A method for implementing a jte junction termination in a gan vertical structure pn diode

Abstract

This invention discloses a method for achieving JTE junction termination in a GaN vertical structure pn diode, belonging to the field of wide bandgap semiconductor materials. The invention involves hydrogen plasma treatment near the etch boundary of the heavily doped p-type GaN layer, causing H ions to form Mg-H complexes with Mg acceptors in the heavily doped p-type GaN layer. Simultaneously, thermal annealing is used to diffuse H ions within the heavily doped p-type GaN, creating a gradually varying hole concentration gradient from the main junction region to the junction edge, thereby achieving JTE junction termination. Compared to existing junction termination technologies, this invention involves no etching, low damage, and effectively weakens the electric field accumulation effect, improving the device's breakdown voltage.

Description

Technical Field

[0001] This invention belongs to the field of power diode devices in gallium nitride (GaN), a wide bandgap semiconductor material, and specifically relates to a method for realizing junction termination extension (JTE) in a GaN vertical structure pn diode. Background Technology

[0002] The operation and development of modern society are inextricably linked to electricity, and power electronic systems are indispensable in the generation, transmission, and use of electrical energy. Power electronic devices are primarily responsible for the conversion and transmission of electrical energy in power electronic systems, determining the system's operating efficiency and power quality. Traditional power electronic devices, limited by their material properties, can no longer meet the diverse application scenarios. Compared to first- and second-generation semiconductor materials such as silicon (Si) and gallium arsenide (GaAs), third-generation semiconductor materials, led by gallium nitride (GaN), possess characteristics such as a large bandgap, high saturated electron drift velocity, and high critical breakdown field strength, making them highly promising in high-frequency, high-efficiency, and high-power power electronics fields. GaN power devices can be classified into horizontal and vertical structure power devices according to their structural type. Horizontal structure power devices are limited by factors such as the trade-off between lateral dimensions and voltage withstand capability, difficulties in thermal management, and poor reliability. GaN vertical structure power devices, however, do not have these problems and have good application prospects in the future medium- and high-voltage power device fields. GaN vertical structure power devices can be classified into diodes and transistors according to device type. Diodes include Schottky Barrier Diodes (SBDs) and pn diodes. PN diodes have a higher barrier height and are easier to implement into high-voltage devices.

[0003] Because GaN vertical structure pn diodes exhibit an electric field accumulation effect at the junction edge, leading to premature breakdown, designing a suitable junction termination to weaken this effect is crucial for improving the breakdown voltage of pn diodes. Junction termination extension (JTE), a highly effective junction termination technology, has been widely used in power devices such as Si and silicon carbide (SiC), achieving an ultra-high breakdown voltage of 20kV in SiC through JTE junction termination. JTE junction termination is achieved by forming a gradient hole distribution in the p-type layer at the junction edge. This allows the excess lateral ionized donor electric field lines in the n-type drift layer at the junction edge to uniformly fall onto the gradient-distributed ionized acceptors in the JTE, thereby weakening the electric field accumulation effect. However, GaN lacks effective selective p-type doping techniques. The main problem with conventional Mg ion implantation for selective p-type doping is the contradiction between annealing activation and the high-temperature decomposition of GaN. Therefore, achieving efficient JTE junction termination in GaN has always been a challenging problem. Summary of the Invention

[0004] The purpose of this invention is to provide a method for achieving JTE junction termination in a GaN vertical structure pn diode. This method achieves a gradient hole density-JTE (GHD-JTE) termination by hydrogen treatment and thermal annealing at the pn junction edge, resulting in a gradient distribution of hole concentration from the main junction region to the junction edge. This effectively weakens the electric field accumulation effect and improves the device's breakdown voltage.

[0005] The technical solution provided by this invention is as follows:

[0006] A method for achieving JTE junction termination in a GaN vertical structure pn diode, wherein the GaN vertical structure pn diode comprises, from top to bottom: an epitaxial heavily p-doped GaN layer, a lightly n-doped GaN drift layer, a heavily n-doped GaN current spreading layer, and a homogeneous heavily n-doped GaN substrate. An anode metal is disposed on the surface of the uppermost heavily p-doped GaN layer to form an ohmic contact, and a cathode metal is disposed on the back side of the lowermost homogeneous heavily n-doped GaN substrate to form an ohmic contact. The method is characterized by performing hydrogen plasma treatment near the etch boundary of the heavily p-doped GaN layer, causing hydrogen ions to form Mg-H complexes with Mg acceptors in the heavily p-doped GaN layer, thereby passivating the p-type GaN in the hydrogen-treated region. Simultaneously, thermal annealing is used to diffuse hydrogen ions in the heavily p-doped GaN to form a gradient distribution, thereby creating a gradually changing hole concentration gradient distribution between the main junction region and the junction edge, ultimately achieving JTE junction termination.

[0007] Furthermore, the hydrogen plasma treatment employs inductively coupled plasma (ICP), and the treatment conditions are as follows: ICP power = 500–1000 W, RF power = 10–25 W, H2 flow = 40–50 sccm, Pressure = 2–3 Pa, and time = 100–200 s.

[0008] Furthermore, the conditions for the thermal annealing treatment are: nitrogen atmosphere, temperature range of 400-450℃, and time of 15s-12min.

[0009] Furthermore, the doping concentration of the heavily doped n-type GaN current spreading layer is higher than 3E18 cm⁻¹. -3 The thickness is 0.5 to 1 μm.

[0010] Furthermore, the doping concentration of the lightly doped n-type GaN drift layer is lower than 2E16 cm⁻¹. -3 The thickness is greater than 3.0 μm.

[0011] Furthermore, the doping concentration of the heavily doped p-type GaN layer is 2E18 to 1E19 cm⁻¹. -3 The thickness is 0.3–0.6 μm.

[0012] Furthermore, the anode metal and cathode metal are selected from one or more combinations of the following conductive materials: titanium, aluminum, nickel, gold, palladium, TiN, polycrystalline silicon, and ITO.

[0013] The GaN all-vertical structure pn diode device of this invention mainly relies on the depletion region expansion of the lightly doped n-type GaN drift layer to bear the breakdown voltage. Since discrete devices require isolation, the heavily doped p-type GaN layer needs to be completely etched, causing the n-type GaN drift layer at the junction edge to expand laterally under reverse bias. This leads to electric field accumulation at the etching boundary of the heavily doped p-type GaN layer. The GHD-JTE junction termination of this invention utilizes hydrogen plasma (H plasma) treatment near the etching boundary of the heavily doped p-type GaN layer. Because H ions can form Mg-H complexes with Mg acceptors in the heavily doped p-type GaN layer, the H plasma treatment region in the heavily doped p-type GaN layer becomes passivated and becomes high-resistance. Simultaneously, because H... Plasma has a low diffusion barrier in heavily p-doped GaN layers. Experiments have shown that annealing can enable H to diffuse laterally without escaping. This invention uses thermal annealing to diffuse H ions in heavily p-doped GaN layers, forming a concentration gradient of H ions in the heavily p-doped GaN layers, thereby creating a gradient distribution of hole concentration between the main junction region and the junction edge, achieving JTE junction termination.

[0014] This invention can be applied to all P-GaN electric field focusing devices, such as: p-GaN gate high electron mobility transistors, GaN vertical structure transistors, lateral SBDs with p-GaN cap layers, and lateral pn diodes.

[0015] This invention proposes a GHD-JTE junction termination technology, which, compared to other existing junction termination technologies, is an etching-free and low-damage technology. Specifically, compared to etched field plate junction terminations, it eliminates the introduction of etching, thus reducing etching damage; and without the field plate dielectric, there are no reliability issues. Compared to N and Ar ion-implanted junction terminations, H ion implantation causes less damage, without introducing a large number of defect states or affecting reverse leakage current. Furthermore, compared to junction-free devices, its breakdown voltage is significantly improved without affecting the device's forward characteristics. The GHD-JTE junction termination has a lower annealing temperature, which does not damage the original ohmic contact characteristics. The junction termination method of this invention is simplified and easy to implement. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of the GHD-JTE junction-terminated GaN fully vertical pn diode of the present invention;

[0017] Figure 2This is a schematic diagram of the structure of a GaN quasi-vertical pn diode with a GHD-JTE junction termination.

[0018] Figure 3 This is a cross-sectional view of the GaN epitaxial material structure;

[0019] Figure 4 This is a cross-sectional view of a device isolated by shallow etching after photolithography.

[0020] Figure 5 This is a cross-sectional view of the device after the front anode metal has been vapor-deposited.

[0021] Figure 6 This is a cross-sectional view of the device after the cathode metal has been vapor-deposited on the back side.

[0022] Figure 7 This is a cross-sectional view of the device after photolithography and H plasma processing;

[0023] In the picture:

[0024] 1—Anode metal; 2—p + -GaN;

[0025] 3——n - -GaN; 4-n + -GaN;

[0026] 5—Semiconductor substrate; 6—Cathode metal;

[0027] 7 - Photoresist. Detailed Implementation

[0028] The following description, in conjunction with the accompanying drawings, provides a further explanation of the implementation method for JTE junction termination in a GaN vertical structure pn diode according to the present invention through specific embodiments.

[0029] GaN vertical structure pn diodes can be classified into fully vertical structures (e.g., GaN self-supporting substrates) and quasi-vertical structures (e.g., Si, sapphire, SiC heterostructures) based on whether the substrate and buffer layer are conductive.

[0030] like Figure 1As shown, the fully vertical pn diode, from top to bottom, comprises an epitaxial heavily p-doped GaN layer, a lightly n-doped GaN drift layer, a heavily n-doped GaN current spreading layer, and a homogeneous heavily n-doped GaN substrate. Ohmic contacts are formed on the surface of the heavily p-doped GaN layer and the back side of the homogeneous heavily n-doped GaN substrate, respectively, with anode and cathode metals forming ohmic contacts. Hydrogen plasma treatment is performed on the surface of the heavily p-doped GaN layer near the pn junction etching boundary using inductively coupled plasma (ICP). ICP power = 500–1000 W, RF power = 10–25 W, H2 After rapid thermal annealing (nitrogen atmosphere, temperature range 400-450℃, time 15s-12min) with H ions and Mg acceptors in the heavily p-doped GaN layer, a Mg-H complex is formed. This passivates the hydrogen plasma-treated region in the heavily p-doped GaN layer into a high-resistivity region. At the same time, hydrogen ions have a low diffusion barrier in the heavily p-doped GaN layer, forming a gradient distribution of H concentration decreasing from the junction edge to the main junction region. Due to the passivation of Mg acceptors in the heavily p-doped GaN layer by H ions, a gradient distribution of hole concentration increasing from the main junction region to the junction edge can be formed, thus realizing the JTE junction termination.

[0031] like Figure 2 As shown, the quasi-vertical pn diode, from top to bottom, comprises an epitaxial heavily p-doped GaN layer, a lightly n-doped GaN drift layer, a heavily n-doped GaN current spreading layer, a stress modulation layer, and a heterogeneous substrate (such as Si, sapphire, SiC, etc.). Ohmic contacts are formed on the surfaces of the heavily p-doped GaN layer and the heavily n-doped GaN current spreading layer, respectively. The surface of the heavily p-doped GaN layer near the pn junction etching boundary is treated with hydrogen plasma (ICP power = 500–1000 W, RF power = 10–25 W, H2). After rapid thermal annealing (nitrogen atmosphere, temperature range 400-450℃, time 15s-12min), H ions form Mg-H complexes with Mg acceptors in the heavily p-doped GaN layer. This passivates the hydrogen plasma-treated region in the heavily p-doped GaN layer into a high-resistivity region. At the same time, hydrogen ions have a low diffusion barrier in the heavily p-doped GaN layer, which can form a gradient distribution of hole concentration from the main junction region to the junction edge, thus realizing JTE junction termination.

[0032] Taking a fully vertical structure device on a GaN self-supporting substrate as an example, the specific implementation steps are as follows: Figures 3-7 As shown: (The quasi-vertical structure device with heterogeneous substrate in this example can be deduced by analogy)

[0033] 1. Epitaxy was performed on a GaN self-supporting substrate using MOCVD. The epitaxial structure was: p + -GaN[Mg:2e18 cm -2 ,0.5μm] / n - -GaN[Si:2e16 cm -2 , 7.5μm] / n + -GaN[Si:5e18 cm -2 [0.5μm] / GaN self-supporting substrate, and then thermally annealed at 800℃ and in a nitrogen atmosphere for 10 min to activate p + -GaN layer, such as Figure 3 As shown;

[0034] 2. After photolithography, shallow etching is performed to create isolation mesa for the device (for quasi-vertical structure devices on heterogeneous substrates, deep etching is also required, with an etching depth reaching n). + -GaN is sufficient), then it is treated with tetramethylammonium hydroxide (TMAH) in a water bath at 85°C for 1 hour. Figure 4 As shown;

[0035] 3. Electron beam evaporation deposits Ni / Au (10 / 50nm) anode metal on the front side of the device, followed by thermal annealing at 550℃ in an oxygen atmosphere for 5 minutes to form an anode ohmic contact. Figure 5 As shown;

[0036] 4. Electron beam evaporation deposits cathode metal Ti / Al / Ni / Au (20 / 150 / 50 / 80nm) on the back of the device. (For quasi-vertical structure devices with heterogeneous substrates, the cathode metal is instead deposited on deeply etched n...) + -Cathode metal deposited on GaN), such as Figure 6 As shown;

[0037] 5. After photolithography, using photoresist as a mask, surface H-plasma treatment is performed on the p-type GaN layer near the etching boundary. Inductively coupled plasma (ICP) treatment is used under the following conditions: ICP power = 500W, RF power = 25W, H2 flow = 50 sccm, Pressure = 2 Pa, time = 200 s. Figure 7 As shown;

[0038] 6. Then, perform heat annealing at 450℃ to achieve lateral diffusion of H. The heat annealing time is approximately 4 minutes. Figure 1As shown (if it is a quasi-vertical structure device with a heterogeneous substrate, then as shown in the figure) Figure 2 As shown in the figure, the GHD-JTE junction is finally terminated in the GaN vertical structure pn diode.

[0039] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention, or modify them into equivalent embodiments, without departing from the scope of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the scope of the present invention, shall still fall within the protection scope of the present invention.

Claims

1. A method for implementing JTE junction termination in a GaN vertical structure pn diode, wherein the GaN vertical structure pn diode comprises, from top to bottom: The system comprises an epitaxial heavily p-doped GaN layer, a lightly n-doped GaN drift layer, a heavily n-doped GaN current spreading layer, and a homogeneous heavily n-doped GaN substrate. An anode metal is disposed on the surface of the uppermost heavily p-doped GaN layer to form an ohmic contact, and a cathode metal is disposed on the back side of the lowermost homogeneous heavily n-doped GaN substrate to form an ohmic contact. The system is characterized by performing hydrogen plasma treatment near the etching boundary of the heavily p-doped GaN layer, causing hydrogen ions to form Mg-H complexes with Mg acceptors in the heavily p-doped GaN layer, thereby passivating the p-type GaN in the hydrogen-treated region. Simultaneously, thermal annealing is used to diffuse hydrogen ions in the heavily p-doped GaN, forming a gradient distribution, thus creating a gradually changing hole concentration gradient distribution between the main junction region and the junction edge, ultimately achieving JTE junction termination.

2. The method as described in claim 1, characterized in that, The hydrogen plasma treatment employs inductively coupled plasma (ICP) under the following conditions: ICP power = 500–1000 W, RF power = 10–25 W, H2 flow = 40–50 sccm, Pressure = 2–3 Pa, and time = 100–200 s.

3. The method as described in claim 1, characterized in that, The heat annealing process is performed under the following conditions: nitrogen atmosphere, temperature range of 400–450°C, and time of 15–12 minutes.

4. The method as described in claim 1, characterized in that, The doping concentration of the heavily doped n-type GaN current-spreading layer is higher than 3E18 cm⁻¹. -3 The thickness is 0.5 to 1 μm.

5. The method as described in claim 1, characterized in that, The doping concentration of the lightly doped n-type GaN drift layer is less than 2E16cm⁻¹. -3 The thickness is greater than 3.0 μm.

6. The method as described in claim 1, characterized in that, The doping concentration of the heavily doped p-type GaN layer is 2E18~1E19 cm⁻¹ -3 The thickness is 0.3–0.6 μm.

7. The method as described in claim 1, characterized in that, The anode metal and cathode metal are selected from one or more combinations of the following conductive materials: titanium, aluminum, nickel, gold, palladium, TiN, polycrystalline silicon, or ITO.

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