Method for improving performance of beta-Ga2O3 Schottky diode based on fluorine plasma passivation

Abstract

The invention discloses a method for improving the performance of a beta-Ga2O3 Schottky diode based on fluorine plasma passivation, the diode comprises a beta-Ga2O3 single crystal substrate with a front surface and a back surface which are oppositely arranged, the front surface of the beta-Ga2O3 single crystal substrate is provided with a beta-Ga2O3 epitaxial layer, and the front surface of the beta-Ga2O3 single crystal substrate is provided with an SF6 / Ar mixed gas. According to the invention, fluorine plasma processing is carried out on the beta-Ga2O3 epitaxial layer by using an ICP plasma etching process so as to passivate the surface of the beta-Ga2O3 epitaxial layer, thereby improving the performance of the beta-Ga2O3 Schottky diode. F introduced through the method enters the surface of the epitaxial layer in the form of filling oxygen vacancies on the surface of the epitaxial layer or replacing original lattice oxygen, shallow energy level donor impurities are formed, defects are passivated, meanwhile, growth of the high-resistance GaFx passivation layer is inhibited through Ar plasma, and the forward on resistance of the beta-Ga2O3 Schottky diode is improved.

Description

Technical Field

[0001] This invention belongs to the field of power device technology, specifically relating to a method for improving power efficiency based on fluorine plasma passivation. β Methods for assessing the performance of Ga2O3 Schottky diodes. Background Technology

[0002] With the rapid advancements in power electronics, there is a growing demand for high-performance power semiconductor devices in various high-voltage, high-current applications (including electric vehicles, renewable energy conversion, and industrial control). Against this backdrop, power diodes, which combine high efficiency and low loss, are particularly crucial. While traditional silicon-based power diodes have been deployed on a large scale and partially meet application requirements, their inherent physical limitations, such as low breakdown electric field strength (approximately 0.3 MV / cm) and high on-resistance, are becoming bottlenecks for continuous performance optimization. In recent years, wide-bandgap semiconductor materials, such as silicon carbide (SiC) and gallium nitride (GaN), have demonstrated significant advantages in high-voltage (e.g., electric vehicles, power grids) and high-power applications due to their wider bandgap (~3.3 eV), higher thermal conductivity, and higher breakdown electric field strength. However, in the pursuit of higher performance limits, especially in cutting-edge applications requiring ultra-high voltage (>10kV), extreme power density, and higher energy conversion efficiency (such as ultra-high voltage smart grids, next-generation rail transit traction systems, and power equipment in extreme environments), even SiC and GaN face insurmountable challenges.

[0003] Gallium oxide ( β Ga2O3, as an emerging ultrawide bandgap semiconductor (bandgap width ~4.8eV), has rapidly become the focus of international research and development due to its extremely high theoretical breakdown electric field strength (8MV / cm, far exceeding SiC ~3MV / cm and GaN ~3.3MV / cm), its potential to grow low-cost large-size single crystal substrates through melt method, and its excellent Baliga's Figure of Merit (BFOM). β The excellent physical properties of Ga2O3 mean that power devices based on this material can operate in higher voltage environments with lower on-state resistance. Furthermore, its excellent thermal stability and chemical inertness further solidify its position as a leading power source. β Ga2O3 forms a solid foundation as a core material for next-generation high-efficiency power electronic devices. Currently βThe performance improvements of Ga2O3 Schottky diodes have primarily focused on refining the anode structure, such as trench MIS structures, field plates (sloping field plates, stepped field plates), and MESA structures. These improvements mainly aim to increase the reverse breakdown voltage of the device, neglecting the role of interface modulation. Furthermore, the etching process during fabrication can introduce unintended damage with limited repair methods, resulting in abundant dangling bonds and interface states on the β-Ga2O3 surface. These defect states also act as charge traps or generate recombination centers, becoming the main leakage paths and significantly increasing the reverse bias leakage current of the device.

[0004] Patent CN 113964183 A discloses a fluorine plasma-injected terminal gallium oxide power diode and its fabrication method, using CF4 as a single gas in... β Fluorine plasma is injected intermittently within the Ga2O3 drift layer. Using a single CF4 layer may result in a thicker GaF layer. x GaF x The very low conductivity constitutes a high-resistivity region. Patent CN 119584689 A discloses a p-type gallium oxide thin film and an ultraviolet photodiode fabricated using fluorine ion implantation, along with a method for their preparation. This method utilizes an ion implanter... β -Ga2O3 injection F + Fluoride ions (F⁻) are electronegative due to their high electronegativity. + It attracts electrons bound by existing Ga-O bonds at other sites, thereby creating holes at the original sites. It acts as an acceptor impurity, increasing the hole concentration and thus forming a p-type structure. β -Ga2O3. Patent CN117995663A discloses a method for controlling the donor concentration of gallium oxide semiconductor materials through anion doping, which mainly considers the... β Bulk doping of Ga2O3 and high-energy ion implantation facilitate the... β Ga2O3 crystals cause lattice damage.

[0005] Therefore, it is necessary to study a control strategy that starts from the interface to optimize it. β -The Ga2O3 interface enhances device performance, combining passivation and doping to improve carrier concentration. Summary of the Invention

[0006] In view of the problems existing in the prior art, the present invention provides a method for improving the treatment efficiency using an SF6 / Ar mixed gas. β A method for improving the performance of Ga2O3 Schottky diodes aims to achieve shallow donor doping, increase electron concentration, and form Ga-F bonds for passivation using F-based plasma bombardment. β -Ga2O3 surface and internal traps, while effectively controlling the high-resistivity GaF layer through Ar ion bombardment. xThickness is used to improve passivation effect, thereby optimizing β -Ga2O3 Schottky diode forward characteristics ultimately realize high-performance power diodes.

[0007] To solve the technical problem, the present invention adopts the following technical solution: This invention first discloses a method for improving performance based on fluorine plasma passivation. β The method for assessing the performance of Ga2O3 Schottky diodes, the aforementioned β -Ga2O3 Schottky diodes include front and back sides with opposite orientations. β -Ga2O3 single crystal substrate, in β -The front side of the Ga2O3 single crystal substrate has β -Ga2O3 epitaxial layer, using SF6 / Ar mixed gas and ICP plasma etching process to etch the layer. β - The Ga2O3 epitaxial layer is subjected to fluorine plasma treatment for passivation. β - The surface of the Ga2O3 epitaxial layer, thereby improving the β Performance of Ga2O3 Schottky diodes.

[0008] Furthermore, to achieve passivation, the fluorine plasma injection depth is controlled between 0.1 nm and 10 nm.

[0009] Furthermore, the specific process conditions of ICP plasma treatment, including the gas used, excitation, bias power, cavity pressure, and injection time, will all affect the formed GaF. x The thickness and fluorine plasma implantation depth have a significant impact, thus affecting the passivation effect. This invention utilizes an ICP plasma etching process to... β The conditions for fluorine plasma implantation into Ga2O3 epitaxial layers are as follows: excitation power of 300-400W, bias power of 50-100W, processing time of 10-30 min, chamber pressure of 0.8 Pa-2 Pa, total flow rate of SF6 / Ar mixed gas of 20 sccm, and SF6 flow rate of 15-19 sccm. Higher excitation power leads to higher etching efficiency, thus affecting the surface doping and passivation effects; lower bias power affects implantation efficiency, while higher bias power also increases etching efficiency but increases etching damage. Using an SF6 / Ar mixed gas, Ar participates in the etching process, effectively controlling the surface GaF... x The thickness thus reflects the effect of F doping and passivation. This invention utilizes the extra electrons released after F replaces O, therefore F in... β - In Ga2O3, it acts as a shallow donor impurity, which can provide additional free electrons, thereby reducing the specific on-resistance and increasing the forward current density.

[0010] This invention further discloses a high-performance fluorine plasma passivation-based method. β -Ga2O3 Schottky diode, comprising a front side and a back side having opposite orientations. β -Ga2O3 single crystal substrate, in β -The front side of the Ga2O3 single crystal substrate has β -Ga2O3 epitaxial layer, the β The surface of the Ga2O3 epitaxial layer was passivated using the method described above.

[0011] As a preferred option: the β - The doping concentration of the Ga2O3 single crystal substrate is 10. 18 ~10 19 cm -3 The thickness is 500~1000μm; β The doping concentration of the Ga2O3 epitaxial layer is 10. 16 ~10 17 cm -3 The thickness is 5~20μm.

[0012] As a preferred option: after passivation β A metal anode is deposited on the Ga2O3 epitaxial layer, in which... β A metal cathode is deposited on the back side of a Ga2O3 single crystal substrate.

[0013] Preferably, the metal anode is either a Ni / Au composite electrode or a Ni / Pt composite electrode with a total thickness of 100-300 nm, wherein the Ni layer thickness is 10-40 nm, and the remaining thickness is an Au or Pt layer. The desired composite electrode is formed by depositing the corresponding metal layer by layer. After the metal film used as the metal anode is deposited, it is thermally annealed at 500-600°C for 1-5 min in an N2 atmosphere to form the metal anode.

[0014] Preferably, the metal cathode is any one of a Ti / Au composite electrode, a Ti / Al / Ti / Au composite electrode, and a Ti / Al / Ni / Au composite electrode with a total thickness of 100-300 nm, wherein the Ti layer thickness is 10-20 nm, the Al or Ni layer thickness is 10-30 nm, and the thickness margin is an Au layer. The desired composite electrode is formed by depositing the corresponding metal layer by layer. After the metal film used as the metal cathode is deposited, it is thermally annealed at 400-500°C for 1-5 min in an N2 atmosphere to form the metal cathode.

[0015] Compared with existing technologies, the beneficial effects of this invention are reflected in: 1. This invention utilizes SF6 / Ar plasma treatment to allow fluorine atoms to occupy oxygen vacancies (V...o Passivating deep-level traps reduces carrier scattering centers and forms shallow donor states (Fi). o Increasing surface electron concentration, thereby optimizing β The forward characteristics of Ga2O3 Schottky diodes ultimately enable high-performance power diodes, improving upon traditional... β -Ga2O3 Schottky diodes suffer from problems such as excessive conduction losses due to interface defect scattering and reduced reverse breakdown voltage due to low barrier height.

[0016] 2. The method of the present invention has wide applicability and can be combined with other structures. β -Ga2O3 Schottky diodes can function in combination with field plate structures or mesa structures.

[0017] 3. The process of this invention is simple. The desired passivation effect can be obtained by reasonably controlling the etching power, gas ratio and cavity pressure without introducing new damage. Attached Figure Description

[0018] Figure 1 Provided by the present invention β -A schematic diagram of a Ga2O3 Schottky diode. In the diagram, numbered 1 represents the metal cathode, 2 represents... β -Ga2O3 single crystal substrate, 3 is β -Ga2O3 epitaxial layer, 4 is metal anode.

[0019] Figure 2 This invention is based on fluorine plasma passivation β - Schematic diagram of the fabrication process of Ga2O3 Schottky diode.

[0020] Figure 3 for β - Comparison of XRD patterns of Ga2O3 epitaxial layer before and after ICP treatment.

[0021] Figure 4 for β XPS spectrum of the F 1s peak on the surface of the Ga2O3 epitaxial layer after ICP treatment.

[0022] Figure 5 for β - Surface roughness variation of Ga2O3 during ICP etching with different gas ratios.

[0023] Figure 6 The figure shows the capacitance-voltage characteristic curve of the unpassivated sample in the example at 500 kHz.

[0024] Figure 7 The capacitance-voltage characteristic curve of the passivated sample in the example is shown at 500 kHz.

[0025] Figure 8 The voltage-current density characteristic curves of the unpassivated sample, the SF6 single-source passivated sample, and the passivated sample in the examples are shown under forward bias.

[0026] Figure 9 The on-resistance characteristic curves of the unpassivated sample, the SF6 single-source passivated sample, and the passivated sample in the examples are shown under forward bias.

[0027] Figure 10 The voltage-current density characteristics of the unpassivated and passivated samples in the examples are shown in reverse bias. Detailed Implementation

[0028] The embodiments of the present invention are described in detail below. These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments.

[0029] See Figure 1 This embodiment provides a method based on fluorine plasma passivation. β -Ga2O3 Schottky diode, comprising a front side and a back side having opposite orientations. β -Ga2O3 single crystal substrate 2, in β -The front side of the Ga2O3 single crystal substrate has β -Ga2O3 epitaxial layer 3, and ICP plasma etching process for... β The Ga2O3 epitaxial layer underwent fluorine plasma implantation for passivation. β -The surface of the Ga2O3 epitaxial layer. A metal anode 4 is disposed on the epitaxial layer. β A metal cathode 1 is disposed on the back side of the Ga2O3 single crystal substrate.

[0030] like Figure 2 As shown in this embodiment β Ga2O3 Schottky diodes are prepared using the following steps: 1. Take the front setting as an example. β -Ga2O3 epitaxial layer β -Ga2O3 single crystal substrate, wherein: β The doping concentration of the Ga2O3 single crystal substrate is 6 × 10⁻⁶. 18 cm -3 The thickness is 500 μm; β The doping concentration of the Ga2O3 epitaxial layer is 2×10⁻⁶. 16 cm -3 The substrate was 10 μm thick. It was then ultrasonically cleaned with acetone, isopropanol, and deionized water for 10 min and dried.

[0031] 2. Using ICP in β The passivation treatment was performed on the Ga2O3 epitaxial layer under the following conditions: excitation power of 375W, bias power of 85W, SF6 flow rate of 18sccm, Ar flow rate of 2sccm, cavity pressure of 0.8Pa, and treatment time of 30min.

[0032] Figure 3 for β The XRD patterns of the Ga2O3 epitaxial layer surface before and after passivation treatment show that the crystal integrity is good after ICP treatment and no new damage is generated.

[0033] Figure 4 for β XPS spectra of the F 1s peak on the surface of the Ga2O3 epitaxial layer after passivation treatment, compared with the surfaces after 5 nm and 10 nm were removed by sputtering with an argon ion sputtering gun integrated in the XPS. The results show that the F implantation depth is in the range of 5-10 nm.

[0034] Figure 5 for β The surface roughness variation diagram of Ga2O3 during ICP etching with different gas ratios shows that the surface roughness decreases as the SF6 ratio increases, which supports the selection of SF6:Ar=18sccm:2sccm in this embodiment.

[0035] The above data demonstrates the successful implantation of F, and the reduction in roughness and crystal integrity also provide subsequent support for the passivation effect.

[0036] 3. Using electron beam lithography, patterning is performed on the epitaxial layer to develop a circular pattern with a diameter of 50 μm for depositing the anode electrode. Using electron beam evaporation, 30 nm Ni / 100 nm Au are sequentially deposited on top of the epitaxial layer. After removing the unexposed photoresist, the layer is annealed in a rapid annealing furnace at 540 °C for 5 min in a N2 atmosphere to obtain the anode electrode layer.

[0037] 4. Using electron beam evaporation technology, 20nm Ti / 80nm Au were sequentially deposited on the back side of the substrate, followed by rapid thermal annealing at 470℃ for 1 min in a N2 atmosphere to obtain the cathode electrode layer and the SF6 / Ar mixed gas passivated sample (hereinafter referred to as the passivated sample).

[0038] To verify the impact of ICP passivation on device performance, this embodiment also prepared samples without step 2 passivation and samples that were passivated using only SF6 (20 sccm) as the etching gas.

[0039] Figure 6 and Figure 7The figures show the capacitance-voltage characteristics of the unpassivated and passivated samples at 500 kHz, respectively. From the fitting calculations, the carrier concentration N of the unpassivated sample can be obtained. d =1.89×10 16 cm -3 Built-in potential qV bi =1.36 eV; Carrier concentration N of the passivated sample d =2.14×10 16 cm -3 Built-in potential qV bi =1.52eV, which represents an increase in carrier concentration and built-in potential compared to the unpassivated sample.

[0040] Figure 8 The voltage-current density characteristics of the unpassivated sample, the SF6 single-source passivated sample, and the passivated sample under forward bias are shown. It can be seen that the current density of the passivated sample at a 3V forward bias is 1.57 times that of the unpassivated sample. However, the current density of the SF6 single-source passivated sample is significantly lower than that of the unpassivated sample, indicating that passivation with a single SF6 gas source... β The state of the Ga2O3 surface is different from that after etching using an SF6 / Ar mixed gas source in this invention. β The optimization trend for Ga2O3 surfaces is completely opposite.

[0041] Figure 9 The on-resistance characteristics of the unpassivated sample, the SF6 single-source passivated sample, and the passivated sample under forward bias are shown. It can be seen that the lowest on-resistance of the passivated sample is 2.61 mΩ·cm. 2 The lowest specific on-resistance of the unpassivated sample was 4.45 mΩ·cm. 2 The lowest specific on-resistance of a single SF6 passivated sample is 4.92 mΩ·cm. 2 .

[0042] Figure 10 The voltage-current density characteristics of the unpassivated and passivated samples under reverse bias are shown. Compared with the unpassivated sample, the leakage current of the passivated sample before breakdown is lower throughout the entire process, and the breakdown voltage is 53V higher than that of the unpassivated sample.

[0043] Depend on Figures 6 to 10 The results show that using an SF6 / Ar mixed gas and ICP etching... β The Ga2O3 surface not only effectively increases the carrier concentration and optimizes the forward characteristics, but also reduces surface states by occupying oxygen vacancies with F, passivating deep level defects, thereby optimizing the reverse leakage current and breakdown voltage.

[0044] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for improving performance based on fluorine plasma passivation β The method for assessing the performance of Ga2O3 Schottky diodes, the aforementioned β -Ga2O3 Schottky diodes include front and back sides with opposite orientations. β -Ga2O3 single crystal substrate, in β -The front side of the Ga2O3 single crystal substrate has β -Ga2O3 epitaxial layer, characterized in that: Using an SF6 / Ar mixed gas, an ICP plasma etching process was employed to etch the [material / material]. β - The Ga2O3 epitaxial layer is subjected to fluorine plasma treatment for passivation. β - The surface of the Ga2O3 epitaxial layer, thereby improving the β Performance of Ga2O3 Schottky diodes.

2. The method for improving performance based on fluorine plasma passivation according to claim 1 β A method for assessing the performance of Ga2O3 Schottky diodes, characterized by: To achieve passivation, the fluorine plasma injection depth is controlled between 0.1 nm and 10 nm.

3. The method for improving performance based on fluorine plasma passivation according to claim 1 or 2 β A method for assessing the performance of Ga2O3 Schottky diodes, characterized in that... The process of etching the material using ICP plasma etching β The conditions for fluorine plasma treatment of Ga2O3 epitaxial layers are as follows: excitation power of 300~400W, bias power of 50~100W, treatment time of 10~30min, cavity pressure of 0.8Pa~2Pa, total flow rate of SF6 / Ar mixed gas of 20sccm, and SF6 flow rate of 15-19sccm.

4. A method based on fluorine plasma passivation β -Ga2O3 Schottky diode, characterized in that: The β -Ga2O3 Schottky diodes include front and back sides with opposite orientations. β -Ga2O3 single crystal substrate, in β -The front side of the Ga2O3 single crystal substrate has β -Ga2O3 epitaxial layer, the β The surface of the Ga2O3 epitaxial layer is passivated according to the method described in any one of claims 1 to 3.

5. The fluorine plasma passivation based method according to claim 4 β -Ga2O3 Schottky diode, characterized in that: The β - The doping concentration of the Ga2O3 single crystal substrate is 10. 18 ~10 19 cm -3 The thickness is 500~1000μm; β The doping concentration of the Ga2O3 epitaxial layer is 10. 16 ~10 17 cm -3 The thickness is 5~20μm.

6. The fluorine plasma passivation based method according to claim 4 β -Ga2O3 Schottky diode, characterized in that: After passivation β A metal anode is deposited on the Ga2O3 epitaxial layer, in which... β A metal cathode is deposited on the back side of a Ga2O3 single crystal substrate.

7. The fluorine plasma passivation based method according to claim 6 β -Ga2O3 Schottky diode, characterized in that: The metal anode is either a Ni / Au composite electrode or a Ni / Pt composite electrode with a total thickness of 100-300 nm, wherein the Ni layer thickness is 10-40 nm and the thickness margin is an Au layer or a Pt layer.

8. The fluorine plasma passivation based method according to claim 7 β -Ga2O3 Schottky diode, characterized in that: After the metal film used as the metal anode is coated, it is heat-annealed at 500~600℃ for 1~5 minutes in an N2 atmosphere to form the metal anode.

9. The fluorine plasma passivation based method according to claim 6 β -Ga2O3 Schottky diode, characterized in that: The metal cathode is any one of Ti / Au composite electrode, Ti / Al / Ti / Au composite electrode and Ti / Al / Ni / Au composite electrode with a total thickness of 100~300nm, wherein the thickness of the Ti layer is 10~20nm, the thickness of the Al or Ni layer is 10~30nm, and the thickness margin is the Au layer.

10. The fluorine plasma passivation based method according to claim 9 β -Ga2O3 Schottky diode, characterized in that: After the metal film used as the metal cathode is coated, it is heat-annealed at 400~500℃ for 1~5 minutes in an N2 atmosphere to form a metal cathode.

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