A preparation method of a gallium nitride PN diode based on a metal phase molybdenum disulfide

Abstract

The application discloses a preparation method of a gallium nitride PN diode based on metal-phase molybdenum disulfide, which comprises the following steps: growing an n-GaN layer doped with Si on a GaN single crystal substrate, and growing a p-GaN layer doped with magnesium on the n-GaN layer; evaporating a metal film on the back of the GaN single crystal substrate after polishing to form an ohmic contact electrode, and annealing after gold lifting and glue removing; shielding a preset passivation area by using photoresist, exposing the passivation area after photoetching and development, vertically etching the p-GaN layer downward, forming a step on the surface of the device, performing photoetching on the step surface of the p-GaN layer, exposing the prepared passivation area after development, depositing an Si3N4 layer on the surface of the device in a nitrogen atmosphere, cleaning the Si3N4 on the step of the p-GaN layer by using a glue removing liquid, and performing polishing treatment; preparing a single-layer MoS2 doped with Re on the surface of the passivation layer, and making Re / Mo=2 / 3-7 / 3 after doping, so that the obtained molybdenum disulfide is in a metal phase. The field plate is prepared by using the metal-phase molybdenum disulfide, the thickness of the device is reduced, the ultra-thin device is facilitated to be prepared, the electric field aggregation at the edge is reduced, the device withstand voltage is improved, and the price is reduced.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor technology, and particularly relates to a method for fabricating a gallium nitride PN diode based on metallic molybdenum disulfide. Background Technology

[0002] In recent years, gallium nitride (GaN), a wide-bandgap semiconductor, has been widely used in power and radio frequency devices due to its superior material properties. Its advantages, such as high voltage resistance, high temperature resistance, and small size, have attracted significant attention and widespread application. The main characteristics of this device are: (1) it can withstand high voltage and has good conductivity; (2) it has a small size, which can significantly reduce the device's dimensions; and (3) it has high area utilization, making it suitable for conducting large currents and blocking large voltages.

[0003] Existing GaN PN devices have some problems that need to be improved: (1) Unterminated devices have low withstand voltage; when reverse voltage is applied, a large leakage current will be generated. (2) When an external voltage is applied, the electric field distribution tends to concentrate at the edge, which causes the device to break down prematurely, resulting in irreversible damage to the device. (3) The price of field plate metal materials is relatively high. Summary of the Invention

[0004] This invention provides a method for fabricating a gallium nitride PN diode based on metallic molybdenum disulfide, comprising:

[0005] A Si-doped n-GaN layer is grown on a GaN single crystal substrate, and a magnesium-doped p-GaN layer is grown on the n-GaN layer.

[0006] After polishing the back of the GaN single crystal substrate, a metal film is deposited to form an ohmic contact electrode, and the gold is peeled off and the adhesive is removed before annealing.

[0007] The passivation area is masked by photoresist. After photolithography and development, the passivation area is exposed. The p-GaN layer is etched vertically downward to form a step on the device surface. Photolithography is performed on the p-GaN layer step surface. After development, the passivation area is exposed. A Si3N4 layer is deposited on the device surface under a nitrogen atmosphere. The Si3N4 on the p-GaN layer step is cleaned with a photoresist remover and then polished.

[0008] A Re-doped monolayer of MoS2 was prepared on the surface of the passivation layer, and the Re / Mo ratio was adjusted to 2 / 3-7 / 3 after doping to make the resulting molybdenum disulfide a metallic phase.

[0009] Furthermore, the thickness of the n-GaN layer is 15μm-40μm, and the Si doping concentration is 1×10⁻⁶. 16 cm -3 -2×10 16 cm -3 .

[0010] Furthermore, the thickness of the p-GaN layer is 70nm-100nm, and the Mg doping concentration is 0.8×10⁻⁶. 18 cm -3 -1×10 18 cm -3 .

[0011] Furthermore, the thickness of the metallic MoS2 layer is 0.5-1.5 nm.

[0012] Furthermore, the thickness of Si3N4 is 70nm-100nm.

[0013] Furthermore, the thickness of the gallium nitride single crystal substrate is 300-500 μm, and the Si doping concentration is 5×10⁻⁶. 18 cm -3 -8×10 18 cm -3 .

[0014] Furthermore, the metal deposited in the ohmic contact is Ti / Al / Ni / Au.

[0015] Furthermore, the back side of the GaN single crystal substrate is polished to 250-350μm.

[0016] Furthermore, the p-GaN layer was etched using a vertical downward dry etching method with Cl2 / SiCl4.

[0017] Furthermore, SiC substrates are used instead of GaN single-crystal substrates.

[0018] In this invention, molybdenum disulfide (MoD) is used instead of conventional metals to fabricate the field plate and anode. Its advantages are: using MoD to fabricate the field plate results in a thinner plate, significantly reducing the overall thickness of the device and facilitating the fabrication of ultra-thin devices; it also reduces electric field concentration at the device edges, improving the device's withstand voltage and lowering the cost of device fabrication. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 A schematic diagram of the epitaxial process and ohmic contact formation provided for embodiments of the present invention;

[0021] Figure 2 A schematic diagram illustrating the fabrication of steps provided for an embodiment of the present invention.

[0022] Figure 3 A schematic diagram of the passivation layer preparation process provided for an embodiment of the present invention.

[0023] Figure 4 A schematic diagram of the preparation process of the metallic molybdenum disulfide field plate and anode provided for embodiments of the present invention.

[0024] Figure 5 This is a schematic diagram of a vertical gallium nitride PN diode with molybdenum disulfide as the field plate and anode, provided as an embodiment of the present invention. Detailed Implementation

[0025] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0026] This invention provides a method for fabricating a gallium nitride PN diode based on metallic molybdenum disulfide, comprising:

[0027] Step 1: Grow a Si-doped n-GaN layer on a GaN single crystal substrate, and then grow a magnesium-doped p-GaN layer on the n-GaN layer;

[0028] Specifically, the thickness of the gallium nitride single crystal substrate is 300-500 μm, preferably 300 μm, and the Si doping concentration is 5 × 10⁻⁶. 18 cm -3 -8×10 18 cm -3 Preferably 8×10 18 cm -3 In other embodiments, a SiC substrate can be used instead of a GaN single-crystal substrate. The thickness of the n-GaN layer is 15μm-40μm, and the Si doping concentration is 1×10⁻⁶. 16 cm -3 -2×10 16 cm -3 Preferably, the Si doping depth is 40 μm, and the Si doping concentration is 1 × 10⁻⁶. 16 cm -3 -2×10 16 cm -3 The thickness of the p-GaN layer is 70nm-100nm, preferably 80nm. The Mg doping concentration is 0.8×10⁻⁶. 18 cm -3 -1×10 18 cm -3 Preferably 1×10 18 cm -3 .

[0029] Step 2: After polishing the back of the GaN single crystal substrate, a metal film is deposited to form an ohmic contact electrode. After removing the gold and adhesive, the substrate is annealed.

[0030] Specifically, the back side of the GaN single-crystal substrate is polished to 250-350 μm, preferably 300 μm. The metal deposited in the ohmic contact is Ti / Al / Ni / Au.

[0031] Step 3: Use photoresist to block the preset passivation area, expose the passivation area after photolithography and development, etch the p-GaN layer vertically downward to form a step on the device surface, perform photolithography on the p-GaN layer step surface, expose the passivation area after development, deposit a Si3N4 layer on the device surface under a nitrogen atmosphere, clean the Si3N4 on the p-GaN layer step with a photoresist remover, and polish.

[0032] Specifically, the p-GaN layer is etched using a vertically downward dry etching method with Cl2 / SiCl4. The thickness of Si3N4 is 70nm-100nm, preferably 80nm.

[0033] Step 4: Prepare a Re-doped monolayer MoS2 on the surface of the passivation layer. After doping, make Re / Mo = 2 / 3-7 / 3 so that the resulting molybdenum disulfide is a metallic phase.

[0034] Specifically, the thickness of the metallic MoS2 layer is 0.5-1.5 nm, preferably 1 nm.

[0035] This invention innovatively proposes a gallium nitride PN diode using molybdenum disulfide as the field plate and anode. Compared with traditional GaN PN diodes, the use of a thin film of molybdenum disulfide instead of traditional metal can greatly reduce the thickness and size of the device under the same conditions, resulting in smaller devices, higher reliability, and higher withstand voltage. At the same time, the price is lower than that of traditional metal field plates, making it cheaper.

[0036] One embodiment of the present invention, such as Figures 1-4 The method for fabricating a gallium nitride PN diode using molybdenum disulfide as the field plate and anode is shown below:

[0037] 1. A 40 μm Si-doped n-GaN layer is grown on a GaN single-crystal substrate using hydride vapor phase epitaxy (HVPE). An 86 nm magnesium-doped p-GaN layer is grown on the n-GaN layer using hydride vapor phase epitaxy (HVPE), molecular beam epitaxy (MBE), or metal-organic chemical vapor deposition (MOCVD). The back side, i.e., the substrate surface, is polished to 300 μm; the thickness should be appropriate, as a thinner layer can reduce the on-resistance of the device. A schematic diagram of the structure is shown below. Figure 1 As shown.

[0038] 2. On the back of the GaN substrate, ohmic contacts are formed by thermal evaporation of metal, such as Ti (25 nm) / Al (100 nm) / Ni (20 nm) / Au (80 nm). After removing the gold and adhesive, the substrate is annealed at 800℃ and N2 for 60 seconds.

[0039] 3. For ICP etching of the stepped areas, first use photoresist to block the parts to be etched. After photolithography, develop to expose the areas to be etched. Use Cl2 / SiCl4 for vertical downward dry etching of the p-GaN layer, such as... Figure 2 As shown. After the step is fabricated, photolithography is used on the upper surface to expose the area where the passivation layer needs to be fabricated. Using ALD, a uniform Si3N4 layer with a thickness of 86 nm is deposited on the surface under a nitrogen atmosphere. After the coating is completed, the surface is cleaned with a resist remover to remove excess Si3N4. The surface is then polished to 80 nm with an appropriate thickness, ensuring the p-GaN layer is the same thickness as the Si3N4 layer to achieve a smooth surface. Specific device fabrication process. Figure 3 As shown.

[0040] 4. Re-doped monolayer MoS2 is prepared on the surface using chemical vapor deposition (CVD). After doping, the Re / Mo ratio is set to 2 / 3 to 7 / 3. At this point, molybdenum disulfide is a metallic phase with a band gap of 0 eV and exhibits electrical conductivity. (Specific details are as follows...) Figure 4 As shown.

[0041] Another embodiment of the present invention, such as Figure 5 The diagram shows a schematic of a vertical gallium nitride PN diode using molybdenum disulfide as the field plate and anode. It includes: a gallium nitride single-crystal substrate 5 with a thickness of 400 μm, using silicon as the dopant with a doping concentration of 8 × 10⁻⁶. 18 cm -3 The fourth n-GaN layer has a thickness of 40 μm and uses Si as a dopant with a doping concentration of 2 × 10⁻⁶. 16 cm -3 The third p-GaN layer is 80 nm thick and uses magnesium as a dopant with a doping concentration of 1 × 10⁻⁶. 18 cm -3 Si3N4 layer 2, with a thickness of 80 nm; MoS2 metal phase layer 1, with a thickness of 1 nm, using Re as a dopant, with a doping amount of Re / Mo = 2 / 3~7 / 3; cathode 6, composed of Ti (25 nm) / Al (100 nm) / Ni (20 nm) / Au (80 nm).

[0042] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. 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 list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

[0043] The above description is only a partial embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for fabricating a gallium nitride PN diode based on metallic molybdenum disulfide, characterized in that, include: A Si-doped n-GaN layer is grown on a GaN single crystal substrate, and a magnesium-doped p-GaN layer is grown on the n-GaN layer. After polishing the back of the GaN single crystal substrate, a metal film is deposited to form an ohmic contact electrode, and the gold is peeled off and the adhesive is removed before annealing. The passivation area is masked by photoresist. After photolithography and development, the passivation area is exposed. The p-GaN layer is etched vertically downward to form a step on the device surface. Photolithography is performed on the p-GaN layer step surface. After development, the passivation area is exposed. A Si3N4 layer is deposited on the device surface under a nitrogen atmosphere. The Si3N4 on the p-GaN layer step is cleaned with a photoresist remover and then polished. A Re-doped monolayer of MoS2 is prepared on the surface of the passivation layer. After doping, the Re / Mo ratio is set to 2 / 3-7 / 3 so that the resulting molybdenum disulfide is a metallic phase. The metallic molybdenum disulfide is used as the field plate and anode of the gallium nitride PN diode.

2. The preparation method according to claim 1, characterized in that, The thickness of the n-GaN layer is 15μm-40μm, and the Si doping concentration is 1×10⁻⁶. 16 cm -3 -2×10 16 cm -3 .

3. The preparation method according to claim 1, characterized in that, The p-GaN layer has a thickness of 70nm-100nm and a Mg doping concentration of 0.8×10⁻⁶. 18 cm -3 -1×10 18 cm -3 .

4. The preparation method according to claim 1, characterized in that, The thickness of the metallic MoS2 layer is 0.5-1.5 nm.

5. The preparation method according to claim 1, characterized in that, The thickness of Si3N4 is 70nm-100nm.

6. The preparation method according to claim 1, characterized in that, The thickness of the gallium nitride single crystal substrate is 300-500 μm, and the Si doping concentration is 5×10⁻⁶. 18 cm -3 -8×10 18 cm -3 .

7. The preparation method according to claim 1, characterized in that, The metals deposited by ohmic contact vapor deposition are Ti / Al / Ni / Au.

8. The preparation method according to claim 1, characterized in that, The back side of the GaN single crystal substrate is polished to 250-350μm.

9. The preparation method according to claim 1, characterized in that, The p-GaN layer was etched using a vertical downward dry etching method with Cl2 / SiCl4.

10. The preparation method according to claim 7, characterized in that, Use SiC substrates instead of GaN single crystal substrates.

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