A method for manufacturing a gallium nitride schottky diode

Abstract

The application relates to the field of semiconductor devices, in particular to a preparation method of a gallium nitride Schottky diode. The preparation method comprises the following steps: providing a substrate provided with a gallium nitride drift layer; forming a groove on the gallium nitride drift layer; performing first low-energy ion implantation on the bottom wall area of the groove to form a first ion implantation area; growing a gallium nitride epitaxial layer in the groove to fill the groove; and performing second low-energy ion implantation on the surface of the gallium nitride epitaxial layer to form a second ion implantation area, wherein the second ion implantation area is connected with the first ion implantation area, and the cross-sectional area and shape of the second ion implantation area are consistent with those of the first ion implantation area in the direction perpendicular to the ion implantation direction. The high-depth ion implantation is realized by adopting the cooperation of the two low-energy ion implantations, the technical difficulty and machine cost for realizing the high-depth ion implantation are reduced, and the danger of high-energy ion implantation is avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of semiconductor devices, in particular to a preparation method of a gallium nitride Schottky diode. BACKGROUND

[0002] Gallium nitride (GaN) as a representative material of the third generation of semiconductors, due to the characteristics of wide band gap, high breakdown voltage, high thermal conductivity and high thermal stability, is widely used in power devices and radio frequency devices. Among them, the gallium nitride Schottky diode has attracted great attention and application due to its high voltage resistance, high working frequency and low reverse leakage current and a series of excellent performances.

[0003] However, in the traditional gallium nitride Schottky diode, the Schottky junction formed by the contact between the metal and the semiconductor will be affected by the mirror force under high electric field, which will induce the reduction of the Schottky barrier and the reverse leakage problem, thereby causing the increase of the opening voltage and the reverse leakage current of the diode, and further causing the edge electric field of the diode to be gathered under the action of the applied electric field, thereby reducing the breakdown voltage and causing the premature breakdown of the diode, which limits the application of the gallium nitride Schottky diode. Therefore, in the existing gallium nitride Schottky diode, ions are usually implanted to enhance the stability of the device under high electric field, reduce the edge gathering, prevent the premature reduction of the Schottky barrier, and thus improve the breakdown voltage of the device.

[0004] In order to ensure the depth of ion implantation, in the current preparation process of gallium nitride Schottky diode, high-depth ion implantation is usually realized by means of one-time high-energy ion implantation, that is, by applying high energy to the ions to make the ions penetrate the material to a deeper level. However, on the one hand, the high-energy ion implantation method requires very high mechanical equipment, which needs to withstand high-energy ion beams and maintain precise control; on the other hand, high-energy ion beams have certain danger, and strict safety measures need to be taken to ensure the safety of the operators, therefore, the high-energy ion implantation method has high equipment cost and high requirements for the operators, which is not conducive to the wide production and application of gallium nitride Schottky diode. SUMMARY

[0005] Therefore, the technical problem to be solved by the present application is to overcome the defects of the preparation method of the gallium nitride Schottky diode in the prior art, such as high cost and high danger, which is not conducive to the wide production and application of the gallium nitride Schottky diode, and to provide a preparation method of a gallium nitride Schottky diode.

[0006] A preparation method of a gallium nitride Schottky diode, comprising the following steps:

[0007] providing a substrate, wherein a gallium nitride drift layer is arranged on the substrate;

[0008] forming a trench on the gallium nitride drift layer;

[0009] performing a first low-energy ion implantation on a bottom wall region of the trench toward a side where the substrate is located to form a first ion implantation region;

[0010] growing a gallium nitride epitaxial layer in the trench, the gallium nitride epitaxial layer filling the trench;

[0011] performing a second low-energy ion implantation on a surface of the gallium nitride epitaxial layer toward the side where the substrate is located to form a second ion implantation region connected to the first ion implantation region, and in a direction perpendicular to the ion implantation direction, the second ion implantation region has the same area and shape as a cross section of the first ion implantation region.

[0012] In one embodiment, the first low-energy ion implantation has a depth equal to a depth of the trench, and the second low-energy ion implantation has a depth greater than or equal to the depth of the trench.

[0013] In one embodiment, the first low-energy ion implantation has a depth, the trench has a depth, and the second low-energy ion implantation has a depth, each of which is 1 μm.

[0014] In one embodiment, the ions used in the first low-energy ion implantation and the second low-energy ion implantation each include at least one of helium, fluorine, carbon, silicon, oxygen, and magnesium.

[0015] In one embodiment, the gallium nitride drift layer has a thickness of 10 μm to 50 μm, and before the first low-energy ion implantation, the method further includes etching a mesa surface on an edge of the gallium nitride drift layer, the mesa surface having a thickness of 2 μm to 5 μm.

[0016] In one embodiment, the gallium nitride epitaxial layer is grown at a temperature of 500 °C to 700 °C.

[0017] In one embodiment, the method further includes forming a metal cathode on a side of the substrate opposite the gallium nitride drift layer, the metal cathode including at least one of a titanium layer having a thickness of 25 nm, an aluminum layer having a thickness of 100 nm, a nickel layer having a thickness of 20 nm, and a gold layer having a thickness of 60 nm.

[0018] In one embodiment, the method further includes forming a metal anode on a side of the gallium nitride drift layer opposite the substrate, the metal anode including a nickel layer having a thickness of 20 nm and / or a gold layer having a thickness of 60 nm.

[0019] In one embodiment, the substrate is one of a gallium nitride single crystal substrate, a silicon carbide substrate, a silicon substrate, a sapphire substrate, or a diamond substrate.

[0020] The technical scheme of the present application has the following advantages:

[0021] 1. The preparation method of the gallium nitride Schottky diode provided by the present application realizes high-depth ion implantation by twice low-energy ion implantation, which has lower requirements for the machine equipment, is relatively simple to operate, and has lower requirements for the operator, thereby reducing the technical difficulty and machine cost required for realizing high-depth ion implantation, avoiding the danger of high-energy ion implantation, making high-depth ion implantation easier to realize, and thus facilitating the wide preparation and application of gallium nitride. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the technical scheme in the specific embodiments or prior art of the present application, the drawings needed in the specific embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0023] Figure 1 is a process flow chart of the preparation method of the gallium nitride Schottky diode in an embodiment of the present application;

[0024] Figure 2 is a process flow chart of the preparation method of the gallium nitride Schottky diode in another embodiment of the present application. DETAILED DESCRIPTION

[0025] The following embodiments are provided in order to better further understand the present application, and are not limited to the best embodiments, and do not constitute a limitation on the content and protection scope of the present application. Any person who obtains any product the same as or similar to the present application under the inspiration of the present application or by combining the present application with other prior art features falls within the protection scope of the present application.

[0026] The specific experimental steps or conditions not mentioned in the embodiments can be performed according to the conventional experimental steps described in the literature in the art or the operation or conditions. The reagents or instruments not mentioned by the manufacturer are conventional reagent products that can be obtained by purchase.

[0027] The present application provides a preparation method of a gallium nitride Schottky diode, which is used for preparing a gallium nitride Schottky diode that is not easy to be broken down in advance.

[0028] Reference is made to Figure 1In one embodiment, the method for fabricating a gallium nitride Schottky diode includes the following steps:

[0029] S1. A substrate is provided, on which a gallium nitride drift layer is disposed;

[0030] S2. Form trenches on the gallium nitride drift layer;

[0031] S3. Perform the first low-energy ion implantation on the bottom wall region of the trench facing the substrate to form the first ion implantation region. Figure 1 (Medium gray area);

[0032] S4. A gallium nitride epitaxial layer is grown in the trench, and the gallium nitride epitaxial layer fills the trench.

[0033] S5. Perform a second low-energy ion implantation on the side of the gallium nitride epitaxial layer facing the substrate to form a second ion implantation region. Figure 1 The gray area within the trench), the second ion implantation region is connected to the first ion implantation region, and in the direction perpendicular to the ion implantation direction, the area and shape of the cross-section of the second ion implantation region and the first ion implantation region are the same.

[0034] The gallium nitride Schottky diode fabrication method provided in this embodiment achieves high-depth ion implantation by employing two low-energy ion implantations. Low-energy ion implantation has lower requirements for equipment and is relatively simple to operate, requiring fewer operators. Therefore, it can reduce the technical difficulty and machine cost required to achieve high-depth ion implantation, and avoid the dangers of high-energy ion implantation, making high-depth ion implantation easier to achieve, thereby promoting the widespread fabrication and application of gallium nitride.

[0035] Furthermore, the gallium nitride Schottky diode fabrication method provided in this embodiment, by performing ion implantation in two stages, allows for precise control of the ion implantation depth by adjusting the energy and dosage of each ion implantation, thus meeting specific application requirements. Moreover, optimizing the implantation parameters can reduce material damage and improve the overall performance of the material.

[0036] Meanwhile, the gallium nitride Schottky diode fabrication method provided in this embodiment, by performing ion implantation after forming trenches, can make the ion doping region more precise and deeper, which helps to improve the conductivity of the device, reduce the on-resistance, and reduce the power consumption of the device under normal operating conditions.

[0037] In one embodiment, the substrate is a gallium nitride single crystal substrate with a thickness of 300 μm, and Si is used as the dopant with a doping concentration of 2.5 × 10⁻⁶. 18 cm -3In other embodiments, the substrate can also be one of a silicon carbide substrate, a silicon substrate, a sapphire substrate, or a diamond substrate.

[0038] In one embodiment, the thickness of the gallium nitride drift layer is 20 μm, is grown using a hydride vapor phase epitaxy (HVPE) method, and is also doped using Si with a doping concentration of 2-5 x 1018cm-3. 16 cm -3 In other embodiments, the thickness of the gallium nitride drift layer only needs to be in the range of 10 μm-50 μm, can also be obtained using a molecular beam epitaxy (MBE) or a metal organic chemical vapor deposition (MOCVD) method, and in addition, the gallium nitride drift layer can also not be ion doped.

[0039] In one embodiment, the trench is a trench with a circular ring-shaped bottom surface obtained using a dry etching process, and the diameter of the outer circle is 10 μm larger than the diameter of the inner circle, and the depth of the trench is 1 μm.

[0040] Specifically, the trench can be formed according to the following steps: first, using a photoresist blocking process, a SiO2 hard mask is used to expose the etching area; a RIE-ICP plasma etching process is used to etch the trench area of the gallium nitride drift layer, and the etching gas uses Cl2 / BCl3 (Cl2 flow rate is 20 sccm, BCl3 flow rate is 1 sccm), the working pressure in the plasma cavity is maintained at 5 mTorr, and the power is 250 W.

[0041] Generally, after etching is completed, a large number of etching damages are formed inside the trench, and the damage inside the trench can be treated, and a tetramethylammonium hydroxide (TMAH) aqueous solution is used to treat the damage inside the trench, and is soaked at 80°C for 2 hours to repair the sidewall and bottom of the trench. Finally, piranha solution (H2SO4 and H202 in a ratio of 10:1) and BOE (buffered oxide etchant, mainly mixed from NH4F and HF) are used for soaking, first soaked in piranha solution for 2 hours, and then soaked in BOE solution for 10 minutes, to smooth the trench.

[0042] In other embodiments, the shape of the trench can also be a cube or a cuboid, and the like. The diameter difference between the outer circle and the inner circle of the trench can also be 11 μm, 12 μm, or 13 μm, and the like, which can be adjusted according to the ion implantation requirements. The depth of the trench can also be between 1-1.5 μm, which can also be adjusted according to the ion implantation requirements.

[0043] In one embodiment, the first low-energy ion implantation is performed using an ion implanter, the energy of the first low-energy ion implantation is 350 keV, the ion used is He ion, the cross-sectional shape of the first ion implantation region is consistent with the cross-sectional shape of the trench, and is also a circular ring shape, and the diameter difference between the outer circle and the inner circle of the bottom surface of the first ion implantation region is also 10 μm, the diameter of the outer circle of the bottom surface of the first ion implantation region is 20 μm, and the implantation depth is 1 μm.

[0044] In other embodiments, the energy of the first low-energy ion implantation is limited to a range of equal to or less than 350 keV, which is low in power and non-hazardous to the equipment. In other embodiments, the diameter difference between the outer circle and the inner circle of the bottom surface of the first ion implantation region is also 11 μm, 12 μm, 15 μm, etc., and the implantation depth is in the range of 1-1.5 μm. Specifically, the width and depth of the first ion implantation region can be adjusted according to the final required ion implantation depth, as long as the implantation can be completed at low energy. The ion selected for the first low-energy ion implantation can also be at least one of fluorine, carbon, silicon, oxygen, and magnesium.

[0045] As shown in FIG. 1, Figure 2 In one embodiment, for the convenience of ion implantation, before the first low-energy ion implantation, a step of etching a mesa surface at the edge of the gallium nitride drift layer is further included. That is, a photoresist is used as a barrier, a 7 μm positive photoresist process is used, a Cl2 / BCl3 plasma inductively coupled etching machine is used for variable rate dry etching, the Cl2 flow rate is 20 sccm, the BCl3 flow rate is 1 sccm, the working pressure in the plasma cavity is maintained at 5 mTorr, and the power is 250 W; the surrounding area is etched away, and a "raised" mesa is formed after etching in the middle, the thickness of the mesa is 3 μm.

[0046] In other embodiments, the thickness of the mesa can be controlled to be in the range of 2 μmˉ5 μm.

[0047] In one embodiment, after the first low-energy ion implantation, an annealing step is further included, the annealing temperature is 800 °C, and the annealing process can activate the implanted ions and repair the damage to the lattice caused during the implantation process, thereby ensuring the performance of the device after the first low-energy ion implantation.

[0048] In one embodiment, the gallium nitride (GaN) epitaxial layer is grown using molecular beam epitaxy (MBE), with a thickness of 1 μm and a growth temperature of 600°C. In other embodiments, the GaN epitaxial layer can be formed using hydride vapor phase epitaxy (HVPE) or metal-organic chemical vapor deposition (MOCVD). The thickness of the GaN epitaxial layer can also be greater than 1 μm, provided that the thickness is greater than or equal to the trench depth to ensure complete trench filling. The growth temperature of the GaN epitaxial layer needs to be controlled between 500-700°C to ensure that the implanted ions do not diffuse away due to high temperatures.

[0049] In one embodiment, a second low-energy ion implantation is performed using an ion implanter. The energy of the second low-energy ion implantation is 350 keV, and the ions used are He ions. The cross-sectional shape of the second ion implantation region is identical to that of the first ion implantation region, being annular, and the difference in diameter between the outer and inner circles of the bottom surface of the second ion implantation region is also 10 μm. The outer diameter of the second ion implantation region is 20 μm, and the implantation depth is 1 μm. That is, the second ion implantation region and the first ion implantation region are opposite each other in the ion implantation direction and have the same shape. The connection between the second and first ion implantation regions forms a deeper ion implantation region, thereby enabling the device to achieve better reverse breakdown voltage performance.

[0050] In other embodiments, the power of the second low-energy ion implantation can also be in the range of greater than 350 keV and less than 450 keV, the diameter of the outer circle of the bottom surface can also be 80 μm, 130 μm, 180 μm, 330 μm, etc., the diameter difference between the outer circle and the inner circle of the bottom surface can also be 11 μm, 12 μm, 15 μm, etc., and the implantation depth can be in the range of 1-1.5 μm. The specific values ​​can be adjusted according to the final required ion implantation depth. The ions selected for the second low-energy ion implantation can also be at least one of fluorine, carbon, silicon, oxygen, and magnesium.

[0051] like Figure 2 As shown, in one embodiment, the method for fabricating a gallium nitride Schottky diode further includes the step of forming a metal cathode on the side of the substrate opposite to the gallium nitride drift layer. Specifically, the metal cathode is formed by depositing a metal film on the substrate to form an ohmic contact using magnetron sputtering or electron beam evaporation deposition, followed by annealing in a nitrogen atmosphere at 800°C for 60 seconds.

[0052] In one embodiment, the metal cathode is a stack formed by combining a titanium layer with a thickness of 25 nm, an aluminum layer with a thickness of 100 nm, a nickel layer with a thickness of 20 nm, and a gold layer with a thickness of 60 nm. In other embodiments, the metal cathode may also consist of at least one layer selected from the following: a titanium layer with a thickness of 25 nm, an aluminum layer with a thickness of 100 nm, a nickel layer with a thickness of 20 nm, and a gold layer with a thickness of 60 nm.

[0053] like Figure 2 As shown, in one embodiment, the method for fabricating a gallium nitride Schottky diode further includes the step of forming a metal anode on the side of the gallium nitride drift layer opposite to the substrate after a second low-energy ion implantation. Specifically, the metal anode is formed by depositing a metal film on the gallium nitride drift layer and the second ion implantation layer using methods such as magnetron sputtering, thermal evaporation, or electron beam evaporation in conjunction with photolithography to form a Schottky contact, and then removing excess metal film using a lift-off process.

[0054] In one embodiment, the metal anode is a stack of a nickel layer with a thickness of 20 nm and a gold layer with a thickness of 60 nm. In other embodiments, the metal anode may be a single nickel layer or a single gold layer.

[0055] The gallium nitride Schottky diodes fabricated by the method provided in this embodiment of the invention integrate pre-etched trench technology and high-depth ion implantation technology during the fabrication process. The pre-etched trench technology optimizes the electric field distribution, while the high-depth ion implantation technology forms an effective barrier layer on the gallium nitride drift layer. This significantly enhances the stability of the device under high electric fields, effectively reduces edge electric field accumulation, prevents premature reduction of the Schottky barrier, and thus greatly increases the breakdown voltage of the device, preventing premature breakdown. Simultaneously, due to the effective control of reverse leakage current, the energy loss of the device in standby or reverse blocking states is also greatly reduced, further improving the overall energy efficiency.

[0056] 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.

Claims

1. A method of fabricating a gallium nitride Schottky diode, comprising: The method comprises the following steps: ​ providing a substrate with a gallium nitride drift layer formed thereon; forming a trench on the gallium nitride drift layer; performing a first low-energy ion implantation on a bottom wall region of the trench toward a side where the substrate is located, to form a first ion implantation region; growing a gallium nitride epitaxial layer in the trench, which fills the trench; performing a second low-energy ion implantation on a surface of the gallium nitride epitaxial layer toward the side where the substrate is located, to form a second ion implantation region connected to the first ion implantation region, and in a direction perpendicular to the ion implantation direction, the second ion implantation region has the same area and shape as a cross section of the first ion implantation region; the first low-energy ion implantation has a depth equal to a depth of the trench, and the second low-energy ion implantation has a depth greater than or equal to the depth of the trench.

2. The production method according to claim 1, characterized by, The depth of the first low-energy ion implantation, the depth of the trench, and the depth of the second low-energy ion implantation are all 1 μm.

3. The preparation method according to claim 1, characterized in that, The ions used in the first low-energy ion implantation and the second low-energy ion implantation all comprise at least one of helium, fluorine, carbon, silicon, oxygen, and magnesium.

4. The production method according to claim 1, characterized by, The gallium nitride drift layer has a thickness of 10-50 μm, and before the first low-energy ion implantation, a step of etching a mesa surface at an edge of the gallium nitride drift layer is further included, and the mesa surface has a thickness of 2-5 μm.

5. The method of claim 1, wherein, The gallium nitride epitaxial layer is grown at a temperature of 500-700 °C.

6. The method of claim 1, wherein, The preparation method further comprises a step of forming a metal cathode on a side of the substrate opposite to the gallium nitride drift layer, and the metal cathode comprises at least one of a titanium layer with a thickness of 25 nm, an aluminum layer with a thickness of 100 nm, a nickel layer with a thickness of 20 nm, and a gold layer with a thickness of 60 nm.

7. The production method according to claim 1 or 6, characterized by, The preparation method further comprises a step of forming a metal anode on a side of the gallium nitride drift layer opposite to the substrate after the second low-energy ion implantation, and the metal anode comprises a nickel layer with a thickness of 20 nm and / or a gold layer with a thickness of 60 nm.

8. The method of claim 1, wherein, The substrate is one of a gallium nitride single crystal substrate, a silicon carbide substrate, a silicon substrate, a sapphire substrate, or a diamond substrate.

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