A GaN-based pn junction diode device with a polarized beveled termination structure and its fabrication method

Abstract

This invention relates to a GaN-based pn junction diode device with a polarized beveled termination structure and its fabrication method. The device includes a cathode, a GaN substrate, an epitaxial layer, and an anode. The epitaxial layer comprises a lightly doped n-type GaN layer, an intrinsic GaN layer, and a p-type doped GaN layer grown in a single epitaxial growth process. The anode ohmic contact metal is placed on the p-type doped GaN layer, and the cathode ohmic contact metal is placed on the back side of the GaN substrate. It also includes a polarized beveled termination structure formed at the interface containing the pn junction, using inductively coupled plasma reactive ion etching (ICP-R) and a photoresist mask. The photoresist mask is formed using thick photoresist, followed by high-temperature heating and annealing to form the reflow morphology of the photoresist. Finally, wet repair and a passivation layer are applied to suppress the beveled n-type donor surface states of the polarized beveled termination structure. This invention effectively alleviates the boundary electric field concentration problem of GaN-based pn junctions and improves the breakdown voltage of GaN-based pn junctions.

Description

Technical Field

[0001] This invention relates to the field of semiconductor device technology, and more specifically, to a GaN-based pn junction diode device with a polarized beveled termination structure and its fabrication method. Background Technology

[0002] As GaN lateral structure power electronic devices on Si substrates gradually enter the industrialization stage, GaN vertical structure power electronic devices are gradually becoming the next research hotspot. For high-voltage vertical conduction structure devices, the following three key technical problems need to be overcome in order to achieve high voltage withstand characteristics: suppressing the background carrier concentration in the drift region, selecting the region P-type doping technology and the termination structure.

[0003] The breakdown voltage of GaN semiconductor power devices is related to the electric field distribution within the structure. High electric fields can occur both inside the power device and at its edges. The industry typically uses special junction terminations at the edges of the power device to alleviate this problem; these are called termination structures. Currently, there are three main types of termination structures for power devices: field-plate termination structures, junction termination extension structures, and beveled termination structures. Considering the ease of fabrication and the long-term reliability of the termination structure, the beveled termination structure is currently the most promising. However, existing beveled termination structures exhibit concentrated electric fields at the GaN-based pn junction boundaries and poor breakdown voltage performance. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, this invention provides a GaN-based pn junction diode device with a polarized oblique-edge termination structure and its fabrication method, which can effectively alleviate the problem of electric field concentration at the boundary of the GaN-based pn junction and improve the breakdown voltage of the GaN-based pn junction.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0006] A GaN-based pn junction diode device with a polarized beveled termination structure includes, from bottom to top, a cathode ohmic contact metal, a conductive self-supporting GaN substrate, an epitaxial layer on the GaN substrate, and an anode ohmic contact metal. The epitaxial layer includes an n-type lightly doped GaN layer, an intrinsic GaN layer, and a p-type doped GaN layer grown in a single epitaxial growth. The anode ohmic contact metal is placed on the p-type doped GaN layer, and the cathode ohmic contact metal is placed on the back side of the GaN substrate. The device also includes a polarized beveled termination structure formed at the pn junction interface using inductively coupled plasma reactive ion etching (ICP-RIE) and a photoresist mask. The photoresist mask is formed using thick photoresist, followed by high-temperature heating and annealing to form the reflow morphology of the photoresist. Finally, wet repair and a passivation layer are used to suppress the beveled n-type donor surface states of the polarized beveled termination structure.

[0007] TCAD simulations revealed the presence of polarization charges at the beveled edges of GaN materials, which significantly suppress the boundary electric field. Furthermore, the GaN-based pn junction with the beveled-edge termination structure exhibited a donor surface state density suppression down to 1 × 10⁻⁶. 13 cm -2 When the following conditions are met, avalanche capability can be achieved, demonstrating the superior characteristics of this terminal structure.

[0008] Based on the above technical means, this invention alleviates the problem of electric field concentration at the boundary of the pn junction through a GaN-based polarized oblique-edge termination structure, thereby improving the withstand voltage by suppressing premature breakdown of the boundary electric field; it has the ability to achieve stable performance and repeatable avalanche capability; the termination structure is simple to fabricate and provides support for the application of high-voltage GaN longitudinal conduction devices.

[0009] This invention proposes a beveled termination structure utilizing the polarization characteristics of group III nitride semiconductor materials. The structure aims to alleviate edge electric field congestion by utilizing the beveled polarization charge, thereby reducing the likelihood of premature breakdown at the boundary and maintaining high material figure of merit. The key technologies are the beveled fabrication process and the growth of the beveled passivation layer. The purpose is to maintain the presence of polarization charge at the beveled edge through the growth of the passivation layer, which regulates the peak electric field at the device edge, achieving high voltage withstand capability for GaN materials. This termination structure is simple to fabricate and will support the application of high-voltage GaN vertically conductive devices.

[0010] In one embodiment, the tilt angle of the inclined side of the polarized inclined end structure is 1° to 90°.

[0011] In one embodiment, the GaN substrate is a heavily doped GaN substrate, wherein the doping concentration of the heavily doped GaN substrate is 10. 18 Above this value, light doping is indicated; or, the GaN substrate is composed of a low-resistivity silicon substrate or a low-resistivity silicon carbide and a conductive buffer layer.

[0012] In one embodiment, the semiconductor material with the beveled terminal structure may also be a group III nitride such as AlN, InN, InGaN, AlGaN, etc., or other semiconductor materials with polarization characteristics.

[0013] In one embodiment, the n-type lightly doped GaN layer has a doping concentration of less than 1 × 10⁻⁶. 18 cm -3 The GaN, wherein the thickness of the n-type lightly doped GaN layer is 10 nm to 500 nm.

[0014] In one embodiment, the thickness of the intrinsic GaN layer is 1 μm to 50 μm.

[0015] In one embodiment, the p-type doped GaN layer is a p-type doped AlGaN layer or a doped high-resistivity AlGaN layer; the doping elements of the doped high-resistivity GaN layer and AlGaN layer include, but are not limited to, carbon or iron; the thickness of the p-type doped GaN layer is 10 nm to 500 nm.

[0016] In one embodiment, the passivation layer is made of SiO2 or SiN. x , Al2O3, AlN, HfO2, MgO, Sc2O3, Ga2O3, AlHfO x Or HfSiON, wherein the thickness of the passivation layer is 1nm-100nm.

[0017] In one embodiment, the cathode ohmic contact metal is a Ti / Al / Ni / Au alloy, a Ti / Al / Ti / Au alloy, or a Ti / Al / Mo / Au alloy. Other metals or alloys capable of achieving ohmic contacts can be used as source and drain materials. The anode ohmic contact metal is a Ni / Au alloy, a Pt / Al alloy, or a Pd / Au alloy. Other metals or alloys capable of achieving p-type GaN ohmic contacts can be used as anode materials.

[0018] This invention also provides a method for fabricating a GaN-based pn junction diode device with a polarized beveled termination structure, comprising the following steps:

[0019] S1. An n-type lightly doped GaN layer, an intrinsic GaN layer, and a p-type doped GaN layer are epitaxially grown on a conductive self-supporting GaN substrate.

[0020] S2. A thick photoresist layer is grown on p-type doped GaN as a mask layer;

[0021] S3. The photoresist is annealed after being heated at high temperature by a heating plate to form a reflow morphology. Inductively coupled plasma reactive ion etching is used to form a polarized oblique terminal structure at the interface containing the pn junction.

[0022] S4. Repair the etching damage of the polarized beveled terminal structure using wet method; remove the mask layer above the p-type doped GaN layer;

[0023] S5. Passivation layer growth: Anode ohmic contact metal is deposited in the anode region, and cathode ohmic contact metal is deposited on the back side of the GaN substrate.

[0024] In one embodiment, the growth method of the intrinsic GaN layer and the p-type doped GaN layer in step S1 is metal-organic chemical vapor deposition or molecular beam epitaxy; the growth method of the passivation layer in step S5 is plasma-enhanced chemical vapor deposition, atomic layer deposition, physical vapor deposition or magnetron sputtering; in step S3, inductively coupled plasma reactive ion etching based on Cl2 is used; and in step S4, wet repair is performed using TMAH.

[0025] Compared with the prior art, the beneficial effects are as follows: The GaN-based pn junction diode device with a polarized oblique-edge termination structure and its fabrication method provided by the present invention alleviate the problem of electric field concentration at the pn junction boundary by means of the GaN-based polarized oblique-edge termination structure, thereby improving the withstand voltage by suppressing premature breakdown of the boundary electric field; it has the ability to achieve stable performance and repeatable avalanche capability; the fabrication method of the diode device provided by the present invention is simple and provides support for the application of high withstand voltage GaN longitudinal conduction devices. Attached Figure Description

[0026] Figures 1 to 8 This is a schematic diagram of the manufacturing process of the diode device of the present invention.

[0027] Figure 9 This is a schematic diagram of the device structure of Embodiment 1 of the present invention.

[0028] Figure 10 This is a TCAD simulation diagram of the device structure in Embodiment 1 of the present invention.

[0029] Figure 11 This is a schematic diagram illustrating the impact of donor surface states on the congestion of the boundary electric field.

[0030] Figure descriptions: 1. GaN substrate; 2. n-type lightly doped GaN layer; 3. Intrinsic GaN layer; 4. p-type doped GaN layer; 5. Passivation layer; 6. Cathode ohmic contact metal; 7. Anode ohmic contact metal; 8. Mask layer. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. The present invention will be described in one embodiment below with reference to specific embodiments. The accompanying drawings are for illustrative purposes only and represent schematic diagrams, not actual pictures, and should not be construed as limiting the present patent. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged, or reduced, and do not represent the actual product size. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0032] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, if the embodiments of this invention involve descriptions of "first," "second," etc., such descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the meaning of "and / or" throughout the text is to include three parallel solutions; for example, "A and / or B" includes solution A, solution B, or a solution that simultaneously satisfies A and B.

[0033] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0034] Example 1:

[0035] like Figure 8 and Figure 9As shown, a GaN-based pn junction diode device with a polarized beveled termination structure includes, from bottom to top, a cathode ohmic contact metal 6, a conductive self-supporting GaN substrate 1, an epitaxial layer on the GaN substrate 1, and an anode ohmic contact metal 7. The epitaxial layer includes an n-type lightly doped GaN layer 2, an intrinsic GaN layer 3, and a p-type doped GaN layer 4, all grown epitaxially in a single step. The anode ohmic contact metal 7 is placed on the p-type doped GaN layer 4, and the cathode ohmic contact metal 6 is placed on the back side of the GaN substrate 1. The device also includes a polarized beveled termination structure, which is formed at the interface containing the pn junction. The structure is formed by inductively coupled plasma reactive ion etching and photoresist masking. The photoresist mask is formed using thick photoresist, followed by high-temperature heating and annealing to form the reflow morphology of the photoresist. Finally, wet repair and a passivation layer 5 are applied to suppress the beveled n-type donor surface states of the polarized beveled termination structure.

[0036] Through TCAD simulation, such as Figure 10 and Figure 11 As shown, polarization charges are found at the beveled ends of GaN materials, and these charges have a significant suppressive effect on the boundary electric field. Figure 11 As shown in (e), when the donor surface state density at the hypotenuse exceeds 1 × 10 13 cm -2 Subsequently, the electric field at the boundary of the sloping pn junction became congested. When the surface state density of the sloping donors was controlled using wet repair and passivation layer methods, as... Figure 11 As shown in (a), the GaN-based pn junction with a beveled termination structure has its donor surface state density suppressed to 1×10⁻⁶. 13 cm -2 When the following conditions are met, avalanche capability can be achieved, demonstrating the superior characteristics of this terminal structure.

[0037] Based on the above technical means, this invention alleviates the problem of electric field concentration at the boundary of the pn junction through a GaN-based polarized oblique-edge termination structure, thereby improving the withstand voltage by suppressing premature breakdown of the boundary electric field; it has the ability to achieve stable performance and repeatable avalanche capability; the termination structure is simple to fabricate and provides support for the application of high-voltage GaN longitudinal conduction devices.

[0038] Specifically, the tilt angle of the inclined edge of the polarization inclined edge terminal structure is 1° to 90°. GaN substrate 1 is a heavily doped GaN substrate 1, and the doping concentration of the heavily doped GaN substrate 1 is 10. 18 Above this value, light doping is indicated; or, GaN substrate 1 is composed of a low-resistivity silicon substrate or a low-resistivity silicon carbide and a conductive buffer layer.

[0039] In addition, semiconductor materials with beveled terminal structures can also be group III nitrides such as AlN, InN, InGaN, and AlGaN, as well as other semiconductor materials with polarization properties.

[0040] Among them, the n-type lightly doped GaN layer 2 has a doping concentration of less than 1×10⁻⁶. 18 cm -3 The thickness of the n-type lightly doped GaN layer 2 is 10 nm to 500 nm. The thickness of the intrinsic GaN layer 3 is 1 μm to 50 μm. The p-type doped GaN layer 4 is a p-type doped AlGaN layer or a doped high-resistivity AlGaN layer; the doping elements of the high-resistivity GaN layer and AlGaN layer include, but are not limited to, carbon or iron; the thickness of the p-type doped GaN layer 4 is 10 nm to 500 nm.

[0041] In addition, the material of passivation layer 5 is SiO2 or SiN. x , Al2O3, AlN, HfO2, MgO, Sc2O3, Ga2O3, AlHfO x Alternatively, HfSiON can be used, with the passivation layer 5 having a thickness of 1 nm to 100 nm.

[0042] Among them, the cathode ohmic contact metal 6 is a Ti / Al / Ni / Au alloy, Ti / Al / Ti / Au alloy, or Ti / Al / Mo / Au alloy. Other metals or alloys that can achieve ohmic contact can be used as source and drain materials. The anode ohmic contact metal 7 is a Ni / Au alloy, Pt / Al alloy, or Pd / Au alloy. Other metals or alloys that can achieve p-type GaN ohmic contact can be used as anode materials.

[0043] This embodiment provides a GaN-based pn junction diode device with a polarized beveled termination structure. It utilizes the beveled polarization charge to alleviate edge electric field congestion, reducing the likelihood of premature breakdown at the boundary and maintaining high material figure of merit. The key technologies are the beveled fabrication process and the growth of the beveled passivation layer 5. The purpose is to maintain the presence of polarization charge at the beveled edge through the growth of the passivation layer 5, thereby modulating the peak electric field at the device edge and achieving the high figure of merit of GaN material with high voltage withstand capability. This termination structure is simple to fabricate and provides support for the application of high-voltage GaN longitudinally conducting devices.

[0044] Example 2

[0045] like Figures 1 to 8 As shown, this embodiment provides a method for fabricating a GaN-based pn junction diode device with a polarized beveled termination structure, including the following steps:

[0046] S1. An n-type lightly doped GaN layer 2, an intrinsic GaN layer 3, and a p-type doped GaN layer 4 are epitaxially grown on a conductive self-supporting GaN substrate 1.

[0047] S2. A thick photoresist layer is grown on p-type doped GaN as a mask layer 8;

[0048] S3. The photoresist is annealed after being heated at high temperature by a heating plate to form a reflow morphology. Inductively coupled plasma reactive ion etching is used to form a polarized oblique terminal structure at the interface containing the pn junction.

[0049] S4. Repair the etching damage of the polarized oblique edge terminal structure using wet method; remove the mask layer 8 above the p-type doped GaN layer 4;

[0050] S5. Passivation layer 5 is grown; anodic ohmic contact metal 7 is deposited in the anodic region, and cathode ohmic contact metal 6 is deposited on the back side of GaN substrate 1.

[0051] Based on the above technical means, this embodiment alleviates the problem of electric field concentration at the boundary of the pn junction through a GaN-based polarized beveled termination structure, thereby improving the breakdown voltage by suppressing premature breakdown at the boundary electric field. It also possesses stable performance and repeatable avalanche capability. This termination structure is simple to fabricate and provides support for the application of high-voltage GaN longitudinally conducting devices. The approach and fabrication method utilize beveled polarization charges to alleviate electric field congestion at the device edge, reducing the possibility of premature breakdown at the boundary and maintaining high material figure of merit. The key technologies are the beveled fabrication process and the growth of the beveled passivation layer 5. The purpose is to maintain the presence of polarization charges at the beveled edge through the growth of the passivation layer 5, thereby regulating the peak electric field at the device edge and achieving the high breakdown voltage capability of GaN materials. This termination structure is simple to fabricate and provides support for the application of high-voltage GaN longitudinally conducting devices.

[0052] Example 3

[0053] This embodiment is the same as the steps in Embodiment 2. In this embodiment, the growth methods of the intrinsic GaN layer 3 and the p-type doped GaN layer 4 in step S1 are metal-organic chemical vapor deposition or molecular beam epitaxy; the growth methods of the passivation layer 5 in step S5 are plasma-enhanced chemical vapor deposition, atomic layer deposition, physical vapor deposition or magnetron sputtering; in step S3, inductively coupled plasma reactive ion etching based on Cl2 is used; and in step S4, wet repair is performed using TMAH.

[0054] 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 will recognize that other variations or modifications can be made 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 GaN-based pn junction diode device of a polarized bevel termination structure, characterized by, From bottom to top, it comprises a cathode ohmic contact metal (6), a conductive self-supporting GaN substrate (1), an epitaxial layer on the GaN substrate (1), and an anode ohmic contact metal (7); the epitaxial layer comprises a first epitaxially grown n-type lightly doped GaN layer (2), an intrinsic GaN layer (3), and a p-type doped GaN layer (4); the anode ohmic contact metal (7) is disposed on the p-type doped GaN layer (4), and the cathode ohmic contact metal (6) is disposed on the back of the GaN substrate (1); it further comprises a polarization bevel termination structure formed at the interface containing the pn junction, which is formed by inductively coupled plasma reactive ion etching and photoresist mask, wherein the photoresist mask is photoetched by thick photoresist, then reflowed by high-temperature heating of a hot plate after annealing, and finally wet repaired and inhibited by a passivation layer (5) on the bevel n-type donor surface state of the polarization bevel termination structure; the existence of the polarization charge at the bevel is maintained by the growth of the passivation layer (5), which plays a role in regulating the edge peak electric field of the device and relieving the congestion of the edge electric field of the device by the polarization charge at the bevel.

2. The polar bevel termination structure GaN-based pn junction diode device of claim 1, wherein, The inclination angle of the bevel of the polarization bevel termination structure is 1°-90°.

3. The polar bevel termination structure GaN-based pn junction diode device of claim 1, wherein, The GaN substrate (1) is a heavily doped GaN substrate (1), or the GaN substrate (1) is composed of a low-resistance silicon substrate or a low-resistance silicon carbide and a conductive buffer layer.

4. The polar bevel termination structure GaN-based pn junction diode device of claim 1, wherein, The n-type lightly doped GaN layer (2) is GaN with a doping concentration less than 1 x 1018 18 cm -3 -3, and a thickness of 10 nm to 500 nm.

5. The polar bevel termination structure GaN-based pn junction diode device of claim 1, wherein, The thickness of the intrinsic GaN layer (3) is 1 μm-50 μm.

6. The polar bevel termination structure GaN-based pn junction diode device of claim 1, wherein, The p-type doped GaN layer (4) is a p-type doped AlGaN layer; the thickness of the p-type doped GaN layer (4) is 10 nm-500 nm.

7. The polar bevel termination structure GaN-based pn junction diode device of claim 1, wherein, The material of the passivation layer (5) is SiO2, SiN x , Al2O3, AlN, HfO2, MgO, Sc2O3, Ga2O3, AlHfO x or HfSiON, and the thickness of the passivation layer (5) is 1 nm to 100 nm.

8. The polar bevel termination structure GaN-based pn junction diode device of claim 1, wherein, The cathode ohmic contact metal (6) is Ti / Al / Ni / Au alloy, Ti / Al / Ti / Au alloy, or Ti / Al / Mo / Au alloy; the anode ohmic contact metal (7) is Ni / Au alloy, Pt / Al alloy, or Pd / Au alloy.

9. A method of fabricating a GaN-based pn junction diode device of the polar-tilt-edge termination structure according to claim 1, characterized by, It comprises the following steps: S1. Epitaxially growing an n-type lightly doped GaN layer (2), an intrinsic GaN layer (3), and a p-type doped GaN layer (4) on a conductive self-supporting GaN substrate (1); S2. Growing a thick photoresist layer on the p-type doped GaN as a mask layer (8); S3. Forming a reflowed morphology of the photoresist by high-temperature heating of a hot plate after annealing, and etching by inductively coupled plasma to form a polarization bevel termination structure at the interface containing the pn junction; S4. Wet repairing the etching damage of the polarization bevel termination structure; removing the mask layer (8) on the p-type doped GaN layer (4); S5. Growing a passivation layer (5); evaporating an anode ohmic contact metal (7) on the anode region, and evaporating a cathode ohmic contact metal (6) on the back of the GaN substrate (1).

10. The method of fabricating a GaN-based pn junction diode device with a polarized bevel termination structure according to claim 9, wherein The growth method of the intrinsic GaN layer (3) and the p-type doped GaN layer (4) in the step S1 is metal organic chemical vapor deposition or molecular beam epitaxy; the growth method of the passivation layer (5) in the step S5 is plasma enhanced chemical vapor deposition, atomic layer deposition, physical vapor deposition or magnetron sputtering; the inductively coupled plasma reactive ion etching based on Cl2 is adopted in the step S3; and the wet repair is performed by using TMAH in the step S4.

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