.

[0023] Figures 3(a) to 3(c) The device of this invention operates under thermal equilibrium, forward bias, and reverse bias conditions in p-NiO X Schematic diagram of the band structure and carrier transport of / n-AlN heterojunction;

[0024] Figure 4 This is a schematic diagram of the device structure in Embodiment 2 of the present invention;

[0025] Figure 5 This is a schematic diagram of the device structure in Embodiment 3 of the present invention;

[0026] Figure 6 This is a schematic diagram of the device structure in Embodiment 4 of the present invention;

[0027] Figures 7(a) to 7(b) This is a comparison of the breakdown characteristics of the device of the present invention under three structures: with field plate, without field plate, and with junction termination. Detailed Implementation

[0028] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0029] Example 1:

[0030] This embodiment provides an AlN heterojunction diode structure that combines high breakdown voltage and low leakage current. The diode includes a substrate layer, an AlN buffer layer, and an n-AlN layer arranged sequentially from bottom to top. A downwardly recessed groove is formed on the upper surface of the n-AlN layer corresponding to the anode region, and p-NiO is disposed within the groove. X Layer. The p-NiO X The layer comprises a first portion located within a groove and a second portion located on the surface of the n-AlN layer, wherein the first portion fills the groove and forms p-NiO with the n-AlN layer. X The n-AlN heterojunction, the second portion extends laterally from the groove opening along the surface of the n-AlN layer towards the cathode to form a junction termination structure. The p-NiO XAn anode metal layer is disposed above the n-AlN layer, cathode metal layers are disposed on both sides of the surface of the n-AlN layer, and a passivation layer is disposed on the surface of the diode structure, the passivation layer covering the anode edge region and the p-NiO layer. X The area where the second part of the layer is located.

[0031] In this embodiment, p-NiO is located in the groove X The first part of the layer forms an interleaved Type-II p-NiO layer with the n-AlN layer. X / n-AlN heterojunction. As shown in Figure 3, this heterojunction can suppress electron leakage across the interface by utilizing the interface band shift under reverse bias conditions, thereby helping to reduce the reverse leakage current of the device. Simultaneously, p-NiO located on the surface of the n-AlN layer and extending laterally along the cathode direction from the groove opening... X The second part of the layer constitutes the junction termination structure. The junction termination structure, together with the groove structure and the surface passivation layer, can jointly regulate the surface potential distribution and electric field distribution near the anode edge, so that the depletion region expands more gently in the edge region, thereby reducing the local peak electric field, alleviating the electric field concentration phenomenon at the anode edge, and thus helping to improve the reverse breakdown capability and operating stability of the diode.

[0032] In this embodiment, the depth of the groove is 0 to the full thickness of the n-AlN layer; the p-NiO X The layer includes a first portion located within the groove and a second portion located on the surface of the n-AlN layer. The second portion is disposed in the corresponding region of the anode metal layer, and its thickness is 0 to the height of the bottom of the anode metal layer. It extends from the opening of the groove along the surface of the n-AlN layer toward the cathode, and the extension length is 0 to the position of the cathode metal layer. The thickness of the passivation layer can be 20 to 500 nm.

[0033] In this embodiment, the thickness of the AlN buffer layer can be 300–500 nm, and the thickness of the n-AlN layer can be 50–200 nm; the n-AlN layer is an n-AlN layer formed by intentional Si doping, and the doping concentration can be 10. 17 ~10 18 cm -3 .

[0034] In this embodiment, the material of the anode metal layer may include one or more of Ni, Ti, Al, Au, W, Cr, Ta, Mo, or TiN; the material of the cathode metal layer may include one or more of Ni, Ti, Al, Au, TiN, W, Ta, Pt, or Pd.

[0035] The AlN heterojunction diode structure described in this embodiment can be prepared according to the following method:

[0036] S1: An AlN buffer layer is epitaxially grown on the AlN substrate using metal-organic chemical vapor deposition (MOCVD); then silane (SiH4) is introduced as an n-type dopant source to epitaxially grow an n-AlN layer on the AlN buffer layer, as shown in Figure 2.(a).

[0037] S2: The epitaxial wafer obtained in step S1 is cleaned, and a cathode contact region is defined on the surface of the n-AlN layer using photolithography. Subsequently, a cathode metal layer is deposited using electron beam evaporation, and the cathode metal is formed by a lift-off process. Then, thermal annealing is performed in an N2 atmosphere to form an ohmic contact, as shown in Figure 2(b).

[0038] S3: A groove mask pattern is formed at the preset anode position of the n-AlN layer using photolithography; then, an inductively coupled plasma (ICP) dry etching process is used, with a mixture of chlorine (Cl2) and boron trichloride (BCl3) as the etching gas, to etch the unmasked n-AlN layer to form a groove of 30-150 nm, as shown in Figure 2.(c).

[0039] S4: p-NiO is formed using photolithography. X A deposition window is established, covering the interior of the groove and the area extending outward from the groove opening; subsequently, p-NiO is deposited using radio frequency (RF) magnetron sputtering in an Ar / O2 mixed atmosphere. X After deposition, excess film is removed by a stripping process to form p-NiO. X The layer is shown in Figure 2.(d).

[0040] S5: p-NiO formed in step S4 X Based on the layer, a secondary processing window is formed in the pre-defined anode metal contact area using photolithography, and the p-NiO in this area is then processed. X The surface of the layer is subjected to oxygen-rich heavy doping treatment to form oxygen-rich heavy doped p-NiO in the surface region in contact with the anode metal layer. X Layer. Preferably, the oxygen-rich heavy doping treatment can be achieved by secondary radio frequency magnetron sputtering under increased oxygen partial pressure conditions, oxygen plasma treatment, oxygen-rich annealing treatment, or a combination thereof, to reduce the subsequent anode metal layer and p-NiO. X Contact resistance between layers.

[0041] S6: The anode metal region is defined using photolithography; subsequently, the anode metal layer is deposited using electron beam evaporation, and then oxygen-rich heavily doped p-NiO is added via a lift-off process. X An anode metal layer is formed on the layer, as shown in Figure 2.(e).

[0042] S7: A Si3N4 insulating passivation layer with a thickness of 20-500 nm is formed on the diode surface using plasma-enhanced chemical vapor deposition (PECVD) or atomic layer deposition (ALD) technology, as shown in Figure 2.(f).

[0043] S8: Using photolithography and etching processes, openings are formed on the Si3N4 insulating passivation layer to form the anode node pad area and the corresponding area of ​​the cathode metal layer for subsequent external electrical connection, thereby completing the fabrication of the AlN heterojunction diode structure.

[0044] Example 2:

[0045] This embodiment is basically the same as Embodiment 1, as shown in Figure 3, the difference being: the p-NiO X The layer is a composite p-NiO X The layer, namely the p-NiO X The layer has a three-level acceptor concentration distribution along the vertical direction, consisting of light doping, heavy doping, and light doping. In step S4 of Example 1, by adjusting the oxygen partial pressure during the RF magnetron sputtering process, three layers are deposited sequentially: the first lightly doped p-NiO layer near the n-AlN layer. X The second heavily doped p-NiO layer in the middle X and the third lightly doped p-NiO layer near the metal electrode X The light doping concentration range is set to 10. 16 ~10 17 cm -3 The heavy doping concentration range is set to 10. 17 ~10 18 cm -3 .

[0046] Through the above-described layered doping design, p-NiO can be optimized while taking into account the heterojunction interface modulation effect. X Carrier transport characteristics within the layer.

[0047] Example 3:

[0048] This embodiment is basically the same as Embodiment 1, such as... Figure 4 As shown, the difference lies in that the substrate layer is a low-resistivity n-Si substrate. In this embodiment, before step S1 of embodiment 1, an AlN nucleation layer with a thickness of 30-200 nm is first grown on the Si substrate layer using the MOCVD method, and then a buffer layer is grown on the AlN nucleation layer; the buffer layer can be an AlN / AlGaN superlattice buffer layer with a thickness of 0.5-2 μm, or an AlN / AlGaN superlattice buffer layer with a thickness of 10 nm-10 μm. x Ga 1-x N-variable component buffer layer.

[0049] This embodiment demonstrates that the structure of the present invention can be constructed not only on AlN substrates but also on silicon substrates, thus exhibiting good substrate compatibility.

[0050] Example 4:

[0051] This embodiment is basically the same as Embodiment 1, such as... Figure 5 As shown, the difference lies in that the device further includes a heat dissipation enhancement structure. In this embodiment, the anode metal layer and cathode metal layer are designed to be thickened, with a total thickness of 1–5 μm; furthermore, a high thermal conductivity auxiliary heat dissipation film layer with a thickness of 50–200 nm can be disposed above the passivation layer, and the auxiliary heat dissipation film layer can be a diamond-like carbon film. The heat dissipation enhancement structure helps to improve the thermal diffusion conditions during device operation.

[0052] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A high-power, low-loss AlN diode structure, characterized in that: The diode structure includes, from bottom to top, a substrate layer (6), an AlN buffer layer (5), an n-AlN layer (4), and a p-NiO layer. X Layer (3), anode metal layer (1), cathode metal layer (2) and passivation layer (7); a groove is formed in the middle of the surface of the n-AlN layer, and p-NiO is disposed in the groove. X Layer; the p-NiO X The layer includes a first portion located within the groove and a second portion located on the surface of the n-AlN layer, wherein the first portion forms p-NiO with the n-AlN layer. X The n-AlN heterojunction, wherein the second portion extends laterally from the opening of the groove along the surface of the n-AlN layer towards both cathode directions to form a junction termination structure; the p-NiO X An anode metal layer is disposed above the n-AlN layer; cathode metal layers are disposed on both sides of the surface of the n-AlN layer; and a passivation layer is disposed on the surface of the diode structure.

2. The AlN diode structure according to claim 1, characterized in that: The n-AlN layer is an n-type AlN epitaxial layer formed by intentional doping.

3. The AlN heterojunction structure according to claim 1, characterized in that: The n-AlN layer has grooves formed on its upper surface, the depth of which is 0 to the full thickness of the n-AlN layer; the p-NiO X The layer includes a first portion located within the groove and a second portion located on the surface of the n-AlN layer. The second portion is disposed in the corresponding region of the anode metal layer, with a thickness of 0 to the height of the bottom of the anode metal layer, and extends from the opening of the groove along the surface of the n-AlN layer toward the cathode, with an extension length of 0 to the location of the cathode metal layer.

4. The AlN heterojunction diode structure according to claim 1, characterized in that: p-NiO X The first part of the layer forms an interleaved Type-II p-NiO layer with the n-AlN layer. X / n-AlN heterojunction.

5. The AlN diode structure according to claim 1 or 4, characterized in that: p-NiO X The surface region of the layer in contact with the anode metal layer is an oxygen-rich, heavily doped layer to reduce the interaction between the anode metal layer and p-NiO. X Contact resistance between layers.

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