Preparation method of gallium nitride Schottky diode

Abstract

The invention 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; first-time low-energy ion implantation is carried out on the side, facing the substrate, of 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; second low-energy ion implantation is carried out on the side, facing the substrate, of the surface of the gallium nitride epitaxial layer to form a second ion implantation region, the second ion implantation region is connected with the first ion implantation region, and the area and the shape of the cross section of the second ion implantation region are consistent with those of the cross section of the first ion implantation region in the direction perpendicular to the ion implantation direction. High-depth ion implantation is achieved through cooperation of two times of low-energy ion implantation, the technical difficulty and machine cost for achieving high-depth ion implantation are reduced, and danger of high-energy ion implantation is avoided.

Description

Technical Field

[0001] The invention relates to the field of semiconductor devices, and in particular to a method for preparing a gallium nitride Schottky diode. Background Art

[0002] As a representative material of the third-generation semiconductor, gallium nitride (GaN) is widely used in the field of power devices and radio frequency devices due to its large bandgap, high breakdown voltage, high thermal conductivity and high thermal stability. Among them, gallium nitride Schottky diodes have attracted great attention and application due to their excellent performance such as high withstand voltage, high operating frequency and low reverse leakage current.

[0003] However, in traditional GaN Schottky diodes, the Schottky junction formed by the contact between metal and semiconductor is usually affected by the image force under high electric field, which induces the problem of lowering the Schottky barrier and reverse leakage, resulting in an increase in the diode's turn-on voltage and reverse leakage current, which in turn causes the diode's edge electric field to aggregate under the action of an external electric field, reducing the breakdown voltage and causing the diode to break down prematurely, limiting the application of GaN Schottky diodes. Therefore, existing GaN Schottky diodes are usually injected with ions to enhance the stability of the device under high electric field, reduce edge aggregation, and prevent the premature reduction of the Schottky barrier, thereby increasing the device's breakdown voltage.

[0004] In order to ensure the depth of ion implantation, in the current preparation process of GaN Schottky diodes, high-depth ion implantation is usually achieved by one-time high-energy ion implantation, that is, by applying higher energy to the ions so that the ions penetrate the material to a deeper level. However, on the one hand, high-energy ion implantation has very high requirements for mechanical equipment, requiring the equipment to be able to withstand high-energy ion beams and maintain precise control; on the other hand, high-energy ion beams are dangerous and strict safety measures need to be taken to ensure the safety of operators. Therefore, the equipment cost of high-energy ion implantation is high, and the requirements for operators are also high, which is not conducive to the widespread production and application of GaN Schottky diodes. Summary of the invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the defects of the prior art method for preparing gallium nitride Schottky diodes, which is high in cost and risk and is not conducive to the widespread production and application of gallium nitride Schottky diodes, thereby providing a method for preparing gallium nitride Schottky diodes.

[0006] A method for preparing a gallium nitride Schottky diode comprises the following steps:

[0007] Providing a substrate, on which a gallium nitride drift layer is disposed;

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

[0009] Performing a first low-energy ion implantation on a side of the bottom wall region of the trench facing the substrate to form a first ion implantation region;

[0010] Growing a gallium nitride epitaxial layer in the trench, wherein the gallium nitride epitaxial layer fills the trench;

[0011] A second low-energy ion implantation is performed on the surface of the gallium nitride epitaxial layer on the side facing the substrate 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 and the first ion implantation region have the same cross-sectional area and shape.

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

[0013] In one embodiment, 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.

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

[0015] In one embodiment, the thickness of the gallium nitride drift layer is 10 μm-50 μm. Before the first low-energy ion implantation, the method further includes a step of etching an edge of the gallium nitride drift layer to form a mesa table, and the thickness of the mesa table is 2 μm-5 μm.

[0016] In one embodiment, the growth temperature of the gallium nitride epitaxial layer is 500-700°C.

[0017] In one embodiment, the preparation method also includes the step of forming a metal cathode on the side of the substrate opposite to the gallium nitride drift layer, and the metal cathode includes 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.

[0018] In one embodiment, the preparation method further includes the step of forming a metal anode on a side of the gallium nitride drift layer opposite to the substrate, and the metal anode includes a nickel layer with a thickness of 20 nm and / or a gold layer with 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 solution of the present invention has the following advantages:

[0021] 1. The preparation method of the gallium nitride Schottky diode provided by the present invention realizes high-depth ion injection by adopting the combination of two low-energy ion injections. The low-energy ion injection has low requirements on machinery and equipment, and is relatively simple to operate, and has low requirements on operators. Therefore, the technical difficulty and machine cost required for high-depth ion injection can be reduced, and the danger of high-energy ion injection is avoided, making high-depth ion injection easier to achieve, which is conducive to promoting the widespread preparation and application of gallium nitride. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0023] Figure 1 is a process flow chart of a method for preparing a gallium nitride Schottky diode in one embodiment of the present invention;

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

[0025] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.

[0026] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0027] The invention provides a method for preparing a gallium nitride Schottky diode, which is used for preparing a gallium nitride Schottky diode which is not prone to premature breakdown.

[0028] See also Figure 1In one embodiment, the method for preparing a gallium nitride Schottky diode comprises the following steps:

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

[0030] S2, forming a groove on the gallium nitride drift layer;

[0031] S3, performing a first low-energy ion implantation on the bottom wall area of ​​the trench toward the side where the substrate is located, forming a first ion implantation area ( Figure 1 medium gray area);

[0032] S4, growing a GaN epitaxial layer in the trench, so that the GaN epitaxial layer fills the trench;

[0033] S5, performing a second low-energy ion implantation on the side of the surface of the gallium nitride epitaxial layer facing the substrate to form a second ion implantation area ( Figure 1 The second ion implantation region is connected to the first ion implantation region, and in a direction perpendicular to the ion implantation direction, the cross-sectional area and shape of the second ion implantation region and the first ion implantation region are consistent.

[0034] The method for preparing a gallium nitride Schottky diode provided in this embodiment realizes high-depth ion implantation by adopting a combination of two low-energy ion implantations. Low-energy ion implantation has low requirements for machinery and equipment, and is relatively simple to operate, and has low requirements for operators. Therefore, the technical difficulty and machine cost required for achieving high-depth ion implantation can be reduced, and the danger of high-energy ion implantation is avoided, making high-depth ion implantation easier to achieve, which is conducive to promoting the widespread preparation and application of gallium nitride.

[0035] In addition, the method for preparing the gallium nitride Schottky diode provided in this embodiment divides the ion implantation into two times, so that the depth of the ion implantation can be precisely controlled by adjusting the energy and dosage of each ion implantation to meet specific application requirements. In addition, the material damage can be reduced and the overall performance of the material can be improved by optimizing the implantation parameters.

[0036] At the same time, the preparation method of the gallium nitride Schottky diode provided in this embodiment can make the ion doping area more precise and deep by performing ion implantation after forming the groove, which helps to improve the conductivity of the device, reduce the on-resistance, and reduce the power consumption of the device under normal working 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 a dopant with a doping concentration of 2ˉ5×10 18 cm -3In other embodiments, the substrate may also be a silicon carbide substrate, a silicon substrate, a sapphire substrate, or a diamond substrate.

[0038] In one embodiment, the GaN drift layer has a thickness of 20 μm and is grown by hydride vapor phase epitaxy (HVPE) and is also doped with Si at a doping concentration of 2ˉ5×10 16 cm -3 In other embodiments, the thickness of the GaN drift layer only needs to be in the range of 10 μmˉ50 μm, and it can also be obtained by molecular beam epitaxy (MBE) or metal organic chemical vapor deposition (MOCVD). In addition, ion doping may not be performed in the GaN drift layer.

[0039] In one embodiment, the groove is a groove with a circular bottom surface obtained by 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 groove is 1 μm.

[0040] Specifically, the groove can be formed according to the following steps: first, a photolithography blocking process is used to form a SiO 2 Make a hard mask to expose the etching area; use RIE-ICP plasma etching process to etch the groove area of ​​the GaN drift layer, and the etching gas is Cl 2 / BCl 3 (Cl 2 The flow rate is 20 sccm, BCl 3 The flow rate is 1 sccm), the working pressure in the plasma chamber is maintained at 5 mTorr, and the power is 250 W.

[0041] Generally, after etching is completed, a large amount of etching damage will be formed inside the groove. The damage treatment inside the groove can be carried out by using tetramethylammonium hydroxide (TMAH) aqueous solution to treat the damage inside the groove and soaking it at 80°C for 2 hours to repair the sidewalls and bottom of the groove. Finally, piranha solution (H 2 SO 4 With H 2 0 2 ratio of 10:1) and BOE (buffered oxide etchant, mainly NH 4 F and HF mixture) were soaked in piranha solution for 2 hours and then in BOE solution for 10 minutes to smooth the grooves.

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

[0043] In one embodiment, an ion implanter is used to perform a first low-energy ion implantation. The energy of the first low-energy ion implantation is 350 keV, and the ions used are He ions. Viewed along a direction perpendicular to the ion implantation direction, the cross-sectional shape of the first ion implantation region is consistent with the cross-sectional shape of the groove, and is also a circular ring. 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 outer circle diameter 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 less than or equal to 350 keV. Within this power range, the requirements for equipment are low and non-hazardous. In other embodiments, the diameter difference between the outer circle and the inner circle of the bottom circle of the first ion implantation area is also 11 μm, 12 μm, 15 μm, etc., and the implantation depth is within the range of 1-1.5 μm. Specifically, the width and depth of the first ion implantation area can be adjusted according to the final required ion implantation depth, as long as the implantation can be completed at low energy. The ions selected for the first low-energy ion implantation can also be at least one of fluorine, carbon, silicon, oxygen, and magnesium.

[0045] like Figure 2 As shown, in one implementation, to facilitate ion implantation, before the first low-energy ion implantation, a step of etching the edge of the gallium nitride drift layer to form a mesa table is also included. That is, using a photolithography process, using photoresist as a barrier, using a 7μm positive photoresist process, and using a plasma inductively coupled etcher with Cl 2 / BCl 3 Variable rate dry etching, Cl 2 The flow rate is 20 sccm, BCl 3 The flow rate is 1 sccm, the working pressure in the plasma chamber is maintained at 5 mTorr, and the power is 250 W; the surrounding area is etched away, and a "convex" mesa is formed after etching in the middle, and the thickness of the mesa is 3 μm.

[0046] In other embodiments, the thickness of the mesa table can be controlled within 2 μm-5 μm.

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

[0048] In one embodiment, the gallium nitride epitaxial layer is grown by molecular beam epitaxy (MBE), the thickness of the gallium nitride epitaxial layer is 1 μm, and the growth temperature is 600°C. In other embodiments, the gallium nitride epitaxial layer can be formed by hydride vapor phase epitaxy (HVPE) or metal organic chemical vapor deposition (MOCVD). The thickness of the gallium nitride epitaxial layer can also be greater than 1 μm, and the thickness of the gallium nitride epitaxial layer only needs to be greater than or equal to the depth of the groove to ensure that the groove can be filled. The growth temperature of the gallium nitride epitaxial layer needs to be controlled at 500-700°C to ensure that the injected ions will not diffuse away due to high temperature.

[0049] In one embodiment, an ion implanter is used to perform a second low-energy ion implantation, the energy of the second low-energy ion implantation is 350keV, the ions used are He ions, and along the direction perpendicular to the ion implantation direction, the cross-sectional shape of the second ion implantation region is consistent with the cross-sectional shape of the first ion implantation region, which is also a circular ring, and the diameter difference between the outer circle and the inner circle of the bottom surface of the second ion implantation region is also 10μm, and the outer circle diameter of the second ion implantation region is 20μm, and the implantation depth is 1μm. That is, the second ion implantation region and the first ion implantation region are opposite in position in the ion implantation direction and have the same shape, and the second ion implantation region and the first ion implantation region are connected to form a deeper ion implantation region, so that the device achieves a better reverse withstand voltage effect.

[0050] In other embodiments, the power of the second low-energy ion implantation can also be in the range of greater than 350keV and less than 450keV, the diameter of the outer circle of the bottom surface can also be 80μm, 130μm, 180μm, 330μm, etc., the diameter difference between the outer circle and the inner circle of the bottom surface can also be 11μm, 12μm, 15μm, etc., the implantation depth is in the range of 1-1.5μm, and can be specifically adjusted according to the final required implantation ion 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 preparing the gallium nitride Schottky diode further includes the step of forming a metal cathode on a side of the substrate opposite to the gallium nitride drift layer. Specifically, the metal cathode is formed by evaporating a metal film on the substrate by magnetron sputtering or electron beam evaporation deposition to form an ohmic contact, and then annealing in a nitrogen atmosphere at 800°C for 60s.

[0052] In one embodiment, the metal cathode is a stacked layer formed by 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 be composed of 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.

[0053] like Figure 2 As shown, in one embodiment, the method for preparing the 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 the second low-energy ion implantation. Specifically, the metal anode is formed by combining a photolithography process with a method such as magnetron sputtering, thermal evaporation, or electron beam evaporation to evaporate a metal film on the gallium nitride drift layer and the second ion implantation layer to form a Schottky contact, and then removing excess metal film using a stripping 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 also be a single nickel layer or a single gold layer.

[0055] The gallium nitride Schottky diode prepared by the preparation method provided by the embodiment of the present invention integrates pre-etched groove technology and high-depth ion implantation technology during the preparation process, wherein the pre-etched groove technology can optimize the electric field distribution, and the high-depth ion implantation technology can form an effective barrier layer on the gallium nitride drift layer, thereby significantly enhancing the stability of the device under high electric fields, effectively reducing the edge electric field aggregation, and preventing the premature reduction of the Schottky barrier, thereby greatly improving the breakdown voltage of the device and preventing the device from breaking down prematurely. At the same time, due to the effective control of reverse leakage, the capacity loss of the device in the standby or reverse blocking state is also greatly reduced, further improving the overall energy efficiency.

[0056] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A method for preparing a gallium nitride Schottky diode, characterized in that: The following steps are involved: Providing a substrate, on which a gallium nitride drift layer is disposed; forming a groove on the gallium nitride drift layer; Performing a first low-energy ion implantation on a side of the bottom wall region of the trench facing the substrate to form a first ion implantation region; Growing a gallium nitride epitaxial layer in the trench, wherein the gallium nitride epitaxial layer fills the trench; A second low-energy ion implantation is performed on the surface of the gallium nitride epitaxial layer on the side facing the substrate 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 and the first ion implantation region have the same cross-sectional area and shape.

2. The preparation method according to claim 1, characterized in that: The depth of the first low-energy ion implantation is equal to the depth of the trench, and the depth of the second low-energy ion implantation is greater than or equal to the depth of the trench.

3. The preparation method according to claim 2, characterized in that: 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.

4. 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 both include at least one of helium, fluorine, carbon, silicon, oxygen, and magnesium.

5. The preparation method according to claim 1, characterized in that: The thickness of the gallium nitride drift layer is 10 μm-50 μm. Before the first low-energy ion implantation, the method further includes a step of etching the edge of the gallium nitride drift layer to form a mesa table, and the thickness of the mesa table is 2 μm-5 μm.

6. The preparation method according to claim 1, characterized in that: The growth temperature of the gallium nitride epitaxial layer is 500-700°C.

7. The preparation method according to claim 1, characterized in that: The preparation method also includes the step of forming a metal cathode on a side of the substrate opposite to the gallium nitride drift layer, wherein the metal cathode includes 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.

8. The preparation method according to claim 1 or 7, characterized in that: The preparation method further comprises the 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, wherein the metal anode comprises a nickel layer with a thickness of 20 nm and / or a gold layer with a thickness of 60 nm.

9. The preparation method according to claim 1, characterized in that: 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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